Well thanks for the introduction Chris and
I appreciate the opportunity to be here

will be to discuss a little bit of work
in my group related to trying to replace

chlorine from chemical industry with more
environmentally sound and sustainable

oxidants and so this is one of century
two thrusts in our lab we're focused

on trying to develop chemistries that
are going to allow us to understand and

develop catalytic processes to produce
fuels and chemicals in a more sustainable

way and in all the projects we've
developed in the group we've tried to

essentially identify a particular problem
that the tallis has can help solve in this

particular instance but all discussed
today is the elimination of chlorine and

chlorinated products and contaminants from
the environment that are associated with

the chemistry required to activate
strong bonds and on the other side

of things work that I will not discuss
today we're thinking about ways to take

biomass which many of you are familiar
with and either make chemicals or

fueled by one of two pathways I did
either building up the complexity

from small monomers biomass for mentation
products or taking larger products and

breaking them down by hydrogen also
the chemistry to break C.C. or seal bonds.

Now and all these problems we try to
understand complex reaction networks and

we use a couple of sets of tools to do
that including great measurement and

spectroscopy as well as collaboration
with people in computational Catullus and

that's important for us because we
like to be able to link structure and

function together and identifying
a bottleneck in reaction network and

then coming in and trying to engineer
a way to reduce that bottleneck to great

greater selectivity or throughput and
it all comes around the idea of

trying to make a better catalyst for
these reactions so.

Our tools are kinetic analysis in situ
spectroscopy the use of well defined

materials and then.

Collaboration when necessary and I like to
try to make an analogy to an audience here

and this is basically a photo from when
I checked into the hotel last night so

this is from the Georgia Tech
wonderful hotel conference.

I know where it was very comfortable but
I was concerned when I checked into that

room because I initially found this box
sitting on the counter in the bathroom

now I don't know if you stay there if
you were recruited maybe you did but

you'll look at the front of and you can
read the label it says exfoliating skin

care far right and
there's a hole through the box and

there's not necessarily anything inside
the box as I could hold it up and

look at the straight through so I like
an example like this because the what that

means can be ambiguous it's what I would
get if I used a certain set of tools to

try to understand what's happening
in a particular system so

in a similar way when I simply use one
set of my tools usually making a great

measurements in isolation I can
come up with inconclusive or

ambiguous conclusions now however if I
go ahead and apply a second technique

spectroscopy visual spectroscopy in this
case I could open up the box port out and

see what's inside and it's not really
the conclusion I was expecting to have

when I checked into the hotel room who
puts a hole in a bar of soap I know

times are tough in the state education
systems but I guess you have to find ways

to save money any place you can so
that's the motivation I could see here and

so hopefully that analogy holds water
just a tiny bit or doesn't hold water and

has a hole in it and I'm just going to
move forward and try to tell you a little

bit about the chemistry that I'm going to
will focus on today using the same tool

box essentially I think is chemical
engineers many of you know that Apoc sides

are key intermediates for
lots of chemistry we use them and

at the high volume low cost flavor
ethylene oxide propylene oxide and Hundred

chloral hydrate here to make polymers on
the other side of things we have the very

high value low volume pot sides which
are precursors and intermediates for

the formation of bioactive molecules
things like fragrances and

biologically active
therapeutic treatments.

Now how do you make these species Well
usually start off with a hydrocarbon of

some type and typically those hydrocarbons
come from fossil fuels so they lacked

many functions which you can often do
is the hydrogenated to make an album.

If you do this for a small molecule
something like ethylene it's easy appox

dies as I can use a highly promoted silver
catalyst simply dissociate oxygen from

air on that material and
not add an oxygen atom across that C.C.

bond it's an inexpensive oxidant
it's highly selective you can get it

in excess of ninety percent selective
eighty and it's relatively cheap and

easy to do however once you begin to add
on to this position here you have a lick.

Position you can begin to D.

hydrogenated that point and further do
you hydrogenated small kewl break C.-C.

bonds combusted eventually because
you have very low selectivity is for

anything higher than C.

to now your options at this point are to
move to other oxidants so you can take

an alkie react with something like
an organic Peroxide or this butyl peroxide

as an example that's effective a transfer
an option across the C.C. double bind but

the problem is I now have a co-product
which I need to either regenerate or

sell in some marketable way that
constrains the economics of my process so

this might not be desirable at certain
times in addition to this older

technology involves the use of something
like chlorine as a strong reaction to come

here and start to activate those positions
on the core hiding process we contact this

reactor with dye chlorine we've been in
contact with the base that closes the ring

and makes the pox a product the problem
is that chlorine is really insidious and

has a tendency to leak
out of processes and

get into the environment and
even at small levels you make

products which are harmful to human health
as well as environmental health nearby.

So the issue is really amplified when
you simply look at the scale which we

use chlorine so worldwide we use more
than forty five million tonnes per year

all right and about sixty five
percent of that is actually for

products if you choir chlorine
story geometrically so

you see chlorine in that final species
that you form in about thirty five percent

of these processes we're only using it to
oxidize something initially and then move

on to other chemistry so as an example
here's a flow diagram for the chloride and

process I'll introduce propylene and
chlorine in the bottom of basically a tube

I introduce that with water they rise
up I undergo hypo chlorination to make

this corridor an intermediate at that
point then I'll begin to neutralize and

sodium hydroxide and perform a string of
separations to recover propylene oxide

here at the outlet is well as my spent
reactant and a salty solution a byproduct

Now there are a couple problems with this
well the chemistry is very selective you

have really significant costs for capital
because you're dealing with alternately

low ph and high ph solutions
you generate a lot of waste and

you have to neutralize it as well so
you generate about forty two tons of salty

high ph water for every ton of protein
oxide you produce so that's a very high E.

factor that's got a large environmental
impact and this was perhaps OK from

an economic standpoint when you could
dump the salty water in the river but

now we have to remediate it to be
responsible and that adds cost so people

are trying to move away from this and
one alternative oxen is to use hydrogen

peroxide can come in and use hydrogen
peroxide to activate species and prefer.

Bleaching the pope and textiles
disinfection of my disaffection of water

edging Microelectronics used for
mining for extracting ores and for

the purpose of the talk today we're
going to talk about its use for

these Apoc sedation reactions as
a replacement for Korean now so

the market has grown quite a bit and one
of the reasons why the market has grown is

because essentially we've introduced a new
form of chemistry pioneered by down B.S.F.

in a joint venture about ten years ago
called The hydrogen peroxide propylene

oxide process it's relatively simple in
concept we're going to co-locate anthro

can own oxidation facility next to
an appropriate up oxidation reactor so

will do is make the hydrogen peroxide sold
across the fence in a diluted form and

recover that solvent regenerate
it we save a lot of energy and

a lot of transportation costs in
operating costs by doing so and

this is responsible for about fifty
percent of all new proclaim oxide capacity

which has been added in the last eight
years to worldwide so it's catching on

quite a bit the problem is you can see
the scale this operation you have to make

the plants three hundred killed
tons per year large reason for

that is that this facility
here is very capital intensive

I need to make hydrogen peroxide using
a string of separation processes so

they don't mix hydrogen and oxygen
react in streams and blow the plant up

I also need to be able to separate
the catalyst extract that region and

concentrate in appropriate solvent to
be able to promote this chemistry for

all these reasons I can't
perform it on a small scale but

if I could that I could think about moving
towards other nice oxidation reactions

that are not performed at one
hundred killed on per your scale so

there's a market that's available for that
chemistry now to enable that we need to

come up with essentially a new method for
making hydrogen peroxide One option

would be the direct synthesis which is
deceptively simple I'm just going to take

Dihydrogen Di oxygen combine them on
a small metal nanoparticle at room

temperature in liquid and make hydrogen
peroxide The problem however is a more

often than not I make the thermodynamic
the preferred product which is water and

so that's a serious significant issue so

I'm going to try to answer a few questions
in the first half of this talking.

First talk about direct synthesis in
the mechanism of this reaction and

the second half of the talk a little bit
about what we've learned about the methods

for activating hydrogen peroxide and
using it for those Apoc sedation reactions

All right so regarding propylene
hydrogen peroxide formation we're going

to study the mechanism of this and try
to understand the reactive intermediates

are involved I'm going to try to answer
a question which has been bothering me for

about five years now which is as you
peruse the literature why is it that every

paper uses these sorts of alchemical
which is broods of salts acids and

alcohol is combined in order to get great
selective use why are these species so

important I can't perform
the chemistry and pure water.

And finally as you move towards
more environmentally sound

solutions will incorporate
gold atoms of these police him

clusters because that improves selectively
We just don't understand why that happens.

So I need to tell you a little bit about
the machinery behind these measurements so

we do everything at steady state we
measure steady state reaction rates

which is a typical for
this field of chemistry and we do so

in this flow reactor which is basically
a packed bed reactor into which we

introduce dilute hydrogen oxygen streams
here in nitrogen we do a gas liquid

separation collect the products
analyze hydrogen conversion by G C and

the product collection by Eve is
titrations this is a system that was built

by the student mentioned previously Jason
Adams a graduate here about a little over

a year ago and he's done this in his
first year so he's on a track for

success so far now what we've done is to
make sure that we avoid all the types of

artifacts that could lead to corruptions
or kinetic data so we make sure that there

are no concentration grade it's across the
particles and throughout the reactor so

that when I tell you a rate I'm
really measuring kinetics and

not some couple process of diffusion and
reaction so

how is it that these products
form on our catalysts So

the first thing is I'll show you a plot
of turnover rate versus hydrogen pressure

which you can see here in methanol
near about forty degrees Celsius

reaction rates increase of a linear
dependence on the hydrogen pressure.

Approach a half order dependence a higher
hundred pressures simultaneously if I look

at the auction pressure dependence you
can see that it's actually independent of

the auction pressure has no effect Now let
me turn to the other product water and

usually have a half order dependence on
hydrogen pressure here approaches zero

dependence on higher hydrogen pressures
and again we see that it does not depend

on the auction pressure that you use
whatsoever there are a few quick

observations I can take away from this
firstly it seems that our surfaces

are saturated by some side of sort of
dioxin derived reaction in our media

we propose that these could be things
like molecular auction or super oxide at

the lower hydrogen pressures which convert
into a hydro peroxide type intermediate

and higher hydrogen pressures the reason
we think that because of the simultaneous

change in the hydrogen pressure dependence
would be quite a coincidence if it wasn't

reflecting a change in the most
abundant reactive Intermedia.

Now another conclusion I can
take away from this initial data

is that the Seems to be inconsistent
with a typical Langer Henshilwood type

reaction mechanism which would
suggest that reactance exist or

compete for a particular site on that
catalyst surface which you can see as I

increase the hydrogen pressure
rates never decrease and

lengthier Henschel would predict that they
would at some point because eventual E.

for a by molecular reaction pathway
that hydrogen atom would displace hydro

peroxide and the rate would suffer as
a consequence of removing one species from

the surface so this let us early on in
the project to basically have an initial

hypothesis the option has been reduced I
can see that from the mass balance but

it doesn't seem the hydrogen atoms
are the reduction what else could it be.

So we looked around the literature and

work in the Shannon stalls group of
the Universe us constant the chemistry

department had implicated proton type
transfer steps in the reduction of dioxin

the hydro peroxide hydrogen peroxide
on homogeneous Palladium complexes and

work from the University of Virginia Bob
Davis and Madurai had a similarly involved

liquid phase intermediate hydroxide and
ions in this case and

the oxidation of alcohol is near a gold
surface so these are sort of coupled.

Steps in which they asked us to lead us
to the conclusion that perhaps as dioxin

reduces on the surface as we first absorb
it at hydrogen sequentially make hydrogen

peroxide perhaps one of our reactions is
actually coming from a liquid phase so

we thought maybe this is proton
transfer so as you can imagine if you

have a protein protein needed for methanol
you can transfer a proton to species and

eventually form peroxide in the way have
depicted these steps is mathematically

consistent with the way with the rate data
that I showed you so far however this is

one of those ambiguous conclusions to
which I'd like to get additional evidence

to support so we can do a simple
experiment in a semi battery actually

measure the hydrogen peroxide turnover
rate in methanol and water solutions we

can see that there are large measurable as
I move away from those products solvent

is something which is a product that's
a seed in my trial carbonate and

I metal self oxide you can see the rates
become in measurable dropping by more than

three orders of magnitude so protons seem
to be involved in some form or fashion.

And this point Jason joined the group and

he was working this summer on a few simple
kinetic isotope effect measurements

what we did is again that semi battery
actor we basically look at the change in

the hydrogen peroxide concentrations
a function of time in a dye hydrogen and

Per hydrogenated methanol solvent
we saw this initial increase and

it's that essentially reaching a steady
state concentration is rates of

the composition or formation became equal
by now moved to a deuterated form of

methanol where the hydroxyl group is now
deuterated specifically we can see that

those formation rates drop significantly
as to the steady state concentrations and

that reflects a primary kinetic isotope
which is actually quite large in

this case it's about a factor of seven
which is larger than what I physically

see in heterogeneous palaces
where that reflected essentially

a difference in the zero point energy
is of react in state with respect to

the transition state which is kinetically
relevant for that particular step now

what that implies is particularly
that hydroxyl group.

Group on the species is involved in
kinetically relevant step in its reaction

I can try to probe a little
bit further by simply.

Changing the form of my hydrogen now
to D two in hydrogenated methanol we

also see a kinetic isotope effect here
however it's smaller What does that mean

well it suggests in fact that we have
some sort of scrambling at the surface so

I bring Dihydrogen down or deuterium
it dissociates through some step I

transfer some of those hydrogen atoms to
the methanol to scramble the solvent and

that would be partially responsible for
this kinetic isotope a fact that we

see here we can do a post reaction
proton and a marvelous solvent and

actually demonstrate in fact the deuterium
atoms are incorporated those positions

which also supports this
interpretation Now the problem

is I haven't balanced my reaction
entirely on balance of mass but I haven't

balanced charge I should probably balance
both of them if I'm a chemical engineer so

you can see that I haven't described
where these electrons are coming from.

Recall that if I move to low hydrogen
pressures my rates become a measurable so

hydrogen is clearly necessary for

this reaction I can't reduce
oxygen from ethanol alone so

what we did is a scrambling experiment
if it H two N D two in the reactor and

we saw the rate of formation that
scrambled product it's about one hundred

times larger than the formation rate
of our product hundred peroxide that

implies that these hydrogen oxidation
steps down here are in fact abraded

if you put all this together we're going
to explain this in more detail if you like

basically we have a couple reaction
here where we're undergoing hydrogen

oxidation on one side of this cluster
electro chemically to form protons and

electrons and on the other part of
this cluster we're basically doing

oxygen reduction reaction the two electron
pathway to make form hydrogen peroxide So

this is very different than any sort of
mechanism we ever anticipated scene so

this is been really interesting result for
our group now I've described that

model to you qualitatively to reassure
you that quantitatively we fitted this

data with a series of twelve
elementary steps we've made

assumptions about which steps are quasi I
will break which ones are a determining

for the hydrogen peroxide formation if I
simply assume the second proton electron

transfer Stepan's rate determining I can
derive a rate expression that appears like

this where the denominator shows
the presence of dioxin peroxide type

surface intermediates exist in the high
concentrations in those reactor sites and

the numerator shows
essentially the rate for

that second proton
electron transfer stuff.

Now simultaneously a form of water which
can be described by a series of other

pathways these are then also described
by Jim domestic a modest amount or

caucus of the universe he was constant and

our conclusions agree with there's
water primarily forms to dissociate

of an auction auction bought and
peroxide on the surface when I modeled.

That with a kinetic rate expression
again I can quantitatively match

the rate measurements we saw before and
this occurs again on a dioxin and

hydro peroxide saturated surface So

overall if I look at our observations
combination of rate measurements.

Describing the effect of hydrogen oxygen
pressure the need to perform this

chemistry successfully in a proto solvent
and the presence of a strong kinetic

isotope effect implying that the protons
are directly involved acting either as

a reduction or if you want to co catalyst
or proton shuttle all of these really can

only be explained by the mechanism that
we've been proposing so far now what

that tells us is the hydrogen peroxide
formed by Proton electron transfer and

simultaneously water the undesirable
product is forming by a purely home

a little reaction pathway which breaks
an auction auction bottom that surface so

this is an interesting conclusion because
it tells me that I might be able to fiddle

with the different knobs in my system
changing the solve in the surface

properties and have a greater effect
on one reaction pathway than the other

so overall if you think about
this essentially we're doing two

electro chemical half reactions
on a single mental cluster.

Of course there are answered
questions related as chemistry so

one thing that you should take issue with
it's somewhat controversial thing to

propose is the dioxin in their super oxide
type intermediates exist on these metal

clusters at room temperature in liquids
that would be something unexpected so

we're currently performing in
situ Ramadhan A.T.R. F.B.I.

our studies vibrational spectroscopy
trying to observe these species

in directly and implicate them in
the reaction pathways we've got really

plenary data at this point but essentially
what we're able to show through

these types of Raman spectrum of our
Palladium play you modify clusters and

a reaction conditions where we're just
introducing oxygen so we have a strong

feature implying that there is an oxide
phase present initially and then

close that feature there's a little peak
which we need to confirm through isotope

labeling studies that could correspond to
basically symmetric stretch of a play D.M.

die auction type ring now would be
consistent assignments and literature.

But this is still early days and I have
to do more work before I can report back

inclusively simultaneously we want to try
to understand the phase of these Palladium

clusters are the metallic or the oxide So
this particular cluster was an oxide

because we started off by preoccupies in
it but I then take that same material and

I follow essentially the intensity
of that features a function of time

in flowing liquid So this is in
situ Remonde now we're basically

seen that these clusters rapidly reduces
over the course of two hours or so

in similar measurements where you compare
rates on oxidize clusters reduce clusters

also imply that were most likely dealing
with completely reduced mental cluster

during the talents will be
confirming those with X.

ray absorption spectroscopy
measurements at S S R L or

on Stanford in the near future.

So finally let me address the point
we've got these clusters we

think we understand something about the
mechanism I have some idea why we might

need these types of solvent nearby because
proton transfer steps are important and

I want to understand why when I add
gold atoms to the surface you see

dramatic increases in selectivity so
work from Gram Hutchings.

Group some time ago now shows quite
conclusively that if you take a play game

on carbon catalyst you add an equal
mass amount of gold to that cluster you

can increase the selective use
by about a factor of two and

increase increase the formation rates
simultaneously but these studies did

not shed a great deal of light on exactly
why this happened to since then people

have been using computational chemistry
to try to understand these changes and

there are some hypotheses that seem quite
reasonable the general idea is if you

start off with a palladium one one one
surface and I begin to substitute more and

more gold Adams into that surface
eventually I'll reach the point where Adam

on America laid him species surrounded
by gold nearest neighbors and

the density of states on that plate atom
are much different than what you'd have

on continuous believe in one one one so
I shift the electron density down I can

no longer donate into anti-body or
bills of dioxin quite as easily and

the barriers to making water by cleaving
that auction auction Bond go up

these are predictions these
are predictions that are made

on a slab in a vacuum on a computer and so

it's interesting to try to determine if
those experience predictions can be borne

out by experiment Furthermore we'd like to
understand how this affects the hydrogen

peroxide formation specifically which also
involves that solvent quite directly.

So the way we did this is we've
basically followed a recipe for

my group at Rice University we made Cloyd
all suspensions of gold nanoparticles

using the reduction of a gold salt
the presence of tri sodium citrate

historic acid these coal colleagues were
then isolated by centrifuge geisha and

we added Palladium saw a little bit
of hydrogen which undergoes electro

list deposition now to deposit played in
specifically on the play them on the gold

nanoparticles Now these the types of
bimetallic structures which we can use to

test our hypothesis I'll take those
clusters I'll load them on tone up or

a silica oxidize it reduces remove
all the organic matter now I have

small the particles which are relatively
uniform that's my hypothesis.

So I'll take a series of
materials that are all about.

Ten enemy or clusters going from pure
Palladium to gold twelve Palladium one by

ball composition and a look at how
hydrogen peroxide selective exchange

where you can see as they uniformly
increase as we add more and

more gold this is in line with those
observations from Hutchings group

however taking a slightly
different reaction conditions so

the question is why does that happen
as a difference in the mechanism or

is it a change simply in the activation
ample piece of the barriers for

these different reaction bound means or

perhaps I'm introduced special types of
sites which have unique reactivity for

this chemistry so I will test
the mechanism first applied again turnover

rates as a function the hydrogen pressure
Palladium clusters This is data similar to

what I showed you before those trends were
peer Palladium clusters are very similar

to what you see for gold twelve
Palladium and gold one Palladium and

so they have similar dependencies
on the hydrogen pressure.

They also as I showed you before do
not depend on the auction pressure so

so far it appears the kinetics
are about the same.

Our proton electron transfer reaction
mechanism describes the state of much

better than we see from Langerhans or
what type expressions and

when I finally do the experiment where I
try the reaction the presence of protons

and then also in the absence of protons we
can again see this very direct evidence of

protons are necessary so for all intents
and purposes I can see that there's

no change in the mechanism so
what is changing the same mechanism I

simply redrawn it here without showing the
math at all for clarity what is changing.

Well I propose then what is likely
changing is basically activation entropy

as are activation energies if you will and
so I should be able

to link those to the structure of the cap
what I'll do is interpret those changes as

plot the entropy as a function position
on the reaction coordinate and

I'm going to map this on the calyx like
that in mechanism I described earlier so

I start off with a dioxin covered
surface of hydrogen the fluid phase

through a series of hypothetical
elementary steps I'm going to oxidize

that hydrogen transfer protons
eventually made peroxide on the surface

now move the kinetically relevant
transition state and when I do that

I'm basically transferring that second
proton and I measure an activation and for

this process through the equilibrium
that exists between these species

I'm essentially looking at the entropy
differences between that transition state

and the surface intermediates
from which I'm measuring.

Those differences as
a function of composition and

you can see they uniformly increase by
about twenty killed jewels per boll so I'm

shutting down hydrogen peroxide formation
as I make the catalyst more gold rich.

Simultaneously I'll do the same analysis
for the second pathway this time it's

the one that breaks the oxygen option
bond I plot those and will be differences

as a function of composition you can see
they increase to now there is a small

difference there the difference is where
really all the details in the important

line so one increases by about twenty
killed all the other one in a creases by

about twenty five children so the home
a little pathway which requires perhaps

perhaps a greater ensemble of sides on
that catalyst surface has a stronger

dependence on the surface composition and
structure because essentially.

Bond order conservation type arguments
you'd say I may be making more oxygen

metal bonds in one case than
I am in the other case so

if I increase the strength or weaken
the strength of an auction metal bond

I should influence the stability of one
transition state more than the other and

that's kind of consistent with where
we are in terms of the explanation so

even though that's a small difference
about five killed that is actually

consistent with the increases in
selective use that you might see so

just remember the chemistry is
performing very low temperatures so

a small activation energy
difference woud a large effect so

that kind of brings me to the conclusion
of the first part of this talk so what

I did is I try to motivate the chemistry
by looking at the first side of the H.P.O.

process and describing how we might try
to replace the entropy known oxidation

facility with the direct synthesis reactor
now let's move to the other side and

look at what Al King Apoc sedation
from what I'm going to do

is essentially tell you a bit about how
this is conducted currently what we do

is we use a trans TS one
catalyst that is a small pores.

The pores around five angstroms in
size and you substitute in titanium

atoms in the framework positions those
titanium atoms are effective and

activated hydrogen peroxide to make
different types of reactive species

which can then react with propylene to
make the Apoc sites with selective use in

the range of about ninety five percent so
works quite well but if you think about

all the details of this species how is
it that we ended up with titanium of all

metals on the periodic table in a zero
light with this particular structure.

When there are so
many other options that we could have so

what we're in do is kind of dive in try to
answer a couple simple questions firstly

what forms are activate hydrogen
peroxide on these sites.

How is that related to the identity of
the metal that I choose to put into

that framework and how do rates on the sly
to use for that a pot sedation process

changes a result that I like to develop
some connections between these properties

after I tell you about that work a little
bit we're going to see what happens as I

begin to go from the particulars Eli we
use in this case beta which has a seven

Angstrom bore is something which has a
much larger pour about fifty angstroms to

see how the pore size influences
the chemistry as well and so I'm choosing

a different catalyst in different metals
and what you see in the current process

because this metal Beta is a sample that
our group who are not synthetic experts

can modify in a relatively routine way
to test these different questions.

So the way we approach this is similar to
work I think done in the Sievers group

we basically taking a limit of beta
we reflux that in nitric acid for

a period of time who we
form a lot of knocks.

In the hood we then end up
with a defective silicon beta

material Now this is nearly perfectly
Silas all the aluminum ahead for

the most part has been removed and we are
left with these tetrahedral voids of D.

facts into which I can substitute no
matter what I'll do is all contact is with

a metal chloride solution or a mental
side and solid state heated up and

through processes of absorption
diffusion decomposition will

eventually integrate some of these
metal atoms into the framework

we've done that with these series of group
for group five transition metals and

in the end we don't actually end up with
a perfect defect Fritzi a light we're

integrating in a very small number of
these transition metal atoms we've done

that for a very specific reason we want to
isolate these metal as in the framework so

there are no diffusion constraints so
again the feeling modules in the system

is very small in addition I'm going
to essentially end up with a uniform

distribution of sites and
because it's unlikely that these

atoms will be sited near one another and
find them and end up with the hydrophilic

material which has a number of these
hydroxyl groups in the vicinity of these.

Different metal atoms we've been able to
reach using inclusions using a series of

characterization techniques and Amar
Singhji compositional analysis X R D And

P.S. as well as other techniques so

with these materials in hand I can
start to answer a simple question

how is it that I actually activate hundred
Proxima Well this might seem actually.

A little bit simple and naive to ask work
has been done this area by Sylvia board

for a long time working specifically
on the TS one system and they

propose that there is a super peroxide
type intermediate there that exists and

is easily seen by even spectroscopy So
we did this experiment we put our titanium

data in the small in situ you have as
reactor flow the hydro peroxide over it

and what we can see is the emergence of a
strong you've even speech are all right so

I've subtracted out the background from
the catalyst itself so this is simply

the difference spectra Now that could be
this peroxide intermediate There's also a.

Peroxide type species which
has been proposed to exist and

they are thought to be in equilibrium
with one another simply through a proton

transfer type mechanism so I see two peaks
in the U.V. visited are good like to D.

convolute them assign them to specific
species so I'll do a test I'll change

the basis of the or
the acidity of the solution of a seed and

I try that and
flowing over the system and as I do that

you can see the change in the intensity of
those two features within the spectrum.

By plot the ratios of those two
intensities as a function of over as

a function of the PH if you will although
you cannot measure ph in the system

you go from a basic to an acidic solution
you can see there's a systematic change

that as I add those protons I propose that
I have actually increased the number of

hydro peroxide intermediates by
proceeding those species and

shifting equilibrium now you've even this
is not a very definitive spectroscopy

good method to use you have to do a lot of
work to design the peaks correctly so what

we've done is to use a standard So this is
a titanium peroxide sulfate species which

is formed by taking the salt exposing
the hydrogen peroxide you can confirm

the structure Crystal graphically and we
do a little bit of Raman at this point so

Raman spectroscopy shows this vibrational
feature associated with that three atom

group quite strongly strong absorbance
here about six hundred twenty nanometers

away members we see a similar feature on
the activated titanium beta sample so

that suggests indeed that species
is present as proposed and

although we cannot see
the hydro peroxide do

maybe it's Raman insensitivity in this
case we can suppose that it does exist

equilibrium so now I have a little bit
more certainty about the identities of

these two features now what
I'll do is take that system and

try to run a state and I trial over for a
period of time to figure out what happens

especially nothing happens I can contact
with a seed in my trial or water for

a period of hours and those features just
stay rock solid so that hydrogen peroxide

is activated irreversibly to form
a reactive species which is lacking

a reaction partner at this point
if I bring it all off and.

Cycle has seen I read it readily make
cycle have seen oxide and I look

at the intensity of this ramen feature in
situ as a bunch of times you can see it's

quickly attenuated I can actually plot
that difference is a function of the peak

intensity as a function of time capturing
these transit kinetics with Raman and

see the consumption of that super peroxide
in the formation of the cycle hexing oxide

which occupies that same site so
basically this binds.

The problem is I don't know which
of these species is reactive

I was able to observe one and
I saw that it changed but

the other species might have actually
be involved in chemistry and

like to identify not ambiguously which one
of them is responsible for approximation

so what I'm going to do now is turn to the
U.V. Visigoth now I have some certainty in

the pigs that I've assigned to normalize
intensity of the hydro peroxide or

peroxide peaks as a function of time on
a semi log plot here which you can see for

titanium as they both decrease quite
rapidly in an exponential manner

all right that implies that I have
reactions consuming the peroxide

reaction consuming the peroxide as well as
the concurrent I somber ization by that

equilibrium there is of
the proton transfer type stuff.

If I knew merely model this data
simply assuming this is something

like a batch reactor I can estimate
the values of these rate concerts and I

see the one rate constant after the hydro
peroxide intermediates about two orders of

magnitude larger than the other that might
suggest that is actually the reactive

species as has been proposed before on
titanium catalysts So that's a little bit.

Indirect evidence let me talk about the
other metals and I'll show you more direct

evidence for the reaction involved
in those particular situations but

I don't want to point out to you that
we've done the same thing now on the opium

tantalums or Coney Island hafnium
containing zeal lights in all cases we

see the emergence of these two peaks and
you leave it is we didn't convolute them

we fit their decay is in an exponential
way with time as eye contact in the cycle

has seen and we can basically
see the depletion of these

reactive intermediates from the surface
as in all cases these three metals ten.

Weight quite quickly they are very
reactive these other metals are gone even

half to relatively inactive.

So I can see now as I regress
those rate constants titanium seem

to react to a peroxide species whereas
the group five transition metals seem

to react through a peroxide intermediate
I can't get anything useful Tony and

have to because nothing happens so I need
another technique and use a simple probe

reaction to investigate stereo chemistry
for a moment what will do is will contact

these activated materials with cysts being
it's basically two benzene rings with

a bridging body between them with
a couple carbon atoms there so if I add

the oxygen across the pond depending
on the mechanism I give that molecule

an opportunity to rotate OK so if I do
this reaction in a concerted mechanism.

Of mechanism this is supposed to happen
in a concerted way I basically form both

carbon auction bonds at the same time I
retain the stereo chemistry the product is

system being oxide if I undergo
a sequential reaction mechanism this

is proposed to happen by first forming one
carbon auction bond and then another one I

have an opportunity now to I summarise OK
if that happens I'll mix make more equable

or mixtures of system trans isomers in
the approximate product so we're going

to use that as a probe when I plot the
ratios of those sister trans products for

the group for the group five metal bait as
ample as you can see that the group for

metals are enriching the product which
implies that the peroxide Intermediate

is the reactive intermediate and for

the tantalum group five transition
metals we see those species are now

nearly equal or so suggest this move back
in ism the sequential mechanism through

the peroxide Intermediate is
actually the active case so

now I've seen the reactive species I have
a few forms of evidence to suggest which

one is actually involved in this
reaction so that's useful but

I'd like to also understand the mechanism
overall in a complete catalytic cycle and

the under stand the reasons for
these differences and

reactivity among the metals So

what we're going to do quickly is try
to probe that mechanism I'll show you

the change in the turnover rate is a
function of the cycle hexing concentration

this is the opium beta and you can see
a lot of cycle hexing concentrations of

essential a first order dependence
which approaches that independent.

Function concentration the higher
concentrations described here and

then as I go those higher higher
cycle hexing concentration they

become independent cycle X.

and concentration and I develop
a dependency on the hydrogen peroxide and

the cycle actually oxide concentrations
which I'm not showing you at this time for

the sake of brevity if I go across all the
other metals titanium tantalum zirconium

and half and we can see the trends are
basically the same it's also the same for

the pox I dependence on the hydrogen
peroxide dependence so this seems

to suggest once again I have a common
mechanism as I saw a direct synthesis

I'm just changing something about barriers
perhaps I move between reacting between

different catalysts that mechanism in this
case involves taking my initial show for

a group for transition mental framework
site I can absorb a cycle hexing from

that site I can buy hydrogen peroxide and
then I can irreversibly activate hydrogen

peroxide to make that form of the reactive
intermediate which is responsible for

the Apoc sedation at that point I have a
choice I can decompose or I can go forward

to make the apartheid product I go forward
do that your reverse of the reaction

cycle have seen and make the Apoc
side which can then be absorbed and

if I react instead with another hydrogen
peroxide molecule this is going to lead

to a nonproductive pathway
which reduces selectively

what happens in that case if you actually
have more of all of water and dioxin.

All right so
have a cycle which is consistent

with all the data I'm showing you here.

Now there is something which is
obvious in that previous plot

if I look at the turnover rate across the
different metals we can see that they vary

quite a bit here is just the turnover
rate for appox I'd formation on the O.B.

I'm if I plot those at
standard conditions for

titanium tantalum half humans are Tony and
they vary they vary significantly by fat.

One hundred thousand Ok that is
an interesting detail in itself and

the student working on the project found
that to be a less interesting detail

because it essentially made his life very
difficult for a period of time trying to

figure out how to actually measure these
rates down here there were some very long

days and very large batches of catalyst
he had to use to actually get anything

measurable but so that's interesting
in itself now what I think

is actually more exciting is the fact the
selectivity increases in the same way so

as I go to Titanium I get one hundred
thousand times more reactive but

I also become one hundred
times more selective for

this chemistry it's not often that
you seem comparisons a trend in

the same direction like that usually we
shut down undesirable reaction pathways

the sacrifice of activity in canals so
why are these differences occurring what

is important about the identity of that
mental electronic structure that dictates

these differences well we're not the first
people to ask these types of questions so

born out of korma Spain about ten
years ago started looking at similar

chemistry of basically a pot sedation of
one octane over titanium zirconium in

ten Beta samples they saw that they could
measure the rate of POC side formation on

a titanium beta and they were in
measurable rates on the other two

catalysts they tried to answer the
question as to why this difference existed

by looking at the position the energy
level of the lowest on occupied molecular

orbital of that titanium atom itself or of
these or Tony Matador of the ten atom and

they saw there was a correlation the lower
energy that lies that means the more

interested it isn't attracting electrons
the more reactive the species seems to be

now just a note science group in
northwestern looked at the same kinds of

comparisons correlating Now the initial
turnover rate for cycle had seen

oxide formation on these are porous
silicone which they grafted group for

group five transition metals and they're
able to correlate again the formation

rates there's some measure of something
like the electronegativity they

call this the ionic character
of the metal action bond

by looking up electronegativity
values from the periodic table.

We've tried to make those same comparisons
this time to the activation and

will be for a box of Asian.

Using the same measures from
the notes group where we see there's

poor correlation so for all these
five metals it works out quite well

Titanium the most interesting
metal falls far from this line so

this is clearly not capturing whatever
is important for that difference so

what is it all of these analyses seem to
have in mind one common factor that is

if I like to attract electrons I'm going
to do this reaction more selectively in

a higher rate it's how can I probe that So
as an experimentalist we came up with

a simple idea we're going to try measuring
pizza by Universe based molecules

something is going to donate electrons
that Lewis at that site we used purity in

we see the nitrogen we use the deuterated
form of a seed in my trial

where I can basically flow that with
helium over my catalyst and a constant

concentration change of temperature and
see the evolution of these features so

the coverage of the species on the surface
goes down as a function temperature.

So if I look specifically at the feature
which has been assigned to a seed and

I trial by only to the Lewis acid
sites now I can interrogate fops for

absorption specifically at that site among
all other science exist on the surface

I do very often Alice's And when I've
calculated that I can extract an empathy

for Dorgan to see tonight trial and
those sites and compare the activation and

copies for approximation and

you can see there is a century of strong
when your correlation here Alright so

as I change that Lewis acidity if
you will it's not a true measure but

it's something like it I change
the barriers for appox occasion and

I also change the barriers for hydrogen
peroxide composition undesirable path

they are both linearly correlated they
are both decreasing as I go to more static

material so that explains why rates get
larger However there slopes are different

they begin to converge which means I gain
more in terms of increasing the rate of

a pox occasion than I do affect the rate
of decomposition as I go to more acidic

materials so
that's a probe of the properties of

the catalytic site let me tell
you something about the catalytic

intermediates Now remember
the plot this was the U.V.

this specter I showed you what
I've done is I've become.

Involuted you even specter of the reactive
species specifically the ones I assigned

by looking at the system being
a pox product distribution

now going to take the leg of the metal
charge transfer energy from the peoples

nations of each one of these so

the general idea is if I have a stronger
ass I'm going to pull Exxon's more readily

towards the metal that will make the leg
of the metal charge transfer energy

smaller it's now easier to move those
electrons when excited with the light so

these species are more polarized and
it seems like they're more reactive

because once again I can construct a
linear correlation between activation and

copies for appox anation those rajin
peroxide the composition this time scale

by the elect measure of the electronic
structure of those reactive species and

see there's a when your correlation it's
stronger for the appox nation reaction so

this is really useful insight
because now what I know

is I should try to make species which
are more acidic and stronger Lewis acidity

I can start by looking at the periodic
table and simply choosing elements

to put on my surface which might have
a greater electronegativity All right.

So let me think now about
the other knob I can turn for

this a positive action catalyst that
is the size of the void surrounding

the active site I've been doing all this
chemistry so far in a beta sample which is

a poor of about seven angstroms I'm going
to focus on a subset of those metals

Titanium the opium and tantalum the ones
with measurable rates to be easier and

Daniel is doing the measurements we're
going to team up with just a note science

group his student Dick Thornburgh and
they're going to graft those same metals

on to me as a porous silica so to make
equivalent types of sites highly dispersed

metal atoms spread out across the surface
in one case I'm surrounded by seven

Angstrom void in other cases
the fifty extra weight and

what I'm going to tell you quickly because
I'm beginning to run out of time is that

nothing really changes mechanistically in
the scenario so if I activate hydrogen

peroxide those materials here are the U.V.
visit on the beta sample and

see those two peaks for each sample I
told you about before in which we D.

convoluted if I do it on the metal
silica metal and MS Of course silica

we see similar distributions of species
there shifted slightly in energy.

You would expect that Crystal field theory
the bond angles and lengths are going to

be slightly different because this
material is amorphous that materials

Crystal Now what happens with the reactive
intermediates they're the same so

it makes systems being over the surface
for my distributions of products and

well see the sample data I showed you
before for titanium beta I tend to make

the product implying that I don't peroxide
was a reactive species from the tantalum

of the peroxide intermediate because these
quantities are nearly equable or for

the means of course silicones I'm
in rich once again in the system

products of titanium so I don't peroxides
reactive intermediate these peroxides

are once again the reactive species
they're reactive intermediates the same

electronic structure is the same
in this case I'm going to look at

stiring approximation you change a reactor
when you want to write another paper and

so you look at a mechanism
Kalak cycle it's the same

the kinetic relevance of all those steps
is exactly the same so what is changed.

Well let me look in detail the position of
these little charge transfer energies so

for the reactive species I'll plot
the activation and will be for

appox occasions a function of that value
once again which I just proved to you on

metal beta is correlated linearly
with the activation puppies so

those are the data I showed
you before if I now do this

on the means of course material I'll
see that I have a similar slope but

that the entire curve is offset and
shifted up by about twenty killed.

So what's responsible for that change well
you have to think about what's changing

the scallop excited as you move from
the reactance state to the transitions

essentially when I have a most abundant
reactor media which is one of these docs

I dioxin intermediates I take styrene from
the fluid phase I'm going to first Zorba

into that poor in the vicinity of the
active site and the next step I'm going to

go to transfer the oxygen to that
double barn to make the Apoc side so

this can be decomposed in a couple
values when I measure an activation and

will be what I'm reporting right
here is the difference between that

transition states the building the raw.

State of that system which has
styrene in the food I can decompose

that into the other two quantities
the heat of absorption or the F.O.P.

of absorption moving stiring into
the pour and the intrinsic activation and

will be to form that a POC side product.

They can be related by the simple.

Magic relationship two of these parameters
depend on the port diameter because in

these two processes moving from this state
to the transition state or moving from

this state to the inside of the poor I am
changing the salvation I am pushing some

solvent molecules out the styrene
is now inside the ports interacting

with the walls or disperse interactions
I can measure that entropy of absorption

directly using very old techniques
basically measure the uptake as a function

temperature back out the entropy of
absorption what you can see is that it's

basically thirty six killed on Beta
seventeen killed from all of the means of

more silica the difference of about twenty
killed jewels per Mall with more strongly

inside beta which is consistent with these
changes actually take those values put

them back into this equation and calculate
now the intrinsic activation empathy for

these materials as a function of the leg
in a metal charge transfer energy to see

if there is any effect change electronic
structure of the reactive side

you can see everything basic lapses on
a single line which means these barriers

are function of salvation forces
the Allow me to stabilize a particular

species over another
one inside the poor and

the electronic structure of those reactive
species of form The depend on the mental

identity now the last thing I'll say
is that as I move towards the other

reaction pathway hydrogen peroxide
composition you need to think of one thing

hygiene products as a lot smaller than
styling so as I move it inside the poor

it doesn't have the opportunity to
feel the poor walls to the same extent

salvation forces are essentially
less important and you'll see that

there's actually a linear correlation
meaning no change in the barrier for

activation of hydrogen peroxide and

the composition between these of course
material and the light sample so

because of the differences in the sizes of
these transitions States I can select a.

We stabilized one over the other the
consequences of this are that the Hydra

peroxide selectively is well as the rate
increases I go to the smaller and

smaller poor size so I've been able to get
higher selectivity on the titanium beta

much lower selective use and also much
lower rates on these of course samples

All right so this kind of brings me to the
conclusion which is that I think through

a combination of the methods we've been
describing we can disentangle a lot of.

Simultaneous factors that influence
chemistry in this series of systems

this is all motivated by this hydrogen
peroxide propylene oxide process and

want to make hydrogen peroxide activate it
perform some useful oxidation reaction and

do this in colocated way which requires
that I have intensive processes for

making hydrogen peroxide that involves
direct synthesis that happens by reaction

mechanism which we did not anticipate seen
and one which evolves different pathways

which sense the surface of the cabinets
differently given me opportunities for

changes like to be dramatically by changes
in composition as I move the Apoc sedation

chemistry we saw that there was
a single constant cycle for

this chemistry and it depended quite
strongly on both measures of the.

Electron affinity of the reactive sites
as well as the electronic structure

of the reactive intermediates
of forms on those sites

we could correlate those to get
some idea of where we should move

we should make more acidic materials
which may cause an acidic materials and

smaller boards so with that like just
to thank the people who did the work so

this was performed by a series of
three excellent graduate students.

Broadly Priyadarshini they worked on
direct synthesis and then we're going to

Jason Adam is the Georgia Tech graduate
and recently joined about a year ago and

he performed all the kinetic facts like to
thank our collaborators as well as funding

from sources here specifically N.S.F.
and the Army Research Office thanks for

your attention I'll be happy
to answer any questions.

Well.

But.

I.

Felt.

We don't know what the phases
were trying to study that now so

you will tend to make a play dim
hydride if you expose a just a few K.P.

at room temperature the problem is we're
exposed to a mixture of oxygen and

hydrogen in our solvent so we've
written proposals reviewed quite well

if I'm in Karim of the Virginia Tech
we're going to synchrotron basically

the century create a phase diagram now
of these plate Amana particles under

different compositions of hydrogen oxygen
to figure out of dislike to any difference

as you move to play them gold perhaps by
suppressing the formation of a hydride.

So that's an interesting system I didn't
know that fact it's been determined and

shown by others if you take a small
plate and cluster and you throw in

a sprinkle of platinum rates go up
significantly selectively is don't really

change we're not sure why that happens it
could be due to some again maybe some sort

of change in phase but it could also be
due to essentially mediating different

parts of this caliber cycle to different
agree platinum could be better for

example doing a job than when you.

We haven't found a good way to
actually measure those yet but

the kinetic suggests that all
of the sides which are active

are saturated by that intermediate
whenever it happens to be.

Yeah.

So.

Yeah I don't want to wanted to do too
much semantics here but the ligand that

ensemble effects people talked about for
metal hours for a long time are a little

bit confusing to me I don't think there
be many examples except maybe for

a reaction like SIO oxidation which
involves basically perhaps just one or

two metal atoms where you can completely
decouple these two effects so

the hallmark examples of a on sample
effect from experimentalists point of view

which is the point of view I have is that
you see a change in the rate or a change

in the selectively without seeing a change
in the activation empathy which suggests

I'm simply rebalancing the populations of
sites in this particular case we did see

a change in the activation and will be if
I just simply write a ratio of rates which

tell me how selective you should depend on
the change in both competing activation

Appleby's for the different pathways we
can actually explain everything we see

terms of selectively so that's a just the
electronica facts through the activation

energy can explain everything now I'm sure
that the local structure of those groups

of science whether it's two or
three played a madam surrounded by gold or

something else is responsible for
that change but

we would define that as
an electronic effect.

Not regarding the synthesis of last.

Season I mean have you thought about
putting forth a little cluster inside.

Of your life material for instance or
even though you might like debate.

Could be possible you
like it you enjoy for

example that getting beat up to be called.

Something you said is art.

So doing sort of in-situ generation of the
peroxide to activate within micro meters

or nanometers So yes we've thought about
that people have proposed that idea for

a while there's a great deal of research
on particular system which is gold and

Ts one so the same catalyst they
put the small gold clusters inside.

I think it could have potential
the problem that people in industry

specifically Dow explain to me is that
at the temperatures where you do this

chemistry to have high enough space
velocities and throughputs be profitable

you tend to decompose the catalyst so
the gold clusters they

can actually engineers they don't center I
don't know how they do that honestly but

the titanium in the framework of that is
oxidative Lee cleaved So every time I X.

come in and actually break a framework
titanium bond I make a better median and

hydroxyl group nearby if I do that
again before I consume the hydro

peroxide now I've lost two framework Pons
if I do it again now it's on the ice form

species which can detach move along the
poor they don't glom rate in the titanium

oxide nanoparticles are inactive so the
way they can tell this is they can look

at small shifts and you've even spectra
they can see that basically leave the band

gap get smaller and smaller as these
agglomerate they can also see that they're

irreversible deactivation of the catalyst
over a really long periods of time if you

go the liquid phase at lower temperatures
you don't have this problem but presumably

they don't want to do that because
the economics are poor because you don't

actually have a high enough throughput for
that particular in situ generation.

I don't know about the stability to be in
one state versus another state but I think

they'd be susceptible to be activated
by the same type of mechanism I think

it depends on how quickly you're able to
scrub off those intermediates before you

leave another framework beyond and I
can't exactly predict what that would be.

So we operate a low hydrogen pressures for
safety reasons if you want to practice

this in industry you're going to operate
in multiple bars of hydrogen we go up

to about four at most so what we've been
able to get up to is about sixty percent

selectively if you look at our trends are
every year to extrapolate the conditions

people are using we can approach ninety
percent with Palladium gold catalysts and

we have bimetallic nanoparticles of
other compositions which meet that or

exceed it and if you start to experiment
now with adding in those promoters you can

get it up to ninety five percent selective
eighty The problem is those promoters Hale

ides acids since I'm going to take that
stream now pump it over here to the TS one

TS one isn't like that so much and so you
need to find ways to actually remove those

species that's energy intensive so
right now we don't have a solution.

How do we count the sides in the ceiling
So currently we are assuming that every

site in there is active so we look at the
composition on top of that we use You've

even is in deploy determinant the charge
transfer energy has shifted quite high but

there's a reasonable chance that we have
an extra framework sites and certainly

some open and some closed sites which
could be convoluted in these are facts.

So.

It is.

More like.

It.

Yeah.

So you know you'll notice when
the types of correlations we use

actually does not depend on the turnover
rate measurement because we're looking

at changes in those measurements as a
function of temperature that's one reason

why we made those activation of the
measurement so if I were to miscount sides

for example and I still see the energy
differences correspond between and

speeds of absorption and
also the metal charge transfer energy

that correlation would not be affected one
way or another by miscounting sites but

I do have a distribution of sites however
the math is wrapped up in there and

it could introduce some uncertainty
because now instead looking one population

looking the sum total of two populations
so we do need to use better materials and

that's why we're trying to reach out to
sympathetic synthesis groups with that.

Up and told point yeah yeah.

I think will depend on the reactive
species of the substrate the old and

the Al-Q..

Obviously if they can't fit inside
the poor then you have a problem but

before that happens even those vendor
walls are dispersing interactions they

fall like a winner Jones type potential So

there is a specific distance I would like
to be in equilibrium distance away from

the poor walls I think about a poor being
a cylinder now I have to somehow find

the minimum energy point where it's
balancing its interactions both

the chemical interactions like on exchange
with the site as well as those dispersion

interactions integrated across
the curvature of the pore.

Those are things that people spend a great
deal of time calculating We have a again

a blunt tool to use Chris's words to
reprogram by measuring heat of absorption.

But I would expect at some point as I got
smaller and smaller cycle that comfortably

activation will actually begin to go up
again and some point I won't even fit

inside so I think it depend on the alkie
that you choose to parts of eyes.

So I

would use a classic I think that's O.-O.
O.

if it's using CLOS just Clapper on
which is essentially similar to as

I look basically a change in the coverage
of the quantity that's there is a function

of temperature and from that I'm able
to determine that heat of absorption.

Thank you.