Effects of Pd-Addition on the Reaction Pathways of the Aqueous Phase Reforming of Ethanol over Pt/γ-Al2O3
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Rettstatt, Michael Jeffrey
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Abstract
Aqueous phase reforming (APR) is a sustainable liquid-phase process that converts biomass into clean hydrogen energy. APR is generally limited to pure feedstocks containing fully oxygenated hydrocarbons of the form CxH2x+2Ox, while functional groups like alkanes are underutilized and require further investigation. This study utilizes Fourier-transform infrared spectroscopy to elucidate the reaction paths of ethanol APR over monometallic and Pd-doped Pt/γ-Al2O3 catalysts. Two reaction paths are identified; both the monometallic and bimetallic catalysts follow both paths to differing degrees. Path 1 is the decarbonylation of ethanol into surface carbon monoxide and a surface methyl species, while Path 2 involves C-C coupling of the acetaldehyde intermediate to form C4 carbonaceous species, resulting in a lower theoretical hydrogen yield and increased catalyst deactivation. Path 1 dominates over Pt/γ-Al2O catalysts, while bimetallic PtPd/γ-Al2O3 catalysts follow Path 2. It was found that co-adsorption of water reduces the formation of C-C coupling products on PtPd/Al2O3, likely due to blockage of Pd sites and geometric effects that prevent adjacent acetaldehyde molecules from coupling. Due to the increased oxophilicity of Pd compared to Pt, water will bind more strongly to Pd and block potential active sites for the undesirable C-C coupling reaction, evidenced by the decrease in intensity of bands around 1575cm-1.
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2024-12-09
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