Nanostructured ceria supported Pt and Au catalysts for the reactions of ethanol and formic acid

Abstract

Decomposition reactions of ethanol and formic acid were studied over a series of Au and Pt nanoparticle catalysts. CeO2 nanorods and nanocubes served as model supports representing the {110} and {100} surfaces of CeO2 nanocrystals. Pt was more active than Au in low temperature (below 400°C) steam reforming, oxidation and decomposition (without an oxygen source) of ethanol. Similar trends were observed in the WGS reaction. Different from Au, for Pt the initial step of ethanol dehydrogenation to acetaldehyde is followed by the cleavage of the CC bonds of acetaldehyde to CH4 and CO due to the higher PtC bond strength when compared to that of AuC. The catalysts supported on nanorod-shaped ceria were more active than those derived from nanocube-shaped ones in ethanol steam reforming and WGS reactions due to the abundance of OH species formed by activation of water on the oxygen vacancies in the CeO2{110} surfaces of ceria nanorod supported catalysts. Complete oxidation of ethanol to CO2 and H2O was observed over the Pt and Au supported CeO2(rod) catalysts. For the former, complete oxidation took place starting from temperatures as low as 150°C. These catalysts were active for decomposition of formic acid starting from near-ambient temperatures (T>50°C) up to 200°C, at which temperature formic acid was completely converted over all the catalysts. Au was more active and it selectively dehydrogenated formic acid into CO2 and H2. The intrinsic activity of the CN-leached Au/CeO2(rod) catalyst containing highly dispersed sub-nanometer Au clusters was higher than the parent catalyst. Pt, on the other hand, showed lower selectivity toward the dehydrogenation pathway due to its higher activity in WGS reaction and enhanced PtO bond strength resulting in decarbonylation of formic acid.