Influence of Ag metal dispersion on the thermal conversion of ethanol to butadiene over Ag-ZrO2/SiO2 catalysts

Atomistic scale models were developed and coupled with experimental investigation to deliver a functional understanding of catalytic activity and selectivity in the conversion of ethanol to 1,3-butadiene over Ag/ZrO2/SiO2. A detailed evaluation of the structural and electronic properties of the resultant catalyst models led to the identification of critical active sites of the catalyst. More importantly, the extent of Ag dispersion on the SiO2 support and relative proximity to ZrO2 were found to vary with the oxidation state of Ag and local coordination environment (Ag-OSiO2), allowing for critical control of ethanol conversion towards butadiene or ethylene. Simulations revealed that less dispersed or clustered Ag contain predominantly Ag-0 charge state and promote conversion of ethanol to ethylene. The well-dispersed Ag/ZrO2/SiO2 catalyst instead contain a larger fraction of cationic Ag delta+ and predominantly promote ethanol dehydrogenation and subsequent production of butadiene. The theoretical insights drawn were validated and confirmed experimentally using TEM, XRD and reactivity measurements demonstrating the effect of Ag dispersion on the selectivity of ethanol conversion. (C) 2020 Elsevier Inc. All rights reserved.