The overlayer trade-off

Abstract

Methanol is a valuable platform chemical and energy carrier, which can be produced by hydrogenation of carbon dioxide in a catalytic process. Most catalysts, however, suffer from low CO2 conversion, selectivity to methanol or long-term stability. Indium oxide recently emerged as an excellent catalyst for this process, but while it is highly selective to methanol, its activity is limited by the H2 activation step. Various promoters have been explored to facilitate this particular step on In2O3-based catalysts and thus increase the rate of methanol production, but this has typically compromised its methanol selectivity. Now, a team led by Javier Pérez-Ramírez at ETH Zürich, in collaboration with researchers at the Institute of Chemical Research of Catalonia, the Paul Scherrer Institute and Total Research & Technology Feluy, present a comprehensive evaluation of the effects of In2O3 promotion by Ni on CO2 hydrogenation. They found that the catalysts prepared via dry impregnation, with Ni loadings from 1 to 10 wt%, form two-dimensional InNi3 structures on the In2O3 particles. These alloy structures promote H2 dissociation, which in turn boosts CO2 conversion and methanol formation — with respect to the bare In2O3 catalyst — after hydrogen species spill over to the In2O3 phase where CO2 is activated. The competing reverse water–gas shift reaction is likewise promoted, resulting in a slightly increased CO selectivity. CO becomes the dominant product at Ni loadings higher than 10 wt% due to the formation of InNi3 nanoparticles. At these higher loadings Ni nanoparticles are also formed, which promote CO2 methanation. The researchers conclude that the optimal Ni loading is 1 wt%, where the methanol space-time yield (STY) is maximized with just a slight compromise in its selectivity. The particular interactions between In2O3 and Ni determine the product distribution and overall catalytic performance. Further exploring what governs these interactions and their generalizability could provide us with a set of design principles for superior CO2 hydrogenation catalysts.