Abstract

Cu-based catalysts promoted with elements such as Zn or Ga are the most studied for CO2 hydrogenation to methanol due to their low cost and high activity. However, the fundamental causes of promotion are still not fully understood. In this work we assessed the effect that these promoters have on the number and intrinsic activity of surface sites using steady state isotopic transient kinetic analysis (SSITKA). We found an order of magnitude increase in the concentration of surface intermediates leading to CO when Zn and Ga are added. At the same time, it reduced the intrinsic rate of CO formation by a similar magnitude, leading to a similar macroscopic CO formation rate as compared with non-promoted Cu. The quantification of surface intermediates showed that only a small fraction of the surface is occupied by intermediates leading to CO and methanol, experimentally confirming theoretical studies who described the unique configuration of active sites for this reaction. (C) 2022 Elsevier Inc. All rights reserved.