Influence of water vapor on the performance of Au/ZnO catalysts in methanol synthesis from CO2 and H2: A high-pressure kinetic and TAP reactor study

Abstract

As part of an ongoing study on the performance and function of highly active Au/ZnO catalysts in the green synthesis of methanol, from H2 generated using renewable energies and CO2, we have systematically investigated the influence of water vapor on the reaction behavior. Water is a stoichiometric byproduct both in methanol formation and in the competing reverse water-gas shift (RWGS) reaction, and therefore its formation together with methanol formation is unavoidable. Changes in the reaction behavior, and possible physical or mechanistic reasons underlying these changes were addressed by high-pressure kinetic measurements, ex situ catalyst characterization and temporal analysis of products (TAP) reactor measurements. Already 2 % of water vapor led to a substantial but reversible lowering of both the methanol and the CO formation rate, and they decreased even more upon adding larger amounts. Possible reasons for this and consequences on the performance of Au/ZnO catalysts in this reaction are discussed.