Impact of Daily Startup-Shutdown Conditions on the Production of Solar Methanol over a Commercial Cu-ZnO-Al2O3 Catalyst

Methanol production with the use of syngas derived from solar-driven splitting of CO2 and H2O is a promising route to sustainable liquid fuels. Herein, we investigated the effect of using a CO2-rich syngas with the same composition as that obtained in a solar thermochemical reactor and of applying a daily startup-shutdown (DSS) routine matching the intermittent solar operation over a benchmark Cu-ZnO-Al2O3 catalyst. The catalyst reached fast equilibration (10 h) in the presence of this syngas mixture and reversibly responded to changes in the concentrations of CO and CO2 by mimicking fluctuations in the feed composition. Remarkably, its deactivation was even less pronounced over 27 cycles under a DSS regime than for a corresponding time on stream under uninterrupted operation if the reactor was purged with H-2-free syngas upon shutdown. Characterization and modeling indicated that this purging avoided the formation of inactive ZnCO3 and minimized the oxidation of the Cu surface atoms.