ZnO-Promoted Inverse ZrO2-Cu Catalysts for CO2-Based Methanol Synthesis under Mild Conditions

Abstract

CO2-based methanol synthesis is an important catalytic technology developed to utilize CO2 as a feedstock to mitigate climate change and supply green chemicals and energy carriers. While the transformation has been typically studied at rather high temperatures and pressures, milder conditions would enable an environmentally friendlier process, but sufficiently active catalysts are lacking to this end. Here, ZnO promotion of inverse ZrO2-Cu catalysts is investigated for CO2-to-methanol conversion at 473 K and 20 bar. The catalyst activity increases upon incorporating up to 6 wt % of ZnO and remains at similar levels at higher promoter contents. A remarkable methanol space-time yield of 0.45 g(MeOH) h(-1) g(cat)(-1) is attained, 2.3 and 1.3 times higher than those for the ZnO-free analogue and conventional Cu-ZnO-ZrO2 catalysts, respectively, and sustained for 100 h on stream. In-depth characterization identifies a key structural role of ZnO, reducing the copper particle size fostering hydrogen activation. This is complemented by a volcano-like trend in CO2 activation ability, owing to the improved and then lowered copper oxide interface due to ZnO agglomeration at higher promoter contents. Our study uncovers new facets of ZnO promotion on innovative oxide-on-copper materials and introduces a system with potential for sustainably producing a key commodity and prospective fuel.