(425g) Synergy between Different Active Sites in Affecting CO2 Hydrogenation Kinetics and Selectivity

Authors: 
Peng, Z., The University of Akron
Yao, L., The University of Akron
Shen, X., University of Akron
Pan, Y., University of Akron
CO2 conversion into value-added chemicals offers one promising route to recycle the carbon source and has received wide research interest. In particular, there have been intensive research efforts on catalytic hydrogenation of CO2 into methanol and dimethyl ether (DME). This is because these chemicals are not only important feedstocks in chemical industry, but also promising fuels for transportation applications. Although the reactions are thermodynamically favored, it remains challenging primarily caused by the lack of efficient catalyst that can achieve satisfactory reaction kinetics and product selectivity properties. To advance methanol and DME synthesis through CO2 hydrogenation, development of new catalyst materials with good activity and high selectivity and fundamental mechanism understanding are essential.

We report the synthesis of Cu-In-Zr-O (CIZO) mixed oxide-based nanomaterials and study of the materials as CO2 hydrogenation catalyst. Influences of the two components, as well as their inter-component interactions and compositions, on the CO2 hydrogenation were studied. Mechanistic insights of CO2 hydrogenation mechanism and the synergy between different active sites were obtained using in situ DRIFTS study. It was discovered that defective In2O3 sites have strong adsorption of CO2, which results in a large barrier for direct CO2 dissociation and thus suppresses CO production. Metallic Cu sites adsorb and dissociate H2 for providing adsorbed hydrogen atoms, which react with adsorbed CO2 at adjacent In2O3 sites following the formate-methoxy-methanol pathway. Bifunctionality of the Cu and In2O3 active sites and their cooperation create their synergy in CO2 hydrogenation catalysis and results in promotion in both CO2 conversion and methanol selectivity compared to the individual components. A high selectivity towards DME production was achieved when zeolite was used in combination with CIZO catalyst. It was discovered that DME could be formed via a shortcut methoxy-DME pathway instead of a typical methoxy-methanol-DME route, which was attributed to synergy between CIZO sites and zeolite acid sites. The use of different active sites and the discovery of their synergy in promoting both CO2 hydrogenation kinetics and selectivity demonstrate an effective strategy to develop active and selective catalyst materials.