(202c) The Role of Surface Chemical Reactivity in Artificial Photocatalysis

Authors: 
Poudyal, S., University of Tennessee
Laursen, S., University of Tennessee

Surface chemical reactivity is the engine that drives heterogeneous catalytic reactions. However, the degree at which innate surface chemical reactivity determines the overall catalytic performance in heterogeneous photocatalytic reduction of CO2 and water-splitting reactions remains elusive. A combination of the first principles quantum chemical modeling and experiments has been applied to investigate the role of surface chemical reactivity in promoting overall catalytic activity and controlling the selectivity in photocatalytic CO2 reduction towards the production of CH3OH, CH4, and H2 production. Photocatalytic reduction of CO2 for the production of CH3OH, CH4, H­2 over TiO2, SiC, GaN:ZnO, CdS, GaP, and Bi2S3 was investigated.  We found that the energetics for CO2 and H2O dissociation, the stability of organic intermediates, and the chemical nature of surface bound atomic hydrogen collectively contribute to the selectivity of the reaction.  For instance, organic intermediates are found to be stable on SiC due to its greater surface chemical reactivity towards carbon.  This enhanced stability correlates well with SiC ability to selectively produce CH4. On the contrary, moderate surface chemical reactivity towards oxygen and hydrogen, in case of Bi2S3 and CdS, appears to correlate with their ability to selectively produce CH3OH.  Results suggest that CH3OH production hinges upon inhibiting the second C-O bond-breaking step.  Finally, the catalysts with low surface chemical reactivity towards oxygen and hydrogen – TiO2 and GaN – preferentially produce H2 since all organic intermediates are unstable and rapidly consumed in reverse reactions.