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CO Self-Promoting Hydrogenation on CO-Saturated Ru(0001): A New Theoretical Insight into How H₂ Participates in CO Activation

Zhao, Peng, He, Yurong, Cao, Dong-Bo, Xiang, Hongwei, Jiao, Haijun, Yang, Yong, Li, Yong-Wang, Wen, Xiao-Dong
Journal of physical chemistry 2019 v.123 no.11 pp. 6508-6515
adsorption, carbon monoxide, catalytic activity, chemical bonding, cleavage (chemistry), hydrogen, hydrogenation, ruthenium, thermodynamics
Dissociation of CO often occurs on Ru surfaces with dense chemisorbed CO (CO*) adlayers, ubiquitous in the practice of catalysis, where the strong bond in CO tends to weaken via bimolecular reactions with H₂ before cleavage. Nevertheless, H₂ adsorption on CO*-crowded Ru surfaces is a rare event because of the CO*-induced barrier and the competitive adsorption between CO and H₂. Here, we thereby performed a comprehensive ab initio study of the coadsorption of CO and H₂ as well as the following initiation reaction on Ru(0001). At 100–550 K (3 MPa, H₂/CO = 2), Ru(0001) is always saturated, covered by CO with a “hexagonal” pattern, where H₂ adsorption is neither kinetically nor thermodynamically favored. On the basis of a systematic analysis of the electronic structure, we find that two adjacent coadsorbed CO* can serve as a promoter for the scission of the H–H bond in H₂(g), leading to the simultaneous formation of two COH* molecules in one step (Eₐ = 1.64 eV). This so-called CO self-promoting hydrogenation route offers new insights into the fundamental mechanism for CO activation on CO*-crowded low-index Ru surfaces.