Catalytic activity of Co–Ag nanoalloys to dissociate molecular hydrogen. New insights on the chemical environment. (22nd May 2022)

• Record Type: Journal Article
• Authors: Ortega, Guillermo; Germán, Estefanía; López, María J.; Alonso, Julio A.
• Is Part Of: International journal of hydrogen energy. Volume 47:Number 44(2022)
• Page Start: 19038
• Page End: 19050
• Publication Date: 2022-05-22
• Subjects: Nanoalloys -- Co–Ag clusters -- Hydrogen adsorption -- Heterogeneous catalysis; Hydrogen as fuel -- Periodicals; Hydrogène (Combustible) -- Périodiques; Hydrogen as fuel; Periodicals; 665.81
• DOI: 10.1016/j.ijhydene.2022.04.090
• Languages: English
• ISSNs: 0360-3199

Abstract

Abstract: Adsorption of molecular hydrogen on the surface of catalytic metal nanoparticles and its dissociation in atomic hydrogen are processes of interest in many chemical technologies. As in other chemical reactions, alloying can improve the efficiency of the catalysts. By focusing on Co6, Co5 Ag, Co3 Ag3 and CoAg5, we explore the effect of changing the relative concentration of the two components in small Com Agn clusters, a peculiar nanoalloy because Co and Ag do not form bulk solid alloys. Molecular hydrogen adsorbs preferentially on the Co atoms, and the binding is mainly due to the electrical polarization of the charges of adsorbate and host. The preference for Co sites and the trend in the strength of the H2 -cluster binding are explained by the combination of two effects characterizing the host environment. One of these is geometric, arising from the degree of exposure of the host atom: the lower the atomic coordination of the host atom, the stronger its bonding with H2 . The second effect, newly identified, reveals the importance of the chemical nature of the host atom environment: host Co atoms having both Co and Ag neighbors maintain their capacity to bind hydrogen more intact than those with only Co neighbors. The alloy nanoclusters catalyze the dissociation of adsorbed H2 by building up quite small activation barriers. After dissociation, the H atoms occupy bridge positions between Co atoms (between Co and Ag in CoAg5 ). H2 adsorption and dissociation may trigger structural transformations of the cluster. The work shows that the adsorption and dissociation properties of H2 can be tuned by varying the relative composition of the two atomic species in the nanoalloy. Highlights: Alloying Co clusters with Ag improves their catalytic activity towards hydrogen. Hydrogen adsorbs preferentially on the Co atoms of the CoAg nanoalloys. Adsorption sites are determined by host coordination and chemical environment. Activation barriers for H2 dissociation on CoAg nanoalloys are small.