resumo
The role of the step sites in the water gas shift reaction catalyzed by Cu surfaces has been studied by using the Cu(321)-stepped surface as a representative model and periodic density functional theory within a supercell approach. Several reaction pathways were considered and the corresponding transition states for the elementary steps on each pathway were located and characterized. It was found that the presence of steps favors the associative route through the carboxyl intermediate assisted by co-adsorbed OH. The presence of step sites decreases the activation energy barriers for the rate-limiting steps, compared to the perfect Cu(111) surface. Reaction rate constants for the different pathways involved in the two molecular mechanisms, obtained from transition state theory, are reported. Finally comparison to previous work allows one to propose a useful Bronsted-Evans-Polanyi relationship. (C) 2009 Elsevier Inc. All rights reserved.
palavras-chave
GENERALIZED GRADIENT APPROXIMATION; DENSITY-FUNCTIONAL THEORY; TOTAL-ENERGY CALCULATIONS; AUGMENTED-WAVE METHOD; CO OXIDATION; GOLD NANOPARTICLES; METHANOL SYNTHESIS; CU(HKL) SURFACES; AU(321) SURFACE; ACTIVE-SITES
categoria
Chemistry; Engineering
autores
Fajin, JLC; Cordeiro, MNDS; Illas, F; Gomes, JRB
nossos autores
José R. B. Gomes
Investigador Principalagradecimentos
Financial support from FEDER, Portuguese Fundacao para a Ciencia e Tecnologia (FCT), Conselho de Reitores das Universidades Portuguesas (CRUP), and Spanish Ministerio de Ciencia e Innovacion (MICCIN) through Grants Programa Ciencia 2007, Accao E43/08, FIS2008-02238, and HP2007-0042 is fully acknowledged. JLCF thanks FCT for a post-doctoral grant (Ref. SFRH/BPD/27167/2006).