Role of excited atomic states in the active sites of transition metals for oxidative and reductive catalytic processes
Por:
Garcia-Prieto J., Ruiz M.E., Novaro O.
Publicada:
1 ene 1985
Resumen:
Model potential configuration-interaction calculations using a variational reference state of ?100 configurations and a Møller-Plesset perturbational study including another ?750 000 configurations are addressed in the study of a model for the oxidative and reductive processes that occur at a metallic copper catalyst. The main goal is to show the central role that is played by the excited states of a transition metal, since without their detailed knowledge, one may grossly overestimate the activation barrier for the H-H bond breaking in the chemisorption process of a H2 molecule. The potential energy surfaces relevant to the study of the oxidative and reductive processes include those used before in the study of the photochemical reaction of a Cu atom with a H2 molecule at matrix isolation conditions and also additional calculations for a total three-dimensional image of these important potential energy surfaces. We also study the relative minima for the intermediate CuH2 system, which is unobservable for the photochemical process as reported elsewhere, but very crucial here as a model of the chemisorbed species of the oxidative and reductive catalytic processes. In consequence a very detailed description of the bent and linear geometries of the CuH2 complex is given, with emphasis on the molecular orbital structures, charge transfer, etc. From all this we conclude that two possible chemisorbed forms of H2 on copper exist: one with a very weak H-H bond, another with only atomic hydrogen on the copper sites. Our calculations predict an energy barrier for chemisorption of 28 kcal/mol, virtually identical with the experimental dissociative adsorption energy for H2 on copper. © 1985 American Chemical Society.
Filiaciones:
Garcia-Prieto J.:
Instituto Mexicano del Petróleo, Investigación Básica de Procesos, A.P. 14-805 07730 D.F, United States
Ruiz M.E.:
Instituto Mexicano del Petróleo, Investigación Básica de Procesos, A.P. 14-805 07730 D.F, United States
Novaro O.:
Instituto de Física, U.N.A.M., A.P. 20-364 01000 D.F, United States
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