The UBI-QEP method: Mechanistic and kinetic studies of heterogeneous catalytic reactions

Applications of the unity bond index-quadratic exponential potential ( UBI-QEP) method in mechanistic and kinetic studies of complex heterogeneous catalytic reactions are discussed. It is shown how UBI-QEP energetics helps to answer specific questions regarding the mechanisms of various reactions on metal surfaces. Examples of the following reactions are considered: elementary reactions of hydrogen transfer ( from one carbon atom connected to the metal surface to another such atom in a different surface species), H-X bond breaking with the assistance of coadsorbed oxygen, methanol synthesis, Fischer-Tropsch synthesis, ammonia synthesis and decomposition, and partial methanol oxidation to formaldehyde. Then, examples of kinetic simulations using UBI-QEP energetics are considered for the following processes: ethane hydrogenolysis, water-gas shift reaction, selective hydrogenation of acetylene in ethylene-rich mixtures, oxidative conversions of hydrogen and methane on Pt and Rh surfaces, ammonia decomposition, C-1-C-2 product formation in Fischer Tropsch synthesis over cobalt, and steam reforming of methane. It is shown how the use of UBI-QEP and Monte Carlo methods makes it possible to calculate reaction parameters that depend on temperature in the equilibrium and kinetic regimes. To increase the accuracy of simulations, we added nonenergetic parameters affecting energetics at nonzero coverages: a spatial constraint on the distance between adsorbed atoms and the distance of hot atom traveling upon oxygen dissociation on metal surfaces. The UBI-QEP/ Monte Carlo simulation method is illustrated by the study of molecular oxygen adsorption on single crystalline nickel surfaces. In most UBI-QEP-based mechanistic and kinetic studies of heterogeneous catalytic reactions, good agreement is observed with experimental observations, in many cases on a quantitative level. Taking into account diversity of reactions to which the method has been applied the agreement with experiments supports the efficiency of the method in solving mechanistic and kinetic problems.