Effect of Zn 2+/Zn layer on H 2 dissociation on Ruthenium (0001) surface: A first principles density functional study

Abstract

For the sake of improving the performance of Ru-based catalyst used in partial hydrogenation of benzene to cyclohexene, the effect of Zn 2+/Zn layer on the adsorption and dissociation of H 2 on Ru (0001) surface was investigated by applying density function theory (DFT) calculations. Calculation results show that the dissociation of H 2 occurs only after its being chemisorbed horizontally at atop site. Because of the influence of Zn 2+ on the electron delocalization between molecular orbit of H 2 and valence orbits of atop Ru atom, a remarkable increase in the H 2 dissociation barrier is noticed, which results in zones of sparse chemisorbed H around Zn 2+. Adsorbed Zn 2+ can be reduced by chemisorbed H, and the H 2 dissociation kinetics varies little in the presence of Zn atoms at adjacent sites. Split zones of chemisorbed H are formed at a high coverage of Zn layer. The consecutive or synchronous hydrogenation of benzene is disturbed when benzene is adsorbed in zones of sparse chemisorbed H or split zones of chemisorbed H. It is therefore deducted that a high coverage layer of some transition metal atoms on catalyst surface should be helpful for maintaining the hydrogenation activity of the catalyst and improving the cyclohexene yield.