Surface investigation by X-ray photoelectron spectroscopy of Ru-Zn catalysts for the partial hydrogenation of benzene

Abstract

Partial hydrogenation of benzene with ruthenium-supported catalysts is an interesting alternative route to produce cyclohexene, an intermediate in the production of nylon 6.6 and other fine chemicals. In this work, ruthenium chloride solution was added to xZnO/Al2O3 by wetness impregnation. The supports were derived from hydrotalcite compounds and tested on the partial hydrogenation of benzene. The catalyst with 10 wt.% of ZnO (Ru10ZnAl) presented the best catalytic performance reaching total conversion in 40 min of the reaction, and a maximum yield of 35% using pure benzene (without water, salts or other additives). The samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF), X-ray diffraction (XRD), temperature programmed reduction (TPR) and H2 Chemisorption. Metallic and partially reduced ruthenium surface species were identified on the surface of the Ru10ZnAl catalyst and the electronic vicinity of Ru is proposed to be responsible for promoting the cyclohexene desorption, revealing a synergistic effect. In this sense, the electronic surroundings modification of surface zinc species with ruthenium species, followed by reduction, was evidenced by using the Modified Auger Parameter (MAP). These species played an important role in the reaction.