DRIFT, XPS and XAS Investigation of Au–Ni/Al2O3 Synergetic Catalyst for Allylbenzene Isomerization.

Au/Al2O3 and Ni/Al2O3 prepared by deposition-precipitation and impregnation methods, respectively, and Au–Ni/Al2O3 prepared by impregnation of the Au/Al2O3 system with nickel have been studied by physicochemical methods. The catalysts were tested in allylbenzene isomerization at 443 K. The isomerization on Au/Al2O3 proceeds with a rather low rate, while monometallic Ni/Al2O3 is inactive. Unlike monometallic catalysts, Au–Ni/Al2O3 demonstrates a strong synergetic effect: the isomerization rate on the bimetallic sample exceeds the sum of the rates over the individual metals by an order of magnitude. The catalysts structure was estimated by XPS, DRIFT, and XAS techniques. It was revealed that nickel in Au–Ni/Al2O3 and Ni/Al2O3 exist as Ni2+ cations with the coordination state close to that in the precursor, gold in Au/Al2O3 exist as Au0 nanoclusters, whereas the Au0 nanoclusters co-exist with Au3+ cations in the bimetallic Au–Ni/Al2O3 sample. Reasons of the synergetic catalytic effect for Au–Ni/Al2O3 are discussed in terms of the formation of new positively charged Au catalytic centers. [ABSTRACT FROM AUTHOR]