The effect of second-phase oxides on the catalytic properties of dispersed metals: Cobalt supported on 12% WO 3/Al 2O 3

Abstract

The differences in the amphoteric properties Of WO 3 and Al 2O 3 were exploited and cobalt precursors were selectively mounted on the tungsten oxide phase of a 12% WO 3/Al 2O 3 composite. Temperature-programmed reduction (TPRd), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and catalyst performance testing using H 2/CO methanation as a test reaction revealed that this composite-supported catalyst's properties were significantly different from cobalt supported on alumina. Cobalt crystallites as well as a CoAl 2O 4 type of surface species are formed on the Al 2O 3 support. The presence of WO 3 as a second-phase oxide offers the possibility for a greater number of surface compounds to be formed on the composite. Specifically, cobalt-tungsten interaction species are formed. We provide evidence that strongly suggests the active catalytic center in the conversion of H 2 and CO to methane is a (cobalt-tungsten) interaction species. These active centers. are present on CO/WO 3, Co/12% WO 3/Al 2O 3, and a commercial cobalt/tungsten oxide compound. A portion of the cobalt: in these active centers is not reduced to the metallic state.