Surface properties and catalytic activity of a Mo-fixed catalyst. Structure of the active site and mechanism for selective oxidation of ethyl alcohol

Abstract

The physico-chemical properties of the surface of a Mo-fixed catalyst obtained by a ready reaction between Mo(π-C₃H₅)₄ and surface OH groups of SiO₂ were investigated by X-ray photoelectron spectroscopy, photoluminescence technique, u.v. diffuse reflectance spectroscopy, i.r. spectrometry and H₂/O₂ uptake. The difference between the surface properties of the fixed catalyst and the conventional impregnation catalyst is discussed. The Mo-fixed catalyst showed higher activity and selectivity than the conventional impregnation catalyst in the ethyl alcohol oxidation. Selective oxidation to form acetaldehyde proceeded by a two-stage redox (Mo⁶⁺⇌ Mo⁴⁺) mechanism. Coordinatively unsaturated dioxomolybdenum of uniform nature in a tetrahedral coordination is the active species in the selective oxidation of ethyl alcohol.