Active fixed chromium catalysis for CO oxidation. Preparation and active structure of fixed Cr and Cr 2 catalysts

Abstract

The catalytic oxidation of CO with O 2 (398–509 K) over fixed Cr or Cr 2 catalysts, prepared by the fixing reaction of Cr(η 3-C 3H 5) 3 or Cr 2(η 3-C 3H 5) 4 with surface OH groups of SiO 2, was studied to determine the structure and environment of active sites in terms of catalytic activities, activation energies, Racah parameters, ESR peak widths, photoluminescence and adsorptions of CO or O 2. The monochromate structure fixed on originally acidic OH groups of the SiO 2 surface was easily rearranged by three redox treatments to form the surface cluster, ▪ with one vacant site on a Cr 3+ ion and with a suitable exchange interaction between the Cr 3+ ions. This rearranged surface showed a much higher activity than the virgin fixed Cr catalyst with mainly monochromate species, the fixed Cr 2 catalyst with mainly dichromate species and a conventional impregnation catalyst.