Surface Chemistry of Supported Chromium Oxide Catalysts

✍ Scribed by D.S. Kim; I.E. Wachs

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 362 KB
• Volume: 142
• Category: Article
• ISSN: 0021-9517
• DOI: 10.1006/jcat.1993.1198

✦ Synopsis

A series of (1 / % \mathrm{CrO}{\text {, }}) supported on different oxide supports (\left(\mathrm{Al}{2} \mathrm{O}{3}, \mathrm{TiO}{2}, \mathrm{ZrO}{2}, \mathrm{Nb}{2} \mathrm{O}{5}, \mathrm{SiO}{2}\right.), and (\mathrm{MgO})) was structurally characterized by Raman spectroscopy and chemically probed by methanol oxidation. The Raman results reveal that the polymeric chromium oxide species possessing two terminal (\mathrm{Cr}=\mathrm{O}) bonds preferentially exist on the (\mathrm{Al}{2} \mathrm{O}{3}, \mathrm{TiO}{2}, \mathrm{ZrO}{2}), and (\mathrm{Nb}{2} \mathrm{O}{5}) supports, and isolated chromate species with two (\mathrm{Cr}=\mathrm{O}) ) bonds predominate on the (\mathrm{SiO}{2}) support. Nonstoichiometric compounds such as (\mathrm{Mg}{1} /\left(\mathrm{CrO}{+}\right)), are present on the (\mathrm{MgO}) support due to the strong acid-base interaction of (\mathrm{CrO}{4}^{--})with (\mathrm{MgO}). The methanol oxidation reaction reveals that the reactivity of the surface chromium oxide species was primarily controlled by the specific oxide support which acts as a ligand, and not the molecular structure of the surface chromium oxide species. The selectivity of the supported chromium oxide catalysts in influenced by the acid-base characteristics of the oxide supports. " 1993 Acadlemic Press. Inc.