Supported chromium oxide catalysts using metal carboxylate complexes: dehydrogenation of propane

The present paper constitutes the first stage of a systematic study of the influence of precursor nature and structure on the catalyst behavior in deh ydrogenation of propane, by varying the nature of the ligands and the nucle arity of the starting compounds at fixed net surface potentials. We show re sults obtained by the use of different Cr carboxylates to design the Cr2O3/ gamma-Al2O3 catalyst at low loadings and these results are compared with th ose obtained for chromic acid. The following short chain chromium compounds were selected as precursors: citrate (Cr(In)), dimer monohydrate acetate ( Cr(II)), acetyl acetonate (Cr(III)) and hydroxyacetate (Cr(III)). An exhaus tive characterization by means of BET surface, XPS, XRD, X-ray fluorescence , laser Raman spectroscopy, EPR and catalytic test in propane dehydrogenati on enabled us to draw relevant conclusions. Low metal-support interaction m ight be the major cause of polymerization in Carbox. The interaction betwee n the chromia phase and the support surface, which stabilizes different oxi dation stages and coordinations of the chromia species, defines the surface architecture. Part of the Cr3+ is, incorporated in the vacant octahedral s ites of the spinel surface. The larger extension of this phenomenon in Cral might be responsible for surface inactive species that could cause a loss of catalytic activity. Deactivation between cycles might depend on the cata lyst stabilization by the incorporation of Cr3+ into the support structure. The surface array of monomer species in a polymer species environment stab ilizes the catalyst architecture and confers characteristics of high stabil ity between cycles. The above considerations permit to infer that chromium carboxylates are interesting precursors for the control of surface species in chromia/Al2O3 catalysts. (C) 1999 Elsevier Science B.V. All rights reser ved.