Of. Gorriz et Le. Cadus, Supported chromium oxide catalysts using metal carboxylate complexes: dehydrogenation of propane, APP CATAL A, 180(1-2), 1999, pp. 247-260
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.