Structure of rhodium in an ultradispersed rhodium/alumina catalyst as studied by EXAFS and other techniques

Abstract

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Preparation of a rhodium catalyst from rhodium trichloride on a flat, conducting alumina support studied with static secondary ion mass spectrometry and monochromatic X-ray photoelectron spectroscopy

“…This first step is only partially complete after reduction at 100~ and complete after the same treatment at 200~ The second step involves the removal of residual chlorine from the support, reduction at 300~ is sufficient to decrease the CI-and C10-intensities to typical background levels. Porous alumina-supported catalysts retain considerably more chlorine [4,5], also after reduction at 300~ We think that diffusion limitations and readsorption, which are present in porous but absent in flat supports, may explain the difference in behavior with respect to C1 retention.…”

“…At low pH, negatively charged complexes may adsorb on the positively charged alumina surface. Chlorine is known to be retained in significant amounts by alumina supports [4,5] and is expected to affect the catalytic properties of rhodium surfaces [6]. In this letter we use static secondary ion mass spectrometry (SIMS) and monochromatic X-ray photoelectron spectroscopy (XPS) to characterize the state of the catalyst in various stages of the preparation, and we investigate in particular whether chlorine residues from the catalyst precursor are in contact with rhodium in the reduced catalyst.…”

The morphology of rhodium supported on TiO2 and Al2O3 as studied by temperature-programmed reduction-oxidation and transmission electron microscopy

“…For Rh/TiOz this occurs for metal loadings below 0.5%, and for Rh/ AlZ03 even for metal loadings up to 5%. Although in this study only two catalysts with an H/I& value above unity were investigated, we have reported about other ultradispersed systems elsewhere (32,36). In our opinion, if one accepts that a metal atom such as rhodium can adsorb two or more CO molecules, one should not reject the idea of that same atom adsorbing more than one hydrogen atom.…”

“…Upon CO adsorption the very small rhodium particles are broken up into Rh(I)(CO)z species, which give the twin IR absorption. EXAFS proof for this explanation has been published elsewhere (36).…”

Structure and Reactivity of Bimetallic FeIr/SiO2 Catalysts after Reduction and during High-Pressure CO Hydrogenation

“…CO-induced changes in structure are also known to occur in different types of supported noble metal catalysts (32)(33)(34). Nevertheless, the structure of the activated FeM/SiO 2 catalysts has not yet received much attention.…”