Steam dealkylation of aromatic hydrocarbons. II. Role of the support and kinetic pathway of oxygenated species in toluene steam dealkylation over group VIII metal catalysts. [Catalyst support comparison]
The role of support in steam dealkylation (SDA) is studied on a series of Group VIII metal catalysts supported on alumina, silica, and titania. When possible turnover frequencies are given on the basis of the free metal fraction during the reaction, the values are generally constant with time-on-steam and represent the actual turnover frequency of the catalysts. Metals can be classified into two groups, namely, support-sensitive metals (Pt,Rh,Pd) and support-insensitive metals (Ni,Co,Ru and to a certain extent Ir). Support sensitivity is related to the oxidizability of the metallic surface. For metals of the first group, the reaction is probably governed by a noncompetitive mechanism in which the metal coverage by the oxygenated species is negligible. Kinetic derivation leads to a rate law where there is at once intervention of the support site concentration and of the specific perimeter of the metal/support interface. One can thus explain the support effect for this metal group and the slight sensitivity to the crystallite size observed in the Rh/Al/sub 2/O/sub 3/ series. For metals of the second group, a competitive mechanism probably takes place on the metal. Kinetic derivation leads to a rate law independent of the support site concentration and accounting for the slight negative order with respect to toluene as previously reported. The conspicuous parallelism between the selectivities of the various metals in SDA, in hydrodealkylation , and in hydrogenolysis is also discussed. In addition to the metal, the support and the crystallite size are determining factors of the selectivity to benzene in SDA.
- Research Organization:
- Group de Recherche sur la Catalyse en Chimie Organique, Poitiers, France
- OSTI ID:
- 6938714
- Journal Information:
- J. Catal.; (United States), Journal Name: J. Catal.; (United States) Vol. 75:1; ISSN JCTLA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
AROMATICS
CATALYST SUPPORTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISORPTION
COBALT
COMPARATIVE EVALUATIONS
DATA
DEALKYLATION
ELEMENTS
EXPERIMENTAL DATA
HYDROCARBONS
INFORMATION
KINETICS
METALS
NICKEL
NUMERICAL DATA
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PLATINUM METALS
REACTION KINETICS
SEPARATION PROCESSES
SILICON COMPOUNDS
SILICON OXIDES
SORPTION
TITANIUM COMPOUNDS
TITANIUM OXIDES
TOLUENE
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS