Surface reactions of hydrocarbons as a probe for the characterization of RhCu/SiO sub 2 catalysts

Journal Article · Thu Jun 15 04:00:00 EDT 1989 · Journal of Physical Chemistry; (USA)

DOI:https://doi.org/10.1021/j100349a045· OSTI ID:7022173

Coq, B; Dutartre, R; Figueras, F ^[1]; Rouco, A ^[2]

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1. ENSCM, Montpellier (France)
2. Plapiqui (UNS CONICET), Bahia Blanca (Argentina)

RhCu/SiO{sub 2} catalysts of various compositions were prepared from nitrate precursors and characterized by transmission electron microscopy and chemisorption. The catalytic properties were determined in a flow microreactor, at low conversion, for the hydrogenation of benzene, poisoned or not by thiophene, and the conversion of a series of alkanes: n-hexane (n-H), 2-methylpentane (2MP), 2,2-dimethylbutane (22DMB), 2,2,3,3-tetramethylbutane (2233TMB), methylcyclopentane (MCP). The conversion of alkanes at 493 K gives mainly hydrogenolysis of C-C bonds. The rate of cleavage depends on the degree of substitution of the carbon atoms and on the Cu/Rh ratio. Cu inhibits all reactions; however, the magnitude of this effect depends on the structure of the reactant. The comparison of the alloying effect with the effect of Rh particle size on the same set of reactions (Coq et. al.) shows that on the one hand 2233TMB has a lower sensitivity to alloying than to particle size; the selectivity to i-C{sub 4} remains high and characteristic of large particles of rhodium up to Cu/Rh = 1. On the other hand n-H, 2MP, and MCP are more sensitive to alloying than to change of particle size. These results suggest that Cu occupies preferentially the sites of low coordination, edges, and corners, and Rh the sites of high coordination on dense planes. This set of reactions, therefore, probes the extent of surface segregation on RhCu-supported particles.. By addition of thiophene a monotonic decrease of activity in the hydrogenation of benzene occurs due to sulfurization of the surface. The rate of poisoning is faster when the local density of states at the Fermi level of Rh surface atoms is higher. Dilution of Rh by Cu has little effect on the thioresistance which remains low even at high Cu content. Very likely little electronic interaction occurs between Rh and Cu.

• OSTI ID: 7022173
• Journal Information: Journal of Physical Chemistry; (USA), Journal Name: Journal of Physical Chemistry; (USA) Vol. 93:12; ISSN 0022-3654; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
CATALYSTS
CHALCOGENIDES
COPPER
DATA
DATA ANALYSIS
ELEMENTS
EXPERIMENTAL DATA
HYDROCARBONS
INFORMATION
MEASURING INSTRUMENTS
MEASURING METHODS
METALS
NUMERICAL DATA
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PLATINUM METALS
RHODIUM
SILICON COMPOUNDS
SILICON OXIDES
SURFACE PROPERTIES
TRANSITION ELEMENTS