Pt/MgO as catalyst for hydrogenolysis reactions of C[sub 5] and C[sub 6] hydrocarbons: Evidence for metal-support interactions

Journal Article · Wed Sep 01 04:00:00 EDT 1993 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1006/jcat.1993.1259· OSTI ID:5548180

Clarke, J K.A.; Bradley, M J ^[1]; Garvie, L A.J.; Craven, A J; Baird, T ^[2]

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1. Univ. College Dublin, Belfield (Ireland)
2. Univ. of Glasgow (United Kingdom)

Pt/magnesia catalysts having high metal dispersion (av. dia. 21 [angstrom]) have been prepared employing nonaqueous impregnating solutions and an incipient wetness technique. Both chlorine-free and residual-chlorine-containing catalysts were studied, the latter being prepared from platinum (IV) chloride. Both types of catalyst are of negligible sulphur content (<2ppm). Comparison of hydrogen chemisorption and transmission electron microscopy results for both [open quotes]chlorine-free[close quotes] and chlorine-containing Pt/MgO catalysts showed that (i) chemisorption capacity was substantially as expected from TEM-derived particle size following a reduction temperature of 593 K (LTR), and (ii) chemisorption was depressed to 40% or less of expectation when a reduction temperature of 753 K (HTR) was used. Reactions of saturated hydrocarbons in a flow of hydrogen (p[sub hydrocarbon] = 8-16 Torr, balance to 760 Torr hydrogen) showed hydrogenolysis to be a prominent reaction. With LTR chlorine-free catalysts, hydrogenolysis of n-pentane was almost exclusively by central scission. The chlorine-containing HTR catalyst yielded largely terminal scission. HTR chlorine-free catalysts and LTR chlorine-containing catalysts gave an intermediate behavior. Thus, both higher reduction temperature and presence of chlorine act to move scission of the C-C chain from the center to the ends. Hydrogenolysis of neohexane showed increased direct demethanation to give n-butane with the presence of chlorine in the catalyst. Ring scission of methylcyclopentane depressed hydrogen chemisorption and the carbanionic reactivity in these cracking reactions are interpreted in terms of a moderately strong metal-support interaction with a shift of negative charge from the magnesia O[sup 2[minus]] ions to the platinum. This interaction is increased by the presence of chlorine in the catalysts. 40 refs., 4 figs., 7 tabs.

• OSTI ID: 5548180
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 143:1; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

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ALKALINE EARTH METAL COMPOUNDS
ALKANES
CATALYSIS
CATALYST SUPPORTS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTIONS
CHEMISORPTION
ELECTRON MICROSCOPY
ELEMENTS
HETEROGENEOUS CATALYSIS
HEXANE
HYDROCARBONS
HYDROGEN
HYDROGENATION
MAGNESIUM COMPOUNDS
MAGNESIUM OXIDES
METALS
MICROSCOPY
NONMETALS
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PARTICLE SIZE
PENTANE
PLATINUM
PLATINUM METALS
REDUCTION
SEPARATION PROCESSES
SIZE
SORPTION
TRANSITION ELEMENTS
TRANSMISSION ELECTRON MICROSCOPY