The hydrogenation of toluene and o-, m-, and p-xylene over palladium. I. Kinetic behavior and o-xylene isomerization

Journal Article · Tue Jan 01 00:00:00 EST 1991 · Journal of Catalysis; (USA)

OSTI ID:5650462

Rahaman, M V; Vannice, M A ^[1]

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1. Pennsylvania State Univ., University Park (USA)

The vapor-phase hydrogenation of toluene and o-, m-, p-xylene was studied over Pd powder and Pd dispersed on MgO, SiO{sub 2}, Al{sub 2}O{sub 3}, and TiO{sub 2}. As with benzene, the use of the last two acidic oxides can markedly enhance activities, but the relative change diminishes as methyl groups are added; for example, the average enhancement in turnover frequency was 8 for toluene while the lowest was 3 for m-xylene. The turnover frequency decreased in the following order: benzene > toluene {ge} p-xylene {ge} m-xylene > o-xylene; however, the differences were less pronounced for Pd powder and Pd/MgO compared to Pd/SiO{sub 2}-Al{sub 2}O{sub 3} and Pd/TiO{sub 2}. This trend is attributed to an electronic effect on the aromatic ring related to the addition of methyl groups although steric hindrance also appears to be responsible for the consistently low rates for 0-xylene hydrogenation. All reactions were first order in H{sub 2} and zero order in the aromatic compound, and activation energies were near that of benzene and did not vary significantly, as average values were 11.8, 12.0, 12.7, and 13,7 for toluene, m-xylene, o-xylene, and p-xylene, respectively. Isomerization of o-xylene to m-xylene was observed over all the Pd catalysts thus verifying the presence of acid sites on the support.

• DOE Contract Number: FG02-84ER13276
• OSTI ID: 5650462
• Journal Information: Journal of Catalysis; (USA), Vol. 127:1; ISSN 0021-9517
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
02 PETROLEUM
COAL LIQUIDS
REFINING
PALLADIUM
CATALYTIC EFFECTS
TOLUENE
HYDROGENATION
XYLENES
ISOMERIZATION
ACTIVATION ENERGY
ALUMINIUM OXIDES
BENZENE
CATALYST SUPPORTS
CHEMICAL REACTION KINETICS
COMPARATIVE EVALUATIONS
MAGNESIUM OXIDES
SILICON OXIDES
TITANIUM OXIDES
ALKALINE EARTH METAL COMPOUNDS
ALKYLATED AROMATICS
ALUMINIUM COMPOUNDS
AROMATICS
CHALCOGENIDES
CHEMICAL REACTIONS
ELEMENTS
ENERGY
FLUIDS
HYDROCARBONS
KINETICS
LIQUIDS
MAGNESIUM COMPOUNDS
METALS
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PLATINUM METALS
PROCESSING
REACTION KINETICS
SILICON COMPOUNDS
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
010402* - Coal
Lignite
& Peat- Purification & Upgrading
020400 - Petroleum- Processing