Characterization of the adsorbed state of isoprene on alumina and copper-alumina catalysts by sup 13 C NMR and in situ diffuse reflectance infrared spectroscopy

Journal Article · Thu Aug 23 00:00:00 EDT 1990 · Journal of Physical Chemistry; (USA)

DOI:https://doi.org/10.1021/j100380a040· OSTI ID:6331228

Rigole, M; Depecker, C; Wrobel, G; Legrand, P; Guelton, M; Bonnelle, J P ^[1]

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1. Universite des Sciences et Techniques de Lille Flandres-Artois, Villeneuve d'Ascq (France)

In situ {sup 13}C NMR spectroscopy and diffuse reflectance infrared spectroscopy (DRIFTS) have been used to characterize the adsorbed states of isoprene on both {gamma}-Al{sub 2}O{sub 3} and Cu/{gamma}-Al{sub 2}O{sub 3} catalysts. Both techniques have been shown to be quite complementary and provide very fine information. Isoprene molecules are physisorbed only at room temperature on alumina. On reduced copper-alumina, isoprene is mainly physisorbed, but a few chemisorbed species are evidenced. Taking into account the {sup 13}C NMR line-width variations and the IR results, an adsorption model is proposed for Cu/{gamma}-Al{sub 2}O{sub 3}: reduced copper induces a selective orientation for the physisorbed isoprene molecules. The chemisorbed species detected by DRIFTS is attributed to a {pi}-complex of isoprene with Cu{sup +} sites on the reduced copper-alumina spinel surface. The physisorbed species is the precursor of this {pi}-complex, and this view agrees with the selectivity of isoprene hydrogenation on copper catalysts.

• OSTI ID: 6331228
• Journal Information: Journal of Physical Chemistry; (USA), Journal Name: Journal of Physical Chemistry; (USA) Vol. 94:17; 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
ADSORPTION
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CATALYSTS
CHALCOGENIDES
CHEMICAL REACTIONS
CHEMISORPTION
COPPER
DIENES
ELEMENTS
HYDROCARBONS
HYDROGENATION
INFRARED SPECTRA
ISOPRENE
METALS
NMR SPECTRA
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
POLYENES
SEPARATION PROCESSES
SORPTION
SPECTRA
TRANSITION ELEMENTS