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Electronic state and catalytic activity of SiO 2 doped γ–Al 2 O 3
Author(s) -
Bertóti I.,
Mink G.,
Székely T.,
Varsányi G.,
Réti F.
Publication year - 1986
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.740090407
Subject(s) - catalysis , x ray photoelectron spectroscopy , doping , auger , chemistry , cracking , acceptor , analytical chemistry (journal) , monolayer , materials science , chemical engineering , atomic physics , organic chemistry , biochemistry , physics , optoelectronics , engineering , condensed matter physics
Silica‐alumina catalysts have been applied for a long time in cracking and reforming reactions. Lewis type surface sites are generally accepted to serve as active centers. In this respect, surface properties of these materials are of main concern. In the present work SiO 2 doped γ‐Al 2 O 3 with less than a monolayer coverage were prepared by the reaction of SiCl 4 (g) with γ‐Al 2 O 3 at 820‐1120 K. Catalytic activity of the samples was tested by a model reaction of n ‐hexane cracking. Surface composition and electronic state were evaluated by XPS investigations performed on a KRATOS XSAM 800 instrument. Catalytic activity (conversion) varies remarkably with increasing Si content showing a sharp maximum at low Si coverage. The observed shift of Al 2p lines with increasing Si content is interpreted as an enhancement of the acceptor or acidic character of the surface Al atoms. The Auger parameter for Si(α' Si ), (composed by addition of Si 2p BE and Si (KLL) KE values) passes also through a maximum at the same Si‐content, as does the conversion curve. A close correlation of the Auger parameter and the catalytic activity is established for samples with (Si/Al)≲7%. This leads to a conclusion, that the rise in extra‐atomic relaxation energy may serve as an additional indication of enhanced catalytic activity.