Quantitative determination of the number of active surface sites and the turnover frequencies for methanol oxidation over metal oxide catalysts - I. Fundamentals of the methanol chemisorption technique and application to monolayer supported molybdenum oxide catalysts

Citation
Le. Briand et al., Quantitative determination of the number of active surface sites and the turnover frequencies for methanol oxidation over metal oxide catalysts - I. Fundamentals of the methanol chemisorption technique and application to monolayer supported molybdenum oxide catalysts, CATAL TODAY, 62(2-3), 2000, pp. 219-229
Citations number
22
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
CATALYSIS TODAY
ISSN journal
09205861 → ACNP
Volume
62
Issue
2-3
Year of publication
2000
Pages
219 - 229
Database
ISI
SICI code
0920-5861(20001010)62:2-3<219:QDOTNO>2.0.ZU;2-G
Abstract
A detailed study of the methanol chemisorption and oxidation processes on o xide surfaces allowed the development of a method to quantify the number of surface active sites (N-S) of metal oxide catalysts. In situ infrared anal ysis during methanol adsorption showed that molecular methanol and surface methoxy species are co-adsorbed on an oxide surface at room temperature, bu t only surface methoxy species are formed at 100 degreesC. Thermal stabilit y and products of decomposition of the adsorbed species were determined wit h temperature programmed reaction spectroscopy (TPRS) experiments. Controll ed adsorption with methanol doses resulted in a stable monolayer of surface methoxy species on the oxide surfaces. The stoichiometry of methanol chemi sorption resulted in one surface methoxy adsorbed pier three Mo atoms for p olymerized surface molybdenum oxide structures, regardless of surface molyb denum oxide coordination. The activity of the catalysts per surface active sites (turnover frequencies - TOF) was calculated in order to quantitativel y compare the reactivity of a series of monolayer supported molybdenum oxid e catalysts. The TOF value trends reflect the influence of the bridging Mo- O-Support bond and the electronegativity of the metal cation of the oxide s upport, (C) 2000 Elsevier Science B.V. All rights reserved.