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
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
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.