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

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.