Heat of adsorption of carbon monoxide on a Ru/Al2O3 catalyst using adsorption equilibrium conditions at high temperatures

Citation
O. Dulaurent et al., Heat of adsorption of carbon monoxide on a Ru/Al2O3 catalyst using adsorption equilibrium conditions at high temperatures, APP CATAL A, 201(2), 2000, pp. 271-279
Citations number
29
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physical Chemistry/Chemical Physics","Chemical Engineering
Journal title
APPLIED CATALYSIS A-GENERAL
ISSN journal
0926-860X → ACNP
Volume
201
Issue
2
Year of publication
2000
Pages
271 - 279
Database
ISI
SICI code
0926-860X(20000710)201:2<271:HOAOCM>2.0.ZU;2-Y
Abstract
The adsorption of CO on a reduced 3.5%Ru/Al2O3 catalyst has been studied by means of FTIR spectroscopy between 298 and 740 K at a constant partial pre ssure P-a=1000 Pa. At 300 K, three adsorbed species were detected on the Ru particles: a linear CO species (strong IR-band at 2047 cm(-1)), a bridged CO species (weak IR band at 1750 cm(-1)) and a gem-dicarbonyl species (weak IR bands at 2135 and 2080 cm(-1)). The FTIR spectra show how the coverage theta of the linear CO species evolves with the adsorption temperature T-a. This cannot be achieved for the bridged CO species or for the gem-dicarbon yl species due to the weak intensities of their IR bands. At T-a>600 K, the curve theta=f(T-a) is in very good agreement with Temkin's adsorption mode l. Moreover, it is shown that, in the range 300-720 K, the curve agrees wel l with an adsorption model considering (a) an immobile adsorbed species; an d (b) a linear decrease in the heat of adsorption with the increase in thet a. This leads for the linear CO species to the heat of adsorption E-theta, at various coverages theta: from E-0=175 kJ mol(-1) at theta=0 to E-1=115 k J mol(-1) at theta=1. This procedure for the determination of the heat of a dsorption of CO on Ru particles is simple (it requires a single isobar) and accurate (approximate to+/-5 kJ mol(-1)). It constitutes a well adapted to ol to study the modifications of this parameter with the method of preparat ion of the catalyst (precursor, support, particle size). (C) 2000 Elsevier Science B.V. All rights reserved.