JOURNAL OF CATALYSIS 135, 1-12 (1992) MoO3/MgO Systems: Effect of Preparation Method on Their Physicochemical Properties Jos~ M. M. LLORENTE, *A VICENTE RIVES, *'2 PILAR MALET,t AND FRANCISCO J. GIL-LLAMBfAS:~ *Departamento de Qulmica lnorgdnica, Universidad de Salamanca, Facultad de Farmacia, 37007-Salamanca, Spain; ?Departamento de Quimica lnorgdnica, Universidad de Sevilla, Facultad de Qulmica, 41012-Sevilla, Spain; and ~;Departamento de Quimica, Facultad de Ciencia, Universidad de Santiago de Chile, Chile Received January 2, 1991; revised August 16, 1991 MoO3/MgO systems have been prepared and characterized by X-ray diffraction, specific surface area and porosity measurements, visible-ultraviolet (diffuse reflectance) and Fourier transform infrared spectroscopies, differential thermal analysis, determination of the surface isoelectric point, and temperature-programmed reduction to analyze how the preparation method and pretreatments regulate their surface properties. Formation of MgMoO4 on the surface of the support under certain experimental conditions stabilizes the surface of the support, thus avoiding its sintering during calcination at high temperature; in addition, reduction of Mo(VI) species in this case is more difficult, taking place at temperatures higher than those for bulk or supported molybdena. © 1992 AcademicPress,Inc. INTRODUCTION It has often been mentioned that the type of material used as a support for a heteroge- neous catalyst, in addition to playing the expected role of dispersing the active phase, may play a specific role in the catalyzed reaction itself, and in this regard, the so- called Strong metal-support interactions, existing between metals and semiconductor oxide supports such as titania and other ox- ides, are very well known (1). In catalysts formed by metallic oxides supported on other metallic oxides, cur- rently used to catalyze total or partial oxida- tion reactions, selection of a support is criti- cal to increase the activity in one reaction or another. Thus, vanadia best oxidizes naphthalene (2) when supported on silica, on anatase is very effective at oxidizing o-xylene (3), and on alumina is especially I Present address: Escuela Universitaria Polit6cnica de Zamora, Spain. 2 To whom correspondence should be addressed. active in benzene oxidation (4, 5); magne- sium vanadates are very active catalysts for oxidative dehydrogenation of ethylbenzene to styrene (6). A similar behavior is ob- served with molybdena: reduction of NO with hydrogen is very effective when per- formed on MoO3/ZrO2, while reduction with ammonia is more effective when MoO3/TiO2 is used as catalyst (7). In previous papers we have studied the incorporation of V205 on the surface of mag- nesia (8), silica, alumina, rutile (9), and ana- tase (10), and we have found that a relation- ship seems to exist between the basic-acidic character of the support and the way in which the supported phase interacts with it. Fransen et al. (11) have studied the proper- ties of molybdena monolayer catalysts sup- ported on several oxides, and they find the formation of bulk MoO 3or a highly disperse phase, depending on the stoichiometry of the support. We have also studied (8-10) the effects of the use of several preparation methods on the properties of the catalysts obtained therefrom, as dispersion of the 0021-9517/92 $3.00 Copyright© 1992 by Academic Press, Inc. All rightsof reproductionin any formreserved.