ELSEVIER Colloids and Surfaces A: Physicochemical and Engineering Aspects 136 (1998) 237-243 COLLOIDS AND i SURFACES Consequences of foreign salt additives on the structure and texture of some metal oxides Ahmed K.H. Nohman, Hamdy M. Ismail * Chemistry Department, Faculty of Science, Minia University, El-Minia 61519, Egypt Received 30 April 1997; accepted 2 November 1997 Abstract The influence of foreign salt additives, namely (NHz)/CO and NH4NO3, on the structure and texture of ZrO2, Nb2Os, La203 and ThO2, produced by thermal decomposition of their nitrates, has been investigated. Thermal behaviour of oxide precursors (metal nitrates) as well as additive salts (pure and impregnated into the oxides) was explored by thermogravimetry. Accordingly, the calcination products of the additive-free and additive-containing oxides were obtained at the appropriate temperatures. The final oxide materials, with and without additives, were characterized by X-ray diffractometry. Slight structural modifications were detectable, viz. a retardation to crystallinity and particle size decrease. Texture assessment (surface area and porosity) was carried out via analysis of nitrogen adsorption isotherms (at -196°C) adopting BET- and t-methods. The additives, particularly of urea, were found to improve notably the surface area and porosity. This was correlated with the structural modifications conceded by the material bulk. © 1998 Elsevier Science B.V. Keywords: Zirconium; Niobium oxides; Lanthanum and thorium nitrates; Thermogravimetry; X-ray diffraction; Nitrogen adsorption 1. Introduction Metal oxides are widely used in the field of heterogeneous catalysis, both as catalyst and sup- port material for the so-called monolayer-type catalysts. In such applications, the performance is determined by parameters like the oxide surface area, porosity, high adsorptive capacity and ther- mal stability [1-5]. Accordingly, metal oxides must have high stability as well as high surface area under conditions of their use both as catalysts or support materials [6-8]. Indeed, both catalytic [9,10] and supporting [11] performances of solids are shown in several research works to be mainly * Corresponding author. 0927-7757/98/$19.00 © 1998 ElsevierScience B.V. All rights reserved. PII S0927-7757(97)00358-0 controlled by surface textural characteristics, such as number, shape and size of surface pores [12]. Many attempts have been made to synthesize metal oxides with tailored pore structure and high surface area. For example, the use of novel oxide precursors [13,14], or the addition to the oxide and/or the oxide precursor, of readily decomposa- ble additive materials have been attempted [7,15]. Some previous studies [7,15,16] have discussed and stated that many readily decomposable addi- tives can have marked effects on the surface texture when applied at different stages during the course of the preparation of the adsorbent solid material. The metal oxides selected in this study find many catalytic applications, and hence it would be worth trying to improve their surface texture. Among these catalytic applications, ZrO2, for instance,