Abstract

Several mixed oxides CeO₂-Bi₂O₃, with Bi/Ce molar ratios of 1:9, 2:3 and coded Ce₉Bi₁ and Ce₆Bi₄ respectively, were prepared by co-precipitation method. Single oxides were prepared by calcination of their nitrate salts. All solids were characterized by XRD, SEM, BET and O₂-TPD. The catalytic activity was evaluated by toluene total oxidation reaction. 

Only peaks of CeO₂ cubic phase are observed in XRD with slight increase of cell parameters. Therefore, there is probably a small amount of Bi³⁺ replacing Ce₄+ in the CeO₂ crystalline lattice and the remaining amount of Bi³⁺ formed the Bi₂O₃ phase. The latter could be well dispersed on CeO₂ surface and causes the sintering of CeO₂ particles and then the decrease of BET surface area. However, the results of toluene total oxidation reaction, on the obtained solids, show the following order of catalytic activity : CeO₂>>Ce₉Bi1>Ce₆Bi₄>>Bi₂O₃. The O₂-TPD measurements allowed evidencing different mobile oxygen species in the catalysts. The results showed that the specific surface areas and -2 oxygen species play the main important role in toluene total oxidation.

INTRODUCTION

Volatile Organic Compounds (VOC) are considered as one of major source for atmospheric pollution. They are released from chemical, petrochemical and several related industries. The release of VOC into the atmosphere leads to stratospheric ozone depletion and photochemical smog. Moreover, many VOC are toxic and several of them are considered to be carcinogenic, mutagenic or teratogenic (1). Catalytic oxidation technology seems to be a promising way to resolve this problem by its high selectivity into nontoxic products and the low operating temperature (2). There are two main groups of catalysts for VOC treatment: one based on noble metals (Pt, Pd, Au) (3-5) and the other on metal oxides (Co₃O₄, MnOx, LaCoO₃) (6-8). In comparison with oxides, the based – noble metal catalysts present higher activity. However, they are more expensive. Hence, recently, researchers have attempted to develop transitional rare-metal oxide catalysts. Among them, CeO₂ could be an attractive alternative since it is known to be an important component of three-way catalyst to treat automotive exhaust gas. In fact, CeO_{2 ...} ...