CeO2-Bi2O3 catalysts’ supports for toluene total oxidation
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.
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