Search

The surface behavior of a series of SnO2 (5, 10 and 20 wt.%) - CeO2 catalyst samples prepared by impregnation method and also pure SnO2, CeO2, was studied based on the response of the ac electrical conductivity. The electrical measurements were carried out in operando conditions in order to obtain information about the surface interaction with reactants during CO/hydrocarbon oxidation over these catalysts. The apparent activation energies of conduction in presence of CO:O2 and C3H6:air mixtures were presented. The catalyst samples were tested in catalytic oxidation of CO and C3H6 at temperature range of room temperature up to 400 C. The catalytic activity in both oxidation reactions and selectivity towards CO2 in propylene oxidation at 400 C exhibited by the SnO2-CeO2 systems were significantly higher to those exhibited by the pure ceria catalyst.

Newly prepared SnO2-CeO2 catalyst samples used as depollution catalysts were characterized applying low-temperature nitrogen adsorption (BET), X-ray diffraction (XRD), thermo-gravimetry (TG-dTG) and temperature-programmed reduction (TPR) methods. Pure SnO2 has higher surface area (17 m2/g) than the pure CeO2 (8 m2/g). Addition of organic tin oxide precursor to ceria in amount of 5 wt% slightly decreases the surface area of CeO2 (SSn5-Ce= 7 m2/g). The increase of tin oxide content to 10 and 20 wt% increases the surface area of the catalyst (SSn10-Ce= 9 m2/g; SSn20-Ce= 10 m2/g). A similar effect was observed for pores of 1.7-300nm size. Catalyst sample Sn5-Ce exhibited the lowest pore volume, which increases with increasing the amount of tin oxide. Tin dioxide in Sn-Ce samples with lower loadings of SnO2 (.10 wt%) were well dispersed showing amorphous structure. High loading (20 wt%) of tin dioxide in Sn-Ce showed XRD lines of formation of cassiterate crystalline structure of SnO2 without evidence of solid solution formation. In case of SnO2 the TPR profile exhibits a major peak at about 545 C with much greater intensity than in case of CeO2, revealing that SnO2 was more easily reducible than CeO2. Sn-Ce samples exhibit reducibility at lower temperatures (between 545-635 C) compared to the single tin dioxide (750 C).