Effects of preparation and structure of cerium-zirconium mixed oxides on diesel soot catalytic combustion

摘要

Mixed oxides of Ce_xZr_(1-x)O2 (0.1 ≤ x ≤ 0.9) were prepared by sol-gel method, in aqueous ammonia solution with CeCl3·7H2O and ZrOCl2·8H2O as precursors, and employed in diesel soot combustion. The catalysts were characterized by XRF/EDX, nitrogen adsorption, TGA/DTG, powder XRD, FTIR/DRIFTS and Raman. In addition, the acidity was evaluated by adsorption and desorption of pyridine. XRD indicated the formation of solid solutions that progressively distorted from cubic into tetragonal lattices. Raman studies confirmed that the Ce-O bonding was stronger in the mixed oxide series because of the cell contraction, as a result of the zirconium insertion. Ce_(0.8)Zr_(0.2)O2 was the most acidic and active material, shifting the combustion temperature (T_m) from 622 to 547°C (loose contact) or 404°C (tight contact). The calculated activation energy for the catalytic combustion of this optimized oxide attested that the combustion temperature was lower under all conditions, compared to the thermal process. The catalyst was utilized five times without any appreciable loss of activity and maintained its structural properties.