Effect of Fe/Co-ratio on the phase composition of Pd-integrated perovskites and its H2-SCR of NOx performance

摘要

La-based perovskites doped with palladium were synthesized by a modified citrate route and calcined at high temperature. The Fe/Co-ratio at the B-site of the perovskite (LaFe_(0.95-x)CO_xPd_(0.05)O3, x = 0.475, 0.4, 0.3) was intentionally varied in order to produce a single phase catalyst and to correlate the phase(s) variations with its catalytic performance during the H2-SCR of NOx. A mixture of crystal phases containing orthorhombic and cubic perovskites, cobalt oxide and strongly bonded palladium oxide were observed in the sample with Fe/Co = 1. Single orthorhombic perovskite phase with traces of iron oxide and weak bonded palladium oxide was obtained with Fe/Co ≈ 2.2. The perovskite with Fe/Co = 1 displayed better NOx-reductions and N2-selectivities than the perovskite with Fe/Co ≈ 2.2 ratio during dry H2-SCR of NOx. The same was observed with H2O + CO2 and in the presence of CO in the feed. The observed catalytic behaviour of both perovskites is discussed in association with the state of palladium in each investigated composition since the Pd-free perovskite displayed an extremely low NOx-reduction (below 4%).