Sulfated zirconia and tungstated zirconia as effective supports for Pd-based SCR catalysts

It is now well established that even though Pd supported on acidic zeolites is :highly selective for CH4-SCR, zeolitic structures are susceptible to dealumination under hydrothermal environments. In this contribution, we have investigated the ability of non-zeolitic acidic materials to promote the SCR selectivity and stability in the presence of H2O and SO2. The results of catalytic activity measurements and characterization tests indicate that sulfated zirconia and tungstated zirconia are supports as effective as the zeolites for the promotion of SCR activity. The high SGR activity of these catalysts can be ascribed to the formation of isolated Pd2+ ions on acid sites. It is proposed that the stabilization of Pd2+ on these supports is similar to the stabilization previously reported for acidic zeolites. The remarkable characteristic of these Pd catalysts supported on sulfated zirconia and tungstated zirconia is that when they were tested over a 40 h reaction period in the presence of H2O and SO2, they appeared to be significantly more resistant than zeolite-based catalysts. (C) 2000 Published by Elsevier Science B.V.