Robert J. Kudla

Characterization of Ag/γ-Al2O3 catalysts and their lean-NOx properties

Ag supported on a nonporous γ-alumina was shown to have an optimal metal loading of about 2 wt% Ag for NOx conversion of simulated lean-NOx, automotive exhaust. Ag was primarily in an oxidized state during reaction. O2 adsorption and H2O2 titration were measured at 170°C after catalyst reduction at 250°C to determine metal dispersion. The results indicate an unusual increase in apparent metal dispersion with increased metal loading below 3 wt% Ag. Above 3 wt%, the apparent dispersion decreased with Ag loading. The observed trend for apparent dispersion was attributed to a metal-support interaction. No XRD pattern could be detected for the proposed phase which would suggest a surface rather than bulk phenomenon. Comparison of the adsorption data to a simple model for dispersed metal particles also indicated the likelihood for a metal-support interaction. The model also suggests that apparent dispersions may be significantly different from true metal dispersions even for fairly large particles. O2 TPD and lean-NOx reaction results indicate that the proposed metal-support interaction is relatively stable under inert and net-oxidizing conditions. Extended reduction at mild temperature (170°C) diminished the extent of the metal-support interaction. A 2 wt%Ag/γ-Al2O3 catalyst prepared by multiple impregnation was more active for lean-NOx reaction than one prepared using a single impregnation step. This would suggest that Ag alumination results in more active catalysts for lean-NOx applications.

Composition of Pd-La/α-Al2O3 catalysts

The objective of this study is to investigate the structure of the Pd-La/α-Al2O3 catalyst. X-ray diffraction (XRD) and temperature-programmed reduction (TPRd) were used as characterization techniques. Contrary to the assertions in the literature, XRD studies conducted on La/α-Al2O3 composite oxides and Pd-La/α-Al2O3 catalysts show that Pd catalyzes the solid state reaction between A12O3 and Al2O3 to form LaAlO3. TPRd studies conducted on Pd/α-Al2O3, Pd/La2O3, Pd/LaAlO3, and Pd-La/α-Al2O3 catalysts suggest that Pd in the Pd-La/α-Al2O3 catalyst interacts more strongly with LaAlO3 than with α-Al2O3. Reaction studies were conducted to investigate the activity of Pd/α-Al2O3, Pd/La2O3, Pd/LaA103, and Pd-La/α-Al2O3 catalysts for nitric oxide (NO) reduction. These studies show that Pd/LaAlO3 catalysts are most active for NO removal at stoichiometric and under net reducing conditions.