Stabilizing effect of Nd2O3, La2O3 and ZrO2 on Pt·PdO/Al2O3 during catalytic combustion of methane Original Research Article

The additive effects of lanthanum oxides, neodymium oxides and zirconia in Pt·PdO/Al2O3 on the catalyst durability during CH4 combustion at 1073 K were studied using a fixed-bed flow reactor at atmospheric pressure. The surface properties of the catalysts were investigated using CO chemisorption, XRD, TPD after CH4 adsorption, and X-ray photoelectron spectroscopy (XPS). The catalysts were deactivated by the transformation of PdO to Pd-Pt and by the growth of PdO and Pd-Pt particles rather than by the decrease in the surface area of the supports, volatilization of the active species and carbon deposition. The addition of La2O3, Nd2O3 and ZrO2 to Pt·PdO/Al2O3 lowered the temperature of O2 desorption from bulk PdO in TPD. This prevented the growth of PdO and Pd-Pt particles during the combustion. The XPS analysis after TPD indicated that the addition of both La2O3 and Nd2O3 to Pt·PdO/ZrO2·Al2O3 kept the valence of the surface Pd at 1100 K higher than of the other catalysts. The lifetime of the La2O3·Nd2O3-Pt·PdO/ZrO2·Al2O3 catalyst depended on the particle growth of PdO and Pd-Pt more strongly than on the transformation of PdO to Pd-Pt. Consequently, the La2O3·Nd2O3-doped Pt·PdO/ZrO2·Al2O3 catalyst showed a significantly longer lifetime than the other catalysts.