Flame-made Pd/La2O3/Al2O3 nanoparticles: thermal stability and catalytic behavior in methane combustion

Palladium nanoparticles supported on lanthanum-stabilized alumina were prepared by flame spray pyrolysis. The as-prepared materials were characterized by high-resolution transmission electron microscopy, CO chemisorption, nitrogen adsorption, X-ray diffraction and temperature programmed reduction. These materials were tested for the catalytic combustion of methane with a focus on the thermal stability of the support and the palladium particles. Flame spray pyrolysis afforded small palladium particles (<5 nm) attached to the surface of the supporting La2O3/Al2O3 ceramic nanoparticles with specific surface areas in the range of 50–180 m2 g−1. Compared to commercial reference materials the flame-made catalysts showed excellent thermal stability in terms of specific surface area up to 1200 °C and retarded γ- to α-alumina transformation. Catalysts were tested as-prepared (small Pd particles, <5 nm) and after sintering at 1000 °C (large Pd particles, 50–150 nm). By cycling the temperature several times from 200 to 1000 °C during catalytic combustion, it could be shown that all catalytic materials, regardless of specific surface area, lanthanum content, and preparation method (flame-synthesis or impregnated), exhibited similar catalytic performance after an initial conditioning cycle.