The effects of dopant on catalytic activity of Pd/mesoporous alumina for toluene oxidation.

A series of mesoporous alumina (MA) doped with acidic (Ti, W) or alkaline earth (Ba, Mg) elements were prepared. They were used as the supports for Pd catalysts. These catalysts were characterized by N2 sorption, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy of CO adsorption and temperature-programmed reduction. Complete oxidation of toluene on these catalysts was tested in a fixed-bed micro-reactor. The results of in situ IR of CO adsorption indicated that the doping of basic element was beneficial for the dispersion of PdO particles, while the doping of acid element suppressed the dispersion of PdO particles. The binding energy of Pd in Pd/Ba-MA shifted to high energy, indicating that the interaction between PdO and support was enhanced. The results of H2-TPR showed that the reducibility of PdO doped with alkaline element was stronger than those of catalysts doped with acidic element. The doping of basic elements promoted the dispersion of PdO particles, changed the electronic state of Pd and enhanced the reducibility of PdO, which led to its high activity. The catalysts doped with the basic elements had higher activities than those doped with acidic elements, among which the Pd/Ba-MA catalyst had the highest activity among all catalysts. [ABSTRACT FROM AUTHOR]