Improved catalytic oxidation of propane over phosphate-modified Pd/Al2O3-TiO2 catalyst

Al-Ti oxides supported noble-metal catalysts were prepared by combining the mechanical ball-milling method and incipient wetness impregnation method, in which the Al-Ti mixed oxides were etched by various concentrations of phosphoric acid for improving the performance of propane oxidation. Phosphate-modified Pd/Al2O3-TiO2 catalyst with Al/P ratios of 3:1 showed high catalytic activity that more than 90 % C3H8 was converted completely at 380 °C and GHSV of 100000 h−1, with 5 vol% H2O and 10 vol% CO2. Characterization results revealed that the mixing of Al2O3 and TiO2 provided a high specific surface area and excellent pore structure, while the modification of phosphate supplied a stronger interaction between Pd species and supporter which is favorable to their dispersion and enhancing the catalytic stability in the tough conditions. The H2-TPR and O2-TPD results suggested that marked brilliant redox ability and abundant surface oxygen species of phosphate-modified Pd/Al2O3-TiO2 catalysts are beneficial to the activation of O2 and the increase of catalytic activity. Moreover, the XPS spectra indicated that phosphate induced some electromigration and made the content of Pd0 and Pd2+ in an appropriate ratio which enable the Pd species to display brilliant ability in supplying active oxygen species and breaking the C-H bond, which improved the C3H8 catalytic activity of noble-metal catalyst greatly.