High performance for oxidation of low-concentration methane using ultra-low Pd in silicalite-1 zeolite

0.123%Pd encapsulated in nanosized silicalite-1 (MFI) zeolite catalysts has been prepared by direct hydrothermal conditions, and its catalytic performance at the low concentration methane combustion was studied. The temperatures for methane ignition (T-10%), the half-conversion temperature (T-50%) and the total conversion temperature (T-90%) over Pd/S-1-in (in-situ method) catalyst are 261, 329 and 382 degrees C, respectively, which are lower than the corresponding temperatures of Pd/S-1-im (incipient impregnation method) catalyst. Moreover, the properties are further enhanced by introducing CeO2 into the Pd/S-1-in catalyst. The conversion rate decreased slightly from 91 to 85% when the reaction is carried out at 450 degrees C for 100 hat the gas hourly space velocities (GHSV) of 112500 mL g(-1) h(-1). The XPS analysis showed that Pd clusters were encapsulated within the porous rather than on the surface of the crystal by in-situ method. The HRTEM studies demonstrated that the Pd particle encapsulated within Silicalite-1 zeolites are well dispersed and evenly distributed throughout the Silicalite-1 zeolites. The average size of in situ Pd particle encapsulated in Silicalite-1 zeolite is 1.7 nm, which is much smaller than the impregnated Pd/S-1-im catalyst (2.8 nm).