Synthesis And VOCs Catalytic Oxidation Properties Of Short Channeled Pd/Zr-Ce-SBA-15 Catalysts

Conventional SBA-15 usually has a fibrous macrostructure. Molecular diffusion through the lengthy mesochannels and pore blockage along the channels are the main concern when applying these materials for adsorption and catalysis. Inorder to overcome these drawbacks, we propose to synthesis short channeled Zr-Ce-SBA-15(ZCS) mesoporous materials with hexagonal platelet morphologies. ZCS was synthesized through a hydrothermal route without addition of mineral acids by using Pluronic P123 as a template, tetraethyl orthosilicate as a silica source, ZrOCl2·8H2O and Ce (NO3)3·6H2O as precursors. The obtained materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission microscopy (TEM), nitrogen adsorption-desorption, Fourier-transform infrared spectroscopy (FTIR) and pepsin immobilization experiment.0.5wt% palladium was incorporated into ZCS supports via ethanol reduction approachs, impregnation approachs and ethylene glycol reduction approachs, respectively. The influce of different preparation methods on the catalysts structures was invesgated. By choosing toluene as the target polloutant, we studied the performance of supported palladium catalysts. The effect of the channels length on the catalytic activity was also evaluated. Furthermore, we briefly studied the chemical reaction kinetics of toluene oxidation over Pd/ZCS. The results showed that:1. ZCS exhibits unique hexagonal platelet morphologies and short channels. The average thickness of the platelets for ZCS is only 400-500nm, which is only one-third of the length of the channels for conventional SBA-15. ZCS possesses an ordered 2D hexagonal mesoporous structure, high BET surface area (805m2·g-1), large pore volume (1.03cm3·g-1) and pore diameter (9.2nm). Furthermore, the pepsin immobilization experiment indicated that the ZCS materials have higher adsorption rates and adsorption capacities compared with SBA-15.2. The preparation methods have no influence on the morphologies of the supported Pd catalysts. The preparation methods have differernt influences on the structures and the distribution of active component. The obtained catalysts which were prepared by ethanol reduction approachs retained well ordered mesoporous structures and narrow pore size distribution. Palladium species present in supports as well dispersed PdO nanocrystals with small diameter (5～6nm).3. All of the catalysts prepared by different preparation methods exhibited good low-temperature catalytic activity for the catalytic oxidation of toluene. Meanwhile, Pd/ZCS has improved performance for the catalytic oxidation of toluene compared with Pd/SBA-15. which is ascribed to short channeled supports facilitating the molecular diffusion.4. The preparation methods and the operating conditions used (such as gas hourly space velocities and toluene concentration) are also important influence on the catalytic performance. The order of catalytic activity decreases as follows:catalysts prepared by ethanol reduction approachs> catalysts prepared by ethylene glycol reduction approachs> catalysts prepared by impregnation approachs; low GHSVs>middle GHSVs>high GHSVs; 800ppm of toluene concentration> 1200 of toluene concentration.5. The obtained Pd/ZCS prepared by ethanol reduction approachs possesses well stability and durability. The results of kinetic study indicated that the Eley-Rideal mechanism and Arrhenius equation can be applied to describe the experimental data by using pseudo-first-order reaction.The activation energy and frequency factor are 63.38kJ/mol and 8.43×107 s-1, respectively.