Pd/SAPO-41 Bifunctional Catalysts with Enhanced Pd Dispersion Prepared by Ultrasonic-Assisted Impregnation: High Selectivity for n-Hexadecane Hydroisomerization

The preparation of bifunctional catalysts with high catalytic selectivity for the n-alkanes hydroisomerization still remains challenging for the production of bio-diesel. Herein, two series of Pd/SAPO-41 bifunctional catalysts are prepared by the ultrasonic-assisted impregnation (xPd/S41-U) with different treating time and conventional incipient wetness impregnation methods (0.30Pd/S41-I) on the SAPO-41 molecular sieve, respectively. The physico-chemical property of the synthesized SAPO-41 and prepared catalysts were studied by XRD, SEM, ICP, N2 physical adsorption, H2 chemisorption and Py-IR measurements. The catalytic performance for the n-hexadecane hydroisomerization over all catalysts is also studied. The characteristic results indicate that the xPd/S41-U catalysts show stronger Bronsted acidity compared with the 0.30Pd/S41-I catalyst. In addition, the Pd dispersion of the xPd/S41-U catalysts is almost two times higher than that of the 0.30Pd/S41-I catalyst, which leads more Pd cluster to enter into the micropores of the SAPO-41 molecular sieve. Furthermore, the 0.30Pd/S41-U catalyst with 0.30 wt % Pd loading shows promoted catalytic performance than that of the 0.30Pd/S41-I catalyst with the same Pd loading because of the stronger metal function and more favourable metal-acid balance caused by the larger CPd/CH+ ratio. Therefore, the ultrasonic-assisted impregnation prepared Pd/SAPO-41 catalysts are potential to be widely employed for the n-alkane hydroisomerization.