Effect of diffusion and metal-acid synergy on catalytic behavior of the Pd/Hierarchical SAPO-31 nanoparticles for hydroisomerization of n-hexadecane

The hydroisomerization of long-chain n-alkanes proves to be an effective approach for the production of renewable second-generation biodiesel, and the development of bifunctional catalysts with synergistic effect between metal and acidic sites was the key to increase the yield of iso‐alkanes. Herein, novel hierarchical SAPO-31 nanoparticles (S31-Hi) were synthesized with varied amounts of the growth inhibitor 1-octyl-3-methylimidazolium chloride ionic liquid (OMIMCl IL) in a one-stage crystallization, and a proposed formation process was discussed. The 0.1Pd/S31-Hi bifunctional catalysts were prepared by loading only 0.1 wt% Pd based on the S31-Hi by wetness impregnation method and their catalytic performances were evaluated for the hydroisomerization of n-hexadecane. The catalytic performance of 0.1Pd/S31-H based on the S31-H synthesized by adding an appropriate amount of OMIMCl ILs was significantly improved, which can be attributed to the enhanced diffusion originating from its smaller crystal size, higher Pd dispersion, and larger CPd/CH+ value, which was beneficial for achieving synergistic catalysis. The iso‐hexadecane yield of 77.8% and proportion of multi-branched isomers of 51.5%, and catalytic stability within 100 h time on stream was obtained over the 0.1Pd/S31-H at n-hexadecane conversion of 89.3%. These catalysts have application potential for the production of second-generation clean biodiesel with excellent low temperature fluidity.