Synergetic effect between the metal and acid sites of Pd/SAPO-41 bifunctional catalysts in n-hexadecane hydroisomerization

Silicoaluminophosphate molecular sieves (SAPO-41) with different SiO2/Al2O3 ratios were synthesized using di-n-butylamine (DBA) as template. All of the samples were characterized by XRD, SEM, TEM, N-2 adsorption, Si-29 MAS NMR and IR spectroscopy of adsorbed pyridine. Based on the SAPO-41 molecular sieve, a series of nPd/S41(x) bifunctional catalysts with different SiO2/Al2O3 molar ratios (x = 0.2-0.7) and Pd loadings (n = 0.1-1.0 wt%) were prepared. Their catalytic performance was investigated in n-hexadecane hydroisomerization using a fixed-bed flow reactor system. The influence of the acidity and ratio between the accessible Pd sites and Bronsted acid sites on the catalytic performance of the prepared samples was studied by adjusting the composition of the initial gel in the synthesis of SAPO-41 molecular sieves and the Pd loadings during preparation process. The results indicated that the 0.8Pd/S41(0.6) catalyst exhibited excellent catalytic performance due to a suitable acidity, high Pd dispersion and appropriate ratio (0.58), which was beneficial for the synergetic effect between the (de)hydrogenating and acid functions of the bifunctional catalyst. The highest iso-hexadecane yield of 89% was obtained at an n-hexadecane conversion of 94% over the 0.8Pd/S41(0.6) catalyst.