Hydroisomerization of n-hexadecane over a Pd-Ni2P/SAPO-31 bifunctional catalyst: synergistic effects of bimetallic active sites

A series of bifunctional catalysts are prepared by loading Pd, Ni2P and bimetallic Pd-Ni2P on di-n-butylamine(DBA)-templated SAPO-31 molecular sieves through either impregnation or impregnation combined with temperature-programmed reduction methods. All bifunctional catalysts are characterized using XRD, N-2 adsorption, Al-27 and P-31 MAS NMR, SEM, TEM, IR spectroscopy of adsorbed pyridine, XPS, H-2 chemisorption, ICP, and TG-DTG measurements. The catalytic performance over all prepared bifunctional catalysts is compared for n-hexadecane hydroisomerization. The obtained results demonstrate that the 0.05Pd-4Ni(2)P/S31 catalyst produces a higher iso-C-16 yield of 72.7% with n-C-16 conversion of 83.1% compared with the other two catalysts. This result is attributed to two reasons: i) the bimetallic Pd-Ni2P component possesses stronger (de)hydrogenation functionality than Ni2P does, and ii) the bimetallic bifunctional catalyst has a better balance between metal and acid functionality than the monometallic catalysts do. Moreover, the 0.05Pd-4Ni(2)P/S31 catalyst also shows the best catalytic stability among all catalysts, since the n-C-16 conversion and iso-C-16 selectivity are still above 80% and 90%, respectively, even after 100 h of long-term testing. Therefore, the present study has provided a novel idea for the design of bimetallic bifunctional catalysts for long-chain n-alkane hydroisomerization.