Hydroisomerization of n-decane over the Pd/ZSM-22 bifunctional catalysts: The effects of dynamic and static crystallization to the zeolite

Abstract Two series of pure nanosized ZSM-22 zeolites (Z-22 ( x D) and Z-22 ( x S)) with different SiO 2 /Al 2 O 3 molar ratios are synthesized with 1,6-diaminohexane (DAH) template by the hydrothermal method under dynamic and static crystallization conditions, respectively. The effects of crystallization conditions on the characteristic properties of ZSM-22 zeolites are investigated by XRD, SEM, HR-TEM, N 2 adsorption, 29 Si and 27 Al MAS NMR, NH 3 -TPD, Py-IR and H 2 chemisorption measurements. The results show that Z-22 ( x D) samples reveal smaller crystal size, larger mesoporosity, weaker Bronsted acid strength and lower Bronsted acid density compared with Z-22 ( x S) samples. The Pd/Z-22 ( x D) and Pd/Z-22 ( x S) bifunctional catalysts are prepared by loading 0.5 wt% Pd on the corresponding zeolite samples, respectively, and the catalytic performance over all bifunctional catalysts is tested in the hydroisomerization of n- decane. The catalytic test results indicate that the Pd/Z-22 ( x D) catalysts show higher selectivity for both mono-branched and multi-branched iso -decanes than those of Pd/Z-22 ( x S) catalysts, because of the smaller crystal size and lower Bronsted acidity. Therefore, the dynamic hydrothermal crystallization is an effective way to synthesize ZSM-22 zeolites with improved catalytic behaviors for the n-alkane hydroisomerization.