Synthesis and characterization of mesoporous ZSM-12 by using carbon particles

The generation of mesoporosity in 1-dimensional zeolite ZSM-12 was explored by using carbon black as template for the expected mesoporosity during synthesis. After the carbon particles were burned off, intracrystalline mesopore networks were formed. For relatively high C/Si and H2O/Si ratios, there is higher opportunity to generate mesoporosity. All the samples were characterized by X-ray diffraction, nitrogen physisorption, SEM, ICP and FT-IR. Mesoporous ZSM-12 samples with nominal Si/Al ratios of 40, 60, 75, 100 in the gel, were successfully synthesized. The mesopore volumes were in the range of 0.15–0.19 cm3/g and the mesopores distributed in the range of 10–50 nm were determined by nitrogen physisorption. The STPD and FT-IR results revealed that these mesoporous ZSM-12 samples possess the same number of acid sites as regularly synthesized ZSM-12 samples for comparable Si/Al ratios. For the synthesis gel containing the same Si/Al ratios, Si/Al ratios were almost the same in both the mesoporous and conventional ZSM-12 products, which indicated that the carbon black involved in the synthesis did not affect the crystallization efficiency of aluminum during the nucleation. The conversion of n-tridecane and 1,3-dimethylcyclohexane were chosen as test reactions. The mesoporous ZSM-12 samples (“Swiss Cheese” like) are found to exhibit higher activity compared to conventional ones especially under high WHSVs. The enhanced activity we observed can be attributed to the introduction of the mesopores in the zeolite crystals, which decreases the intracrystalline mass transfer limitations. Moreover, the mesoporous samples promoted the production of longer and more branched products than the case of the traditional samples since the former ones favor to a higher extent the outwards diffusion of the products.