## 4 Hierarchical Porous Composite Catalysts
We have successfully synthesized several kinds of hierarchical porous zeolites (silicalite-1 [161], ZSM-5 [162], ZSM-11 [163], Beta [163]) by using nanosized CaCO\({}_{3}\), starch and polyvinyl butyl gel as templates (Figure 6). Upon the direct hydrothermal crystallization of templates/silica composite, the silica was transformed into zeolite, whereas the templates were incorporated in the zeolite crystals. Removal of the templates inside the zeolite composite yielded the opening of micropores and mesopores in zeolites, respectively (Figure 6). The characterization techniques confirmed that the obtained porous materials had well-defined microporosity and irregular mesoporousity. The porous structures of mesopore ZSM-5 prepared by starch templates have been studied by continuous-flow laser-hyperpolarized \({}^{129}\)Xe-NMR [164]. Different adsorption domains of Xe in these hierarchical porous zeolites can be directly observed by variable-temperature experiments. The exchange of Xe atoms in different types of pore environments is very fast at ambient temperatures. Combining with nitrogen physisorption, we found that the Si/Al ratios of resultant samples have great influence on the mesopore size distribution and mesopore volume in meso-ZSM-5. Two dimensional exchange NMR spectroscopy (EXSY) has been used for the first time on such hierarchical zeolites, and the result showed that Xe atoms still undergo faster exchange between different types of pores in the meso-ZSM-5 than in the mechanically mixed ZSM-5/silica counterparts even at very low temperature. The result demonstrated that microporous and mesoporous domains in the meso-ZSM-5 may stay much closer and have better connectivity than in the conventional physical mixture, which facilitate the Xe atoms diffusion and exchange. The cracking of 1,2,4-trimethylbenzene and 1,3,5-trimethylbenzene had been detected over the conventional ZSM-11 and mesoporous ZSM-11, respectively [163]. The conversion of trimethylbenzene is much higher in the mesoporous ZSM-11 than in the conventional ZSM-11. Apparently, the presence of mesopores in the ZSM-11 crystals makes for short diffusion paths within the zeolite particles, which facilitates reactant accessibility to the active sites on the interior surfaces. Experimental results also show that there are some differences in the product distribution between the mesoporous zeolite and conventional zeolite. In contrast to conventional ZSM-11 catalysts, the mesoporous zeolite can stimulate the formation of bulky molecules, namely, C\({}_{10}\) aromatics, in the trimethylbenzene cracking reaction. At the same temperature, the amount of C\({}_{10}\) aromatics is larger in the mesoporous ZSM-11  
Figure 6: Hierarchical porous zeolites: **(a)** mesoporous silicalite-1 synthesized with nano CaCO\({}_{3}\) templates. Adapted from Reference [161]; **(b)** mesoporous ZSM-5 synthesized with starch templates. Adapted from Reference [162]; **(c)** mesoporous ZSM-11 synthesized with polyvinyl butyl gel templates. Adapted from Reference [163]; **(d)** mesoporous Beta zeolite synthesized with polyvinyl butyl gel templates. Adapted from Reference [163]. than in the conventional ZSM-11, which may be a result of the higher conversion of trimethylbenzene in mesoporous ZSM-11. We also compare the product distribution when the conversions reach the same level at different temperature. For example, the conversion of 1,2,4-trimethylbenzene on the mesoporous ZSM-11 at 350\({}^{\circ}\)C (33.57%) is nearly equal to that on conventional ZSM-11 at 390\({}^{\circ}\)C (32.35%), but there are more C\({}_{10}\) aromatics with the former zeolite (2.14%) than with the latter zeolite (1.65%). Also, in the 1,2,4-trimethylbenzene cracking reaction, the conversion of 1,2,4-trimethylbenzene on the two ZSM-11 zeolites reaches the same level at 410 \({}^{\circ}\)C (52.78% for the mesoporous ZSM-11 and 50.10% for the conventional ZSM-11), but the amount of C\({}_{10}\) aromatics on mesoporous ZSM-11 (5.00%) is about twice as much as that seen on conventional ZSM-11 (2.91%).