## 3 Composite Zeolites by Co-Crystallization or Overgrowth  
Composite zeolites, especially micro/microporous composites [106, 107, 108, 109, 110, 111] and micro/mesoporous composites [112, 113, 114, 115, 116], have been researched because of their synergistic performance in catalytic reactions. Generally, a pure zeolite phase can be obtained only when the synthesis parameters are well controlled, while the variation in the zeolite synthesis conditions will lead to the formation of cocrystallized zeolites with different phases. They may be regarded as the physical mixture in many cases, and their structure and properties are neglected. Only a few examples of intergrowth zeolites from cocrystallization, such as the intergrowth of zeolites X/A [117], MFI/MEL [118], FAU/EMT [119], and STF/SFF [120] with the analogous basic structures, have been reported so far. In some cases, composite materials are preferred in the catalytic reactions because of the combination of different structures and better performance [121, 122]. [PERSON] _et al._ observed that the isomerization and hydrogen-transfer reactions could be inhibited within the pore systems of ZSM-5/ZSM-11 intergrowth zeolites for the n-decane cracking [123]. Besides, another ZSM-5/ZSM-11 composite, a co-crystalline zeolite [106], showed a high activity, selectivity and stability for the alkylation reaction of benzene with the dilute ethylene in FCC off gas, and ZSM-5/ZSM-11 intermediate [124, 125] effectively catalyzed the conversion of methanol and the alkylation of aromatics. ZSM-5/Y composites consisting of either the mechanical mixture of ZSM-5 and Y [126] or the _in situ_ synthesized ZSM-5/Y composites [127] were reported to exhibit a notable synergy in the catalysis. Recently, more microporous/mesoporous composites such as ZSM-5/MCM-41, Beta/MCM-41, Y/MCM-41 and Ti-Beta/SBA-15 are seeding catalytic applications as they can combine the advantages of microporous materials with high activity and stability and of mesoporous materials with large pore size [128]. At the same time, composite zeolites with binary structure also lead to special properties which can improve its catalytic performance. We carried out a series of investigations on MWW/FER composite zeolite [129]. It was found that MCM-22/ZSM-35 composites could be rapidly crystallized at 174 \({}^{\circ}\)C with an optimal gel composition of SiO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\) = 25, Na\({}_{2}\)O/SiO\({}_{2}\) = 0.11, HMI/SiO\({}_{2}\) = 0.35, and H\({}_{2}\)O/SiO\({}_{2}\) = 45 (molar ratio), of which the weight ratio of ZSM-35 zeolite in the composite relied on the crystallization time. Besides, a novel route for synthesis of MCM-49/ZSM-35 composite zeolites with different compositions in a mixed amine system containing hexamethyleneimine (HMI) and cyclohexamine (CHA) has been developed [130]. The MCM-49/ZSM-35 composites with more content of ZSM-35 zeolite can be prepared under conditions of larger CHA/HMI molar ratio, higher Na\({}_{2}\)O/Al\({}_{2}\)O\({}_{3}\) molar ratio and longer crystallization time. In the same system, both MCM-49 zeolite and ZSM-35 zeolite can also be successfully synthesized by adjusting the synthesis conditions. One- and two-dimensional \({}^{129}\)Xe-NMR spectroscopy is a powerful tool for probing the porosity and species distribution in porous materials which has been employed to study the porosity of cocrystallized MCM-49/ZSM-35 zeolites under a continuous flow of hyperpolarized xenon gas. It was found by variable temperature experiments that Xe atoms can be adsorbed in different domains of MCM-49/ZSM-35 cocrystallized zeolites and the mechanically mixed counterparts [131]. The exchange of Xe atoms in different types of pores is very fast at ambient temperature. Even at very low temperature two-dimensional exchange spectra (EXSY) show that Xe atoms still exchange between MCM-49 and ZSM-35 analogues in the co-crystallized zeolites much faster than in the mechanical mixture.