Unique Role of GeO2 as a Noninvasive Promoter of Nano-Sized Zeolite Crystals

The synthesis of zeolites with nano-sized dimensions is often limited to a narrow design space that conventionally relies upon the design of organics to direct hierarchical materials. Here, it is demonstrated that the addition of an inorganic modifier, germanium oxide (GeO₂ ), to a zeolite growth mixture directs the formation of crystals with ultrasmall dimensions. This effect is observed for zeolites ZSM-11 and ZSM-5 over a range of synthesis conditions wherein the role of GeO₂  in zeolite crystallization deviates from its typical function as a heteroatom. Notably, the final products contain trace amounts of Ge, which indicates the inorganic modifier does not compete for sites in the zeolite framework based on its formation of a discrete phase that enables GeO₂  recovery. Catalytic tests using the methanol-to-hydrocarbons reaction reveal significant enhancement in the performance of zeolite catalysts prepared with GeO₂  compared to reported examples of nano-sized zeolites. These findings highlight a potentially generalizable and commercially viable synthesis method to reduce mass-transport limitations in zeolites for diverse applications.

Recent advances in the synthesis of TS-1 zeolite

Heteroatomic zeolites as an important class of zeolites, have been widely applied in industrially catalytic processes due to their unique properties. As one of the most representative heteroatomic zeolites, titanosilicate zeolites have been extensively used in the selective oxidations of organic substrates with H2O2 such as cyclohexanone ammoximation, epoxidation of alkenes, and phenol hydroxylation. In this review, recent advances in the synthesis of TS-1 zeolite are briefly summarized, including use of low-cost raw materials (organic templates, silicon, and titanium sources), development of new synthesis routes (post-treatment synthesis, dry-gel conversion synthesis, solvent-free synthesis, and microwave-assisted synthesis), and new strategy for enhanced mass transfer in TS-1 crystals (synthesis of hierarchical and nanosized TS-1 zeolite). This review might help researchers to have a deep understanding on the synthesis of TS-1 zeolite and provide a new opportunity for the design and preparation of highly efficient TS-1 catalysts in the future.

Accessibility enhancement of TS-1-based catalysts for improving the epoxidation of plant oil-derived substrates

TS-1-based catalysts with different textural features, namely layered TS-1, pillared TS-1, and Ti-pillared TS-1 as well as mesoporous TS-1, were investigated in the liquid-phase epoxidation of methyl oleate as a model compound for plant oil-derived substrates with hydrogen peroxide at 50 °C.

Preparation and Catalytic Performances of Ultralarge-Pore TiSBA-15 Mesoporous Molecular Sieves with Very High Ti Content

Highly ordered TiSBA-15 mesoporous molecular sieves with different nSi/nTi ratios and tunable pore diameters have been prepared through direct synthesis under various hydrochloric acid concentrations and synthetic temperatures. The structure and the textural parameters of the materials were investigated by powder X-ray diffraction and nitrogen adsorption/desorption measurements. Decrease of the acid concentration and nSi/nTi ratio in the synthetic gel enhanced the amount of Ti incorporation in SBA-15 materials without affecting their structural order and textural parameters. Highly ordered mesoporous TiSBA-15 with a very high Ti content up to a nSi/nTi ratio of 1.9 was prepared for the first time under the optimized synthesis conditions. Control of synthetic temperature resulted in tuning of pore geometries without structural deterioration and Ti content. Ultralarge-pore TiSBA-15 with a pore size of 12.6 nm and a pore volume of 1.3 cm3 g-1 was also synthesized. The nature and the coordination of the Ti atoms in SBA-15 prepared under various synthesis conditions were investigated by UV-vis spectroscopy. It has been found that the Ti atoms are well-dispersed and mostly occupy the tetrahedral coordination under the optimized synthesis conditions. Catalytic performance of the obtained TiSBA-15 materials was also investigated through oxidation of styrene by hydrogen peroxide and tert-butylhydroperoxide as oxidants.