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

Abstract

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-11and 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.