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-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.