A comparative study of the desilication of channel- and cage-like zeolites*

Zeolites are very important catalysts in the chemical industry, but their intrinsic narrow micropore system often restricts the mass transport of reactant and product molecules. These mass transport limitations can be overcome by introducing a second larger pore system (meso-/macropores) into the zeolite crystals. Over the past decade, desilication of zeolites has emerged as a simple post-synthetic process to implement mesoporosity into zeolites. Here we present the investigation of the influence of framework topology on the formation of mesoporosity by the desilication process. For this purpose, the desilication behaviour of a channel-like system (ZSM-5/MFI-type) and a cage-like system (SSZ-13/CHA-type) are compared. It has been found that cage-like zeolite (SSZ-13) is more susceptible to the desilication process. The desilication of SSZ-13 zeolite resulted in drastic reduction of microporosity and crystallinity, while the microporosity and crystallinity of ZSM-5 gradually decreased with desilication time. By systematically studying the influence of various desilication parameters (e.g. treatment time, temperature and alkaline concentration), it has been found that there exists a direct correlation between the extraction of silicon and mesoporosity formation for the channel-like zeolite (ZSM-5) whereas in case of cagelike zeolite (SSZ-13) no direct correlation has been found.

Automated summary

Zeolites are important catalysts in the chemical industry, but their narrow micropore system limits mass transport. Introducing a second larger pore system through desilication can overcome these limitations. The influence of framework topology on the formation of mesoporosity by desilication was investigated, and it was found that cage-like zeolites are more susceptible to desilication.