Catalyst design strategy to logically control product selectivity by tailoring void environments around active sites

Abstract

Selectivity, activity, and stability are the most crucial criteria for screening catalysts for catalytic reactions. Porous materials such as zeolites and metal-organic frameworks have been studied to understand the role of the microporous environment on reaction rates, and previous research has reported that the different sizes of microporous void environments enable selective uptake of molecules and modification of product selectivity, while the transition state leading to desired products was close to the void size. Therefore, we aim to explore a design strategy to create zeo-type catalysts with desired microstructures, and depending on the size of the microporous structure, these catalysts are able to control product selectivity for plenty of reactions. This work demonstrates a bottom-up synthesis method of tailoring the microporous SiO2 void environments around the active sites on TiO2 catalysts, which controls product selectivity for aldol condensation catalysis. We showed that microporous SiO2 layers can prevent unwanted parallel esterification reactions by destabilizing the relevant transition state that leads to esterification products and suppressing unwanted sequential reactions that form bulkier products by imposing steric barriers. This work provides a methodological framework for controlling product selectivity via a bottom-up design strategy, which can be applied to other catalytic applications in a broader area.