Rational design of zeolite catalysts

摘要

The identification of organic structure-directing agents capable of tailoring the physicochemical properties of microporous materials has remained a challenge. Now, a unique methodology to design organic mimics of reaction intermediates provides a route to optimize the selectivity of zeolite catalysts. The demand for more efficient zeolite catalysts has spurred efforts to supplant trial and error synthesis methods with those based on rational design. The ability to control zeolite formation and resultant properties is difficult owing to the complexity of crystal growth. Notably, zeolites are inherently metastable relative to other (more dense) minerals with little separation in the thermodynamics of formation. This places greater emphasis on controlling the kinetics of growth through the use of organic structure-directing agents (OSDAs), which are molecules that possess a shape and size that is commensurate with the channels/ cages of zeolite crystals, and thus facilitate the formation of pores. This gives rise to a unique characteristic of zeolite catalysts - shape selectivity - which is derived from the geometry of confined void spaces that impact molecular adsorption on active sites (Bronsted acids).