Delaminated zeolite precursors as selective acidic catalysts

Abstract

Heterogeneous catalysis is important in fine-chemical and pharmaceutical manufacture and in petroleum refining¹. Many of the catalysts used by these industries are based on aluminosilicates, which combine high stability with excellent activity in acid-mediated reactions². Within this class of material, zeolites — microporous crystalline aluminosilicates with three-dimensional framework structures — have attracted particular attention: they are significantly more active than the layered structures (clays)³ and mesoporous structures (whose walls are amorphous)⁴,⁵, and they impart shape selectivity on the reaction products. The selectivity arises from the fact that the catalytically active acid sites have to be accessed through uniformly sized pores and voids, imposing size constraints on the accessibility to reactants and the nature of the intermediates and products¹. Providing access for larger molecules to the catalytic sites would expand the range of reactions that zeolites can catalyse. But attempts to increase the pore size of zeolites⁶ have met with only limited success. Here we describe an approach in which a layered zeolite precursor⁷,⁸ is delaminated, in much the same way as the layered structure of a clay may be unbound. The result is an aluminosilicate whose zeolite-type catalytic sites are contained within thin, readily accessible sheets. Performance tests show that the delamination process improves the accessibility of the catalytic sites without affecting their activity. We expect that our approach could be adapted to other layered zeolite precursors⁵,^7,8,9,10,11, thus paving the way to exfoliated zeolite precursors as a new class of catalysts.