From rays to structures: Representation and selection of void structures in zeolites using stochastic methods

•Accessible voids are compared through stochastic distributions of ray lengths.•Ray histograms encode the shape, topology, distribution and size of voids.•Void similarity determined with Euclidean distance metrics.•Potential catalytically relevant zeolites are presented using similarity searches.

Voids within crystalline microporous solids are represented here using stochastic distributions of rays placed and oriented randomly within the accessible void space, represented using Voronoi decompositions. This algorithm is provided in the Zeo++ software for open use. In this method, ray lengths are depicted as two-dimensional histograms that complement alternate descriptors, such as free and included sphere diameters. We illustrate the specific use of these methods as a tool to narrow the range of zeolites useful for a given catalytic application because of the shape and size of voids. DAC, AFS, AFY, SFO and EON zeolites contain void spaces similar, as suggested by Euclidean distance values between histograms, to those within MOR 8-MR side pockets, which stabilize the transition states that mediate dimethyl ether carbonylation to methyl acetate; these alternate structures offer different connecting void environments, which can enhance or restrict molecular access and influence the effectiveness of the 8-MR protons. NES, EON and USI zeolites exhibit histogram features similar to those of 12-MR MOR channels, where protons selectively catalyze alkylation of biphenyl and naphthalene to 4,4′-diisopropylbiphenyl and 2,6-diisopropylnaphthalene, respectively, with propene. SBT, FAU and SBS contain voids similar in topology to the 12-MR channels of LTL zeolites, within which Pt clusters remain active and stable during the dehydrocyclization of light alkanes, but without the one-dimensional nature of LTL channels. The approach and implementation of these methods are applicable to any microporous or mesoporous solids and to adsorption processes driven by van der Waals contacts between hosts and guest molecules.

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