(407d) Inspired Characterization: Combining Modeling with Experiment to Study Solid Base Zeolite Catalysts

Zeolites transformed the petrochemicals industry when they hit the scene decades ago: processes that once were difficult or impossible, such as catalytic cracking, suddenly had reasonable selectivity using relatively cheap catalytic materials.  All told, the zeolite community has identified 225 different zeolite frameworks, many of them largely untested, with compositions ranging from pure silicon dioxide and aluminosilicates on one end (often called "traditional" zeolites) to aluminum phosphates, borosilicates, gallosilicates, and germanium-silicates on the other.  This rich variety lends itself naturally to a gigantic parameter space, one which is difficult to explore by trial-and-error, and one that is even more difficult to explore throughly.  Despite this enormous parameter space, there is continual pressure to introduce still more new parameters into the field of zeolite synthesis and use, specifically with respect to introducing base-catalytic activity.  Solid base catalysts are typically much easier to separate from reacting mixtures than their homogeneous counterparts, and using a solid zeolite-like catalyst holds the possibility of introducing still more selectivity based on size and/or shape.  Our early work combined experiments and modeling to produce a "computational spectrum":  a prediction of the silicon-29 NMR spectrum of FAU zeolites that had been "nitrided" in an effort to introduce base-catalytic activity.  Follow-up studies have indicated that such zeolites have base-catalytic properties, but are unstable in aqueous solution---this last fact is often a property of non-nitrided zeolites as well.  Our present work is a survey of zeolite framework structure and local composition with several goals in mind:  (a) Identify base-catalyzed reactions that will benefit from a confined environment, (b) Suggest choices of zeolite framework and local composition that maximize catalytic activity and lifetime while providing adequate selectivity (c) Identify diffusion barriers and adsorption sites, particularly whether Bronsted base sites create sufficient local strain that they change the diffusion and/or adsorption characteristics of the material.