Thomas Pinnavaia

The focus of my research program is the intercalation and surface chemistry of lamellar compounds, particularly complex layered oxides (CLO). The term intercalation is generally applied to the interaction of a guest species (ion or molecule) with the intracrytalline surfaces of a host solid. Two dimensional solids are renowned for their ability to accommodate guest species in the interlamellar or gallery regions of their structures. Molecular chemists routinely modify the structures reactivities and properties of molecules by simply replacing one or more atomic constituents. Analogous dramatic alterations in properties of lamellar solids can be accomplished by mediating the guest species encapsulated in their galleries.There are three classes of complex layered oxides whose intercalation chemistry is of primary importance to our program:swelling layered silicate clays (LSC);layered double hydroxides (LDH);layered silicic acids (LSA).The LSC have structuresin which two dimensional aluminosilicate layers are separated by sheets of hydrated cations. The hydrated cations in the gallery region between the aluminosilicate layers can be replaced with almost any desired cation by simple ionexchange reaction. Typical LSC (for instance, the clay mineral montmorillonite) have enormous intracrystalline surface areas approaching 750 M{2}/g. Thus almost any combination of neutral molecules and cations can be accommodated on the intracrystalline surfaces. The possibilities for the formation of LSC intercalated derivates are almost endless.The LDH have structures which are complementary to LSC. In this case, the layers are two dimensional hydroxy metal cations and hydrated anions occupy the gallery region between the layers. As in LSC, the gallery ions are replaceable by simple ion exchange reactions. Therefore, we have the ability to encapsulate cationic complexes in LSC and anionic complexes in LDH.Layered silicic acids are a relatively new class of crystalline forms of hydrated silica. These host structures can be intercalated by a variety of metal complex cations and polymers in a manner analogous to LSC.The gallery regions of layered compounds, in general, and CLO, in particular, represent a fascinating new arena for carrying out chemical transformations. These highly anisotropic intracrystalline environments allow reaction pathways to be mediated in ways undreamed of in homogeneous solution. The design of intercalated LSC as shape selective catalysts for hydrogenation, hydroformylation, dealkylation, dehydrogenation, and isomerization reactions has been well demonstrated. Also, a new class of microporous LSC catalysts known as pillared and delaminated clays have been synthesized. These materials have pore structures much larger than those of conventional zeolites. We believe that pillared clays can be designed as new generations of petroleum refining catalysts and as catalysts for the synthesis of synthetic fuels to meet our future energy needs.To illustrate the flavor of a typical research project in this area of inorganic materials chemistry, consider the question of designing LSC as shape selective microporous catalysts for chemical conversions. The catalytic properties of pillared and delaminated clays are a consequence of two fundamental processes, namely physical access and chemical reactivity. Access refers to the process by which to be catalyzed traverses the host medium to reach a chemically active catalytic site. One of the primary objectives of our program is to develop models for access in the two dimensional porous systems represented by pillared and delaminated clays. The access phenomenon can be related to percolation on a two dimensional normal (euclidian) or fractal (noneuclidian) lattice. Two key features which affect access are the rigidity of the layers and the distribution of the pillaring ions. We are examining the access phenomenon in a novel series of experimental and theoretical studies of clays which contain two different sized gallery cations. By observing the sagging of the layers by Raman, neutron and X-ray scattering methods, we can quantify the fundamental property of layer rigidity.Because of the interdisciplinary nature of our work, we collaborate extensively with researchers in other scientific disciplines including physics, soil science, mineralogy, and chemical engineering. We also make use of a broad arsenal of spectroscopic and physical techniques characterization. Thus, my research is extensively involved with chemical synthesis, spectroscopic characterizations techniques, heterogenous catalysis. solid state chemistry, surface coordination chemistry, and a variety of surfacecharacterization techniques.

I have served in the following capacities: consultant on the industrial applications of clay minerals; Director: Center for Fundamental Materials Research at Michigan State University; President: Clay Minerals Society; Michigan State University Section of the American Chemical Society; Michigan Catalysis Society; Editorial Advisory Board: "Chemistry of Materials."; G.W. Brindley Award Lecturer, Clay Minerals Society, 1991; Senior Research Award, Sigma Xi, 1982.