(689g) Selective Oxidation of n-Butane to 1-Butanol over Transition Metal Catalysts Encapsulated By Metal-Organic Frameworks
Density functional theory (DFT) is used to model reaction pathways of the oxidation of n-butane to 1-butanol over several different metal alloy and pure metal catalysts under steric constraints, and the implications on designing MOF-encapsulated catalysts are discussed. MOFs are porous crystalline solids comprised of metal-based nodes connected by organic â??linkerâ? molecules. Recently, they have been successfully grown around metal nanoparticles, creating porous networks at the MOF/catalyst interface, which have been shown to promote the regioselective hydrogenation of trans-1,3-hexadiene to 3-hexene. In this work, we explore the use of sterically constrained catalysts for selective alkane oxidation. We are specifically interested in n-butane oxidation to 1-butanol, which is important in the pharmaceuticals, energy, and specialty chemicals industries. It is a useful reaction for studying regioselectivity since 2-butanol is thermodynamically more stable than 1-butanol. In this work, we investigate n-butane oxidation to 1-butanol, 2-butanol, 1-butanal, and 1-butene oxide on the (111) facets of Ag3Pd, Cu3Pd, PdZn, Cu, and Pd. We use a â??surrogate poreâ? comprised of helium atoms to model the MOF pores. We compute the energies of reaction intermediates and transition states involved in 90 total reactions using DFT, and we develop scaling relationships linking these energies to more simple â??descriptorsâ? of catalytic activity. These relationships are used in coordination with microkinetic modeling. We identify the best descriptors for this mechanism along with the dominant reaction pathways and the catalytic rates as functions of the descriptor values. The descriptor values that optimize activity and selectivity toward 1-butanol are identified, and predictions about which materials will be optimal for this reaction along with predictions about their stabilities are discussed.