(44c) Synthesis and Characterization of Zeolite-Encapsulated Organometallic Complexes for Oxidation Chemistries

We hypothesized that metal phthalocyanines (MPCs) encapsulated in faujasite (FAU) zeolites (MPC@FAU) can selectively activate methane using nitrous oxide as an oxidant, due to their similarities to metal-containing porous materials that perform this reaction (~393 K). Existing catalysts have inherent heterogeneity in metal species, rendering it difficult to compare reactivity across varied catalyst formulations without first developing active site quantification protocols. MPCs contain divalent central metal atoms in square planar geometry. The supercage of FAU can host MPCs, together serving as a well-defined active center for experimental and computational catalyst characterization. Deviations in zeolite synthesis conditions from prior literature were required to obtain phase-pure FAU, free from undesired impurity phases (e.g., SOD, LTA, GIS) and amorphous material. Deposition of MPCs on the exterior of FAU (MPC/FAU) is unavoidable during hydrothermal synthesis, however, we have developed a reliable washing procedure to remove MPC/FAU species. Metal disulfonate, perchloro- perfluoro-, and perhydrogenated phthalocyanines (MPC-(SO₄)_2, MCl₁₆PC, MF₁₆PC, and MPC; M= Co, Cu, Fe, Zn), were encapsulated into FAU via hydrothermal synthesis (MPC@FAU) and deposited onto the external surfaces by post-synthetic deposition (MPC/FAU). The amount of MPC encapsulated correlates with solubility of the MPC in the zeolite synthesis gel, which varies with the identity of the central atoms and peripheral ligands. XRD patterns and N₂ micropore volumes demonstrate that the obtained materials are crystalline FAU. Collection of electron paramagnetic resonance and diffuse reflectance UV-Visible spectra of the recovered solids were used to identify which solvent(s) effectively remove MPC/FAU species. X-ray absorption spectroscopy was used to verify the square planar structure of metal central atoms by comparison to MPC reagents. Ongoing studies of this single atom catalyst platform will allow for determination of desired characteristics of CO, alcohol, and alkane oxidation catalysts without the contributions from a distribution of metal species.