(706c) Low Temperature Cyclohexane Oxidation over Catalysts Containing M-N4 Active Sites

Nylon polymers have a range of applications from textiles to agricultural machinery. An important precursor for synthesis of Nylon-6 and Nylon-6,6 is a combination of cyclohexanol and cyclohexanone known as “KA oil,” which is obtained from the oxidation of cyclohexane. Molecular complexes such as metal phthalocyanines (MPCs) and porphyrins have been shown to oxidize cyclohexane to KA oil, but these studies typically focus on a single metal. Here, MPCs (M = Fe, Mn, Co, Cu, Cr, and Ni) both deposited onto and encapsulated within faujasite zeolites (“MPC/FAU” and “MPC@FAU”, respectively), were synthesized and characterized for use in comparative studies of the reaction rate, apparent reaction orders and activation energies, and product selectivity in oxidation of cyclohexane using tert-butyl hydrogen peroxide (TBHP) as the oxidant. Metal‑nitrogen-doped carbon catalysts (MNCs) were also tested as they contain sites with similar local structures to MPCs; specifically, isolated single metal atoms coordinated to four nitrogens with square planar geometry. Reactions were performed in a sealed glass batch reactor at 303 K. MNC, MPC/FAU, and MPC@FAU catalysts with Fe active sites outperformed all other tested transition metals within these supports. Per-metal-atom site-time-yields (STYs) for each of the sample types followed the following reactivity trends: Fe > Co > Cu > Ni > Mn for MNCs, Fe > Mn > Co > Cu > Cr > Ni for MPC/FAU, and Fe > Mn > Cr ≈ Cu for MPC@FAU samples. Replacing peripheral hydrogens in MPC with more electron withdrawing groups, such as halogens, resulted in higher initial STYs over FePC samples. With these results and further study, we aim to probe the effects of transition metal identities on catalytic performance in cyclohexane oxidation and to determine the effectiveness of studying well-defined MPC@FAU materials as models for the less-uniform metal active sites of MNCs.