Adsorption and Reaction of Porphyrinic Metal Organic Frameworks: DFT and Simulations Study

We investigate two types of porphyrinic MOFs, i.e., porphyrin-paddlewheel framework (PPF-1) and ZnMn-RPM, with application in gas adsorption and catalyst, respectively. Using density functional theory and Grand canonical Monte Carlo simulations, we find that the N₂ and CO₂ isotherm at 77 and 298 K, respectively, based on optimized structure 1 and 2 of PPF-1, are in reasonalbe agreement with experimental data, while the crystal structure based isotherms greatly overestimate experimental data, indicating that the crystal structure shrinks during the activation of solvents and the free volume in the material is greatly reduced. A two-step reaction is proposed to epoxidation of styrene with ZnMn-RPM as catalysis. Energy barriers are calculated to be 0.10 and 0.33 eV for the two step reactions, respectively, which is much smaller than that (1.95 eV) of the catalysis free reaction in gas phase. The much smaller energy barrier for the reaction with ZnMn-RPM well explains the catalytic activity of this material, and the fact that no observation of the reaction without ZnMn-RPM dues to the difficulty in overcoming the large barrier.