Calculating the Energy Barriers Required to Join Metal-Organic Framework Synthesis Intermediates with Non-Equilibrium Molecular Simulation
August 1, 2015.
Metal organic frameworks (MOFs) are synthetic materials made of a cage-like lattice of metal nodes connected by organic linkers. The pores between the nodes define the characteristics of the material. A MOF, MIL-101, has shown great capacity in the adsorption of carbon dioxide and methane, as well as in hydrogenation catalysis with palladium. While there has been success in synthesizing MIL-101 and other MOFs, the mechanistic details behind their assembly remain unknown. Understanding the synthesis mechanism is necessary to understand the kinetics involved and be able to produce this useful material on an industrial scale. Using MIL-101 as a prototypical system, we calculated the energy barriers needed to join synthesis intermediate species of MIL-101 with non-equilibrium molecular dynamics simulations. The umbrella sampling technique is used, where classical dynamics simulations with high spatial force constraints on the reaction coordinate of the system are performed. A potential of mean force at all points along the reaction coordinate is obtained revealing the total energy required, which determined the rate for joining two intermediates together. The simulation protocol developed will be employed to obtain the energy barriers to join possible MIL-101 intermediates, and these barriers combined into a kinetic model of overall MOF formation.
Dynamic Systems | Materials Chemistry
Pacific Northwest National Laboratory (PNNL)
This material is based upon work supported by the S.D. Bechtel Jr. Foundation and is made possible with contributions from the National Science Foundation under Grant No. 1340110, Howard Hughes Medical Institute, Chevron Corporation, National Marine Sanctuary Foundation, and from the host research center. Any opinions, findings, and conclusions or recommendations expressed in this material are solely those of the authors. The STAR Program is administered by the Cal Poly Center for Excellence in STEM Education on behalf of the California State University system.