Abstract
A combination of Molecular Dynamics (MD) simulations and Quasielastic Neutron Scattering (QENS) experiments has been used to investigate the dynamics and structure of benzene in MCM-41 based catalysts. QENS experiments of benzene as both an unconfined liquid and confined in the catalyst Pt/MCM-41 find that the mobility of benzene decreases upon confinement as shown by the decreased diffusion coefficients. Complementary MD simulations on benzene in MCM-41 show agreement with the QENS experiments when using a novel fully flexible model of MCM-41. Structural information from the MD simulations show that benzene in MCM-41 has a significantly different structure from that of the bulk liquid; with benzene molecules closer together and no prefered orientation.
Highlights
Despite the widespread industrial applications of micro- and meso-porous catalysts, there is often little understanding of the structure, or dynamical processes which occur within the catalyst pores
In order to obtain this information Quasielastic Neutron Scattering (QENS) techniques coupled with Molecular Dynamics (MD) simulations provide an excellent combination, which relate the dynamics obtained via experimentation to the dynamics and structure from simulation
The results from the MD simulations using the flexible framework are compared to those calculated using a rigid framework model, where the atomic positions of all the MCM-41 atoms are kept frozen throughout the simulation and the new fully flexible model, where there are no restrictions on the movement of MCM-41 atoms
Summary
Despite the widespread industrial applications of micro- and meso-porous catalysts, there is often little understanding of the structure, or dynamical processes which occur within the catalyst pores. In order to obtain this information Quasielastic Neutron Scattering (QENS) techniques coupled with Molecular Dynamics (MD) simulations provide an excellent combination, which relate the dynamics obtained via experimentation to the dynamics and structure from simulation We have used this combination to elucidate the structure and dynamics of benzene confined within the mesoporous catalyst Pt/MCM-41. The large (circa 30 Å) pores allow for bulky guest molecules to diffuse It is very suitable for combining QENS and MD, which provide complementary information on molecular dynamics as discussed by both O’Malley et al.[3] and Jobic and Theodorou.[4] It is well known that confining a fluid within a porous solid will alter its physicochemical properties, such as adsorption and transport properties. Our simulation studies are complemented by the new QENS data which accord well with the modelling studies; and the combination of the two techniques yields detailed insight into the benzene dynamics when confined in the pores of this catalyst
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