Probing the dynamics and structure of confined benzene in MCM-41 based catalysts

Abstract

Combined MD simulations and QENS experiments on benzene in MCM-41 provide insight into the dynamics and structure of benzene

Ultrafast Dynamics and Liquid Structure in Mesoporous Silica: Propagation of Surface Effects in a Polar Aprotic Solvent

“…In particular, liquids in mesoporous silicas (pore diameter 2–50 nm) have broad importance, e.g., hybrid electrolytes, , heterogeneous catalysis, , and carbon capture . Due to the ubiquity and importance of aqueous systems, the structure and dynamics of confined water have been studied extensively. − Simulation − and experimental − (neutron scattering, optical Kerr effect, and NMR) confinement studies have been conducted for a few simple organic liquids like acetonitrile and benzene. In general, dynamics slow with increasing confinement, but the rate of formation of an imidazolium-based ionic liquid (IL) by chemical reaction from 1-methylimidazole increased upon confinement in mesoporous silica .…”

Level Crossing Resonance Studies of the Muoniated Cyclohexadienyl Radical (MuĊ6H6) Interacting with Uncapped Gold Nanoparticles in Porous Silica Hosts

“…The acidic properties of such environments ,− are also important, via proton or H atom transfer reactions to guest molecules ,,,− ,− that can also form free-radical intermediates, important to hydrogenation reactions in general , and for benzene in particular. ,,,, Other than from muon science ,,,− though, exemplified by the present paper as well, there are very few examples of the direct observation of such H-adduct free radicals by spectroscopic techniques, notable exceptions relevant here being the HĊ 6 H 6 cyclohexadienyl radical seen in ZSM-5 zeolite and the ethyl CH 3 ĊH 2 and HĊ 6 H 6 radicals interacting with PdNPs investigated by ESR in silica environments . While ESR would generally be the technique of choice for the investigation of free radicals, the confined geometries of mesoporous silica environments can facilitate radical–radical recombination reactions, reducing signal amplitudes which are generally quite weak to begin with, particularly at higher temperatures, as well as likely affecting the measurements of reaction rates in such confined environments …”

“…The peak amplitudes of both resonances are consistently lower though at the lower loadings. That the Δ 1 resonances are clearly visible near 300 K in both the silica and AuNP environments (Figures –), in contrast to bulk benzene at temperatures just above its melting point, could be indicating an effect of the constricted environments of the silica mesopores on the melting points and dynamics of benzene and the MuĊ 6 H 6 radical within these mesopores. ,− …”

“…5 , 1 5, 1 6, 34, 40 Other than from muon sci- ence 11,13,22,41−46 though, exemplified by the present paper as well, there are very few examples of the direct observation of such H-adduct free radicals by spectroscopic techniques, notable exceptions relevant here being the HC ̇6H 6 cyclohexadienyl radical seen in ZSM-5 zeolite 15 and the ethyl CH 3 C ̇H2 and HC ̇6H 6 radicals interacting with PdNPs investigated by ESR in silica environments. 16 While ESR would generally be the technique of choice for the investigation of free radicals, the confined geometries of mesoporous silica 47 environments can facilitate radical−radical recombination reactions, 48 reducing signal amplitudes which are generally quite weak to begin with, particularly at higher temperatures, as well as likely affecting the measurements of reaction rates in such confined environments. 49 The Mu atom has thus emerged as key in investigating the dynamics and hyperfine coupling constants of H-adduct free radicals in different environments, forming their muoniated isotopic equivalents 7,11,13,17,22,42−44 by Mu addition reactions, wherein the basic μSR (muon spin rotation, resonance, relaxation) technique effectively allows only one muoniated radical in the system at a time.…”

Mapping of Guest Localization in Mesoporous Silica Particles by Solid-State NMR and Ab Initio Modeling: New Insights into Benzoic Acid and p-Fluorobenzoic Acid Embedded in MCM-41 via Ball Milling

“…These phenomena are of great importance to understand drug release kinetics, or a tailored design of novel catalysts, where small molecules can act as valuable probes addressing these questions. This has been illustrated by Dervin et al, studying the structure and diffusion of benzene confined in a mesoporous-silica-based catalyst. The mesoporous material with larger pores compared to microporous zeolites have the potential for greater freedom of movement, where the hydrogenation was found to be internally limited by mass transport.…”