Rational Catalyst Design: A Multifunctional Mesoporous Silica Catalyst for Shifting the Reaction Equilibrium by Removal of Byproduct

Controlling reactivity of nanoporous catalyst materials by tuning reaction product-pore interior interactions: Statistical mechanical modeling

“…Multifunctionalization of MSN to include hydrophobic groups, as well as catalytic groups, has been observed to significantly enhance reactivity in several such systems. [4][5][6] This effect has been explained as a result of functionalization converting an intrinsically hydrophilic interior pore surface of MSN into a hydrophobic environment thereby "expelling" the product water and shifting the equilibrium of the reversible esterification reaction. The greatest enhancement to date has been achieved through solvent-mediated control of the configuration of hydrophobic 3-(pentafluorophenyl) propyl groups which are induced to lie prone on silica surface thereby min- evans@ameslab.gov imizing the interaction of the product water with the hydrophilic MSN surface groups.…”

“…The greatest enhancement to date has been achieved through solvent-mediated control of the configuration of hydrophobic 3-(pentafluorophenyl) propyl groups which are induced to lie prone on silica surface thereby min- evans@ameslab.gov imizing the interaction of the product water with the hydrophilic MSN surface groups. 6,7 In fact, there are several possible scenarios wherein functionalization to tune product-pore interactions can influence both the thermodynamics and the kinetics of transport and reaction, and thereby impact reactivity in meso-or nanoporous reaction systems. First, we discuss thermodynamic factors.…”

Multi-functionalization of nanoporous catalytic materials to enhance reaction yield: Statistical mechanical modeling for conversion reactions with restricted diffusive transport

“…For dehydration reactions with H 2 O as the product, one scenario is direct repulsive interaction of hydrophobic organic groups with H 2 O [5]. For PFP-functionalized MSN, solid-state NMR studies have shown that PFP lies prone in the presence of H 2 O, thus covering hydrophilic groups on the MSN surface [4,12]. DFT analysis consistently shows that the attractive interaction of the PFP group with small clusters representing surface groups (in the absence of solvent) exceeds that of H 2 O [12].…”

“…In addition to functionalization of the interior pore surface with catalytic groups, multifunctionalization by additional groups could modify selectivity if the groups act as "gatekeepers" near the pore openings [2], or tune activity, e.g., by strongly interacting with one of the products to alter the reaction equilibrium [4]. We focus on the latter effect where one expects that making the pore interior unfavorable to a reaction product should lower its equilibrium concentration inside the pore, thus shifting the reaction equilibrium to higher conversions.…”

“…One motivation for these studies is that esterification of fatty acids with methanol to produce methyl esters is a pretreatment step in the production of bio-diesel. Here, multi-functionalization to include hydrophobic as well as catalytic groups has been shown to significantly enhance reactivity in several systems [4,5], most dramatically by utilizing hydrophobic 3-(pentafluorophenyl) polypropyl (PFP) groups [4].…”