Consequences of Pore Polarity and Solvent Structure on Epoxide Ring-Opening in Lewis and Brønsted Acid Zeolites.

The structure of solvent molecules within zeolite pores influences the rates and selectivities of catalytic reactions by altering the free energies of reactive species. Here, we examine the consequences of these effects on the kinetics and thermodynamics of 1,2-epoxybutane (CHO) ring-opening with methanol (CHOH) in acetonitrile (CHCN) cosolvent over Lewis acidic (Zr-BEA) and Brønsted acidic (Al-BEA) zeolites of varying (SiOH) density. Despite ostensibly identical reaction mechanisms across materials, turnover rates depend differently on (SiOH) density between acid types.

Influence of Ti-incorporated Zeolite Topology and Pore Condensation on Vapor Phase Propylene Epoxidation Kinetics with Gaseous HO.

Vapor-phase propylene (CH) epoxidation kinetics with hydrogen peroxide (HO) strongly reflects the physical properties of Ti-incorporated zeolite catalysts and the presence of spectating molecules ("solvent") near active sites even without a bulk liquid phase. Steady-state turnover rates of CH epoxidation and product selectivities vary by orders of magnitudes, depending on the zeolite silanol ((SiOH)) density, pore topology (MFI, *BEA, FAU), and the quantity of condensed acetonitrile (CHCN) molecules nearby active sites, under identical reaction mechanisms sharing activated HO intermediates on Ti surfaces. Individual kinetic analyses for propylene oxide (PO) ring-opening, homogeneous diol oxidative cleavage, and homogeneous aldehyde oxidation reveal that secondary reaction kinetics following CH epoxidation responds more sensitively to the changes in zeolite physical properties and pore condensation with CHCN.

Engineering intraporous solvent environments: effects of aqueous-organic solvent mixtures on competition between zeolite-catalyzed epoxidation and HO decomposition pathways.

Solvent molecules alter the free energies of liquid phase species and adsorbed intermediates during catalytic reactions, thereby impacting rates and selectivities. Here, we examine these effects through the epoxidation of 1-hexene (CH) with hydrogen peroxide (HO) over hydrophilic and hydrophobic Ti-BEA zeolites immersed in aqueous solvent mixtures (acetonitrile, methanol, and γ-butyrolactone). Greater HO mole fractions provide greater epoxidation rates, lower HO decomposition rates, and hence improved HO selectivities to the desired epoxide product in each combination of solvent and zeolite.

Influence of solvent structure and hydrogen bonding on catalysis at solid-liquid interfaces.

Solvent molecules interact with reactive species and alter the rates and selectivities of catalytic reactions by orders of magnitude. Specifically, solvent molecules can modify the free energies of liquid phase and surface species solvation, participating directly as a reactant or co-catalyst, or competitively binding to active sites. These effects carry consequences for reactions relevant for the conversion of renewable or recyclable feedstocks, the development of distributed chemical manufacturing, and the utilization of renewable energy to drive chemical reactions.