Consequences of Intrapore Liquids on Reactivity, Selectivity, and Stability for Aldol Condensation Reactions on Anatase TiO2 Catalysts

0561373 - ÚFCH JH 2023 RIV DE eng J - Článek v odborném periodiku
Kadam, Shashikant Arun - Hwang, A. - Iglesia, E.
Consequences of Intrapore Liquids on Reactivity, Selectivity, and Stability for Aldol Condensation Reactions on Anatase TiO2 Catalysts.
ChemCatChem. Roč. 14, č. 13 (2022), č. článku e202200059. ISSN 1867-3880. E-ISSN 1867-3899
Institucionální podpora: RVO:61388955
Klíčová slova: Aldol reaction * Capillary condensation * Heterogeneous catalysis * Solvent effects * Titania
Obor OECD: Physical chemistry
Impakt faktor: 4.5, rok: 2022
Způsob publikování: Omezený přístup

This study provides evidence and mechanistic interpretations for the significant consequences of intrapore non-polar liquids on acetone aldol condensation turnover rates, selectivity to primary dimer products, and catalyst stability for reactions at Lewis acid-base site pairs on TiO2 surfaces. These non-polar liquids confer such benefits through the preferential stabilization of transition states (TS) for adsorption (entry) and desorption (exit) steps, which place their respective reactants or products within a solvating outer sphere environment. The extent to which non-polar fluids (n-heptane) form an intrapore liquid phase within TiO2 voids was obtained from N-2 uptakes using established formalisms that consider the different molal volume, surface tension, and volatility between N-2 and n-heptane. Acetone condensation rates are limited by C-H activation, an ´entry´ step that forms bound prop-1-en-2-olates via a TS stabilized by intrapore liquids, leading to higher aldol condensation turnover rates as n-heptane pressure increases and active TiO2 surfaces become increasingly immersed within a non-polar liquid phase. These liquids solvate the late TS structures that mediate the desorption of primary C-6 condensation products even more effectively than those involved in prop-1-en-2-olate formation or in nucleophilic attack events that later form C-C bonds. Such preferential solvation favors desorption over C-C coupling events, thus disfavoring the formation of larger oligomers that become stranded at active sites, thus leading to much slower deactivation. Moreover, solvation by non-polar liquids also leads to C-6 alkanones as the sole products formed in a single surface sojourn. These effects of a non-polar dense phase circumvent the inherent stability, reactivity, and selectivity hurdles that have precluded practical aldol condensation catalysis on Lewis acid-base pairs at oxide surfaces. These consequences are demonstrated here for TiO2 catalysts, acetone aldol condensation reactions, and n-heptane as the non-polar liquid but through strategies, concepts, and mechanistic features that extend to other systems. More generally, these observations and their mechanistic origins demonstrate how a contacting liquid preferentially solvates TS structures for elementary steps that involve either reactants arriving from or products entering into an outer sphere environment that contains a dense non-polar phase.
Trvalý link: https://hdl.handle.net/11104/0334934