Heterogeneous enantioselective hydrogenation over size-controlled Pt nanoparticles

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Enhancing Effect of Residual Capping Agents in Heterogeneous Enantioselective Hydrogenation of alpha-keto Esters over Polymer-Capped Pt/Al2O3

Heterogeneous enantioselective catalysis is considered a promising strategy for the large-scale production of enantiopure chemicals. In this work, polymer-capped Pt nanocatalysts having a uniform size were synthesized using poly(vinyl pyrrolidone) (PVP) and poly(vinyl alcohol) and supported on gamma-Al2O3. After a facile heat treatment process, their catalytic performance for enantioselective hydrogenation of alpha-keto esters, a structure-sensitive reaction, was investigated. The presence of residual capping agents on the Pt surface often perturbs the adsorption of reacting species and reduces performance in structure-sensitive reactions. However, the 1 wt % PVP-Pt/Al2O3 catalyst exhibited an enhancement in both activity and enantioselectivity compared to a reference Pt/Al2O3 catalyst prepared by wet impregnation. Under optimized reaction conditions, the cinchonidine-modified PVP-Pt/Al2O3 gave an enantiomeric excess of 95% for the enantioselective hydrogenation of methyl pyruvate despite the low Pt loading. We demonstrate that depending on the type of polymers, the residual capping agents can lead to site-selective blockage of the Pt surface, that is, defects or terraces. Quantitative and qualitative analyses also show that the noticeable improvement in enantioselectivity is attributed to the stable adsorption of chiral modifiers on selectively exposed Pt terrace sites. The findings of this work provide a promising strategy to prepare metal nanoparticles having selectively exposed sites and offer insights into the enhancing effect of residual capping agents on the catalytic properties in structure-sensitive reactions.11Nsciescopu

Site-selective blockage of Pt surface by residual capping ligand and its enhancing effect in heterogeneous enantioselective hydrogenation

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Comparative study of chiral modifiers over Pt supported on mesocellular silica foam in enantioselective Hydrogenation

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Effects of selectively exposed Pt sites using residual capping agents on heterogeneous enantioselective hydrogenation

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High-performance Pt catalysts supported on amine-functionalized silica for enantioselective hydrogenation of alpha-keto ester

Heterogeneous enantioselective catalysis is an attractive approach to produce enantiopure chemicals, which are key intermediates for pharmaceutical products. Herein, mesocellular silica foams (MCFs) functionalized by primary, secondary, and tertiary amine groups were used as supports for Pt nanoparticles. The catalytic performances of the Pt/amine-functionalized MCFs were evaluated for the enantioselective hydrogenation of methyl pyruvate in the presence of cinchonidine. Compared to Pt/MCF, the Pt/amine-functionalized MCFs exhibited enhanced activity and enantioselectivity. Particularly, 0.5 wt% Pt/NH2MCF showed a superior performance than 5 wt% Pt/Al2O3, a highly efficient catalyst in the enantioselective hydrogenation of a-keto esters, despite a 10 times lower Pt loading. Furthermore, the Pt/NH2-MCF yielded 100% conversion and 96% ee at 0.1 MPa H-2 pressure during nine successive cycles, thus showing high reusability. The excellent performance of the Pt/amine-functionalized MCFs is attributed to the formation of electron-deficient Pt species through strong interactions between the Pt nanoparticles and amine groups. (C) 2021 Elsevier Inc. All rights reserved.11Nsciescopu

Heterogeneous enantioselectove hydrogenation over Pt supported on M-doped alumina ( M = Mg, Ti, Ce and Y)

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Modulation of Co-Al interaction by V in alumina supported Co-V oxide catalysts and its consequences for propane dehydrogenation

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Enantioselective hydrogenation of methyl pyruvate over Pt catalysts supported on amine-functionalized silica

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Effects of heat-treatment atmosphere and temperature on cobalt species in Co/Al2O3 catalyst for propane dehydrogenation

Co-based catalysts have attracted increasing attention as promising catalysts for propane dehydrogenation (PDH) because of their C–H bond activation ability. Co species in Co/Al2O3 are present in various forms, such as Co3O4, CoAl2O4, CoO, and metallic Co. However, the catalytic properties of the various Co species in PDH are unclear. In this work, we prepare Co/Al2O3 with different compositional distribution of Co species by heat-treating the supported Co precursor under O2, Ar, and H2 atmospheres at temperatures between 500 and 600 °C. H2-treated Co/Al2O3 results in superior performance compared to O2- and Ar-treated catalysts. This is attributed to the relatively high Co surface concentration and relatively high ratio of tetrahedral Co2+ stabilized in CoAl2O4 to the total Co species. A detailed study shows that both tetrahedral Co2+ and metallic Co in Co/Al2O3 are active for PDH, but the former is more selective.11Nsciescopu