Pt Nanoparticles Entrapped Into The Periodic Mesoporous Resols For Hydrogenation Of Ethyl Pyruvate And Aldehydes

FDU-type periodic mesoporous resols(PMRs),are a class of newly-developed advanced materials possessing tunable mesostructures,textural properties of mesoporous materials and the merits of organic polymers.These materials,with three-connected benzene-ring framework,large surface area and uniform pore sizes, can be derived from resols precursor(phenol/formaldehyde) with triblock copolymers via a solvent evaporation induced self-assembly(EISA),or through a simple dilute aqueous strategy.They are stable even under acidic and basic conditions.They exhibit unique hydrophobic affinity towards organic reactants or solvents,quite different from their silica-based inorganic analogues.However,the application of FDU-type PMRs in catalysis has been rarely reported up to now.The heterogeneous asymmetric catalysis can induce the enatioselectivity. Enantioselective hydrogenation ofα-functionalized ketones catalyzed by cinchona alkaloids chirally-modified supported platinum catalysts has been extensively studied for a few decades.In this paper,four Pt catalysts supported on FDU-type resols were prepared and investigated in the enantioselective hydrogenation of ethyl pyruvate.The precursors of Pt catalysts and the preparation methods of Pt catalysts have been explored in detail.Calcination under vacuum at a high temperature for Pt/FDU-14 catalyst derived from H₂PtCl₆ made the aggregation of Pt particles.As a result, catalyst FDU-H₂PtCl₆ has an average Pt particle size of about 5 nm;while catalyst FDU-H₂PtCl₆-350 has a slightly larger Pt particle size of about 8 nm.For Pt(NH₃)₄Cl₂ derived Pt/FDU-14 catalyst,calcination under vacuum at a high temperature is beneficial for the dispersion of Pt particles instead.In particular,the catalyst FDU-Pt(NH₃)₄Cl₂ showed the highest enantioselectivity of 81%ee when acetic acid was used as solvent.While the catalyst FDU-H₂PtCl₆ exhibited the highest activity, with the TOF reaching 21902 mol mol^-1 h^-1 for the chiral hydrogenation of ethyl pyruvate in acetic acid,and affording 77%ee value as well.Furthermore,the Pt nanoparticles can be stabilized inside the mesopores via the interaction between the metal particles and aromatic moiety.As a result,the catalyst is expected to show the promising stability and remarkable reusability in acetic acid and in water and the catalyst FDU-H₂PtCl₆ can be recycled for at least 25 times in acetic acid without distinct loss of activity or enantioselectivity.Besides the asymmetric hydrogenation of ethyl pyruvate,we also investigated the catalytic performance of catalyst Pt/FDU-14 in the hydrogenation of benzaldehydes.Our results show that Pt/FDU-14 worked well as an efficient catalyst for the liquid-phase hydrogenation of various benzaldehydes under mild conditions. Water was confirmed to be a better choice of solvent for the hydrogenation of benzaldehydes on the Pt/FDU-14 catalyst.It showed the highest activity(turnover frequency) of about 5700 mol mol^-1 h^-1 for 3-fluorobenzaldehyde hydrogenation in water and no distinct loss of activity or selectivity was observed after the catalyst was recycled nine times.Compared with the commercial Pt/Al₂O₃ catalyst,the Pt/FDU-14 catalyst showed superior performance,particularly for the para-substituted benzaldehydes,which is mainly owing to the more hydrophobic nature of FDU-based catalyst.