Pingping Zhao

Polyoxometalate-based amino-functionalized ionic solid catalysts lead to highly efficient heterogeneous epoxidation of alkenes with H2O2

Polyoxometalate(POM)-based ionic hybrid nanospheres prepared by protonating and anion-exchanging amino-attached ionic liquid cations with Keggin POM-anions have proven to be highly efficient heterogeneous catalysts for the epoxidation of alkenes with H2O2, presenting advantages of convenient recovery, steady reuse, simple preparation, and flexible composition.

Heteropolyacid salts of N-methyl-2-pyrrolidonium as highly efficient and reusable catalysts for Prins reactions of styrenes with formalin

New organic heteropolyacid (HPA) salts prepared by exchanging counter protons of Keggin HPAs with N-methyl-2-pyrrolidonium proved to be highly efficient, conveniently recoverable, and steadily reusable heterogeneous catalysts for the organic solvent-free Prins reactions of styrenes with formalin.

Phase-transfer hydroxylation of benzene with H2O2 catalyzed by a nitrile-functionalized pyridinium phosphovanadomolybdate†

A new nitrile-tethered pyridinium polyoxometalate (POM) was prepared by anion-exchange of the ionic liquid precursor [N-butyronitrile pyridine]Cl ([C3CNpy]Cl) with the Keggin phosphovanadomolybdic acid H5PMo10V2O40 (PMoV2), and the obtained organic POM salt [C3CNpy]4HPMoV2 was characterized by XRD, SEM, TG, 1H NMR, 13C NMR, ESI-MS, CHN elemental analysis, nitrogen sorption experiment, and melting point measure. When used as a catalyst, [C3CNpy]4HPMoV2 causes the first example of reaction-controlled phase-transfer hydroxylation of benzene with H2O2, showing high activity and stable reusability. Based on spectral characterizations and comparisons of reaction results, plus the reversible color change between fresh and recovered catalyst, a unique reaction mechanism is proposed for understanding the highly efficient [C3CNpy]4HPMoV2-catalyzed phase-transfer catalysis. The formation of dissolvable active species [VO(O2)]+ is responsible for the phase-transfer behavior, while the intramolecular charge transfer and the protonated nitrile in cations accelerate the reaction and favor a better catalyst recovery rate.

Schiff Base Structured Acid-Base Cooperative Dual Sites in an Ionic Solid Catalyst Lead to Efficient Heterogeneous Knoevenagel Condensations

An acid-base bifunctional ionic solid catalyst [PySaIm](3)PW was synthesized by the anion exchange of the ionic-liquid (IL) precursor 1-(2-salicylaldimine)pyridinium bromide ([PySaIm]Br) with the Keggin-structured sodium phosphotungstate (Na(3) PW). The catalyst was characterized by FTIR, UV/Vis, XRD, SEM, Brunauer-Emmett-Teller (BET) theory, thermogravimetric analysis, (1)H NMR spectroscopy, ESI-MS, elemental analysis, and melting points. Together with various counterparts, [PySaIm](3)PW was evaluated in Knoevenagel condensation under solvent and solvent-free conditions. The Schiff base structure attached to the IL cation of [PySaIm](3)PW involves acidic salicyl hydroxyl and basic imine, and provides a controlled nearby position for the acid-base dual sites. The high melting and insoluble properties of [PySaIm](3)PW are relative to the large volume and high valence of PW anions, as well as the intermolecular hydrogen-bonding networks among inorganic anions and IL cations. The ionic solid catalyst [PySaIm](3)PW leads to heterogeneous Knoevenagel condensations. In solvent-free condensation of benzaldehyde with ethyl cyanoacetate, it exhibits a conversion of 95.8 % and a selectivity of 100 %; the conversion is even much higher than that (78.2 %) with ethanol as a solvent. The solid catalyst has a convenient recoverability with only a slight decrease in conversion following subsequent recyclings. Furthermore, the new catalyst is highly applicable to many substrates of aromatic aldehydes with activated methylene compounds. On the basis of the characterization and reaction results, a unique acid-base cooperative mechanism within a Schiff base structure is proposed and discussed, which thoroughly explains not only the highly efficient catalytic performance of [PySaIm](3)PW, but also the lower activities of various control catalysts.

A dicationic ionic liquid-modified phosphotungstate hybrid catalyst for the heterogeneous oxidation of alcohols with H 2 O 2

An ionic hybrid catalyst 1,1′-(butane-1,4-diyl)-bis(3-methylimidazolium) phosphotungstate (abbreviated [Dmim]1.5PW) has been prepared by anion-exchange of the divalent ionic liquid (IL) 1,1′-(butane-1,4-diyl)-bis(3-methylimidazolium) di(bromide) with the Keggin phosphotungstic acid H3PW12O40, and characterized by IR, 1H NMR, 13C NMR, ESI-MS, TG, SEM, XRD, BET surface area measurements, elemental analysis, and melting point. The hybrid material was evaluated as a catalyst for the oxidation of alcohols with aqueous hydrogen peroxide under various conditions. The catalytic performance of [Dmim]1.5PW was also compared with related catalysts bearing other cations or anions. The new hybrid [Dmim]1.5PW proved to be an efficient liquid-solid heterogeneous catalyst for H2O2-based oxidation of alcohols, with the advantages of high conversion and selectivity, easy recovery, and quite good reusability.

Direct hydroxylation of benzene to phenol with hydrogen peroxide catalyzed by a quinine heteropolyacid hybrid

Abstract A new heterogeneous hybrid catalyst designed for direct hydroxylation of benzene to phenol was prepared through modification of Keggin-structured phosphovanadomolybdate with quinine. The structure of the catalyst was fully characterized by Fourier transform infrared and ultraviolet-visible spectroscopies, X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, nitrogen sorption experiments, and CHN elemental analysis. The results indicated that the hybrid catalyst was a semi-amorphous heteropolyacid salt with high thermal stability, surface area, and pore volume. The catalytic activity of the hybrid for the hydroxylation of benzene with H 2 O 2 was assessed. The hybrid catalyst forms a liquid-solid biphasic system and exhibits high activity, convenient recovery, and reusability. The strong electronic interactions and hydrogen bonding networks formed between the π-electron-rich quinine framework and heteropolyanions are responsible for the solid nature and insolubility of the catalyst. The high surface area and improved redox properties of the Keggin heteropolyacid account for its excellent catalytic performance. The results of this work reveal a new, more facile way to prepare an efficient polyoxometalate-based catalyst for heterogeneous hydroxylation of benzene to phenol.将奎宁与Keggin结构磷钼钒杂多酸结合制备出一种新颖的多相苯羟基化杂化催化剂,采用傅里叶变换红外光谱、紫外-可见光谱、X射线衍射、扫描电镜、热重、N2吸附-脱附和CHN元素分析等表征手段对催化剂进行了分析.结果表明,该催化剂是一种具有较高比表面积和孔体积的半无定形有机杂多酸盐.在H2O2为氧源的苯羟基化反应中,杂化催化剂引导了液-固两相催化体系,表现出较高催化活性和重复使用稳定性.催化剂中奎宁与杂多阴离子间的氢键和电子相互作用赋予了其高熔点和难溶性,而高比表面积和因奎宁而改善的杂多阴离子的氧化还原性是其获得优异催化性能的主要原因.这为多相苯羟基化反应提供了一种新的且制备便捷的基于多金属氧酸盐的高效催化剂.

Article (Dedicated to Professor Yi Chen on the occasion of his 80th birthday)Direct hydroxylation of benzene to phenol with hydrogen peroxide catalyzed by a quinine heteropolyacid hybrid

Abstract A new heterogeneous hybrid catalyst designed for direct hydroxylation of benzene to phenol was prepared through modification of Keggin-structured phosphovanadomolybdate with quinine. The structure of the catalyst was fully characterized by Fourier transform infrared and ultraviolet-visible spectroscopies, X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, nitrogen sorption experiments, and CHN elemental analysis. The results indicated that the hybrid catalyst was a semi-amorphous heteropolyacid salt with high thermal stability, surface area, and pore volume. The catalytic activity of the hybrid for the hydroxylation of benzene with H 2 O 2 was assessed. The hybrid catalyst forms a liquid-solid biphasic system and exhibits high activity, convenient recovery, and reusability. The strong electronic interactions and hydrogen bonding networks formed between the π-electron-rich quinine framework and heteropolyanions are responsible for the solid nature and insolubility of the catalyst. The high surface area and improved redox properties of the Keggin heteropolyacid account for its excellent catalytic performance. The results of this work reveal a new, more facile way to prepare an efficient polyoxometalate-based catalyst for heterogeneous hydroxylation of benzene to phenol.将奎宁与Keggin结构磷钼钒杂多酸结合制备出一种新颖的多相苯羟基化杂化催化剂,采用傅里叶变换红外光谱、紫外-可见光谱、X射线衍射、扫描电镜、热重、N2吸附-脱附和CHN元素分析等表征手段对催化剂进行了分析.结果表明,该催化剂是一种具有较高比表面积和孔体积的半无定形有机杂多酸盐.在H2O2为氧源的苯羟基化反应中,杂化催化剂引导了液-固两相催化体系,表现出较高催化活性和重复使用稳定性.催化剂中奎宁与杂多阴离子间的氢键和电子相互作用赋予了其高熔点和难溶性,而高比表面积和因奎宁而改善的杂多阴离子的氧化还原性是其获得优异催化性能的主要原因.这为多相苯羟基化反应提供了一种新的且制备便捷的基于多金属氧酸盐的高效催化剂.