Heterogenization of Phosphotungstate Clusters into Magnetic Microspheres: Catalyst for Selective Oxidation of Alcohol in Water

Abstract

A polyamine-mediated bioinspired method is demonstrated to heterogenize and stabilize isolated phosphotungstic acid (PTA) Keggin units, which allows formation of a multicomponent microcapsule structure under ambient conditions. Utilizing the supramolecular aggregation property of polyamines in the presence of suitable multivalent anions, it is shown that the resulting aggregates, while facilitating the encapsulation of negatively charged Fe 3 O 4 nanoparticles (magnetic component), further facilitate the assembly of PTA nanoclusters (catalytic component) to generate magnetic microcapsule structures (PTA@MMS). As revealed from a detailed analysis, the interaction of polyamines with PTA is the key for the Keggin units to remain stable and isolated as desirable for catalytic applications. Investigation on the catalytic activity in oxidation of benzyl alcohol with H 2 O 2 as the oxidant in water shows that these isolated PTA units render better catalytic activity and product selectivity toward aldehyde under green conditions compared to the other reported PTA-based noble-metal-free catalysts. Moreover, the presence of magnetic nanoparticles leads to convenient catalyst separation and reuse. Therefore, the method is believed to provide ways for further developments in POM-based heterogeneous catalysts with opportunities to impart multifunctionality for sustainable organic transformations.

Magnetic-responsive Pickering emulsions based on MFe2O4 (M = Mn, Fe, Co, Ni, Cu, Zn) for green and efficient oxidation of benzyl alcohol

“…Upon heating these Pickering emulsions to 80 °C in the presence of oxidants such as H 2 O 2 , benzyl alcohol was successfully oxidized into benzyl aldehyde. The turnover number (TON) of the ferrite nanoparticles in PIC (48-55) was found to be 1.5-4 times higher than that in acetonitrile (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30). The reaction followed first-order kinetics for MnFe 2 O 4 , and the reaction constants in PIC and acetonitrile were determined to be 0.712 h −1 and 0.310 h −1 , respectively.…”

“…[1][2][3] In the past decades, great efforts have been devoted to designing and preparing efficient heterogeneous catalysts for alcohol conversion. [4][5][6][7] Noble metal-based catalysts, such as palladium, [8][9][10][11] platinum, 12,13 and gold, 14,15 have been widely used due to their ability to activate O 2 into reactive oxygen species. However, the high cost and limited availability of noble metals restricted their widespread use as catalysts.…”

“…As a result, researchers have explored the use of inexpensive and earth-abundant elements with good catalytic activity and selectivity, such as Zn–Co–LDH, 16 V–C, 17 Fe–N–C, 18 W/NS@C, 19 and PTA@MMS. 20 Despite the promising results achieved with these alternative catalysts, the insufficient interaction between reactants and heterogeneous catalysts, caused by poor miscibility or agglomeration, often leads to time-consuming alcohol oxidation processes.…”

Flowerlike Nanosheet-Based High-Entropy Oxides as Catalysts for Aerobic Oxidation of Benzyl Alcohol

“…1 Aromatic alcohols, as popular platform molecules derived from petrol or regenerable biomass, draw massive researchers to investigate their selective aerobic oxidation. 2 It is attributed to the fact that the oxidation products of aromatic alcohols have a wide range of applications in many industries such as organic synthesis, pigments, pharmaceutical molecules, preservatives, and fragrances. Benzyl alcohol (BAL), the simplest of the most aromatic alcohols, has been widely investigated as a characteristic reactive molecule.…”

“…The selective aerobic oxidation of alcohols is a typical reaction that plays an important role in the fields of pharmaceuticals and fragrances as well as the fine chemical industry for the preparation of aldehydes, ketones, acids, ethers, and esters . Aromatic alcohols, as popular platform molecules derived from petrol or regenerable biomass, draw massive researchers to investigate their selective aerobic oxidation . It is attributed to the fact that the oxidation products of aromatic alcohols have a wide range of applications in many industries such as organic synthesis, pigments, pharmaceutical molecules, preservatives, and fragrances.…”