Mechanistic Insights into Aerobic Oxidative Methyl Esterification of Primary Alcohols with Heterogeneous PdBiTe Catalysts

Electron Structure Tuned Oxygen Vacancy-Rich AuPd/CeO2 for Enhancing 5-Hydroxymethylfurfural Oxidation

The design of high activity catalyst for the efficiently conversion of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) gains great interest. The rationally tailoring of electronic structure directly affects the interaction between catalysts and organic substrates, especially molecular oxygen as the oxidant. This work, the bimetallic catalysts AuPd/CeO2 were prepared by the combining method of chemical reduction and photo-deposition, effectively concerting charge between Au and Pd and forming the electron-rich state of Au. The increasing of oxygen vacancy concentration of CeO2 by acidic treatment can facilitate the adsorption of HMF for catalysts and enhance the yield of FDCA (99.0 %). Moreover, a series of experiment results combining with density functional theory calculation illustrated that the oxidation performance of catalyst in HMF conversion was strongly related to the electronic state of interfacial Au-Pd-CeO2. Furthermore, the electron-rich state sites strengthen the adsorption and activation of molecular oxygen, greatly promoting the elimination of β-hydride for the selective oxidation of 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) to FDCA, accompanied with an outgoing FDCA formation rate of 13.21 mmol ⋅ g-1 ⋅ min-1 at 80 °C. The perception exhibited in this research could be benefit to understanding the effects of electronic state for interfacial sites and designing excellent catalysts for the oxidation of HMF.

One-Step Hydrothermal/Solvothermal Preparation of Pt/TiO2: An Efficient Catalyst for Biobutanol Oxidation at Room Temperature

The selective oxidation of biobutanol to prepare butyric acid is an important conversion process, but the preparation of low-temperature and efficient catalysts for butanol oxidation is currently a bottleneck problem. In this work, we prepared Pt-TiO2 catalysts with different Pt particle sizes using a simple one-step hydrothermal/solvothermal method. Transmission electron microscopy and X-ray diffraction results showed that the average size of the Pt particles ranged from 1.1 nm to 8.7 nm. Among them, Pt-TiO2 with an average particle size of 3.6 nm exhibited the best catalytic performance for biobutanol. It was capable of almost completely converting butanol, even at room temperature (30 °C), with a 98.9% biobutanol conversion, 98.4% butyric acid selectivity, and a turnover frequency (TOF) of 36 h-1. Increasing the reaction temperature to 80 and 90 °C, the corresponding TOFs increased rapidly to 355 and 619 h-1. The relationship between the electronic structure of Pt and its oxidative performance suggests that the synergistic effect of the dual sites, Pt0 and Pt2+, could be the primary factor contributing to its elevated reactivity.

N-doped carbon nanotube encapsulated cobalt for efficient oxidative esterification of 5‑hydroxymethylfurfural

The cobalt nanoparticles embedded into graphitic nitrogen-rich carbon nanotube (Co/GCN) was prepared with a facile method and employed as an efficient catalyst for oxidative esterification of 5-hydroxymethylfurfural (HMF). The introduction...

Chitosan-starch biopolymer modified kaolin supported Pd nanoparticles for the oxidative esterification of aryl aldehydes

A mild and efficient green protocol has been disclosed for selective oxidative esterification of various aldehydes over a novel Pd fabricated chitosan-starch polyplex encapsulated Kaolin (Kaolin@CS-starch-Pd) as a heterogeneous and reusable biocompatible nanocatalyst. Molecular oxygen was used as an oxidizing agent to generate water as the sole by-product. A wide variety of aldehydes was converted to their methyl esters in high yields. The process involved gentle reaction conditions to avoid any type of pre-activation. Structural features of the catalyst were determined through FT-IR, FE-SEM, TEM, EDX, elemental mapping, XRD and ICP-OES analyses. The material was found to be stable enough toward Pd leaching. Durability of Kaolin@CS-starch-Pd was further justified by retaining its catalytic activity through successful reusability for several times.

Co-N-Si/AC Catalyst for Aerobic Oxidation of Benzyl Alcohols to Esters under Mild Conditions

A stable, earth-abundant, reusable cobalt-based heterogeneous catalyst is developed for the oxidative esterification of alcohols under ambient conditions, featuring broad substrate scope, providing good to excellent product yields. This protocol enables easy recyclability of the catalyst, measured up to five times without significant loss of efficiency. The active sites of Co-N-Si/AC are proposed to be Co-N species.

Zn Promoted Mg-Al Mixed Oxides-Supported Gold Nanoclusters for Direct Oxidative Esterification of Aldehyde to Ester

The synthesis of ester compounds is one of the most important chemical processes. In this work, Zn-Mg-Al mixed oxides with different Zn²⁺/Mg²⁺ molar ratios were prepared via co-precipitation method and supported gold nanoclusters to study the direct oxidative esterification of aldehyde and alcohol in the presence of molecular oxygen. Various characterization techniques such as N₂-physical adsorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and CO₂ temperature programmed desorption (TPD) were utilized to analyze the structural and electronic properties. Based on the results, the presence of small amounts of Zn²⁺ ions (~5 wt.%) provoked a remarkable modification of the binary Mg-Al system, which enhanced the interaction between gold with the support and reduced the particle size of gold. For oxidative esterification reaction, the Au₂₅/Zn_0.05MgAl-400 catalyst showed the best performance, with the highest turnover frequency (TOF) of 1933 h⁻¹. The active center was believed to be located at the interface between metallic gold with the support, where basic sites contribute a lot to transformation of the substrate.

Multichannel gas-uptake/evolution reactor for monitoring liquid-phase chemical reactions

The design of a headspace pressure-monitoring reactor for measuring the uptake/evolution of gas in gas-liquid chemical transformations is described. The reactor features a parallel setup with ten-reactor cells, each featuring a low working volume of 0.2-2 ml, a pressure capacity from 0 to 150 PSIa, and a high sensitivity pressure transducer. The reactor cells are composed of commercially available disposable thick-walled glassware and compact monolithic weld assemblies. The software interface controls the reactor temperature while monitoring pressure in each of the parallel reactor cells. Reactions are easy to set up and yield high-density gas uptake/evolution data. This instrument is especially well suited to acquire quantitative time-course data for reactions with small quantities of gas consumed or produced.

Additive-Mediated Selective Oxidation of Alcohols to Esters via Synergistic Effect Using Single Cation Cobalt Catalyst Stabilized with Inorganic Ligand

The direct catalytic oxidation of alcohols to esters is very appealing, but the economical-friendly catalysis systems are not yet well established. Herein, we show that a pure inorganic ligand-supported single-atomic cobalt compound, (NH₄)₃[CoMo₆O₁₈(OH)₆] (simplified as CoMo₆), could be used as a heterogeneous catalyst and effectively promote this type of reaction in the presence of 30% H₂O₂ using KCl as an additive. The oxidative cross-esterification of various alcohols (aromatic and aliphatic) could be achieved under mild conditions in nearly all cases, affording the corresponding esters in high yields, including several drug molecules and natural products. Detailed studies have revealed that chloride ion is able to bind to the CoMo₆ to form a supramolecular dimer 2(CoMo₆∙Cl), which can effectively catalyze the reaction via a synergistic effect from chloride ion and CoMo₆. Mechanism studies and control reactions demonstrate that the esterification proceeds via the key oxidative immediate of aldehydes.

Renewable chitosan-derived cobalt@N-doped porous carbon for efficient aerobic esterification of alcohols under air

The direct oxidation of alcohols to esters through a green and cost-effective strategy is a fascinating chemical synthesis route. In this study, an environmentally friendly N-doped porous carbon encapsulated Co-based nano-catalyst was prepared via a simple carbonization procedure, utilizing renewable chitosan, accessible dicyandiamide and low-cost Co(OAc)2 as co-precursors. The obtained Co@NC-2-T catalysts were successfully used in selective oxidation of aromatic alcohols with methanol to esters under atmospheric reaction conditions. The Co@NC-2-900 catalyst (added with 2 g dicyandiamide and pyrolyzed at 900 °C) shows optimal activity and applicability and can also be reused at least six times in the oxidative esterification of aromatic alcohols with excellent stability. The presence of superoxide anion radicals in the current catalytic system was detected by the EPR method, and a possible mechanism of alcohol oxidation to ester was proposed on this basis. Thus, this study provides a facile, eco-friendly, and highly efficient catalytic system for oxidative esterification of alcohols.

Pd-Colloids-Catalyzed/Ag2 O-Oxidized General and Selective Esterification of Benzylic Alcohols

Palladium colloids obtained from the degradation of Hermann-Beller palladacycle proved to be an efficient catalytic system in combination with silver oxide as a selective oxidant for the oxidative esterification of differently substituted benzyl alcohols in MeOH as solvent. Excellent reactivity exhibited by the catalytic system also allowed the alcoholic coupling partner to be changed from MeOH to a wide range of alcohols having diverse functionalities. The mildness of the developed protocol also made it possible to employ propargyl alcohol as the coupling partner without any observation of any interference of the terminal alkyne. Selective oxidative coupling of a primary alcoholic functional group over secondary in the case of glycols and glycerols was also made possible using the developed catalyst system. To test the relevancy of Pd/Ag combined catalysis mixed Pd/Ag colloids were synthesized, characterized by TEM, XRD and XPS and applied to oxidative-esterification successfully.