Catalytic Oxidation Reactions Research Articles

2‐Hydroxyadipic Acid Production by Oxidation of 2‐Hydroxycyclohexanone with Molecular Oxygen

AbstractOxidation of 2‐hydroxycyclohexanone (2‐HCO) which can be synthesized from both petroleum and biomass was investigated with heteropolyacids and oxygen as catalysts and oxidant, respectively. 2‐Hydroxyadipic acid (2‐HAA) was obtained in moderate yields, and H4PVW11O40 gave the highest yield (39 %). 2‐HAA is a dicarboxylic acid expected to be a monomer, and this work is the first report for production of 2‐HAA by catalytic oxidation reactions. The oxidation of 1,2‐cyclohexanedione (CHDO), which is a potential intermediate of 2‐HCO oxidation, produced similar yield of 2‐HAA even without catalyst. The effects of catalyst amount (first order), oxygen pressure (almost zero order) and the addition of radical scavenger (no effect) on the 2‐HCO oxidation with H4PVW11O40 catalyst were similar to those in a related case of 2‐methoxycyclohexanone oxidation to adipic acid with heteropolyacid catalyst. 2‐HCO is proposed to be oxidized to CHDO as a precursor of 2‐HAA in a similar mechanism to 2‐methoxycyclohexanone oxidation.

Engineering Active Surface Oxygen Sites of Cubic Perovskite Cobalt Oxides toward Catalytic Oxidation Reactions

Engineering Active Surface Oxygen Sites of Cubic Perovskite Cobalt Oxides toward Catalytic Oxidation Reactions

Tribo-catalysis triggered the in-situ formation of amphiphilic molecules to reduce friction and wear

A coating composed of Au/Ag/Cu was deposited onto steel surfaces to catalyze the tribochemical reaction of polyalphaolefin (PAO), resulting in the formation of amphiphilic molecules. The coated surface showed a reduction in friction coefficient and wear track width by 24.9∼43.0% and 61.4∼68.9%, respectively, compared to the bare steel surface. The in situ formed amphiphilic molecules were chemically bonded on tribopair surface after deprotonation, and then formed a tribofilm. This tribofilm exhibited low interfacial adhesion at nano scale, contributing to low friction and wear. Density functional theory simulations reveals that the dissociation energy of C-H bond on Au surface was much lower than that on iron surface, favoring the catalytic oxidation reaction of PAO into amphiphilic molecules.

C−H Bond Activation in Ru‐Catalyzed Reactions of Arenes with Olefins: Theoretical Insights into Hydroarylation and Oxidative Coupling Mechanisms

AbstractA detailed mechanistic density functional theory (DFT) and coupled cluster study of Csp²−H activation in benzene and methyl acrylate by the catalyst RuClm(CO)n (m=2,3; n=0–4) is presented. We trace the entire reaction pathways from the precursor to the active form of the catalysts followed by catalytic hydroarylation and oxidative coupling reactions. Our results reveal that both computational methods provide very similar qualitative pictures, but only the coupled cluster DLPNO‐CCSD(T1) results are quantitatively consistent with experiment. At the latter level of theory, the Ru(II) and Ru(III) catalyst precursors transform into the same active form of the catalyst, which explains the experimental results. Oxidative addition is extremely endergonic, especially in the presence of CO. Oxidative hydrogen migration (OHM) occurs in complexes with a low Ru coordination number and leads to olefine hydroarylation. Strongly bound carbonyl ligands suppress this interaction. Concerted metalation‐deprotonation (CMD) of the aromatic C−H bond and σ‐bond metathesis mechanisms of catalyst regeneration do not involve Ru−H bonding and form the energetically favorable catalytic cycle of the oxidative coupling reaction. The key interaction in CMD mechanisms consists of proton abstraction by an inner‐sphere Cl‐anion. Carbonyl ligands facilitate CMD by weakening the Ru−Cl bond. An excess of CO slows the interaction by leading to replacement of the reactants in the Ru coordination sphere.

ABOUT THE POSSIBILITY OF USING THERMOCHEMICAL GAS ANALYZERS IN A MULTICOMPONENT MIXTURE

Kinetic parameters finding’s method of heterogeneous catalytic oxidation reactions of combustible gas’s small impurities in air on a thin platinum wire was described. It consists in obtaining from the wire’s current-voltage characteristic the dependence of the critical current values on its mass fraction in air. They corresponding to the catalytic ignition and extintion of the gas impurity. A method of determining the content of two combustible gases in the air, what based on processing the platinum wire’s current-voltage characteristic, was proposed. Depending on the level of the total gases concentration in the air, the determining experimental characteristics are not only the wire (catalyst) overheating relative to the inert wire under the conditions of catalytic ignition, but also the wire overheating during catalytic extinguishing or under conditions of self-sustaining catalytic combustion (without electric current heating).

Dual-Atomic-Site Catalysts for Molecular Oxygen Activation in Heterogeneous Thermo-/Electro-catalysis.

Efficient molecular oxygen activation (MOA) is the key to environmentally friendly catalytic oxidation reactions. In the last decade, single-atomic-site catalysts (SASCs) with nearly 100% atomic utilization and unique electronic structure have been widely investigated for MOA. However, the single active site makes the activation effect unsatisfactory and difficult to deal with complex catalytic reactions. Recently, dual-atomic-site catalysts (DASCs) have provided a new idea for the effective activation of molecular O2 due to more diverse active sites and synergetic interactions among adjacent atoms. In this review, we systematically summarized the recent research progress of DASCs for MOA in heterogeneous thermo- and electrocatalysis. Finally, we look forward to the challenges and application prospects in the construction of DASCs for MOA.

Dual‐Atomic‐Site Catalysts for Molecular Oxygen Activation in Heterogeneous Thermo‐/Electro‐catalysis

AbstractEfficient molecular oxygen activation (MOA) is the key to environmentally friendly catalytic oxidation reactions. In the last decade, single‐atomic‐site catalysts (SASCs) with nearly 100 % atomic utilization and unique electronic structure have been widely investigated for MOA. However, the single active site makes the activation effect unsatisfactory and difficult to deal with complex catalytic reactions. Recently, dual‐atomic‐site catalysts (DASCs) have provided a new idea for the effective activation of molecular oxygen (O2) due to more diverse active sites and synergetic interactions among adjacent atoms. In this review, we systematically summarized the recent research progress of DASCs for MOA in heterogeneous thermo‐ and electrocatalysis. Finally, we look forward to the challenges and application prospects in the construction of DASCs for MOA.

Adsorption-enhanced catalytic oxidation for long-lasting dynamic degradation of organic dyes by porous manganese-based biopolymeric catalyst

Improving the adsorption kinetics of metal-oxide catalysts is critical for the enhancement of catalytic performance in heterogeneous catalytic oxidation reactions. Herein, based on the biopolymer pomelo peels (PP) and metal-oxide catalyst manganese oxide (MnOx), an adsorption-enhanced catalyst (MnOx-PP) was constructed for catalytic organic dyes oxidative-degradation. MnOx-PP shows excellent methylene blue (MB) and total carbon content (TOC) removal efficiency of 99.5 % and 66.31 % respectively, and keeps the long-lasting stable dynamic degradation efficiency during 72 h based on the self-built continuous single-pass MB purification device. The chemical structure similarity and negative-charge polarity sites of the biopolymer PP improve the adsorption kinetics of organic macromolecule MB, and construct the adsorption-enhanced catalytic oxidation microenvironment. Meanwhile, the adsorption-enhanced catalyst MnOx-PP obtains lower ionization potential and O2 adsorption energy to promote the continuous generation of active substance (O2*, OH*) for the further catalytic oxidation of adsorbed MB molecules. This work explored the adsorption-enhanced catalytic oxidation mechanism for the degradation of organic pollutants, and provided a feasible technical idea for designing adsorption-enhanced catalysts for the long-lasting efficient removal of organic dyes.

Tuning the surface reactivity of oxides by peroxide species

The Mars-van Krevelen mechanism is the foundation for oxide-catalyzed oxidation reactions and relies on spatiotemporally separated redox steps. Herein, we demonstrate the tunability of this separation with peroxide species formed by excessively adsorbed oxygen, thereby modifying the catalytic activity and selectivity of the oxide. Using CuO as an example, we show that a surface layer of peroxide species acts as a promotor to significantly enhance CuO reducibility in favor of H2 oxidation but conversely as an inhibitor to suppress CuO reduction against CO oxidation. Together with atomistic modeling, we identify that this opposite effect of the peroxide on the two oxidation reactions stems from its modification on coordinately unsaturated sites of the oxide surface. By differentiating the chemical functionality between lattice oxygen and peroxide, these results are closely relevant to a wide range of catalytic oxidation reactions using excessively adsorbed oxygen to activate lattice oxygen and tune the activity and selectivity of redox sites.

Transition Metal (Fe2O3, Co3O4 and NiO)-Promoted CuO-Based α-MnO2 Nanowire Catalysts for Low-Temperature CO Oxidation

As a toxic pollutant, carbon monoxide (CO) usually causes harmful effects on human health. Therefore, the thermally catalytic oxidation of CO has received extensive attention in recent years. The CuO-based catalysts have been widely investigated due to their availability. In this study, a series of transition metal oxides (Fe2O3, Co3O4 and NiO) promoted CuO-based catalysts supported on the α-MnO2 nanowire catalysts were prepared by the deposition precipitation method for catalytic CO oxidation reactions. The effects of the loaded transition metal type, the loading amount, and the calcination temperature on the catalytic performances were systematically investigated. Further catalyst characterization showed that the CuO/α-MnO2 catalyst modified with 3 wt% Co3O4 and calcined at 400 °C performed the highest CO catalytic activity (T90 = 75 °C) among the investigated catalysts. It was supposed that the loading of the Co3O4 dopant not only increased the content of oxygen vacancies in the catalyst but also increased the specific surface area and pore volume of the CuO/α-MnO2 nanowire catalyst, which would further enhance the catalytic activity. The CuO/α-MnO2 catalyst modified with 3 wt% NiO and calcined at 400 °C exhibited the highest surface adsorbed oxygen content and the best normalized reaction rate, but the specific surface area limited its activity. Therefore, the appropriate loading of the Co3O4 modifier could greatly enhance the activity of CuO/α-MnO2. This research could provide a reference method for constructing efficient low-temperature CO oxidation catalysts.

Operando CO Infrared Spectroscopy and On-Line Mass Spectrometry for Studying the Active Phase of IrO2 in the Catalytic CO Oxidation Reaction

We combine operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) with on-line mass spectrometry (MS) to study the correlation between the oxidation state of titania-supported IrO2 catalysts (IrO2@TiO2) and their catalytic activity in the prototypical CO oxidation reaction. Here, the stretching vibration of adsorbed COad serves as the probe. DRIFTS provides information on both surface and gas phase species. Partially reduced IrO2 is shown to be significantly more active than its fully oxidized counterpart, with onset and full conversion temperatures being about 50 °C lower for reduced IrO2. By operando DRIFTS, this increase in activity is traced to a partially reduced state of the catalysts, as evidenced by a broad IR band of adsorbed CO reaching from 2080 to 1800 cm−1.

Sulfide Removal by Catalitic Oxidation From Rayon Waste

Catalytic oxidation of spent sulfidic caustic consist of SH- ion or NaHS compound by H 2 O2 in neutral or acidic solution to elemental sulphur may provide a convenient and economical method for the control of sulphide wastes and their associated odors at pulp, paper and textile industry. Oxidation of sulfide in rayon waste by hydrogen peroxide was investigated in the presence of ferric sulfate catalyst. Kinetic equations and activation energies of H 2 O2 and SH- ion to total sulphur and sulphate in rayon waste for catalytic oxidation reaction were calculated based on the experimental results. For the removal of sulfide from sulfide solution the most common process involves its catalytic oxidation to a more benign form sulfate. The rate of sulfidic catalytic oxidation was found higher at lower initial sulphide concentration and the rate of sulphide catalytic oxidation was found directly proportional to loading and hydrogen peroxide addition. Optimum total sulphide concentration was achieved when sulphide solutions in the presence of H 2 O 2 in the ratios SH-/H 2 O 2 1:4.2. The potential user of H 2 O 2 determine the optimal conditions for control of odor, corrosion and waste treatment cost due to sulfide consisting of sulphur ion, sulphate ion, etc. The catalytic oxidation of sulphides into sulphates by H 2 O 2 may be applied directly to aqueous wastes containing these odorants

Modulating the Coordination of Single Co Atoms to Trigger the Catalytic Oxidation of Formaldehyde at Room Temperature.

Designing efficient and stable non-precious metal catalysts remains a significant challenge for formaldehyde (HCHO) oxidation, which is an expected way to replace the employment of noble-metal catalysts. Herein, a series of atomically dispersed Co catalysts are optimized by evaporating nitrogen atoms and exploring their HCHO oxidation catalytic performance. The results show that the prepared temperature can effectively control the coordination regulation of the Co atomic site, which in turn affects the catalytic oxidation activity. Our best catalyst, the Co-N/C prepared at 1000 °C, exhibits superior activity with 92.8% of conversion at room temperature at a gas hourly space velocity (GHSV) of 72,000 mL·g-1·h-1. Extensive characterizations combined with theoretical calculations reveal that the high catalytic activity is attributed to the low-coordinated center, which can be tailored by pyrolysis temperature. This work provides an innovative strategy for catalyst design in the catalytic oxidation reaction.

Nitrogen-doped Ti3C2 MXene quantum dots as an effective FRET ratio fluorometric probe for sensitive detection of Cu2+ and D-PA

In this work, a ratiometric fluorescence sensing platform was established to detect Cu2+ and D-PA (d-penicillamine) based on nitrogen-doped Ti3C2 MXene quantum dots (N-MODs) that was prepared via a simple hydrothermal method and exhibited strong fluorescent and photoluminescence performance as well as excellent stability. Since the oxidation reaction between o-phenylenediamine (OPD) and Cu2+ induced the formation of 2,3-diaminophenazine (ox-OPD) which not only can emerge an emission peak at 570 nm, but also inhibit the fluorescence intensity of N-MQDs at 450 nm, a ratiometric reverse fluorescence sensor via fluorescence resonance energy transfer (FRET) was designed to sensitively detect Cu2+, where N-MQDs acted as energy donor and ox-OPD as energy acceptor. More importantly, another considerably interesting phenomenon was that their catalytic oxidation reaction can be restrained in the presence of D-PA because of the coordination of Cu2+ with D-PA, further triggering the obvious changes in ratio fluorescent signal and color, thus a ratiometric fluorescent sensor of determining D-PA was proposed also in this work. After optimizing various conditions, the ratiometric sensing platform showed rather low detection limits for Cu2+ (3.0 nM) and D-PA (0.115 μM), coupled with excellent sensitivity and stability.

Effect of Temperature and SO2 on Mercury Removal Performance on a Ce-Cu/Al Catalyst in Low-Temperature Flue Gas

The effects of flue gas temperature and SO2 content on the catalytic oxidation of 2Ce-4Cu/Al catalysts for cooperative control of Hg0 and NO were investigated. The results show that the optimum activation temperature is 200°C. And when the concentration of SO2 in the gas reaches 600ppm, the comprehensive conversion efficiency of Hg0 and NO is optimal, the conversion efficiency remains above 70%. The results of the catalyst analysis before and after the reaction show that both lattice oxygen and chemisorption oxygen are involved in the reaction. Cu and Ce have a cooperative reaction on the catalyst surface. The interconversion between Ce and Cu ions of different values contributes to the formation of surface lattice oxygen, which promotes the Hg0 catalytic oxidation reaction and NH3-SCR reaction.

Fluidized Immobilized Carbon Catalytic Oxidation Reactor for Treating Domestic Wastewater.

Treating wastewater and reusing it have become normal in the present era since the scarcity of fresh water prevails in many parts of the world. There are numerous techniques for treating domestic wastewater, and many have been explored to advance the ones already in use. This study is taken up to explore the new technology called fluidized immobilized carbon catalytic oxidation (FICCO). Usually, both organic and inorganic materials are present in residential wastewater. In this study, catalyst-activated carbon produced from rice husk is added to a FICCO reactor to test the effectiveness of decreasing organic contaminants in wastewater. Six FICCO models were fabricated in this research study, and tests were conducted. The effectiveness of COD and BOD removal was investigated using six FICCO models with activated carbon made from rice husk as a catalyst and presented in this paper. The FICCO reactor was also used to treat organic contaminants such as surfactants, starch, oil, and protein with rice husk as activated carbon as a catalyst. Organic pollutants used the FICCO reactor; COD removal varied from 75.6% to 92.4%, BOD removal ranged from 74.9% to 89.5% at the optimum contact time, and catalyst rice husk-activated carbon application. The optimum catalyst dosage was 12 g per 620 ml of wastewater, which is the capacity of each reactor and a substantial reduction in sludge.

Nepenthes-inspired hierarchical ZnIn2S4/Ru nanotubes with chemical bond-mediated interface enable efficient photocatalytic benzyl alcohol oxidation

In nature, Nepenthes has a unique tubular structure for harvesting and preserving goals. Herein, inspired by Nepenthes, we report the selective photocatalytic oxidation of benzyl alcohol by using the hierarchical ZnIn2S4/Ru nanotubes. The tubular chamber with abundant active sites not only facilitates enriching the target molecules but also shortening the bulk-to-surface distance, and the Zn-S-Ru interfacial bonds creates direct charge transfer channels for the activating O2 to generate •O2– species boosting the benzyl alcohol selective conversion to benzaldehyde. The photocatalytic benzyl alcohol oxidation reaction has a high conversion rate of 68.2 % as well as a benzaldehyde selectivity of 99 % under visible light irradiation. The effects of Zn-S-Ru interfacial bonds on modulating the carrier transfer dynamics for the selective catalytic oxidation reaction are investigated by electrochemical characterization and density functional theory simulation. This work offers an inspiration on regulating the interfacial charge transfer channel for the photo-driven selective oxidation reaction.

Transition metal and Pr co-doping induced oxygen vacancy in Pd/CeO2 catalyst boosts low-temperature CO oxidation

Cerium oxide-based materials have wide application prospects in catalytic oxidation reactions. Doping valence metals in CeO2 is an effective strategy to increase the content of oxygen vacancy of CeO2 and regulate the surface and interface structure of CeO2 supported metal catalysts. In this work, transition metal (M = Fe, Co and Mn) and Pr co-doped CeO2 nanorod were prepared by hydrothermal method and used to support Pd, which significantly improved the activity of CO catalytic oxidation. Under dry and wet condition, the T99 (temperature to achieve 99% conversion of CO) decreased from 190 °C and 165 °C for single-doped Pd/Pr-CeO2 catalyst (Pd content of 0.2 wt%) to 125 °C and 107 °C for co-doped Pd/FePr-CeO2 catalyst under reaction condition with GHSV (gas hourly space velocity) of 70, 000 mL gcat.-1h−1, respectively. Moreover, the Pd/FePr-CeO2 catalyst showed an excellent stability and kept its activity more than 2400 min. The systematic characterizations revealed that the outstanding CO catalytic performance is attributed to the co-doping of Pr and Fe, which increases the oxygen vacancy content on the catalyst surface, promotes the activation of lattice oxygen in the support, and strengthens the interaction and electron transport ability between Pd and the support. This work opens promising perspectives to enhance the activity of supported metal catalysts in oxidation reactions by co-doping of valence metals in oxide supports.

Oxygen vacancy engineering for tuning the catalytic activity of LaCoO3 perovskite

Herein, we attempted to engineer oxygen vacancies on the surface of LaCoO3 perovskite through simple post-treatments (acid or reductive thermal treatments). Acid treatment induces oxygen vacancies through the selective etching of the La cations, whereas thermal treatment in a reducing atmosphere generates oxygen vacancies by directly removing lattice oxygen. The characterization results confirm that the number of surface oxygen vacancies, which are crucial in various catalytic oxidation reactions, considerably increases in the LaCoO3 catalysts treated with acid or reducing gas. Acid treatment enriches the oxygen vacancies while maintaining the structure of the LaCoO3 catalysts, which can not be achieved through reductive thermal treatment. Therefore, the acid treatment is considered a promising technique for oxygen vacancy engineering of perovskite catalysts for tuning their catalytic activities. Furthermore, the catalytic activities of the posttreated LaCoO3 catalysts for CO oxidation were evaluated and are noted to be considerably better than those of the pristine LaCoO3 catalyst due to their abundant oxygen vacancies. Consequently, we conclude that the oxygen vacancies of perovskite catalysts can be effectively engineered via two simple methods and play a significant role in CO oxidation.

Study on the Mechanism and Control Strategy of Advanced Treatment of Yeast Wastewater by Ozone Catalytic Oxidation

In this paper, the yeast wastewater secondary treatment effluent using catalytic odor oxidation treatment, using an orthogonal reaction experiment to determine the best reaction conditions, and the online monitoring of the pH, oxidation-reduction potential (ORP), and liquid ozone concentration monitoring, to the catalytic odor oxidation reaction, chemical oxygen demand (COD), and color removal effect were analyzed. The results showed that the optimal reaction condition for the advanced treatment of yeast wastewater by catalytic ozonation was accomplished with manganese dioxide used as the catalyst and a catalyst dose of 6 g·L−1, pH of 12, and catalytic ozonation reaction time of 20 min. The COD was effectively reduced from 880 mg·L−1 to 387 mg·L−1 under this condition, the chroma was reduced from 700 times to 40 times, and these two parameters of the effluent could meet the standard of GB25462-2010. The real-time monitoring system showed that the whole reaction can be divided into two processes. The first 14 min was the indirect reaction of ozone and then the direct oxidation reaction of ozone. This process was further verified by the change trend of COD and the amount of ozone depletion by COD removal. The average ozone consumption levels of the two stages were 1.97 and 4.91 mgO3·mgCOD−1. This system can effectively monitor the reaction of the catalytic odor oxidation in the complex system to guide the effective use of ozone in practical engineering applications.