Catalysts For Oxidation Research Articles

Research progress of molecular sieve supported catalysts in catalytic oxidation of chlorine-containing volatile organic compounds

Chlorinated Volatile Organic Compounds (CVOCs) come from a wide range of sources and are common precursors of PM2.5 and ozone pollution, which pose a serious threat to the environment and have adverse effects on human health. Catalytic degradation is one of the effective methods to solve CVOCs pollution, which has the advantages of low operating temperature, less chlorine-containing by-products and high degradation efficiency. The core of this technology is to design and develop catalyst materials with excellent stability and catalytic performance. At present, molecular sieve catalysts have attracted extensive attention because of their acidity and unique pore structure. In this paper, the current research status of catalysts supported by molecular sieve, such as noble metals, transition metal oxides and perovskites, and their activity, acidity, stability and selectivity in CVOCs catalytic reactions were summarized and analyzed, and the future development direction of CVOCs molecular sieve supported catalysts was prospected.

Controlled synthesis of Co3O4@CoP heterostructured nanoarrays as efficient electrocatalysts in alkaline seawater and urea

How to prepare clean energy has always been a problem to be solved by the modern green chemical industry. Compared with the electrolysis of water to produce hydrogen, electrolysis of seawater for raw material requirements are lower and more widely used. However, the lacks of maturity of the technology, the high cost and the generation of harmful gases such as chlorine in the electrocatalytic process have hindered the development of this process. This study demonstrates a construction of heterogeneous structure based on Co ions as an efficient multifunctional catalyst for overall seawater splitting and urea oxidation. This hybrid structure can combine nanosheets and nanowires, thus exposing the catalyst to more active sites and shortening the ion diffusion path. Comparing the hybrid structure with the single structure, Co3O4@CoP exhibits excellent multifunctional catalytic activity in alkaline seawater and urea. In the oxygen evolution reaction, the working potential is only 1.60 V and 1.70 V at a current density of 50 mA/cm2 and 100 mA/cm2. And in the hydrogen evolution reaction, the working potential was only −0.16 V at a current density of −10 mA/cm2, demonstrating excellent bifunctional activity. On this basis, the catalyst also demonstrated excellent activity for urea oxidation reaction in alkaline environment, with an operating potential of only 1.28 V at a current density of 10 mA/cm2. And the durability of this catalyst is good, it can keep 5 mA/cm2 for 12 h under the constant voltage of 1.45 V, but the initial potential falls off too fast, and there is a decline in performance, which is closely related to the corrosion of Cl- present in seawater. It was shown by density functional theory (DFT) that hierarchical nanostructures can increase the transfer rate of reaction intermediates and the water adsorption energy. At the end of this study, by comparing single nanostructures with hybrid nanostructures, it can be reasonably conjectured that the accompanying increase in the number the heterostructure is resistant to Cl- corrosion in seawater.

Nitridated Nickel Mesh as Industrial Water and Alcohol Oxidation Catalyst: Reconstruction and Iron‐Incorporation Matters

AbstractNickel mesh (NM) is used in industrial alkaline water electrolyzers due to its cost‐effectiveness and conductivity. However, the decisive factors that advance the efficiency and sustainability of such electrodes are only partially understood. Herein, an efficient NM‐based electrocatalyst for the oxygen evolution reaction is developed via a single‐step nitridation route on a commercially used NM substrate and sheds light on the role of reconstruction and iron content to boost catalyst performance and durability. Remarkably, the activated Ni3N/NM catalyst required an overpotential of 0.46 V to deliver 1 A cm−2 in ambient conditions (1 M KOH, 25 °C). This overpotential decreases substantially to 0.28 V in industrially relevant conditions (6 M KOH, 85 °C) and is maintained for 235 h. Ni3N/NM partially transformed into NiFe layered (oxy)hydroxide in both conditions, while the active structure's Fe content is reconstruction condition dependent (temperature and KOH concentration). Electrodes reconstructed under industrially relevant conditions performed better than ambient reconstructed ones due to a more pronounced iron‐incorporation from KOH and the evolution of porous morphologies. In industrial environments, activated Ni3N/NM excels in selectively converting benzyl alcohol to benzoic acid, achieving an impressive yield of 96%.

Ca-Cu/Al2O3 catalysts for H2S removal at near ambient temperature: Synthesis, characterization, DFT calculation, and mechanistic insights

A series of Ca-doped CuxO/Al2O3 catalysts were developed using the excessive impregnation method for H2S catalytic oxidation at near-ambient temperatures. Ca(NO3)-CuxO/Al2O3 catalyst with 2.5 wt% Ca exhibited optimal H2S desulfurization performance at 60 °C and RH 60%, achieving an H2S removal capacity of 401.34 mg/g. Experimental, characterization, and DFT calculation results demonstrate that during the catalytic oxidation of H2S, H2O can be catalytically convert into ·OH while simultaneously capturing and dissociating H2S. The ·OH and NO3- then catalyze the oxidation of HS-/S2- to elemental S. Moreover, the redundant OH adsorbed on the basic sites can buffer the pH and promote the dissociation of H2S. The above cyclic process could alleviate the deactivation of the Ca-Cu/Al2O3 catalyst. Therefore, a ·OH-induced desulfurization mechanism assisted with Ca2+ buffer the pH and NO3- cyclic oxidation of H2S has been proposed. This work contributes to the preparation of high-capacity mental-based catalysts for H2S oxidation.

Quantitative Chemical Mapping of Pt/Rh Gauze Catalysts for Ammonia Oxidation using Resonant X-ray Tomography

Quantitative Chemical Mapping of Pt/Rh Gauze Catalysts for Ammonia Oxidation using Resonant X-ray Tomography

Cobalt and nitrogen co-modified hollow periodic mesoporous organosilica spheres for selective oxidation of aryl alkanes

Hollow periodic mesoporous organosilica spheres (HPMOs) have stimulated great research interest owing to its unique organic–inorganic hybrid skeleton. In this work, HPMOs were synthesized by hydrothermal method, and then cobalt and nitrogen co-doped carbon catalyst was prepared by using HPMOs as supports. The optimal catalyst (Co-Nx/HPMOs-D) performed excellent activity in the selective oxidation reaction of aryl alkanes, with the conversion of ethylbenzene up to 97.0% and the selectivity of acetophenone was 98.9%, which was attributed to the Co-Nx active species and the unique HPMOs supports. The unique amphiphilic property of Co-Nx/HPMOs-D could better facilitate the adsorption and diffusion of organic substrates in the aqueous phase. The addition of dicyandiamide not only enhanced the nitrogen content in the catalyst, but also promoted the conversion of pyrrolic-N to pyridinic-N during the pyrolysis process, thus strengthened the interaction between the substrate and cobalt and improved the stability of the catalyst. This work presented a green and environmentally friendly method for the preparation of HPMOs and a facile strategy to obtain high performance catalysts for selective oxidation of aryl alkanes.

Integrating CO2 reduction, H2O oxidation and H2 evolution catalysts into a dual S-scheme artificial photosynthetic system for tunable syngas production

It remains a challenge to achieve overall photocatalytic conversion of CO2 with H2O into tunable syngas and O2. Herein, by inserting BiVO4 into the heterointerface of hollow core-shell CdS@T-COF S-scheme photocatalyst, an innovative CdS/BiVO4@T-COF dual S-scheme heterojunction is developed, which gives an almost stoichiometric evolution of syngas (453.6 μmol gcat−1 h−1) and O2 (230.5 μmol gcat−1 h−1). Moreover, the CO output and selectivity only decline by around 20% when pure CO2 is replaced by diluted CO2 (15%) atmosphere. The BiVO4 embedding not only augments the internal electric field and band bending, upgrading the separation efficiency of active carriers, but also alters the roles of the components involved, separating the occurrence of CO, O2 and H2 evolution on T-COF, BiVO4 and CdS in lower energy barriers. Besides, varying the T-COF thickness can modulate the availability of CO2, H2O and photon to different sites, thereby adjusting the CO/H2 ratio in a wide window. This work opens an avenue for customizing three-in-one artificial photosynthetic systems for coupling three half reactions.

Regulating the valence and size of the active center of Co/Al2O3 catalyst improved the performance and selectivity of NH3-SCO

To improve the activity of Co/Al2O3 catalysts in selective catalytic oxidation of ammonia (NH3-SCO), valence state and size of active centers of Al2O3-supported Co catalysts were adjusted by conducting H2 reduction pretreatment. The NH3-SCO activity of the adjusted 2Co/Al2O3 catalyst was substantially improved, outperforming other catalysts with higher Co-loading. Fresh Co/Al2O3 catalysts exhibited multitemperature reduction processes, enabling the control of the valence state of the Co-active centers by adjusting the reduction temperature. Changes in the state of the Co-active centers also led to differences in redox capacity of the catalysts, resulting in different reaction mechanisms for NH3-SCO. However, in situ diffuse reflectance infrared Fourier transform spectra revealed that an excessive O2 activation capacity caused overoxidation of NH3 to NO and NO2. The NH3-SCO activity of the 2Co/Al2O3 catalyst with low redox capacity was successfully increased while controlling and optimizing the N2 selectivity by modulating the active centers via H2 pretreatment, which is a universal method used for enhancing the redox properties of catalysts. Thus, this method has great potential for application in the design of inexpensive and highly active catalysts.

Insights into the Performance of Bimetallic Ru-Co/TiO2 Catalysts Carrying out a Low Temperature C3H8 Oxidation Reaction

AbstractThe performance of a set of bimetallic Ru-Co catalysts dispersed on the TiO2 anatase phase, synthesized by the co-deposition–precipitation with urea method, was tested in the CO2 production by the entire oxidation of C3H8. The presence of properly dispersed ruthenium nanoparticles on a Co/TiO2-anatase support was notably favorable for enhancing the C3H8 activity/selectivity. Likewise, an increase in the combined acidity (Brönsted and Lewis) was also observed, and the interaction between Ru0-CoOx species stabilized on TiO2 prompted the C3H8 oxidation at low temperature. The performance of bimetallic Ru-Co/TiO2 catalysts was enhanced by increasing Ru0 species and loading, showing more efficient C3H8 oxidation by the combination of Ru0-CoOx, as revealed by DRIFTS, XPS, H2-TPR, and HAADF-STEM characterization outcomes. The higher acidity of the catalysts containing Ru (1.5 wt%) and Co (3 wt%) as well as the reducibility enhancement of the Ru and Co species led to the best capacity of these catalysts for C3H8 oxidation to CO2 under the experimental conditions employed in this study. Graphical Abstract

Unveiling the crucial active sites responsible for CO, n-heptane, and toluene oxidation over Pt/ZrO2 catalyst

The surface Pt species and adsorbed oxygen on the Pt/ZrO2 catalyst were successfully modulated by altering the preparation methods, resulting in distinct catalytic behaviors for CO, n-heptane, and toluene oxidation. The Pt/ZrO2 catalyst was initially prepared via wetness impregnation and subsequently reduced in an H2 atmosphere to obtain the Pt/ZrO2-R catalyst. In contrast, the Pt/ZrO2-E catalyst was synthesized using ethanol solvent (also serving as a reducing agent) instead of water during wetness impregnation. Moreover, the pre-prepared Pt nanoparticles were loaded onto the ZrO2 surface using polyvinylpyrrolidine (as a protective and structure directing agent) dissolved in ethanol solvent to fabricate the Pt/ZrO2-EP catalyst. Among these catalysts, the Pt/ZrO2-R exhibits superior catalytic activity towards CO oxidation due to its abundant metallic Pt species. It is found that activity of Pt/ZrO2 catalyst for n-heptane oxidation is positively correlated with its surface adsorbed oxygen concentration, thus the highest activity is achieved over the Pt/ZrO2-EP catalyst possessing a higher concentration of surface adsorbed oxygen species. Unlike CO and n-heptane oxidation, toluene oxidation activity is affected by multiple factors, it is primarily promoted by synergistic catalysis between metallic Pt species (Pt0) and surface adsorbed oxygen species over the Pt/ZrO2-EP catalyst. Our preliminary findings underscore that precise modulation of sensitive active sites on surfaces plays a critical role in specific catalytic reactions.

Fully Exposed Pd Ensembles on Ultrathin Co3O4 Nanosheets: A Reductive–Oxidative Dual-Active Catalyst for the Detoxification of Chlorophenol

Fully Exposed Pd Ensembles on Ultrathin Co₃O₄ Nanosheets: A Reductive–Oxidative Dual-Active Catalyst for the Detoxification of Chlorophenol

CoFe-Layered Double Hydroxide Needles on MoS2/Ni3S2 Nanoarrays for Applications as Catalysts for Hydrogen Evolution and Oxidation of Organic Chemicals

CoFe-Layered Double Hydroxide Needles on MoS₂/Ni₃S₂ Nanoarrays for Applications as Catalysts for Hydrogen Evolution and Oxidation of Organic Chemicals

Photoelectrochemical Cells with a Pyridine-Anchored Bilayer Photoanode for Water Splitting.

A dye-sensitized photoanode is prepared by coassembling a Ru complex photosensitizer and a Ru water oxidation catalyst (WOC) on a TiO2 substrate, in which the WOC molecules are immobilized in a layer-by-layer fashion through metal-pyridine coordination with the aid of a bifunctional anchoring and bridging molecule containing multiple pyridine groups. Under visible-light irradiation, an anodic photocurrent of around 200 μA/cm2 has been achieved with O2 and H2 being generated at the photoanode and Pt counter electrode, respectively. The pyridine anchoring strategy provides a simple method to prepare photoelectrodes for applications in photoelectrochemical cells.

Nano-crystalline NiO-MgO/NiAl2O4 catalyst for coking free low temperature partial oxidation of methane

Here, we report an ultra-small-sized nano-crystalline NiO-MgO/NiAl2O4 catalyst for coking-free partial oxidation of methane reaction at low temperature (450 °C). The catalyst was tested in a packed-bed reactor over a temperature range of 350 to 850 °C. The NiO-MgO/NiAl2O4 catalyst was optimized for calcination temperature and nickel content. The best-optimized sample was then tested for different gas hourly space velocities (GHSVs), resulting in 99 % CH4 conversion and varying H2/CO selectivities from 90 % to 70 % at 450 °C. A stability test was conducted at 500 °C for 100 h for stream on reaction conditions, resulting in 95 % CH4 conversion, 90 % H2 selectivity, and 60 % CO selectivity without any significant deactivation. The excellent catalytic activity and stable performance were attributed to the ultra-small size and nanocrystalline structure of NiO-MgO, as well as the presence of lattice oxygen reservoirs. Additionally, the synergistic interaction between the NiO-MgO solid solution and the support NiAl2O4 contributed to these properties.

Highly productive V/Zn-SiO2 catalysts for the selective oxidation of methane

The production of formaldehyde on industrial scale requires huge amounts of energy due to the involvement of reforming processes in combination with the demand in the megaton scale. Hence, a direct route for the transformation of (bio)methane to formaldehyde would decrease costs and puts less pressure on the environment. Herein, we report on the use of zinc modified silicas as possible support materials for vanadium catalysts and the resulting consequences for the performance in the selective oxidation of methane to formaldehyde. After optimization of the Zn content and reaction conditions, a remarkably high space-time yield of 12.4 kgCH2O·kgcat−1·h−1 was achieved. As a result of the extensive characterization by means of UV–vis, Raman, XANES and NMR spectroscopy it was found that vanadium is in the vicinity of highly dispersed zinc atoms which promote the formation of active vanadium species as supposed by theoretical calculations. This work presents a further step of catalyst development towards direct industrial methane conversion which may help to overcome current limitations in the future.

Modulating the steric effect over high-index facet of MnOx catalysts to enhance toluene oxidation

Engineering surface structures of metal-oxide catalysts are of utmost significance for boosting their catalytic performances. In this work, we reported the high-index (310) facets catalysts (MnOx-AAUS) with oxygen vacancies for VOCs degradation, which was synthesized via an ultrasonic-assisted redox precipitation process. Interestingly, the excellent catalytic performance of MnOx-AAUS catalysts was due to the steric effect between high-index facet with reactants and the simultaneous adsorption-activation of toluene and gaseous oxygen on the high-index (310) facets with oxygen vacancies. The T90% value of the (310) facets catalysts (600 ppm toluene, GHSV = 60,000 mL/g·h, 21 % O2/N2) was significantly lower than that of the previous (001) facets catalysts. Density functional theory (DFT) calculations, along with in-situ FT-IR spectra, revealed that the tilted adsorption configuration of toluene was conducive to simultaneous reaction with the surrounding activated oxygen species. Such the adsorption configuration of toluene/oxygen contributed to the substantially enhanced catalytic activity of the MnOx-AAUS catalyst for VOCs oxidation. This work provides new insights into the roles of high-index facets with oxygen vacancies of MnOx catalysts in the toluene oxidation and paves new avenues for the rational design of highly efficient catalysts for oxidation reactions.

Constructing a Titanium Silicon Molecular Sieve-Based Z-Scheme Heterojunction with Enhanced Photocatalytic Activity.

Titanium silicon molecular sieve (TS-1) is an oxidation catalyst that possesses a long lifetime of charge transfer excited state, high Ti utilization efficiency, large specific surface area, and good adsorption property; therefore, TS-1 acts as a Ti-based photocatalyst candidate. In this work, TS-1 coupled Bi2MoO6 (TS-1/BMO) photocatalysts were fabricated via a facile hydrothermal route. Interestingly, the optimized TS-1/BMO-1.0 catalyst exhibited a decent photodegradation property toward tetracycline hydrochloride (85.49% in 120 min) under the irradiation of full spectrum light, which were 4.38 and 1.76 times compared to TS-1 and BMO, respectively. The enhanced photodegradation property of the TS-1/BMO-1.0 catalyst could be attributed to the reinforced light-harvesting capacity of the photocatalyst, high charge mobility, and suitable band structure for tetracycline hydrochloride degradation. In addition, the mechanism of photocatalytic degradation of tetracycline hydrochloride by the TS-1/BMO-1.0 catalyst was reasonably proposed based on the band structure, trapping, and ESR tests. This research provided feasible ideas for the design and construction of high-efficiency photocatalysts for contaminant degradation.

Adsorption effects of electron scavengers and inorganic ions on catalysts for catalytic oxidation of sulfamethoxazole in radiation treatment

This study aimed to investigate adsorption effects of electron scavengers (H2O2 and S2O82−) on oxidation performance for mineralization of sulfamethoxazole (SMX) in radiation treatment using catalysts (Al2O3, TiO2). Hydrogen peroxide (H2O2, 1 mM) as an electron scavenger showed weak adsorption onto catalysts (0.012 mmol g−1-Al2O3 and 0.004 mmol g−1-TiO2, respectively), leading to an increase in TOC removal efficiency of SMX within the absorbed dose of 30 kGy by 12.3% with Al2O3 and by 8.0% with TiO2. The weak adsorption of H2O2 onto the catalyst allowed it to act as an electron scavenger, promoting indirect decomposition reactions. However, high adsorption of S2O82− (1 mM) onto Al2O3 (0.266 mmol g−1-Al2O3) showed a decrease in TOC removal efficiency of SMX from 76.2% to 30.2% within the absorbed dose of 30 kGy. The high adsorption of S2O82− onto the catalyst inhibited direct decomposition reaction by reducing adsorption of SMX on catalysts. TOC removal efficiency for Al2O3 without electron scavengers in an acidic condition was higher than that in a neutral or alkaline condition. However, TOC removal efficiency for Al2O3 with S2O82− was higher in a neutral condition than in other pH conditions. This indicates that the pH of a solution plays a critical role in the catalytic oxidation performance by determining surface charges of catalysts and yield of reactive radicals produced from water radiolysis. In the radiocatalytic system, H2O2 enhances the oxidation performance of catalysts (Al2O3 and TiO2) over a wide pH range (3–11). Meanwhile, S2O82− is not suitable with Al2O3 in acidic conditions because of its strong adsorption onto Al2O3 in this study.

Dihalosalicylaldehyde based molybdenum(VI) complexes: Synthesis, spectral characterization, crystal structures, and catalytic activities for the selective oxidation of benzylic alcohols

Three ONO donor Schiff base ligands were obtained by the condensation of 3,5-dihalosalicylaldehydes with nicotinoylhydrazide (H2Cl2SN: (E)-N'-(3,5-dichlorosalicylaldehyde) nicotinoylhydrazone, H2Br2SN: (E)-N'-(3,5-dibromosalicylaldehyde) nicotinoylhydrazone, and H2I2SN: (E)-N'-(3,5-diiodosalicylaldehyde) nicotinoylhydrazone on refluxing in ethanol. The treatment of [MoO2(acac)2] (acac = acetylacetonato) with these ligands in methanol afforded cis-dioxidomolybdenum(VI) complexes [MoO2(Cl2SN)(CH3OH)] (1), [MoO2(Br2SN)(CH3OH)] (2), and [MoO2(I2SN)(CH3OH)] (3). Various techniques like NMR (1H and 13C), FT-IR, Mass, TGA, elemental (CHN), and single-crystal X-ray diffraction analysis (for H2Cl2SN·H2O, 2a, [MoO2(Br2SN)(C2H5OH)], and 3a, [MoO2(I2SN)(H2O)].DMF) were utilized to characterize the synthesized compounds. The data collected from diffraction studies revealed that the geometry around Mo(VI) ions was distorted octahedral. Additionally, all complexes were successfully screened as catalysts for the selective oxidation of benzylic alcohols employing ethanol and hydrogen peroxide.

Unraveling the Oxygen Vacancy Site Mechanism of a Self-Assembly Hybrid Catalyst for Efficient Alkaline Water Oxidation

Unraveling the Oxygen Vacancy Site Mechanism of a Self-Assembly Hybrid Catalyst for Efficient Alkaline Water Oxidation