Efficient Oxidation Catalysts Research Articles

Pt/N co-doped porous carbon derived from bio-tar: A remarkable catalyst for efficient oxidation of 5-hydroxymethylfurfural under alkali-free condition: Performance, mechanism and kinetics

Green production process of high value-added bio-platform compounds is appealing yet challenging due to low catalyst performance and demand for acid or alkali conditions. Herein, we fabricated a tailored bio-tar derived super porous carbon material supported nano Pt catalyst via tuning the alkalinity by nitrogen doping. This novel catalyst realized an enhanced catalytic performance in selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) in alkaline free conditions, in which 97.8 % HMF conversion and 54.7 % FDCA selectivity were achieved under mild temperature (90 °C). The kinetic study revealed that the process is multi-step parallel reactions of 2,5-diformylfuran (DFF) and 5-formylfuran-2-carboxylic acid (FFCA) as intermediates from HMF, and the oxidation of carbonyl group in FFCA is the rate-determining step. This work provides a new synthesis method of low-cost catalyst by using organic waste and inspires a sustainable process for bio-platform compounds production with significant environmental benefits.

Nitrogen-rich cobalt (II) MOFs as efficient bifunctional catalysts for single or tandem oxidation and CO2 conversion reactions

The development of efficient catalysts that include the advantages of homogeneous and heterogeneous catalysts is a challenge that can be achieved with metal-organic frameworks (MOFs) since they can incorporate different functionalities in their structure that make them promising catalysts for different processes. Herein, two new isoreticular nitrogen-rich naphthalene cobalt-MOFs, Co-NDTz and Co-NDPhTz, were successfully prepared under solvothermal conditions from the corresponding linkers (H2NDTz=2,6-naphthaleneditetrazole and H2NDPhTz=2,6-bis(4-(1H-tetrazol-5-yl)phenyl)naphthalene). These Co-tetrazole-based MOFs combine Lewis acid and redox functionalities and good CO2 adsorption and after being thermally activated resulted to be excellent efficient catalysts for the epoxidation of alkenes and CO2 cycloaddition to epoxides yielding cyclic carbonates, reaching turnover numbers up to 2500. Furthermore, these two reactions take place following a highly desired one-pot tandem process and a cyclic carbonate was obtained from styrene and CO2 under solvent-free conditions. In addition, the heterogeneous catalysts are easily recycled without noticeable loss of catalytic activity and without important structural deterioration.

Co@CoO: An efficient catalyst for the depolymerization and upgrading of lignocellulose to alkylcyclohexanols with cellulose intact

The depolymerization and upgrading of lignin from raw biomass, while keeping cellulose intact is important in biorefinery and various metal-based catalysts have been used in reductive catalytic fractionation, a key method in “lignin-first” strategy. Recently, we found that a core–shell structured Co@CoO catalyst with CoO shell as the real active site had excellent performance in the hydrogenolysis of 5-hydromethylfurfural to 2,5-dimethylfuran due to its unique ability to dissociate H2 and yield active Hδ− species (Xiang et al., 2022). In this work, we report a one-pot depolymerization and upgrading of lignocellulose to alkylcyclohexanols, a flavour precursor, with intact cellulose over this unique core–shell structured catalyst, Co@CoO. Lignin model compounds (β-O-4, 4-O-5, α-O-4) were first used to clarify the activity of Co@CoO catalyst. Then, the one-pot conversion of various organosolv lignin (birch, pine and poplar) to alkylcyclohexanols was realized with the mass yield of alkylcyclohexanols up to 25.8 wt% from birch lignin under the reaction condition of 210 °C, 1 MPa H2, 16 h. Finally, the corresponding woody sawdusts were used as feedstocks and found that the Co@CoO catalyst indeed preferentially depolymerized and upgraded the lignin part and obtained the same alkylcyclohexanols products with the retention of cellulose-rich pulp. The collected alkylcyclohexanols were further esterified to obtain value-added esters, which can be used as flavors. This work will inspire the design of new efficient metal oxide catalysts in lignin fractionation and depolymerization to high-value-added chemicals with intact cellulose.

Facile synthesis of polyoxometalate supported on magnetic graphene oxide as a hybrid catalyst for efficient oxidation of aldehydes

In the present study, Anderson-type polyoxometalate [N(C4H9)4] [FeMo6O18(OH)6] (FeMo6) was immobilized on amino-modified magnetic graphene oxide and employed as a new hybrid catalyst in oxidation of aldehydes to carboxylic acids. The synthesized hybrid catalyst Fe3O4/GO/[FeMo6] was characterized using thermogravimetric analysis (TGA), scanning electron microscopies (SEM), Fourier transform infrared (FT-IR), vibrating sample magnetometry (VSM), energy-dispersive X‐ray analysis (EDX), Raman spectroscopy and inductively coupled plasma atomic emission spectroscopy (ICP-OES). The results indicated that our catalyst was quite active in oxidizing the aldehydes to their corresponding carboxylic acids in the presence of hydrogen peroxide. The synthesized catalyst can be easily separated from the reaction medium and reused for six consecutive runs without a significant reduction in reaction efficiency.

Benzotiyofen@Pd as an efficient and stable catalyst for the electrocatalytic oxidation of hydrazine

• New organic molecule was synthesized and investigated its anode catalyst performance. • CV, CA, and EIS methods are used to determination of the hydrazine oxidation activities. • The specific activity of organic catalyst is found as 25.811 mA/cm 2 . • Pd metal is electrochemically deposited on the organic catalyst, the catalytic activity increased the 80.930 mA/cm 2 . • This activity is higher than the current expensive metal anode catalyst. An efficient methods for the synthesis of 2-(2,5-dimethylphenyl)-3-iodobenzo[ b ]thiophene ( 4 ) is described, and investigated its anode catalyst performance by using electrochemical methods (CV, CA and EIS). When 2-(2,5-dimethylphenyl)-3-iodobenzo[ b ]thiophene ( 4 ) is applied, the specific activity is found as 25.811 mA/cm 2 . Interestingly, when Palladium (Pd) is electrochemically deposited on the benzothiophene derivative, the catalytic activity increased the 80.930 mA/cm 2 . This result is highest than the current metal based anode catalyst. Moreover, EIS and CA measurements display that Pd doped benzothiophene organic catalyst have high stability, and give the low charge transfer resistance. Energy dispersive X-ray (SEM-EDX), electron microscopy, TEM are used for the determination of its surface morphology. As a result, 2-(2,5-dimethylphenyl)-3-iodobenzo[ b ]thiophene ( 4 ) may be alternative electro-catalysts in fuel cell applications.

Fabricating PdCe/OMS-2 catalysts with boosted low-temperature activity for toluene deep degradation

Porous cryptomelane-type octahedral molecular sieve (OMS-2) with mixed Mn valence and abundant lattice oxygen species has attracted much attention in volatile organic compounds (VOC) catalytic elimination. However, complete conversion of arene over OMS-2 catalysts at relatively low temperature is still a challenge due to its limited crystal structure and inferior stability. Here, a series of PdCe/OMS-2 catalysts with different Pd/Ce molar ratios was fabricated by a facile impregnation method and the physicochemical properties of which were extensively characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), Brunauer–Emmett–Teller (BET) method, X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction of H2 (H2-TPR), Raman, In situ diffused reflectance infrared Fourier transform spectra (DRIFTS), and density functional theory (DFT) calculations. Results show that the total conversion of toluene can be achieved at 207 °C over PdCe2 with apparent activation energy as low as 62.6 kJ/mol. The strong synergistic effect between Pd and Ce remarkably boosts the catalytic activity of OMS-2, attributed to the abundant Mn3+–O bands and active surface oxygen species. DFT results reveal that oxygen vacancy can be formed over PdCe2 much easily than that of Pd/OMS-2 and Ce/OMS-2 with the oxygen vacancy formation energy of 2.42, 2.83 and 2.68 eV, respectively. Simply increasing the Pd content cannot promote the catalytic activity although PdO is a critical active center in toluene oxidation. Oxygen vacancy attributed to the integrative effect of Pd, Ce and Mn species plays a prominent role over prepared catalysts in toluene activation process. The findings reported in this work showed new insights into the designing of highly efficient OMS-2 catalysts for VOC deep oxidation by tuning oxygen vacancy concentration.

Ni-Mn spinel aerogel catalysts with adsorption induced superior activity for Low-Temperature toluene oxidation

The development of a highly efficient oxide catalyst is crucial for thermal and environmental catalytic reactions. Herein, a facile and eco-friendly strategy is developed to synthesize a series of Au-modified hollow Ni–Mn spinel nanospheres decorated on graphene aerogels (GAs) (termed Auy-hNixMn3−x/GAz) composite catalysts for deep catalytic oxidation of Volatile organic compounds (VOCs). The introduction of hollow structure leads to a larger specific surface area and more accessible active sites. The subsequent cooperation of Au further strengthens the low-temperature reducibility along with more active surface oxygen species. After being embedded into the graphene network, the composite catalyst shows an improvement in electron transfer and accessibility to active metal sites. The adsorption capacity of the catalyst for toluene is greatly improved by the above steps, thus facilitating the catalytic performance. The resulting Au1-hNi1Mn2/GA0.5 composite catalyst exhibits optical activity for VOCs removal, reaching 100 % toluene and benzene (500 ppm) oxidation at 155 °C and 148 °C, respectively. Meanwhile, the catalyst shows extraordinary catalytic stability, selectivity, moisture tolerance and compressibility making it a promising catalyst for industrial thermal catalysis. Moreover, an in situ DRIFTS study is carried out for the exploration of the reaction pathway and a modified Mars van Krevelen (MVK) catalytic mechanism was proposed as well.

Nickel nanocrystals anchored nitrogen-doped carbon derived from eggshell membrane as an efficient catalyst for the electrocatalytic oxidation of urea

The urea oxidation is an effective method to treat wastewater containing urea and energy production. Here, an eggshell membrane (ESM) was immersed in a solution of nickel salts to form Ni(II)@ESM, which was freeze-dried and pyrolyzed to prepare the optimal Ni-N@C-400 composite. The Ni-N@C-400 composite is mesoporous network-interlaced structure, in which Ni nanocrystals are anchored on nitrogen-doped carbon. Furthermore, electrochemical tests show that Ni-N@C-400 composite has the current density (j) of 10 mA cm−2 for urea oxidation reaction (UOR) at a potential of 1.37 V vs RHE, and its performance is comparable to those reported in some literatures, which is mainly due to that the mesoporous structure of the composite facilitates the penetration of electrolyte and electron transfer, the presence of pyrrole/pyridine nitrogen in the composite provides active sites for UOR. In addition, the Ni-N@C-400 sample showed a j retention rate of 96% after a long 12 h CA cycling test, which exceeds that of commercial Pt/C, and is mainly attributed to the fact that the Ni nanocrystals are anchored on nitrogen-doped carbon to avoid shedding of the active components. Based on the excellent UOR performance, Ni-N@C-400 composite is expected to be a potential inexpensive UOR electrocatalyst.

Advances in nonprecious metal catalysts for efficient water oxidation in alkaline media

Advances in nonprecious metal catalysts for efficient water oxidation in alkaline media

La-Cu based heterogeneous perovskite catalyst for highly selective benzene hydroxylation under mild conditions.

Direct hydroxylation of benzene towards phenol with high conversion and selectivity remains a great challenge. We report herein an efficient La2 CuO4 perovskite catalyst for one-step oxidation of benzene using hydrogen peroxide under mild conditions. The catalyst was characterized using XRD, TEM, XPS, TG-DTA, and other advanced techniques. The one-pot hydroxylation reaction carried out at 60 °C under optimum reaction conditions in the presence of catalytic material shows benzene to phenol transformation with 51% conversion with >99% selectivity with 65 percent peroxide efficiency, respectively. The influence of reaction conditions such as temperature, amount of oxidant, reaction time and mode of addition of the oxidant was crucial in selectivity optimization.

Effect of the Potentiostatic and Potentiodynamic Dealloying on the Structure and Chemical Distribution of Ag Atoms in Au-Enriched Nanoparticles

Recently, nanoporous gold (np-Au) prepared by dealloying has emerged as an efficient and durable catalyst for electrochemical oxidation of small alcohols. [1] An additional increase of surface-to-volume ratio by nano-sizing of AuxAg1-x master alloy might improve the catalytic methanol oxidation reaction (MOR). Only few research groups have recently shown that the morphology, structure and elemental distribution of dealloyed nanoparticles (NPs) depend on the various parameters such as initial particle size and composition.[2-4] Starting from AuxAg1-x alloy NPs, it is, however, unclear how the different dealloyed Au-rich NP motifs such as core-shell, hollow or porous NPs and the Ag distribution influence the catalytic MOR performance.In this work, we have investigated the effects of potentiodynamic and potentiostatic dealloying methods on the structure and chemical distribution of the residual Ag atoms for dealloyed Au-rich NPs. First, two size types of Ag-rich AuxAg1-x alloy NPs were prepared by one pot colloidal route and wet impregnation route. Larger Au23Ag77 NPs (size of 77 ± 26 nm) form a homogeneous disordered alloy, while the Au14Ag86 NPs with a size of 12 ± 5 nm show a strong enrichment of Ag atoms at the particle surface, referred to as core-shell arrangement. Subsequently, the as-prepared NPs with two sizes (12 nm and 77 nm) were electrochemically dealloyed using a potentiodynamic (cyclic voltammetry, CV) or potentiostatic (chronoamperometry, CA) method in 0.1 M HClO4. We observed that the CV method leads to the formation of pores inside the initial 77 nm NPs. Very interestingly, high-resolution STEM-EDX shows the appearance of Ag-rich regions near to the pore network of these dealloyed NPs. Unlike, after the dealloying by CV method the initial 12 nm NPs are still dense and solid, forming a thin Au-rich particle shell. After the exposure to air, the internal Ag atoms tend to segregate to the particle surface. In the CA method, we pointed out that the applied anodic potential has a strong influence of the surface diffusion behavior of the remaining Au atoms. Below a critical potential of 1.3 V vs. RHE, the dealloying process is kinetically hindered by the passivation of Au surface atoms. This critical potential in the CA method is strongly different to the critical dissolution potential of Ag atoms for AgxAu1-x NPs obtained from the CV profile (around 1.05 V vs. RHE). However, when the applied potential is larger than the critical potential, e.g. 1.6 V vs. RHE, the difference in the obtained structure and composition of dealloyed 77 nm NPs is negligible between potentiodynamic and potentiostatic approaches. On the other hand, the potentiostatic dealloying at 1.6 V vs. RHE leads to higher surface content of residual Ag for dealloyed NPs with 12 nm compared to potentiodynamic. This increased enrichment of the residual Ag atoms near the particle surface is also supported by XPS.In summary, we correlate the structural parameters (initial particle size, composition/distribution) of dealloyed AgxAu1-x NPs with the electrochemical dealloying methods (potentiostatic vs. potentiodynamic). Tailoring the surface diffusion rate of the Au atoms and the Ag distribution helps to improve the catalytic performance for MOR.

Low-temperature CO oxidation on CuO-CeO2 catalyst prepared by facile one-step solvothermal synthesis: Improved activity and moisture resistance via optimizing the activation temperature

Development of a highly efficient Cu-based catalyst for low-temperature CO oxidation under moisture condition remains a grand challenge. In this paper, effect of activation temperature (350–800 °C) on catalytic performance of CuO-CeO2, prepared by facile one-step solvothermal synthesis, in CO oxidation was investigated, and the catalysts’ physicochemical properties were studied by TG-DSC, ICP-AES, N2 sorption, XRD, TEM, Raman spectroscopy, XPS, in-situ DRIFTS, H2-TPR, CO-TPD, and O2-TPD. It was found that activation at 550 °C is beneficial for the interaction between CuO and CeO2, leading to the formation of more Cu+ species and oxygen vacancies advantageous for improving the catalytic activity. Activation at 800 °C, nevertheless, would weaken the interaction between CuO and CeO2 due to the sintering of CuO and CeO2, thus decreasing the catalytic activity and moisture resistance. Interestingly, no deactivation was observed over the optimal catalyst (activated at 550 °C) after 50 h testing at a low temperature of 87 °C (at which 90% CO conversion was obtained), even when 4.2% water vapor was added into the feed gas.

Pt/NiCo2O4 nanowire arrays on Ni foam as catalysts for efficient formaldehyde oxidation at room temperature

Catalytic oxidation of formaldehyde (HCHO) at room temperature is a low-cost and efficient solution for indoor HCHO removal. In this work, NiCo2O4 nanowires were in-situ synthesized on nickel foam (NF) by a simple hydrothermal reaction and then decorated with platinum nanoparticles (NPs). The Pt/NiCo2O4-NF catalyst exhibited excellent HCHO oxidation capacity at ambient temperature, realizing a conversion rate of 90 % within 60 min. The nickel foam substrate prevents the aggregation of NiCo2O4 nanowire arrays. It also enables the growth of large-area and aligned nanowires, contributing to the uniform dispersion of Pt NPs. Moreover, due to the unique redox property and high reactivity of NiCo2O4, numerous surface oxygen vacancies and active oxygen species are generated together with Pt by NaBH4 reduction, which is beneficial to the adsorption and oxidation of HCHO. Moreover, the hierarchical macro-/mesoporous structure of Pt/NiCo2O4-NF facilitates the diffusion of gaseous reactants and provides easily accessible active sites. In contrast with nanosized catalysts, the three-dimensional (3D) Pt/NiCo2O4-NF catalyst possesses high machinability and practicability. This work may shed light on the fabrication of 3D hierarchical catalysts for oxidative HCHO removal and indoor air purification.

Nitrogen atom coordination tuned transition metal catalysts for NO oxidation and reduction

Developing an efficient catalyst for NO oxidation and reduction at ambient temperature is a significant challenge. Recent studies have suggested that the N-coordinated transition metal (TM) single atom catalysts (SACs) have high catalytic activity and stability. Herein, we report the activation potential of a series of 3d TM atoms supported on N coordination-tuned graphene (GR) for NO oxidation and reduction. The results show that the N coordination pattern can greatly alter the catalytic reactivity of TM on the catalysts, and the TM atom on the catalysts with three-coordinated pyridinic nitrogen TM-N3@GR exhibit the strongest chemical activity. Among the TM-N3@GR catalysts, Ti–N3@GR is the most promising candidate. The rate constants and equilibrium constants were calculated to evaluate the kinetic and thermodynamic feasibility of the catalytic reaction, respectively. Our results demonstrate that the reduction of NO to N2 on Ti–N3@GR can occur at ambient temperature with a large exotherm of 6.99 eV, and the oxidation of NO to NO2 on Ti–N3@GR can easily proceed when the temperature reaches 360 K with a large equilibrium constant. Our studies are of great significance for understanding the performance of N coordination-tuned catalysts and designing Ti-based catalysts for NO oxidation and reduction.

Bismuth Sulfide Doped in Graphitic Carbon Nitride Degrades Nitric Oxide under Solar Irradiation.

This study developed and examined the application of bismuth sulfide doped on graphitic carbon nitride (Bi2S3@g-C3N4) in the degradation of NO under solar irradiation. Bi2S3@g-C3N4 was prepared through the calcination method. The morphological structure and chemical properties of the synthesized photocatalyst were analyzed before the degradation tests. After doping with Bi2S3@g-C3N4, the bandgap was reduced to 2.76 eV, which increased the absorption of solar light. As a result, the Bi2S3@g-C3N4 achieved higher NO degradation (55%) compared to pure Bi2S3 (35%) and g-C3N4 (45%). The trapping test revealed that the electrons were the primary species responsible for most of the NO degradation. The photocatalyst was stable under repeated solar irradiation, maintaining degradation efficiencies of 50% after five consecutive recycling tests. The present work offers strong evidence that Bi2S3@g-C3N4 is a stable and efficient catalyst for the photocatalytic oxidation of NO over solar irradiation.

Waste eggshell membrane-templated three-dimensional CoOx catalyst for efficient low-temperature toluene oxidation with strong thermal stability

Eggshell membrane was used as the template to synthesize three-dimensional network CoOx catalysts. Besides, hydrogen reduction at 650 °C was adopted to simultaneously remove poisoned sulfur species and produce metal Co, which was self-oxidized on the catalyst surface at room-temperature, accompanied with better reducibility. Compared to counterpart CoOx (direct calcination of C4H6CoO4∙4 H2O), CoOx synthesized by using eggshell membrane possesses more Co3+ and lattice oxygen because its three-dimensional network structure is beneficial to the mass transfer of the reaction. The structure of applied catalyst will be reformed during the oxidation process. Although the active Co species are Co3+, the spillover of hydrogen from Co0 to surface leads to a better reducibility of ESM-CoOx, which significantly improves the low-temperature toluene oxidation activity of the catalyst. As a result, ESM-CoOx exhibits a best low-temperature catalytic activity of toluene oxidation (reaching 99% conversion at 250 °C, toluene reaction rate at 225 °C is 2.98 μmol gcat−1 s−1). Importantly, the above cobalt catalyst shows excellent thermal stability and 5 vol% water resistance at 250 °C. This work thus provides a novel process to tail highly active CoOx catalyst for low-temperature volatile organic chemicals oxidation in real application.

Hematite Photoanodes Decorated with a Zn-doped Fe2O3 Catalyst for Efficient Photoelectrochemical Water Oxidation

Hematite Photoanodes Decorated with a Zn-doped Fe2O3 Catalyst for Efficient Photoelectrochemical Water Oxidation

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Atomically precise thiolate‐protected gold nanoclusters are ideal model systems for investigating the influencing factors of catalysis. In this work, three structurally related nanoclusters with reported star Au25 kernels have been synthesized to unify kernels‐isomerization, modification of peripheral ligands, electronic effects, and their correlation to catalytic performances into one system to design an efficient catalyst for oxidation of organosilanes. More details are given in the article by Zhang et al. on page 2575—2581.image

Interstitial nitrogen-induced efficiency alcohol oxidation over heterogeneous N–CoMn2O4 catalyst under visible-light

Developing highly efficient and recyclable photocatalysts through harvesting solar light as energy is crucial to oxidation for industrial implementation, especially for simple transition metal oxidic catalysts without precious/heavy/rare metal dopants. Herein, we like to report the use of nitrogen-doped CoMn2O4 oxide (N–CoMn2O4) as a heterogeneous catalyst for efficient oxidation of various alcohols such as p/m/o-methyl-substituted aromatic alcohols, p-substituted aromatic alcohols including electron-donating and electron-withdrawing substituents, heterocycle-based alcohols and secondary aromatic alcohols to the corresponding aldehydes/ketones, under visible light (>420 ​nm) illumination and mild condition of oxygen as oxidant and room temperature. The relation of various Co-based oxides to their catalytic performance was studied. It is shown that the Co2+ species in N–CoMn2O4, obviously increased by the doping of nitrogen, are acted as catalytic active species coupled with the synergistic effect between Co and Mn species for the enhanced visible-light selective oxidation of alcohols to aldehydes. A plausible catalytic mechanism is proposed basis of control experiments and published studies, which suggests that this oxidation process probably occurs on Co2+ sites via an ionic reactive oxygen species pathway and 1O2 and O2·− species are the reactive oxygen species. This simple transition metal oxide-catalyzed aerobic oxidation provides a green alternative for the manufacture of aldehydes/ketones from alcohols.

Porous Heteroatom‐Doped Carbons: Efficient Catalysts for Selective Oxidation of Alcohols by Activated Persulfate

AbstractAldehydes are essential chemicals for industrial feedstock. However, the traditional processes to produce these chemicals face many limitations, such as waste generation, low selectivity, or high cost. Herein, we report the synthesis and characterization of a group of porous heteroatom (P, B or N)‐doped carbons and their use as catalysts for the oxidation of primary alcohols by activating peroxydisulfate. Among the heteroatom‐doped carbons, porous N‐doped carbons pyrolyzed at 700 or 800 °C show the highest activity. Experimental studies were performed suggesting a considerable contribution of a non‐radical oxidation process. Furthermore, N‐doped carbons can act as a catalyst in the oxidation of a large substrate scope of substituted alcohols.