Catalysts For Oxidative Coupling Research Articles

Unraveling defect chemistry in doped-ceria catalyst for oxidative coupling of lignin-based aniline and benzyl alcohol

Unraveling defect chemistry in doped-ceria catalyst for oxidative coupling of lignin-based aniline and benzyl alcohol

Cu@CuOx/WO3 with photo-regulated singlet oxygen and oxygen adatoms generation for selective photocatalytic aromatic amines to imines

Photocatalysts can absorb light and activate molecular O2 under mild conditions, but the generation of unsuitable reactive oxygen species often limits their use in synthesizing fine chemicals. To address this issue, we disperse 1 wt% copper on tungsten trioxide (WO3) support to create an efficient catalyst for selective oxidative coupling of aromatic amines to imines under sunlight irradiation at room temperature. Copper consists of a metallic copper core and an oxide shell. Experimental and density functional theory calculations have confirmed that Cu2O is the primary activation site. Under λ < 475 nm, the light excites electrons of the valence bands in Cu2O and WO3, which activate O2 to superoxide radical •O2−. Then rapidly transforms into oxygen adatoms (•O) and oxygen anion radicals (•O−) species on the surface of Cu2O. Simultaneously, it is captured by holes in the WO3 valence band to generate singlet oxygen (1O2). •O bind to 1O2 promoting the coupling reaction of amines. When λ > 475 nm, intense light absorption due to the localized surface plasmon resonance excites numerous electrons in Cu to promote the oxidative coupling with the adsorbed O2. This study presents a promising approach towards the design of high-performance photocatalysts for solar energy conversion and environmentally-friendly oxidative organic synthesis.

Titelbild: Fundamentals of Unanticipated Efficiency of Gd2O3‐based Catalysts in Oxidative Coupling of Methane (Angew. Chem. 14/2024)

Titelbild: Fundamentals of Unanticipated Efficiency of Gd₂O₃‐based Catalysts in Oxidative Coupling of Methane (Angew. Chem. 14/2024)

Cover Picture: Fundamentals of Unanticipated Efficiency of Gd2O3‐based Catalysts in Oxidative Coupling of Methane (Angew. Chem. Int. Ed. 14/2024)

Cover Picture: Fundamentals of Unanticipated Efficiency of Gd₂O₃‐based Catalysts in Oxidative Coupling of Methane (Angew. Chem. Int. Ed. 14/2024)

Fundamentals of Unanticipated Efficiency of Gd2O3-based Catalysts in Oxidative Coupling of Methane.

Improving the selectivity in the oxidative coupling of methane to ethane/ethylene poses a significant challenge for commercialization. The required improvements are hampered by the uncertainties associated with the reaction mechanism due to its complexity. Herein, we report about 90 % selectivity to the target products at 11 % methane conversion over Gd2O3-based catalysts at 700 °C using N2O as the oxidant. Sophisticated kinetic studies have suggested the nature of adsorbed oxygen species and their binding strength as key parameters for undesired methane oxidation to carbon oxides. These descriptors can be controlled by a metal oxide promoter for Gd2O3.

Fundamentals of Unanticipated Efficiency of Gd2O3‐based Catalysts in Oxidative Coupling of Methane

AbstractImproving the selectivity in the oxidative coupling of methane to ethane/ethylene poses a significant challenge for commercialization. The required improvements are hampered by the uncertainties associated with the reaction mechanism due to its complexity. Herein, we report about 90 % selectivity to the target products at 11 % methane conversion over Gd2O3‐based catalysts at 700 °C using N2O as the oxidant. Sophisticated kinetic studies have suggested the nature of adsorbed oxygen species and their binding strength as key parameters for undesired methane oxidation to carbon oxides. These descriptors can be controlled by a metal oxide promoter for Gd2O3.

Macroporous Carbon-Supported Fe-Based Catalysts for the Solvent-Free Oxidative Coupling of Benzylamine

Macroporous Carbon-Supported Fe-Based Catalysts for the Solvent-Free Oxidative Coupling of Benzylamine

Accurate assembly of thiophene-bridged titanium-oxo clusters with photocatalytic amine oxidation activity.

Designing and synthesizing well-defined crystalline catalysts for the photocatalytic oxidative coupling of amines to imines remains a great challenge. In this work, a crystalline dumbbell-shaped titanium oxo cluster, [Ti10O6(Thdc)(Dmg)2(iPrO)22] (Ti10, Thdc = 2,5-thiophenedicarboxylic acid, Dmg = dimethylglyoxime, iPrOH = isopropanol), was constructed through a facile one-pot solvothermal strategy and treated as a catalyst for the photocatalytic oxidative coupling of amines. In this structure, Thdc serves as the horizontal bar, while the {Ti5Dmg} layers on each side act as the weight plates. The molecular structure, light absorption, and photoelectrochemical properties of Ti10 were systematically investigated. Remarkably, the inclusion of the Thdc ligand, with the assistance of the Dmg ligand, broadens the light absorption spectrum of Ti10, extending it into the visible range. Furthermore, the effective enhancement of charge transfer within the Ti10 was achieved with the successful incorporation of the Thdc ligand, as opposed to PTC-211, where terephthalic acid replaces the Thdc ligand, while maintaining consistency in other aspects of Ti10. Building on this foundation, Ti10 was employed as a heterogeneous molecular photocatalyst for the catalytic oxidative coupling reaction of benzylamine (BA), demonstrating very high conversion activity and selectivity. Our study illustrates that the inclusion of ligands derived from Thdc enhances the efficiency of charge transfer in functionalized photocatalysts, significantly influencing the performance of photocatalytic organic conversion.

Facile fabrication of ternary NiTiFe-LDH ultrathin nanosheets for efficient conversion of amines into imines under visible light.

Ternary NiTiFe-LDH with an ultrathin nanosheet morphology was successfully fabricated via a facile co-precipitation method, followed by refluxing, and was used as a catalyst for oxidative coupling of amines to produce imines under visible light. The obvious superior activity observed in NiTiFe-LDH ultrathin nanosheets compared with binary NiTi-LDH and bulk NiTiFe-LDH can be ascribed to an enhanced light absorption capability caused by the introduction of Fe3+ ions as well as the ultrathin nanosheets which can minimize the recombination of the photogenerated charge carriers and provide more catalytically active sites for the reaction. As a result, more catalytically active O2˙- radicals are generated over NiTiFe-LDH ultrathin nanosheets, which leads to their superior activity. This study not only shows the possibility of using LDHs in photocatalytic organic transformations but also demonstrates an effective strategy to promote the activity of LDH-based photocatalysts via simultaneous composition and morphology modulation of LDHs.

Lithium carbonate-promoted mixed rare earth oxides as a generalized strategy for oxidative coupling of methane with exceptional yields

The oxidative coupling of methane to higher hydrocarbons offers a promising autothermal approach for direct methane conversion, but its progress has been hindered by yield limitations, high temperature requirements, and performance penalties at practical methane partial pressures (~1 atm). In this study, we report a class of Li2CO3-coated mixed rare earth oxides as highly effective redox catalysts for oxidative coupling of methane under a chemical looping scheme. This catalyst achieves a single-pass C2+ yield up to 30.6%, demonstrating stable performance at 700 °C and methane partial pressures up to 1.4 atm. In-situ characterizations and quantum chemistry calculations provide insights into the distinct roles of the mixed oxide core and Li2CO3 shell, as well as the interplay between the Pr oxidation state and active peroxide formation upon Li2CO3 coating. Furthermore, we establish a generalized correlation between Pr4+ content in the mixed lanthanide oxide and hydrocarbons yield, offering a valuable optimization strategy for this class of oxidative coupling of methane redox catalysts.

Support effect of Mn/Na2WO4‐based catalysts in oxidative coupling of methane

AbstractBACKGROUNDIn this work, the supported Mn‐Na2WO4/γ‐Al2O3, Mn‐Na2WO4/γ‐Al2O3‐TiO2 and Mn‐Na2WO4/ γ‐Al2O3‐SiO2 catalysts were prepared using the dry impregnation procedure and tested for suitability to the oxidative coupling of methane (OCM) reaction. The synthesized catalyst was characterized by various techniques such as X‐ray diffraction (XRD), Fourier transform infrared (FTIR), X‐ray photon spectroscopy (XPS), temperature‐programmed reduction (TPR), Brunauer–Emmett–Teller (BET) surface area and field emission scanning electron microscopy (FESEM), and the support effect of the prepared catalysts in the OCM reaction was evaluated.RESULTSThe XPS results showed that the tetrahedral WO42− phase is presented in all prepared catalysts and it is expected that the presence of this phase is correlated with high OCM activity. The XPS results show that the amount of O2− in the treated Mn‐Na2WO4/γ‐Al2O3‐TiO2 catalyst at 800 °C is higher than that in the Mn‐Na2WO4/γ‐Al2O3 and Mn‐Na2WO4/γ‐Al2O3‐SiO2 catalysts, but is reduced with increasing temperature. At 850 °C, the amount of O2− in the treated Mn‐Na2WO4/γ‐Al2O3 catalyst is higher than in the Mn‐Na2WO4/γ‐Al2O3‐TiO2 and Mn‐Na2WO4/γ‐Al2O3‐SiO2catalysts.CONCLUSIONThe results show that the MnSiO3 and MnTiO3 sites may deliver a much easier Mn2+↔Mn3+ cycle than the MnAl2O4 and MnWO4 sites at low temperatures, and may play a principal role in enhancing the catalyst activity in the OCM reaction at 800 °C. © 2023 Society of Chemical Industry (SCI).

Performance and reaction mechanism of Mg-doped and Li-doped La2O3 catalysts in oxidative coupling of methane: DFT and experiment study

Lanthanum oxide (La2O3) catalyst is a promising catalytic system for oxidative coupling of methane (OCM) reaction, while low activity for methane dissociation restricts its widespread application. Low-value dopants can enhance methane conversion activity on La2O3 catalysts. This work systematically studied the mechanism and catalytic performance of OCM reaction on Mg-doped and Li-doped La2O3 catalysts using a combination of DFT and experimental methods. The results show that Mg-doped and Li-doped can significantly improve CH4 dissociation activity and C2H4 selectivity on La2O3(001) surface. The microscopic property analysis shows that the p-band center of lattice oxygen on Mg-doped and Li-doped La2O3(001) is closer to the Fermi level, compared with undoped La2O3(001), which is more conducive to the activation of methane. Furthermore, Mg-doped and Li-doped La2O3 catalysts are prepared and their OCM catalytic performance are investigated. The catalytic performance of Mg-doped La2O3 catalyst reaches its best at 750 °C, with a high CH4 conversion (above 30.9 %) and the highest C2+ hydrocarbons selectivity (about 47.5 %) and C2+ yield (about 14.7 %). However, Li-doped La2O3 shows poorer catalytic performance than undoped La2O3, primarily due to the loss of the doped Li during the OCM process. In addition, the OCM reaction cycle and the mechanism of action of oxygen species on Mg doped La2O3(001) have been studied. The results show that lattice oxygen and peroxide species are the major active oxygen species for activating methane.

A highly efficient defective carbon catalyst for oxidative coupling of amines

A highly efficient defective carbon catalyst for oxidative coupling of amines

Lanthanum based catalysts for oxidative coupling of methane: Effect of morphology and structure

Lanthanum based catalysts for oxidative coupling of methane: Effect of morphology and structure

Synthesis of NaKCO3@(Mn-Na2 WO4/SiO2) core-shell catalyst for oxidative coupling of methane

Oxidative Coupling of Methane (OCM) is a process to produce ethylene as one of the most widely used petrochemicals from methane natural gas. The core–shell nano-catalyst of NaKCO3@(Mn-Na2WO4/SiO2) was prepared with different ratios of Na/K, and its activity in the OCM process was investigated and its performance was compared with the conventional Mn-Na2WO4/SiO2 nano-catalyst. The effect of temperature and methane-to-oxygen ratio on nano-catalyst performance was investigated. The performance criteria included methane conversion, ethylene selectivity, and C2+ yield. The formation of the core–shell structure has been deliberated using XRD and FE-SEM characterization tests. The results of characterization and reactor experiments indicated that the best performance was related to the nano-catalyst prepared with a ratio ofNa/K = 2/2.4, operating conditions: 850 °C, atmospheric pressure, and CH4/O2 ratio = 2 in the reaction feed. The formation of the core–shell structure does not reduce the nano-catalyst activity, but rather increases the selectivity of the main product, ethylene, by improving the nano-catalyst performance even at 850 °C. Stability tests were performed to examine the catalytic activity under high temperatures.

Enhancement of oxygen vacancy sites of La2-xMxCe2O7-δ (M = Ca, Ba, Sr) catalyst for the low temperature oxidative coupling of Methane: A combined DFT and experimental study

This study investigated the effect of different alkaline earth metals doped La2-xMxCe2O7-δ (M = Ca, Sr, Ba and x = 0.30) catalysts prepared by one-step hydrothermal method for the low-temperature methane oxidative coupling (OCM) to olefins. The presence of a disordered cubic fluorite phase of synthesized catalysts was detected by powder XRD and Raman analysis. The surface analysis by XPS and Raman shows the presence of oxygen vacancy sites, which are responsible for the formation of electrophilic superoxide O2– species in presence of molecular oxygen. We observed that the ratio of active oxygen species (O2− and O22−) to lattice oxygen (O2–) was linearly correlated with the number of basic sites. The catalytic activity of different catalysts for the OCM reactions follows the order: La1.7Ca0.3Ce2O7-δ > La1.7Sr0.3Ce2O7-δ > La1.7Ba0.3Ce2O7-δ > La2Ce2O7. The reactivity order follows the same trend as the amount of basic sites and reactive oxygen species. According to this study, the best catalyst is La1.7Ca0.3Ce2O7-δ, which gives the highest C2 yield and C2 selectivity of 23.6 % and 78.8 %, respectively, at 650 °C. DFT studies revealed that substitution of La by Ca in the La2Ce2O7 catalyst significantly reduces the oxygen vacancy formation energy by about 100 kJ/mol compared to the undoped LaCe-oxide. We believe that the superior activity of La1.7Ca0.3Ce2O7-δ catalyst is attributed to the higher amount of basicity and electrophilic oxygen content, which are the governing factors in OCM for CH4 conversion and C2 product selectivity as well.

Mechanochemical synthesis of a high-surface-area Pd/α-Al2O3 catalyst for CO oxidative coupling to dimethyl oxalate reaction

High-surface-area α-Al2O3 with abundant hydroxyls is synthesized by a ball-milling method. It demonstrates high catalytic activity and excellent stability for the CO oxidative coupling to dimethyl oxalate reaction.

Indirect design of OCM catalysts through machine learning of catalyst surface oxygen species

Catalysts for oxidative coupling of methane (OCM) were designed through machine learning of a property of surface oxygen species on the basis of the knowledge that catalytic performance for the OCM is affected by catalyst surface oxygen species.

Regulating the metal-support interactions by tuning the ratios between N and B based on the C2N motif to develop efficient Pd-based catalysts for CO oxidative coupling to DMO: A DFT study

The CO oxidative coupling to dimethyl oxalate (DMO) is a crucial step in the coal to ethylene glycol, but the industrial catalysts have drawbacks: high Pd loading and low Pd utilization, dramatically increasing the cost. There is an urgent need to develop low-cost and high-performance Pd-based catalysts for the CO oxidative coupling to DMO. Given the excellent properties of the 2D materials, we used the DFT calculations to design three Pd-based catalysts based on the C2N motif to investigate their catalytic performance in the CO oxidative coupling to DMO. Since the electronegativity of Pd is between N and B, on the one hand, by adjusting the relative ratios of N and B in the support, the valence state of Pd can be transformed from the highly oxidized state to the metallic state through charge transfer between the support and Pd. On the other hand, the activities of the different CO and CC coupling can be modulated by the metal-support interactions strength, tuning the main product from dimethyl carbonate to DMO. The work provides a theoretical viewpoint by regulating the MSI and the valence state of Pd to explore the efficient Pd-based catalysts for the CO oxidative coupling to DMO.

Perovskite catalysts for oxidative coupling of methane improved by Y‐doping

AbstractOxidative coupling of methane (OCM) is an effective route for methane direct conversion to ethylene. Perovskite oxides (ABO3) with variable properties are potential catalysts for OCM by adjusting the compositions. In this study, four perovskite catalysts, BaMO3‐δ and BaM1‐xYxO3‐δ (M = Zr, Ce; x = 0.2), were prepared by the sol–gel method to explore their catalytic performance of OCM. All catalysts are active toward OCM and reach the highest catalytic performance at 800°C. The OCM performance of Ce‐based catalysts is higher than that of Zr‐based catalysts. The selectivity of C2 compounds is significantly improved by Y‐doping. At CH4/O2 mol ratio of 8, a C2 selectivity of 67% was achieved on BaCe0.8Y0.2O3‐δ. Compared with Zr‐based catalysts, more amounts of active oxygen species, which are beneficial to OCM, were observed on BaCeO3‐δ and BaCe0.8Y0.2O3‐δ. Meanwhile, higher contents of moderate and strong basic sites, which are beneficial to OCM, were found on the Y‐doped catalysts. This is attributed to the generation of oxygen vacancies caused by Y‐doping in the B‐site. Therefore, BaCe0.8Y0.2O3‐δ with more active oxygen species and stronger basicity exhibits the highest performance among the four catalysts.