Selective Oxidation Of Methanol Research Articles

Selective Oxidation of Methanol to Methyl Formate on Gold: The Role of Low-Coordinated Sites Revealed by Isothermal Pulsed Molecular Beam Experiments and AIMD Simulations.

To elucidate the role of low-coordinated sites in the partial methanol oxidation to methyl formate (MeFo), the isothermal reactivity of flat Au(111) and stepped Au(332) in pulsed molecular beam experiments was compared for a broad range of reaction conditions. Low-coordinated step sites were found to enhance MeFo selectivity, especially at low coverage conditions, as found at higher temperatures. The analysis of the transient kinetics provides evidence for the essential role of Au x O y phases for MeFo formation and the complex interplay of different oxygen species for the observed selectivity. Ab initio molecular dynamic simulations yielded microscopic insights in the formation of Au x O y phases on flat and stepped gold surfaces emphasizing the role of low-coordinated sites in their formation. Moreover, associated surface restructuring provides atomic-scale insights which align with the experimentally observed transient kinetics in MeFo formation.

High-Dimensional Nb2O5 with NbO6 Octahedra for Efficient Electrocatalytic Upgrading of Methanol to Formate.

Facilitating the selective electrochemical oxidation of methanol into value-added formate is essential for electrochemical refining. Here we propose a high-dimensional Nb2O5 on Ni foam (Nb2O5-HD@NF) composite as anode for methanol oxidation reaction (MOR) for efficient production of formate. In an electrolyte containing 3 M methanol aqueous solution, the Nb2O5-HD@NF anode requires only 240 mV overpotential to deliver an industrial-level current density of 100 mA cm-2 with a formate Faraday efficiency of 100%. In situ Raman and electrochemical kinetic analyses reveal that the origin of the excellent activity in 3 M methanol electrolyte can be ascribed to the NbO6 octahedra as active sites and the Lewis acid sites on the surface of Nb2O5-HD. This work may pave a way for the design of non-noble metal electrocatalysts with surface acidity engineering for the effective electrocatalytic upgrading of biomass molecules.

A Highly Efficient Electrosynthesis of Formaldehyde Using a TEMPO-Based Polymer Electrocatalyst.

In the chemical industry, formaldehyde is an important bulk chemical. The traditional synthesis of formaldehyde involves an energy intensive oxidation of methanol over a metal oxide catalyst. The selective electrochemical oxidation of methanol is challenging. Herein, we report a catalytic system with an immobilized TEMPO electrode that selectively oxidizes methanol to formaldehyde with high turnover numbers. Upon the addition of various organic and inorganic bases, the activity of the catalyst could be tuned. The highest Faradaic efficiency that was achieved was 97.5 %, the highest turnover number was 17100. Additionally, we found that the rate determining step changed from the step in which the carbonyl specie is created from the methanol-TEMPO adduct to the oxidative regeneration of the TEMPO+ species. Finally, we showed that the system could be applied to the oxidation of other aliphatic alcohols.

Ampere-Level Electrolytic Coproduction of Formate with Coupled Carbon Dioxide Reduction and Selective Methanol Oxidation

Ampere-Level Electrolytic Coproduction of Formate with Coupled Carbon Dioxide Reduction and Selective Methanol Oxidation

Concentrated formate produced through co‐electrolysis of CO2 and methanol in a zero‐gap electrolyzer

AbstractRecent progresses have highlighted the enormous potentials of renewable electricities driven carbon dioxide (CO2) electrolysis in achieving carbon neutrality. However, its further industrial application is limited by low liquid product concentrations, which requires energy‐intensive downstream separation processing. Herein we report a CO2 and methanol co‐electrolysis strategy to produce formate at both electrodes and collect highly concentrated formate in zero‐gap CO2 electrolyzers. An anion exchange membrane was employed to enable formate product crossover from cathode to anode. A bismuth silicate derived nanofiber electrocatalyst with rich grain boundaries was synthesized and exhibited excellent formate selectivity (Faradaic efficiency >95%), high activity (partial current density >500 mA cm−2), as well as good stability (>120 h). Coupled with NiOX anode catalyst for methanol selective oxidation to formate in a zero‐gap electrolyzer, we demonstrate a ~180% of formate Faradaic efficiency and a full‐cell voltage of 2.43 V at an industrially relevant current density of 0.2 A cm−2. By decoupling product generation and collection, our electrolyzer produced a highly concentrated formate of 3.24 M, which could be directly used as anode fuel for fuel cells.

Interfacial Electronic Modulation of Dual-Monodispersed Pt–Ni3S2 as Efficacious Bi-Functional Electrocatalysts for Concurrent H2 Evolution and Methanol Selective Oxidation

HighlightsThe well-conceived Pt–Ni3S2 heteronanocrystals with dual-monodispersed characteristics are synthesized through interfacial electronic modulation.The asymmetrical charge distribution at Pt–Ni3S2 hetero-interface results in the formation of high-valent Ni sites and negatively-charged Ptδ−.It eventually accelerates water dissociation and achieves the steady concurrent generation of value-added formate and hydrogen.

Selective oxidation of methanol to green oxygenates on vanadium-aluminum phosphate based catalysts

The methanol transformation reaction in the presence of oxygen was carried out in the temperature range of 210–310 ºC, over vanadium catalysts based on vanadium oxide (V2O5) and on vanadium-phosphorus oxide (VPO) calcined at 450 ºC in air. Specifically, the vanadium oxide systems with V2O5 loadings below, above or corresponding to the theoretical monolayer (1–34 wt% of V2O5) were obtained by the impregnation of a mesoporous amorphous aluminum phosphate, AlPO4, calcined at different temperatures (from 350 ºC to 650 ºC) with vanadyl oxalate. Additionally, mechanical mixtures of either VPO or V2O5 with AlPO4 were also employed. Under the experimental conditions employed, with a methanol enriched feed (O2/methanol molar ratio=0.6), formaldehyde and dimethoxymethane were the main products obtained with all the catalysts studied. Vanadyl phosphate (VPO) exhibited slightly lower activity than vanadium oxide, formaldehyde being the main product (SFA ≥ 95%). The conversion of both vanadium oxide and vanadyl phosphate appreciably increased when mixed with the AlPO4, also promoting the formation of dimethoxymethane. The interaction of the vanadium species with the aluminum phosphate surface took place preferentially through the surface Al-OH groups, the vanadium species with less development being the most active in the formation of formaldehyde and dimethoxymethane, per at-g of vanadium.

Chemical looping methanol oxidation using supported vanadium phosphorous oxide carriers for formaldehyde production

A novel chemical looping scheme for selective oxidation of methanol has been reported, using silica-supported vanadium phosphorous oxide as the oxygen carrier.

Hybrid Acid/Base Electrolytic Cell for Hydrogen Generation and Methanol Conversion Implemented by Bifunctional Ni/MoN Nanorod Electrocatalyst.

Combining the methanol oxidation reaction (MOR) and hydrogen evolution reaction (HER) within an integrated electrolytic system may offer the advantages of enhanced kinetics of the anode, reduced energy consumption, and the production of high-purity hydrogen. Herein, it is reported the construction of Ni─MoN nanorod arrays supported on a nickel foam substrate (Ni─MoN/NF) as a bifunctional electrocatalyst for electrocatalytic hydrogen production and selective methanol oxidation to formate. Remarkably, The optimal Ni─MoN/NF catalyst displays exceptional HER performance with an overpotential of only 49mV to attain 10mAcm-2 in acid, and exhibits a high activity for MOR to achieve 100mAcm-2 at 1.48V in alkali. A hybrid acid/base electrolytic cell with Ni─MoN/NF electrode as anode and cathode is further developed for an integrated HER-MOR cell, which only requires a voltage of 0.56V at 10mAcm-2 , significantly lower than that of the HER-OER system (0.70V). The density functional theory studies reveal that the incorporation of Ni effectively modulates the electronic structure of MoN, thereby resulting in enhanced catalytic activity. The unique combination of high electrocatalytic activity and excellent stability make the Ni─MoN/NF catalyst a promising candidate for practical applications in electrocatalytic hydrogen production and methanol oxidation.

Ultrafast electron transfer from CdS quantum dots to atomically-dispersed Pt for enhanced H2 evolution and value-added chemical synthesis

Photocatalytic hydrogen production is enchanting in solar energy utilization. And mechanism elucidation in interfacial electron transfer rate is a prerequisite for performance improvement. Herein, atomically dispersed Pt-modified CdS quantum dots (Pt-CdS QDs), prepared by a facile one-step in-situ deposited method, are used as a prototype. Benefiting from the maximized utilization of Pt cocatalyst as well as the strong electronic metal-support interaction, ultrafast electron transfer from CdS to Pt (∼1.7 ps) is achieved, as revealed by femtosecond transient absorption spectra. The optimal sample simultaneously realizes photocatalytic hydrogen evolution coupled with selective oxidation of 2-thiophene methanol (TM) into 2-thiophenecarboxaldehyde (TD). Specifically, it exhibits an enhanced H2-evolution rate, which is 70-fold higher than pristine CdS QDs. Moreover, a TM conversion rate of 95.3 % with a TD selectivity of 87.2 % is reached after 4 h. This work will provide some guidance for the design of photocatalytic systems with efficient interfacial electron transfer.

In-situ Raman unveiled Nb-O-bond-dependency selectivity for methanol electro-oxidation at high current density

Selective methanol oxidation reaction (MOR) to value-added formate can maximize the energy utilization by replacing the high onset-potential and sluggish oxygen evolution reaction. However, to date, only first-row 3d transition metal oxides exhibit the capacity of selective MOR, motivating the design of new kinds of electrocatalysts to further enhance the performance. Here we develop amorphous Nb2O5 as an efficient electrocatalyst, for the first time, for selective MOR to formate, with a low operating potential of 1.47 V vs. RHE to achieve the industry-relevant current densities (>100 mA cm−2) with a formate Faradaic efficiency of ∼100 %. We demonstrate, via operando Raman measurements, that this superior electrochemical MOR capacity originates from the in-situ induced short Nb-O bonds from the amorphous structure. Besides, the interface between amorphous Nb2O5 and nickel foam could also faciltate the MOR. This work may provide insights for designing novel transition metal oxides as efficient catalysts for selective MOR.

Co–Ni–P Nanoneedle Array Heterostructures with Built-In Potential for Selective Methanol Oxidation Coupled with H2 Evolution

Electro-oxidation of methanol (MOR) coupling with the hydrogen evolution reaction (HER) is a meaningful innovation strategy to realize energy-saving production of H2 and value-added chemical products. In this study, a self-supported cobalt nickel bimetallic phosphide nanoneedle array (Co–Ni–P/NF) is designed to realize excellent bifunctional activity for the HER and MOR. Studies prove that the p–n heterogeneous junctions formed in between nickel phosphide and cobalt phosphide promote the accumulation of electrons on CoP, favoring the absorption of H* and boosting HER activity, whereas the increased MOR activity is due to in situ generated holes in Ni2P. Benefiting from the optimized interface/surface electronic structures, the Co–Ni–P/NF produces 100 mA cm–2 current density in a two-electrode electrolyzer with a significantly low cell voltage of 1.45 V. The faradic efficiencies up to 100% for both the HER and MOR are obtained, showing the excellent bifunctional catalytic activity of Co–Ni–P/NF nanoneedle arrays. This work throws light on developing novel bifunctional electrocatalysts for value-added chemical production and highly efficient hydrogen evolution.

Preparation of mespore load composite metal oxide catalyst and selective benzoyl methanol oxide

The CoMn2O4 precursor was prepared by hard template method using mesoporous material SBA-15 as template material, n-hexane as solvent, manganese and cobalt nitrate as raw materials. After calcination at 600 °C, porous composite metal oxide catalyst CoMn2O4 was formed. The samples are characterized by X-Ray Diffraction (XRD), Thermogravimetric Analysis-Differential Scanning Calorimeter (TG-DSC), Scanning Electron Microscopy (SEM), and Energy Dispersive X-Ray Spectroscopy (EDX). Using benzyl alcohol as a model compound, the selective oxidation of benzyl alcohol by CoMn2O4 under different catalytic conditions was studied. The oxidation products are analyzed by High Performance Liquid Chromatography (HPLC). The results show that the pure CoMn2O4 can be prepared at 500 °C to 800 °C, and the samples are spherical particles. The optimal conditions for oxidation are as follows: The amount of catalyst was 4 g/L, the molar ratio of H2O2 to benzyl alcohol was 1:1, the reaction temperature was 80 °C, and the reaction time was 4h. The conversion rate of benzyl methanol is 78.2%, the selective conversion of benzaldehyde is 94.8%. This indicates that the CoMn2O4 is a composite metal oxide with high selective oxidation of benzene methanol.

Selective Methanol Oxidation to Green Oxygenates—Catalyst Screening, Reaction Kinetics and Performance in Fixed-Bed and Membrane Reactors

Experimental and simulation-based investigations are carried out for the selective oxidation of green methanol to the oxygenates dimethoxymethane (DMM) and methyl formate (MF), including an initial catalyst screening, the derivation of a reaction kinetic model, and a feasibility study of a fixed-bed and a membrane reactor with oxygen distribution. The catalyst screening of different supports and loading of vanadium revealed a 6.6 wt.-% VOx/TiO2 catalyst offering the highest potential to the formation for the target products. Kinetic experiments performed in a broad range of operation conditions, e.g., residence time, temperature, and oxygen concentration, are used for the postulation of a reaction network, providing the basis for mathematical modeling of the individual five reaction rates with a reduced mechanistic approach. A simulation study based on the derived reaction kinetics and parameters revealed the high potential of a distributed oxygen dosing at high residence times, outperforming the conventional fixed-bed reactor by up to 6% in the yield of DMM and up to 19% in the yield of MF. The formation of DMM is favored at low temperatures, whereas the formation of MF is supported by high temperatures.

High quantum efficiency of hydrogen production from methanol aqueous solution with PtCu-TiO2 photocatalysts.

Methanol with 12.5 wt% H2 content is widely considered a liquid hydrogen medium. Taking into account water with 11.1 wt% H2 content, H2 synthesis from the mixture of water and methanol is a promising method for on-demand hydrogen production. We demonstrate an atomic-level catalyst design strategy using the synergy between single atoms and nanodots for H2 production. The PtCu-TiO2 sandwich photocatalyst achieves a remarkable H2 formation rate (2,383.9 µmol h-1) with a high apparent quantum efficiency (99.2%). Furthermore, the oxidation product is a high-value chemical formaldehyde with 98.6% selectivity instead of CO2, leading to a nearly zero-carbon-emission process. Detailed investigations indicate a dual role of the copper atoms: an electron acceptor to facilitate photoelectron transfer to Pt, and a hole acceptor for the selective oxidation of methanol to formaldehyde, thus avoiding over-oxidation to CO2. The synergy between Pt nanodots and Cu single atoms together reduces the activation energy of this process to 13.2 kJ mol-1.

Inhibitor and Activator: Dual Role of Subsurface Sulfide Enables Selective and Efficient Electro-Oxidation of Methanol to Formate on CuS@CuO Core-Shell Nanosheet Arrays.

Selective electro-oxidation of aliphatic alcohols into value-added carboxylates at lower potentials than that of the oxygen evolution reaction (OER) is an environmentally and economically desirable anode reaction for clean energy storage and conversion technologies. However, it is challenging to achieve both high selectivity and high activity of the catalysts for the electro-oxidation of alcohols, such as the methanol oxidation reaction (MOR). Herein, a monolithic CuS@CuO/copper-foam electrode for the MOR with superior catalytic activity and almost 100% selectivity for formate is reported. In the core-shell CuS@CuO nanosheet arrays, the surface CuO directly catalyzes MOR, while the subsurface sulfide not only serves as an inhibitor to attenuate the oxidative power of the surface CuO to achieve selective oxidation of methanol to formate and prevent over-oxidation of formate to CO2 but also serves as an activator to form more surface O defects as active sites and enhances the methanol adsorption and charge transfer to achieve superior catalytic activity. CuS@CuO/copper-foam electrodes can be prepared on a large scale by electro-oxidation of copper-foam at ambient conditions and can be readily utilized in clean energy technologies.

MXene Aerogel Derived Ultra-Active Vanadia Catalyst for Selective Conversion of Sustainable Alcohols to Base Chemicals.

Selective oxidation reactions are an important class of the current chemical industry and will be highly important for future sustainable chemical production. Especially, the selective oxidation of primary alcohols is expected to be of high future interest, as alcohols can be obtained on technical scales from biomass fermentation. The oxidation of primary alcohols produces aldehydes, which are important intermediates. While selective methanol oxidation is industrially established, the commercial catalyst suffers from deactivation. Ethanol selective oxidation is not commercialized but would give access to sustainable acetaldehyde production when using renewable ethanol. In this work, it is shown that employing 2D MXenes as building blocks allows one to design a nanostructured oxide catalyst composed of mixed valence vanadium oxides, which outperforms on both reactions known materials by nearly an order of magnitude in activity, while showing high selectivity and stability. The study shows that the synthesis route employing 2D materials is key to obtain these attractive catalysts. V4C3Tx MXene structured as an aerogel precursor needs to be employed and mildly oxidized in an alcohol and oxygen atmosphere to result in the aspired nanostructured catalyst composed of mixed valence VO2, V6O13, and V3O7. Very likely, the bulk stable reduced valence state of the material together coupled with the nanorod arrangement allows for unprecedented oxygen mobility as well as active sites and results in an ultra-active catalyst.

Selective Oxidation of Methanol to Green Oxygenates – Feasibility Study of Fixed‐Bed and Membrane Reactors

AbstractA feasibility study of a conventional fixed‐bed reactor and a packed‐bed membrane reactor (PBMR) in distributor configuration is carried out for the selective oxidation of methanol to the oxygenates dimethoxymethane and methyl formate on a VOx/TiO2 catalyst. Kinetic experiments provided the reaction network and a reliable kinetic model of six main reactions involved. The PBMR offers significant advantages and potential for the formation of both target products due to an effective kinetic coupling of the oxidative dehydrogenation of methanol and the consecutive reaction steps to dimethoxymethane and methyl formate in a broad range of operation conditions.

Power management and system optimization for high efficiency self-powered electrolytic hydrogen and formic acid production

Hydrogen energy is regarded as an attractive carbon-based fuel alternative due to its advantages of zero pollution and high energy density. Water electrolysis driven by triboelectric nanogenerators (TENGs) has been considered a promising approach for green hydrogen production and the storage of renewable energy in chemicals. However, it is impeded by the slow green hydrogen production rate driven by TENGs and the low value of anodic oxygen product. In this paper, an advanced integrated system of hydrogen evolution reaction coupled with methanol selective oxidation reaction driven by a unidirectional current rotational freestanding triboelectric-layer mode Pulsed-TENG (UDC RF-Pulsed-TENG) after power management was developed, which produced green hydrogen at the cathode while producing the value-added chemical product formic acid at the anode. After power management, a constant voltage of 1.8 V can be applied to the electrochemical cell. Compared with the traditional non-constant voltage power management mode using a switch, the rate of green hydrogen production is increased by 1.68 times. The whole system can realize the green hydrogen production rate of 14.69 µL min−1, with the H2 Faraday efficiency (FE) of 100 %. High value-added formic acid can be prepared simultaneously and the yield of formic acid is 12.50 µg min−1, with the FE of 99.75 %. This research provides an effective method to realize the simultaneous and rapid production of high-purity green hydrogen and value-added formic acid driven by clean energy sources.

Highly efficient and robust nickel-iron bifunctional catalyst coupling selective methanol oxidation and freshwater/seawater hydrogen evolution via CO-free pathway

The production of green hydrogen by water electrolysis is often kinetically limited by the sluggish oxygen evolution reaction (OER) at the anode. Here, we prepared a bifunctional nickel foam supported NiFe2O4 spinel catalyst (i.e. NiFe2O4/NF) that is capable of facilitating the coupling of hydrogen evolution reaction (HER) with selective methanol oxidation reaction (SMOR) in seawater to produce formate via a CO-free pathway. At a cell potential of 2.0 V, the NiFe2O4/NF||NiFe2O4/NF catalyzed HER-SMOR system produces remarkably high current density (>800 mA cm−2) with high Faradaic efficiencies (FE) at both electrodes (>96 % for HER and >95 % for SMOR to formate). The NiFe2O4/NF||NiFe2O4/NF HER-SMOR system also exhibits excellent stability over 48 h of continuous operation. With H2 being the only gaseous product, the HER-SMOR electrolysis system could operate in the absence of a membrane. Furthermore, the NiFe2O4/NF||NiFe2O4/NF electrodes are sufficiently robust for continuously catalyzing HER-SMOR in seawater electrolysis, showing no sign of deactivation or chlorine oxidation reactions over 6 h of continuous operation at a high current density of 700 mA cm−2. Mechanistic investigation and DFT calculations reveal that SMOR proceeds via a CO-free pathway, with Ni and Fe as the active sites for methanol and OH activation, respectively.