Methyl Formate Selectivity Research Articles

Two-Membrane Dual Non-Aqueous/Aqueous Electrolyte Flow Cell Operation for Electrochemical Conversion of CO2 to Methyl Formate.

Recently, tandem cathodic reactions have been demonstrated in non-aqueous solvents to couple CO2 reduction to a secondary reaction to create novel species that are not produced in aqueous CO2 electrolysis. One reaction that can be performed with high selectivity and durability is the electrochemical conversion of CO2 to formic acid and in-situ esterification with methanol to produce methyl formate. However, the translation to a high-performance flow electrolyzer is far from trivial, as the non-aqueous catholyte leads to reactor challenges including flooding the gas diffusion electrode. Here, a two-membrane flow electrolyzer with both anion and cation exchange membranes was used with flowing methanol catholyte and aqueous anolyte. This design prevented methanol from flooding the cathode, which was a pervasive limiting issue for electrolyzers with a single membrane. Methyl formate production at 42.9 % faradaic efficiency was achieved with pure methanol in a flow electrolyzer with stable performance beyond 80 min. However, low-water-content catholyte compositions also led to increased cell resistance and lower operating current densities. Thus, with the present ionomer materials there is a tradeoff between methyl formate selectivity and current density depending on water concentration, highlighting a need for new ionomers tailored for desirable non-aqueous solvents such as methanol.

Unsaturated Penta-Coordinated Mo5c5+ Sites Enabled Low-Temperature Oxidation of C-H Bonds in Ethers.

Selective oxidation of C-H bonds under mild conditions is one of the most important and challenging issues in utilization of energy-related molecules. Molybdenum oxide nanostructures containing Mo5+ species are effective for these reactions, but the accurate identification of the structure of active Mo5+ species and the catalytic mechanism remain unclear. Herein, unsaturated penta-coordinated Mo5c5+ with a high fraction in MoOx fabricated by the hydrothermal method were identified as the active sites for low-temperature oxidation of dimethyl ether (DME) by the deep correlation of characterizations, density functional theory calculations, and activity results, giving a methyl formate selectivity of 96.3% and DME conversion of 12.5% at unreported 110 °C. Low-temperature electron spin resonance (ESR) and quasi in situ X-ray photoelectron spectra (XPS) with the designed experiments confirm that the Mo5c5+ species can be formed in situ. Molybdenum located at the pentachronic site is preferable to significantly promote the oxidation of the C-H bond in CH3O* at lower temperatures.

Probing synergistic effect of active Cu0 species and surface acidity of chainlike ZSM-5 supported copper catalysts in methanol dehydrogenation to methyl formate

A series of chainlike ZSM-5 supported Cu catalysts with the addition of citric acid (CA) was conveniently prepared using a complexation-impregnation method and employed in the methanol dehydrogenation to methyl formate (MF). The catalytic performance of Cux/CZ5 first increased and then decreased with increasing CA/Cu ratio, reached 35.0% methanol conversion and 88.3% MF selectivity for Cu1.8/CZ5, significantly higher than that of Cu/CZ5. The superior catalytic performance might be principally explained by the higher Cu0 concentration combined with abundant Brønsted acid sites, which are responsible for methanol conversion and MF selectivity, respectively. This work provides new insights into the synergy between Cu0 species and surface acidity of Cux/CZ5 catalysts for methanol dehydrogenation and offers a feasible and effective strategy for enhancement of the catalytic performance of copper-based catalysts.

Atomically precise copper dopants in metal clusters boost up stability, fluorescence, and photocatalytic activity

The structurally precise alloy nanoclusters have been emerged as a burgeoning nanomaterial for their unique physical/chemical features. We here report a rod-like nanocluster [Au12Cu13(PPh3)10I7](SbF6)2 (Au12Cu13), which was generated through a transformation of a [Au9(PPh3)8]3+ intermediate in the presence of CuI, unveiled by time-dependent UV-vis spectroscopy, electrospray ionization mass spectrometry as well as single crystal X-ray diffraction. Au12Cu13 is comprised of two pentagonal bipyramids Au6Cu units and a pentagonal prism Cu11 unit, where the copper and gold species are presented in +1 and 0 chemical states. The Cu-dopants significantly improved the stability and fluorescence (quantum yield: ~34%, 34-folds of homo-Au25(PPh3)10Br7). The high stability of Au12Cu13 is attributed to the high binding energy of iodine ligands, Au-Cu synergistic effects and its 16-electon system as an 8-electron superatom dimer. Finally, the robust Au12Cu13 exhibited high catalytic activity (~92% conversion and ~84% methyl formate-selectivity) and good durability in methanol photo-oxidation.

Crystalline Microporous MoVBiO Polyoxometalates for Indirect Oxidation of Methanol to Methyl Formate: Effects of Organic Additives on Crystals Size and Catalytic Performance

AbstractCrystalline porous Mo‐V‐Bi oxides (MoVBiO) were prepared by hydrothermal synthesis approach. The effects of organic additives (methanol and tartaric acid) on the morphology and particle size of the MoVBiO crystals were investigated. The size of MoVBiO crystals was tuned in the range of 30–300 nm. It was found that methanol accelerated the formation of crystal nuclei resulting in the crystallization of small particles (30 nm), while tartaric acid inhibited the nucleation thus resulting in MoVBiO crystals with a size of 300 nm. The as‐synthesized MoVBiO samples were used in the indirect oxidation of methanol to methyl formate. The MoVBiO crystals with a size of 30 nm, synthesized with methanol, showed a high methyl nitrite conversion of 92 % and methyl formate selectivity of 94 % at 140 °C. The catalyst exhibited a relatively slow but almost constant deactivation over 50 h due to deposition of reaction species. The small MoVBiO crystals (30 nm) with more surface active sites and accessibility showed high performance in the oxidation of methanol to methyl formate in contrast to the big crystals (300 nm).

Understanding of photocatalytic partial oxidation of methanol to methyl formate on surface doped La(Ce)[sbnd]TiO2: Experiment and DFT calculation

The photocatalytic partial oxidation of methanol to methyl formate (MF) under visible light irradiation on surface doped La(Ce)TiO2 was studied by the experimentation and DFT calculation. The La or Ce atoms could be doped in the surface lattice of TiO2 to form the bond of La(Ce)OTi but could not be doped in the body of TiO2. The crystal size of TiO2 was restrained from growth due to the surface lattice distortion resulted from La(Ce) bonding with surface oxygen. The band structure and surface hydroxyls can be tuned by the La or Ce distribution on the surface of TiO2. The rare earth on the surface of TiO2 can form impurity levels in the valence band and conduction band, reduce the band gap, change surface electron states, decrease the potential energy for surface hydroxyl formation, and reduce the energy barriers of the transition states from methoxy via formaldehyde to MF. The doped catalyst exhibited superior methanol conversion and MF selectivity in photocatalytic partial oxidation of methanol to MF under visible light irradiation. The surface hydroxyl group plays an important role in the reaction and were positively related to the methanol conversion and MF selectivity. The La doped catalysts exhibited better methanol conversion and MF selectivity than the Ce doped catalysts due to the faster recoverable surface hydroxyls and lower energy barriers to transition states. This study may contribute to design new visible light responsive catalyst for photocatalytic partial oxidation reaction and provide applicable green route to MF synthesis.

Methanol oxidation on Au(332): methyl formate selectivity and surface deactivation under isothermal conditions

Surface deactivation for partial methanol oxidation to methyl formate on Au(332) under oxygen-deficient conditions at low temperatures suggests a small number of highly active sites for methyl formate formation.

Effect of calcination temperature on the structure and performance of molybdenum-tin catalyst for DME oxidation

The Mo1Sn2 catalysts with a Mo/Sn molar ratio of 1:2 were prepared by the hydrothermal method, and their structure was regulated by changing the calcination temperature (400–700 °C). The effect of the structural transformation of catalysts on the performance of selective oxidation of dimethyl ether (DME) to methyl formate (MF) was studied. It was found that the Mo1Sn2 catalyst calcined at 400 °C exhibited good performance in the oxidation of DME to methyl formate, showing a DME conversion of 9.2% and the MF selectivity of 86.9% at 110 °C and under atmospheric pressure without the generation of COx. The catalysts were systematically characterized by XRD, Raman, XPS, TPD, H2-TPR and in-situFT-IR. The results showed that the low-temperature calcination was favorable for the formation of MoOx structure and more Mo5+ species on the catalyst surface, resulting in the enhanced acidity and redox ability of the catalyst, and the increase of medium to strong basic sites on the catalysts. In such case, the activity and methyl formate production of the catalyst were significantly promoted.

CuO Nanoparticle-Decorated TiO2-Nanotube Heterojunctions for Direct Synthesis of Methyl Formate via Photo-Oxidation of Methanol.

Methyl formate is widely employed as one of the important organic intermediates in C1 chemistry and as an environmentally benign chemical in the emerging area of “green chemistry”. We here study the catalytic effectiveness of CuO/TiO2-nanotube nanocomposites for the direct synthesis of methyl formate via methanol photo-oxidation in this paper. The CuO/TiO2-nanotube nanocomposites with 7% CuO weight loading give a promising photocatalytic performance (over 93.3% methanol conversion and 89.4% methyl formate selectivity) at 25 °C under 365 nm UV irradiation. The turnover frequency and the apparent quantum efficiency reach up to 22.9 molmethanol gcat–1 h–1 and 57.6% over 7% CuO/TiO2-nanotube, respectively, which is mainly because of the effective minimization of the recombination of photogenerated electrons and holes by the surface ultrasmall-sized CuO particles. Furthermore, these CuO/TiO2-nanotube nanocomposites exhibit excellent durability and robust nature during the catalytic processes of the methanol photo-oxidation to methyl formate. The experimental results demonstrate the promise of the robust CuO/TiO2 nanocomposites for efficient and green production of methyl formate, which may offer guidelines for the design of efficient catalysts for selective alcohol conversion to other valuable chemicals.

PdCu Single Atom Alloys for the Selective Oxidation of Methanol to Methyl Formate at Low Temperatures

The selective catalytic oxidation of methanol to methyl formate (MF) has been considered as an attractive route to produce MF, an important precursor in the chemical industry. Although supported Pd nanoparticles are active for the selective oxidation of methanol to MF, the relatively low MF selectivity and yield remains an unsolved issue. Herein, we show that adding a small amount of Pd into Cu forming PdCu single atom alloy (SAA) catalysts can catalyze the oxidation of methanol to MF selectively at low temperatures, with a high catalyst stability. The atomic dispersion of Pd atoms in the Cu matrix was confirmed by various in-situ characterization techniques. The activity and selectivity of PdCu SAA catalysts were compared to monometallic Cu and Pd catalysts, in a flow reactor at similar conditions. This work may guide the design of new SAA based catalysts for selective oxidation reactions.

MoO3-SnO2 catalyst prepared by hydrothermal synthesis method for dimethyl ether catalytic oxidation

Abstract MoO3-SnO2 composite metal oxide catalyst was synthesized by one-step hydrothermal synthesis method without precipitant. The effect of MoOx dispersion state on the catalytic performance of MoO3-SnO2 catalysts with different Mo/Sn molar ratios was investigated for dimethyl ether (DME) low-temperature oxidation to methyl formate (MF). MF selectivity reaches 77.6% with DME conversion of 22.0% over Mo1Sn2 at 150°C. The physiochemical properties of these catalysts were characterized by TEM, XRD, Raman, FT-IR, NH3-TPD and H2-TPR. The results showed that the addition of SnO2 into MoO3 affected the crystal structure of catalysts, forming MoOx species with different degree of dispersion on the surface of SnO2. The special architecture of MoOx-SnO2 plays a major role in modifying the acidity and the oxidizability of MoO3-SnO2 catalysts, leading to the obvious differences in catalytic activity.

Textual properties of Cu–Mn mixed oxides and application for methyl formate synthesis from syngas

Abstract Cu–Mn mixed oxides with different calcination temperatures were prepared using ammonia complexing method and evaluated for methyl formate (MF) synthesis from syngas with CaO–ZrO2 as co-catalyst. The influence of calcination temperature on the structure and properties of Cu–Mn mixed oxides was investigated by appropriate characterizations. Cu1.5Mn1.5O4 formed during the calcination of Cu–Mn catalyst at 450 °C and played a significant role in the MF synthesis. However, it partially decomposed into CuO and MnO2 when the calcination temperature exceeded 550 °C. Results showed that the optimum MF selectivity was obtained on Cu–Mn catalyst calcined at 450 °C, and the highest CO conversion was obtained on the Cu–Mn sample with calcination temperature of 550 °C. The reaction mechanism of MF synthesis from syngas over Cu–Mn mixed oxides and CaO–ZrO2 co-catalyst was thoroughly studied via typical model reactions, and the nucleophilic addition–elimination reaction mechanism was proposed.

Formation of Pt–Ag alloy on different silicas – surface properties and catalytic activity in oxidation of methanol

Pt–Ag alloy is formed on silicas if Ag/Pt ≥ 2.5 and gives the highest methyl formate selectivity in methanol oxidation.

Direct synthesis of methyl formate from syngas on Cu–Mn mixed oxide catalyst

Cu–Mn mixed oxides with different Cu/Mn molar ratios were prepared by ammonia complexation method, and their catalytic performances have been evaluated for the direct synthesis of methyl formate (MF) from syngas. The catalysts were characterized by N2 adsorption-desorption isotherm, XRD, TEM, SEM, FT-IR, XPS and TPR measurements. Results revel that incomplete spinel of Cu1.5Mn1.5O4, CuO and amorphous Mn species are formed in all Cu–Mn catalysts. The interaction between Cu and Mn in Cu–Mn catalyst delays the reduction of samples compared with pure Cu oxide. For the direct synthesis of MF from syngas, Cu–Mn catalysts showed higher catalytic activities and MF selectivities than pure Cu or Mn oxides. CO conversion increases and MF selectivity decreases with the rise of Cu/Mn ratios in catalysts, which could be attributed to the phase compositions, specific surface areas, and the reducibility of the catalysts.

Highly Efficient and Stable Vanadia–Titania–Sulfate Catalysts for Methanol Oxidation to Methyl Formate: Synthesis and Mechanistic Study

Vanadia–titania–sulfate nanocatalysts for methanol oxidation to methyl formate (MF) were prepared by coprecipitation. When calcinated at 400 °C, both methanol conversion and MF selectivity reached ∼98.5% at reaction temperatures of 140–145 °C. Characterizations with several experimental techniques revealed the catalysts as highly dispersed vanadia supported by anatase titania with acidic sites of significant strength and density. The catalysts also showed very high stability with lifetime exceeding 4500 h. Extensive density functional theory calculations using both cluster and surface models revealed MF to form via the hemiacetal mechanism, involving the condensation of methanol and formaldehyde at acidic sites and methanol and hemiacetal oxidations at redox sites. The alternative formyl mechanism was predicted kinetically much less favorable, showing these catalysts to work in a distinct mechanism from the rutile titania photocatalyst. Interestingly, methanol chemisorption at redox sites leads to the formation of acidic sites capable of catalyzing the condensation reaction.

Preparation and evaluation of Cu-Mn/Ca-Zr catalyst for methyl formate synthesis from syngas

Cu-Mn/Ca-Zr catalysts were prepared by mechanical mixing, sol-gel and impregnation methods. The phase structure, surface morphology and the chemical states of catalysts were characterized by XRD, TEM, SEM and XPS. The basic property and reducibility of catalysts were investigated by CO2-TPD and H2-TPR techniques. Several types of basic sites with different basicity could be observed on the surface of catalysts. The sample prepared by impregnation method has the lowest reducibility, and the sample prepared by sol-gel method shows the highest reducibility. The catalytic performance was evaluated for the direct synthesis of methyl formate from syngas in a slurry phase. The catalyst prepared by mechanical mixing method shows the highest CO conversion of 14.2% and methyl formate selectivity of 83.4% among these catalysts, which could be attributed to the large amounts of strong basic sites and low reducibility of the catalyst.

Thin-sheet microfibrous-structured nanoporous gold/Al fiber catalysts for oxidative coupling of methanol to methyl formate

Active, selective, and stable nanoporous gold (NPG) catalysts supported on Al fiber, with enhanced heat transfer, have been developed for the oxidative coupling of methanol to methyl formate. The NPG/Al fiber catalysts are obtainable by galvanically depositing AuAg alloy on a thin-sheet microfibrous structure using 50-μm Al fiber and subsequently dealloying by leaching Ag using HNO3 aqueous solution. At 100°C, NPG-7/Al fiber (Au loading: 7wt%) catalyst is capable of achieving ∼100% methyl formate selectivity with ∼25% methanol conversion of a 10vol% methanol feed at 5000mLgcat.−1h−1. Gold loading can be reduced to 1wt% with acceptable reactivity (35% conversion with 85% selectivity at 160°C). The catalyst is stable for at least 300h without NPG sintering. Lowering the Ag residual content of the NPG catalysts is essential for higher selectivity of methanol, by nature, due to the reduction in the amount of unselective surface O species.

Promoting effect of chloride ions on selective oxidation of methanol to methyl formate over zirconia-supported ruthenium oxide catalysts

The effect of chloride ions on a monoclinic ZrO2-supported RuOx (RuOx/m-ZrO2) catalyst with a Ru surface density of 0.3 Ru/nm2 was studied in the selective oxidation of methanol to methyl formate (MF) at a low temperature of 373 K. The m-ZrO2 support was Cl-free, and Cl− ions were introduced into the RuOx/m-ZrO2 catalyst by impregnation with zirconium oxychloride or ammonium chloride and subsequent thermal treatment in air at 673 K. The structures of these catalysts were characterized by X-ray diffraction, Raman and X-ray photoelectron spectroscopies. Their reducibility was probed by temperature-programmed reduction in H2. The RuOx domains were present as highly dispersed RuO2−4 structure on m-ZrO2 with similar reducibility for the RuOx/m-ZrO2 samples irrespective of modification with or without Cl− ions. Introduction of appropriate amounts of zirconium oxychloride into RuOx/m-ZrO2 led to a remarkable increase in the methanol oxidation rate and MF selectivity, whereas introduction of ammonium chloride or zirconyl nitrate significantly inhibited the catalytic performance of RuOx/m-ZrO2. The promoting effect of Cl− ions derived from zirconium oxychloride can be tentatively attributed to their roles in facilitating the adsorption of methanol and desorption of MF product or its intermediates. This finding provides novel insights into the promoting effect of Cl− ions on oxides-based catalysts for selective oxidation reactions.

Selective oxidation of dimethyl ether to methyl formate over trifunctional MoO3–SnO2 catalyst under mild conditions

Dimethyl ether oxidation was conducted over MoO3–SnO2 catalysts prepared from different Sn salt precursors. Over the MoO3–SnO2 catalyst prepared from SnCl4, methyl formate selectivity reached 94.1% at 433 K without the formation of COx. The performance of the catalyst was determined by the existence form of MoO3 and the different surface bonding of Mo and O of the catalyst.

Effective Dawson type polyoxometallate catalysts for methanol oxidation

Dawson type polyoxometallates K6P2MoxW18−xO62 (x=0, 5, 6) and α1 and α2-K7P2Mo5VW12O62 were prepared and characterized by BET, IR, UV–vis and 31P NMR spectroscopies and thermal analysis (TG and DTA) and tested in methanol oxidation at 260°C in the presence of molecular oxygen. The Dawson compounds were found to be active in this reaction and the product distribution (formaldehyde, methyl formate, dimethylether, dimethoxymethane) depends on the polyanion composition and on the framework symmetry. α-K6P2W18O62 exhibits an excellent catalytic performance with ca. 27% of methanol conversion and 98% of dimethylether selectivity. α1-K7P2Mo5VW12O62 and α2-K7P2Mo5VW12O62 show a similar activity (17–19% of conversion) with 49% of methyl formate selectivity and 41% of formaldehyde selectivity respectively. α-K6P2Mo6W12O62 is the most oxidizing catalyst and the most selective toward the methyl formate (ca. 53%).