Search

A thermodynamic analysis of the conversion of dimethoxymethane by steam reforming and partial oxidation into a hydrogen-rich gas for fuel cell feeding has been carried out. Calculations were carried out at a pressure of 1 atm, temperatures of 100–1000°C, and the molar ratios O2/DMM = 0.5–3.5 and H2O/DMM = 1–5. The effects of temperature and reaction mixture composition on the equilibrium reaction product distribution and carbon (graphite) formation boundaries have been studied. The calculated data are compared with the known experimental results. [ABSTRACT FROM AUTHOR]

A composite material Fe–V/g-C3N4 prepared by impregnation achieved an efficient performance for heterogeneously catalytic oxidation of methanol to dimethoxymethane (DMM) and poly(oxymethylene) dimethyl ethers (POM) by O2 oxidant in batch reactor, exhibiting 34.3% conversion and > 99.0% selectivity to DMM and POM. However, a pioneered strategy for tuneable synthesis of DMM and POM was realized by controlling the reaction time. The experimental results revealed that FeVO4 and V2O5 nanoparticle crystallizes served as the active sites and higher specific areas 29.3–51.9 m3/g for the catalysts were jointly responsible for the high activity. Besides, the catalyst could be easily recovered and effectively reused. A composite material Fe–V/g-C3N4 with higher specific area exhibited efficient performance for heterogeneously catalytic oxidation of methanol to dimethoxymethane (DMM) and polyoxymethylene dimethyl ether (POM) in batch reactor using O2 oxidant. Moreover, a pioneered strategy for tunable synthesis of DMM and POM was realized by controlling the reaction time. The catalyst was easily recovered and had excellent recycle lifetime and stability. [ABSTRACT FROM AUTHOR]

Acidic zeolites are considered a kind of efficient catalysts in the synthesis of polyoxymethylene dimethyl ethers (PODEn) with the fomula of CH3O–(CH2O)n–CH3, a promising green diesel fuel or additive from methanol derivatives; however, the crucial parameters that determine PODEn yield and reaction mechanism over zeolite catalyst remains rather ambiguous. In this work, the relationship between the catalytic performance of HZSM-5 zeolite and Si/Al ratio and reaction temperature was revealed through PODEn synthesis from dimethoxymethane (DMM) and trioxymethylene (TOM). The results indicate that the Si/Al ratio and reaction temperature are interdependent in determining the PODEn yield; High Al HZSM-5 zeolites(Si/Al ≤ 50) show the highest PODE2-8 selectivity and yield only at 70–90 °C, whereas low Al zeolites (Si/Al ≥ 109) possess the better activity to PODE2–8 at 70–150 °C. The reaction mechanism was then investigated through in-situ IR characterization and DFT calculation. The important intermediates ZO-CH2OCH2OCH2OH, ZOCH2OCH3 and ZO(CH2O)nCH3 (ZOH: HZSM-5 zeolite) were detected by In situ IR spectra during the exposure of HZSM-5 to TOM, DMM and co-feed. DFT calculations further verified above reaction intermediates and elucidated the reaction elementary steps. Reaction mechanism was proposed as follows: the Brönsted acidic sites provided by Al–OH of HZSM-5 zeolite promote the dissociation of TOM to monomer CH2O and transform DMM to ZOCH2OCH3 and CH3OH; Next, the CH2O species react with short chain ZO(CH2O)nCH3, forming long chain ZO(CH2O)nCH3; After that, the PODEn products are formed by sealing ZO(CH2)nOCH3 with CH3OH. Ultimately, the difference of catalytic performance resulting from the effect of Si/Al ratio and reaction temperature, based on the proposed mechanisms, was given a logical explanation. The detailed reaction mechanism in the synthesis of polyoxymethylene dimethyl ethers from dimethoxymethane and trioxymethylene over HZSM-5 zeolite were investigated through a series of in-situ IR characterization and DFT calculation. Subsequently, the difference of catalytic performance resulting from the effect of Si/Al ratio and reaction temperature, was given a possible explanation. [ABSTRACT FROM AUTHOR]

Catalytic partial oxidation (PO) of dimethoxymethane (DMM) to syngas was investigated in a fixed-bed continuous flow reactor under ambient pressure and at 250–500 °C over Pt-, Rh- and Ru-supported on Ce0.75Zr0.25O2–δ catalysts. The Pt catalyst was found to be the most active and selective. It provided complete conversion of DMM to gas mixture containing ˃ 60 vol% of H2 and CO at 400 °C, GHSV = 10,000 h−1 using a reaction mixture: DMM:O2:N2 = 28.6:14.3:57.1 (vol%). [ABSTRACT FROM AUTHOR]

In this study, Cu/Zn/Al2O3-AC (AC = activated carbon) catalyst was synthesized and evaluated for dimethoxymethane (DMM) reformation to hydrogen. The Cu/Zn/Al2O3-AC catalyst was prepared using high surface area metal organic frameworks (MOFs) consisting of Cu3(BTC)2 (MOF-199) and Zn4O(BDC)3 (MOF-5) for Cu(II) and Zn(II) sources respectively, as precursors while γ-Al2O3 was applied as support. The synthesized catalyst was investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Brunauer-Emmett-Teller analysis (BET), Temperature programmed desorption (NH3-TPD) and Energy-dispersive X-ray spectroscopy (EDX) techniques. Complete DMM conversion was observed over Cu/Zn/Al2O3-AC catalyst (Cu:Zn:Al mole ratio of 6:3:2) under atmospheric pressure, T = 533 K, GHSV = 20 NL h−1 gcat−1, N2/H2O/DMM = 24/5/1 volume percent (vol%) with hydrogen productivity of 12.8 L H2 h−1 gcat−1 and 64% hydrogen concentration. Application of MOFs as precursors and modified activated carbon as an acidic component provided the catalyst with the porous structure and high specific surface area for the hydrolysis of DMM, subsequently, high selectivity and productivity of hydrogen was obtained. [ABSTRACT FROM AUTHOR]

The gas-phase carbonylation reaction of dimethoxymethane (DMM) to methyl methoxyacetate on different solid acids was studied. It was established that this reaction was accompanied by the occurrence of a side reaction of DMM disproportionation into dimethyl ether and methyl formate. It was shown that the activity of solid acids in both of the reactions depends on the strength of Brønsted acid sites according to an equation like the Brønsted–Evans–Polanyi–Semenov correlations. [ABSTRACT FROM AUTHOR]

The structure of catalysts based on vanadium oxide supported on different oxides (SiO, γ-AlO, ZrO, and TiO) was investigated. Their catalytic properties in the selective oxidation of methanol in a temperature range of 100-250°C were studied. It was shown that the nature of the support determines the structure of the oxide forms of vanadium. The supporting of vanadium on SiO and γ-AlO leads to the preferred formation of crystalline VO; the surface monomeric and polymeric forms of VO are additionally formed on ZrO and TiO. It was established that the crystalline VO oxide is least active in the selective oxidation of methanol; the polymeric forms are more active than monomeric ones. The mechanism of the selective oxidation of methanol to dimethoxymethane and methyl formate on the vanadium oxide catalysts is considered. [ABSTRACT FROM AUTHOR]

Formaldehyde (FA) biofiltration was evaluated over 310 days with and without ozone addition. Without ozone, the biofilter was able to treat formaldehyde at inlet loads (ILs) lower than 40 g m h, maintaining, under this condition, an average removal efficiency (RE) of 88 % for a few days before collapsing to zero. The continuous addition of ozone (90 ppbv) helped to recover the RE from zero to 98 ± 2 % and made it possible to operate at an IL of 40 g m h for long periods of operation (107 days). Furthermore, the ozone addition aided in operating the biofilter at a formaldehyde IL of up to 120 g m h values that have never before been reached. GC-mass spectrometry (MS) analysis showed that dimethoxymethane was the common compound in leachate during the performance decay. Also, the addition of ozone aided in maintaining an optimal pH in the biofilter with values between 7.5 and 8.2, due to the carbonate species formed during the ozone reactions with formaldehyde and its by-products. Thus, the pH control was confirmed and the alkalinity of the biofilter increased from 334.1 ± 100.3 to 1450 ± 127 mg CaCO L when ozone was added. Ozone addition diminished the exopolymeric substances (EPS) content of biofilm and biofilm thickness without affecting cell viability. Kinetic parameters suggested that the best conditions for carrying out FA biofiltration were reached under ozone addition. The addition of ozone during formaldehyde biofiltration could be a good strategy to maintain the pH and the steady state of the system under high ILs and for long periods of operation. [ABSTRACT FROM AUTHOR]

Ti-MWW was hydrothermally synthesized employing a SiO2–TiO2 xerogel. Characterization was performed using XRD, SEM, ICP, NH3-TPD, FT-IR, UV–vis spectroscopy, and the catalytic properties of Ti-MWW was evaluated over 1-hexene epoxidation, oxidative desulfurization of model sulfur compounds, direct conversion of methanol to dimethoxymethane, and allyl chloride epoxidation using H2O2. [ABSTRACT FROM AUTHOR]

The surface acidic properties of sulfated vanadia–titania catalysts prepared by various methods were investigated by adsorption microcalorimetry, using ammonia as probe molecule. The acidic characteristics of the samples were shown to be strongly affected by the preparation method, calcination temperature, and sulfur content. The samples prepared by sol–gel and mechanical grinding exhibited higher acidity than co-precipitated samples. Moreover, increasing the calcination temperature of co-precipitated samples resulted in a decrease in surface area from 402 to 57 m2 g−1 and sulfur content from around 4 to 0.2 mass%, but up to a certain point generated a stronger acidity. The optimal calcination temperature appeared to be around 673 K. [ABSTRACT FROM AUTHOR]

The VO x-TiO2 (VT-RC) and sulfated VO x-TiO2 (VTS-RC) catalysts were prepared by rapid combustion method (RC) and evaluated by the one-step oxidation of methanol to dimethoxymethane (DMM). The results showed that the VT-RC and VTS-RC catalysts were consisted of nano-particles and exhibited pore structure. Compared with the coprecipitated VO x-TiO2 (VT-CP) catalyst, the VT-RC catalyst showed more acidic sites and stronger reducibility. The addition of sulfate into VT catalyst further increased the number of acidic sites and had little effect on the reducibility. The catalytic test showed that the VT-RC catalyst exhibited high DMM selectivity (89.96% at 35% methanol conversion), which was further increased on VTS-RC catalyst (91.76% at 48% methanol conversion), and that was due to the larger number of acidic sites and stronger reducibility on these catalysts. Compared with the VT-CP catalyst, the VT-RC catalyst exhibited higher methanol conversion and DMM selectivity, which were further increased on VTS-RC catalyst.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Nitrogen-containing mesoporous carbon (N-MC) was synthesized by a templating method using SBA-15 and polypyrrole as a templating agent and a carbon precursor, respectively. The N-MC was then modified to have a positive charge, and thus, to provide a site for the immobilization of [PMo10V2O40]5−. By taking advantage of the overall negative charge of [PMo10V2O40]5−, H5PMo10V2O40 (PMo10V2) catalyst was chemically immobilized on the N-MC support as a charge-matching component. Characterization results showed that nitrogen in the N-MC played an important role in forming a nitrogen-derived functional group (amine group), and PMo10V2 catalyst was finely and chemically immobilized on the nitrogen-derived functional group of N-MC support. In the vapor-phase selective conversion of methanol, the PMo10V2/N-MC catalyst showed a higher conversion of methanol than the bulk PMo10V2 catalyst. Furthermore, the PMo10V2/N-MC catalyst showed a higher selectivity for dimethoxymethane (a product formed by bifunctional oxidation-acid-acid catalysis) and a higher selectivity for methylformate (a product formed by bifunctional oxidation-acid-oxidation catalysis) than the PMo10V2 catalyst. Reaction pathway for selective conversion of methanol to dimethoxymethane over PMo10V2/N-MC catalyst could be controlled by changing the methanol feed rate. [ABSTRACT FROM AUTHOR]

A series of SBA-15 supported H3PMo12O40 catalysts were prepared for the one-step oxidation of methanol to dimethoxymethane (DMM). The evaluation and characterization revealed that higher DMM selectivity obtained on the incipient wetness impregnation (IM) catalyst was related to the instability of H3PMo12O40 on it. Raman spectra showed that 12-molybdophosphoric acid was more stable on the direct synthesis (DS) catalyst than on the IM catalyst and the existence of SBA-15 support enhanced the stability of H3PMo12O40. Moreover, higher H3PMo12O40 loading resulted in more acid sites and low DMM selectivity, furthermore the thermal pretreatment on H3PMo12O40 influenced its structure and thus affected DMM selectivity. [ABSTRACT FROM AUTHOR]

The thermal conductivity of liquid dimethoxymethane was measured by the transient hot-wire method using a bare platinum wire in a temperature range from 240 to 360 K. The experimental data were fitted by a function of temperature. The average absolute deviation of experimental data from those calculated by the equation was 0.18%, and the maximum deviation was 0.41%. The uncertainty of the thermal conductivity was less than ± 2% with a coverage factor of k = 2. The uncertainty of the temperature was within ± 10 mK ( k = 2). [ABSTRACT FROM AUTHOR]