CeO2 supports were prepared by calcination or precipitation method and 5% MoO3/CeO2 catalysts were prepared by incipient-wetness impregnation method. The catalytic performance of the 5% MoO3/CeO2 catalysts toward sulfur-resistant methanation was investigated. The results showed that the Mo/Ce-1 catalysts with CeO2 support prepared by calcination method exhibited the best sulfur-resistant methanation activity and stability with CO conversion as high as 75% while the Mo/Ce-3 catalysts the poorest. The supports and catalysts were characterized by N2-adsorption–desorption, temperature-programmed reduction (TPR), X-ray diffraction (XRD), Raman spectroscopy (RS) and scanning electron microscope (SEM). The results indicated that the saturated monolayer loading MoO3 on Ce-3 support was lower than 5% and there were some crystalline MoO3 particles on the surface of the Mo/Ce-3. The preparation method of CeO2 had a big influence on the specific surface area, the crystalline of CeO2, and the catalytic performance of the corresponding Mo-based catalyst for sulfur-resistant methanation.CeO2 support was prepared with calcinations and precipitation methods for sulfur-resistant methanation. The conversion of CO is as high as 75% under 1.2% H2S atmosphere on MoO3/CeO2 catalysts whose support is prepared with calcination method.Download high-res image (108KB)Download full-size image

•A novel double-chamber DBD reactor was designed for degrading aqueous MB.•Air can inhibit MB decomposition, while O2 can enhance MB decomposition.•The change of NO2−, NO3−, total oxidants and H2O2 was different in air and O2.•The MB degradation is the combined effects of high energy electron, O3 and OH.The decomposition of methylene blue (MB) via a novel double-chamber dielectric barrier discharge (DBD) reactor in different carrier gases (air and oxygen) was investigated. The results showed that the degradation efficiency of MB was 99.98% using O2 plasma for 20 min, while it was only 85.3% using air plasma for 100 min. In addition, the concentrations of nitrite, nitrate, ozone and hydrogen peroxide in aqueous phase and the oxidizing ability of the oxidants were measured to explore the various results obtained in different carrier gases. The formation of nitrogenous species was considered to be the main reason for the low degradation efficiency of the air plasma. The accumulation of oxidants enhanced the degradation efficiency of the MB in the O2 plasma. Both the combined effects of ozonation and plasma with oxygen bubbling and the reaction poisoning with air bubbling were enhanced in the double-chamber DBD reactor. The decomposition routes of MB and byproducts formation were also proposed.Download high-res image (93KB)Download full-size image

•The monolayer saturated coverage of MoO3 on CeO2 is about 5 wt.%.•CeO2 can be sulfided to Ce2O2S in sulfidation and/or methanation reaction.•Ce2O2S has higher catalytic activity toward sulfur-resistant methanation reaction.•5 wt.% MoO3/CeO2 possesses the best sulfur-resistant methanation performance.•The best calcination temperature of 5 wt.% MoO3/CeO2 is 600 °C.Synthetic natural gas (SNG) production from coal is reconsidered for the rising prices for natural gas and the hope for less dependency on natural gas import and reduction of greenhouse gas CO2 emission. In this paper, the effects of MoO3 loading amounts and calcination temperature on the catalytic performance of MoO3/CeO2 toward sulfur-resistant methanation were investigated. All the catalysts were prepared by incipient-wetness impregnation method and further characterized by N2 adsorption–desorption, temperature-programmed reduction (TPR), X-ray diffraction (XRD) and Raman spectroscopy (RS). The results show that CO conversion reached optimal value when loading 5 wt.% of MoO3 on the CeO2 support. Also, the “monolayer” saturated coverage of MoO3 over the prepared CeO2 support is about 5 wt.%. The MoO3/CeO2 catalyst with MoO3 loading amount of 5 wt.% and calcination temperature of 500 °C exhibits the highest activity for CO conversion.

Non-thermal plasma is an effective technology that produces hydrogen from methanol by plasma reforming. In this study, hydrogen was produced via methanol steam reforming in a dielectric barrier discharge micro-plasma reactor filled with a Cu/Al2O3 catalyst. Comparative experimental results obtained using the reactor with and without catalyst are reported. The methanol conversion and hydrogen yield with the activated catalyst were 17.89 and 21.86 % higher than those without the catalyst. The primary gaseous products changed from H2 and CO to H2 and CO2 after adding the Cu/Al2O3 catalyst. Methanol conversion increased with the discharge frequency and input power and decreased with an increase in the liquid feed rate. Methanol conversion reached 78.48 % over the Cu/Al2O3 catalyst at a 1.0 steam-to-carbon ratio, an 18.00 ± 0.05 kHz discharge frequency, 18.70 W of input power, 10.0 mL/min Ar flow rate and 0.0165 mL/min liquid feed rate. A plausible mechanism for hydrogen generation during steam–methanol reforming using the plasma–catalyst synergy effect is presented.

The effect of the sulphidation temperature on the activity and selectivity of a NiO–MoO3/γ-Al2O3 catalyst for sulphur-resistant methanation was systematically investigated. The prepared catalysts were subsequently characterised by N2-physisorption, temperature-programmed sulphidation, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The results obtained from characterisation demonstrated that the NiMoO4 species in the NiO–MoO3/γ-Al2O3 catalyst was sulphided when the sulphidation temperature was at or above 300 °C. Evaluation of the catalysts in sulphur-resistant methanation from syngas indicated that the sample sulphided at 400 °C has the highest likelihood of possessing a greater NiMoS type I structure. The catalytic activity decreased when the sulphidation temperature was above 400 °C. This decrease was primarily caused by the formation of MoS2 crystals and the progressive transformation of the NiMoS phase with increasing sulphidation temperature. The NiMoS type II structure did not display good performance for sulphur-resistant methanation because it resulted in the over-sulphidation of the NiMoS structure to form crystalline MoS2, which exhibited lower methanation activity.

Co3O4 catalyst was studied with respect to methanation in synthetic natural gas (SNG) production. Nanosized Co3O4 particles were prepared using a facile precipitation method. The different chemical valence states of Co species were obtained by adopting various reduction processes prior to methanation. The physicochemical properties of the obtained catalysts were characterized by N2-physisorption, TPR, TEM, XRD, XPS and TG technologies. The catalytic activities for CO methanation were investigated over catalysts with different reduction treatments. The catalyst subjected to a mild reduction process with the appearance of CoO species immediately exhibited 100% conversion of CO with a high space velocity of 11500 mL g−1 h−1 at 300 °C, 3 MPa. The catalyst without reduction of Co3O4 achieved the same high activity after 3 h exposure to syngas. When Co oxides were fully reduced to metallic Co, they showed no activity for methanation. Combining the results of characterization with evaluation of catalytic performance, it can be concluded that CoO is the active phase for CO methanation. The reduction treatment can improve the stability of the catalyst.

The effect of sulfidation temperature on the catalytic activity of CoO–MoO3/γ-Al2O3 catalyst toward sulfur-resistant methanation was studied. The prepared catalysts were characterized by N2-physisorption (BET), Temperature-programmed sulfidation (TPS), X-ray diffraction (XRD), Raman spectroscopy (RS), and Transmission electron microscope (TEM). The combined results of TPS, XRD, and RS indicated that CoMoO4 species in CoO–MoO3/γ-Al2O3 catalyst would be sulfided when the sulfidation temperature was at or higher than 300 °C. The catalyst sulfided at 400 °C exhibited the highest catalytic activity because there were the most CoMoS structures in the catalyst. When the sulfidation temperature was higher than 400 °C, the catalytic activity decreased with increasing sulfidation temperature. This decline was primarily caused by the formation of Co9S8 and MoS2 crystals. The CoMoS(II) formation did not favor the catalytic activity, because the formation of this species resulted in the occurrence of Co9S8 and crystalline MoS2 in catalysts.

•CuO/TiO2-GR composites are prepared by a two-step process.•Synergistic effect between CuO and GR enhances the photocatalytic activity of P25.•A optimal mass of graphene is reported in TiO2-GR and CuO/TiO2-GR composites.•The mechanism of electron transfer among the components is discussed.A highly efficient and visible-light-responsive CuO/TiO2-GR photocatalyst had been synthesized by a two-step process. The as-prepared CuO/TiO2-GR composites were characterized by X-ray diffraction, N2-physisorption, transmission electron microscope, X-ray photoelectron spectroscopy, Raman spectra, UV–vis diffuse reflectance spectra and Photoluminescence spectra. The results indicated that a chemical bond formed between GR and TiO2 in CuO/TiO2-GR composites. CuO/TiO2-GR composites had a higher photocatalytic activity for hydrogen production due to a synergistic effect between CuO and GR. The synergistic effect could efficiently suppress charge recombination, improve interfacial charge transfer, enhance visible-light adsorption and provide plentiful phtotocatalytic reaction active sites. The maximum hydrogen evolution rate of CuO/TiO2-GR-0.5 was 2905.60 μmol/(h·g), which was 20.20 times larger than pure P25.

A gliding arc discharge (GRD) reactor was used to decompose ethanol into primarily H2 and CO with small amounts of CH4, C2H2, C2H4, and C2H6. The ethanol concentration, electrode gap, input voltage and Ar flow rate all affected the conversion of ethanol with results ranging from 40.7% to 58.0%. Interestingly, for all experimental conditions the SH2/SCO selectivity ratio was quite stable at around 1.03. The mechanism for the decomposition of ethanol is also described.

Ceria–alumina composite supports were prepared by the co-precipitation (cop), impregnation (imp) or deposition–precipitation (dp) methods. Co–Mo catalysts supported on these composite supports were prepared by the imp method and their catalytic activities for sulfur-resistant methanation of synthesis gas were investigated. The catalysts were characterized by nitrogen adsorption, X-ray diffraction (XRD), and hydrogen temperature-programmed reduction (TPR). It was found that the preparation method of ceria–alumina composite support had a marked influence on the surface area, the interaction between ceria and alumina, and the catalytic performance for sulfur-resistant methanation. Among them, the ceria–alumina composite support prepared by dp method achieves the best methanation activity due to its smaller ceria particle size, better ceria dispersion, weak interaction between ceria–alumina as suggested by XRD and TPR results.

The hydrogen fuel cell is a promising option as a future energy resource and the production of hydrogen is mainly depended on fossil fuels now. In this paper, methanol reforming to produce H2 through dielectric-barrier discharge (DBD) plasma reaction was studied. Effects of the power supply parameters, reactor parameters and process conditions on conversion of methanol and distribution of products were investigated. The best reaction conditions were following: input power (45 W), material of inner electrode (stainless steel), discharge gap (3.40 mm), length of reaction zone (90.00 mm), dielectric thickness (1.25 mm), and methanol content (37.65%). The highest conversion of methanol and the yield of H2 were 82.38% and 27.43%, respectively.

Methane coupling to produce C2 hydrocarbons through a dielectric-barrier discharge (DBD) plasma reaction was studied in four DBD reactors. The effects of high voltage electrode position, different discharge gap, types of inner electrode, volume ratio of hydrogen to methane and air cooling method on the conversion of methane and distribution of products were investigated. Conversion of methane is obviously lower when a high voltage electrode acts as an outer electrode than when it acts as an inner electrode. The lifting of reaction temperature becomes slow due to cooling of outer electrode and the temperature can be controlled in the expected range of 60°C–150°C for ensuring better methane conversion and safe operation. The parameters of reactors have obvious effects on methane conversion, but it only slightly affects distribution of the products. The main products are ethylene, ethane and propane. The selectivity of C2 hydrocarbons can reach 74.50% when volume ratio of hydrogen to methane is 1.50.

We reported a coaxial, micro-dielectric barrier discharge (micro-DBD) reactor and a conventional DBD reactor for the direct conversion of methane into higher hydrocarbons at atmospheric pressure. The effects of input power, residence time, discharge gap and external electrode length were investigated for methane conversion and product selectivity. We found the conversion of methane in a micro-DBD reactor was higher than that in a conventional DBD reactor. And at an input power of 25.0 W, the conversion of methane and the total C2+C3 selectivity reached 25.10% and 80.27%, respectively, with a micro-DBD reactor of 0.4 mm discharge gap. Finally, a nonlinear multiple regression model was used to study the correlations between both methane conversion and product selectivity and various system variables. The calculated data were obtained using SPSS 12.0 software. The regression analysis illustrated the correlations between system variables and both methane conversion and product selectivity.The dielectric barrier discharge technology is a promising method for direct methane conversion. The conversion of methane was high and the carbon deposition reached the minimum for the micro-DBD reactor.Download full-size image

AbstractDielectric barrier discharge (DBD) was used for the generation of hydrogen from ethanol reforming. Effects of reaction conditions, such as vaporization temperature, ethanol flow rate, water/ethanol ratio, and addition of oxygen, on the ethanol conversion and hydrogen yield, were studied. The results showed that the increase of ethanol flow rate decreased ethanol conversion and hydrogen yield, and high water/ethanol ratio and addition of oxygen were advantageous. Ethanol conversion and hydrogen yield increased with the vaporization room temperature up to the maximum at first, and then decreased slightly. The maximum hydrogen yield of 31.8% was obtained at an ethanol conversion of 88.4% under the optimum operation conditions of vaporization room temperature of 120°C, ethanol flux of 0.18 mL/min, water/ethanol ratio of 7.7 and oxygen volume concentration of 13.3%.

The conversion of CH4 with oxygen and steam in a dielectric barrier discharge (DBD) was studied in the paper to discuss the effects of different factors, such as the content of feed-in gas, the applied voltage and frequency. The results showed that a lower ratio of CH4 to O2 always resulted in a higher conversion of CH4. When it was 2, the conversion reached 32.43% without steam introduced into the system. The main effect of steam was increasing the selectivity to CO. The reaction was accelerated and the selectivities to CO and hydrocarbons were enhanced by increasing the applied voltage. It was also observed that a higher frequency led to a lower current and then restrained the reaction.

Methyl glycolate is a good solvent and can be used as feedstock for the synthesis of some important organic chemicals. Catalytic hydrogenation of dimethyl oxalate (DMO) over copper-silver catalyst supported on silica was studied. The Cu-Ag/SiO2 catalyst supported on silica sol was prepared by homogeneous deposition-precipitation of the mixture of aqueous cuprammonia complex and silica sol. The proper active temperature of Cu-Ag/SiO2 catalyst for hydrogenation of DMO was 523-623 K. The most preferable reaction conditions for methyl glycolate (MG) were optimized: temperature at 468-478 K, 40-60 mesh catalyst diameter, H2/DMO ratio 40, and 1.0 h−1 of LHSV.

AbstractDirect decomposition of methanol has been investigated using gliding arc gas discharge (GRD) at atmospheric pressure. Depending on the experimental conditions of Ar flow rate, methanol concentration, the electrode gap, input voltage and vaporization room temperature (VRT), different conversions are achieved ranging from 51.0% to 81.7%. Interestingly, the selectivity to the production of hydrogen and carbon monoxide is kept almost constant under all the experimental conditions. The formation of little methane and C2Hx as a byproduct, and trace quantity of carbon dioxide are detected. The reaction channels of methanol decomposition induced by GRD plasma is proposed in detail.

Gliding arc gas discharge plasma was used for the generation of hydrogen from steam reforming of dimethyl ether (DME). A systemic procedure was employed to determine the suitable experimental conditions. It was found that DME conversion first increased up to the maximum and then decreased slightly with the increase of added water and air. The increase of total feed gas flow rate resulted in the decrease of DME conversion and hydrogen yield, but hydrogen energy consumption dropped down to the lowest as total feed gas flow rate increased to 76 ml·min−1. Larger electrode gap and higher discharge voltage were advantageous. Electrode shape had an important effect on the conversion of DME and production of H2. Among the five electrodes, electrode 2# with valid length of 55 mm and the radian of 34 degrees of the top electrode section was the best option, which enhanced obviously the conversion of DME.

The direct synthesis of C2 hydrocarbons (ethylene, acetylene and ethane) from methane is one of the most important task in C1 chemistry. Higher conversion of methane and selectivity to C2 hydrocarbons can be realized through plasma reaction. In order to explore the reaction process and mechanism, the possible reaction paths (1)–(4) were proposed on coupling reaction of methane through plasma and studied theoretically using semi-PM3 method [PM3 is parameterization method of modified neglect of diatomic overlap (MNDO)] including determining the transition state, calculating the activation energy and thermodynamic state functions and analyzing the bond order and intrinsic reaction coordinate. The reaction heat results indicate that the reactions (2) and (4) are exothermic, while reactions of (1) and (3) are endothermic. The activation energy results show that activation energy for reactions (1) and (2) was much lower than that of reaction paths (3) and (4). Therefore, paths (1) and (2) is the favorable reaction path energetically. More interestingly by comparing the intrinsic reaction coordinated (IRC) of the reaction paths (1) and (2), it is found that the variations of bond lengths in reaction path (1) has a crucial effect on the potential energy, while in reaction path (2), the adjustment of the system geometry also contributes to the whole potential energy of the system.

Citric acid hold great promise to improve the Mo-based catalyst performance for hydrogenation reaction applications. MoO3/CeO2-Al2O3 catalysts were prepared by impregnation method with adding citric acid into CeO2-Al2O3 composite supports and tested for sulfur resistant methanation. The syngas methanation activity increased with the increase of citric acid additive amount, and CO conversion could reach up 60% when the molar ratio of citric acid to Ce was 3. The prepared catalysts were characterized by BET, H2-TPR, XRD and XPS. The increased catalytic performance was mainly attributed to the increased amount of Ce species on the surface of catalysts which could decreased the interaction force between MoO3 and CeO2-Al2O3 supports. Additionally, the increased specific surface of CeO2-Al2O3 composite support was also in favor of catalytic performance.

Effects of additive gases on dimethyl ether (DME) conversion through dielectric barrier discharge (DBD) were investigated. Most of the additive gases tested in this work increased the conversion of DME, but decreased the yield of liquid product. However, the addition of O2 markedly increased both the conversion of DME and the yield of liquid product. The results show that when O2 volume fraction was 39.95%, the conversion of DME was close to 100% and the yield of liquid product reached 34.43%. Different additive gases resulted in different mass fractions variation of components in liquid products.

The effect of sulfidation temperature on the catalytic activity of CoO–MoO3/γ-Al2O3 catalyst toward sulfur-resistant methanation was studied. The prepared catalysts were characterized by N2-physisorption (BET), Temperature-programmed sulfidation (TPS), X-ray diffraction (XRD), Raman spectroscopy (RS), and Transmission electron microscope (TEM). The combined results of TPS, XRD, and RS indicated that CoMoO4 species in CoO–MoO3/γ-Al2O3 catalyst would be sulfided when the sulfidation temperature was at or higher than 300 °C. The catalyst sulfided at 400 °C exhibited the highest catalytic activity because there were the most CoMoS structures in the catalyst. When the sulfidation temperature was higher than 400 °C, the catalytic activity decreased with increasing sulfidation temperature. This decline was primarily caused by the formation of Co9S8 and MoS2 crystals. The CoMoS(II) formation did not favor the catalytic activity, because the formation of this species resulted in the occurrence of Co9S8 and crystalline MoS2 in catalysts.