Unique catalysis of Ni-Al hydrotalcite derived catalyst in CO_2 methanation: cooperative effect between Ni nanoparticles and a basic support

Ni-Al hydrotalcite derived catalyst （Ni-Al2O3-HT） exhibited a narrow Ni particle-size distribution with an average particle size of 4.0 nm. Methanation of CO2 over this catalyst initiated at 225℃ and reached 82.5% CO2 conversion with 99.5% CH4 selectivity at 350℃, which was much better than its impregnated counterpart. Characterizations by means of CO2 microcalorimetry and 27 Al NMR indicated that large amount of strong basic sites existed on Ni-Al2O3-HT, originated from the formation of Ni-O-Al structure. The existence of strong basic sites facilitated the activation of CO2 and consequently promoted the activity. The combination of highly dispersed Ni with strong basic support led to its unique and high efficiency for this reaction. Keywords

Improved activity of Ni/MgAl_2O_4 for CO_2 methanation by the plasma decomposition

CO2 methanation has been a hot topic because of its important application in the spacecraft and potential utilization of carbon dioxide. Nickel catalyst is active for this reaction. However, its activity still needs to be improved. Dielectric barrier discharge （DBD） plasma, initiated at ambient condition and operated at -150 ℃, has been employed in this work for decomposition of nickel precursor to prepare Ni/MgAl2O4. The plasma decomposition results in high dispersion, unique structure, enhanced reducibility of Ni particles and promoted catalyst-support interaction. An improved activity of CO2 methanation with a higher yield of methane has been achieved over the plasma decomposed catalyst, compared to the catalyst prepared thermally. For example, the methane yield of the plasma prepared catalyst is 71.8% at 300 ℃ but it is 62.9% over the thermal prepared catalyst. The catalyst characterization confirmed that CO2 methanation over the DBD plasma prepared catalyst follows pathway of CO methanation.

CO_2 methanation over TiO_2–Al_2O_3 binary oxides supported Ru catalysts

TiO_2 modified Al_2O_3 binary oxide was prepared by a wet-impregnation method and used as the support for ruthenium catalyst. The catalytic performance of Ru/TiO_2–Al_2O_3catalyst in CO_2 methanation reaction was investigated. Compared with Ru/Al_2O_3 catalyst, the Ru/TiO_2–Al_2O_3catalytic system exhibited a much higher activity in CO_2 methanation reaction. The reaction rate over Ru/TiO_2–Al_2O_3 was 0.59 mol CO_2·(g Ru)1·h-1, 3.1 times higher than that on Ru/Al_2O_3[0.19 mol CO_2·(gRu)-1·h-1]. The effect of TiO_2 content and TiO_2–Al_2O_3calcination temperature on catalytic performance was addressed. The corresponding structures of each catalyst were characterized by means of H_2-TPR, XRD, and TEM. Results indicated that the averaged particle size of the Ru on TiO_2–Al_2O_3support is 2.8 nm, smaller than that on Al_2O_3 support of 4.3 nm. Therefore, we conclude that the improved activity over Ru/TiO_2–Al_2O_3catalyst is originated from the smaller particle size of ruthenium resulting from a strong interaction between Ru and the rutile-TiO_2 support, which hindered the aggregation of Ru nanoparticles.

Influence of Zr, Ce, and La on Co_3O_4 catalyst for CO_2 methanation at low temperature

The Co3O4 and Zr-,Ce-,and La-Co3O4 catalysts were prepared,characterized,and applied to produce CH4 from CO2 catalytic hydrogenation in low temperature as 140–220℃.The results indicated that the addition of Zr,Ce,or La to the Co3O4 decreased the crystallite sizes of Co and the outer-shell electron density of Co^3＋,and increased the specific surface area,which would provide more active sites for the CO2 methanation.Especially,the addition of Zr also changed the reducing state of Co3O4 via an obvious change in the interaction between Co3O4 and ZrO2.Furthermore,Zr doped into the Co3O4 increased the basic intensity of the weak and medium basic sites,as well as the amount of Lewis acid sites,and Bronsted acid sites were also found on the Zr-Co3O4 surface.The introduction of Zr,Ce,or La favored the production of CH4,and the Zr-Co3O4catalyst exhibited the highest CO2 conversion（58.2%）and CH4 selectivity（100%）at 200℃,and 0.5 MPa with a gaseous hourly space velocity of 18,000 ml·g^-1（cat）·h^-1,and the catalytic activity of CO2methanation for the Zr-,Ce-,and La-Co3O4 exhibited more stable than Co3O4 in a 20-h reaction.

Methane reforming with CO_2 to syngas over CeO_2-promoted Ni/Al_2O_3-ZrO_2 catalysts prepared via a direct sol-gel process

CeO2-promoted Ni/Al2O3-ZrO2 （Ni/Al2O3-ZrO2-CeO2） catalysts were prepared by a direct sol-gel process with citric acid as gelling agent. The catalysts used for the methane reforming with CO2 was studied by infrared spectroscopy （IR）, thermal gravimetric analysis （TGA）, microscopic analysis, X-ray diffraction （XRD） and temperature-programmed reduction （TPR）. The catalytic performance for CO2 reforming of methane to synthesis gas was investigated in a continuous-flow micro-reactor under atmospheric pressure. TGA, IR, XRD and microscopic analysis show that the catalysts prepared by the direct sol-gel process consist of Ni particles with a nanostructure of around 5 nm and an amorphous-phase composite oxide support. There exists a chemical interaction between metallic Ni particles and supports, which makes metallic Ni well dispersed, highly active and stable. The addition of CeO2 effectively improves the dispersion and the stability of Ni particles of the prepared catalysts, and enhances the adsorption of CO2 on the surface of catalysts. The catalytic tests for methane reforming with CO2 to synthesis gas show that the Ni/Al2O3-ZrO2-CeO2 catalysts show excellent activity and stability compared with the Ni/Al2O3 catalyst. The excellent catalytic activity and stability of the Ni/Al2O3-ZrO2-CeO2 are attributed to the highly, uniformly and stably dispersed small metallic Ni particles, the high reducibility of the Ni oxides and the interaction between metallic Ni particles and the composite oxide supports.

Preferential adsorption behaviour of CH_4 and CO_2 on high-rank coal from Qinshui Basin,China

In order to better understand the prevailing mechanism of CO2 storage in coal and estimate CO2 sequestration capacity of a coal seam and enhanced coalbed methane recovery （ECBM） with CO2 injection into coal, we investigated the preferential adsorption of CH4 and CO2 on coals. Adsorption of pure CO2, CH4 and their binary mixtures on high-rank coals from Qinshui Basin in China were employed to study the preferential adsorption behaviour. Multiple regression equations were presented to predict CH4 equi- librium concentration from equilibrium pressure and its initial-composition in feed gas. The results show that preferential adsorption of CO2 on coals over the entire pressure range under competitive sorption conditions was observed, however, preferential adsorption of CH4 over CO2 on low-volatile bituminous coal from higher CH4-compostion in source gas was found at up to 1O MPa pressure. Preferential adsorp- tion of CO2 increases with increase of CH4 concentration in source gas, and decreases with increasing pressure. Although there was no systematic investigation of the effect of coal rank on preferential adsorp- tion, there are obvious differences in preferential adsorption of gas between low-volatile bituminous coal and anthracite. The obtained preferential adsorption gives rise to the assumption that CO2 sequestration in coal beds with subsequent CO2-ECBM might be an ootion in Qinshui Basins, China.

Study on the Methane Coupling under Pulse Corona Plasma by Using CO_2 as Oxidant

In this paper, the conversion of CO2/CH4 by using pulse corona plasma was studied at atmospheric pressure and ambient temperature. The effects of ratio of CO2/CH4, pulse voltage and repeated frequency of plasma discharge were first studied in the system.

Studies on the Reaction Mechanism of CO_2-Reforming of Methane over Co/γ-Al_2O_3 Catalyst

TPPR and XPS characterizations were combined to study the reaction mechanism of CO2reforming of methane to syngas over Co/γ-Al2O3 catalysts. CH4 shows a tendency to form surface carbons by deep dissociation at high temperatures. CO2 dissociation reaction also occurs at >673K. It is believed that carbide carbons are active species to generate CO by rcacting with o atoms dissociated from CO2. In the reaction,Co(0) particles are responsible for dissociating CH4 to form active C. abstracting an O atom from CO2 molecule, and transferring O atom to C to form CO.

A fluidized-bed model for NiMgW-catalyzed CO2 methanation

The reduction of carbon dioxide to methane by hydrogen("CO2 methanation")using renewable energy is a promising process for recycling CO2.Better catalysts and better reactors are both required for the practical application of CO2 methanation.This study examines how the operating parameters affect CO2 methanation in a highly efficient fluidized-bed reactor.We first measured the kinetics of the CO2 methanation reaction using an NiMgW catalyst,which has been reported to exhibit superior catalytic performance.We then developed a fluidized-bed reactor model based on an earlier model for CO2 methanation.The fluidized bed model indicated that the NiMgW was indeed superior to two other previously studied catalysts in terms of faster conversion of reactants and higher concentrations of product CH4 throughout the reactor.The overall rate of production of CH4 increased with temperature and H2/CO2 ratio and decreased as the inlet reactant flow rate,catalyst particle diameter,and catalyst particle sphericity increased.

Three-dimensionally ordered macroporous perovskite materials for environmental applications

Three-dimensionally ordered macroporous(3DOM)perovskite materials have attracted the interest from researchers worldwide due to their unique macroporous structure,flexible composition,tailorable physicochemical property,high stability and biocompatibility.In particular,they were widely used in environmental field,such as photocatalysis,catalytic combustion,catalytic oxidation and sensors.In this review,the recent progresses in the synthesis of 3DOM perovskite materials and their environmental applications are summarized.The advantages and the promoting mechanisms of 3DOM perovskite materials for different applications are discussed in detail.Subsequently,the challenges and perspectives on the topic are proposed.