The Study Of Co/AC Catalyst For Syngas Production From Methane Reforming Carbon Dioxide

Greenhouse (CO2+CH4) gas can be converted into syngas (CO+H2), which is an ideal raw material for Fischer-Tropsch synthesis to liquid fuel, methanol and dimethyl ether and other chemical products. But in view of Methane has a three-dimensional molecular structure rssults in a high degree of symmetry and stability. The electron transfer of the CO2needs20.4eV of energy, which has strong stability. For methane reforming carbon dioxide reaction achieves high transformation efficiency. It is necessary to solve the problem of high-temperature reactivity and selectivity of CH4-CO2reforming by the thermodynamic limit. Well known, catalyst could reduce the energy barrier of reforming reaction and improve the conversion efficiency of the feed gas. Obtaining the catalyst with low cost, high activity and high stability has always been a hot topic in this field.Currently, a large number of studies have focused on non-precious metals catalysts like nickel, cobalt catalyst. However, the active component loss and serious cokeing lead to the poor stability of the catalyst.The study found that active carbon has some merits such as well-developed porosity, high surface area, low cost to get, strong heat resistance, acid and alkali resistance and corrosion resistance, which are required to be carrier in the preparation of supported catalysts. In this paper, taking activated carbon (AC) as the carrier, cobalt, zirconium and cobalt as active components, using impregnation method to load active components, the reforming reaction investigated the catalytic performance by methane carbon dioxide.Though testing performance of catalysts, instrutment analysising, kinetic analysising, the main research achievments are as follows:1. The optimized and evaluated preparation condition and of Co/AC catalysts is that:adopting excess impregnation method to load active constituent, the optimum impregnation amount of active precursor Co (NO3)2·6H2O is1.14mol/L, the optimum calcination temperature is300℃, the calcination time is4h, the reduction temperature is550℃. The preparation conditions of the catalyst prepared in above conditions exhibits good catalytic activity, selectivity and stability at atmospheric pressure and900℃during45hours.2. H2-TPR characterization showed that the Co/AC catalyst has good performance reduction,the reduction of the intrinsic temperature is550℃, XRD, BET, SEM-EDX analysis showed the active ingredient of catalyst prepared by excess impregnation has more homogeneous distribution. Excessive active substance loading, high calcination temperature, Calcination time would form larger grain size of active metal on the carrier surface, thereby reduces the active ingredient surface area, blocks pore structure of the carrier,which is negative for the activity of the reforming reaction.3. The Co-Zr/AC catalyst prepared by co-impregnation has a good could catalytic performance under the middle temperature conditions, using co-impregnation method to load the active component,the Co(NO3)2·6H2O of optimum impregnation amount is1.14mol/L, the Zr(NO3)2·5H2O of optimum impregnation amount is0.10mol/L,the optimum calcination temperature is600℃, calcination time is4h, the reduction temperature is550℃. The preparation conditions of the catalyst prepared in above conditions exhibits good catalytic activity, selectivity and stability at atmospheric pressure and750℃during45hours.4. According to TG-DSC, H2-TPR, XRD, XPS, SEM-EDX analysis, compared the Co-Zr/AC catalyst and Co/AC catalyst cobalt, the addition of zirconium enhances the metal-support interaction effect, the bimetallic synergy action improves the active species dispersion on the carrier. Cobalt and zirconium alloy formed on the surface of the carrier suppresses the migration of cobalt species on the support, improves the ability of resistance to sintering of the catalyst, thereby increasing the catalyst activity and stability.5. Screening the optimum conditions of thermostatic and pressurized impregnation method by orthogonal test, the optimum impregnation amount of Co(NO3)2·6H2O and Zr(NO3)2·5H2O is1.14mol/L and0.10mol/L,respectively.The impregnation temperature is85℃, impregnation pressure is1.5MPa, impregnation time is1h. On the basis of same amount of impregnation, appropriately increasing the temperature of impregnating solution could accelerate diffusion rate of the active ingredient in the pore, thereby shortening the impregnation time. During the methane reforming carbon dioxide reaction enhancing reaction temperature is conducive to promote the reaction to carry out in the positive direction. Different H/C ratios of syngas could be achieved by adjusting the ratio of CH4/CO2in feed gas.6. The reaction of methane reforming carbon dioxide dynamics over Co-Zr/AC catalyst in the temlerature range of600～800℃is divided into two stages, firstly,the methane pyrolysis is dominant reaction in the temperature range of600～700℃and the reaction rate constants are as follows,k1=2.8×104×exp(-12142/RT),KCH4,1=6.07×10-3×exp(-44089/RT),Kco2;1=0.209xexp(-72747/RT). Secondly,the reaction of methane reforming carbon dioxide is dominant in the temlerature range of700～850℃and the reaction rate constants are as follows, k2=1.72×104×exp(-71432/RT),KCH4,2=5.3×10-3×exp (18722/RT), Kco2,2=0.183×exp(13709/RT).Comparin-g and analysising the experimental values and theoretical values on the basis of LH model, Basic model, Eley-Rideal I model, Eley-Rideal II model, we find the LH model has better fitting degree and shows the change in the reaction system with the varying of gas partial pressure.