Catalitic Reforming Of CH₄ With CO₂ Over Ni（Mo）/(Ce_0.8Zr_0.2O₂)MgAl（O） Catalysts

Carbon dioxide reforming of methane (CRM) utilizes two abundantly available green-house gases to produce industrially important syngas, which can be used as the suitable feedstock for methanol, dimethyl ether, Fischer-Tropsch and Oxo synthesis due to the H2:CO ratio of about 1:1. CRM technology is not only applicable to industrially use methane in the dryland but also the technical backstopping for converting syngas by landfill gas or together gasification gas with pyrolysis gas of coal. So the CRM reaction has attracted widespread attention over the world in recent years. Non-noble metal Ni-based catalysts have been expected to be great potential of industrial application. However, Ni-based catalysts deactivate easily due to carbon deposition and/or metal sintering. Thus, it becomes shackles in industrial applications.Nano-Ni-Mg-Al mixed metal oxide catalysts have been widely used in catalytic reactions due to some excellent properties, such as moderate basicity, large specific surface, uniform particle size and ordered layer structure. In this work, Ni/MgAl(O) oxides nanocomposties were used for CRM. Ni-Mg-Al layered double oxides (LDO) derived from calcination of layered double hydroxides (LDH) that are prepared by co-precipitation method. In order to improve performance of catalysis, physicochemical properties and microstructur of Ni/MgAl(O) oxides nanocomposties was modified by surfactant.The effect of the surfactant-modified catalyst on performance of catalysis was investigated. In order to combine the coke formed during reforming reaction, a series of Ni-Mo/MgAl(O) catalyst were synthesized by adding small amount of Mo in Ni-Mg-Al system, it is desirable to further improve performance of catalysis. Try to take advantage of oxygen storage-release capacity and redox cycling property of CeZrO2 to eliminate carbon to improve performance of catalysis. Then a series of Ni-Mo/Ce0.8Zro.202-MgAl(O) catalyst were synthesized by adding different amounts of Ce0.8Zr0.2O2 in Ni-Mo-Mg-Al system.Catalysts mentioned above were evaluated in a fixed bed flow reactor at atmospheric pressure under GHSV= 60000 mL/gcat..h (CH4/CO2=l). After that the activity and stability of catalysts was examined.The relations between structure, physicochemical properties of catalyst and performance of catalysis were analyzed and discussed in detail by many characterization techniques such as N2 adsorption, XRD, TEM, SEM, H2-TPR, CO2-TPD-MS, NH3-TPD-MS and TPO-MS. The main conclusions in this article are as follows:The surfactant-modified catalyst displays different catalytic Performance.TEM shows that active site Ni of catalyst was well dispersed or partially encapsulated in other mediums. TPAOH makes particles uniformly isolate from each other to avoid aggregation while CTAB can non-uniformly encapsulate metal particals. So, only TH-LDO showed more than 95% initial conversion of CH4 and CO2. CB-LDO showed an induction period during reaction. However, the activity and stability was excellent at the temperature higher 800 ℃ such as 900℃ and 100℃.Ni-Mo/MgAl(O) catalyst exhibited excellent activity and stability. The addition of Mo could improve the nickel concentration on the catalyst surface. Therefore, the probability of Ni(200) growed by more active sites formed with the increase of the nickel concentration on the surface of the catalyst, MO0.6 had good reproducibility and showed optimal catalytic activity and stability, CH4 and CO2 conversions remained at 70% after 72h reaction.Ni-Mo/Ce0.8Zro.202-MgAl(O) catalyst showed good activity but weak stability. Some reasons can explain this trend. First of all, the mesoporous structure of hydrotalcite precursor was destroyed when CeZrO2 added. Secondly, the reaction temperature can not reach the thermodynamic temperature of the carbon elimination reaction.The activity of the catalyst was directly affected by the relative intensity of Ni (200) plane. Besides, texture, surface acidity or basicity of catalyst and strong metal-support interaction (SMSI) would inevitably affect the activity and stability. Carbon deposition is the. most significant mechanism of catalyst deactivation for DRM. The carbon deposited on the surface of the catalyst differs in morphology, such as nanotubes, graphene type, shell-type graphitic and filamentous, which causes blockage of the active sites and subsequent deactivation.