Study On Performance For Partial Oxidation Of Methane By Honeycomb-like Ni-Based Catalysts And The Material Preparation

During the process of exploiting coal,it was often accompanied by the exposure to the environment of methane gas that was absorbed or dissociated on the coal,once the flame came out,that was easily caused to explode at any time.Taking into account the safe of mining work and avoiding waste of resources,people need to take measures for methane applied.After a simple treatment for high-concentration methane gas,it could be used for power generation and residential heating,etc;However,low-concentration methane gas will be directly discharged to the atmosphere or burnt because of the high cost of processing and low economic benefits.Taking this approach was not only harmful to the environment,but also a great waste of methane resources.In this study,low-concentration methane gas was converted into a middle-downstream product syngas by catalytic reaction,achieving the utilization of methane gas.Here,we choosed methane and air as raw materials to carry out partial oxidation of methane（POM）,it was significant for researcher to study catalysts at POM reaction,especially,the catalyst tended to reducing the catalytic activity and even deactivation afer carbon deposition and sintering happen under high temperature.In order to solve two unfavorable factors of coking deposition and sintering,a honeycomb-like Ni-based catalyst was prepared to improve the catalytic activity and stability by Ni nanoparticles were confined to a honeycomb-like support.The synthesized catalysts were characterized by SEM、TEM、XRD、H₂-TPR/TPD、TGA and N₂ adsorption-desorption techniques and so on,also investigated the effects of temperature and space velocity on POM reaction.Specific work as follows:1.3D honeycomb-like silica（3HL-SiO₂）was prepared via sol-gel coating method and ZrO₂ as layer for further modification（3HL-ZrO₂-SiO₂）.The average cell diameter of prepared material is about 10nm.The active component Ni particles were highly dispersed on the support.Compared with the activity of conventional catalysts was in order of Ni/3HL-ZrO₂-SiO₂<Ni/3HL-SiO₂<Ni/ZrO₂-SiO₂<Ni/SiO₂,the honeycomb-like catalysts had higher activity than conventional catalysts based on SiO₂ support,as a result of the limitation of the pore structure.The Ni/3HL-ZrO₂-SiO₂ catalyst showed superior anti-sintering and coking ability,CH₄ conversion up to 90%-92%was obtained.Improving the oxygen storage capacity from ZrO₂ and highly dispersed active-sites afford excellent catalytic activity.Furthermore,It was observed that the Conversion of CH₄ increases evidently with the increase of temperature at 600-900℃and the selectivity and conversion were lower than the equilibrium numerical values.The high temperature reaction was controlled by thermodynamics.2.The synthesis of different metal oxides（Nitrate as metal oxide La₂O₃、Yb₂O₃、CeO₂ raw materials）modified Ni/3HL-X-SiO₂（X:metal oxides）catalyst and compared with the first section ZrO₂ modified.The catalytic properties of Ni/3HL-CeO₂-SiO₂ and Ni/3HL-ZrO₂-SiO₂ were found to be arrounded to 90%.However,CeO₂ was used as coating modified material to make the product selectivity higher,H₂/CO value closed to 2:1.Moreover,nitrate as the raw material of CeO₂ was more economical compared to ZrO₂originates from metal alkoxides.3.During the honeycomb-like support synthesis process,the pore size of support was controlled by crystallization temperature was adjusted at 100℃、140℃、180℃and 210℃,respectively.The results showed that the specific surface area decreases and the pore size gradually increases with the increase of crystallization temperature,the honeycomb-like structure may partially collapse when the crystallization temperature was 210°C.Compared with the catalytic performance of Ni/3HL-CeO₂-SiO₂ synthesized at different crystallization temperature,it was found that the highest methane conversion（about 90%）when crystallization temperature was choosed for 140℃.Meanwhile,we investigated the influence of different airspeeds on the catalytic performance of the Ni/3HL-CeO₂-SiO₂ catalyst,it was found that the CH₄ conversion decreases and H₂、CO selectivity increased with the continuous increase of gas space velocity within a certain range.In addition,F127 was substituted in order of P123、PEG20000、CTAB and PVP surfactants,which were used as templates to synthesize different morphology of supports under the same condition.The CH₄ conversion was as high as 88%with mesoporous Ni/mCeO₂-SiO₂ catalyst that synthes ized via PVP surfactant.