Synthesis Of Core-shell Ni?Pd?/CeO₂ Nanorod@SiO₂ Catalyst For Partial Oxidation Of Methane

Partial oxidation of methane?POM?reaction is currently one of the most effective methods for preparing synthesis gas,due to its advantages of high reaction efficiency,low energy consumption,and low investment cost.Ni-based catalysts and Pd-based catalysts have fairly good catalytic activity,and their applications are relatively extensive in the POM reaction.However,the biggest problem of these catalysts is that they are easier tend to agglomerate and sinter with the increase in reaction temperature,and the active sites covered by carbon deposits,leading to degradation and even deactivation of the reaction performance for the catalyst.Therefore,it is of great significance to study and develop catalysts with better high-temperature stability for the partial oxidation of methane under high temperatures.With its unique versatility and controllability,the core-shell catalysts can form different geometric effects,photoelectric effects and isolation and protection effect between core and shell layers.Selecting suitable nanomaterials to construct core-shell nanocatalysts can significantly improve the anti-sintering and anti-carbon deposit abilities of catalyst in the high temperature POM reaction.Among abundant core-shell materials,SiO₂ is a traditional wrapping material,which has good chemical inertness and can well improve the stability of the core particles,with relatively deep research and wide application.In this thesis,the application of Ni-based catalysts for the partial oxidation of methane was studied.The core-shell Ni/nanorod-CeO₂@SiO₂ catalyst was synthesized by microemulsion method.The experimental results show that choosing Ce02 nanorods as support can enhance the metal-support interaction,and promote the dispersion of active metals and inhibit the aggregation of metal particles.Meanwhile,a large number of surface lattice oxygens and adsorption oxygen provide by nanorods CeO₂ can reduce the formation of carbon deposition.With assistance of encapsulation effect of SiO₂,the catalyst not only maintain a highed metal dispersion,lower metal particle size under high temperature conditions,but also keep perfect rod-like CeO₂ morphology.Therefore,under high temperature and high space velocity,the initial methane conversion for the core-shell Ni/nanorod-CeO₂@SiO₂ catalyst with 5 wt%loading was 89%,and the CO selectivity was 96%.After 140 h in the high temperature POM reaction,the methane conversion and the CO selectivity would be steady to 86%and 94%,respectivily,exhibiting excellent POM catalytic performance and high temperature stability.A core-shell Pd/nanorod-CeO₂@SiO₂ catalyst was also prepared by microemulsion method investigated the relationship of Pd metal,support,and coating layer.Combined the structure properties of the core-shell catalyst studied through a series of characterization methodsand the performance evaluation of POM reaction.The results show that after 70 h in the high temperature POM reaction,the Pd/nanorod-Ce02@SiO₂ catalyst with 1 wt%loading still retains 81%methane conversion and 93%CO selectivity.It also has excellent catalytic performance and high temperature stability.