Controlled Synthesis Of Ni@Al₂O₃ Core Shell Catalyst For Dry Reforming Of Methane For Hydrogen Production

Based on global issues such as energy crisis and environmental pollution,adjusting energy structure and developing clean green energy have become an important guarantee for the"low carbon"of the economy.Hydrogen as a green energy source is a hot research point around the word in recent years.The efficient utilization of methane can alleviate energy crisis of coal and oil and pollution to the environment.Dry reforming of methane?DRM?has been extensively investigated since it can convert two greenhouse gases into H₂ and CO.However,at elevated temperature,severe coke and aggregation of active sites results in rapid deactivation.Industrial Ni-Al₂O₃ catalysts have been investigated extensively on account of their low cost and high initial activity for the DRM reaction.However,the major drawback of Ni-based catalysts is their deactivation at high operating temperatures caused by severe coking and the sintering of the active Ni species.Previous studies have shown that increasing the coke-resistance of Ni-Al₂O₃ catalyst is the driving force for the industrialization of methane dry reforming.Accordingly,in this study,Ni@Al₂O₃ core-shell catalysts have been prepared using a simple technique,which control the size of Ni nanoparticle and improve the interaction between Ni active species and the supports.In addition,the cold plasma was used to modify Ni@Al₂O₃ catalysts and combine with the confinement of core-shell structure to further enhance interaction between Ni and supports,thus improve coke resistance of catalysts for DRM reaction.The following researches include two parts.Part 1:Ni@Al₂O₃ core-shell catalysts were prepared by using an inverse micro-emulsion technique for methane dry reforming.It is revealed by TEM that the core-shell structure of Ni@Al₂O₃ have been synthesized successfully,in which Ni nanoparticle cores with an mean size of approximately 10.2 nm are encapsulated by Al₂O₃ shells with a thickness of approximately 3 nm.Compared with catalysts prepared by impregnation method,the structure confinement can decrease the Ni grain size and inhibit the agglomeration of Ni at high temperature,which was revealed by XRD and H₂ adsorption–desorption analysis.The results display that the stability and activity of catalysts was improved because of their confinement effect of Ni nanoparticles by the Al₂O₃ shell.XPS results prove that core-shell catalyst have more loose active oxygen species than Ni/Al₂O₃ catalyst,which is benefit for DRM reaction.In summary,the preparation of controllable structure Ni@Al₂O₃ play an important role for improving the catalytic performance of catalysts,which might offer a new method optimizing industry Ni-Al₂O₃ catalysts.Part 2:In this study,we focus on the aspect that confinement effects of the core-shell catalysts was treated by cold plasma and corresponding catalytic performance for DRM reaction for hydrogen.XRD results proved that much smaller Ni grain sizes and higher metallic Ni active surface areas can be achieved in the core–shell catalyst treated by cold plasma,which is major factor for superior DRM performance.After stability test,Ni crystallite sizes of core-shell catalysts treated by cold plasma still remain invariant,indicating that plasma treatment can inhibit the aggregation of Ni nanoparticle at temperature.This is one of the major reasons according for activity of catalysts for DRM reaction.TG-DSC and Raman results demonstrated that plasma treatment and confinement effects have benefits for coke with a low degree of graphitization.TPR results showed that samples treated by plasma increase desperation of Ni nanoparticles which can enhance the interaction between the active metallic Ni sites and Al₂O₃ supports.Much small Ni size and high Ni desperation can be achieved in the core-shell catalysts by plasma treatment,which could improve catalysts with industrial application potential for DRM for hydrogen and syngas production.