Preparation Of Highly Efficient Ni/La₂O₃ Catalyst For Dry Reforming Of Methane And Reaction Mechanism Study

As one of the three major fossil fuels,natural gas is abundant and clean.With the breakthrough of shale gas mining technology,the amount of natural gas extraction is gradually increasing.Therefore,how to efficiently convert and utilize methane has become a hot topic in the world.Compared to other methane conversion technologies,dry reforming of methane(DRM)is receiving increasing attention because of its ability to produce syngas from natural gas with high levels of CO₂.Carbon deposition is the most serious problem in DRM.La₂O₃ has been widely studied due to its excellent carbon deposition resistance,but La₂O₃ has the disadvantage of small specific surface area.Firstly,in view of this disadvantage,a new method for synthesizing ordered mesoporous La₂O₃ support was proposed.The corresponding Ni/La₂O₃ catalyst was prepared and applied to DRM.The experimental results show that the mesoporous La₂O₃ support can increase the dispersion of Ni due to its large specific surface area and inhibit the sintering of Ni by the confinement effect of its mesoporous structure.Therefore,the catalyst has better activity and stability.The behavior of CO₂ activation at the interface between Ni and La₂O₃ was also explored,which provided a new understanding of the bifunctional mechanism of Ni/La₂O₃ catalyst.It is found that the interface between Ni and La₂O₃ can promote the formation of bidentate carbonate,and the bidentate carbonate can react with the coke precursor to inhibit the formation of coke.Therefore,the prepared mesoporous Ni/La₂O₃ catalyst increases the number of interface sites between Ni and La₂O₃ by promoting the dispersion of Ni,and thus has better performance of suppressing carbon deposition.La₂O₃ modified Ni/Al₂O₃ catalyst can easily cause Ni to be covered.The second work describes a new method of La₂O₂CO₃ modified Ni/Al₂O₃ catalyst to expose more Ni sites.The experimental results show that when La₂O₂CO₃ is used to modify Ni/Al₂O₃ catalyst,La₂O₂CO₃ can prevent Ni from entering the subsurface of alumina and forming NiAl₂O₄,increasing the number of Ni active sites.At the same time,La can cover the acidic sites of alumina and increase the alkalinity of the catalyst,thereby promoting carbon dioxide adsorption and activation,and inhibiting carbon deposition.This modification method can simultaneously improve the reactivity and stability of catalyst.