| With the large-scale development and application of fossil fuels by humans,environmental and climate issues have become increasingly prominent.It has become the consensus of all countries to reduce carbon dioxide emissions and explore new ways to store or transform the emitted carbon dioxide.Among them,carbon dioxide methanation requires relatively low conditions,and the products can be transported and applied on the basis of existing natural gas pipelines,which is a very promising direction.The metals Ru and Ni both show excellent catalytic performance in the catalytic carbon dioxide methanation,but Ni-based catalysts have a series of problems such as low unit activity,easy carbon deposition,and easy sintering.As a precious metal,Ru has higher activity.Stability is stronger.But at the same time,carbon dioxide methanation reaction still has a series of problems such as low low temperature activity and poor stability.Therefore,it is very important for Ru-based catalysts to improve metal dispersion,catalyst stability,and carbon dioxide adsorption and activation ability by adjusting the support.In summary,in this paper,metallic Ru is used as the active component,and the highly dispersed Ru is achieved by preparing an alumina carrier containing Al unsaturated coordination sites(Al3+penta)to directionally anchor Ru.By adjusting the hydrotalcite as The basicity of the metal oxide support of the precursor improves the ability of the catalyst to adsorb and activate C02,thereby realizing the development of a Ru-based catalyst with high activity and high selectivity for the methanation of carbon dioxide.The specific work is as follows:(1)Preparation of alumina oriented Ru-based catalyst and its catalytic performance for carbon dioxide methanationUsing sodium borohydride as the precipitant,pseudo-boehmite was prepared by the nucleation crystallization isolation method,and it was calcined and used to support Ru to obtain an Al3+penta anchored Ru-based catalyst.The directional anchoring effect of Al3+penta and Ru increases the dispersion of Ru and promotes the dissociation of H2 by Ru.At the same time,the residue of B can inhibit the formation of inactive carbonate during the reaction,which makes the catalyst exhibit The content of Al3+penta can be adjusted by changing the amount of sodium borohydride.As the content of Al3+penta increases,the catalyst performance will gradually improve.At 350℃,GHSV=12000 mlg-lh-1 The highest conversion rate of the catalyst reaches 77%,and the selectivity exceeds 99%.A 53-hour stability test was performed on the catalyst.The performance of the catalyst did not decrease under high temperature conditions,which proved that the interaction between Al3+penta and Ru is stable.(2)Preparation of metal oxide supported Ru-based catalyst with hydrotalcite as the precursor and study on its methanation performanceLanthanum calcium magnesium aluminum quaternary hydrotalcite was prepared by co-precipitation method,which was used to load Ru and directly reduce it to evaluate the performance of carbon dioxide methanation.Characterization and performance evaluation of a series of calciummagnesium-aluminum hydrotalcite-supported Ru catalysts with different La doping levels showed that the carbon dioxide conversion rate and selectivity reached the highest level with a suitable amount of La.The characterization found that the introduction of La changed the number and strength of the basic sites on the catalyst surface.Under the appropriate amount of La introduced,the number of basic sites on the catalyst reached the highest level.Further increasing the amount of La would destroy the hydrotalcite structure and cause alkalinity.Sex sites are reduced.At the same time,the introduction of an appropriate amount of La can change the reaction path of methanation.In the absence of La,methanation will be the path of CO and formate,and the introduction of appropriate amount of La will be the formate path without CO,thereby increasing Catalyst selectivity. |
