Construction And Performance Study Of Highly Stable Ruthenium-based Methane Dry Reforming Catalys

The excessive use of fossil energy has led to a sharp increase in carbon dioxide（CO₂）emissions.As one of the main greenhouse gases,CO₂ accelerates global warming,bringing a series of serious problems such as glacier melting,ocean acidification and soil desertification.In order to slow down the greenhouse effect,the Chinese Government solemnly pledged to the world to implement“the Double Carbon Strategy”.Of course,completely replacing traditional fossil fuels with clean energy can effectively control CO₂ emissions.However,due to the limitation of clean energy raw materials and grid connection,it is still difficult to completely replace fossil energy.Therefore,CO₂ fixation must be realized,and the best way is to realize the resource utilization of pollutants through the efficient catalytic transformation of CO₂.Dry reforming of Methane（DRM）is one of the important ways to realize CO₂recycling.The combination of CO₂“oxygen supply”reduction reaction and methane（CH₄）“oxygen demand”oxidation reaction generates syngas（H₂ and CO）,which provides important raw materials for new chemical products.Due to the strong stability of CH₄ and CO₂ molecules,DRM as a strong endothermic reaction requires high temperature（>640°C）.The catalyst agglomeration deactivation and high energy consumption caused by high temperature reaction are the key problems to be solved in the field.In addition,DRM is affected by methane decomposition or other side reactions,resulting in carbon deposits covering the catalyst surface,which affects the diffusion,adsorption and reaction of reactant molecules on the catalyst,resulting in catalyst deactivation.Therefore,the carbon deposition problem of DRM also needs to be solved urgently.Compared with traditional nickel（Ni）based catalysts,ruthenium（Ru）based catalysts exhibit superior carbon deposition resistance in DRM reaction.There is still a disadvantage that metal active centers are easy to agglomerate and sinter under high temperature conditions,and the thermal stability still needs to be improved.In this paper,the following four parts of work were carried out around the construction of highly stable Ru based catalysts and the structure-activity relationship of catalysts to DRM.First,with the aim to inhibit the gathering of Ru active sites at high temperature,a core-shell Ru@Si O₂ catalyst was developed by encapsulating Ru nanoparticles in a thermally stable carrier Si O₂ by an inverse microemulsion method.The Ru nanoparticles of Ru@Si O₂ exhibited the enhanced ability in anti-agglomeration at high temperature（700°C）owing to the support-metal interaction and the confinement effect of Si O₂ shell on Ru nanoparticles.Compared with uncoated Ru nanoparticles and supported Ru/Si O₂ catalyst prepared by traditional impregnation method,core-shell catalyst Ru@Si O₂ shows excellent stability and high CH₄ and CO₂conversion（～75%）.In addition,the trace carbon deposit produced in the catalytic DRM reaction is mainly amorphous,and the graphitization carbon deposit is effectively suppressed.Ru@Si O₂ still shows high activity and long lifetime under very low Ru loading（0.58%）and high WHSV of 34.8 L·g^-1·h^-1.Secondly,in order to solve the problem of high energy consumption in DRM reaction,Ce O₂ rich in redox electron pair Ce³⁺/Ce⁴⁺was introduced on the basis of core-shell structure catalyst Ru@Si O₂ to synthesize Ru@Si O₂-Ce_0.4.The redox electron pair Ce³⁺/Ce⁴⁺is conducive to improving the reaction rate,and the introduction of Ce O₂ leads to the formation of Ce-O-Si bond,which is conducive to promoting the adsorption and activation of CO₂ on the catalyst,and is conducive to improving the DRM activity.The effective catalysis of DRM is realized at lower reaction temperature（<640°C）.In addition,the enhancement of CO₂adsorption and activation increases the performance of oxidative removal of carbon species during the reaction to further inhibit carbon deposition.600c Ru@Si O₂-Ce_0.4 can realize the efficient catalysis of DRM at low temperature within the temperature range of 400°C to 600°C.In particular,the conversion of CH₄ and CO₂ at 600°C is 63%and 65%respectively,close to the thermodynamic equilibrium conversion.In order to further improve the stability of the catalyst,a new process for stabilizing Ru based catalyst by Ni embedded in the Mg O lattice was proposed.Ru_1.5/Ni₁-Mg O with Ni embedded in Mg O lattice was prepared by coprecipitation method.Under the conditions of high temperature and reducing atmosphere,the electronic structure of active metal Ru is regulated by the electron transfer from Ni to Ru,which leads to interaction.At the same time,the Ni-Ru interaction inhibits the agglomeration of Ru sites in the high-temperature reaction process,and improves the stability of the catalyst.The results showed that after stable operation at 800°C for1200 h,the conversion of CH₄ and CO₂ remained at about 90%,and there was no sign of deactivation.Since DRM reaction needs to be carried out at high temperature,it is very important to break through the traditional theory and technology and develop high temperature stable catalysts.In this paper,a strategy of vacancy stable metal catalysts was developed.Doped with Al³⁺in Mg O,a large number of Mg²⁺vacancies were generated by argon（Ar）heat treatment at high temperature,which stabilized Ru species.Subsequently,the catalyst with small size Ru active site was obtained by high temperature reducing gas activation.Ru₈/Mg O（Al）-Ar showed excellent activity,anti-carbon deposition performance and high stability in DRM at 800°C.The conversion rates of CH₄ and CO₂ were 92%and 96%,respectively.Almost no decrease in activity was observed after 100 h of reaction.