Design And Performances Evaluation Of Heteroatoms Modified Ruthenium Catalysts For Acetylene Hydrochlorination

Polyvinyl chloride,as one of the largest plastic products in the world,is widely used in construction,agriculture,industry and daily necessities.Under the constraints of the“Minamata Convention”and the“Double-Carbon Goals”,higher requirements have been placed on the green and sustainable development of the PVC industry.Based on our country’s energy structure,it is mainly reflected in the influence of coal,lake salt and well salt resources.Vinyl chloride is mainly produced by acetylene hydrochlorination.Mercury dichloride catalyst is currently the main catalyst for acetylene hydrochlorination due to its high stability and high conversion.However,mercury dichloride is highly toxic and sublimation,and mercury-containing wastes are expensive to deal with and cannot be completely disposed,causing great damage to the human body and the environment.Therefore,it is urgent to develop green-friendly non-mercury catalysts to replace mercury-based catalysts.In recent years,scholars at home and abroad have carried out extensive research on noble metal catalysts for acetylene hydrochlorination.However,the ruthenium catalyst was deactivated due to the reduction of the active ruthenium species,the sintering of the active component due to high temperature,and the deposition of carbon covering the active site during the reaction process.Therefore,it is of great significance to explore the effective modification method and accurate catalytic mechanism to design and prepare ruthenium catalyst.First,a series of triazine ligands containing heteroatoms（N,O,S）with regular structure were selected as ligands to form stable complexes with the precursor ruthenium chloride trihydrate,and then the ruthenium-based carbon-supported catalysts for acetylene hydrochlorination were prepared on coconut shell activated carbon as a carrier and was then applied to acetylene hydrochlorination.The combined experiment and characterization results show that the catalyst with 1,3,5-triazine as the ligand has the best catalytic performance,and the acetylene conversion reaches 96.15%at 180℃and 360 h^-1.After 300 h reaction at 180℃and 90 h^-1,the acetylene conversion remained above 85%.The presence of heteroatom-containing azine ligands can effectively anchor and disperse the active components,and the local active components of the catalyst can achieve atomic-level dispersion.The DFT simulation results show that the strong coordination between the ligands and the ruthenium active components increases the adsorption and activation ability of the catalyst to the reactants,and the presence of the ligand effectively reduces the reaction energy barrier of the reaction and therefore accelerates the reaction rate.Secondly,a series of azole ligands containing N heteroatoms with regular structures were selected as ligands to form stable complexes with the precursor ruthenium chloride trihydrate,and the ruthenium-based carbon-supported catalyst prepared on coconut shell activated carbon as a carrier was applied to acetylene hydrochlorination.The combined experiment and characterization results show that the catalyst with1-isopropyl imidazole as the ligand has the best catalytic performance,and the acetylene conversion reaches 99.95%at 180℃and 180 h^-1.After 150 h reaction at 180℃and 180 h^-1,the acetylene conversion only decreased by 8.55%.The presence of azole ligands can effectively anchor and disperse the active components,and the local active components of the catalyst can achieve atomic-level dispersion.The DFT simulation results show that the strong coordination between the ligands and the ruthenium active components stabilizes the Ru species in a high valence state and makes the reduction of the Ru species more difficult,while increasing the catalyst’s ability to adsorb and activate reactants.Thirdly,a series of ionic liquids containing P heteroatoms with regular structure were selected as auxiliary agents to form stable complexes with the precursor ruthenium chloride trihydrate;then,ruthenium-based carbon-supported catalysts were prepared using coconut shell activated carbon as a carrier and applied in acetylene hydrochlorination.The experimental and characterization results show that the catalyst with butyltriphenylphosphonium chloride as the promoter has the best performance.Under the reaction conditions of 180℃and 720 h^-1,the acetylene conversion rate can reach 99.97%,and the catalyst stability test showed that the acetylene conversion did not decrease significantly after the reaction at 180℃and 180 h^-1for 200 h.The introduction of ionic liquid significantly improved the dispersity of the active component,and the stronger the interaction between anion and anion,the weaker the alkalinity of anion.The interaction between Cl^-and P⁺is enhanced with the increase of the alkyl side chain length,which further leads to the enhanced proton-accepting ability of Cl^-,which consolidates the interaction between the promoter and Ru species,and the ruthenium active species of high-valence content of the catalysts increased.The calculation of the reaction path by DFT simulation shows that the strong interaction between the promoter and the ruthenium active component effectively reduces the reaction energy barrier and accelerates the reaction rate.Finally,based on the economical consideration of the catalyst and the above research results,mesoporous spherical activated carbon was prepared with aniline as the precursor,and the single-atom catalyst was prepared by reacting with the precursor metal ruthenium chloride trihydrate for acetylene hydrochlorination.Combined with the experimental and characterization results,the acetylene conversion rate of ruthenium single-atom catalyst reached 98.05%at 180℃and 90 h^-1.The catalyst stability test showed that the acetylene conversion did not decrease significantly after the reaction at 180℃and 50 h^-1for 500 h.The ruthenium active components supported by the mesoporous functional carbon material prepared by using aniline as a precursor exists in the form of a single ruthenium atom,which greatly improves the utilization rate of noble metal atoms.The DFT simulation calculation of the reaction path shows that the reaction energy barrier can be lowered by activating the adsorption of C₂H₂at the vacancy defect Ru site.Moreover,the existence of Ru-N bond further adsorbed and activated HCl molecules,and therefore accelerated the reaction rate.