Study On Copper Based SAPO-34 Molecular Sieve For Low Temperature NH₃-SCR

Ammonia selective catalytic reduction of nitrogen oxides（NH₃-SCR）technology is the most widely used technology in denitration industry at present.For the sake of economy,the research on its low temperature is a hot spot.Its catalyst is easily affected by water vapor（H₂O）in flue gas at low temperature.Cu/SAPO-34 molecular sieve is a typical microporous molecular sieve with CHA structure.Because of its good low temperature denitrification activity and excellent high temperature hydrothermal stability,it has been widely studied in ammonia selective catalytic reduction of nitrogen oxides（NH₃-SCR）.At low temperature,the water molecules in flue gas will hydrolyze the Si-OH-Al bond of Cu/SAPO-34 molecular sieve,reduce the number of acid sites,and cause the loss of isolated Cu²⁺in active sites,resulting in the obvious decrease of activity of molecular sieve after low temperature hydrothermal treatment.Therefore,the Cu/SAPO-34 molecular sieves were modified by increasing the number of Cu²⁺and inhibiting the adsorption of H₂O.Firstly,Cu/SAPO-34 molecular sieves with double template agent system were synthesized to improve the acid properties of the molecular sieves.The molecular sieves with triethylamine（TEA）and morpholine（Mor）as double template agents were synthesized with large specific surface area and grain size,which were conducive to the adsorption and activation of reaction gas.Moreover,more acidic sites of the molecular sieves promoted the storage and migration of NH₃species.The temperature range of Cu/SAPO-34 molecular sieves is widened by 50 ^oC,but the increase of Cu²⁺quantity by this method is limited,and the water resistance of molecular sieves is not significantly improved,so only the improvement of acidity can not significantly improve the water resistance of molecular sieves.The synthesis of M-Cu/SAPO-34 molecular sieves with bimetallic system aims to increase the number of Cu²⁺active sites.Ce-Cu/SAPO-34 molecular sieves have excellent denitration activity and water resistance.The introduction of Ce can inhibit the production of Cu O and promote its conversion to Cu²⁺,thus improving the denitration activity of the catalyst.Compared with Cu/SAPO-34,the denitration rate of the catalyst in 150 ^oC aqueous flue gas has increased by about 8%.In addition,the effect of water molecules on Cu/SAPO-34 begins with its adsorption on the surface of molecular sieve,then enters the framework of molecular sieve,hydrolyzes Si-OH-Al bond,dealuminates Cu/SAPO-34 molecular sieve,and collapses the framework,resulting in the deactivation of molecular sieve.In this paper,we innovatively prevent the further diffusion of water molecules from the first step,and utilize the hydrophobicity of Silicalite-1 molecular sieve,The surface of Cu/SAPO-34 molecular sieves was coated with it to protect Cu/SAPO-34 molecular sieves and weaken the adsorption of water molecules.In this paper,the crystal was synthesized by secondary growth method and seed guide liquid method respectively Cu/SAPO-34@Silicalite-1 Compared with the core-shell molecular sieve,the water resistance of the molecular sieve synthesized by seed directed liquid method is better.The introduction of F^-ions into the seed guiding solution not only increases the proportion of Cu²⁺,but also makes the Silicalite-1 zeolite membrane more uniform and dense,and its water resistance is significantly improved.Compared with the core phase molecular sieve,the denitration rate of the Silicalite-1 zeolite membrane in the flue gas containing water at 150 ^oC has increased by about 12%.