Effect Of Sulfation By SO₂ And Regeneration For Cu/SSZ-13 Catalyst

Ammonia-selective catalytic reduction（NH₃-SCR）technology is one of the important means to effectively remove NO_x,whose core is the development of SCR catalyst with high performance.Cu/SSZ-13 is expected to be the only choice for the new generation of vehicle de NO_x catalyst,because of its excellent NH₃-SCR activity,wide temperature window and high N₂ selectivity.As sulfur is contained in the fuel,SO₂ in the exhaust gas will affect the activity of Cu/SSZ-13 catalyst.In this paper,the effects of SO₂ poisoning and regeneration on Cu/SSZ-13 catalyst were studied.The sulfurization deactivation mechanism of Cu/SSZ-13 catalyst was investigated through a series of samples with different degrees of sulfation,which were prepared by changing the SO₂ concentration and sulfation time.The results show that sulfation treatment has no effect on the CHA structure of Cu/SSZ-13catalyst.During the sulfation process,Cu²⁺reacts with SO₂,which leads to a decrease of Cu²⁺and appearance of Cu SO₄.The activity of catalyst at lower temperature decreased significantly because of the decrease of Cu²⁺.The regeneration mechanism of sulfur-poisoned Cu/SSZ-13 catalyst was investigated through a series of samples with different degree of regeneration,which were obtained by changing temperature and time during the regeneration process.The results show that hydrothermal regeneration treatment at a temperature lower than 700℃ has no effect on the CHA structure of Cu/SSZ-13 catalyst.Nonetheless,dealumination occurs when the regeneration temperature is higher than 700℃.During the regeneration process,Cu SO₄ decomposes into Cu O,and Cu O migrated to Cu²⁺,which makes the content of Cu²⁺gradually recovers and the activity at lower temperature improved.However,when regeneration temperature is higher than 700℃,the Br?nsted acid site will decrease,which leads to a decrease of activity at higher temperature.At the same time,Cu²⁺could not be completely restored due to dealumination,so the catalyst could not completely restore its activity to the level of the fresh sample.Hence the regeneration temperature should not be higher than 700℃ in the application.