Effect Of Different Chemical Components In Vehicle Exhaust On The Catalytic Performance Of One-pot Synthesized Cu-SSZ-13

With the increasingly stringent emission standard for the lean-burn vehicles,selective catalytic reduction of NOx with NH₃ has been widely applied in the after-treatment system to control the NOx emission.The Cu-SSZ-13 was developed as the new commercial SCR catalyst,due to its excellent de NOx activity and superior hydrothermal stability.In the past five years,a lot of fundamental investigations have been done on Cu-SSZ-13,clarifying its active sites,reaction pathway as well as the deactivation mechanism during hydrothermal treatment.The topic of this thesis focus on investigation on the poisoning effect of pollutants in exhaust on Cu-SSZ-13.This work shows the poisoning ability of different pollutants to Cu-SSZ-13 and reveals their mechanism of poisoning effect on the catalysts.Moreover,regeneration strategies are proposed for the poisoned catalysts based on the poisoning mechanism.This provides theoretical guidance for improving the durability of Cu-SSZ-13 in applications.The Cu-SSZ-13 catalysts are prepared and compared with two different methods,i.e.one-pot method using Cu-TEPA as template and Cu ion-exchange method.It is easier to get the Cu-SSZ-13 with larger content of isolated Cu²⁺ions using one-pot method,causing the its better SCR activity than the sample prepared by Cu ion-exchange.Therefore,the one-pot Cu-SSZ-13 is selected for further poisoning investigation.SO₂ mainly suppress the activity of Cu-SSZ-13 in the temperature range in100-300 ?.The deposition of(NH₄)₂SO₄,the chemisorption of SO₂ on isolated Cu²⁺ions as well as the formation of Cu SO₄ cause the deactivation of Cu-SSZ-13.The blockage of pores due to deposition of(NH₄)₂SO₄ on Cu-SSZ-13 is the main reason.Regeneration at 600 ? removes both the(NH₄)₂SO₄ and chemisorbed SO₂ on pensioned Cu-SSZ-13,recovering most of the de NOx activity.However,the ultra-stable Cu SO₄ results in the incomplete recovery of the activity for the poisoned catalyst after regeneration at 600 ?.Impregnation of phosphoric acid on Cu-SSZ-13 is used to mimic the poisoning of the catalyst by phosphate in the exhaust gas.The P poisoning cause the loss of low-temperature activity of Cu-SSZ-13,due to the formation of Cu-phosphate species.However,the formation of aluminophosphate during hydrothermal treatment retard the dealumination for Cu-SSZ-13,improving its hydrothermal stability.Pt decreases the activity of Cu-SSZ-13 in 200-550 ?.In 200-350 ?,the Pt accelerate the reaction rate of NH₃ oxidation to N₂,causing the decline of de NOx activity of Pt doping Cu-SSZ-13.In 350-460 ?,the Pt promotes the reaction rate of NH₃ oxidation to NOx and reaction rate of NO oxidation to NO₂,further reducing the activity.Pt⁰ acts as the active site for those side reactions.However,during hydrothermal treatment,Pt⁰ is oxidized to PtOx,weakening the poisoning effect of Pt on Cu-SSZ-13.