Investigation On The Strategies For Promoting Sulfur-resistance Of NH₃-SCR Catalysts

Nitrogen oxide（NO_x）,the main gaseous pollutant in the atmosphere,are harmful to human health and the environment.The emission control of NO_x has become a topic of extensive attention by researchers.Selective catalytic reduction of ammonia（NH₃-SCR）is widely used to remove NO_x from mobile source tail gas and fixed source flue gas.Among them,the commercial vanadium catalyst is difficult to achieve the NO_x removal requirements due to the narrow active temperature window,high temperature side reaction,biological toxicity and other defects.Ce based oxide catalyst is considered to be a promising alternative to V based catalyst due to its excellent oxygen storage/release performance and redox capacity.However,Ce-based catalyst is easily deactivated by SO₂ poisoning,which limits its further application.According to the above,the regeneration of sulfur poisoning catalyst and the improvement of sulfur resistance of CeTi catalyst were studied in this paper.Mo modified CeTi catalyst was prepared by different methods respectively,meanwhile the regeneration mechanism and anti-sulfur poisoning mechanism of catalyst were preliminarily investigated.（1）In this study,NH₄HSO₄ were loaded on CeTi composite oxide and Mo-doped formula to investigate the regeneration process and mechanism of these simulated S-poisoned catalyst.Compared with thermal regeneration,the cold plasma assisted regeneration process showed unique advantages.Through the characterizations of the regenerated catalysts,it was confirmed that the cold plasma treatment could not only maintain the structure of the catalysts but also accelerate the decomposition of NH₄HSO₄ and the desorption of sulfur species by optimizing the atmosphere.Although the NH₃-SCR activity of catalyst could not be recovered after the cold plasma regeneration process,the physicochemical property can be reconstructed by calcining the catalyst in pure O₂ atmosphere,resulting in the recovery of the catalytic activity.In summary,the path of regenerating S-poisoned catalyst,"poisoning-regeneration-reconstruction",was initially established,which provided an effective method for the regeneration of S-poisoned NH₃-SCR catalysts.（2）In order to improve the SO₂ resistance of CeTi catalyst,the CeTi@Mo catalysts were prepared by combining the self-polymerization of dopamine hydrochloride under alkaline conditions and its complexation with molybdate to enhance the sulfur resistance of CeTi catalysts.A series of characterizations revealed that most of the Mo was embedded in the CeTi catalyst lattice.The molybdenum interacts strongly with CeTi catalyst and substitution of some metal sites to change the structure of the physical phase.This change affects the valence distribution of the active component Ce to enhance the proportion of Ce³⁺,resulting in a significant enhancement of the redox performance of the modified catalyst.As a result,the low-temperature activity and sulfur resistance of the catalyst were enhanced.The mechanism of sulfur resistance of catalysts was investigated by in situ DRIFTS.The result showed that the excellent sulfur resistance of CeTi@Mo-10Mo catalyst may be attributed to its lower surface sulfate deposition rate.At the same time,the interaction between Mo and Ce makes it more difficult for Ce species to combine with sulfur to form bulk metal sulfates.