SO2-tolerant NOx reduction over SO42--coordinated Cu-SAPO-34 catalysts via protecting the reduction and re-oxidation of Cu sites

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Selective catalytic reduction of NOx from mobile source over Cu-SAPO-34 catalysts always suffer from sulfur poisoning in practical applications. The pore blockage and loss of active Cu species after sulfur poisoning seriously damage the NOx reduction ability of Cu-SAPO-34 catalysts. In this work, we used SO42--coordinated Cu-SAPO-34 catalysts to improve the sulfur resistance, which can still maintain over 90% NO conversion after 24 h of reaction in an SCR feed with high concentration of SO2. A series of characterization revealed that the process of CuII species being reduced to CuI and the reoxidation of CuI species to CuII is usually inhibited after SO2 poisoning in Cu-SAPO-34 catalysts, which in turn leads to the accumulation of ammonium bisulfate species (ABS) and the sulfation of Cu sites. The directed coordination of SO42- on Cu sites in Cu-SAPO-34 catalyst decreases the adsorption of SO2, hence the deposition of ABS is reduced and the sulfation of Cu sites is inhibited as well. This SO42--coordinated Cu-SAPO-34 catalyst can still carry out a complete SCR reaction cycle under the poison of SO2, which is resulted from the well-maintained reduction and re-oxidation process of Cu active sites. This work paves a way for the development of highly efficient anti-poisoning SCR catalysts in practical applications.