title: Comparison of preparation methods for ceria catalyst and the effect of surface and bulk sulfates on its activity toward NH3-SCR.
abstract: A series of CeO2 catalysts prepared with sulfate (S) and nitrate (N) precursors by hydrothermal (H) and precipitation (P) methods were investigated in selective catalytic reduction of NOx by NH3 (NH3-SCR). The catalytic activity of CeO2 was significantly affected by the preparation methods and the precursor type. CeO2-SH, which was prepared by hydrothermal method with cerium (IV) sulfate as a precursor, showed excellent SCR activity and high N2 selectivity in the temperature range of 230-450 °C. Based on the results obtained by temperature-programmed reduction (H2-TPR), transmission infrared spectra (IR) and thermal gravimetric analysis (TGA), the excellent performance of CeO2-SH was correlated with the surface sulfate species formed in the hydrothermal reaction. These results indicated that sulfate species bind with Ce(4+) on the CeO2-SH catalyst, and the specific sulfate species, such as Ce(SO4)2 or CeOSO4, were formed. The adsorption of NH3 was promoted by these sulfate species, and the probability of immediate oxidation of NH3 to N2O on Ce(4+) was reduced. Accordingly, the selective oxidation of NH3 was enhanced, which contributed to the high N2 selectivity in the SCR reaction. However, the location of sulfate on the CeO2-SP catalyst was different. Plenty of sulfate species were likely deposited on CeO2-SP surface, covering the active sites for NO oxidation, which resulted in poor SCR activity in the test temperature range. Moreover, the resistance to alkali metals, such as Na and K, was improved over the CeO2-SH catalyst.
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control (SKLESPC), School of Environment, Tsinghua University, Beijing 100084, China.
authors.forename: Huazhen
authors.initials: H
authors.lastname: Chang
authors.forename: Lei
authors.initials: L
authors.lastname: Ma
authors.forename: Shijian
authors.initials: S
authors.lastname: Yang
authors.forename: Junhua
authors.initials: J
authors.lastname: Li
authors.forename: Liang
authors.initials: L
authors.lastname: Chen
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.forename: Jiming
authors.initials: J
authors.lastname: Hao
mesh_terms: D000393:Air Pollutants / Q000737:chemistry*; D000641:Ammonia / Q000737:chemistry*; D002384:Catalysis; D002563:Cerium / Q000737:chemistry*; D009569:Nitric Oxide / Q000737:chemistry*; D013431:Sulfates / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D000393:Air Pollutants; D013431:Sulfates; D002563:Cerium; D009569:Nitric Oxide; C030583:ceric oxide; D000641:Ammonia
keywords: CeO(2); Hydrothermal method; NH(3)-SCR; Surface sulfate species