Influence of thiourea modification on the NH3-SCR activity of CeO2: Simultaneous tuning morphology and surface acidity

Herein, thiourea (TA) was firstly used as the structure-directing agent to simultaneously tune the morphology and surface acidity of CeO2(w/o) synthesized via one-pot hydrothermal treatment, and exhibits better enhancement on its NH3-SCR activity than urea (UA). In addition, CeO2-TA(10) obtained at the suitable TA/Ce molar ratio of 10 presents the superior NH3-SCR activity in a broad temperature window. The introduction of thiourea promotes the formation of cubic CeO2 nanocubes in catalyst, but not the nanoparticles formed in CeO2(w/o) and CeO2-UA(10). Furthermore, the cubic CeO2 nanocubes mainly expose the crystal faces of {100}, which is helpful to the formation of more oxygen vacancies on the surface of CeO2-TA(10). At the same time, the formation of the specific sulfate species (CeOSO4) is also promoted under the influence of thiourea, thus simultaneously tunes the surface acidity of CeO2(w/o) by enhancing the Brønsted acid sites, although its Lewis acid sites are significantly decreased due to the diminution of the BET surface area. Compared with urea, the using of thiourea as the structure-directing agent also adjusts the physical-chemical properties of CeO2(w/o) and promotes its chemisorbed oxygen concentration. The results presented herein give a new thought for the development of state-of-the-art cerium-based catalysts for the NH3-SCR reaction.