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Ceria catalysts have attracted considerable interest in the NH3-SCR reaction. The modification of SO42− into CeO2 promotes the NH3-SCR reaction. NH3 adsorption property and four possible reaction paths are further design over CeO2 (111) and SO42−–CeO2 (111) surface. The results reveal that NH3 adsorption of the Lewis acid site is stronger than the Brønsted acid site, and the adsorption energies of the Lewis acid site range from − 0.397 to − 0.963 eV with the modification of SO42−. Thus, the introduction of SO42− into CeO2 increases the adsorption site stability of NH3. NH3 adsorption is the first step in NH3-SCR reaction, and then, the key intermediates such as NH2, NH2NO, NNOH, NH3NO2 species are found. Standard SCR reaction and fast SCR reaction constitute a catalytic cycle in CeO2 catalyst. The different paths of NH3NO2 and NH2NO formation are different, and it led to NNOH only emerge in the fast SCR reaction. Lewis acid site is main reaction site for the standard SCR reaction. Energy barriers of Lewis acid site range from 15.82 to 15.68 kcal/mol by the introduction of SO42−, which makes the NH3-SCR reaction easily occur. [ABSTRACT FROM AUTHOR]

For the selective catalytic reduction (SCR) of NO x by NH 3 , a variety of SO 4 2−/α-Fe 2 O 3 catalysts were created and utilized. The consequences manifest that the sulfation treatment signally boosted the NO x conversion of α-Fe 2 O 3. With varying SO 4 2− loadings, the T 90 of SO 4 2−/α-Fe 2 O 3 catalysts ranges from 10% SO 4 2−/α-Fe 2 O 3 (301 °C) > 15% SO 4 2−/α-Fe 2 O 3 (306 °C) > 5% SO 4 2−/α-Fe 2 O 3 (314 °C) > 20% SO 4 2−/α-Fe 2 O 3 (321 °C). The optimum concentration of sulfate treatment samples was 10% wt., producing approximately 100% NO x conversion at 325–400 °C. Although the introduction of SO 4 2− weaken the redox capacity of α-Fe 2 O 3 , the quantity and strength of acidic sites on SO 4 2−/α-Fe 2 O 3 was dramatically enhanced. Meanwhile, introducing SO 4 2− to α-Fe 2 O 3 hindered the ammonia oxidation process and increased the pore volume of the catalyst, enhancing SCR activity. In situ DRIFTS investigations demonstrated that NH 3 adsorbed on Brønsted acid sites displayed better stability over SO 4 2−/α-Fe 2 O 3 catalysts. Due to the decreased capacity of the catalyst surface to adsorb NO x , the E-R route prevails on 10% SO 4 2−/α-Fe 2 O 3 catalyst. [Display omitted] • SO 4 2− could effectively improve the SCR activity of SO 4 2−/Fe 2 O 3 catalyst. • The 10% SO 4 2−/α-Fe 2 O 3 catalyst showed >95% conversion of NO x at 325–400 °C. • SO 4 2− treatment can obviously enhanced the surface acidity of the catalyst. • The 10% SO 4 2−/α-Fe 2 O 3 catalyst mainly follows the E-R mechanism. [ABSTRACT FROM AUTHOR]

[Display omitted] • (NH 4) 2 SO 4 was used instead of liquid H 2 SO 4 to introduce SO 4 2− into V 2 O 5 /CeO 2 ; • NO x conversion is over 95 % at 225–400 °C on 2 %SO 4 2−- V 2 O 5 /CeO 2 ; • The introduction of SO 4 2− enhanced Brønsted acid sites and the formation of polymeric vanadyl species; • The NH 3 -SCR reaction over 2 %SO 4 2−-V 2 O 5 /CeO 2 followed the Langmuir-Hinshelwood and Eley-Rideal routes concurrently. Ceria-supported vanadia (VO x /CeO 2) catalyst has been extensively investigated in the field of NO x selective catalytic reduction with NH 3 (NH 3 -SCR) but is limited in practical application owing to its poor sulfur resistance and high-temperature activity. Herein, a series of SO 4 2− modified V 2 O 5 /CeO 2 catalysts were fabricated to improve the overall catalytic performance. The 2 %SO 4 2−-V 2 O 5 /CeO 2 catalyst exhibited above 95 % NO x conversion, 90 % N 2 selectivity in the temperature range of 225–400 °C and excellent SO 2 + H 2 O tolerance, which was much better than V 2 O 5 /CeO 2 catalyst. Characterization results showed that the introduction of SO 4 2− over V 2 O 5 /CeO 2 increased the Ce3+/(Ce3++ Ce4+) ratio to promote the formation of oxygen vacancies and promoted the generation of more conducive polymeric vanadyl species. The synergistic effect of the redox sites and acid centers provided moderate redox property and enhanced surface acidity, thus improving the adsorption of NH 3 and inhibiting the over-oxidation of NH 3 that occurs on V 2 O 5 /CeO 2. In-situ DRIFTS indicated that the NO x reduction over V 2 O 5 /CeO 2 and 2 %SO 4 2−-V 2 O 5 /CeO 2 followed the Langmuir-Hinshelwood and Eley-Rideal routes concurrently. This study can expound the reasonable design of vanadium-based catalysts for efficient NO x reduction in industry. [ABSTRACT FROM AUTHOR]