1. Metal oxide catalysts for NH₃-SCR reaction

1.1. Design of low V-loaded NH₃-SCR catalyst with high NH₃-SCR performance and study of its structure-activity relationship

By controlling the sulfur content of the TiO₂ support, the catalytically active center, oligomeric vanadia, was successfully designed and synthesized. The low-temperature SCR activity was significantly improved under low vanadium loading (1 wt.%). The whole NH₃-SCR process of V-based catalysts was clarified at the atomic level with DFT calculations. The coupling effect of oligomeric vanadia not only shortens the reaction pathway for the regeneration of redox sites but also substantially reduces the overall reaction barrier of the catalytic cycle. Theoretical and experimental evidence indicates that the oligomeric vanadyl species, rather than monomeric vanadyl species, determine the NH₃-SCR activity of vanadia-based catalysts, especially under low-temperature conditions. These results provide a theoretical basis for the development of high-efficiency NH₃-SCR catalysts, successfully guiding the improvement of the traditional V-based catalyst and realizing the industrial application of high-efficiency V-based catalysts (Sci. Adv., 2018, 4, eaau4637; Chin. J. Catal., 2014, 35, 1438; Catal. Sci. Technol., 2020, 10, 311).

1.2. Novel cerium-based oxide catalysts

Based on the in-depth understanding of the structure-activity relationship of NH₃-SCR catalysts and the reaction mechanism at different temperature ranges, we established a principle for the design of NH₃-SCR catalysts that involves close coupling of the redox and acid sites, which guided the development of metal oxide catalysts with excellent performance.

Through the combination of cerium and titanium oxides as redox and acidic components, respectively, a Ce-based NH₃-SCR catalyst was developed for the first time; through improvement of the preparation method, the coupling of cerium and titanium oxides was enhanced, and the activity of the catalyst was promoted; through the introduction of a promoter, the redox and acidic functions were enhanced simultaneously, and the temperature window was widened; through the complete substitution of Ti with W, the obtained Ce-W oxide catalyst with closely coupled Ce and W exhibited superior performance, enabling the NO_x emissions from a heavy duty diesel engine to meet the Euro V limit (Chinese V limit) in an engine bench test; through the introduction of a third component, recently we further improved the hydrothermal stability of the catalyst. (Catal. Commun., 2008, 9, 1453; Chem. Commun., 2011, 47, 8046; ChemCatChem., 2011, 3, 1286; Appl. Catal. B, 2012,115-116, 100; Chem. Commun. 2014, 50, 8445; Chin. J. Catal., 2014, 35, 1251; Catal. Commun., 2015, 59, 226; Catal. Sci. Technol., 2015, 5, 2290; Environ. Sci. Technol., 2018, 52, 11769; J. Catal., 2019, 369, 372)

1.3. Novel iron-based oxide catalysts

Under the guidance of design principles, a novel iron titanate catalyst was developed, by the combination of Fe oxides with strong redox functions and TiO₂ with excellent acid properties. On this catalyst, the Fe³⁺ and Ti⁴⁺ are connected with double oxygen bridges to form a short-range ordered structure, with redox centers and acid centers closely coupled at the atomic level, providing excellent NH₃-SCR activity and H₂O/SO₂ durability. Recently, through the combination of Fe oxides and WO₃, an Fe-W oxide catalyst with excellent NH₃-SCR performance was developed as well. (Chem. Commun., 2008, 2043; Appl. Catal. B: Environ., 2010, 96, 408; J. Phys. Chem. C, 2010, 114, 16929; App. Catal. B: Environ., 2011,103, 369; App. Catal. B: Environ., 2018, 230, 165) 

The redox-acid site coupling principle has successfully guided the development of highly efficient oxide catalysts, using the variable-valence metals Fe, Ce, and Mn as redox components, and Ti and W as acid components. These achievements provide a strong theoretical basis for the development and application of novel high-efficiency NH₃-SCR catalysts. At the same time, it theoretically guided the improvement of the traditional V-based catalyst and the industrial production of the improved V-based catalyst. The above-mentioned achievements won the second prize of the State Natural Science Award in 2019.

2. Ion-exchanged zeolite catalyst for NH₃-SCR reaction

2.1. Cu-based small-pore zeolites with high NH₃-SCR activity and hydrothermal stability

The DOC+DPF+SCR+AOC aftertreatment technique, which meets the upcoming Diesel Emission Standard China VI, was recently developed. The Cu-based Chabazite (CHA) small-pore zeolites Cu-SSZ-13 and Cu-SAPO-34 with high NH₃-SCR catalytic activity and hydrothermal stability were synthesized via a one-pot method for this application. (Environ. Sci. Technol., 2014, 48, 566; Chem. Eng. J., 2016, 294, 254)

2.2. NH₃-SCR reaction pathway over Cu-SSZ-13

An abnormal fast SCR reaction was found over small-pore Cu-SSZ-13 zeolite: under SCR reaction conditions, the presence of NO₂ inhibits NO_x reduction instead of promoting it. This is because the kinetic diameter of NO₂ is larger than the small pores (3.8 Å) of Cu-SSZ-13, resulting in the formation of NH₄NO₃ with NH₄⁺ on the Bronsted acid sites. The accumulated NH₄NO₃ would block the zeolite pores and further inhibit the NO reduction at Cu active sites. When the reaction temperature is above the decomposition temperature of NH₄NO₃, the NO reduction is recovered. By comparing the standard and fast SCR over the H-SSZ-13 support, it was found that NO can only be reduced at Cu active sites under standard SCR conditions. Under fast SCR conditions, however, NO can be also reduced at acid sites through the fast SCR reaction. (Catal. Sci. Technol., 2014, 4, 1104; J. Phys. Chem. C, 2018, 122, 25948)

2.3. Deactivation mechanism during hydrothermal aging of Cu-SSZ-13

Compared to fresh Cu-SSZ-13 (FR-Cu-SSZ-13), Cu-SSZ-13 hydrothermally aged at 750 ℃ (HA-Cu-SSZ-13) showed marked deactivation of NOx efficiency and a narrower operating temperature window. The activity of Cu-SSZ-13 hydrothermally aged at 750 ℃ decreased progressively in the presence of SO₂ (SA-Cu-SSZ-13), only achieving a maximum NO_x conversion of 85%. The characterization results of H₂-TPR, EPR, DRIFTS, XRD, and NMR techniques showed that the accumulation of CuO_x clusters from active Cu²⁺ and zeolite framework dealumination are the main reasons for hydrothermal aging deactivation. The presence of SO₂ increased the acidity of the aging atmosphere, therefore accelerating the destruction of the zeolite structure and transformation of Cu²⁺ to CuO_x clusters. (Catal. Today, 2019, 320, 84; Appl. Catal. B: Environ., 2020, 266, 118655)

Cu-SAPO-34 has a higher hydrothermal stability at high temperatures compared to Cu-SSZ-13. At low temperatures below 100℃, however, the Si-O-Al in Cu-SAPO-34 is easily broken down in damp environments, resulting in Cu accumulation, which further leads to catalyst deactivation. The low-temperature hydrothermal stability can be improved by introducing a small amount of Ce in the in-situ synthesized Cu-SAPO-34.

2.4. New-type Cu-based small-pore zeolites applied to NH₃-SCR reaction

Cu-SSZ-39 (AEI-type) has an extremely similar structure to that of Cu-SSZ-13 (CHA-type). The difference between the AEI and CHA structures is the connection mode of the double 6-rings (D6R). The neighboring D6Rs have mirror symmetry in AEI while being arranged in parallel in CHA. This leads to AEI zeolite having a more tortuous channel structure than CHA zeolite, which inhibits dealumination during hydrothermal aging and makes the zeolite framework structure more stable. On the other hand, Cu-SSZ-39 zeolite contains more paired framework Al, leading to Cu-SSZ-39 catalysts having more hydrothermally stable Cu²⁺-2Z species as compared to Cu-SSZ-13, and this makes Cu-SSZ-39 accumulate less CuOx during hydrothermal aging. Therefore, Cu-SSZ-39 has higher hydrothermal stability than Cu-SSZ-13. (Appl. Catal. B: Environ., 2020, 264, 118511)

Cu-SSZ-50 with RTH-type structure contains two types of 8MR pores and two active sites, which are highly active Cu²⁺ species (α species) next to 8MR and relatively inactive Cu²⁺ species (β species) next to rth cages. The Cu-SSZ-50 zeolite with active α species showed excellent NH₃-SCR performance, while Cu-SSZ-50 with β species only showed poor NH₃-SCR performance. After hydrothermal aging, active Cu²⁺ species easily transform to inert sites, resulting in low deNO_x activity. High Cu loading in the Cu-SSZ-50 catalyst limits the Cu mobility during hydrothermal aging and preserves more active Cu²⁺ species, resulting in good NH₃-SCR performance. (Catal. Sci. Technol., 2019, 9, 106)

Relevant publications

59) Yulong Shan, Jinpeng Du, Yunbo Yu, Wenpo Shan, Xiaoyan Shi*, Hong He*, Precise control of post-treatment significantly increases hydrothermal stability of in-situ synthesized Cu-zeolites for NH₃-SCR reaction, Appl. Catal. B, 266, (2020) 118655.

58) Yulong Shan, Wenpo Shan, Xiaoyan Shi, Jinpeng Du, Yunbo Yu*, Hong He*, A comparative study of the activity and hydrothermal stability of Al-rich Cu-SSZ-39 and Cu-SSZ-13, Appl. Catal. B, 264, (2020) 118511.

57) Na Zhu, Wenpo Shan*, Zhihua Lian, Yan Zhang, Kuo Liu, Hong He, A superior Fe-V-Ti catalyst with high activity and SO₂ resistance for the selective catalytic reduction of NO_x with NH₃. J. Hazard. Mater., 382, (2020) 120970.

56) Zhihua Lian, Shaohui Xin, Na Zhu, Qiang Wang, Jun Xu, Yan Zhang, Wenpo Shan*, Hong He, Effect of treatment atmosphere on the vanadium species of V/TiO₂ catalysts for the selective catalytic reduction of NO_x with NH₃. Catal. Sci. Technol, 10, (2020) 311-314.

55) Yulong Shan, Xiaoyan Shi, Jinpeng Du, Zidi Yan, Yunbo Yu, Hong He*, SSZ-13 synthesized by solvent-free method: A potential candidate for NH₃-SCR catalyst with high activity and hydrothermal stability, Ind. Eng. Chem. Res., 58, (2019) 5397-5403.  

54) Yulong Shan, Xiaoyan Shi, Zidi Yan, Jingjing Liu, Yunbo Yu, Hong He*, Deactivation of Cu-SSZ-13 in the presence of SO₂ during hydrothermal aging, Catal. Today, 320, (2019) 84-90.  

53) Guangyan Xu, Jinzhu Ma, Lian Wang, Zhihui Lv, Shaoxin Wang, Yunbo Yu*, Hong He*, The mechanism of the H₂ effect on NH₃-SCR over Ag/Al₂O₃: Kinetic and DRIFTS studies, ACS Catal., 9, (2019) 10489-10498.

52) Yulong Shan, Xiaoyan Shi, Jinpeng Du, Yunbo Yu, Hong He*, Cu-exchanged RTH-type zeolites for NH₃-selective catalytic reduction of NO_x: Cu distribution and hydrothermal stability, Catal. Sci. Technol., 9, (2019) 106-115.

51) Guangzhi He, Bo Zhang, Hong He*, Xueyan Chen, Yulong Shan, Atomic-scale insights into zeolite-based catalysis in N₂O decomposition, Sci. Total Environ., 673, (2019) 266-271.

50) Kuo Liu, Zidi Yan, Hong He, Qingcai Feng, Wenpo Shan*, The effect of H₂O on a vanadium-based catalyst for NH₃-SCR at low temperatures: a quantitative study of the reaction pathway and active sites, Catal. Sci. Technol., 9, (2019) 5593-5604.

49) Kuo Liu, Hong He*, Yunbo Yu, Zidi Yan, Weiwei Yang, Wenpo Shan, Quantitative study of the NH₃-SCR pathway and the active site distribution over CeWO_x at low temperatures, J. Catal., 369, (2019) 372-384.

48) Wen Xie, Yunbo Yu*, Hong He*, Shape dependence of support for the NO_x storage and reduction catalyst, J. Environ. Sci. 75, (2019) 396-407.

47) Na Zhu, Zhihua Lian, Yan Zhang, Wenpo Shan*, Hong He, The promotional effect of H₂ reduction treatment on the low-temperature NH₃-SCR activity of Cu/SAPO-18, Appl. Surf. Sci., 483 (2019) 536-544.

46) Na Zhu, Zhihua Lian, Yan Zhang, Wenpo Shan*, Hong He, Improvement of low-temperature catalytic activity over hierarchical Fe-Beta catalysts for selective catalytic reduction of NO_x with NH₃, Chin. Chem. Lett., 30 (2019) 867-870.

45) Zhihua Lian, Wenpo Shan, Meng Wang, Hong He*, Qingcai Feng*, The balance of acidity and redox capability over modified CeO₂ catalyst for the selective catalytic reduction of NO with NH₃, J. Environ. Sci. 79, (2019) 273-279.

44) Guangzhi He, Zhihua Lian, Yunbo Yu, Yang Yang, Kuo Liu, Xiaoyan Shi, Zidi Yan, Wenpo Shan, Hong He*, Polymeric vanadyl species determine the low-temperature activity of V-based catalysts for the SCR of NO_x with NH₃, Sci. Adv., 4, (2018) eaau4637.  

43) Zidi Yan, Xiaoyan Shi*, Yunbo Yu, Hong He, Alkali resistance promotion of Ce doped vanadium-titanic based NH₃-SCR catalysts, J. Environ. Sci., 73, (2018) 155-161.

42) Jingjing Liu, Xiaoyan Shi, Yulong Shan, Zidi Yan, Wenpo Shan, Yunbo Yu, Hong He^*, Hydrothermal stability of CeO₂-WO₃-ZrO₂ mixed oxides for selective catalytic reduction of NO_x by NH₃, Environ. Sci. Technol., 52, (2018) 11769-11777.  

41) Yulong Shan, Xiaoyan Shi, Guangzhi He, Kuo Liu, Zidi Yan, Yunbo Yu, Hong He*, Effect of NO₂ addition on the NH₃-SCR over small-pore Cu-SSZ-13 zeolites with varying Cu loadings, J. Phys. Chem. C, 122, (2018) 25948-25953.

40) Wenpo Shan, Yang Geng, Yan Zhang, Zhihua Lian, Hong He*, A CeO₂/ZrO₂-TiO₂ catalyst for the selective catalytic reduction of NO_x with NH₃, Catalysts, 8, (2018) 592-603.

39) Zhihua Lian, Wenpo Shan, Yan Zhang, Meng Wang, Hong He*, Morphology-dependent catalytic performance of NbO_x/CeO₂ catalysts for selective catalytic reduction of NO_x with NH₃, Ind. Eng. Chem. Res., 57, (2018) 12736-12741.

38) Fudong Liu, Wenpo Shan, Zhihua Lian, Jingjing Liu, Hong He*, The smart surface modification of Fe₂O₃ by WO_x for significantly promoting the selective catalytic reduction of NO_x with NH₃, Appl. Catal. B, 230, (2018) 165-176.

37) Can Niu, Xiaoyan Shi, Fudong Liu, Kuo Liu, Lijuan Xie, Yan You*, Hong He*, High hydrothermal stability of Cu-SAPO-34 catalysts for the NH₃-SCR of NO_x, Chem. Eng. J., 294, (2016) 254-263.

36) Can Niu, Xiaoyan Shi*, Kuo Liu, Yan You, Shaoxin Wang, Hong He, A novel one-pot synthesized CuCe-SAPO-34 catalyst with high NH₃-SCR activity and H₂O resistance. Catal. Commun., 81, (2016) 20–23.

35) Weiwei Yang, Fudong Liu*, Lijuan Xie, Zhihua Lian, Hong He*, The Effect of V₂O₅ Additive on the SO₂ Resistance of Fe₂O₃/AC Catalyst for NH₃-SCR of NO_x at Low Temperatures, Ind. Eng. Chem. Res., 55, (2016) 2677-2685.

34) Shipeng Ding, Fudong Liu*, Xiaoyan Shi, Hong He*, Promotional effect of Nb additive on the activity and hydrothermal stability for the selective catalytic reduction of NO_x with NH₃ over CeZrO_x catalyst, Appl. Catal. B, 180, (2016) 766-774.

33) Xiaoyan Shi*, Hong He, Lijuan Xie, The effect of Fe species distribution and acidity of Fe-ZSM-5 on the hydrothermal stability and SO₂ and hydrocarbons durability in NH₃-SCR reaction, Chin. J. Catal., 36, (2015) 649-656.

32) Shipeng Ding, Fudong Liu*, Xiaoyan Shi, Kuo Liu, Zhihua Lian, Lijuan Xie, Hong He*, Significant promotion effect of Mo additive on novel Ce-Zr mixed oxide catalyst for the selective catalytic reduction of NO_x with NH₃, ACS Appl. Mater. Interfaces., 7, (2015) 9497-9506.

31) Lijuan Xie, Fudong Liu, Xiaoyan Shi, Feng-Shou Xiao, Hong He*, Effects of post-treatment method and Na co-cation on thehydrothermal stability of Cu–SSZ-13 catalyst for the selective catalytic reduction of NOx with NH₃, Appl.Catal. B., 179, (2015) 206-212.

30) Kuo Liu, Fudong Liu, Lijuan Xie, Wenpo Shan, Hong He*, DRIFTS study of a Ce-W mixed oxide catalyst for the selective catalytic reduction of NO_x with NH₃, Catal. Sci. Technol., 5, (2015) 2290-2299.

29) Zhihua Lian, Fudong Liu*, Hong He*, Kuo Liu, “Nb-doped VO_x/CeO₂ catalyst for NH₃-SCR of NO_x at low temperatures, RSC Adv., 5, (2015) 37675-37681.

28) Wenpo Shan, Fudong Liu*, Yunbo Yu, Hong He*, Chenglin Deng, Xinyun Zi, High-efficiency reduction of NO_x emission from diesel exhaust using a CeWO_x catalyst, Catal. Commun., 59, (2015) 226-228. 

27) Zhihua Lian, Fudong Liu, Hong He*, Effect of preparation methods on the activity of VOx/CeO₂ catalysts for the selective catalytic reduction of NO_x with NH₃, Catal. Sci. Technol., 5(1), (2015) 389-396. 

26) Zhihua Lian, Jinzhu Ma, Hong He*, Decomposition of high-level ozone under high humidity over Mn–Fe catalyst: The influence of iron precursors, Catal. Commun., 59, (2015) 156-160.

25) Zhihua Lian, Fudong Liu, Hong He*, Enhanced activity of Ti-modified V₂O₅/CeO₂ catalyst for the selective catalytic reduction of NO_x with NH₃, Ind. Eng. Chem. Res., 53, (2014) 19506-19511.

24) Wenpo Shan, Fudong Liu, Yunbo Yu, Hong He*, The use of ceria for the selective catalytic reduction of NO_x with NH₃, Chin. J. Catal., 35, (2014) 1251-1259.

23) Fudong Liu, Wenpo Shan, Dawei Pan, Tengying Li, Hong He*, Selective catalytic reduction of NO_x by NH₃ for heavy-duty diesel vehicles, Chin. J. Catal., 35, (2014) 1438-1445.

22) Fudong Liu, Yunbo Yu, Hong He*, Environmentally-benign catalysts for the selective catalytic reduction of NO_x from diesel engines: Structure-activity relationship and reaction mechanism aspects, Chem. Commun., 50 (62), (2014) 8445-8463.

21) Zhihua Lian, Fudong Liu, Hong He*, Xiaoyan Shi, Jiansong Mo, Zhongbiao Wu, Manganese–niobium mixed oxide catalyst for the selective catalytic reduction of NO_x with NH₃ at low temperatures, Chem. Eng. J., 250, (2014) 390-398.

20) Lijuan Xie, Fudong Liu, Kuo Liu, Xiaoyan Shi, Hong He*, Inhibitory effect of NO₂ on the selective catalytic reduction of NO_x with NH₃ over one-pot synthesized Cu-SSZ-13 catalyst, Catal. Sci. Technol., 4, (2014) 1104-1110.

19) Lijuan Xie, Fudong Liu, Limin Ren, Xiaoyan Shi, Fengshou Xiao, Hong He*, Excellent performance of one-pot synthesized Cu-SSZ-13 catalyst for the selective catalytic reduction of NO_x with NH₃, Environ. Sci. Technol., 48, (2014) 566-572.

18) Fudong Liu, Hong He*, Lijuan Xie, XAFS study on the specific deoxidation behavior of iron titanate catalyst for the selective catalytic reduction of NO_x with NH₃, ChemCatChem., 5, (2013) 3760-3769.

17) Xiaoyan Shi, Fudong Liu, Lijuan Xie, Wenpo Shan, Hong He*, NH₃‑SCR performance of fresh and hydrothermally aged Fe-ZSM‑5 in standard and fast selective catalytic reduction reactions, Environ. Sci. Technol., 47, (2013) 3293-3298.

16) Fudong Liu, Wenpo Shan, Zhihua Lian, Lijuan Xie, Weiwei Yang, Hong He*, Novel MnWO_x catalyst with remarkable performance for low temperature NH₃-SCR of NO_x, Catal. Sci. Technol., 3, (2013) 2699-2707.

15) Fudong Liu, Hong He*, Zhihua Lian, Wenpo Shan, Lijuan Xie, Kiyotaka Asakura, Weiwei Yang, Hua Deng, Highly dispersed iron vanadate catalyst supported on TiO₂ for the selective catalytic reduction of NO_x with NH₃, J. Catal., 307, (2013) 340-351.

14) Fudong Liu, Kiyotaka Asakurab*, Pengyang Xie, Jianguo Wang，Hong He*, An XAFS study on the specific microstructure of active species in iron titanate catalyst for NH₃-SCR of NO_x, Catal. Today, 201, (2013) 131-138.

13) Wenpo Shan, Fudong Liu*, Hong He*, Xiaoyan Shi, Changbin Zhang, An environmentally-benign CeO₂-TiO₂ catalyst for the selective catalytic reduction of NO_x with NH₃ in simulated diesel exhaust, Catal. Today, 184, (2012) 160-165.

12) Wenpo Shan, Fudong Liu*, Hong He*, Xiaoyan Shi, Changbin Zhang, A superior Ce-W-Ti mixed oxide catalyst for the selective catalytic reduction of NO_x with NH₃, Appl. Catal. B, 115-116, (2012) 100-106.

11) Fudong Liu, Hong He*, Changbin Zhang, Wenpo Shan, Xiaoyan Shi, Mechanism of the selective catalytic reduction of NO_x with NH₃ over environmental-friendly iron titanate catalyst, Catal. Today, 175(1), (2011) 18-25.

10) Wenpo Shan, Fudong Liu*, Hong He*, Xiaoyan Shi, Changbin Zhang, The Remarkable Improvement of a Ce-Ti based Catalyst for NOx Abatement, Prepared by a Homogeneous Precipitation Method, ChemCatChem., 3, (2011) 1286-1289.

9) Wenpo Shan, Fudong Liu*, Hong He, Xiaoyan Shi, Changbin Zhang, Novel cerium-tungsten mixed oxide catalyst for the selective catalytic reduction of NO_x with NH₃, Chem. Commun., 47, (2011) 8046-8048.

8) Fudong Liu, Kiyotaka Asakura, Hong He*, Yongchun Liu，Wenpo Shan, Xiaoyan Shi, Changbin Zhang, Influence of calcination temperature on iron titanate catalyst for the selective catalytic reduction of NO_x with NH₃, Catal. Today, 164, (2011) 520-527.

7) Fudong Liu, Kiyotaka Asakura, Hong He*, Wenpo Shan, Xiaoyan Shi, Changbin Zhang, Influence of sulfation on iron titanate catalyst for the selective catalytic reduction of NO_x with NH₃, Appl. Catal. B, 103, (2011) 369-377.

6) Fudong Liu, Hong He*, Structure-activity relationship of iron titanate catalysts in the selective catalytic reduction of NO_x with NH₃, J. Phys. Chem. C, 114, (2010) 16929-16936.   

5) Fudong Liu, Hong He*, Selective catalytic reduction of NO with NH₃ over manganese substituted iron titanate catalyst: Reaction mechanism and H₂O/SO₂ inhibition mechanism study, Catal. Today, 153，(2010) 70-76.

4) Fudong Liu, Hong He*, Changbin Zhang, Zhaochi Feng, Lirong Zheng, Yaning Xie, Tiandou Hu, Selective catalytic reduction of NO with NH₃ over iron titanate catalyst: Catalytic performance and characterization, Appl. Catal. B, 96, (2010) 408-420.

3) Fudong Liu, Hong He*, Yun Ding, Changbin Zhang, Effect of manganese substitution on the structure and activity of iron titanate catalyst for the selective catalytic reduction of NO with NH₃, Appl. Catal. B, 93, (2009) 194-204.  

2) Wenqing Xu, Hong He*, Yunbo Yu, Deactivation of a Ce/TiO₂ catalyst by SO₂ in the selective catalytic reduction of NO by NH₃, J. Phys. Chem. C, 113, (2009) 4426-4432.

1) Wenqing Xu, Yunbo Yu, Changbin Zhang, Hong He*, Selective catalytic reduction of NO by NH₃ over a Ce/TiO₂ catalyst, Catal. Commun., 9, (2008) 1453-1457.

1.  Criteria of reductant with high efficiency for HC-SCR

1.1. Surface enolic species (R-CH=CH-O^–), produced by the partial oxidation of ethanol, which play a key role in the ethanol-SCR of NOx, were found for the first time on the surface of Ag/Al₂O₃ and reported.

1.2. Alcohols containing at least one α-H and one C-C bond are a prerequisite for partial oxidation to produce active enolic species over Ag/Al₂O₃, providing an intrinsic criterion for alcohol-SCR with high efficiency.

1.3. Hydrocarbons containing at least two carbon atoms are necessary for the formation of active enolic species during their partial oxidation over Ag/Al₂O₃, providing a principle for the improvement of the low-temperature activity of HC-SCR of NOx. (J. Phys. Chem. B, 2003, 107: 13090; Appl. Catal. B, 2004, 49: 159; Catal. Today, 2005, 100: 37; J. Catal., 2010, 271: 343; Catal. Sci. Technol., 2014, 4: 1239; Chem. Commun. 2014, 50: 8445)

2. Structure-activity relationship of HC-SCR system based on chemical bond analysis

2.1. Surface enolic species produced by the partial oxidation of alcohols over Ag/Al₂O₃ preferably adsorb on or close to oxidized Ag sites.

2.2. A mixing of Ag, O, and Al orbitals in the Ag-O-Al_Ⅲ entity significantly decreases the band gap and likely enhances the reactivity of this entity, therefore serving as the active center for ethanol-SCR over Ag/Al₂O₃.

2.3. The synergy of oxidized and metallic silver species enhances the water tolerance of Ag/Al₂O₃ in H₂-assisted HC-SCR.

2.4. The state of silver species affects the mobility of sulfates, and finally governs the sulfur resistance of Ag/Al₂O₃ in HC-SCR. (Catal. Today, 2005, 100: 37; J. Catal., 2012, 293: 13; ACS Catal., 2014, 4: 2776; Chem. Commun., 2014, 50: 8445; J. Phys. Chem. C, 2015, 119: 3132; Appl. Catal. B, 2017, 207: 60; ACS Catal., 2018, 8: 2699; Appl. Catal. B, 2019, 244: 909)

3. Scheme for the design of diesel-SCR

3.1. Diesel-SCR technology with high efficiency for diesel engine emission control: diesel reforming coupled with HC-SCR.

3.2. Principle for diesel reforming: ① transformation of diesel to active small hydrocarbons or oxygenated small hydrocarbons containing at least two carbon atoms, beneficial for the formation of enolic species; ② in situ H₂ production to enhance low-temperature activity and expand the operating temperature window. (Chem. Commun. 2014, 50: 8445)

Relevant publications

42) Guangyan Xu, Jinzhu Ma, Lian Wang, Wen Xie, Jingjing Liu, Yunbo Yu*, Hong He*, Insight into the origin of sulfur tolerance of Ag/Al₂O₃ in the H₂-C₃H₆-SCR of NOx, Appl. Catal. B,244, (2019) 909-918.

41) Guangyan Xu, Yunbo Yu*, Hong He*, Silver valence state determines the water tolerance of Ag/Al₂O₃ for the H₂-C₃H₆-SCR of NO_x, J. Phys. Chem. C, 122, (2018) 670-680.

40) Guangyan Xu, Yunbo Yu*,Hong He*,A low-temperature route triggered by water vapor during the ethanol-SCR of NOx over Ag/Al₂O₃, ACS. Catal., 8, (2018) 2699-2708.

39) Guangyan Xu, Jinzhu Ma, Guangzhi He,Yunbo Yu*, Hong He*, An alumina-supported silver catalyst with high water tolerance for H₂ assisted C₃H₆-SCR of NO_x, Appl. Catal. B, 207, (2017) 60-71.

38) Hua Deng, Yunbo Yu, Hong He*, Adsorption states of typical intermediates on Ag/Al₂O₃ catalyst employed in the selective catalytic reduction of NOx by ethanol, Chin. J. Catal., 36, (2015) 1312-1320.

37) Hua Deng, Yunbo Yu, Hong He*,Water effect on preparation of Ag/Al₂O₃ catalyst for reduction of NOx by ethanol, J. Phys. Chem. C, 120, (2016), 24294-24301.

36) Hua Deng, Yunbo Yu, Hong He*, The role of Ag-O-Al entities in adsorption of NCO species and reduction of NOx, Catal. Today, 258, (2015) 35-40.

35) Hua Deng, Yunbo Yu, Hong He*, Discerning the role of Ag−O−Al entities on Ag/g-Al₂O₃ surface in NOx Selective reduction by ethanol, J. Phys. Chem. C, 119, (2015) 3132–3142.

34) Yunbo Yu, Yi Li, Xiuli Zhang, Hua Deng, Hong He*, Yuyang Li, Promotion effect of H₂ on the ethanol oxidation and NOx reduction with ethanol over Ag/Al₂O₃ catalyst, Environ. Sci. Technol., 49, (2015) 481–488.

33) Hua Deng, Yunbo Yu, Fudong Liu, Jinzhu Ma, Yan Zhang, Hong He*, Nature of Ag Species on Ag/g-Al₂O₃: A Combined Experimental and theoretical study, ACS Catal., 4, (2014) 2776–2784.

32) Fudong Liu, Yunbo Yu, Hong He*, Environmentally-benign catalysts for the selective catalytic reduction of NOx from diesel engines: Structure-activity relationship and reaction mechanism aspects, Chem. Commun., 50 (62), (2014) 8445–8463.

31) Yunbo Yu, Hong He*, Xiuli Zhang, Hua Deng, A common feature of H₂-assisted HC-SCR over Ag/Al₂O₃, Catal. Sci. Technol., 4, (2014) 1239–1245.

30) Zhao Jiaojiao, Yu Yunbo*, Han Xue, He Hong, Fuel reforming over Ni‐based catalysts coupled with selective catalytic reduction of NOx, Chin. J. Catal., 34, (2013) 1407–1417.

29) Yunbo Yu*, Jiaojiao Zhao, Yong Yan, Xue Han, Hong He, A cyclic reaction pathway triggered by ammonia for the selective catalytic reduction of NOx by ethanol over Ag/Al₂O₃, Appl. Catal. B, 136-137, (2013) 103–111.

28) He Hong*, Liu Fudong, Yu Yunbo, Shan Wenpo, Environmental-friendly SCR technique (selective catalytic reduction) for the deNO_x process from diesel engines, SCIENCE CHINA: Chemistry, 42, (2012) 446–468. (in Chinese)

27) Yong Yan, Yunbo Yu*, Hong He, Jiaojiao Zhao, Intimate contact of enolic species with silver sites benefits the SCR of NOx by ethanol over Ag/Al₂O₃, J. Catal.,293, (2012) 13–26.

26) He Hong*, Yu Yunbo, Li Yi, Wu Qiang, Zhang Xiuli, Zhang Changbin, Shi Xiaoyan, Song Xiaoping, Advances in mechanistic and practical studies on the selective catalytic reduction of NOx by oxygenated hydrocarbons over Ag/Al₂O₃, Chin. J. Catal., 31, (2010) 491–501. (in Chinese)

25) Yunbo Yu, Xiaoping Song, Hong He*, Remarkable influence of reductant structure on the activity of alumina-supported silver catalyst for the selective catalytic reduction of NOx, J Catal., 271, (2010) 343–350.

24) Yi Li, Xiuli Zhang, Hong He*, Yunbo Yu, Tao Yuan, Zhenyu Tian, Jing Wang, Yuyang Wang, Effect of the pressure on the catalytic oxidation of volatile organic compounds over Ag/Al₂O₃ catalyst,Appl. Catal. B, 89, (2009) 659–664.

23) Xiuli Zhang, Hong He*, Hongwei Gao, Yunbo Yu, Experimental and theoretical studies of surface nitrate species on Ag/Al₂O₃ using DRIFTS and DFT, Spectrochim. Acta A,71, (2008) 1446–1451.

22) Hong He*, Xiuli Zhang, Qiang Wu, Changbin Zhang, Yunbo Yu, Review of Ag/Al₂O₃-reductant system in the selective catalytic reduction of NOx, Catal. Surv. Asia, 12, (2008) 38–55.

21) Xiuli Zhang, Yunbo Yu, Hong He*, Effect of hydrogen on reaction intermediates in the selective catalytic reduction of NOx by C₃H₆, Appl. Catal. B, 76, (2007) 241–247.

20) Yunbo Yu, Xiuli Zhang, Hong He*, Evidence for the formation, isomerization and decomposition of organo-nitrite and -nitro species during the NOx reduction by C₃H₆ on Ag/Al₂O₃, Appl. Catal. B, 75, (2007) 298–302.

19) Xiuli Zhang, Hong He*, Zichuan Ma, Hydrogen promotes the selective catalytic reduction of NOx by ethanol over Ag/Al₂O₃, Catal. Commun., 8, (2007) 187–192.

18) Shuxia Xie, Jin Wang, Hong He*, Poisoning effect of sulphate on the selective catalytic reduction of NOx by C₃H₆ over Ag-Pd/Al₂O₃, J. Mol. Catal. A: Chem., 266, (2007) 166–172.

17) Qiang Wu, Yunbo Yu, Hong He*, Mechanistic study of selective catalytic reduction of NOx with C₂H₅OH and CH₃OCH₃ over Ag/Al₂O₃ by in situ DRIFTS, Chin. J. Catal., 27(11), (2006) 993–998.

16) Shuxia Xie, Yunbo Yu, Jin Wang, Hong He*, Effect of SO₂ on the performance of Ag-Pd/Al₂O₃ for the selective catalytic reduction of NOx with C₂H₅OH, J. Environ. Sci., 18(5), (2006) 973–978.

15) Qiang Wu, Hongwei Gao, Hong He*, Study on effect of SO₂ on the selective catalytic reduction of NOx with propene over Ag/Al₂O₃ by in situ DRIFTS, Chin. J. Catal., 27(5), (2006) 403–408.

14) Qiang Wu, Hongwei Gao, Hong He*, Conformational analysis of sulfate species on Ag/Al₂O₃ by means of theoretical and experimental vibration spectra, J. Phys. Chem. B, 110, (2006) 8320–8324.

13) Qiang Wu, Qingcai Feng, Hong He*, Disparate effects of SO₂ on the selective catalytic reduction of NO by C₂H₅OH and IPA over Ag/Al₂O₃, Catal. Commun., 7, (2006) 657–661.

12) Hongwei Gao, Hong He*, Yunbo Yu, Qingcai Feng, Density functional theory (DFT) and DRIFTS investigations of the formation and adsorption of enolic species on Ag/Al₂O₃ surface, J. Phys. Chem. B, 109, (2005) 13291–13295.

11) Qiang Wu, Hong He*, Yunbo Yu, In situ DRIFTS study of the selective catalytic reduction of NOx with alcohols over Ag/Al₂O₃ catalyst: role of surface enolic species, Appl. Catal. B, 61, (2005) 107–113.

10) Hong He*, Yunbo Yu, Selective catalytic reduction of NOx over Ag/Al₂O₃ catalyst: from reaction mechanism to diesel engine test, Catal. Today, 100, (2005) 37–47. Invited paper

9) Hongwei Gao, Hong He*, Conformational analysis and comparison between theoretical and experimental vibration spectra for isocyanate species on Ag/Al₂O₃ catalyst, Spectrochim. Acta A,61, (2005) 1233–1238.

8) Jin Wang, Hong He*, Shuxia Xie, Yunbo Yu, Novel Ag-Pd/Al₂O₃-SiO₂ for lean NOx reduction by C₃H₆ with high tolerance of SO₂, Catal. Commun.,6, (2005) 195–200.

7) Jin Wang, Hong He*, Qingcai Feng, Yunbo Yu, Kiyohide Yoshida, Selective catalytic reduction of NOx by C₃H₆ over an Ag/Al₂O₃ catalyst with a small quantity of noble metal, Catal. Today, 93–95, (2004) 783–789.

6) Hong He*, Changbin Zhang, Yunbo Yu, A comparative study of Ag/Al₂O₃ and Cu/Al₂O₃ catalysts for the selective catalytic reduction of NO by C₃H₆, Catal. Today, 90, (2004) 191–197.

5) Yunbo Yu, Hong He*, Qingcai Feng, Hongwei Gao, Xin Yang, Mechanism of the selective catalytic reduction of NOx by C₂H₅OH over Ag/Al₂O₃, Appl. Catal. B, 49, (2004) 159–171.

4) Yunbo Yu, Hong He*, Qingcai Feng, Novel enolic surface species during partial oxidation of CH₃CHO, C₂H₅OH, and C₃H₆ on Ag/Al₂O₃: an in situ DRIFTS study, J. Phys. Chem. B,107, (2003) 13090–13092.

3) Hong He*, Jin Wang, Qingcai Feng, Yunbo Yu, Kiyohide Yoshida, Novel Pd promoted Ag/Al₂O₃ catalyst for the selective reduction of NOx, Appl. Catal. B, 46, (2003) 365–370.

2) Satosi Sumiya, Hong He, Akira Abe, Nobutsune Takezawa, Kiyohide Yoshida, Formation and reactivity of isocyanate (NCO) species on Ag/Al₂O₃, J. Chem. Soc., Faraday Trans., 94(15), (1998) 2217–2219. 1) Satoshi Sumiya, Mika Saito, Hong He, Qingcai Feng, Nobutsune Takezawa, Kiyohide Yoshida, Reduction of lean NO_X by ethanol over Ag/Al₂O₃ catalysts in the presence of H₂O and SO₂, Catal. Lett., 50, (1998) 87–91.

1) Satoshi Sumiya, Mika Saito, Hong He, Qingcai Feng, Nobutsune Takezawa, Kiyohide Yoshida, Reduction of lean NO_X by ethanol over Ag/Al₂O₃ catalysts in the presence of H₂O and SO₂, Catal. Lett., 50, (1998) 87–91.

1. R&D of SCR catalysts with high performance

1.1. Based on the emission features of domestic heavy-duty diesel engines and high sulfur content diesel fuel, vanadium-based catalysts been modified and produced on a large scale, also exhibiting excellent low-temperature activity for NOx reduction and high thermal stability.

1.2. A one-step wash-coating procedure and the parameters for SCR catalyst preparation were successfully developed on the basis of a domestic large-size cordierite support. We also established automatic production lines for the SCR catalytic converter, with an annual output of 700,000 sets. The heavy-duty diesel engines fitted with our SCR catalytic converters achieved national certification, and have been commercially applied on a large scale.

2. Integration and application of the developed after-treatment system

2.1. The developed SCR catalytic converter, urea supply and storage unit, and SCR controller with OBD functions were successfully integrated and certified on different kinds of heavy-duty diesel vehicle engines. Reliability verification related to low-temperature climate compatibility, high-temperature climate compatibility, and high-altitude compatibility was also performed on heavy-duty vehicles fitted with the SCR system at drive distances up to millions of kilometers.

2.2. The developed SCR after-treatment system meets China IV and China V emission standards for heavy-duty diesel vehicles, with a price 50% lower than imported products with similar performance. The developed equipment has been commercially used in 1,500,000 heavy-duty diesel vehicles. Based on the achievements mentioned above, we won the national sciences & technology advanced prize (Second grade, 2014).

Relevant publications

20) Guangzhi He, Zhihua Lian, Yunbo Yu, Yang Yang, Kuo Liu, Xiaoyan Shi, Zidi Yan, Wenpo Shan, Hong He*, Polymeric vanadyl species determine the low-temperature activity of V-based catalysts for the SCR of NOx with NH₃, Sci. Adv.,4, (2018) eaau4637.

19) Zidi Yan, Xiaoyan Shi*, Yunbo Yu, Hong He, Alkali resistance promotion of Ce doped vanadium-titanic based NH₃-SCR catalysts, J. Environ. Sci., 73, (2018) 155-161.

18) Wenpo Shan, Fudong Liu*, Yunbo Yu,Hong He*, Chenglin Deng, Xinyun Zi, High-efficiency reduction of NOx emission from diesel exhaust using a CeWOx catalyst, Catal. Commun., 59 (2015) 226–228.

17) Fudong Liu, Yunbo Yu, Hong He*, Environmentally-benign catalysts for the selective catalytic reduction of NOx from diesel engines: Structure-activity relationship and reaction mechanism aspects, Chem. Commun., 50 (62), (2014) 8445–8463.

16) Fudong Liu, Wenpo Shan, Dawei Pan, Tengying Li, Hong He*, Selective catalytic reduction of NOx by NH₃ for heavy-duty diesel vehicles, Chin. J. Catal., 35, (2014) 1438–1445.

15) Fudong Liu, Wenpo Shan, Xiaoyan Shi, Hong He*, Vanadium-based catalysts for the selective catalytic reduction of NOx with NH₃, Progress in Chemistry, 24, (2012) 445-455. (in Chinese)

14) He Hong*, Liu Fudong, Yu Yunbo, Shan Wenpo, Environmental-friendly SCR technique (selective catalytic reduction) for the deNO_x process from diesel engines, SCIENCE CHINA: Chemistry, 42, (2012) 446–468. (in Chinese)

13) He Hong*, Yu Yunbo, Li Yi, Wu Qiang, Zhang Xiuli, Zhang Changbin, Shi Xiaoyan, Song Xiaoping, Advances in mechanistic and practical studies on the selective catalytic reduction of NOx by oxygenated hydrocarbons over Ag/Al₂O₃, Chin. J. Catal., 31, (2010) 491–501. (in Chinese)

12) Hong He*, Yi Li, Xiuli Zhang, Yunbo Yu, Changbin Zhang, Precipitable silver compound catalysts for the selective catalytic reduction of NOx by ethanol, Appl. Catal. A, 375, (2010) 258–264.

11) Hong He*, Xiuli Zhang, Qiang Wu, Changbin Zhang, Yunbo Yu, Review of Ag/Al₂O₃-reductant system in the selective catalytic reduction of NOx, Catal. Surv. Asia, 12, (2008) 38–55.

10) Hongyi Dong, Shijin Shuai, Rulong Li, Jianxin Wang, Xiaoyan Shi, Hong He, Study of NOx selective catalytic reduction by ethanol over Ag/Al₂O₃ catalyst on a HD diesel engine, Chem. Eng. J., 135, (2008) 195–201.

9) Xiaoyan Shi, Yunbo Yu, Hong He*, Shijin Shuai, Hongyi Dong, Rulong Li, Combination of biodiesel-ethanol-diesel fuel blend and SCR catalyst assembly to reduce emissions from a heavy-duty diesel engine, J. Environ. Sci., 20, (2008) 177–182.

8) Changbin Zhang, Hong He*, Shijin Shuai, Jianxin Wang, Catalytic performance of Ag/Al₂O₃-C₂H₅OH-Cu/Al₂O₃ system for the removal of NOx from diesel engine exhaust, Environ. Pollut., 147, (2007) 415–421.

7) Hongyi Dong*, Shijin Shuai, Wenjuan Zhang, Rulong Li, Jianxin Wang, Xiaoyan Shi, Hong He, An ethanol SCR for NOx purification: performance evaluation on engine bench and demonstration on bus, SAE, 2007–01–1240.

6) Xiaobing Pang, Xiaoyan Shi, Yujing Mu*, Hong He, Shijin Shuai, Hu Chen, Rulong Li, Characteristics of carbonyl compounds emission from a diesel-engine using biodiesel-ethanol-diesel as fuel, Atmos. Environ., 40(36), (2006) 7057–7065.

5) Xiaoyan Shi, Xiaobing Pang, Yujing Mu, Hong He*, Shijin Shuai, Jianxin Wang, Hu Chen, Rulong Li, Emission reduction potential of using ethanol-biodiesel-diesel fuel blend on a heavy-duty diesel engine, Atmos. Environ., 40, (2006) 2567–2574.

4) Hong He*, Yunbo Yu, Selective catalytic reduction of NOx over Ag/Al₂O₃ catalyst: from reaction mechanism to diesel engine test, Catal. Today, 100, (2005) 37–47. Invited paper

3) Shijin Shuai, Jianxin Wang, Rulong Li, Jianjun Sun, Licheng Xiang, Hong He, Xiaoyan Shi, Performance evaluation and application of diesel NOx-SCR catalyst by ethanol reductant, SAE, 2005–01–1089.

2) Xiaoyan Shi, Yunbo Yu, Hong He*, Shijin Shuai, Jianxin Wang, Rulong Li, Emission characteristics using methyl soyate-ethanol-diesel fuel blends on a diesel engine, Fuel, 84(12–13), (2005) 1543–1549.

1) Bang-Quan He*, Shi-Jin Shuai, Jian-Xin Wang, Hong He, The effect of ethanol blended diesel fuels on emissions from a diesel engine, Atmos. Environ., 37, (2003) 4965–4971.