1. Photocatalytic oxidation of indoor air ammonia
A series of C-doped TiO2 catalysts with excellent performance for photocatalytic oxidation of ammonia were prepared, and the catalyst calcined at 400 oC had the best activity. The surface acidity is an important factor affecting the performance of a catalyst. The effects of exposed TiO2 facets and surface F on the activity for photocatalytic oxidation of NH3 were studied. It was found that TiO2 with predominant {001} facets exposed had superior activity compared to TiO2 with {101} or {010} facets exposed, and{001} facets of TiO2 and surface F ions had a remarkable synergistic effect on PCO of NH3. The DRIFTS results suggested that the separation efficiency of photogenerated electrons and holes is the crucial factor affecting the performance of NH3 oxidation, and the main active species for NH3 oxidation is the hole. (Appl. Catal. B, 2014, 152-153, 82; Appl. Catal. B, 2017, 207, 3973; Appl. Catal. B, 2018, 223, 209)
Photocatalytic oxidation of ammonia on titanium-based catalysts
Mechanism of facet effect and surface fluorine on improving the charge separation efficiency
2. Non-photocatalytic oxidation of indoor air ammonia
The Ag species state and Ag particle size have a significant influence on Ag/Al2O3 activity and N2 selectivity in the SCO of NH3 at low temperature. The SCO of NH3 over Ag/Al2O3 follows different routes in different temperature regions. Ag0 is proposed to be an active species at low temperature (< 140 oC)，where NH3 oxidation follows the –NH mechanism. However, at temperatures above 140 oC, Ag+ could also be an active species, and NH3 oxidation follows an in situ selective catalytic reduction of NOx (iSCR) mechanism. (J. Catal., 2009, 268, 18; J. Catal., 2009, 261, 101)
Ag/nano-Al2O3 is an efficient catalyst for NH3-SCO in the low temperature range. A remarkable nanosize effect for Al2O3 was observed in Ag/Al2O3 catalysts for the selective catalytic oxidation of ammonia. Small metallic Ag particles (AgNPs) in Ag/nano-Al2O3 facilitate the NH3-SCO reaction following the new reaction pathway, which was named the N2– mechanism.
Dispersed Ag species on γ-Al2O3 are widely used for catalyzing a variety of reactions, including soot oxidation, ethylene epoxidation, NOx reduction, and selective catalytic oxidation of ammonia (NH3-SCO). The valence state, morphology and dispersion of Ag species can significantly affect the catalytic performance of Ag/γ-Al2O3. Herein, by using a number of surface-science measurements and density-functional theory (DFT) computation, we revealed that the terminal hydroxyl groups on the γ-Al2O3 surface are responsible for anchoring the Ag species. Hence, the presence of abundant terminal hydroxyl groups on nano-sized γ-Al2O3 surface can lead to remarkable single-silver-atom dispersion, thereby resulting in markedly higher performance than found with Ag clusters on micro-sized γ-Al2O3. (ACS Catalysis, 2018, 8, 2670; ACS Catalysis, 2019, 9, 1437; Nat. Commun., 11,
(2020) 529-538.)
Nanosize effect of Al2O3 in Ag/Al2O3 catalyst for the NH3-SCO activity and the anchoring mechanism of Ag species on Al2O3 surface
12. Fei Wang, Jinzhu Ma, Shaohui Xin, Qiang Wang, Jun Xu, Changbin Zhang*, Hong He, Xiaocheng Zeng, “Resolving the puzzle of single-atom silver dispersion on nanosized γ-Al2O3 surface for high catalytic performance.” Nat. Commun., 11, (2020) 529-538.
11. Fei Wang, Guangzhi He, Bo Zhang, Min Chen, Xueyan Chen, Changbin Zhang*, Hong He, “Insights into the activation effect of H2 pretreatment on Ag/Al2O3 catalyst for the selective catalytic oxidation of ammonia”, ACS Catal., 9, (2019) 1437-1445.
10. Fei Wang, Jinzhu Ma, Guangzhi He, Min Chen, Shaoxin Wang, Changbin Zhang*, Hong He, “Synergistic Effect of TiO2−SiO2 in Ag/Si−Ti catalyst for the selective catalytic oxidation of ammonia”, Ind. Eng. Chem. Res., 57, (2018) 11903-11910.
9. Fei Wang, Jinzhu Ma, Guangzhi He, Min Chen, Changbin Zhang*, Hong He*, “Nanosize effect of Al2O3 in Ag/Al2O3 catalyst for the selective catalytic oxidation of ammonia”, ACS. Catal., 8, (2018) 2670-2682.
8. Min Chen, Jinzhu Ma, Bo Zhang, Fei Wang, Yaobin Li, Changbin Zhang*, Hong He, “Facet-dependent performance of anatase TiO2 for photocatalytic oxidation of gaseous ammonia”, Appl. Catal. B, 223, (2018) 209-215.
7. Min Chen, Jinzhu Ma, Bo Zhang, Guangzhi He, Yaobin Li, Changbin Zhang*, Hong He, “Remarkable synergistic effect between {001} facets and surface F ions promoting hole migration on anatase TiO2”, Appl. Catal. B, 207, (2017) 397-403.
6. Hongmin Wu, Jinzhu Ma, Yaobin Li, Changbin Zhang*, Hong He, “Photocatalytic oxidation of gaseous ammonia over fluorinated TiO2 with exposed (001) facets”, Appl. Catal. B, 2014, 152-153, 82-87.
5. Hongmin Wu, Jinzhu Ma, Changbin Zhang*, Hong He, “Effect of calcination temperature on TiO2 for the photocatalytic oxidation of gaseous NH3”, J. Environ. Sci., 2014, 26(3) )1-10.
4. Li Zhang, Hong He*, “Mechanism of selective catalytic oxidation of ammonia to nitrogen over Ag/Al2O3”, J. Catal., 268, (2009) 18-25.
3. Li Zhang, Changbin Zhang, Hong He*, “The role of silver species in Ag/Al2O3 catalysts for the selective catalytic oxidation of ammonia to nitrogen”, J. Catal., 261, (2009) 101-109.
2. Shilong He, Changbin Zhang, Min Yang, Yu Zhang, Wenqing Xu, Nan Cao, Hong He*, “Selective catalytic oxidation of ammonia from MAP decomposition”, Sep. Purif. Technol., 58, (2007) 173-178.
1. Min Yang*, Chengqiang Wu, Changbin Zhang, Hong He, “Selective oxidation of ammonia over copper-silver based catalysts”, Catal. Today, 90, (2004) 263-267.
