Molecular Catalysis
·
2022
·
IF 5.089
Yiqing Zeng,Fengye Lyu,Yanan Wang,Shule Zhang,Qin Zhong,Zhaoxiang Zhong
High N 2 O selectivity of MnO x -TiO 2 catalyst hinders its development in ammonia selective catalytic reduction (NH 3 -SCR) of NO x . Herein, a series of MnO x -TiO 2 catalyst with different Mn/Ti ratio were prepared by wet-impregnation method to study the N 2 O formation during ammonia selective catalytic reduction (NH 3 -SCR) of NO x from the perspective of catalyst. It is found that MnO x and TiO 2 species are the mainly redox and acid sites for the NH 3 -SCR denitration reaction over MnO x -TiO 2 catalyst, respectively. As the Mn/Ti ratio increases, MnO x species layer expanded on TiO 2 support, leading to increase of redox sites but decrease of surface acid sites. These changes contribute to the occurrence of the no-selective oxidation of NH 3 on MnO x species and the over-activation of NH 3 at Mn-Ti interface, resulting in the formation of N 2 O via the route of 2NH 3 + 2O 2 → N 2 O + 3H 2 O and 4NO + 4NH 3 + 3O 2 → 4N 2 O + 6H 2 O, respectively. Through this work, it can be speculated that both improving MnO x dispersion and increasing surface acidity of catalyst are feasible strategy for suppressing the N 2 O formation on MnO x -TiO 2 .
研究领域:
环境科学
·
催化化学
✓ 已验证
产品关联
DOI
高影响因子
CHEMICAL ENGINEERING JOURNAL
·
2019
·
IF 8.355
Zhi Liu,Chong Chen,Jinchong Zhao,Lingzhi Yang,Kaian Sun,Lingyou Zeng,Yuan Pan,Yunqi Liu,Chenguang Liu
Selective catalytic reduction of NO by NH 3 (SCR) at low temperature usually considered to be the combination of NO oxidation and “Fast SCR” process. However, the NO oxidation mechanism and the role of NO 2 over “Fast SCR” process are controversial. Focusing on these problems, the in-deep studies were performed over the typical MnO x /TiO 2 catalysts. Combining in-situ DRIFT, TPD-MS and DFT calculation results, an integrated NO oxidation mechanism was proposed based on an “Nitro-assisted oxygen activation” concept where the activation and transformation of O 2 is linked with the transformation of nitro species. The O O bond of O 2 can be weakened by generating a variation of bidentate nitrates, which can promote the break of O O bond and the formation of NO 2 . The formation of the variation of bidentate nitrates was the rate-determining step over NO oxidation. Additionally, we further reveal that the crucial role of NO 2 over “Fast SCR” process lies in participating the hydrogen abstraction from coordinated NH 3 and promoting the production of NH 2 active species which can direct react with NO to generate N 2 and H 2 O. The removability of NO 2 can coupling the MnO 2 (NO oxidation active component) and TiO 2 support (“Fast SCR” active component) together. Our findings provide insight into the design and improvement of catalysts or reaction pathways over the low-temperature SCR process.
研究领域:
环境科学
·
催化化学
✓ 已验证
产品关联
DOI
高影响因子
CHEMICAL ENGINEERING JOURNAL
·
2018
·
IF 6.735
Chuanzhi Sun,Hao Liu,Wei Chen,Dezhan Chen,Shuohan Yu,Annai Liu,Lin Dong,Shuai Feng
A series of Sm- and/or Zr-doped MnO x -TiO 2 catalysts were prepared, and the catalysts exhibited better N 2 selectivity and SO 2 resistance than the undoped MnO x -TiO 2 catalyst for the selective catalytic reduction of NO by NH 3 (NH 3 -SCR). The reasons for the good N 2 selectivity and SO 2 resistance of the catalysts were proposed. X-ray photoelectron spectroscopy (XPS) combined with density functional theory (DFT) calculations suggested that electron transfer between the manganese and samarium species by Mn 4+ + Sm 2+ ↔ Mn 3+ + Sm 3+ redox cycles occurred in the Sm-containing catalysts. Furthermore, electron transfer from Sm 2+ to Mn 4+ suppressed electron transfer from NH 3 to Mn 4+ , inhibiting the formation of NH 2 or NH. Thus, the pathway for NH generation was removed, and the reaction of 2NH + 4NO → 3N 2 O + H 2 O was prevented. Consequently, the N 2 selectivity of the NH 3 -SCR reaction was enhanced. In situ diffused reflectance infrared Fourier transform spectroscopy ( in situ DRIFTS) combined with thermogravimetry, differential scanning calorimetry and mass spectrometry (TG-DSC-MS) results revealed that the deposition rate of sulfate species decreases after Sm doping, which was also attributed to the suppressed electron transfer from SO 2 to Mn 4+ , i.e., the oxidation of SO 2 to SO 3 . Thus, the catalysts exhibited better SO 2 resistance.
研究领域:
催化化学
·
环境科学
✓ 已验证
产品关联
DOI
高影响因子
CATALYSIS LETTERS
·
2023
·
IF 2.8
Wang Yanghui,Jin Luyao,Xu Xintao,Li Jiaying,Fan Kaihao,Hu Bo,Shen Yi,Liu Xuesong
In this paper, MnO x /TiO 2 catalysts with different manganese contents were prepared by using vacuum over-impregnation method to support manganese on TiO 2 support. However, the activity temperature window was narrow and the denitrification efficiency was only 265–365 °C in the temperature zone above 80%. Therefore, doping W was used to improve the high temperature activity and broaden the activity temperature window. The experimental results show that the active temperature window of the catalyst is expanded to 260–550 °C when doping 20%WO 3 . The effects of tungsten doping on the structure and surface properties of the catalysts were investigated by XRD, TEM, Raman, XPS, H 2 -TPR and NH 3 -TPD. It is found that the increase of manganese content would increase the ratio of Mn 4+ and O α , and then improve the NH 3 -SCR activity at low temperature. Tungsten doping can provide more strong acid sites and improve the high temperature activity of the catalyst by inhibiting the oxidation of ammonia. Graphical Abstract
研究领域:
催化化学
·
环境科学
✓ 已验证
产品关联
DOI
高影响因子
CHEMICAL ENGINEERING JOURNAL
·
2017
·
IF 6.216
Chong Xie,Shenghui Yang,Jianwen Shi,Beibei Li,Chen Gao,Chunming Niu
The stability of MnO x based low temperature SCR catalysts remained to be a serious issue. This report explored use of multi-walled carbon nanotubes (MWCNTs) network with uniform structure as a “rigid” pore template for synthesis of mesoporous MnO x -TiO 2 SCR catalyst with high surface area and high stability. The results showed that MWCNT network imposed MnO x -TiO 2 catalyst a mesoporous porosity with a narrow pore size distribution centered on ∼13.2 nm and a surface area of 131.6 m 2 g −1 stabilized at 500 °C. The mesoporous structure was formed by interconnected nanoparticles, comprised of crystallized rutile TiO 2 core surrounded by amorphous MnOx , with an average diameter of ∼8 nm. The catalyst exhibited an excellent low temperature SCR activity and selectivity as well as high resistance to deactivation and poison by H 2 O and SO 2 . SnO 2 modification led to degradation of catalytic performance in low temperature (60–180 °C) side, but improvement at high temperature side (240–360 °C), especially at high gas velocity, which can be attributed to change in structure, reactivity of MnO x and surface acidity induced by SnO 2 addition.
研究领域:
材料科学
·
环境科学
·
催化化学
✓ 已验证
DOI
高影响因子
Reaction Kinetics Mechanisms and Catalysis
·
2019
·Vol. 128
·期 2
·681-693
·
IF 1.428
Xie Chong,Yang Shenghui,Shi Jian-Wen,Niu Chunming
A novel MnO x –TiO 2 catalyst with hollow silkworm structure was synthesized successfully via an ethanol-thermal strategy by using activated carbon fiber felt as template for the first time. The silkworm-like MnO x –TiO 2 catalyst (MnTi) exhibited higher NO x conversion in the whole experimental temperature region (90–330 °C) under a high space velocity of 36,000 h −1 in comparison with the common MnO x –TiO 2 catalyst without hollow silkworm structure (MnTi-B). The excellent catalytic performance of MnTi can be attributed to its high specific surface area, large content of active surface oxygen species (O S ), and more surface acid sites. In addition, the MnTi catalyst also exhibited excellent resistance to water or SO 2 poisoning.
研究领域:
催化化学
·
环境科学
✓ 已验证
DOI
高影响因子
危险品化学品经营许可证（带存储）