查找使用阿拉丁产品的科研文献

Ca-Poisoning Effect on V2O5-WO3/TiO2 and V2O5-WO3-CeO2/TiO2 Catalysts with Different Vanadium Loading

Yangyang Guo,Xiaofei Xu,Hong Gao,Yang Zheng,Lei Luo,Tingyu Zhu

Ca poisoning behavior is inevitable for high-calcium content flue gas, so V2O5-WO3/TiO2(VWT) and V2O5-WO3-CeO2/TiO2(VWCeT) catalysts with different vanadium content have been prepared and the Ca-doped catalysts are compared in this manuscript. The result shows Ce addition can both promote the NO conversion and the alkali resistance. Lower Ca addition for 0.1VWCeT catalyst promotes its oxidability and Ce modification is more suitable for low vanadium catalysts. The total acidity and the reducibility of catalysts decline after Ca doping, and the reducibility of the active species on catalysts has been strengthened by Ce addition. CeO2based catalysts with lower Ca loading struggle to resist sulfur poisoning, while higher Ca loading favors SO2adsorption and also physically reduces the cerium acidification process. In the presence of SO2, additional Brønsted acid sites are formed in Ca rich catalyst. The dynamic NH3adsorption has been investigated, shows that Ca doping content on catalyst is critical for SCR reaction, and the catalyst is more susceptible to SO2initially in alkali flue gas during the actual application, but the sulfur resistance may increase with the alkali-poisoning effect aggravated by Ca doping.Keywords:Ca-poisoning;SCR reaction;NO reduction;V2O5-WO3/TiO2and V2O5-WO3-CeO2/TiO2catalysts;SO2and water;NO removal efficiency

Catalytic urea hydrolysis by composite metal oxide catalyst towards efficient urea-based SCR process: performance evaluation and mechanism investigation

Li Yuchen,Chen Zhen,Zhang Xiangyu,Yang Kun,Wang Lidong,Li Junhua

As a promising option to provide gaseous NH 3 for SCR system, catalytic urea hydrolysis has aroused great attention, and improving surface area and activity of catalysis are the crucial issues to be solved for efficient urea hydrolysis. Therefore, a composite metal oxide (TiO 2 @Al 2 O 3 ) catalyst was prepared by a simple hydrothermal method, with mesoporous alumina (γ-Al 2 O 3 ) as substrate. The results verify the mesoporous structure and submicron cluster of TiO 2 @Al 2 O 3 , with exposed crystal faces of (101) and (400) for TiO 2 and γ-Al 2 O 3 , respectively. The electronegativity difference of Ti 4+ and Al 3+ changes the charge distribution scheme around the interface, which provides abundant acid/base sites to boost the urea hydrolysis. Consequently, for an optimal proportioning with nano TiO 2 content at 10 wt.%, the hydrolysis efficiency can reach up to 35.2 % at 100 °C in 2 h, increasing by ∼7.1 % than that of the blank experiment. 13 C NMR spectrum measurements provide the impossible intermediate species during urea hydrolysis. Theoretical calculations are performed to clarify the efficient H 2 O decomposition at the interface of TiO 2 @Al 2 O 3 . The result offers a favorable technology for energy-efficiency urea hydrolysis.

A comparative study of hydrothermal aging effect on cerium and lanthanum doped Cu/SSZ-13 catalysts for NH3-SCR

Di Deng,Shujun Deng,Dandan He,Zhiheng Wang,Zhipeng Chen,Yi Ji,Guoping Yan,Guangjin Hou,Licheng Liu,Hong He

Ce- or La-doped Cu/SSZ-13 catalysts were prepared by a hydrothermal method and Cu, Ce or La ions were incorporated through stepwise ion exchange. The catalyst activity was measured for the ammonia selective catalytic reduction reaction. The structure and composition of catalyst were characterized by using X-ray diffraction, scanning electron microscopy, inductively coupled plasma mass spectrometry solid-state NMR, NH 3 -TPD techniques, and the active components were examined by XPS and XANES . The results indicate that the Ce and La doping can both completely preserve the SCR activity of Cu/SSZ-13 above 300 °C, but there is also a decrease of activity below 200 °C. On the other hand, Ce doping is beneficial to the formation of framework aluminum , stabilizes molecular sieve framework and Cu active sites of Cu/SSZ-13, thereby improves the catalyst hydrothermal stability. But La doping will decrease the amount of framework aluminum and Cu active sites of Cu/SSZ-13 after hydrothermally aging, even destroy zeolite CHA structure. This is quite harmful to the catalyst hydrothermal stability.

Low-temperature SCR of NOx by NH3 over MnOx/SAPO-34 prepared by two different methods: a comparative study

Chenglong Yu,Lifu Dong,Feng Chen,Xiaoqing Liu,Bichun Huang

Ce-Doped V2O5-WO3/TiO2 with Low Vanadium Loadings as SCR Catalysts and the Resistance of H2O and SO2

Liu Xiaolong,Zhao Ziwei,Ning Ruliang,Qin Yu,Zhu Tingyu,Liu Fagao

The promoting effect of Ce on V-W/Ti catalyst for selective catalytic reduction (SCR) of NO x by NH 3 was studied. Compared with the original V-W/Ti samples, addition of Ce contributed better NH 3 -SCR performance. The H 2 O and SO 2 resistance of Ce modified V-W/Ti catalyst was improved by the different impregnation sequence of Ce. The catalysts were characterized by NH 3 -temperature programmed desorption (NH 3 -TPD), X-ray photoelectron spectroscopy (XPS), and H 2 -temperature programmed reduction (H 2 -TPR) techniques. The results showed that the impregnation sequence of W and Ce influenced the NH 3 adsorption capacity of the catalysts. In comparison to 0.2V-5Ce-5W/Ti and 0.2V-(5Ce5W)/Ti, 0.2V-5W-5Ce/Ti catalyst contributed better H 2 O and SO 2 resistance, with the highest Ce 3+ /(Ce 4+  + Ce 3+ ) value of 36.6%. Besides, a catalytic mechanism of SCR reactions over Ce-doped V-W/Ti catalysts was proposed. Graphic

SCR denitration performance and mechanism of magnetic separation rare earth tailings activated by Mn combined with NaOH alkaline fusion

Qie Junmao,Cao Mengfei,Zong Jiaqi,Chang Jian,Zhang Shuqi,Xu Tong

Selective catalytic reduction (SCR) is presently the predominant technology for controlling nitrogen oxides (NO x ) emissions from industrial flue gas in China. Central to its operation is the denitration catalyst; however, the conventional systems face constraints such as a limited active temperature range, potential toxicity of certain active components, and high production costs. Bayan Obo rare earth tailings, enriched in catalytically active elements including Fe, Ce, and Nb, present a promising alternative raw material for denitration catalyst development. Currently, catalyst modification to improve denitration performance is a key research focus. In this study, Fe-rich magnetic separation rare earth tailings were obtained via magnetic separation processing of Bayan Obo tailings. We systematically evaluated the denitration performance and mechanism of catalysts prepared from these magnetic separation rare earth tailings through Mn modification in combination with NaOH alkaline fusion activation. Results indicate that when the catalyst is produced under conditions of 3 wt.% Mn loading and an ore-to-alkali ratio of 1:1.5, activated at 200 °C, the denitration efficiency reaches 89.6%. Furthermore, as the reaction temperature increases, the catalyst consistently exhibits high N 2 selectivity, maintaining values above 90% within the 100–300 °C range. The Mn-modified, NaOH alkaline fusion-activated catalyst shows enhanced stable adsorption of ammonia species, suppression of intermediate conversion to N 2 O, and improved N 2 selectivity. This work offers a viable approach for the high-value, sustainable utilization of rare earth tailings in environmentally friendly denitration technologies.

Unusual positive effect of SO2 on Mn-Ce mixed-oxide catalyst for the SCR reaction of NOx with NH3

JiaYu Chen,Peng Fu,Daofei Lv,Yang Chen,Meiling Fan,Junliang Wu,Amogh Meshram,Bin Mu,Xiang Li,Qibin Xia

A high-performance denitration catalyst based on Mn-Ce mixed-oxide derived from a specific Mn/Ce precursorwas fabricated by solvothermal method. It exhibited outstanding low-temperature activity, which achieved above 90% NO x conversion in the temperature of 150–310 °C. Remarkably, Mn-Ce mixed-oxide demonstrated a much better SO 2 tolerance, in which the NO x conversion increased from 92.6% to 97.8% at 150 °C after introducing 200 ppm SO 2 . The synthesized Mn-Ce mixed-oxide has a porous structure with abundant chemisorbed oxygen spices and exposed active sites. In addition, the increased acidity and redox capacity enhanced the catalytic activity after introducing SO 2 . Meanwhile, the injection of SO 2 separates NH 3 adsorption sites from oxidation agents, inhibiting the unwanted oxidization of ammonia to nitrogen oxides. Furthermore, the reaction pathway on Mn-Ce mixed-oxide proved to be the L-H mechanism based on in situ DRIFTS. Thus, the synthesized Mn-Ce mixed oxide demonstrated an excellent denitration performance and the especially high SO 2 tolerance, showing great potential for low-temperature NH 3 -SCR.

High Resistance of SO2 and H2O over Monolithic Mn-Fe-Ce-Al-O Catalyst for Low Temperature NH3-SCR

Shijie Hao,Yandi Cai,Chuanzhi Sun,Jingfang Sun,Changjin Tang,Lin Dong

Monolithic Mn-Fe-Ce-Al-O catalyst with honeycomb cordierite ceramic as a carrier was reported for the first time for low temperature deNOxapplication. In the reaction of selective catalytic reduction (SCR) of NO with NH3, a NO conversion of above 80% at 100 °C was obtained. Notably, the catalyst also showed excellent resistance against SO2and H2O. About 60% NO conversion was maintained after successive operation in the mixed stream of SO2and H2O for 168 h. The Brunner−Emmet−Teller (BET) measurement, SEM, EDS, thermogravimetric analysis (TG), FT-IR, and XPS results of the used catalysts indicated that certain amounts of ammonium sulfate was formed on the surface of the catalyst. XPS results revealed that partial of Fe2+was oxidized to Fe3+during the reaction process, and Fe2+species have strong redox ability, which can explain the decrease in activity after reaction. In addition, SO2and H2O induced a transformation of Ce from Ce4+to Ce3+on the surface of the catalyst, which increased the amount of chemisorbed oxygen. Owing to these factors, the addition of Ce and Fe species contributes to excellent resistance of the catalyst to SO2and H2O.Keywords:honeycomb catalyst;Mn-Fe-Ce-Al-O;low temperature denitration;water and sulfur resistance

Mechanistic assessment of NO oxidative activation on tungsten-promoted ceria catalysts and its consequence for low-temperature NH3-SCR

Wenshuo Hu,Yu Zhang,Xiaoxiang Wang,Weihong Wu,Hao Song,Yang Yang,Shaojun Liu,Chenghang Zheng,Xiang Gao

Ceria has absorbed extensive interests in functioning as catalysts for low-temperature (LT) selective catalytic reduction (SCR) of NOx due to its abundant surface oxygen species and salient redox property. The mechanistic interpretations of how such redox property contributes to its LT-SCR activity, however, still remain debated. Here, we use a model tungsten-promoted ceria catalyst (WO 3 /CeO 2 ), known as preeminent in LT-SCR reactions, and combine steady-state kinetic, structural characteristic and in situ spectroscopic experiments with theoretical treatments to reveal the mechanistic connections between NO oxidative activation and LT-SCR turnovers. We show that, compared with NO oxidation to NO 2 , NO oxidative activation to nitrite intermediates is both kinetically and thermodynamically more favorable; surface nitrate species are not detected in the present case, indicating their more difficult formation than nitrites. All these results thus suggest the prevalence of NO activation to nitrites over NO to nitrates or oxidation to NO 2 and subsequent occurrence of fast SCR in the WO 3 /CeO 2 -catalyzed LT-SCR reaction. These findings progress the understanding of LT-SCR reaction mechanism on CeO 2 -based catalysts and convey a detailed perspective of different reaction intermediates and their consequences for LT-SCR turnovers, which may contribute to the rational design of catalysts towards further improved LT-SCR activity.

Superior resistance to alkali metal potassium of vanadium-based NH3-SCR catalyst promoted by the solid superacid SO42−-TiO2

Yaoyao Peng,Lei Song,Siru Lu,Ziyu Su,Kui Ma,Siyang Tang,Shan Zhong,Hairong Yue,Bin Liang

The significant decrease of acid sites caused by alkali metal poisoning is the major factor in the deactivation of commercial V 2 O 5 -WO 3 /TiO 2 NH 3 -SCR catalysts. In this work, the solid superacid SO 4 2− -TiO 2 modified by sulfate radicals, was selected as the catalyst support, which showed superior potassium resistance. The physicochemical properties and K-poisoning resistance of the V 2 O 5 -WO 3 /SO 4 2− -TiO 2 (VWSTi) catalyst were carried out by XRD, BET, H 2 -TPR, NH 3 -TPD, XPS, in situ DRIFTS and TG. The results pointed out that the introduction of SO 4 2− significantly increased the NH 3 -SCR catalytic activity at high temperatures, with an exceptionally high NO x conversion over 90% between 275 °C and 500 °C. When 0.5% (mass) K 2 O was doped on the catalysts, the catalytic performance of the traditional V 2 O 5 -WO 3 /TiO 2 (VWTi) catalyst decreased significantly, while the VWSTi catalyst could still maintain a NO x conversion over 90% in the range of 300–500 °C. The characterizations suggested that the support of SO 4 2− -TiO 2 greatly increased the number of acidic sites, thereby enhancing the adsorption capacity of the reactant NH 3 . The results above demonstrated a potential approach to achieve superior potassium resistance for NH 3 -SCR catalysts using solid superacid.

Ti species regulated CuO/CeO2 catalyst for efficient simultaneously NH3-SCR denitration and CO oxidation under oxygen-rich conditions

Yiqing Zeng,Weilong Rong,Shule Zhang,Qin Zhong,Zhaoxiang Zhong

Synergistic control of multiple pollutants has high benefits during the control of emissions from fuel utilization, and catalysis can contribute to efficient removal of multiple pollutants. In this work, Ti species regulated CuO/CeO 2 (Cu/Ce) catalyst was constructed to efficient simultaneous NH 3 -SCR denitration and CO oxidation under oxygen-rich conditions. It is found that the introduction of Ti species into Cu/Ce catalyst induces the formation of three-dimensional pore structure and promotes the phase transition from crystalline to amorphous, which significantly enhances the specific surface area and the dispersion of CuO and CeO 2 . The well dispersed CuO and CeO 2 species provide a larger number of adsorbed sites for CO and NO and enhance the Cu-Ce interaction, which can contribute to reducing the competitive adsorption between CO and NO and the formation of a richer surface oxygen vacancies. Owing to above improvements, the Ti species regulated Cu/Ce catalyst can achieve more than 90% removal efficiency of NO x and CO at 148–218 °C, and the active temperature windows widened by 36 °C in comparison with Cu/Ce catalyst. Through this work, we expect to shed some light on the synergistic control of CO and NO x under oxygen-rich conditions.

cStudy on NH3-SCR performance of CoMnFeAl-LDO derived from layered double hydroxides supported on CNTs/TiO2NWs and its mechanism

Zhenzhen Guan,Yuanbin Xia,Dongchen Hang,Gan Chen,Mengyan Zhang,Zhihai Cheng,Xinxia Ma,Jiang Wu

In this study, a series of CoMnFeAl-layered double oxide (LDO) catalysts supported on multi-walled carbon nanotubes (MWCNTs)/titanium dioxide nanowires (TiO 2 NWs) were synthesized via the hydrothermal method. The catalytic performance of the synthesized catalysts was evaluated by the activity tests, and the characterizations and morphologies were measured by using X‐ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of ammonia (NH 3 -TPD), temperature-programmed desorption of sulfur dioxide (SO 2 -TPD), temperature-programmed reduction of hydrogen (H 2 -TPR), and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). The results demonstrated that both CoMnFeAl-LDO/CNT and CoMnFeAl-LDO/TiO 2 NW catalysts achieved 100 % NO x conversion within their optimal temperature ranges and exhibited excellent sulfur resistance. Morphological studies revealed that the introduction of CNTs or TiO 2 NWs effectively mitigated the aggregation and stacking of LDHs during calcination, resulting in enhanced dispersion of active components. Moreover, these modifications increased surface acidity, redox capability, and SO 2 tolerance of the CoMnFeAl-LDO catalyst. The in situ DRIFTS results indicated that the SCR reactions over CoMnFeAl-LDO/CNT and CoMnFeAl-LDO/TiO 2 NW followed both the Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms. This study highlighted the potential of CNTs/TiO 2 NWs to modify CoMnFeAl-LDO catalysts, offering insights for the design of efficient and sulfur-resistant catalysts to address stringent environmental regulations.