SCIENCE OF THE TOTAL ENVIRONMENT
·
2021
·
IF 7.963
Ji Liu,Wei Zhao,Shuang-wei Yang,Bin Hu,Ming-xin Xu,Shan-Wei Ma,Qiang Lu
Incineration of food waste leads to the release of NO x pollutants, whereas the formation mechanism of the NO x precursors (HCN, NH 3 , and HNCO) during the initial pyrolysis process is far from well-studied, limiting the source control on NO x release. In this work, 2,5-diketopiperazine (DKP) was selected as the N-containing model compound to study the formation mechanism of NO x precursors in food waste pyrolysis, by combining experiments and density functional theory (DFT) calculations. The C1-N2 bond broken via the N2-to-N5 H-transfer possesses the lowest energy barrier, together with the largest reaction rate constants in the range of 400–800 °C. NH 3 can be easily generated with low energy barriers and high rate constants at low temperatures (below 630 °C). Whereas, the rate constants of the pathways for HCN formation will exceed those for NH 3 generation in the range of 630–740 °C. In addition, the DKP pyrolysis can also lead to the formation of HNCO with a very low energy barrier, and it can convert into HCN and NH 3 through further hydrogenation and decomposition. These calculation results are exactly consistent with the experimental results that NH 3 was the main precursor in the range of 400–600 °C, and the yield of HCN exceeded that of NH 3 when the temperature was over 600 °C. Our current work on the formation mechanism of NO x precursors during the pyrolysis of DKP can provide theoretical guidance for the development of NO x control technology in the pyrolysis/combustion process of organic waste.
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PubMed
高影响因子
Journal of Environmental Chemical Engineering
·
2021
·
IF 5.909
Zhifei Hao,Guoquan Liu,Nan Ma,He Zhang,Yi Li,Yuguo Xia,Dongpeng Zhang,Sihui Zhan
Acidity and redox properties of the catalyst are two crucial factors affecting the performance of NH 3 -SCR. Herein, we design a novel WO x /Cu-CeO 2 oxide catalyst in which the WO x species are highly dispersed on the {111}/{100}-terminated surface of Cu-doped CeO 2 nanospheres , which exhibits great deNO x activity advantage and wide operating temperature window (200–400 °C, over 85% NO x conversion with a gas hourly space velocity (GHSV) of 60,000 h −1 ), as well as good sulfur resistance and N 2 selectivity . The relationship among the composition, acidity and redox properties of the WO x /Cu-CeO 2 catalyst is established in the NH 3 -SCR reaction. The combined experimental studies and spectroscopic characterization reveal that the introduction of Cu into the lattice of CeO 2 not only increases the surface Ce 3+ and oxygen vacancy concentration but also provides more sites for capture and dispersion of WO x species, thus mediating and improving the Lewis and Brønsted acid sites and reducibility of catalyst. XPS and DFT calculations further demonstrate that electronic interaction between WO x and Cu-doped CeO 2 is enhanced duo to the existence of interactions of short-range Ce-O-Cu and Ce-O-W. Moreover, the NH 3 -SCR reaction over WO x /Cu-CeO 2 may follow both Langmuir-Hinshelwood and Eley-Rideal reaction pathway according to the in situ DRIFTS.
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高影响因子
Advances in Materials Science and Engineering
·
2019
·
IF 1.399
Zhuo Yao,Dianli Qu,Yuxiang Guo,Yujing Yang,Hong Huang
Novel catalysts with high activity for the selective catalytic reduction of NO with NH3 (NH3-SCR) at low temperatures are highly demanded. In this study, mixed-node metal-organic frameworks (MOFs), e.g. Mn@CuBTC with controlled Mn composition in Cu3(BTC)2, were fabricated using postsynthetic exchange method and their structural characteristics and catalytic performances for NH3-SCR reaction were assessed. A series of analyses in terms of structure, surface morphology, texture, and chemical state determined that Mn ions were successfully incorporated into the Cu3(BTC)2 crystal lattice as well as adsorbed on the walls of nanopores in the framework. The pore sizes can be finely tuned in the presence of Mn ions in the cages, which significantly suppressed water adsorption. The NH3-SCR activity of Mn@CuBTC exhibited nearly 100% NOx conversion rate in the temperature range (230–260°C). The superior NH3-SCR performance is attributed to the proper pore sizes, reduced water content, and the synergistic effect between manganese and copper ions in the MOF structure, which enhanced NH3 bound to the active Lewis sites.
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高影响因子
AICHE JOURNAL
·
2019
·Vol. 65
·期 10
·e16684
·
IF 3.463
Lei Song,Kui Ma,Wen Tian,Junyi Ji,Changjun Liu,Siyang Tang,Wei Jiang,Hairong Yue,Bin Liang
A novel FeTiSO x catalyst prepared by a simple hydrolysis coprecipitation method was used for the selective catalytic reduction (SCR) of NO x with NH 3 , which exhibited high catalytic activity (NO x conversion of >97% and N 2 selectivity of >95%) and tolerance for both H 2 O and SO 2 at a broad temperature window of ~325–475°C. The characterization results showed that the formation of Fe–O–Ti and Fe–O–S species could significantly enhance the acidic sites of the catalyst, which play an important role in NH 3 absorption and their catalytic activity. The Fe 3+ ions in the bulk anatase TiO 2 could significantly enhance the redox properties for the SCR reaction and suppress the side reaction of NH 3 oxidation to NO or N 2 O. In addition, the reaction mechanism was discussed based on in situ diffuse reflectance infrared Fourier transform spectroscopy measurements and kinetic investigation, indicating that the reaction was dominated by the Eley–Rideal mechanism over the FeTiSO x catalyst.
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高影响因子
COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS
·
2019
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IF 3.131
Boqiong Jiang,Beilong Lin,Zhiguo Li,Shuang Zhao,Ziying Chen
A series of Mn/TiO 2 catalysts were prepared by ultrasonic spray pyrolysis (USP) method for selective catalytic reduction (SCR) of NOx from flue gas at low temperatures. The highest activity of Mn/TiO 2 was obtained with a Mn/Ti ratio of 0.5. When Fe was doped into Mn(0.5)/TiO 2 , the NOx conversion rate on Fe(0.05)-Mn(0.5)/TiO 2 was increased by approximately 10 % at 120–180 °C. The samples were characterized by XRD , SEM , H 2 -TPR, and N 2 adsorption analyses. Results revealed that Mn(0.5)/TiO 2 with Mn/Ti ratio of 0.5 presented the lowest crystallinity , the highest surface area, and the highest redox ability. Although the surface area was significantly decreased by Fe doping, it also reduced the crystallinity and crystal size of the catalysts, thereby increasing the O concentration on the surface of catalyst. Moreover, Fe(0.05)-Mn(0.5)/TiO 2 displayed a higher redox ability than the other catalysts. At 120–240 °C, the activation energy decreased from 27.65 kJ/mol on Mn(0.5)/TiO 2 to 14.46 kJ/mol on Fe(0.05)-Mn(0.5)/TiO 2 , thereby facilitating the activation of the reaction on Fe(0.05)-Mn(0.5)/TiO 2 . Despite that the NO and NH 3 adsorptions were lower on Fe(0.05)-Mn(0.5)/TiO 2 than on Mn(0.5)/TiO 2 , the intermediates on Fe(0.05)-Mn(0.5)/TiO 2 , particularly nitrates, were easily activated to participate in the reaction, leading to increasing catalytic activity.
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RSC Advances
·
2017
·Vol. 7
·期 60
·37787-37796
·
IF 3.108
Xuesong Liu,Xiaodong Wu,Duan Weng,Zhichun Si,Rui Ran
Cu/SAPO-34 catalysts were prepared by wet impregnation and ion-exchange methods, and both the catalysts were hydrothermally treated at 750 °C in 10 vol% H2O/air for 24 h. Subsequently, the as-received and hydrothermally treated catalysts were exposed to a sulfur poisoning treatment at 350 °C in 100 ppm SO2/10 vol% H2O/air for 24 h and examined for NOx conversion. Sulfur poisoning considerably decreased the NOx conversion efficiency of the catalysts at low temperatures. In contrast, it improved the high-temperature selective catalytic reduction (SCR) activities of the as-received catalysts. The ion-exchange-prepared catalysts displayed higher sulfur tolerance than the impregnation-prepared catalysts at 150–350 °C. The electron paramagnetic resonance, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy and H2-temperature-programmed reduction results showed that sulfur poisoning significantly influenced the migration of the copper species and thereby the amount of active isolated Cu2+. More dispersed CuSO4 was produced on the ion-exchange-prepared catalysts than on the impregnation-prepared catalysts after sulfur poisoning. The dispersed CuSO4 showed considerably higher SCR activity than the crystalline CuSO4. Both the dispersed CuSO4 and remaining isolated Cu2+ determined the low-temperature SCR behavior of the sulfur-poisoned catalysts.
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高影响因子
MICROPOROUS AND MESOPOROUS MATERIALS
·
2022
·
IF 5.876
En-Hui Yuan,Meng Li,Ming-Hui Yang,Xiaosheng Huang,Kun Zhang,Weiliang Han,Zhicheng Tang,Zhong-Wen Liu
A direct hydrothermal synthesis strategy is developed to prepare the Cu–Fe-ZSM-5 zeolites by using the ethylenediaminetetraacetic acid disodium dihydrate (EDTA-2Na·2H 2 O) chelated Cu 2+ and Fe 3+ precursors as metal sources. During the crystallization, the metal chelates were spontaneously embedded into the ZSM-5 crystals and subsequently transformed to the zeolites encapsulated copper and iron species after removing the chelating agent via the high-temperature calcination . Rigorous characterizations indicate that the resulted Cu 2+ /Cu + and Fe 3+ /Fe 2+ species are formed ultra-small nano-composites with an average diameter of ∼2.2 nm and highly dispersed in the ZSM-5 zeolite crystals. The acidity of the ZSM-5 zeolites is subtly modulated by the encapsulated Cu–Fe nano-composite. As expected, the as-prepared Cu–Fe-ZSM-5 exhibits outstanding catalytic performance for the selective catalytic reduction of NO x with ammonia (NH 3 -SCR) in the broad reaction temperature ranges of 220–480 °C, which is much better than the Cu–Fe/ZSM-5 prepared with the conventional wetness impregnation method. Furthermore, the resultant zeolites show high stability and good tolerance to H 2 O and SO 2 , and it is very competitive for practical application to eliminate NO x . The developed one-pot hydrothermal synthesis route by using EDTA-2Na·2H 2 O as chelating agent is very convenient and easily reproducible, providing a general guideline to design and fabricate the superior transition metal modified zeolite catalysts for NH 3 -SCR and the related reactions.
研究领域:
催化
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环境科学
·
材料科学
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高影响因子
SEPARATION AND PURIFICATION TECHNOLOGY
·
2025
·
IF 9
Yanping Yang,Shengchen Li,Shunli Shi,Jie Hu,Zexi Xuchen,Shunmin Ding,Dan zhao,Shengjun Deng,Weiming Xiao,Shuhua Wang,Chao Chen
Manganese oxide (MnO x ) catalysts are promising for low-temperature NH 3 -Selective Catalytic Reduction (NH 3 -SCR) with their superior catalytic performance. However, the presence of alkali metals in flue gases, particularly potassium (K), leads to catalyst deactivation and limits their industrial application. This study investigates the synergistic effects of Ce and Nb doping on the K resistance and low-temperature NH 3 -SCR activity of MnO x . The surface acidity and redox properties of MnO x were modulated by Ce and Nb modification. In addition, the phase structure, surface state and active sites of the catalysts were characterized before and after K poisoning. The results indicated that Nb 0.05 Ce 0.05 MnO x exhibited exceptional low-temperature performance, achieving over 90 % NO conversion at 125-250°C, along with significant resistance to K poisoning·NH 3 -TPD and in-situ experiments revealed that the loss of acid sites is the primary cause of K poisoning. The mechanism follows the L-H mechanism with L-acid sites as the main active sites on the catalyst surface and bridging nitrate as the key intermediate state. This research provides valuable insights into enhancing the industrial applicability of MnO x- based catalysts for low-temperature denitrification.
研究领域:
催化化学
·
环境工程
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高影响因子
RSC Advances
·
2017
·Vol. 7
·期 51
·32146-32154
·
IF 3.108
Chengkai Pang,Yuqun Zhuo,Qiyu Weng
A series of Mn-exchanged SAPO-34 catalysts were synthesized and developed as catalysts for the low temperature selective catalytic reduction (SCR) of NO with ammonia in the presence of excess oxygen. 4Mn/SAPO-34 showed the highest SCR activity in the temperature range of 120–210 °C. The microstructure of zeolite supports, acidity, manganese species and reaction mechanism were investigated in detail by BET, NH3-TPD, UV-Vis, H2-TPR, XPS and in situ DRIFTS. Mn3+ and Mn4+ related species were proved to be the active sites for the SCR reaction. The Eley–Rideal mechanism was proved to be effective on 4Mn/SAPO-34 for the low temperature SCR reaction in which coordinated NH4+ species react with gas-phase NO to form an activated transition state and subsequently decomposed to N2 and H2O.
研究领域:
环境科学
·
催化化学
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高影响因子
CHEMICAL ENGINEERING RESEARCH & DESIGN
·
2025
·
IF 3.9
Chenhui Hu,Kaimin Du,Zuoxi Zhuo,Chunhong Liu,Hongbing Lv,Wanjue Wang
To address the challenges of efficient and safe denitrification under actual flue gas conditions of internal combustion engine, high-temperature SCR molecular sieve catalyst were prepared and evaluated both in laboratory scale and industrial scale. A comprehensive characterization via TG, XRD, N₂ adsorption-desorption, SEM, and TEM confirmed the robust thermal stability of the molecular sieves catalyst. The molecular sieve catalyst system was commissioned in a 4275 kW distributed natural gas internal combustion engine demonstration facility and successfully passed the 72 h trial running, achieving with over 94 % NO x conversion efficiency and less than 40 mg/m 3 outlet NO x concentration at a temperature range of 440–525 °C. Compared to conventional V-based catalyst, the molecular sieve catalyst not only achieved additional reductions of 2 kg/h NO x and 38 kg/h CO 2 emissions, along with a nearly 2 % improvement in internal combustion engine efficiency, but also effectively mitigated the risk of system shutdown caused by low cylinder temperatures in exhaust gas purification systems, being considered as a promising catalyst for high-temperature applications, including gas-fired, hydrogen/ammonia-fueled, and biogas internal combustion engines.
研究领域:
环境催化
·
能源工程
·
污染控制技术
·
材料科学
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高影响因子
INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH
·
2021
·
IF 3.764
Wenshuo Hu,Renzhi Zou,Yi Dong,Yu Zhang,Mingchu Ran,Qi Xin,Yang Yang,Hao Song,Weihong Wu,Shaojun Liu,Chenghang Zheng,Xiang Gao
Enhancement of the low-temperature (LT) performance of selective catalytic reduction (SCR) of NOx with NH3 has been a spotlight in environmental catalysis. Here, we use a bifunctional catalytic system mixing V–W/Ti with an oxidative component, i.e., MnOx/CeO2, to achieve both improved LT-SCR activity and N2 selectivity. An integrated approach of steady-state kinetic measurements, chemical trapping techniques, time-resolved in situ FTIR spectroscopy, and density functional theory (DFT) calculations reveals that such a synergistic enhancement is at a short distance and is significant when V–W/Ti and MnOx/CeO2 are in intimate contact. These findings further suggest a bifunctional LT-SCR pathway mediated by a short-lived, mobile nitrite-precursor intermediate, which is facilely generated on the oxidative component and then communicates with the adjacent SCR phase through reacting with the abundant NH3 adsorbates there. Assembling such a mechanism with commercial SCR catalysts, accordingly, acts as a promising way to enhance the LT-SCR performance.
研究领域:
环境催化
·
材料科学
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DOI
高影响因子
TALANTA
·
2025
·
IF 6.1
Rui Yang,Luji Yang,Jiahui Yang,Zhi-ang Li,Chengbin Zheng
Pollution caused by nitrogen oxides (NO x , mainly NO and NO 2 ) has attracted considerable attention due to its negative implications on the environment and human health. Herein, a novel, portable, and battery-operated system integrating a purge and trap (P&T) system with a miniaturized point discharge optical emission spectrometer ( μ PD-OES) was developed for monitoring atmospheric NO x . Among NO x , NO 2 can be selectively and directly absorbed by sodium hydroxide (NaOH) solution and converted to nitrite (NO 2 − ). In contrast to NO 2 , NO cannot be absorbed by NaOH and must be oxidized to NO 2 by KMnO 4 prior to its absorption. When NO 2 and NO x samplers were exposed simultaneously, NO can be calculated as the difference. The concentration of NO x in the air was determined by analyzing the NO 2 − . The obtained NO 2 − solution was purged with an argon carrier gas at a rate of 400 mL min −1 for 5 min to remove all the volatile organic compounds contained in the solution before reacting with cyclamate to generate volatile cyclohexene, which was efficiently isolated and preconcentrated by P&T. Subsequently, the cyclohexene was desorbed from the P&T unit and swept into the μ PD-OES for its detection under optimized conditions. The system demonstrated a detection limit of 0.02 ppbv (0.04 μg/m 3 ) for NO 2 , surpassing conventional methods. Precision expressed as the relative standard deviation (RSD, n = 11) was better than 3.5 %. The system was validated by analyzing two NO 2 standard gases and fourteen ambient air samples, and the obtained analytical results demonstrated its promising potential for rapid, sensitive, and precise NO x evaluation and monitoring.
研究领域:
环境科学
·
分析化学
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PubMed
高影响因子
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