水泥分解炉高CaO/CO_2环境CO还原NO机制
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摘要
通过流化床反应器模拟水泥分解炉高CaO/CO_2环境,并结合分子动力学广义梯度密度泛函理论,研究了CaO对CO还原NO的催化特性和CO_2促使CaO催化失效规律。在900℃、体积分数15%CO_2下,CaO催化作用可使NO脱除效率提高18%左右。在900℃时,当CO_2体积分数由5%升至30%,CO对NO还原率由97.0%降低到23.4%,且随反应时间增长CaO对CO还原NO的催化作用不断减弱。基于广义梯度密度泛函理论计算,CO_2,CO,NO在CaO表面活性位点的吸附能依次为CO_2(-1.869 eV)>NO(-0.781 eV)>CO(-0.669 eV),随着CO_2体积分数升高或反应时间增长,吸附在CaO表面的CO和NO减少,高体积分数CO_2促使CaO催化作用失效。CO还原NO的反应势垒(10.84 eV)大于CaO表面CO还原NO反应势垒(2.06 eV),CaO易催化CO还原NO。
The reduction of nitric oxide by carbon monoxide catalyzed by calcium oxide and the failure patterns of catalytic activity caused by CO_2 were investigated by means of an experiment in high CaO/CO_2 environment operated by fluidized bed reactor, combined with density functional theory(DFT) calculations with the generalized gradient approximation. At 900 ℃, the efficiency of NO reduction was enhanced by 18% due to the catalytic effect of calcium oxide. NO reduction rate reduced to 23.4% from 97.0% when the volume fraction of CO_2 increased from 5% to 30%. With the increase of reaction time, the catalytic effect of CaO on NO reduction by CO decreases. Based on the density functional theory(DFT) calculations with the generalized gradient approximation, the adsorption energy of CO_2,CO and NO on the active sites of CaO surface decreases with the order of CO_2(-1.869 eV)>NO(-0.781 eV)>CO(-0.669 eV). With the increase of CO_2 volume fraction or reaction time, the amount of CO and NO adsorbed on CaO surface decreases. High volume fraction of CO_2 contributes to the failure of CaO catalytic activity. The energy barrier(10.84 eV) of NO reduction by CO without CaO is higher than that(2.06 eV) of NO reduction by CO on CaO surface. It is easier for CaO to catalyze NO reduction by CO.
The reduction of nitric oxide by carbon monoxide catalyzed by calcium oxide and the failure patterns of catalytic activity caused by CO_2 were investigated by means of an experiment in high CaO/CO_2 environment operated by fluidized bed reactor, combined with density functional theory(DFT) calculations with the generalized gradient approximation. At 900 ℃, the efficiency of NO reduction was enhanced by 18% due to the catalytic effect of calcium oxide. NO reduction rate reduced to 23.4% from 97.0% when the volume fraction of CO_2 increased from 5% to 30%. With the increase of reaction time, the catalytic effect of CaO on NO reduction by CO decreases. Based on the density functional theory(DFT) calculations with the generalized gradient approximation, the adsorption energy of CO_2,CO and NO on the active sites of CaO surface decreases with the order of CO_2(-1.869 eV)>NO(-0.781 eV)>CO(-0.669 eV). With the increase of CO_2 volume fraction or reaction time, the amount of CO and NO adsorbed on CaO surface decreases. High volume fraction of CO_2 contributes to the failure of CaO catalytic activity. The energy barrier(10.84 eV) of NO reduction by CO without CaO is higher than that(2.06 eV) of NO reduction by CO on CaO surface. It is easier for CaO to catalyze NO reduction by CO.
引文
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[2] FU Shilong, SONG Qiang, TANG Junshi, et al. Effect of CaO on the selective non-catalytic reduction de NOx, process: Experimental and kinetic study[J]. Chemical Engineering Journal, 2014, 249(4): 252-259.
[3] 吕刚, 陆继东, 谢新华,等. 水泥分解炉内煤焦及煤粉还原NO的试验[J]. 华中科技大学学报:自然科学版, 2011(8): 124-128.
[4] TSUJIMURA M, FURUSAWA T, KUNII D. Catalytic reduction of nitric oxide by carbon monoxide over calcined limestone.[J]. Journal of Chemical Engineering of Japan, 1983, 16(6): 524-526.
[5] HANSEN P F B, DAM-JOHANSEN K, JOHNSSON J E, et al. Catalytic reduction of NO and N2O on limestone during sulfur capture under fluidized bed combustion conditions[J]. Chemical Engineering Science, 1992, 47(9/10/11): 2419-2424.
[6] ACKE F, DAN S. Apparent activation energies for the reduction of NO by CO and H2 over calcined limestone and CaO surfaces[J]. Energy & Fuels, 1998, 12(5): 945-948.
[7] DAM-JOHANSEN K, HANSEN P F B, RASMUSSEN S. Catalytic reduction of nitric oxide by carbon monoxide over calcined limestone: reversible deactivation in the presence of carbon dioxide[J]. Applied Catalysis B Environmental, 1995, 5(4): 283-304.
[8] 刘亮, 洪迪昆, 冯于川,等. CaO基CO2吸附剂掺杂/负载活性组分的第一性原理[J]. 燃烧科学与技术, 2017, 23(5): 412-417.
[9] LIU Ruiqiu, SHEN Wei, ZHANG Jinsheng, et al. Adsorption and dissociation of ammonia on Au (1 1 1) surface: A density functional theory study[J]. Applied Surface Science, 2008, 254(18):5706-5710.
[10] NOVELL-LERUTH G, VALCARCEL A, CLOTET A, et al. DFT characterization of adsorbed NH(x) species on Pt(100) and Pt(111) surfaces[J]. Journal of Physical Chemistry B, 2005, 109(38):18061-9.
[11] OH S H, FISHER G B, CARPENTER J E, et al. Comparative kinetic studies of CO-O2, and CO-NO reactions over single crystal and supported rhodium catalysts[J]. Journal of Catalysis, 1986, 100(2):360-376.
[12] JIANG Zhao, QIN Pei, FANG Tao. Mechanism of ammonia decomposition on clean and oxygen-covered Cu (1 1 1) surface: A DFT study[J]. Chemical Physics, 2014, 445:59-67.
[13] 何涛,曹彬,胡军印,等. 高温下钙基吸附剂吸附CO2的研究[J].化学工程,2007(12): 8-11.