-
氨选择性催化还原 (NH3 selective catalytic reduction,NH3-SCR) 脱除氮氧化物 (NOx) 技术具有效率高、运行稳定等优点,已广泛应用于各类大型工业连续排放源。NH3-SCR技术关键为催化剂,其应用成本通常占60%[1]。V2O5-WO3(MoO3)/TiO2为最常见的商业催化剂,其温段 (300~400 ℃) 催化活性较高且抗硫抗水性较好[2]。然而,由于脱硝装置布设在除尘和脱硫设备前,SO2可被其催化剂氧化成SO3,进而与还原剂NH3生成(NH4)2SO4和NH4HSO4,附着于催化剂表面,导致催化活性降低[3];同时,烟气中较多的粉尘会对SCR反应器造成冲刷与磨损。为避免上述问题,推荐采用尾部低尘低温 (<250 ℃) 布置方式,将SCR反应器安装于脱硫装置和布袋除尘器之后。目前,我国有100余家大型垃圾焚烧发电厂采用低温SCR技术,其运行温度通常为180~220 ℃。然而,较低的温度使NH3转化率偏低,显著增加氨逃逸[4],因此研发能高效稳定脱硝且减少氨逃逸的低温SCR催化剂成为NH3-SCR领域研究热点。
锰 (Mn) 有多种价态,具有很强的氧化还原活性。Mn基催化剂在低温NH3-SCR催化剂领域应用较多[5]。同时,Cr2O3催化剂表现出良好脱硝活性[6],采用浸渍法对V2O5-WO3/TiO2进行Cr负载改性,可使催化剂的低温脱硝性能和抗硫性有较大提升[7]。负载Cr可增加催化剂表面酸性位点,从而增强催化剂表面氧吸附能力及对NH3的催化氧化能力[8]。此外,Mo负载可提升MnOx催化剂的脱硝性能,有利于Mn3+的形成,并增加烟气中NH3的吸附[9]。亚单层MoO3增加表面强酸位点数量,催化NH3氧化并增加其N2选择性[10]。添加Mo可提高CeO2-TiO2的脱硝效率,增加催化剂抗硫抗水性[11]。因此,本研究尝试将Mn基催化剂负载改性元素铬 (Cr) 和钼 (Mo) ,制备高效且具有降低氨逃逸功能的焚烧烟气低温脱硝制剂。
由于现有Mn基催化剂多使用含Mn的分析纯试剂制备金属氧化物复合物,或以碳纳米管和分子筛等为载体制备负载型Mn氧化物[12-16],使得催化剂生产成本较高。本课题组拟以天然锰矿粉 (manganese ore powder, MOP) 为基质材料制备相关催化剂,从而保证成本足够低廉,且制造的催化剂可以粉体状态直接注入烟气并一次性使用。
本研究拟通过浸渍法制备负载Cr和Mo的MOP催化剂,以天然锰矿粉作为对比,全面考察负载改性MOP催化剂在NH3存在和不存在2种氛围下的脱硝活性,以及NO存在和不存在2种氛围下的脱氨活性,并通过NH3全自动程序升温化学吸附仪及质谱联用 (NH3-TPD-MS) 、X-射线衍射 (XRD) 、场发射扫描电子显微镜 (FE-SEM) —能量色散X射线光谱仪 (EDS) 和X射线光电子能谱 (XPS) 表征分析,观测催化剂酸性位点、形貌、晶型结构及表面元素分布、价态变化,探索Cr和Mo负载改性对MOP脱硝和脱氨性能的影响机理,以期为廉价高效的低温脱硝催化剂制备提供参考。
负载Cr和Mo锰矿粉基催化剂的脱硝脱氨性能
Denitration and deamination performance of manganese ore powder-based catalysts with Cr and Mo loading
-
摘要: 氨选择性催化还原 (NH3-SCR) 技术在焚烧烟气NOx减排控制中广泛应用。然而,目前广泛商业化使用的SCR催化剂价格昂贵且低温活性差。以价格低廉的天然锰矿粉 (MOP) 为载体,采用浸渍法制备了Cr和Mo负载改性MOP,在温度范围150~400 ℃,对比研究了MOP和负载改性MOP的脱硝和脱氨催化效率,并基于NH3-TPD-MS、FE-SEM-EDS、XRD和XPS对所制备的催化剂进行表征。结果表明:MOP具有较高的催化脱硝脱氨活性;Cr负载可大幅提升MOP的氨转化率,且对脱硝效率没有明显影响;Cr主要以无定形Cr2O3形式物理附着于MOP表面,Cr与Mn之间没有明显的相互作用。同时,Mo负载对MOP的氨催化转化也有明显促进作用,2%Mo负载仅轻微减少了MOP在150~250 ℃时的脱硝效率。在5%Mo改性MOP表面,酸性位点数量和NH3吸附能力显著提高,但Mo与K反应生成钾钼盐结晶,导致Mn4+和Oα的相对含量降低。该研究结果可为低温低尘尾部布设SCR的同时脱硝脱氨提供参考。Abstract: NH3-SCR technology is extensively used in control of NOx emission from incineration flue gas. However, in recent decades the widely adopted commercial SCR catalysts were expensive and their activity at lower temperature was decreased. In the experiment, the cheap natural manganese ore powder (MOP) was selected as the carrier, and by impregnation method the modified MOP with Cr and Mo was prepared, respectively. In the temperature range of 150~400 ℃, NO and NH3 conversion efficiency between MOP and modified MOP was compared, and based on NH3-TPD-MS, FE-SEM-EDS, XRD and XPS analysis the prepared catalysts were characterized. The results demonstrated that MOP had high catalytic de-NOx and ammonia removal activity. Cr loading on MOP significantly enhanced NH3 conversion performance, and had no significant effects on the denitration efficiency. Cr was mainly physically adsorbed on the surface of MOP as amorphous Cr2O3. There was no evident interactions occurred between Cr and Mn. Meanwhile, Mo loading also remarkably promoted catalytic deamination activity of MOP, and the denitration efficiency over MOP doped with 2% Mo was only slightly declined at 150~250 ℃. On the surface of 5% Mo-modified MOP, acid sites and NH3 adsorption capacity was notably increased, but crystal K5Mo4O6 was formed due to the reaction between Mo and K, leading to the lowered relative content of Mn4+ and adsorbed oxygen (Oα). In summary, the experiment results provided the important references for simultaneous denitration and deamination of SCR located at the downstream under the conditions of low dust and temperature.
-
Key words:
- manganese ore powder /
- SCR at lower temperature /
- denitration /
- deamination
-
-
[1] 孔杨, 张泽凯, 李浙飞, 等. 近十年来(2011-2021)钒基NH3-SCR催化剂的研究进展[J]. 工业催化, 2022, 30(12): 16-33. [2] 李泽清, 陈红萍, 魏永林. 低温钒基脱硝催化剂的研究进展[J]. 广州化工, 2022, 50(7): 15-18,35. [3] 张延兵. Mn-基低温脱硝催化剂制备、性能及在聚苯硫醚滤料上的应用[D]. 福州: 福州大学, 2017. [4] 盛雨佳. 锰基复合氧化物低温脱硝及氨氧化研究[D]. 合肥: 合肥工业大学, 2021. [5] JO SH, SHIN BK, SHIN MC, et al. Dispersion and valence state of MnO2/Ce(1- x )Zr x O2-TiO2 for low temperature NH3-SCR[J]. Catalysis Communications, 2014, 57: 134-137. doi: 10.1016/j.catcom.2014.08.014 [6] 鲁文质, 赵秀阁, 王辉, 等. NO的催化氧化[J]. 催化学报, 2000, 21(5): 423-427. [7] 李春晓, 李坚, 梁文俊, 等. Cr负载V2O5-WO3/TiO2催化剂的低温NH3-SCR脱硝活性[J]. 高等学校化学学报, 2019, 40(7): 1447-1455. [8] YANG R, HUANG H F, CHEN Y J, et al. Performance of Cr-doped vanadia/titania catalysts for low-temperature selective catalytic reduction of NO x with NH3[J]. Chinese Journal of Catalysis, 2015, 36(8): 1256-1262. doi: 10.1016/S1872-2067(15)60884-1 [9] YANG G, ZHAO HT, LUO X, et al. Promotion effect and mechanism of the addition of Mo on the enhanced low temperature SCR of NO x by NH3 over MnO x /γ-Al2O3 catalysts[J]. Applied Catalysis B:Environmental, 2019, 245: 743-752. doi: 10.1016/j.apcatb.2018.12.080 [10] 杜月瑶. 负载型二维钼基催化剂脱硝性能及抗碱金属中毒性能研究[D]. 厦门: 华侨大学, 2021. [11] LI LL, LI PX, TAN W, et al. Enhanced low-temperature NH3-SCR performance of CeTiO x catalyst via surface Mo modification[J]. Chinese Journal of Catalysis, 2020, 41(2): 364-374. doi: 10.1016/S1872-2067(19)63437-6 [12] LI J, CHANG H, MA L, et al. Low-temperature selective catalytic reduction of NO x with NH3 over metal oxide and zeolite catalysts-A review[J]. Catalysis Today, 2011, 175: 147-156. doi: 10.1016/j.cattod.2011.03.034 [13] 吴大旺, 张秋林, 林涛, 等. Fe对Mn/CeO2-TiO2催化剂低温NH3选择性催化还原NO的影响[J]. 无机材料学报, 2012, 27(5): 495-500. [14] SU Y, FAN B, WANG L, et al. MnO x supported on carbon nanotubes by different methods for the SCR of NO with NH3[J]. Catalysis Today, 2013, 201: 115-121. doi: 10.1016/j.cattod.2012.04.063 [15] MOUSAVI SM, NIAEI A, GÓMEZ MJI, et al. Characterization and activity of alkaline earth metals loaded CeO2-MO x (M=Mn, Fe) mixed oxides in catalytic reduction of NO[J]. Materials Chemistry and Physics, 2014, 143: 921-928. doi: 10.1016/j.matchemphys.2013.09.017 [16] 黄增斌, 李翠清, 王振, 等. 不同分子筛负载锰铈催化剂的低温NH3-SCR脱硝性能[J]. 燃料化学学报, 2016, 44(11): 1388-1393. [17] ZHU M H, LAI J-K, WACHS IE. Formation of N2O greenhouse gas during SCR of NO with NH3 by supported vanadium oxide catalysts[J]. Applied Catalysis B:Environmental, 2018, 224: 836-840. doi: 10.1016/j.apcatb.2017.11.029 [18] ZHENG HL, SONG WY, ZHOU Y, et al. Mechanistic study of selective catalytic reduction of NO x with NH3 over Mn-TiO2: a combination of experimental and DFT study[J]. Journal of Physical Chemistry C, 2017, 121(36): 19859-19871. doi: 10.1021/acs.jpcc.7b06715 [19] QI G, YANG RT. Low-temperature selective catalytic reduction of NO with NH3 over iron and manganese oxides supported on titania[J]. Applied Catalysis B Environmental, 2003, 44(3): 217-225. doi: 10.1016/S0926-3373(03)00100-0 [20] KAPTEIJN F, SINGOREDJO L, ANDREINI A, et al. Activity and selectivity of pure manganese oxides in the selective catalytic reduction of nitric oxide with ammonia[J]. Applied Catalysis B:Environmental, 1994, 3: 173-189. doi: 10.1016/0926-3373(93)E0034-9 [21] 张先龙, 胡晓芮, 刘仕雯, 等. 锰基累托石低温NH3-SCR催化剂的制备方法[J]. 环境化学, 2022, 41(3): 1043-1051. [22] 姜明, 卞国柱, 姜伟, 等. 几种氧化物载体上钾相作用物种的结构形式[J]. 化学物理学报, 1993, 6(4): 370-376.