摘要
火电厂和机动车辆等的NOx排放量与日俱增,NOx的治理已成为环境保护的重要组成部分.以NH3作为还原剂的选择性催化还原(SCR)技术是目前消除NOx最为高效的方法之一.该反应最为典型的催化剂是V2O5–WO3(MoO3)/TiO2,催化活性窗口为250–400o C.国外通常将SCR系统置于省煤器之后,此时烟气温度在300o C以上,催化剂能保持较高的活性,但易受到烟气中高浓度烟尘、SO2和碱金属等的影响,寿命相对较短.此外,高温工艺中副产物硫酸铵的堵塞也是一个不可忽视的问题.因此,将SCR脱硝装置设在脱硫除尘之后成为一种优选技术之一,但烟气温度会降至250o C以下,而常规的钒基催化剂不能满足低温活性要求.通过添加助剂或改变载体可改善钒基催化剂的低温活性,同时保持其高效的抗硫能力.本文以Cr和V为活性组分,Ti O2为载体,采用浸渍法制备了铬钒钛(Cr–VO x/Ti O2)系列催化剂,考察了它们的低温脱硝活性和抗水抗硫性,并通过N2吸附-脱附、X射线衍射、NH3程序升温脱附(NH3-TPD)、H2程序升温还原(H2-TPR)和X射线光电子能谱等手段对催化剂进行了表征,分析了Cr–V催化剂的作用机制.结果显示,当n(Cr):n(V)为0.2:0.8,活性组分负载量为10 wt%时,Cr–VO x/Ti O2催化剂表现出最佳的低温催化活性;当反应温度为160°C时,NO x转化率达到90%以上,明显优于其他催化剂,同时活性窗口(160–300°C)得到拓宽.NH3-TPD结果表明,VO x/Ti O2催化剂表面呈中弱酸性,随着Cr的添加,钒基催化剂的NH3脱附峰向高温拓宽,说明其表面强酸量有所增加,Cr0.2–V0.8/Ti O2在160–300°C范围内均出现了NH3的脱附峰,此时催化剂表面弱酸量最大.当n(Cr):n(V)大于0.2:0.8时,催化剂表面出现强酸位,这种强酸位不利于NH3脱附,从而不利于SCR反应的进行.因此适量Cr的添加有助于提高钒基催化剂表面弱酸及中性酸量.H2-TPR结果发现,助剂Cr的添加使得催化剂表面氧�
Cr–V/TiO2 catalysts with different Cr/V molar ratios for low-temperature selective catalytic reduc-tion （SCR） of NO with NH3 were prepared by impregnation. The samples were characterized using X-ray diffraction, NH3 temperature-programmed desorption, H2 temperature-programmed reduc-tion, and X-ray photoelectron spectroscopy. The results show that doping with Cr ions increased the amounts of weak and medium acid sites on the catalyst surface, as well as the low-temperature reductive capacity for high-valence V ions, and promoted the chemical adsorption of oxygen on the catalyst surface, which enhanced the rate of the SCR reaction. The catalyst with a Cr/V molar ratio of 0.2：0.8 and 10 wt%loading gave the largest amount of weak acid sites and the best NOx-removing performance, with a NOx conversion greater than 90%at 160–300 ℃. This catalyst had high stabil-ity in the presence of 0.01%SO2.
出处
《催化学报》
SCIE
CAS
CSCD
北大核心
2015年第8期1256-1262,共7页
基金
supported by the National Natural Science Foundation of China(21107096)
the Zhejiang Provincial Natural Science Foundation of China(LY14E080008)
the Commission of Science and Technology of Zhejiang Province(2013C03021)~~
关键词
低温
选择性催化还原
氨
铬钒钛催化剂
烟气脱硝
抗硫性
铬掺杂
Low temperature Selective catalytic reduction Ammonia Vanadia/titania catalyst Nitrogen oxide removing Sulfur resistance Chromium doping
