一种新型高比表面积TiO_2载体在NH_3选择性催化还原反应中对V_2O_5分散性的促进作用（英文）

NH_3 selective catalytic reduction of NO: A large surface TiO_2 support and its promotion of V_2O_5 dispersion on the prepared catalyst

燃煤电厂及工业窑炉的氮氧化物减排是改善空气质量的关键.现阶段选择性催化还原氮氧化物是最有效的技术途径,核心是采用以TiO_2为载体的钒基催化剂净化烟气.催化剂的活性是决定烟气净化效率的重要因素.近些年的研究主要集中在活性组分的替换上,但是由于其成本高昂,抗水抗硫性能较差,在实际中使用的效果不佳.本文从载体入手,制备了新型TiO_2载体,并采用特殊制备手段研发了新型高比表面积钒钛体系催化剂.通过对载体和催化剂的物化表征,研究了高比表面积TiO_2载体对于活性组分钒在表面分散的促进作用,及分散性的提高对氧化性和酸性的影响.所制新型TiO_2载体比表面积达到380.5 m^2/g,较商业化TiO_2载体提高了5倍.以此为载体,采用超声浸渍法和分段烧结的热处理方式,制备了钒负载量为5 wt%的新型钒钛催化剂.结果发现,高比表面载体显著提高了钒基催化剂比表面积为117.7 m^2/g,比传统钒钛催化剂提高了38%.计算结果表明,这种方式还提高了钒物种在载体表面的分散性.XRF结果表明,超声浸渍法和普通浸渍法均可将5 wt%的钒成功地负载到了载体上.通过模拟实际烟气成分对催化剂的脱硝效果进行了测试,结果表明,所制催化剂具备更宽的温度窗口及更好的N_2选择性,NO_x转化率在200–450°C时能保持在80%以上,比传统方法制备的催化剂温度窗口宽100°C.且N_2选择性在400°C以上时也明显更高.对两种催化剂样品的抗水抗硫能力进行了考察,发现在烟气中存在H_2O或SO_2时,高比表面积催化剂样品相较传统方法制备的催化剂具有更高的活性.Raman结果发现,在传统商业载体上钒物种由于分散不充分,更易在烧结过程中形成V-O-V物种,从而降低了催化剂的氧化还原性.而新型催化剂表面的V-O-Ti及V=O物种数量更多,这些物种活性更高,从而使得催化剂在低温下具有更高的NO_x转化率.采用NH_3-TPD,H_2-TPR和XPS技术研究了活性提高与催化剂结构的关系.结果发现,高比表面积载体通过对钒物种的分散作用,在载体表面由于二氧化钛载体的孔结构和钒物种的高活性,也使得该催化剂具有较高的酸量和氧化还原性.本文为制备新型烟气脱硝催化剂提供了理论依据,该技术方法具有较高的应用价值.

A titania support with a large surface area was developed, which has a BET surface area of 380.5 m^2/g, four times that of a traditional titania support. The support was ultrasonically impregnated with 5 wt% vanadia. A special heat treatment was used in the calcination to maintain the large surface area and high dispersion of vanadium species. This catalyst was compared to a common V2O5-TiO2 catalyst with the same vanadia loading prepared by a traditional method. The new catalyst has a surface area of 117.7 m^2/g, which was 38% higher than the traditional V2O5-TiO2 catalyst. The selective catalytic reduction（SCR） performance demonstrated that the new catalyst had a wider temperature window and better N2 selectivity compared to the traditional one. The NO conversion was 80% from 200 to 450 °C. The temperature window was 100 °C wider than the traditional catalyst. Raman spectra indicated that the vanadium species formed more V-O-V linkages on the catalyst prepared by the traditional method. The amount of V-O-Ti and V=O was larger for the new catalyst. Temperature programmed desorption of NH3, temperature programmed reduction by H2 and X-ray photoelectron spectroscopy results showed that its redox ability and total acidity were enhanced. The results are helpful for developing a more efficient SCR catalyst for the removal of NOx in flue gases.