基于含钛高炉渣的V2O5-WO3/TiO2-SiO2催化剂制备及NH3-SCR脱硝性能

钒钛基脱硝催化剂，特别是添加WO3 或 MoO3 后，显示出其高催化活性和良好的抗SO2中毒稳定性，在燃烧烟气NH3-SCR脱硝中得到了广泛应用。但该系列的催化剂以昂贵化学前驱体及大量的纳米TiO2为原料，其成本相对较高，限制了催化剂的在中小型工业燃烧烟气中的应用。含钛高炉矿渣（Ti-BFS），富含TiO2、SiO2、CaO和Al2O3，其中TiO2含量约为20-30％，是广泛存在于我国西部地区的钛铁伴生矿且在钢铁冶炼过程产生的大宗废弃物，每年的排放超过360万吨，无有效的处理和利用途径将造成严重的环境问题和资源浪费。本论文以高炉渣中的钛硅资源利用为目标，将其提取制备TiO2-SiO2，并用作脱硝催化剂载体开发低成本高效的V2O5-WO3/TiO2-SiO2 催化剂。首先，通过调控酸解过程H2SO4的浓度和水解pH值，从Ti-BFS出发制备了系列TiO2-SiO2载体，再浸渍钒和钨前驱体使之成为SCR催化剂用于脱硝。通过对V2O5-WO3/TiO2-SiO2催化剂的SCR性能与载体结构进行测试表征后发现，脱硝性能不仅与载体孔道结构有关，且对载体中的SiO2含量及其他炉渣中带入的微量杂质比较敏感。通过对比优化发现，载体中SiO2为9.2％以及适量的Al2O3/Fe2O3/SO42-存在下显示出高效的NO脱除效率。前者SiO2增强了载体酸性和VOx的还原能力，而后者则与载体高比表面积、活性组分VOx的高分散程度，充足的弱酸位点和大量的Oads和V4+物种有关。区别于TiO2与化学合成的TiO2-SiO2载体，从炉渣得到的TiO2-SiO2载体及其催化剂具有催化NO-NH3反应的良好活性，但太多的SiO2 和 SO42-（约3%）将导致TiO2-SiO2粒子的集聚，形成强酸位点和大量的Oads物种，不利于催化剂的选择性和使用寿命。为验证低浓度废酸应用于高炉渣浸取的可能性，进一步采用机械球磨反应的方式，分别采用30%的硫酸溶液和循环废酸制备TiO2-SiO2载体和相应的催化剂粉末，通过优化球磨反应时间、废酸循环次数与载体的组成结构关系，发现使用两次、三次循环废酸进行酸解反应导致产物中SiO2和其他杂质过多，载体中孔道分布范围过宽，不利于反应物在催化剂中的扩散与VOx在催化剂表面上的沉积分散。分别将新鲜酸液和一次循环酸液制备的粉体涂覆在堇青石蜂窝基体表面，制备了两种涂敷型整体式催化剂。而一次废酸循环制备的催化剂粉末和涂敷催化剂表现出更好的NO脱除性能和稳定的抗SO2中毒能力。最后，为实现BFS中Ti的高收率提取，在水热环境中考察了炉渣与硫酸的反应参数。在酸/矿渣质量比为2.0、温度150℃反应2h的条件下，TiO2纯度可达到97％，在颜料，化妆品，瓷器和陶瓷行业具有潜在的应用。在酸/矿渣比(1-2)的条件下，制备的TiO2纯度为88-95％（收率>75％）可作为生产钛金属的高钛渣原料。所得到的TiO2-SiO2, TiO2-Al2O3的混合氧化物可以作为脱硝或是其他催化剂载体，是这类含硅Ti载体的有效利用途径。酸解剩余残渣CaSO4.SiO2具有典型的纤维结构，比表面积为80 m2/g，可以作为良好的保温建材原材料，其中的SiO2的存在会有效的增强石膏板材的性能。通过本论文研究表明，上述三种方法从含钛高炉渣中提取制备TiO2-SiO2载体继而制备脱硝催化剂的思路是可行的。其中采用低浓度废酸的机械研磨反应方法制备的TiO2-SiO2脱硝载体，因反应条件温和，废酸排放最少，具有相对应用优势。以含钛高炉渣作为初始原料，替代现有的钛精矿制备具有高脱硝活性的钛硅载体具有良好的经济效益和应用前景，也为高炉渣的处理利用开辟了方向。;The vanadium-based catalysts, especially V2O5/TiO2 doped with WO3 or MoO3, have achieved great success in selective catalytic reduction (SCR) with NH3 for coal-fired flue gas denitration due to their high activity and durability toward SOx poisoning. Nevertheless, this kind of catalysts has relatively high price by using the Ti and V precursors, which consumes a large amount of high-purity TiO2 and restricts their wide application in industrial boilers furnaces. On the other hand, titanium-bearing blast furnace slag (Ti-BFS), which mainly consists of CaO, TiO2, SiO2 and Al2O3 with their contents of about 20-30%, is a massive solid waste from iron-steel industry. In China, it amounts 3.6 million tons per year, and could cause serious environmental problems if without efficient treatment and reuse. Considering the enriched Ti/Si sources in Ti-BFS, this study is devoted to developing low-cost V-W/Ti-Si catalysts with as well rather high efficiency from Ti-containing slag. The main focus in the thesis was laid on DeNOx performance of slag-based catalysts, but the information on synthesis, characteristics and potential applications of some slag-based products and residue were also addressed to outline a concept for full utilization of Ti-BFS.Through the adjustment of H2SO4 concentration and pH value in precipitation, a series of TiO2-SiO2 supports were obtained from Ti-BFS by conventional sulfate method, and they were further impregnated with V2O5 and WO3 to prepare the SCR catalysts for NOx removal. It was revealed that SCR performance of the resulting V2O5-WO3/TiO2-SiO2 catalysts is directly related to support structure and sensitive with the concentration of SiO2 and unavoidable dopants in support composition. The incorporated SiO2 up to 9.2% and the proper amount of Al2O3/Fe2O3/SO42- unavoidable dopants in the slag-based supports are shown to have very positive impacts on NO conversion. While the former is responsible for the enhancement in the acidity and VOx reducibility, the latter mainly resulted in a large surface area, well-dispersed active VOx species, sufficiently weak acid sites and high amount of Oads and V4+ species. These enabled slag-based catalysts to have good activity for catalyzing NO-NH3 reaction in reference to catalysts synthesized from commercial TiO2 and TiO2-SiO2 reagents. Nonetheless, too much SiO2 and SO42- dopant (about 3%) in the support caused agglomeration of TiO2-SiO2 particles, formation of strong acid sites and a high amount of Oads species to negatively impact the DeNOx activity, selectivity and lifetime of the prepared catalyst.In order to justify the feasibility of leaching process for Ti-BFS using waste acid with low concentration, different powdery TiO2-SiO2 supports and V2O5-WO3/TiO2-SiO2 catalysts were prepared by mechano-chemical reaction using 30% H2SO4 aqueous and recycled H2SO4 aqueous. However, the more recycling times caused excessive SiO2 and dopants in hydrolysis solution, which hampered the nanoporous structure of supports. For the catalyst using support made by recycling acid for two times, its pore size was rather heterogeneous and was mainly around 2 nm. This led to inhibit the mass transformation of the reactant molecules and the deposition of VOx on the surface catalyst, consequently causing an obviously poor DeNOx efficiency. Based on the above results, two monolith catalysts were produced by coating cordierite honeycomb substrate using powder catalysts on slag-based supports that were synthesized using fresh acid solution and the first-recycle filtration solution. Surprisingly, the latter exhibited the better NO reduction efficiency and stability in both powder and coated-monolith forms. It was acquired from the high acid strength and high porosity of such a support to facilitate the formation of abundant surface Oads and reduced V4+ species. Finally, hydrothermal processing of Ti-BFS has been performed to realize a high leaching yield of TiO2 and diversify the slag-based products for a wide range of applications. Almost complete extraction of TiO2 with a purity of 97% was achieved when Ti-slag reacted with concentrated acid in the acid/slag ratio (mass) of 2.0 at 150 oC for 2 h. Meanwhile, this grade of TiO2 has potential application in pigment, cosmetics, porcelains, and ceramic industries. The samples having 88-95% TiO2 with a recovery above 75%, which were obtained under low ratio of H2SO4/slag mass ratio or low acid concentration, can be adopted as the high-titanium slag feedstock for the production of metal Ti. Other TiO2-based oxides including TiO2-SiO2, TiO2-Al2O3 were also synthesized as a new pathway to fully utilize the valuable components in Ti-BFS. The TiO2-SiO2 binary oxide having 5.76% SiO2 was proved to be fitted for SCR of NOx by NH3. The residue of CaSO4.SiO2 was characterized to show a fibrous structure with BET surface area of 80 m2/g, and it could be adopted as the green building materials (synthetic gypsum), whereas SiO2 existed in residue could positively enhance the gypsum properties.All three studied processes have proven their capacity to produce low-cost, stable and high-performance DeNOx catalyst from low-titanium slag. Of them, the mechano-synthesis is the promising approach to prepare SCR support and achieve the highest DeNOx efficiency. The major advantages are that the synthesized TiO2-SiO2 supports can be made under mild reaction conditions with diluted acid, and especially the waste sulfuric acid can be recycled to commence the next cycle of slag digestion. Overall, this thesis demonstrated the possibility of comprehensively utilizing Ti-BFS with the great economic and application interests.