燃煤烟气条件下锰铈基催化剂对邻二甲苯催化氧化

燃煤烟气中有机污染物的排放逐渐引起重视。锰铈（MnCe）基催化剂被认为是一种低温高效、低成本的可应用于燃煤烟气污染物脱除的催化剂。本文通过浸渍法制备了MnCe基催化剂，通过物理化学表征和烟气模拟台架实验，研究了MnCe基催化剂配比、反应工况、烟气复杂组分（H₂O、SO₂、NH₃、NO）以及典型污染物脱除过程（Hg⁰和NO催化转化）对催化脱除烟气中邻二甲苯行为的影响和规律。实验结果表明，Mn和Ce摩尔比为6∶4时催化剂脱除邻二甲苯效率良好。反应空速和MnCe负载量在低温下对催化脱除效率影响显著。烟气中H₂O、SO₂、NH₃、NO等组分对催化产生抑制作用，但抑制程度与作用机理具有显著差异。MnCe基催化剂对烟气SCR脱硝与Hg⁰催化氧化皆具有较高效率，且受烟气中邻二甲苯影响较小；但受SCR气氛与Hg⁰抑制，邻二甲苯催化脱除反应效率明显降低。     

钒钛系脱硝催化剂抗硫酸氢铵中毒改进措施研究进展

NH₃选择性催化还原(SCR)技术具有较高的脱硝效率、优良的选择性和实用性,是当前燃煤电厂去除NO_x的主流方法。其中V₂O₅/TiO₂催化剂在中温段(300～450℃)具有较高的脱硝活性和抗硫性,被广泛应用。但是,烟气中的SO₃、NH₃和水蒸气会发生反应生成硫酸氢铵(ABS)和硫酸铵(AS),其中硫酸氢铵在低温条件下因毛细冷凝现象沉积在V₂O₅/TiO₂催化剂表面致其中毒,活性降低。为了改善低温条件下催化剂中毒问题,本文通过分析ABS在催化剂表面的生成机理、对催化剂的危害及催化剂抗ABS中毒改性研究进展,发现钒钛系脱硝催化剂抗ABS中毒改进措施主要集中在抑制硫酸氢铵生成、促进硫酸氢铵分解两方面。最后,总结了合理调控催化剂壁厚、孔径和隔离层等物理结构以及添加MoO₃、BaO、Nb₂O₅、Fe₂     

锰基催化剂低温催化脱除NOx及CO研究进展

NO_x和CO作为需重点处理的污染物，随钢铁烧结等烟气排放标准进一步提高，传统的NH₃-SCR(NH₃选择性催化还原NO_x)脱硝技术存在明显不足，特别是烧结烟气排放温度低于钒基催化剂窗口温度，导致脱硝催化剂活性不足及生成的硫铵盐堵塞催化剂表面，对CO控制尚缺乏有效手段。因此开发低温催化剂成为脱除低温烟气中NO_x及CO的关键因素。对Mn基催化剂在脱除NO_x和CO方面进展进行论述，对比活性组分、制备方法、载体等方面对锰基低温催化剂催化活性的影响，详细介绍Cu、Ce等金属对于锰基催化剂改性的影响，分析了元素掺杂与催化性能的关系；在此基础上，对近年来CO还原NO技术的最新研究成果进行系统梳理和总结，着重探讨反应机理、O₂在反应中的作用机制，结果表明，Mn元素丰富的核外电子排布是其在脱除NO_x和CO中活性优异的根本原因，但目前研究成果多数仅处于实验室开发阶段，在实际烟气中缺乏大规模验证。最后，展望了Mn基催化剂未来的发展方向...     

烟气及飞灰组分对溴改性飞灰脱汞特性的影响

燃煤飞灰中的未燃碳（unburned carbon,UBC）和金属氧化物因对汞有一定的吸附和氧化作用而被认为是燃煤电厂廉价的潜在脱汞吸附剂,但效率有待提高。文章选取两种UBC含量不同的飞灰,采用质量分数1%的NH₄Br溶液对其浸渍改性,利用固定床汞吸附实验台探究了烟气组分（O₂、SO₂和NO）以及飞灰中无机金属氧化物对汞吸附和氧化的影响,以期获得高效脱汞吸附剂吸附机理。结果表明,O₂对于溴素改性飞灰氧化汞有较小的促进效果,SO₂具有一定的抑制作用,NO促进Hg⁰的氧化效果明显;溴素改性飞灰中的Fe₂O₃和TiO₂对Hg⁰的氧化起着主要作用,原因在于溴素改性增加了金属氧化物Fe₂O₃和TiO₂中的晶格氧含量,促进了Hg⁰的催化氧化,主要遵循Mars-Maessen机理。另外,UBC含量对飞灰脱除Hg⁰的影响很大,溴素嵌入飞灰表面的UBC时,会使其邻域的活性加强,从而增强碳质表面对Hg⁰的吸附能力,促进了后续反应的进行。     

V2O5-MoO3/TiO2 催化剂的NOx选择性催化还原及SO2氧化活性

采用浸渍法以TiO₂为载体制备V₂O₅-MoO₃/TiO₂ 选择性催化还原催化剂,研究V₂O₅和MoO₃负载量对于催化剂选择性催化还原反应及SO₂氧化活性的影响,并考察氧含量、氨氮物质的量比和反应空速对3%V₂O₅-6%MoO₃/TiO₂催化剂选择性催化还原脱硝活性的影响。结果表明,随着催化剂中V₂O₅负载质量分数增加,V₂O₅-MoO₃/TiO₂ 催化剂的选择性催化还原活性和SO₂氧化活性均呈上升趋势。MoO₃的负载对催化剂的SO₂氧化活性有明显抑制作用。MoO₃负载质量分数超过9%,制备的催化剂既保持较高的低温选择性催化还原活性,又使选择性催化还原反应中的SO₂转化率小于1%。     

非贵金属改性钒钛基催化剂NH3-SCR脱硝协同控制VOCs

在钒钛基催化剂上分别负载四种非贵金属(Ce、Cu、Mn、Fe)，研究改性催化剂对中低温选择性催化还原(SCR)脱硝协同挥发性有机物(VOCs)催化氧化的性能。对四种负载金属(Ce、Cu、Mn、Fe)分别进行SCR脱硝和VOCs催化氧化，发现Ce改性的催化剂在低温段具有良好的SCR脱硝活性和VOCs催化氧化性能，被认为具有良好的协同催化潜力。之后对Ce掺杂改性催化剂进行协同评价研究，发现在275～300℃的温度区间内，3V-5Ce/Ti催化剂的NO转化率和VOCs转化率可达到100%。并分别比较了SCR反应协同VOC与未协同VOC时N₂的选择性和CO₂的选择性，发现在低温段时甲苯的引入会显著降低N₂选择性，而随着温度升高，N₂O副产物的产生，N₂的选择性恢复到未引入甲苯时。同时发现协同反应时CO2的选择性有明显下降。对3V-5Ce/Ti催化剂的SEM、XRD、XPS、NH3-TPD表征说明Ce的引入不会破坏载体形貌，可以为催化剂提高更多表面氧空位，从而提高催化剂的氧化还原性能，并...     

溶胶-凝胶原位合成宽活性温度V2O5/TiO2脱硝催化剂

利用溶胶-凝胶技术原位合成一系列不同V₂O₅担载量的V₂O₅/TiO₂催化剂,通过BET、XRD、NH₃-TPD及紫外-可见光等手段对催化剂进行表征。结果表明：制备的催化剂均具有介孔结构,V₂O₅在TiO₂表面高度分散,且存在3种典型的酸性位。通过选择性催化还原反应对V₂O₅/TiO₂催化剂进行活性评价,结果显示随着V₂O₅含量的增加,NO转化率大于75%的温度窗口向低温方向偏移,含10% （质量分数）V₂O₅的催化剂的NO转化率为80%的温度窗口最宽为200～450℃,240℃时20 h连续实验表现出稳定的抗硫抗水性能。结合紫外-可见光谱分析,揭示了钒掺杂所形成的单聚和低聚钒酸盐为催化剂的活性组分。     

Mn-Cu-Ce-Fe/REY系列催化剂上NH3选择性催化还原NO性能

采用正交实验设计和浸渍法制备Mn-Cu-Fe-Ce/REY催化剂。采用固定床微型反应器评价SO₂存在下催化剂在NH₃选择性催化还原NO反应中的活性,考察Mn、Cu、Fe和Ce各活性组分对催化剂活性的影响,并采用XRD、H₂-TPR和SEM等手段对催化剂进行表征。结果表明,Mn、Cu、Fe和Ce各活性组分对催化剂活性影响顺序为：Cu＞Fe＞Ce＞Mn,催化剂的氧化还原性能影响催化剂活性。     

石墨烯改性TiO2催化臭氧氧化降解p-CBA的研究

采用碳化热解法在TiO₂催化剂表面制备石墨烯层，并对其进行XRD、Raman、NH₃-TPD、BET、pH_zpc等表征。以对氯苯甲酸(p-CBA)为目标物，考察石墨烯改性TiO₂在催化臭氧氧化过程中的效能。结果表明，热解温度、碳源投量、固化剂投量等因素对催化剂的活性有较大影响。负载石墨烯层可显著增加TiO₂催化剂的比表面积，并使其表面酸性增强，因而提高其催化臭氧氧化活性。另外，考察了溶液pH、叔丁醇对改性TiO₂催化臭氧氧化过程的影响。溶液pH为6时，对氯苯甲酸的去除率最低。叔丁醇严重抑制了对氯苯甲酸的降解反应，间接证明了羟基自由基是催化臭氧氧化过程中的主要活性氧化物种。重复使用实验结果表明，改性后的催化剂具有良好的稳定性。     

CeO2改性再生SCR催化剂的单质汞氧化特性

对国内某1000MW燃煤发电机组失活选择性催化还原（SCR）催化剂进行CeO₂改性再生。对再生前后样品进行N₂吸附-脱附、扫描电子显微镜（SEM）、X射线荧光光谱（XRF）、傅里叶变换红外光谱（FTIR）对比表征分析。在自制固定床反应系统上对CeO₂改性再生催化剂（CeReCat）进行Hg⁰氧化性能测试,同时研究了SO₂、H₂O、NO和NH₃对Hg⁰氧化性能的影响。结果表明,CeO₂改性再生方法可有效清洗失活SCR催化剂表面杂质,恢复催化剂表面活性位点和孔隙结构,可使Ce、V两种活性元素得到有效负载。CeO₂改性后的样品Hg⁰氧化性能显著提升,3.0 CeReCat具有最佳Hg⁰的氧化效率。此外,烟气中加入600μL/L SO₂后,3.0 CeReCat仍具有高达74.4%的Hg⁰氧化效率,抗SO₂性能较好。烟气中的NO可轻微促进Hg⁰的氧化。由于竞争吸附作用,烟气中的H₂O和NH₃会抑制Hg⁰的氧化。CeO₂改性再生催化剂置于SCR系统下层时,由于烟气NH₃浓度较低而具有较高Hg⁰氧化效率,具有良好的应用前景。     

含钛高炉渣制备SCR烟气脱硝催化剂

以含钛高炉渣为原料,稀硫酸为溶剂提取钛液,钛液经水解、高温焙烧后制得高比表面积的TiO₂,并以其为载体采用分步浸渍法制备了V₂O₅-WO₃/ TiO₂催化剂。优化了含钛高炉渣的酸解条件,对所得TiO₂进行了XRD、XRF、BET表征,用自制催化剂评价系统考察了所制备催化剂的脱硝性能及抗硫抗水性能。结果表明：H₂SO₄浓度40%、酸渣比1.5、酸解温度80℃、酸解时间3 h条件下,TiO₂浸出率可达90%,水解产物主要为锐钛型TiO₂,纯度达到74%,含有21.2%无定形SiO₂及少量其他杂质。SiO₂的存在提高了产物的比表面积、孔径,有利于活性组分的负载。以含钛高炉渣基TiO₂为原料制备的V₂O₅-WO₃/TiO₂脱硝催化剂相比于以商业TiO₂和TiOSO₄制备的催化剂,在250～450℃具有更高的催化活性,且在300℃具有较好的抗硫抗水性能。     

Catalytic performance of a novel ceramic-supported vanadium oxide catalyst for NO reduction with NH3

A novel TiO₂/Al₂O₃/cordierite honeycomb-supported V₂O₅–MoO₃–WO₃ monolithic catalyst was studied for the selective reduction of NO with NH₃. The effects of reaction temperature, space velocity, NH₃/NO ratio and oxygen content on SCR activity were evaluated. Two other V₂O₅–MoO₃–WO₃ monolithic catalysts supported on Al₂O₃/cordierite honeycomb or TiO₂/cordierite honeycomb support, two types of pellet catalysts supported on TiO₂/Al₂O₃ or Al₂O₃, as well as three types of pellet catalysts V₂O₅–MoO₃–WO₃–Al₂O₃ and V₂O₅–MoO₃–WO₃–TiO₂ were tested for comparison. The experiment results show that this catalyst has a higher catalytic activity for SCR with comparison to others. The results of characterization show, the preparation method of this catalyst can give rise to a higher BET surface area and pore volume, which is strongly related with the highly active performance of this catalyst. At the same time, the function of the combined carrier of TiO₂/Al₂O₃ cannot be excluded.     

A pilot plant study for catalytic decomposition of PCDDs/PCDFs over supported chromium oxide catalysts

Chromium oxide catalysts supported on TiO₂ and Al₂O₃ were examined in a fixed-bed flow reactor system for the removal of PCE (perchloroethylene), a simulant of 2,3,7,8-TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin), and in a pilot plant employing actual flue gas from a sintering plant for the removal of PCDDs/PCDFs (poly-chlorinated dibenzo-dioxin/poly-chlorinated dibenzo-furan). The 12.5 wt.% chromium oxides supported on TiO₂ and Al₂O₃ revealed excellent stability and performance of PCE removal in the feed gas stream containing water vapor. In a pilot plant study, the catalysts washcoated on the honeycomb reactor revealed 93–95% of PCDDs/PCDFs removal activity over CrO_x/Al₂O₃-HC20 (CrO_x/Al₂O₃ catalyst washcoated on 20 cell-honeycomb), and more than 99% of the decomposition activity over CrO_x/TiO₂-HC20 (CrO_x/TiO₂ catalyst washcoated on 20 cell-honeycomb) at 325 °C and 5000 h⁻¹ of reactor space velocity without the de novo synthesis of PCDDs/PCDFs. In particular, CrO_x/TiO₂-HC20 showed 94% of PCDDs/PCDFs decomposition activity even at 280 °C reaction temperature. The catalyst also exhibited significant NO removal activity. The chromium oxide seems to be a promising catalyst for the removal of PCDDs/PCDFs and NO_x contained in the flue gas.     

V2O5@CeO2核壳微球结构的脱硝催化剂制备及其抗硫性能

利用静电自组装法制备了V₂O₅@CeO₂核壳微球结构,并负载在TiO₂上。考察了分散剂六偏磷酸钠（SHP（对表面zeta电位的影响,采用扫描电镜（SEM（、投射电镜（TEM（观察了核壳结构的形貌,并在固定床上进行了脱硝性能测试,并通过比表面积（BET（、氨气吸附漫反射（in situ DRIFTS（等进行表征。结果表明：SHP使纳米颗粒表面带负电,且一定范围内SHP浓度越高,zeta电位越大;含质量分数1%V₂O₅、5% CeO₂的催化剂,在260~400℃间具有80%以上的脱硝效率,对比了该核壳结构与传统浸渍法制备催化剂的抗硫抗水性,烟气中含15%（体积分数（H₂O,SO₂含量较低时,脱硝性能优于传统浸渍法制备的催化剂。     

SO2 resistant antimony promoted V2O5/TiO2 catalyst for NH3-SCR of NOx at low temperatures

To get the low temperature sulfur resistant V₂O₅/TiO₂ catalysts quantum chemical calculation study was carried out. After selecting suitable promoters (Se, Sb, Cu, S, B, Bi, Pb and P), respective metal promoted V₂O₅/TiO₂ catalysts were prepared by impregnation method and characterized by X-ray diffraction (XRD) and Brunner Emmett Teller surface area (BET-SA). Se, Sb, Cu, S promoted V₂O₅/TiO₂ catalysts showed high catalytic activity for NH₃ selective catalytic reduction (NH₃-SCR) of NO_x carried at temperatures between 150 and 400 °C. The conversion efficiency followed in the order of Se > Sb > S > V₂O₅/TiO₂ > Cu but Se was excluded because of its high vapor pressure. An optimal 2 wt% ‘Sb’ loading was found over V₂O₅/TiO₂ for maximum NO_x conversion, which also showed high resistance to SO₂ in presence of water when compared to other metal promoters. In situ electrical conductivity measurement was carried out for Sb(2%)/V₂O₅/TiO₂ and compared with commercial W(10%)V₂O₅/TiO₂ catalyst. High electrical conductivity difference (ΔG) for Sb(2%)/V₂O₅/TiO₂ catalyst with temperature was observed. SO₂ deactivation experiments were carried out for Sb(2%)/V₂O₅/TiO₂ and W(10%)/V₂O₅/TiO₂ at a temperature of 230 °C for 90 h, resulted Sb(2%)/V₂O₅/TiO₂ was efficient catalyst. BET-SA, X-ray photoelectron spectroscopy (XPS) and carbon, hydrogen, nitrogen and sulfur (CHNS) elemental analysis of spent catalysts well proved the presence of high ammonium sulfate salts over W(10%)/V₂O₅/TiO₂ than Sb(2%)/V₂O₅/TiO₂ catalyst.     

Catalytic gas phase ammoxidation of o-xylene

The present contribution is a brief account of investigations carried out on the ammoxidation of o-xylene over a few VPO and V₂O₅ based catalysts. The desired reaction product is phthalonitrile, however, phthalimide is the main product in most cases besides carbon oxides. The product distribution between nitrile and imide mainly depends on the reaction conditions and the nature of catalyst used. Influence of various reaction parameters such as effects of (i) reaction temperature, (ii) water vapour addition in the feed gas, (iii) NH₃/o-xylene mole ratio and (iv) space velocity were studied. It is interesting to note that the removal of water vapour from the feed gas has a highly pronounced promotional effect on the selectivity of phthalonitrile. The nitrile selectivity increased from 2.1 to 34% at the expense of phthalimide (decreased from 53 to 9%) with the complete removal of water vapour in the reactant feed mixture. This observation gives an indication that phthalonitrile being formed in the reaction is further getting hydrolysed to phthalimide via amide intermediate in presence of water vapour. Another interesting aspect of the present investigation is that the titania supported catalysts always gave significantly higher selectivities of phthalimide compared to phthalonitrile. Phthalimide yields up to 80% were reached on a VPO/TiO₂ catalyst.     

Ammonia activation over catalysts for the selective catalytic reduction of NOx and the selective catalytic oxidation of NH3. An FT-IR study

The adsorption and transformation of ammonia over V₂O₅, V₂O₅/TiO₂, V₂O₅-WO₃/TiO₂ and CuO/TiO₂ systems has been investigated by FT-IR spectroscopy. In all cases ammonia is first coordinated over Lewis acid sites and later undergoes hydrogen abstraction giving rise either to NH₂ amide species or to its dimeric form N₂H₄, hydrazine. Other species, tentatively identified as imide NH, nitroxyl HNO, nitrogen anions N₂⁻ and azide anions N₃⁻ are further observed over CuO/TiO₂. The comparison of the infrared spectra of the species arising from both NH₃ and N₂H₄ adsorbed over CuO/TiO₂ strongly suggest that N₂H₄ is an intermediate in NH₃ oxidation over this active selective catalytic reduction (SCR) and selective catalytic oxidation (SCO) catalysts. This implies that ammonia is activated in the form of NH₂ species for both SCR and SCO, and it can later dimerize. Ammonia protonation to ammonium ion is detected over V₂O₅-based systems, but not over CuO/TiO₂, in spite of the high SCR and SCO activity of this catalyst. Consequently Brönsted acidity is not necessary for the SCR activity.