Mn-Ce/TiO2低温SCR催化剂成型过程添加剂的影响

催化剂成型过程中添加剂的种类和添加量对成型后催化剂的机械强度、成型效果和催化性能有很大影响.本文研究了Mn-Ce/TiO₂催化剂制备过程中添加剂对催化剂的低温脱硝性能和机械性能的影响.结果表明,添加10%的拟薄水铝石作为黏结剂,可使催化剂具有较强的机械强度;添加2.5%的活性炭作为造孔剂,可以有效改善催化剂的孔结构.催化剂成型后脱硝性能下降,反应温度为90℃和120℃时,催化剂的NO_x转化率分别下降了15%和30%左右,当温度到达150℃及以上时,催化剂成型前后的脱硝性能基本一致.最后,通过BET、FT-IR、NH₃-TPD和H₂-TPR表征分析原因：成型后催化剂比表面积和孔容下降,催化剂的表面酸性位点和氧化还原能力下降都会影响催化剂的脱硝性能,所以催化剂成型后低温活性变差.     

VPO/TiO2催化剂表面酸性位调控及低温NH3-SCR脱硝性能研究

采用HCl调控负载型钒磷氧(VPO/TiO₂)催化剂的表面酸性,用于研究VPO/TiO₂催化剂的NH₃-SCR脱硝性能.结果表明:在HCl/V物质的量比为3～5:1范围内,催化剂的脱硝活性最高,当反应温度达到200℃时脱硝效率接近100%.表征结果表明:HCl的添加能提高催化剂的结晶度,HCl的调控使得VPO/TiO₂催化剂的比表面积略有增加.同时,也使得VPO/TiO₂催化剂中活性组分V⁴⁺的量从38%逐渐升高至46%,提高了催化剂的氧化还原性能.此外,不同HCl/V物质的量比的催化剂中化学吸附氧的相对含量随着HCl加入量的增加而提高.吡啶红外测试结果显示:HCl能影响催化剂酸性位点,HCl/V物质的量比=5的催化剂Lewis酸含量最高,总酸量为0.84×10^-4mol/g.数据拟合进一步表明,所有VPO/TiO₂催化剂的低温脱硝活性均与弱Lewis酸量呈正相关(相关系数>0.9),与活性测试相吻合.     

石家庄某制药企业污水处理过程中NH3排放研究

为了解污水处理过程中各处理单元NH₃的排放特征,采集石家庄某制药企业各污水处理单元以及经过废气治理后排放的样品,计算各采样点NH₃浓度及排放量。结果表明:各污水处理单元中,水解酸化池NH₃浓度和单位体积污水NH₃排放量均为最高,分别为62.89和3 360 mg∕m ³。各污水处理单元NH₃总排放量为0.97 kg∕h,单位体积污水NH₃排放量为9 312 mg∕m ³;经废气治理后,排入环境的NH₃为0.25 kg∕h,单位体积污水NH₃排放量为2 400 mg∕m ³,去除率为74.2%,经治理后NH₃排放量明显降低。南区、北区废气治理采用碱洗+氧化+水洗工艺,NH₃去除率分别为93.3%和83.1%;生物区废气治理采用生物滴滤床工艺,NH₃去除率为39.1%,碱洗+氧化+水洗工艺对NH₃的去除效果好于生物滴滤床工艺。     

Mn-Ce-Co/TiO2催化剂低温脱硝活性研究

以纳米TiO2为载体,通过浸渍法制备一系列改性Mn-Ce/TiO2脱硝催化剂.通过实验考察不同元素组分催化剂的脱硝活性,同时探讨金属氧化物掺杂对提高催化剂低温脱硝活性的机理.活性测试结果显示,Co掺杂能最有效地提高Mn-Ce/TiO2催化剂在低温段的SCR脱硝活性,在n(Co):n(TiO2)=0.08～0.10、体积空速为35100h-1的条件下,催化剂在120℃时就能达到80%以上的NO去除率,140℃左右时的NO去除率接近100%.BET、XRD、TPR、TPD等表征测试结果表明,Co掺杂可改进Mn-Ce/TiO2催化剂的物化特性,增加催化剂表面的活性酸位点及活性氧数量,提高催化剂的氧化还原能力,从而提高Mn-Ce/TiO2催化剂低温SCR脱硝活性.     

DFT模拟VPO/TiO2催化剂表面NO和NH3吸附的研究

氮氧化物(NO_x)作为主要大气污染物之一,严重影响环境安全和人类健康。选择性催化还原法(NH₃-SCR)是目前脱除NO_x最有效的治理方法,尤其是低温SCR脱硝技术具有非常重要的应用前景和研究意义。研究表明VPO/TiO₂催化剂具有优异的低温SCR脱硝活性,本文通过DFT模拟NH₃和NO在V₂O₅和(VO)₂P₂O₇表面的吸附,对VPO催化剂的反应机理进行了微观层面上的研究。研究表明NH₃在V₄P₄O₂₂H₁₄团簇表面的Br?nsted酸和Lewis酸都发生稳定的化学吸附,在Br?nsted酸位点吸附更稳定,并且NH₃在催化剂表面吸附效果佳是因为N的2p轨道和O的2p、V的3d电子轨道能发生了杂化。NO在V₄P_...     

助剂添加对CuO/TiO2催化剂NH3-SCO性能的影响研究

采用浸渍法制备了一系列CuO-MO_x/TiO₂ (M=W,Zr,La)催化剂用于NH3选择性催化氧化(NH₃-SCO),同时探究了SO₂中毒对NH₃氧化性能的影响.结果表明,过渡金属氧化物的添加使Cu/TiO₂催化剂NH₃转化率降低,但显著提高N₂选择性.其中,W0₃具有最好的促进效果,在300℃下催化剂N₂选择性提高了36%.通过H₂-TPR和NH₃-TPD表征发现,WO₃的添加增加了Cu/TiO₂催化剂表面酸性位点的数量,促进NH3的吸附,但降低催化剂氧化还原性能,抑制NH₃氧化为NO_x.经SO₂中毒处理后,CuO-MO_x/TiO₂催化剂N₂选择性进...     

MnOx/TiO2-ZrO2催化剂的制备及低温催化还原NO的研究

采用共沉淀法制备了TiO2-ZrO2复合氧化物,以其为载体采用等体积浸渍法制备了不同负载量的MnOx/Ti02-Zr02催化剂.低温下以NH3为还原剂考察了催化剂选择性催化还原(SCR)NO的活性.借助N2吸附、XRD、热重-差示扫描量热法(TG-DSC)对催化剂进行微观表征和分析.结果表明,负载量为5%时,生成的MnO2高度分散,NO的转化率较高;负载量为10%和15%时,出现MnO2晶相,NO的转化率有所下降.120-240℃、体积空速为10000 h-1的条件下,3种负载量的催化剂上NO转化率均大于90%.     

V2O5-WO3/TiO2系SCR催化剂的钾中毒及再生方法

以钾为代表的碱金属元素会引发严重的SCR催化剂中毒现象.通过浸渍法和干混法使催化剂钾中毒,比较不同K₂O负载量下催化剂脱硝活性的变化.结果表明,采用浸渍法使K₂O的负载量达到1%时,催化剂的最大脱硝效率由100%下降到30%左右;而干混法负载1% K₂O的催化剂样品的脱硝活性变化较小.对浸渍法负载1% K₂O的催化剂样品的再生试验表明,水洗可以使中毒后催化剂的脱硝活性由30%升至70%以上;而使用1%的H₂SO₄溶液酸洗,则可以使350～500 ℃催化剂的脱硝活性高于中毒前.通过扫描电镜和抗压强度的对比分析发现,中毒与再生前后催化剂的微观形貌和机械性能均未发生很大改变.      

喷灌和沟灌方式对农田土壤NH3挥发的影响

研究了2016和2017年传统灌溉（沟灌）和节水灌溉（喷灌）方式氨（NH₃）挥发的季节年际动态变化特征及其影响因素.采用通气法进行原位监测,分析了土壤温度、体积含水量、铵态氮（NH₄⁺-N）、硝态氮（NO₃^--N）以及气温降水等因素对NH₃挥发的影响.结果表明,NH₃挥发速率的峰值出现在施用氮肥后1~2周,喷灌有效降低NH₃挥发峰值,喷灌和沟灌的NH₃挥发速率峰值在2016年分别为2.67kg/（hm²·d）和11.11kg/（hm²·d）,2017年分别为2.42kg/（hm²·d）和11.73kg/（hm²·d）;马铃薯生长季NH₃挥发存在明显的季节变化,挥发高峰主要发生在7~8月,追肥期高于基肥期.2016~2017年农田土壤NH₃累积挥发量均表现为喷灌<沟灌,与沟灌相比,喷灌分别减少58.15%和43.55%.NH₃挥发速率与土壤温度呈显著正相关（P<0.05）,与体积含水量、NH₄⁺-N、NO₃^--N浓度呈极显著正相关（P<0.01）.     

Mn/TiO2和Mn-Ce/TiO2低温脱硝催化剂的抗硫性研究

在低温选择性催化还原(SCR)反应条件下考察了烟气残余SO2对Mn/TiO2和Mn-Ce/TiO2催化剂选择性催化还原活性的影响,同时对SO2的影响机理进行了探讨.结果发现,Mn/TiO2催化剂在SO2反应气氛中失活很快,硫铵盐的沉积和活性组分的硫酸化是催化剂失活的重要原因;Ce的加入可以有效地抑制催化剂活性组分的硫酸化,同时还能降低硫酸盐在催化剂表面的稳定性,从而可以提高催化剂的抗硫性.     

Ce-Mn/TiO2催化剂选择性催化还原NO的低温活性及抗毒化性能

用浸渍法制备了Ce-Mn/TiO2催化剂,考察了其在O2存在条件下选择性催化还原(SCR)NO的活性和抗SO2及H2O毒化的性能.结果表明,反应温度、空间速度、NO进口浓度和NH3/NO摩尔比对NO转化率的影响较小;在120℃的低温条件下,该催化剂显示了良好的催化活性,NO的转化率始终保持在95%以上.该催化剂有良好的同时抗SO2和H2O毒化能力.     

稻壳基活性炭催化剂的低温NH3-SCR抗硫性能

以稻壳基活性炭（DAC）为载体,利用等体积浸渍法制备了DAC负载Mn、Ce氧化物的Mn-Ce/DAC脱硝催化剂,并用于氨法SCR反应.采用N₂吸附、X射线衍射（XRD）、X射线光电子能谱（XPS）和程序升温吸附脱附（TPR/TPD）等手段对催化剂的物理化学性能进行了表征.结果发现与商业木屑基活性炭负载Mn、Ce氧化物催化剂（Mn-Ce/MAC）相比,Mn-Ce/DAC具有更高的Ce³⁺/Ce⁴⁺比率、表面化学吸附氧含量以及表面Brønsted酸性位点,这与其优良的低温SCR活性及抗硫抗水性能直接相关.原位红外光谱结果显示在含硫气氛中Mn-Ce/DAC表面的硫酸盐含量明显低于Mn-Ce/MAC,表明前者具有优良抗硫性能.     

Fe2O3 particles as superior catalysts for low temperature selective catalytic reduction of NO with NH3

Fe203 particle catalysts were experimentally studied in the low temperature selective catalytic reduction （SCR） of NO with NH3. The effects of reaction temperature, oxygen concentration, [NH3]/[NO] molar ratio and residence time on SCR activity were studied. It was found that Fe203 catalysts had high activity for the SCR of NO with NH3 in a broad temperature range of 150-270℃, and more than 95% NO conversion was obtained at 180℃ when the molar ratio [NH3]/[NO] = 1, the residence time was 0.48 seconds and 02 volume fraction was 3%. In addition, the effect of SO2 on SCR catalytic activity was also investigated at the temperature of 180℃. The results showed that deactivation of the Fe2O3 particles occurred due to the presence of SO2 and the NO conversion decreased from 99.2% to 58% in 240 min, since SO2 gradually decreased the catalytic activity of the catalysts. In addition, X-ray diffraction, Thermogravimetric analysis and Fourier transform infrared spectroscopy were used to characterize the fresh and deactivated Fe2O3 catalysts. The results showed that the deactivation caused by SO2 was due to the formation of metal sulfates and ammonium sulfates on the catalyst surface during the de-NO reaction, which could cause pore plugging and result in suppression of the catalytic activity.     

Mn-CeOx/Ti-PILCs for selective catalytic reduction of NO with NH3 at low temperature

Titanium-pillared clays (Ti-PILCs) were obtained by different ways from TiCl₄, Ti(OC₃H₇)₄ and TiOSO₄, respectively. Mn-CeO_x/Ti-PILCs were then prepared and their activities of selective catalytic reduction (SCR) of NO with NH₃ at low-temperature were evaluated. Mn-CeO_x/Ti-PILCs were characterized by X-ray diffraction, N₂ adsorption, Fourier transform infrared spectroscopy, thermal analysis, temperature-programmed desorption of ammonia and H₂-temperature-programmed reduction. It was found that Ti-pillar tend to be helpful for the enlargement of surface area, pore volume, acidity and the enhancement of thermal stability for Mn-CeO_x/Ti-PILCs. Mn-CeO_x/Ti-PILCs catalysts were active for the SCR of NO. Among three resultant Mn-CeO_x/Ti-PILCs, the catalyst from TiOSO₄ showed the highest activity with 98% NO conversion at 220℃, it also exhibited good resistance to H₂O and SO₂ in flue gas. The catalyst from TiCl₄ exhibited the lowest activity due to the unsuccessful pillaring process.     

焙烧温度对Fe2O3/SAPO-34催化剂低温NH3选择性催化还原NO性能的影响

采用尿素沉淀法制备了一系列Fe_2O_3/SAPO-34催化剂,考察了催化剂焙烧温度(200、300、400、500℃)对低温NH_3选择性催化还原(NH_3-SCR)NO性能的影响,并利用X射线衍射(XRD)、N_2吸附-脱附、原子吸收光谱(AAS)、场发射扫描电镜(FE-SEM)、X射线光电子能谱(XPS)、H_2程序升温还原(H_2-TPR)、NH_3程序升温脱附(NH_3-TPD)等多种手段对催化剂的表面结构和物理化学性质进行表征分析.XRD和FE-SEM分析表明,在较低的焙烧温度(400℃)下,铁物种能够高度均匀地负载在SAPO-34表面上.NH_3-TPD和H_2-TPR分析表明,高分散状态的Fe_2O_3使催化剂暴露出更多的强酸位和活性位,有利于提高催化剂的NH_3吸附和活化能力及氧化还原性能,从而使催化剂呈现出更高的低温SCR活性.BET和XPS分析表明,在较低的焙烧温度下,Fe_2O_3/SAPO-34催化剂具有更大的比表面积和更高的化学吸附氧比例,促进NO氧化为中间产物NO_2,从而加快低温SCR反应的进行.活性测试结果表明,300℃焙烧的Fe_2O_3/SAPO-34催化剂具有最佳的低温活性和较强的抗硫抗水性能,在空速为40000 h~(-1)的条件下,且反应温度为190~240℃时,NO转化率达90%以上且N_2选择性接近100%.     

Ultrasound-assistant preparation of Cu-SAPO-34 nanocatalyst for selective catalytic reduction of NO by NH3

The influence of the various preparation methods of Cu-SAPO-34 nanocatalysts on the selective catalytic reduction of NO with NH₃ under excess oxygen was studied. Cu-SAPO-34 nanocatalysts were prepared by using four techniques: conventional impregnation (IM), ultrasound-enhanced impregnation (UIM), conventional deposition precipitation (DP) using NaOH and homogeneous deposition precipitation (HDP) using urea. These catalysts were characterized in detail by various techniques such as N₂-sorption, XRD, TEM, H₂-TPR, NH₃-TPD and XPS to understand the catalyst structure, the nature and the dispersed state of the copper species, and the acid sites for NH₃ adsorption. All of the nanocatalysts showed high activities for NO removal. However, the activities were different and followed the sequence of Cu-SAPO-34 (UIM) > Cu-SAPO-34 (HDP) > Cu-SAPO-34 (IM) > Cu-SAPO-34 (DP). Based on the obtained results, it was concluded that the NO conversion on Cu-SAPO-34 nanocatalysts was mainly related to the high reducibility of the isolated Cu^2 + ions and CuO species, the number of the acid sites and the dispersion of CuO species on SAPO-34.     

Promotional effect of Si-doped V2O5/TiO2 for selective catalytic reduction of NOx by NH3

TiO2 supports doped with different amounts of Si were prepared by a sol-gel method, and 1 wt% vanadia (V2O5) loaded on Si-doped TiO2 was obtained by an impregnation method. The mole ratio of Si/Ti was 0.2, NOx conversion exceeds 94% at 300℃ and GHSV of 41,324 hr-1 , which is about 20% higher than pure V2O5/TiO2 . The catalysts were characterized by XRD, BET, TEM, FT-IR, NH3-TPD, XPS, H2-TPR, Raman and in situ DRIFTS. The results of FT-IR and XPS indicated that Si was doped into the TiO2 lattice successfully and a solid solution was obtained. V2O5 active component could be dispersed well on the support with the increasing of surface area of the catalyst, which was confirmed by Raman and XRD results. Above all, the numbers of acid sites (especially the Br nsted-acid) and oxidation properties were enhanced for Si-doped V2O5/TiO2 catalysts, which improved the deNOx catalytic activity.     

Kinetics of selective catalytic reduction of NO by NH3 on Fe-Mo/ZSM-5 catalyst

The catalyst of Fe-Mo/ZSM-5 has been found to be more active than Fe-ZSM-5 and Mo/ZSM-5 separately for selective catalytic reduction (SCR) of nitric oxide (NO) with NH3. The kinetics of the SCR reaction in the presence of O2 was studied in this work. The results show that the observed reaction orders were 0.74-0.99, 0.01-0.13, and 0 for NO, O2 and NH3, respectively, at 350-450℃. And the apparent activation energy of the SCR was 65 kJ/mol on the Fe-Mo/ZSM-5 catalyst. The SCR mechanism was also deduced. Adsorbed NO species can react directly with adsorbed ammonia species on the active sites to form N2 and H2O. Gaseous O2 might serve as a reoxidizing agent for the active sites that have undergone reduction in the SCR process. It is also important to note that a certain amount of NO was decomposed directly over the Fe-Mo/ZSM-5 catalyst in the absence of NH3.     

高分散MnOx/SAPO-34催化剂的制备及其低温NH3选择性催化还原NO性能

采用改进的溶胶-凝胶法制备一系列MnO_x/SAPO-34催化剂,考察了各制备参数对催化剂的结构及其低温氨选择性催化还原(NH_3-SCR)脱硝性能的影响,并通过X射线衍射、N_2吸附-脱附、透射电镜、X射线光电子能谱、NH_3程序升温脱附等手段对催化剂进行表征.结果表明,当制备参数为n(乙醇)/n(Mn)=15,n(H_2O)/n(Mn)=20,n(柠檬酸)/n(Mn)=1,Mn负载量为15%(质量分数),催化剂焙烧温度为350℃时,制备的高分散15%-MnO_x/SAPO-34-350℃催化剂具有最佳的低温SCR活性,在空速为45000 h~(-1)的条件下,且反应温度在120～240℃范围时均保持90%以上的NO转化率和接近100%的N_2选择性.MnO_x纳米颗粒高度分散在SAPO-34载体表面,平均粒径约为5.46 nm,纳米颗粒的表面效应使得该催化剂具备较大的比表面积,暴露出大量的活性位点和高活性的MnO_2(110)晶面,同时,高Mn~(4+)比例和更多的化学吸附氧以及适宜的表面酸强度和酸量也是15%-MnO_x/SAPO-34-350℃催化剂呈现最佳低温SCR活性的重要原因.