不同SAPO分子筛负载MnOx催化剂的低温NH3-SCR性能研究

以磷酸硅铝分子筛SAPO-5、SAPO~(-1)1和SAPO-34为载体,采用乙醇分散法制备了用于低温氨选择性还原(NH_3-SCR)NO_x的分子筛负载MnO_x催化剂.活性测试结果显示,3种分子筛催化剂均展现出优良的NH_3-SCR活性,但三者在低温区间的SCR活性存在较明显差异,其SCR活性顺序如下:MnO_x/SAPO-34MnO_x/SAPO-5MnO_x/SAPO~(-1)1.借助XRD、N2吸附-脱附、XPS、H2-TPR、NH_3-TPD、NH_3FT-IR等技术对催化剂的表面活性物种及表面酸性等进行表征分析,结果表明,MnO_x主要以无定型状态分散于载体上,负载后载体的比表面积和孔体积均有所下降.XPS和H2-TPR分析证实,不同分子筛载体上MnO_x的表面浓度与氧化态明显不同.NH_3-TPD和NH_3FT-IR分析揭示了催化剂表面均存在Bronsted酸位和Lewis酸位,其中,Lewis酸性位对低温SCR反应起着关键作用.研究表明,催化剂的催化性能会因载体不同而存在差异,高Mn4+表面浓度和丰富的Lewis酸性位对催化剂在低温区间实现优良的催化活性尤为重要.     

Ag/Cu3(BTC)2复合催化剂的制备及其NH3-SCR催化性能

采用紫外还原的方法成功制备出Cu₃（BTC）₂（均苯三甲酸合铜）负载贵金属Ag纳米颗粒的Ag/Cu₃（BTC）₂复合催化剂,并用于氨法脱硝反应.应用X射线衍射（XRD）、透射电子显微镜（TEM）、BET测试等手段对催化剂的物理化学性能进行了表征.结果发现Ag纳米颗粒以球状结构高度均匀分散在Cu₃（BTC）₂骨架结构的表面.负载Ag纳米颗粒和Cu-MOF的协同作用,提高了Ag/Cu₃（BTC）₂催化剂的脱硝效率,负载量为15wt%的催化剂表现出最优脱硝效率,在220～260℃达到100%的NO转化率.同时,利用in-situ FTIR技术对NH₃-SCR的反应机理进行了探究.     

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%.     

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.     

甲烷催化还原NOx中Co基/分子筛催化剂的助剂和载体优化

采用共浸渍法制备了系列Co基/分子筛催化剂,在固定床催化反应器中考察了不同催化剂在甲烷催化还原NO_x中的催化行为,优化了Co基/分子筛催化剂的助剂和载体,并通过催化表征手段阐明了其构效关系.结果表明,Fe和SAPO-34分别作为优化助剂和载体制备得到的Co-Fe/SAPO-34催化剂具有最高的催化活性,在450℃时,NO_x的最大转化率可以达到52.7%.CO_2对Co-Fe/分子筛催化剂活性无明显抑制作用,H_2O对催化剂的活性抑制是可逆的,SO_2对催化剂活性抑制作用明显.Co-Fe/SAPO-34催化剂表面钴物种以CoO和Co(OH)_2为主,Co-Fe/ZSM-5催化剂表面钴物种则以Co_3O_4和Co(OH)_2为主,Co-Fe/Beta催化剂则可能以CoO、Co Al2O_4和Co_3O_4为主.各Co-Fe/分子筛催化剂表面Fe~(2+)/Fe~(3+)含量比依次为Co-Fe/ZSM-5(3.98)Co-Fe/SAPO-34(0.52)Co-Fe/Beta(0.43).活性组分钴物种的形态和合适的Fe~(2+)/Fe~(3+)含量比对Co-Fe/分子筛催化剂上甲烷催化还原NO_x至关重要.Co-Fe/分子筛催化剂上CH_4-SCR反应机制为:NO在Br?nsted酸位上吸附氧化成NO~+,同时CH_4在Br?nsted酸位上吸附活化成—C=O和—COO等活性物种,生成的NO~+在Co2+和Fe~(3+)等催化活性位上转化成硝酸盐等中间产物,中间产物硝酸盐与活化物种(—C=O和—COO)反应生成N_2和CO_2.     

低温条件下Nano-MnOx上NH3选择性催化还原NO

采用流变相法制备了无载体Nano-MnO_x催化剂,在低温条件下(50～150℃)以NH₃为还原剂系统考察了氮氧化物的选择催化还原特性.结果表明,流变相法制备的Nano-MnO_x催化剂具有良好的低温催化活性.实验条件下,80℃即可获得98.25%的NO转化率,100～150℃内NO几乎完全转化;SO₂和H₂Ｏ会与NO和NH₃在催化剂表面产生竞争吸附,导致催化活性下降,但该影响是可逆的.经分析,较大的比表面积和较低的晶化度是Nano-MnO_x具有良好低温活性的2个主要原因.     

超声辅助法制备新型FeMOR分子筛催化NOx还原反应性能研究

采用超声辅助浸渍法成功合成了高铁含量的Fe MOR-5%-UL催化剂,并且测试其催化还原NO性能.研究发现在超声辅助条件下浸渍制得的催化剂可以引入更高比例的离子交换位上的孤立的Fe~(3+),这些铁离子具有更强的NO还原活性,因此超声辅助浸渍法制备的催化剂催化性能显著高于传统的离子交换法和浸渍法.其中活性最高的FeMOR-5%-UL催化剂在添加SO_2等多种气氛时,催化活性下降不显著.并且在持续100 h的汽车尾气条件下进行的稳定性实验中,FeMOR-5%-UL的催化活性没有明显下降.FeMOR-5%-UL的优异的催化活性和稳定性非常具有应用前景和研究价值.     

SO2对CoH-ZSM-5催化CH4还原NO催化性能的影响

研究了富氧条件下SO₂对CoH-ZSM-5上CH₄选择还原NO(CH₄-SCR)的影响,应用SO₂-TPSR,NO+(O₂)-TPD等方法研究了产生中毒的原因并定量研究了被毒化的活性位.反应在773 K进行时,加入体积分数78×10^-6SO₂,NO的转化率由72%逐渐降低并稳定在58%,提高反应温度至823 K,NO稳定转化率上升至62%.同时加入2.5     

γ-Al2O3酸性修饰稀土尾矿NH3-SCR脱硝性能

为增加脱硝催化剂的酸性位点和比表面积,以稀土尾矿为活性主体,通过物理球磨方式添加γ-Al₂O₃,制得NH₃-SCR催化剂,脱硝温度为100～400℃.结果表明:原尾矿脱硝活性为7.6%,γ-Al₂O₃的脱硝活性为9.4%,稀土尾矿添加50%γ-Al₂O₃脱硝活性达到了64.8%,即添50%γ-Al₂O₃后加极大程度地提高了尾矿的脱硝活性.XRD实验结果表明:Al₂O₃不会与尾矿成分发生反应生成新的物质.SEM实验结果表明:当添加γ-Al₂O₃低于50%时,γ-Al₂O₃均匀分散在尾矿表面,当添加65%γ-Al₂O₃和80%γ-Al₂O₃时,γ-Al₂O<...     

球磨制备低钒基催化剂的NH3-SCR脱硝性能

采用球磨混合方法,将催化剂以m（Cu/SAPO-34）:m（VW/TiO₂）为1:1的比例制得干混样品SAPO-Ti。利用固定床实验台架研究了混合催化剂的NH₃-SCR脱硝性能及其抗硫性能。采用 XRD、BET、SEM、H₂-TPR、NH₃-TPD和in-situ DRIFT对材料进行表征,结果显示,球磨混合样品SAPO-Ti同时具有2种催化剂的晶体结构,且酸量增加,中温活性提高。表面形貌研究表明,VW/TiO₂催化剂覆盖在Cu/SAPO-34催化剂表面,对Cu/SAPO-34催化剂起到保护作用;原位红外结果显示,Cu/SAPO-34催化剂硫中毒失活主要是在Cu活性位上形成硫酸盐物种,导致活性位减少,脱硝效率下降,而SAPO-Ti表面形成硫酸盐的数量减少,抗硫性能提高,主要是由于表面VW/TiO₂催化剂具有良好的抗硫性,保护内部Cu2+活性位,以保持高效中温脱硝性能。     

Effect of barium sulfate modification on the SO2 tolerance of V2O5 /TiO2 catalyst for NH3-SCR reaction

Sulfur poisoning of V_2O_5/BaSO_4–TiO_2(VBT),V_2O_5/WO_3–TiO_2(VWT) and V_2O_5/BaSO_4–WO_3–TiO_2(VBWT) catalysts was performed in wet air at 350℃ for 3 hr,and activities for the selective catalytic reduction of NO_x with NH_3 were evaluated for 200–500℃.The VBT catalyst showed higher NO_x conversions after sulfur poisoning than the other two catalysts.The introduction of barium sulfate contributed to strong acid sites for the as-received catalyst,and eliminated the redox cycle of active vanadium oxide to some extent,which resulted in a certain loss of activity.Readily decomposable sulfate species formed on VBT-S instead of inactive sulfates on VWT-S.These decomposable sulfates increased the number of strong acid sites significantly.Some sulfate species escaped during catalyst preparation and barium sulfate was reproduced during sulfur poisoning,which protects vanadia from sulfur oxide attachment to a great extent.Consequently,the VBT catalyst exhibited the best resistance to sulfur poisoning.     

添加硫酸根对燃煤电厂V2O5基脱硝催化剂性能的影响

采用浸渍法分别制得活性物质V2O5的含量均为1%和SO2-4的含量不同的催化剂,并通过实验研究了添加SO-24对燃煤电厂SCR法脱硝技术中V2O5基催化剂活性和热稳定性的影响.在固定床反应器上,在NH3/NOx物质的量比为1.0和模拟烟气流量为72 L·h-1条件下,对几种催化剂的活性进行了测试,结果显示,当负载加入5.01%的SO2-4或使用含有8.91%的SO-24载体制备催化剂时,催化剂的活性提高最为显著;在TGA 92热重.差热分析仪上对这两种催化剂进行了热重实验,结果表明,添加的硫酸根对催化剂的热稳定性也有一定提高,且不会影响电厂SCR催化剂的使用.     

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.     

制备条件对低温NH_3-SCR脱硝催化剂Mn-Ce/TiO_2结构与性能的影响

采用溶胶凝胶法制备了Mn-Ce/TiO2催化剂,以NH3为还原剂,通过程序升温反应考察其选择性催化还原NO的催化性能.同时,着重探讨了焙烧温度、焙烧时间、活性物质负载量及Mn、Ce负载比例对催化剂结构和性能的影响,并用BET、XRD等对催化剂进行了表征.结果表明,活性组分负载量由0增至20%时,NO转化率随着负载量的增加而提高,当(Mn+Ce)质量分数为20%,催化剂活性最高,此后随着活性组分负载量的增加,NO转化率明显下降;Mn与Ce的负载比例为0.85∶0.15时,催化剂比表面积最大,为112.31m2·g-1;焙烧温度500℃时催化剂晶相均为TiO2锐钛矿型结构,焙烧温度升高至600℃,催化剂晶相为TiO2锐钛矿型和金红石型混合结构,且催化剂比表面积急剧减小;焙烧时间对催化剂晶相结构影响不大,焙烧时间为5h时,Mn-Ce/TiO2的脱硝性能最好.     

Alkali resistance promotion of Ce-doped vanadium-titanic-based NH3-SCR catalysts

The effect of K deactivation on V_2O_5/WO_3-TiO_2 and Ce-doped V_2O_5/WO_3-TiO_2 catalysts in the selective catalytic reduction(SCR) of NOxby NH_3 was studied.Ce-doped V_2O_5/WO_3-TiO_2 showed significantly higher resistance to K deactivation than V_2O_5/WO_3-TiO_2.Ce-doped V_2O_5/WO_3-TiO_2 with K/V = 4(molar ratio) showed 90% NOxconversion at 350°C,whereas in this case V_2O_5/WO_3-TiO_2 showed no activity.The fresh and K-poisoned V_2O_5/WO_3-TiO_2 and Ce-doped V_2O_5/WO_3-TiO_2 catalysts were investigated by means of in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS),NH_3-temperature progress decomposition(NH_3-TPD),X-ray photoelectron spectroscopy(XPS) and H2-temperature program reduction(H_2-TPR).The effect of Ce doping on the improving resistance to K of V_2O_5/WO_3-TiO_2 were discussed.     

Effect of Ce doping of TiO2 support on NH3-SCR activity over V2O5-WO3/CeO2-TiO2 catalyst

CeO2–TiO2composite supports with different Ce/Ti molar ratios were prepared by a homogeneous precipitation method, and V2O5–WO3/CeO2–TiO2catalysts for the selective catalytic reduction（SCR） of NOx with NH3 were prepared by an incipient-wetness impregnation method. These catalysts were characterized by means of BET, XRD, UV–Vis,Raman and XPS techniques. The results showed that the catalytic activity of V2O5–WO3/TiO2 was greatly enhanced by Ce doping（molar ratio of Ce/Ti = 1/10） in the TiO2 support.The catalysts that were predominantly anatase TiO2 showed better catalytic performance than the catalysts that were predominantly fluorite CeO2. The Ce additive could enhance the surface adsorbed oxygen and accelerate the SCR reaction. The effects of O2 concentration, ratio of NH3/NO, space velocity and SO2 on the catalytic activity were also investigated. The presence of oxygen played an important role in NO reduction. The optimal ratio of NH3/NO was 1/1 and the catalyst had good resistance to SO2 poisoning.     

NH3-SCR denitration catalyst performance over vanadium-titanium with the addition of Ce and Sb

Selective catalytic reduction technology using NH3 as a reducing agent(NH3-SCR) is an effective control method to remove nitrogen oxides. TiO2-supported vanadium oxide catalysts with different levels of Ce and Sb modification were prepared by an impregnation method and were characterized by X-ray diffractometer(XRD), Brunauer–Emmett–Teller(BET), Transmission electron microscopy(TEM), Fourier transform infrared spectroscopy(FT-IR), UV–Vis diffuse reflectance spectroscopy(UV–Vis DRS), Raman and Hydrogen temperature-programmed reduction(H2-TPR). The catalytic activities of V5 CexS by/TiO2 catalysts for denitration were investigated in a fixed bed flow microreactor. The results showed that cerium, vanadium and antimony oxide as the active components were well dispersed on TiO2, and the catalysts exhibited a large number of d–d electronic transitions, which were helpful to strengthen SCR reactivity. The V5 CexS by/TiO2 catalysts exhibited a good low temperature NH3-SCR catalytic activity. In the temperature range of 210 to 400℃, the V5 CexS by/TiO2 catalysts gave NO conversion rates above 90%. For the best V5Ce35Sb2/TiO2 catalyst, at a reaction temperature of 210℃, the NO conversion rate had already reached 90%. The catalysts had different catalytic activity with different Ce loadings. With the increase of Ce loading, the NO conversion rate also increased.     

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.