钨对高钒燃气脱硝催化剂的改性及SCR反应历程研究

针对燃气工况特点,以高钒SCR脱硝催化剂为研究对象,采用共浸渍法添加钨进行改性,考察了V_2O_5-WO_3/Ti O_2催化剂的SCR脱硝活性,表征了WO_3掺杂对V_2O_5氧化还原能力和酸性位的影响,并研究了该类型催化剂的SCR反应历程。结果表明:对于高钒脱硝催化剂,WO_3掺杂可以显著拓宽催化剂在280～440℃内的活性区间,但无法大幅提高催化剂的最高脱硝效率。活性温度区间得以拓宽的主要原因是WO_3掺杂后与V_2O_5发生强相互作用,在TiO_2表面形成V—O—W物种并提高V~(5+)物种比例,从而增加表面Br■nsted酸和Lewis酸位。在SCR脱硝反应中,催化剂表面酸性位对NH_3的吸附和活化是反应决速步骤,其后与气相NO反应,由气相中O_2补缺催化剂活化NH_3过程中消耗的晶格氧或—OH氧。     

铁锰轻稀土复合氧化物催化剂对苯的完全氧化作用

研究铁轻稀土，铁锰轻稀土复合氧化物催化剂对苯的催化活性，发现铁锰轻稀土复合氧化物催化剂对苯具有较理想的完全氧化活性；同时还研究了稀土用量及添加微量贵金属钯对催化剂性能的影响，发现轻稀土有一个恰当的添加比例，另外还发现添加微量钯可提高催化剂的初活性。     

在Pt/Al2O3催化剂上甲醇深度氧化的稳态及非稳态动力学

用玻璃外循环无梯度反应器研究了在Pt/Al_2O_3催化剂上甲醇深度氧化稳态动力学,甲醇深度氧化稳态动力学服从L-H机理模型。用正交设计法估计了动力学方程中的参数。用脉冲法测定了甲醇、氧及CO_2的吸附热。用脉冲法研究了甲醇在催化剂上吸附量与停留时间的关系,实验中观察到在Pt/Al_2O_3催化剂上甲醇深度氧化的振荡现象。     

FeP改性的Pt/FeP/CNTs催化剂的制备和电化学性能研究

铂基催化剂是目前直接甲醇燃料电池中阳极氧化催化性能最好的,因此提高铂的利用率和稳定性对推动DMFC的商业化十分重要。合成了一种新的催化甲醇氧化反应(MOR)的催化剂Pt/FeP/CNTs。FeP的掺杂可以显著提高Pt的MOR活性,当FeP的负载量为15%时,Pt/FeP/CNTs的MOR活性最佳,可以达到1325 mAmg■,是Pt/CNTs的3.8倍,Pt/C-JM的2.5倍,稳定性也较好。     

颗粒Ru催化剂催化湿式氧化乙酸和苯酚

采用湿式成型法制备了Ru/ZrO₂-CeO₂颗粒催化剂,对乙酸和苯酚进行湿式氧化,研究反应条件对苯酚氧化过程中COD去除的影响,并对催化剂的稳定性进行评价.结果表明,向CeO₂中添加Zr能提高催化剂抗热性能,使用湿式成型法能降低焙烧温度,两者都可以提高比表面积和催化剂活性.Ru/ZrO₂-CeO₂催化湿式氧化苯酚的COD去除率随着反应温度的升高、压力的增大和催化剂使用量的增加而升高,最优反应条件为温度150℃,压力3MPa,催化剂用量35g/L.在110h的动态试验中,COD和苯酚的去除率高于90%,催化剂具有较高活性和良好的稳定性.     

甲醇燃料车尾气净化催化剂的研究(Ⅰ)──单组分催化剂对甲醇的深度氧化

利用色谱－微反联用技术对甲醇深度氧化进行了研究。结果表明：甲醇在所有催化剂上氧化时均产生副产物甲醛及甲酸甲酯;非贵金属氧化物催化剂以Ｃｕ－Ｏ／ｒ－Ａｌ２Ｏ３的活性最优,其最佳负载量为１０％－２０％,不同的制备方法中以均匀沉淀法制备的催化剂最好;贵金属催化剂中Ａｇ／ｒ－Ａｌ２Ｏ３的活性较好,其甲醇氧化的Ｔ５０,Ｔ９５分别只有１３５℃和１９０℃,而且伴生的甲醛及甲酸甲酯浓度也较低。不同催化剂的活性与其     

甲醇燃料车尾气净化催化剂的研究(Ⅱ)──多组分催化剂对甲醇的深度氧化

利用色谱－微反联用技术研究多种多元催化剂对甲醇深度氧化的活性,并借助于ＸＲＤＢＥＴ等手段考察焙 烧温度对活性的影响,结果表明,不同的催化剂对甲醇氧化时均有甲醛及甲酸甲酯伴生,其伴生温度区间及最大伴生浓度随不同催化剂而变化;３２－３７号催化剂的活性明显高于双组分催化剂,添加少量稀土金属氧化物ＣｅＯ２和贵金属Ｐｄ对活性均有一定的改善作用,提高焙烧温度,催化剂表面发生烧结,对活性有不良影响。     

Pt/CeO2催化氧化甲苯反应机制研究

采用浸渍法制备了Pt/CeO_2和Pt/Al2O_3催化剂,并通过XRD、BET、ICP-OES、H2-TPR、XPS等手段表征其物理化学性质.结果发现,Pt/CeO_2和Pt/Al2O_3催化剂上Pt负载量约为0.6%,Al2O_3载体上Pt颗粒尺寸更小,Pt/CeO_2的可还原性更强.甲苯催化氧化活性评价结果表明,Pt/CeO_2催化剂表现出更好的催化活性,T50=170℃,T90=190℃.通过UV-Raman、甲苯TPD、GC/MS、In-situ FTIR等手段进一步研究发现,Pt/CeO_2活化甲苯及反应供氧的机制与Pt/Al2O_3存在区别,其活性更好是因为:(1)负载在CeO_2表面存在高电子密度的Pt原子,具有更强的活化甲苯能力,可以直接使苯基和甲基间的C—C链发生断裂;(2)Pt的负载促进了CeO_2氧空位形成,进一步提高了CeO_2的储氧性能,加速氧循环.除了Pt解离气相氧之外,CeO_2还可以提供活性氧物种参与催化氧化甲苯的反应,进一步提高甲苯催化氧化效率.     

用于燃料电池的甲醇水蒸气重整反应制氢的研究

研究了甲醇水蒸气重整制氢反应过程中各种因素对Cu／ZnO／Al2O3催化剂的活性和选择性的影响。结果表明：Cu／Zn比为2．0的催化剂在250℃反应时，催化剂效果较好，最合适反应条件是：压力0．1MPa，温度250℃，n(H2O)：n(CH3OH)=1．0-1．2，液体流速0．1mL／min。在Cu／ZnO／Al2O3)，催化剂上，甲醇水蒸气重整、甲醇分解和水气转换反应随反应条件的不同而发生相互抑制或促进作用。     

镍—稀土燃烧催化剂的研究

汽车尾气排放的CO、HC、NO_x和工业废气中的CO、烃类及其含氧衍生物,可导致大气污染。用催化剂使可燃污染物转为CO_2、H_2O和N_2等,是治理这类污染的主要方法之一。目前,国内外所用催化剂以贵金属铑、铂、钯为主要成分。为推广催化燃烧技术,我们研制了非贵金属cm系列催化剂,其性能已接近或超过了贵金属催化剂。本文在此基础上,进一步研究镍的加入,对催化剂各种性能的影响。一、实验部分催化剂制备采用浸渍法,使用主要组分为Al_2O_3的蜂窝状载体。催化剂的氧化活性,用稀薄甲苯为模拟气。分析仪器为102G气相色谱仪(氢火焰检测器)。     

N/Ce doped graphene supported Pt nanoparticles for the catalytic oxidation of formaldehyde at room temperature

Pt catalysts with nitrogen-doped graphene oxide (GO) as support and CeO₂ as promoter were prepared by impregnation method,and their catalytic oxidation of formaldehyde (HCHO) at room temperature was tested.The Pt-CeO₂/N-rGO (reduced GO) with a mass fraction of 0.7% Pt and 0.8%CeO₂ exhibited an excellent catalytic performance with the 100% conversion of HCHO at room temperature.Physicochemical characterization demonstrated that nitrogendoping greatly increased the...     

Effects of WOx modification on the activity, adsorption and redox properties of CeO2 catalyst for NOx reduction with ammonia

A series of WO₃/CeO₂ (WOx/CeO₂) catalysts were synthesized by wet impregnation of ammonium metatungstate on a CeO₂ support. The resulting solid acid catalysts were characterized by X-ray diffraction (XRD), UV-Vis spectroscopy (UV-Vis), Raman spectroscopy (Raman), in-situ Fourier transform infrared spectroscopy (in-situ FT-IR) of ammonia adsorption, NH₃-TPD, H₂ temperature-programmed reduction (H₂-TPR), NH₃/NO oxidation and activity measurements for NOx reduction by NH₃ (NH₃-SCR). The results show that polytungstate (WOx) species are the main species of tungsten oxide on the surface of ceria. The addition of tungsten oxide enhances the Brönsted acidity of ceria catalysts remarkably and decreases the amount of surface oxygen on ceria, with strong interaction between CeO₂ and WOx. As a result, the N₂ selectivity of NH₃ oxidation and NH₃-SCR at high temperatures (> 300℃) is enhanced. Therefore, a wide working temperature window in which NOx conversion exceeds 80% (NOx conversion > 80%) from 200 to 450℃, is achieved over 10 wt.% WOx/CeO₂ catalyst. A tentative model of the NH₃-SCR reaction route on WOx/CeO₂ catalysts is presented.     

Effects of tungsten oxide on the activity and thermal stability of a sulfate-derived titania supported platinum catalyst for propane oxidation

A Pt/WO₃/TiO₂ catalyst for propane oxidation was prepared by a stepwise wet impregnation method, and was aged at 800℃ for 5 hr. Compared to the sulfate-derived titania supported catalyst, the introduction of tungsten oxide as stable Bronsted acid sites led to the formation of more metallic platinum active sites at the Pt/WO₃ interface. The dissociation of surface intermediates for propane oxidation was promoted on the WO₃-modified catalyst. This, as well as the inhibition effects of tungsten oxide on the sintering of anatase and the phase transformation to rutile, resulting in a high activity and thermal stability for the Pt/WO₃/TiO₂ catalyst.     

Synergistic effect of Pt nanoparticles and micro-mesoporous ZSM-5 in VOCs low-temperature removal

Micro-mesoporous ZSM-5 zeolites were obtained by the post-treatment of tetrahydroxy ammonium hydroxide (TPAOH) solution with different concentration. The hierarchical pore structure formed during the desilication process facilitates the dispersion of Pt nanoparticles and Pt/ZSM-5 catalysts exhibit rather high catalytic activity for the deep oxidation of various VOCs at low temperature. The catalyst treated with TPAOH of 0.1 mol/L (Pt/ZSM-5(0.1)) shows the lowest degradation temperature (T_90%) of 128 and 142°C, respectively for benzene and n-hexane. Compared with the untreated Pt/ZSM-5 catalyst, the abundant mesopores, small Pt particle size and finely dispersed Pt contribute to the superior catalytic activity and stability of the Pt/ZSM-5 catalysts for VOCs removal. More importantly, the existence of H₂O in the feed gases hardly affected the activity of Pt/ZSM-5(0.1) catalyst at the low reaction temperature of 128°C, which is very important for VOCs low-temperature removal in the future practical applications.     

Effect of CeO2 and Al2O3 on the activity of Pd/Co_3O_4/cordierite catalyst in the three-way catalysis reactions (CO/NO/CnHm)

The present article studies the effect of CeO₂ and Al₂O₃ on the activity of Pd/Co₃O₄/cordierite catalyst in conversion of NO, CO, C_nH_m. The catalysts were characterized by temperature programmed reduction with hydrogen, X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. It is shown that the effect of CeO₂ on the properties of Pd/Co₃O₄/cordierite catalyst depends on preparation method. The catalyst obtained by co-deposition of cerium and cobalt oxides has higher activity in CO oxidation (CO + O₂ and CO + NO) and total hexane oxidation (C₆H₁₄ + O₂). Such phenomenon is probably caused by more than stoichiometric amount of formed oxygen vacancies, an increase in both mobility of surface oxygen and dispersity of components in the catalytic composition. It is demonstrated that CeO₂ addition promotes the SO₂ resistance of Pd/Co₃O₄/cordierite. The second support decreases the activity of Pd/Co₃O₄/cordierite catalyst in the reactions of CO and C₆H₁₄ with oxygen because of CoAl₂O₄ formation.     

Activity and hydrothermal stability of CeO2–ZrO2–WO3 for the selective catalytic reduction of NOx with NH3

A series of CeO_2–ZrO_2–WO_3(CZW)catalysts prepared by a hydrothermal synthesis method showed excellent catalytic activity for selective catalytic reduction(SCR)of NO with NH_3 over a wide temperature of 150–550°C.The effect of hydrothermal treatment of CZW catalysts on SCR activity was investigated in the presence of 10% H_2O.The fresh catalyst showed above 90% NO_x conversion at 201–459°C,which is applicable to diesel exhaust NO_x purification(200–440°C).The SCR activity results indicated that hydrothermal aging decreased the SCR activity of CZW at low temperatures(below 300°C),while the activity was notably enhanced at high temperature(above 450°C).The aged CZW catalyst(hydrothermal aging at 700°C for 8 hr)showed almost 80% NO_x conversion at 229–550°C,while the V_2O_5–WO_3/TiO_2 catalyst presented above 80% NO_x conversion at 308–370°C.The effect of structural changes,acidity,and redox properties of CZW on the SCR activity was investigated.The results indicated that the excellent hydrothermal stability of CZW was mainly due to the CeO_2–ZrO_2 solid solution,amorphous WO_3 phase and optimal acidity.In addition,the formation of WO_3 clusters increased in size as the hydrothermal aging temperature increased,resulting in the collapse of structure,which could further affect the acidity and redox properties.     

Mechanism of Hg oxidation in the presence of HCl over a commercial V2O5–WO3/TiO2 SCR catalyst

Experiments were conducted in a fixed-bed reactor containing a commercial V₂O₅/WO₃/TiO₂ catalyst to investigate mercury oxidation in the presence of HCl and O₂. Mercury oxidation was improved significantly in the presence of HCl and O₂, and the Hg⁰ oxidation efficiencies decreased slowly as the temperature increased from 200 to 400°C. Upon pretreatment with HCl and O₂ at 350°C, the catalyst demonstrated higher catalytic activity for Hg⁰ oxidation. Notably, the effect of pretreatment with HCl alone was not obvious. For the catalyst treated with HCl and O₂, better performance was observed with lower reaction temperatures. The results showed that both HCl and Hg⁰ were first adsorbed onto the catalyst and then reacted with O₂ following its adsorption, which indicates that the oxidation of Hg⁰ over the commercial catalyst followed the Langmuir–Hinshelwood mechanism. Several characterization techniques, including Hg⁰ temperature-programmed desorption (Hg-TPD) and X-ray photoelectron spectroscopy (XPS), were employed in this work. Hg-TPD profiles showed that weakly adsorbed mercury species were converted to strongly bound species in the presence of HCl and O₂. XPS patterns indicated that new chemisorbed oxygen species were formed by the adsorption of HCl, which consequently facilitated the oxidation of mercury.     

Preparation of MnO2 decorated Co3Fe1Ox powder/monolithic catalyst with improved catalytic activity for toluene oxidation

In this paper, KMnO₄ was used to pre-treat Co₃Fe-layered double hydroxides (LDH) precursor to prepare MnO₂ decorated Co₃Fe₁O_x catalyst. The toluene oxidation performance of the catalyst was investigated systematically. The optimized 0.1MnCF-LDO catalyst exhibited the best catalytic performance, and the temperatures of 50% and 90% toluene conversion (T₅₀ and T₉₀) were 218 and 243°C, respectively. The apparent activation energy (E_a) was 31.6 kJ/mol. The characterization results showed that the pre-redox reaction by KMnO₄ could increase the specific surface area, Co³⁺ species amount and oxygen defect concentration of the catalyst, which are the main reason of the improved toluene catalytic activity. Besides, this method was also applied to enhance toluene oxidation of iron mesh based monolithic catalyst. The 0.1MnCF-LDO/Iron mesh (IM) catalyst showed a 90% toluene conversion at around 316°C which was much lower than that of without MnO₂ addition (359°C). In addition, the water resistant of all the catalysts was studied as well, all the samples showed relatively good water resistance. The toluene conversion still remained to be over >80% even in the presence of 10 vol.% water vapor.     

Pd/C气体扩散电极用于电生成H2O2降解苯酚的研究

采用自制的Pd/C气体扩散阴极和Ti/IrO2/RuO2阳极,在无隔膜电解槽中对苯酚模拟废水降解效果及机制进行了研究,采用电子自旋共振法(ESR)对电解体系中产生的羟自由基(·OH)进行了检测.结果表明,在Pd/C气体扩散体系中掺杂Pd催化剂可以促进H2 O2的生成(H2 O2的稳定浓度是7.5 mg/L),有利于·OH的产生.经电化学氧化处理120 min后,苯酚和COD的去除率分别达到97.2%和50%,表明在电催化氧化过程中苯酚被氧化生成了大量低分子量中间产物.废水的BOD5/COD值达到0.73是处理前的9.1倍,苯酚废水的可生化降解性通过电化学氧化处理后显著提高.在该电化学体系中苯酚的降解是在阳极直接、间接氧化及阴极产生的H2 O2、·OH的氧化共同作用下完成的.通过对紫外扫描光谱图的分析推断出苯酚在电解过程中有醌类物质生成;由GC-MS检测到了邻苯二酚、对苯二酚、苯醌等芳香族化合物和己二酸、顺丁烯二酸、反丁烯二酸、丁二酸、丙二酸、乙二酸等短链羧酸,据此提出了苯酚降解的可能历程.