In-situ UV-Raman study on soot combustion over TiO_2 or ZrO_2-supported vanadium oxide catalysts

UV-Raman spectroscopy was used to study the molecular structures of TiO2 or ZrO2-supported vana-dium oxide catalysts.The real time reaction status of soot combustion over these catalysts was de-tected by in-situ UV-Raman spectroscopy.The results indicate that TiO2 undergoes a crystalline phase transformation from anatase to rutile phase with the increasing of reaction temperature.However,no obvious phase transformation process is observed for ZrO2 support.The structures of supported va-nadium oxides also depend on the V loading.The vanadium oxide species supported on TiO2 or ZrO2 attain monolayer saturation when V loading is equal to 4(4 is the number of V atoms per 100 support metal ions).Interestingly,this loading ratio(V4/TiO2 and V4/ZrO2) gave the best catalytic activities for soot combustion reaction on both supports(TiO2 and ZrO2).The formation of surface oxygen com-plexes(SOC) is verified by in-situ UV Raman spectroscopy and the SOC mainly exist as carboxyl groups during soot combustion.The presence of NO in the reaction gas stream can promote the pro-duction of SOC.     

MoO3和Nb2O5助剂对Pt/ZrO2催化剂上短链烷烃燃烧反应的不同促进作用

贵金属Pt催化剂具有高活性和热稳定性,广泛应用于催化挥发性有机物的完全氧化反应(燃烧反应).短链烷烃(甲烷、乙烷、丙烷等)化学性质稳定,是最难氧化的一类有机物,常用作考察燃烧反应催化剂性能的模型反应物.然而,目前报道的研究工作通常仅限于针对某一种烷烃底物的催化燃烧,系统考察催化剂以及助剂对不同短链烷烃的催化燃烧活性鲜有报道.在短链烷烃中,甲烷只有C–H键;而其它烷烃除了C–H键;还有C–C键.因此,研究催化剂对甲烷、乙烷和丙烷燃烧反应催化性能的差异性,对于认识催化剂上C–H键和C–C键的活化具有非常重要的意义.本文制备了MoO3或Nb2O5修饰的Pt/ZrO2催化剂并用于短链烷烃的燃烧反应.研究发现,MoO3助剂对甲烷燃烧有明显的抑制作用,但对乙烷,丙烷和正己烷燃烧反应具有促进作用,促进作用随着烷烃碳链的增长逐渐增加;Nb2O5助剂对甲烷、乙烷、丙烷和正己烷燃烧反应均具有促进作用,然而促进作用随着碳链的增长而逐渐减弱.MoO3和Nb2O5助剂的不同促进作用与助剂影响催化剂表面酸性以及Pt物种的氧化或还原态有关.NH3-TPD结果表明,MoO3助剂可以显著增加Pt/ZrO2催化剂表面强酸位点数量,而Nb2O5助剂可以显著增加Pt/ZrO2催化剂表面中强酸位点数量.HTEM结果表明,两种助剂的添加都不会明显改变Pt物种的颗粒尺寸.在Pt-Mo/ZrO2催化剂上,MoO3覆盖部分Pt物种形成丰富的Pt-MoO3界面,促进了金属Pt物种和强表面酸性位点的生成,提高了丙烷燃烧反应活性;Pt-Nb/ZrO2催化剂上载体表面的部分Nb2O5被Pt物种包覆,使得生成的表面Pt-Nb2O5界面低于Pt-Mo/ZrO2催化剂,但由于催化剂表面酸性位的提升,也促进了丙烷燃烧反应活性的提高.XPS结果表明,在甲烷燃烧反应中,Pt-Nb/ZrO2催化剂上Ptn+物种能够更加稳定地存在,这可能是Nb2O5助剂提高Pt-Nb/ZrO2催化剂上甲烷燃烧活性的关键.而Pt-Mo/ZrO2催化剂上Ptn+物种在甲烷反应中可以更容易地被还原,并且由于MoO3的包裹导致暴露的Pt位点数量降低,使催化剂催化甲烷燃烧的活性受到抑制.可见,MoO3助剂更有利于C–C键活化,而Nb2O5助剂更有利于高键能的C–H键活化.综上,本文系统性地研究MoO3助剂和Nb2O5助剂对Pt/ZrO2催化剂上不同短链烷烃的燃烧反应的影响,证实了两种助剂的促进作用与碳链长度的关系是截然不同的.     

铂基催化剂用于柴油烃氧化

The catalytic performance of Pt-based catalysts for the total oxidation of hydrocarbons was investigated.The activity of supported Pt catalysts(Pt/Al2O3,Pt/ZrO2,Pt/TiO2,and Pt/H-ZSM-5)depends on the metal oxide support.Pt/Al2O3 showed the highest catalytic activity when the catalysts were aged at 750°C for 50 h in air.The activity of Pt/Al2O3 was dependent on the valence state of the Pt surface.Pt/Al2O3 with the Pt surface in the metallic state was more active than with the surface in the cationic state.The surface density of acid and basic sites on the Al2O3 support controlled the valence state of the Pt surface and stability of the Pt particles in the highly dispersed state,respectively.     

Pt／Al_2O_3，Pd／Al_2O_3催化剂上CO氧化与表面氧脱出－恢复性能

Ｐｔ／Ａｌ_２Ｏ_３，Ｐｄ／Ａｌ_２Ｏ_３催化剂上ＣＯ氧化与表面氧脱出－恢复性能周仁贤，郑小明（杭州大学催化研究所，杭州３１００２８）关键词铂，钯，氧化铝，氧化锆，负载型催化剂，一氧化碳，氧化，氧脱附ＡＩ。Ｏ。负载的贵金属（Ｐｔ，Ｐｄ或Ｒｈ等）催化剂对有...     

负载型Cu-Mn-Ce催化剂燃烧VOCs反应的载体效应

以MgO,Al2O3,SiO2,TiO2和ZrO2为载体,采用浸渍法制备了负载型Cu-Mn-Ce(CMC)三元复合氧化物催化剂,并用TG,XRD,BET和H2-TPR对催化剂进行了表征,以甲苯和丙酮催化燃烧为模型反应,考察了该催化剂的催化活性。结果表明,纯CMC催化剂的铈基固溶体结构表现出优良的催化活性,当CMC负载在SiO2和Al2O3上后,其大比表面积和表面羟基均不利于CMC活性固溶体结构的形成,另外Mn,Cu等过渡金属与MgO载体发生相互作用而破坏了CMC的活性结构。TiO2和ZrO2则较好地保持了CMC活性固溶体的结构,并显著提高了CMC催化剂的高温热稳定性。     

净化丙烯腈废气催化剂的研究

研究了贵金属Ｐｄ，Ｐｔ，非贵金属Ｃｕ－Ｍｎ氧化物沸石等催化剂对含－ＣＮ有机物丙烯腈的氧化活性，结果表明，以Ｃｕ－Ｍｎ作活性组分、ＺｒＯ２作助活性组分的催化剂对丙烯腈有较高的氧化活性，较强的控ＮＯｘ能力、较低的起燃温度、较宽的浓度处理范围和较魇空速处理能力，３００ｈ稳定性试验后催化剂活性仍在９９％以上。Ｏ２－ＴＰＤ及扫描电镜表征结果很好地支持了反应结果。     

负载型Ni催化剂高效催化2-羟基四氢吡喃还原胺化制备5-氨基-1-戊醇（英文）

伯胺等含氮化合物是最重要的化工中间体之一,被广泛应用于聚合物、医药、农药、染料和表面活性剂等产品的生产.当前,商业化伯胺主要通过卤代烃或环氧化合物直接胺化以及腈类或酰胺类化合物加氢制备,这些过程受具有特定官能团的有机原料短缺以及产生较多废物等问题的限制,导致其生产成本较高.因此,高效可持续生产伯胺化合物路径的开发得到了广泛关注.醛和酮类化合物直接与氨还原胺化反应所需温度一般较低(≤120℃),为伯胺的高选择性合成提供了一个重要途径.基于此,本文利用2-羟基四氢吡喃能够原位转化为其互变异构体5-羟基戊醛,而5-羟基戊醛中醛基具有较高还原胺化活性的特征,发展了一种以生物糠醛衍生二氢吡喃为原料,通过先水合得到2-羟基四氢吡喃再在温和条件下还原胺化合成5-氨基-1-戊醇的新方法.5-氨基-1-戊醇是一种分子中同时含有羟基和氨基的重要双官能团化合物,广泛用于医药和农药合成,也常被用作有机合成砌块,目前其主要用途是合成具有很高药用价值的生物碱Manzamine A.5-氨基-1-戊醇的一条传统合成路线是以石化基1,5-戊二醇经浓盐酸进行单氯取代制备5-氯戊醇中间体,该中间体经分离后再与氨气反应制得5-氨基-1-戊醇的方法.该方法原料成本高,产生大量废弃物,且只取得中等目标产物收率(66.6%).本文重点研究了不同氧化物载体包括SiO2,TiO2,γ-Al2O3,ZrO2和MgO负载Ni催化剂的2-羟基四氢吡喃还原胺化性能,并对比考察了CuCr2O4,雷尼Ni,Ru/C,Pd/C,Pt/C和Rh/C等商业加氢催化剂的性能.研究发现,ZrO2负载Ni催化剂的活性高于其他氧化物载体负载Ni催化剂的活性,也明显优于所对比的系列商业加氢催化剂.系列物理化学表征结果显示,Ni/ZrO2催化剂同时表现出较高的还原性和表面酸密度,这可能是该催化剂表现出最高5-氨基-1-戊醇收率的原因.以Ni/ZrO2为催化剂,于80℃,2 MPa H2条件下在间歇式反应器中催化2-羟基四氢吡喃水溶液还原胺化可取得90.8%的5-氨基-1-戊醇收率.通过固定床反应器研究了Ni/ZrO2催化剂稳定性,发现5-氨基-1-戊醇初始收率可达83%,反应90 h活性缓慢下降至初活性的81%.Ni流失和表面氧化可能是催化剂的失活的主要原因.通过对反应温度、H2压力、2-羟基四氢吡喃/NH3摩尔比等因素对反应活性调变规律的探究,推测2-羟基四氢吡喃催化还原胺化制备5-氨基-1-戊醇反应机理如下:首先,受化学平衡作用,2-羟基四氢吡喃逐渐转化为其互变异构体5-羟基戊醛;然后,5-羟基戊醛中醛基迅速与NH3反应生成亚胺中间体;最后,亚胺中间体在金属催化剂上加氢得到5-氨基-1-戊醇.     

整体式Mn-Fe/ZrO2-TiO2催化剂的制备及在低温NH3-SCR反应中的性能

以锆钛复合氧化物为载体, 制备整体式Mn基催化剂并研究其在低温氨选择性催化还原(NH3-SCR)氮氧化物反应中的性能; 用BET、XRD、储氧量(OSC)、程序升温还原(TPR)和XPS对催化剂进行表征. 实验结果表明, 与以TiO2为载体的催化剂相比, 以ZrO2-TiO2为载体的催化剂具有较大的比表面积、更稳定的晶相结构和较多的储氧量, 并具有较强的低温氧化性能和较高的表面Mn含量, 表现出良好的低温活性和高温稳定性. 在700 ℃焙烧后, Mn-Fe/ZrO2-TiO2在高空速55000 h-1条件下, 仍具有较好的起燃温度(182 ℃)和NO的转化率(78%), 并具有较强的抗水性能, 表现出很好的应用前景.     

Pd/MWCNTs贫燃甲烷催化燃烧性能研究

以MWCNTs为载体,用HNO_3做氧化剂对MWCNTs进行处理,通过XPS研究了处理前后MWCNTs表面官能团的变化,并采用超声浸渍法制得Pd/MWCNTs催化剂,借助TEM,揭示了Pd粒子在催化剂表面分散度和粒径与MWCNTs表面含氧量、羟基和羰基间的关系。并考察了Pd/MWCNTs催化剂预处理方法对低浓甲烷催化燃烧活性和稳定性的影响,研究表明,Pd的价态以及Pd粒子的粒径,都与催化剂的甲烷燃烧活性直接关联。单质Pd的氧化和Pd粒径的长大是导致催化剂性能衰减的原因。通过原位FT-IR技术对反应气氛下中间物种的监测,提出了Pd/MWCNTs催化剂上的低浓度甲烷催化氧化反应机理。     

Three-dimensionally ordered macro-porous Pt/TiO2 catalyst used for water-gas shift reaction

Three-dimensionally ordered macro-porous (3DOM) Pt/TiO2 catalysts were prepared by template and impregna-tion methods, and the resultant samples were characterized by using TG-DTA, XRD, SEM, TEM, and TPR techniques. The catalytic performance for water-gas shift (WGS) reaction was tested, and the influences of some conditions, such as reduction temperature of catalysts, the amount of Pt loadings and space velocity on catalytic performance were investigated. It was shown that Pt particles were homogeneously dispersed on 3DOM TiO2. The reduction of TiO2 surface was important for the catalyticperformance. The activity test results showed that the 3DOM Pt/TiO2 catalysts exhibited very good catalytic performance for WGS reaction even at high space velocity, which was owing to the better mass transfer of 3DOM porous structure besides the high intrinsic activity of Pt/TiO2.     

Synthesis Gas Production from Natural Gas on Supported Pt Catalysts

Auto-thermal reforming of methane, combining partial oxidation and reforming of methane with CO2 or steam, was carried out with Pt/Al2O3, Pt/ZrO2 and Pt/CeO2 catalysts, in a temperature range of 300-900℃. The auto-thermal reforming occurs in two simultaneous stages, namely, total combustion of methane and reforming of the unconverted methane with steam and CO2, with the O2 conversion of 100% starting from 450 ℃. For combination with CO2 reforming, the Pt/CeO2 catalyst showed the lowest initial activity at 800 ℃, and the highest stability over 40 h on-stream. This catalyst also presented the best performance for the reaction with steam at 800 ℃. The higher resistance to coke formation of the catalyst supported on ceria is due to the metal-support interactions and the higher mobility of oxygen in the oxide lattice.     

Pt/CexZr1-xO2催化剂上丙烷完全氧化性能研究

采用沉淀法制备了ZrO2,CeO2和Ce0.7Zr0.3O2载体,并用浸渍法制备负载型Pt催化剂。考察了500和900℃焙烧催化剂的丙烷完全氧化性能和水汽对丙烷氧化反应的影响。对于500℃焙烧的催化剂,催化剂的丙烷氧化活性顺序为:Pt/ZrO2-500>Pt/CeO2-500>Pt/Ce0.7Zr0.3O2-500;而经900℃焙烧的催化剂活性顺序为:Pt/ZrO2-900>Pt/Ce0.7Zr0.3O2-900>Pt/CeO2-900。反应气氛中水汽的存在对两种Pt/ZrO2催化剂的活性均有抑制作用(T50温度均提高了10~15℃);而对于Pt/CeO2-500催化剂有抑制作用(T50温度提高10℃),但对Pt/CeO2-900催化剂活性有促进作用(T50温度下降25℃);对于两种Pt/Ce0.7Zr0.3O2催化剂活性具有促进作用(T50温度均下降5~25℃)。表征结果表明催化剂的活性与其表面Pt物种价态密切相关,催化剂表面上Pt0物种有利于活性的提高。Pt/Ce0.7Zr0.3O2-500催化剂中只含有氧化态Pt物种(Pt^2+),而Pt/Ce0.7Zr0.3O2-900催化剂中则含有部分金属态Pt物种,因此其活性高于Pt/Ce0.7Zr0.3O2-500催化剂。     

Pt/Ce0.6Zr0.4O2催化剂在水煤气变换反应中的电导研究

采用浸渍法制备了不同载体(Ce0.6Zr0.4O2,CeO2和ZrO2)负载的Pt基水煤气变换反应(WGSR)催化剂, 并对其进行了活性评价. 利用X射线衍射(XRD), 程序升温还原(TPR)和原位电导等技术对样品进行了表征. 结果表明, Ce0.6Zr0.4O2固溶体具有比CeO2更高的氧转移能力, 因此促进了Pt/Ce0.6Zr0.4O2催化剂的WGSR活性.     

Direct gas-phase epoxidation of propylene to propylene oxide using air as oxidant on supported gold catalyst

Gold catalysts supported on SiO2, TiO2, TiO2-SiO2, and ZrO2-SiO2 supports were prepared by impregnating each support with a basic solution of tetrachloroauric acid. X-ray diffraction （XRD）, transmission electron microscopy （TEM）, and X-ray photoelectron spectroscopy （XPS） techniques were used to characterize their structure and surface composition. The results indicated that the size of gold particles could be controlled to below 10 nm by this method of preparation. Washing gold catalysts with water could markedly enhance the dispersion of metallic gold particles on the surface, but it could not completely remove the chloride ions left on the surface. The catalytic performance of direct vapor-phase epoxidation of propylene using air as an oxidant over these catalysts was evaluated at atmospheric pressure. The selectivity to propylene oxide （PO） was found to vary with reaction time on the stream. At the reaction conditions of atmosphere pressure, temperature 325 ℃, feed gas ratio V（C3H6）/V（O2）= 1/2, and GHSV =6000h^-1, 17.9% PO selectivity with 0.9% propylene conversion were obtained at initial 10 min for Au/SiO2 catalyst. After reacting 60 min only 8.9% PO selectivity were detected, but the propylene conversion rises to 1.4% and the main product is transferred to acrolein （72% selectivity）. Washing Au/TiO2-SiO2 and Aa/ZrO2-SiO2 samples with magnesium citrate solution could markedly enhance the activity and PO selectivity because smaller gold particles were obtained.     

Synthesis of conductive rutile-phased Nb0.06Ti0.94O2 and its supported Pt electrocatalysts (Pt/Nb0.06Ti0.94O2) for the oxygen reduction reaction

In this paper, Nb-doped TiO(2) with anatase and rutile phases was synthesized by the acid-catalyzed sol-gel method, and used as catalyst supports for the oxygen reduction reaction (ORR). X-ray diffraction (XRD), transmission electron microscopy (TEM), Energy dispersive X-ray spectroscopy (EDX), and Brunauer-Emmett-Teller (BET) were used to characterize the support materials in terms of material structures, morphology, composition, and surface area. XRD analysis showed that both the high concentration of hydrochloric acid present in the synthesis and the presence of Pt in the support could favor the formation of conductive rutile phased TiO(2), resulting in the improvement of electronic conduction of the Nb-doped TiO(2) support, which was confirmed by measured conductivities. For electrochemical characterization and ORR catalyst activity validation, Pt particles were deposited on the supports synthesized in this paper to form several catalysts, which were tested for electrochemical Pt surface area, ORR mass activity and specific activity. A monotonic increase in Pt ORR mass activity with increasing catalyst support's conductivity suggested that the support conductivity plays an important role in enhancing catalyst mass activity. The results showed that these non-carbon supported catalysts are promising as PEM fuel cell cathode catalysts.     

Pt单层修饰Pd/C氧还原催化剂

分别利用液相热解法和浸渍还原法制备了碳载钯纳米催化剂（Pd/C）,并研究了其对氧还原反应的电催化活性。与浸渍还原法相比,液相热解法得到的Pd/C催化剂虽然粒径较大,但表现出较好的氧还原反应（ORR）活性和稳定性.在所制备的Pd/C催化剂基础上,通过置换欠电势沉积的Cu原子单层,获得了Pt单层修饰的Pd/C催化剂,其ORR活性较Pd/C催化剂有显著提高,且与纯Pt/C催化剂接近,而其耐久性则较纯Pt/C催化剂有显著提升,显示出Pt单层催化剂的潜在优势.     

Pt/γ-Al2O3/CexZr1-xO2催化剂低温催化燃烧去除饮食油烟

以CexZr1-xO2固溶体做载体,制备了系列Pt/γ-Al2O3/CexZr1-xO2催化剂(x=1,0.75,0.5,0.25,0).应用Brunauer-Emmet-Teller(BET)比表面积分析、X射线衍射(XRD)和H2程序升温还原(H2-TPR)等手段对催化剂进行相关表征,并系统研究了催化剂在饮食油烟催化燃烧中的催化活性.BET结果表叫催化剂的比表面积随Ce/Zr摩尔比的减小而减小.XRD结果表明贵金属Pt很好地分散在氧化铝和CexZr1-xO2固溶体上.H2-TPR结果发现催化剂Pt/γ-Al2O3/Ce0.5Zr0.5O2的还原峰面积最大且氧离子的流动性最好.催化活性研究结果表明Pt负载在CexZr1-xO2固溶体上有利于油烟的催化燃烧,降低了反应温度.随着CexZr1-xO2固溶体中Ce/Zr摩尔比的变化,催化剂的活性顺序为Pt/γ-Al2O3/Ce0.5Zr0.5O2＞Pt/γ-Al2O3/Ce0.25Zr0.75O2＞Pt/γ-Al2O3/Ce0.75Zr0.25O2＞Pt/γ-Al2O3/CeO2＞Pt/γ-Al2O3/ZrO2.     

Kinetics of Photogenerated Electrons Involved in Photocatalytic Reaction of Methanol on Pt/TiO2

Time-resolved IR spectroscopy was used to detect the photocatalytic reaction of methanol for H2 production on Pt/TiO2 catalysts. There exists an optimal amount of Pt loading in the Pt/TiO2 catalysts for the reaction of the photogenerated long-lived electrons. For a given amount of Pt loading, the reaction rate of the long-lived electrons on Pt/TiO2 catalysts varies greatly with the di?erent reduction temperature of the catalysts. The possible reason is that the Pt particles occupy the surface active sites for methanol adsorption on Pt/TiO2 catalysts reduced at high temperature. This phenomenon is not observed obviously on Pt/TiO2 catalysts reduced at low temperature. The decay rate of the long-lived electrons evaluated by time-resolved IR method qualitatively correlates well with the activity of H2 production under steady-state irradiation conditions.     

Tailoring the surface structure of iron compounds to optimize the selectivity of 3-nitrostyrene hydrogenation reaction over Pt catalyst

Selective hydrogenation of substituted nitroarenes is an important reaction to obtain amines.Supported metal catalysts are wildly used in this reaction because the surface structure of supports can tune the properties of the supported metal nanoparticles （NPs） and promote the selectivity to amines.Herein,Pt NPs were immobilized on Fe OOH,Fe₃O₄andα-Fe₂O₃nanorods to synthesize a series of iron compounds supported Pt catalysts by liquid phase reduction me...     

以ZrO2-TiO2为载体的整体式锰基催化剂应用于低温NH3-SCR反应

以MnO2为活性组分,Fe2O3为助剂,制备了以TiO2及ZrO2-TiO2为载体的整体式催化剂.考察了它们在不同温度焙烧后应用于富氧条件下,NH3选择性催化还原.(NH3-SCR)氮氧化物的低温反应性能和高温稳定性.用X射线衍射(XRD)实验、比表面积测定(BET)、储氧性能测定(OSC)及程序升温还原(H2-TPR)等方法对催化剂进行了表征.结果表明,以ZrO2-TiO2为载体的催化剂具有很好的高温热稳定性,并具有较高的比表面积和储氧能力.同时具有较强的氧化能力.催化剂的活性测试结果表明,以ZrO2-TiO2为载体的整体式锰基催化剂明显地提高了NH3-SCR反应的低温活性,具有良好的应用前景.