Co/RPSA系列催化剂在N2O分解中的应用

采用正交试验设计方法设计和浸渍法制备分子筛RPSA负载Co、K、Ba和Sr催化剂,使用微型反应器评价催化剂用于直接分解N₂O的催化活性,考察活性组分对催化剂活性的影响。采用XRD、H₂-TPR和NH₃-TPD等方法对催化剂进行表征。结果表明,金属Co和K对催化剂活性影响显著,Co对提高催化剂活性有促进作用,Co含量增加,催化剂活性提高,而K对催化剂活性有抑制作用。催化剂表征结果显示,Co物种主要以Co₃O₄形式存在于载体表面,催化剂的组成和配比影响催化剂活性、氧化还原性能和酸性,催化剂强酸的存在有利于催化剂活性的提高。
     

负载型NiO和CoO催化剂上N2O分解研究

本研究在对多种金属氧化物催化剂进行初步筛选的基础上，研制出以莫来石为载体的负载型NiO、CoO催化剂，考察了分解温度、催化剂组成和负载量对N2O分解率的影响，并对其分解反应动力学进行了研究。结果表明莫来石负载NiO、CoO催化剂对N2O分解有良好的催化性能；其反应速度对N2O均为一级反应；同样负载量下NiO有更好的催化分解活性；这一研究为开发阻力低、催化性能好的工业用蜂窝型规整填料奠定了基础。     

Rh2O3/monoclinic CePO4 composite catalysts for N2O decomposition and CO oxidation

CePO_4(in particular,monoclinic CePO_4)has been rarely used to make supported catalysts.Herein,monoclinic CePO_4 nanoparticles were prepared by calcining hexagonal CePO_4 nanorods(prepared by precipitation)in air at 900℃.Monoclinic CePO_4 nanowires were prepared by calcining hexagonal CePO_4 nanowires(prepared by hydrothermal synthesis at 150℃)in air at 900℃.Both monoclinic CePO_4 materials were used to support Rh_2O_3 by impregnation using Rh(NO_3)_3 as a precursor(followed by calcination).The catalytic performance of Rh_2O_3/monoclinic CePO_4 composite materials in N_2O decomposition and CO oxidation was investigated.It was found that Rh_2O_3 supported on monoclinic CePO_4 nanowires was much more active than Rh_2O_3 supported on monoclinic CePO_4 nanoparticles.The stability of catalysts as a function of reaction time on stream was studied in both reactions.The influence of co-fed CO_2,O_2,and H_2O on the catalytic activity in N_2O decomposition was also studied.These catalysts were characterized by employing N_2 adsorption–desorption,ICP-OES,XRD,TEM,XPS,H_2-TPR,O_2-TPD,and CO_2-TPD.The correlation between physicochemical properties and catalytic properties was discussed.     

The CO methanation over NaY-zeolite supported Ni/Co3O4, Ni/ZrO2, Co3O4/ZrO2 and Ni/Co3O4/ZrO2 catalysts

The CO methanation was studied over zeolite NaY supported Ni, Co₃O₄, ZrO₂ catalysts. The XRD, N₂ physisorption and SEM analysis were used in order to characterize the catalysts. Catalytic activities were carried out under a feed composition of 1% CO, 50% H₂ and 49% He between the 125 °C to 375 °C. Except for the Ni/Co₃O₄/NaY catalyst, all catalysts gave high surface area because of the presence of zeolite NaY. Average pore diameter of the catalysts fell into the mesopore diameter range. The highest CO methanation activity was obtained with Ni/ZrO₂/NaY catalyst at which the CO methanation was started after 175 °C and 100% CO conversion was obtained at 275 °C using the same catalyst.     

Bi-metallic catalysts of mesoporous Al2O3 supported on Fe,Ni and Mn for methane decomposition: Effect of activation temperature

Methane decomposition reaction has been studied at three different activation temperatures (500 °C, 800 °C and 950 °C) over mesoporous alumina supported Ni–Fe and Mn–Fe based bimetallic catalysts. On co-impregnation of Ni on Fe/Al₂O₃ the activity of the catalyst was retained even at the high activation temperature at 950 °C and up to 180 min. The Ni promotion enhanced the reducibility of Fe/Al₂O₃ oxides showing higher catalytic activity with a hydrogen yield of 69%. The reactivity of bimetallic Mn and Fe over Al₂O₃ catalyst decreased at 800 °C and 950 °C activation temperatures. Regeneration studies revealed that the catalyst could be effectively recycled up to 9 times. The addition of O₂ (1 ml, 2 ml, 4 ml) in the feed enhanced substantially CH₄ conversion, the yield of hydrogen and the stability of the catalyst.     

碱土金属修饰的Co/RPSA催化剂催化分解N2O

以RPSA分子筛为载体,采用浸渍法制备了一系列以Co为主活性组分和碱土金属为助剂的CoM/RPSA（M=Mg、Ca、Sr和Ba）催化剂,考察了含硫和含氧条件下直接催化分解N2O的性能。采用X射线衍射、热重-质谱联用系统、NH3-TPD和N2O-TPD等方法对催化剂进行了表征。XRD结果表明,Co物种主要以Co3O4尖晶石形态存在。NH3-TPD和N2O-TPD结果表明,碱土金属的种类影响催化剂酸性和对反应物N2O的吸附-脱附性能,催化剂活性与催化剂酸性及其对反应物N2O的吸附-脱附性能有关。催化剂活性评价结果显示,CoSr/RPSA催化剂的N2O分解活性较好,N2O转化率达到95%时的反应温度为471 ℃。     

Synergy between metals in bimetallic zeolite supported catalyst for NO-promoted N2O decomposition

The detrimental effect of NO on N₂O decomposition over zeolite supported noble metal catalysts can be (partly) eliminated by combining noble metal with iron or cobalt. In the presence of NO, the total conversion of N₂O over these bimetallic-zeolites exceeds the sum of conversions over the monometallic analogues of the individual components. A synergistic effect between the metals is proposed to be responsible for this phenomenon. This synergistic effect gives superior N₂O decomposition activity under realistic conditions, i.e. in the presence of water and NO, at temperatures as low as 350°C. The nature of the synergy is discussed in the light of some preliminary observations.     

N2O直接分解催化剂的研究进展

概述了用于催化分解温室气体N2O的贵金属、金属氧化物、分子筛等催化剂的研究进展,讨论了N2O催化分解的反应机理,分析了不同类型催化剂的特点及存在的问题。通过比较发现金属离子改性的分子筛催化剂活性较优,并展望了N2O催化分解研究的发展趋势。     

单分散Co3O4@SiO2核壳催化剂的制备及N2O催化分解性能

N₂O是一种重要的温室气体,且对臭氧层有很大的破坏作用,而直接催化分解法是除去N₂O最经济有效的方法之一。针对目前报道较多的钴氧化物催化剂活性较差的问题,将包覆型Co₃O₄核壳材料引入N₂O直接催化分解反应,利用核壳结构的限域特性与壳层的多孔孔道使Co₃O₄分散性增加,粒径减小,金属载体相互作用与接触反应界面增强,从而提高了催化剂在N₂O直接催化分解反应中的低温活性。此外,还制备了一系列不同金属含量的Co₃O₄@SiO₂球形核壳催化剂来研究包覆结构对催化剂性能的影响,通过X射线荧光光谱（XRF）、透射电镜（TEM）、X射线衍射（XRD）、N₂物理吸附、H₂-程序升温还原（H₂-TPR）等表征,证实在保证稳定单分散核壳结构的前提下,活性Co₃O₄位点越多,催化剂反应活性越好。     

Rh/γ-Al2O3–sepiolite monolithic catalysts for decomposition of N2O traces

The behaviour of Rh/γ-AlO₃–sepiolite monolithic systems in the N₂O decomposition reaction using catalysts with rhodium contents between 0.2 and 0.8 wt.% were analysed. The observed increase of the catalytic activity with the metal loading was related to an enhancement in the number of active sites. The SEM–EDX results showed that rhodium was mainly located on the alumina particles. The variation of the reaction rate values with the inlet N₂O and O₂ concentrations, suggested an apparent first order equation with respect to N₂O and zero order for O₂. The presence of NH₃ traces or water vapour in the feed decreased the catalytic activity, probably due to the competitive adsorption of NH_x or OH species. The ammonia oxidation reaction took place, producing N₂O as a secondary product. The monolithic catalysts developed operate with a low pressure drop achieving a N₂O conversion higher than 90% at 773 K in the presence of oxygen, ammonia or water vapour in the stream.     

Activation of dihydrogen on supported and unsupported silver catalysts

The activation of dihydrogen on silica, silver, and silica-supported silver (9 wt% Ag) was investigated. Both silica and silver are individually able to dissociate dihydrogen. Silanol groups on silica undergo H → D exchange at 393 K in D₂ as detected by IR spectroscopy. HD is observed in temporal analysis of products (TAP) experiments when H₂ and D₂ are sequentially pulsed on silver at 673 K; even when the time delay between the isotopes is 4 s, HD is formed, indicating that long-lived surface hydrogen species are present. Differential scanning calorimetry (DSC) shows that the activation of dihydrogen is an activated process: heat signals evoked through H₂ pulses on Ag/SiO₂ grow with increasing temperature (373–523 K). Nonetheless, the presence of silver on the silica surface accelerates the Si–OH → Si–OD exchange. Investigation of the exchange kinetics on Ag/SiO₂ shows that diffusion processes of the activated hydrogen species are rate determining at higher temperatures (?373 K), when the activation of D₂ on silver becomes facile. Indications of diffusion limitation are observed already at 313 K on Pt/SiO₂. TAP and DSC measurements show that H₂ is more readily activated on silver that has been treated in O₂ at 673 K followed by reduction in H₂ at 673 K. Morphological changes induced to the silver surfaces or (sub)surface oxygen species are presumed responsible for this effect.     

Room temperature decomposition of N2O in the presence of gaseous oxygen on prereduced Rh supported catalysts

The room temperature decomposition of N₂O over prereduced Rh‐based catalysts (Rh supported on ceria, zirconia and titania–alumina) is studied as a function of the oxygen content in the feed. Results indicate that Rh supported on titania–alumina shows lower degree of inhibition by gaseous oxygen on this reaction, attributed to the role of the metal particle–support interface region in the reaction. The effect of Rh loading and of the reaction temperature are consistent with the hypothesis. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hollow mesoporous silica sphere supported cobalt catalysts for F–T synthesis

High dispersion Co₃O₄ nano-particles supported on hollow mesoporous silica spheres (HMSS) with bimodal pore distribution were prepared by “two-solvent” technique. As-synthesized catalysts were characterized by XRD, N₂ adsorption–desorption, XPS, SEM, TEM, and H₂-TPR. The results showed that Co₃O₄ nano-particles were present inside the pore system of HMSS and the particles sizes increased with the increasing loaded cobalt content. The catalysts show good performance and high selectivity of C₅–C₁₈ hydrocarbon in F–T synthesis, which should attribute to the unique bimodal pore distribution facilitating reactants to access the active sites and to transport higher hydrocarbon products.     

Promoting effect of NiAl2O4 for supported Ni particles on sprayed Ni/Al2O3 catalysts

Ni/Al₂O₃ catalysts were prepared by the spray reaction method. The NiO particles supported on NiAl₂O₄ were stabilized against the aggregation and converted into smaller Ni particles by H₂ reduction. The Ni particles stabilized on NiAl₂O₄ marked anomalous high activity for CO hydrogenation, due to the stronger interaction between Ni and NiAl₂O₄. This revised version was published online in July 2006 with corrections to the Cover Date.     

铜锌掺杂的六铝酸盐分解N2O催化性能研究

采用共沉淀法制备了Cu和Zn取代六铝酸盐（LaCu_xZn_1-xAl₁₁O_19-δ,x=0、0.2、0.4、0.5、0.6、0.8、1.0）催化剂,通过XRD和BET等技术对催化剂进行表征,利用微型固定床反应器考察催化剂对N₂O的分解活性。结果表明,以(NH₄)₂CO₃为沉淀剂制备的催化剂在1 200 ℃焙烧4 h,可以形成完整的六铝酸盐晶型,Cu和Zn能够取代Al³⁺进入六铝酸盐晶体结构。LaCu_xZn_1-xAl₁₁O_19-δ催化剂对N₂O分解有较好的催化活性,其中,LaCu_0.8Zn_0.2Al₁₁O_19-δ活性较好。在LaCu_xZn_1-xAl₁₁O_19-δ六铝酸盐中,Cu为N₂O催化分解的主要活性元素,Zn有助于提高催化剂的稳定性,但由于六铝酸盐的特殊结构,Zn在催化剂中的作用较小。     

二氧化硅微球负载钌催化剂的制备及其在苯乙酮不对称氢转移反应中的应用

采用一步原位聚合诱导沉淀法制得了形貌多样、结构复杂的二氧化硅介孔微球,将其与Noyori配体RuCl(p-cymene)[(R,R)-Ts-DPEN]络合制得负载型钌催化剂并应用于苯乙酮不对称氢转移反应。利用场发射扫描电镜和氮气等温吸脱附手段证明了二氧化硅微球和负载型钌催化剂的微球型介孔结构,结合透射电镜表明了钌元素均匀分布在二氧化硅微球上;通过红外光谱显示该催化剂与反应底物之间存在氢键作用;在此基础上考察了载体孔结构,反应条件等因素对催化性能的影响。研究结果表明,钌配体负载到具有小孔径、高比表面积的二氧化硅微球上有利于苯乙酮的不对称氢转移反应,由此引出介孔氧化硅微球的孔道限域效应对不对称催化反应的活性和光学选择性存在明显的促进作用。在40℃、0.2ml苯乙酮的条件下反应16h,负载型钌催化剂用于苯乙酮不对称转移加氢反应其转化率和对映选择性最高可分别达到64.1%和93.4%。     

Bi-Co3O4 catalyzing N2O decomposition with strong resistance to CO2

Bi added to Co₃O₄ by coprecipitation method significantly decreased the average crystalline size of Co₃O₄ and increased the surface area and the active sites of the catalyst in population for catalyzing the N₂O decomposition. Over Bi_0.02Co that was the optimized from the Bi_xCo catalysts, 2000 ppm of N₂O in pure Ar was completely decomposed at 400 °C in GHSV of 20,000 h^− 1. Outstandingly, the catalyst exhibited a strong resistance to CO₂, stable N₂O conversion larger than 95% was obtained over the catalyst in the presence of 10% CO₂ at the reaction temperature.     

Highly active SO2-resistant ex-framework FeMFI catalysts for direct N2O decomposition

Ex-framework FeMFI catalysts, prepared by isomorphous substitution of iron in the aluminosilicate or gallosilicate MFI-type framework and activation by calcination at 823 K and steaming (300 mbar H₂O in N₂) at 873 K, show high activity and stability in N₂O decomposition in the presence of O₂, CO₂, H₂O, and SO₂. The N₂O conversion of the ex-framework catalysts in simulated tail-gas mixtures was >80% at 800 K and 75,000 h⁻¹. The specific activity per mole of Fe (turnover frequency, TOF) of the ex-framework catalysts in N₂O–He is four to nine times higher than observed for catalysts prepared by conventional solid and liquid-ion exchange, and sublimation methods. The stability of ex-framework catalysts for the direct N₂O decomposition, in the absence of any reductant, is remarkable, showing no significant deactivation (at N₂O conversion levels ranging from 20 to 65%) after 600 h on stream. Sublimed and especially ion-exchanged FeZSM-5 catalysts show a strong irreversible deactivation in feed mixtures containing H₂O and SO₂. The effect of SO₂ on the catalytic performance of FeMFI catalysts is discussed, as well as the applicability of the ex-framework FeMFI catalysts in fluid-bed combustion facilities.     

Manganese and cobalt-terephthalate metal-organic frameworks as a precursor for synthesis of Mn2O3, Mn3O4 and Co3O4 nanoparticles: Active catalysts for olefin heterogeneous oxidation

The thermal decomposition of manganese and cobalt-terephthalate Metal-Organic Framework precursors was utilized as a synthetic route for fabrication of Co₃O₄, Mn₃O₄ and Mn₂O₃ nanoparticles. The prepared metal oxide nanoparticles of Co₃O₄, Mn₃O₄ and Mn₂O₃ possess average size diameter of 40, 60 and 80 nm respectively. The findings demonstrate that spinel structure nanoparticles of Co₃O₄ and Mn₃O₄ exhibit efficient catalytic activity toward heterogeneous olefin epoxidation in the presence of tert-butyl hydroperoxide. In addition, Co₃O₄ and Mn₃O₄ nanoparticles illustrated excellent catalytic stability and reusability for nine and four cycles, respectively, toward olefin oxidation.     

Catalytic decomposition of N2O over supported rhodium catalysts: high activities of Rh/USY and Rh/Al2O3 and the effect of Rh precursors

The catalytic decomposition of nitrous oxide to nitrogen and oxygen has been studied over Al₂O₃-supported and zeolite-supported Rh catalysts. The activities of Rh/Al₂O₃ and Rh/USY (ultrastable Y zeolite) catalysts prepared from Rh(NO₃)₃ were higher than those of Rh/ZSM-5 and Rh/ZnO reported in the literature, while the activity of a Rh/Al₂O₃ catalyst prepared from RhCl₃ was suppressed severely in spite of the high H/Rh and CO/Rh values. The catalytic activity of N₂O decomposition was sensitive not only to the Rh dispersion but also to the preparation variables such as the Rh precursors and the supports used. This revised version was published online in July 2006 with corrections to the Cover Date.