草酸二甲酯气相法加氢制乙二醇催化剂研究进展

乙二醇是重要的化工原料,广泛应用于阻冻剂、燃料电池和聚酯工业等领域。传统制备乙二醇路线有基于石油路线的环氧乙烷水合法以及基于煤和天然气路线的C₁合成法。C₁路线合成乙二醇是CO氧化偶联生成草酸二甲酯,草酸二甲酯再催化加氢合成乙二醇。设计和制备高效草酸二甲酯加氢催化剂是实现煤制乙二醇工业化关键。草酸二甲酯加氢催化剂主要有Ru基均相催化剂和Cu基非均相催化剂,其中,无Cr的Cu基催化剂(Cu/SiO₂) 是研究重点。影响Cu/SiO₂ 催化性能的主要有载体、制备方法和助剂。载体类型不仅影响活性物种与载体之间的相互作用,而且影响活性物种分散度,具有高表面积和有序介孔结构的载体能够提高Cu物种分散度,从而显著提高催化剂活性。制备Cu/SiO₂催化剂的方法有蒸氨法、浸渍法、沉积沉淀法、离子交换法和溶胶-凝胶法等。蒸氨法制备的Cu/SiO₂形成铜氨络合离子,使Cu物种得到很好分散,还原后催化剂表面Cu+含量较高。Mo、Co、Ni和B等助剂的添加可以调变Cu物种的价态和分散度,提高催化剂性能。添加助剂时,要综合考虑助剂的引入对催化剂酸碱性质、活性物种分散度和载体孔径结构等的影响。研究认为,草酸二甲酯加氢机理是Cu⁰与Cu⁺的协同作用,Cu⁰是催化剂上的活性位点,活化H₂;Cu⁺起亲电子的L酸作用,激化CO键提高草酸二甲酯中酯基的反应。催化剂失活的主要原因是产物乙醇酸甲酯在催化剂表面较难脱附以及反应过程中催化剂烧结。Cu/SiO₂催化剂存在热稳定性差等缺陷,制备高稳定Cu基催化剂是今后发展方向。     

煤制乙二醇关键技术:Cu/SiO2催化剂的构效关系及活性位

鉴于我国"富煤缺油少气"的资源结构特点,煤制乙二醇作为现代煤化工五大示范工程之一,已于2009年列入国家石化产业振兴规划中。因此研究以煤为原料经合成气中CO氧化偶联合成草酸酯随后再加氢制乙二醇的工艺具有重要的研究价值及应用前景。基于本工艺的关键步骤草酸酯加氢反应中面临的铜基催化剂构效关系和活性位不明确等问题,本文对铜催化剂中铜物种的结构和价态形成的关系,及草酸二甲酯加氢的活性位等科学问题进行了研究。通过对蒸氨水热法制备Cu/SiO2催化剂的过程进行系统表征,发现制备过程中形成的铜氨络合离子能与混合液中的氧化硅表面的羟基以及带负电的氧原子分别发生脱水反应或静电吸附,能够有效的均匀负载铜物种在载体表面,从而增强载体与金属的相互作用。焙烧后的催化剂结构中主要存在层状硅酸铜和高分散的纳米CuO两种铜物种,在一定条件下还原4h后,在其表面分别形成Cu+和Cu0物种。通过改变Cu/SiO2催化剂的铜负载量的方式进一步调控结构中的层状硅酸铜和纳米CuO的相对含量,可调控还原后表面的Cu0和Cu+的相对量,从而获得了催化剂结构与加氢反应性能的构效关系规律。通过定量表面的Cu0和Cu+,并将其与目标产物的转化频率关联,得出Cu0在加氢反应中作为主要的活性位,而Cu+物种主要促进乙醇酸甲酯等中间产物的转化。同时关联Cu0/(Cu++Cu0)与反应速率发现草酸二甲酯加氢反应存在适宜的Cu0与Cu+比例,两者显示出协同作用。     

CeO_2掺杂对Cu/SiO_2催化剂热稳定性的影响

采用蒸氨法制备了CeO2掺杂的Cu/SiO2催化剂,考查了CeO2掺杂对Cu/SiO2催化剂在草酸二甲酯催化加氢制取乙二醇反应中热稳定性的影响。采用H2-程序升温还原(H2-TPR),透射电镜(TEM)对催化剂的物理化学性能进行了表征。在反应温度T=200℃,压力P=3.0 MPa,液时空速LHSV=0.4 h-1,氢气、草酸二甲酯摩尔比H2∶DMO=80∶1,400℃高温处理2.0 h的条件下测定了催化剂的活性变化。结果表明,CeO2掺杂对Cu物种的分散起到了促进作用,提高了催化剂的热稳定性。     

焙烧温度对Co-Ru-ZrO2/γ-Al2O3F-T合成催化剂性能的影响

采用浸渍法制备钴基催化剂,考察了催化剂焙烧温度对其F-T合成反应性能和产物分布的影响。制备催化剂时,不对催化剂进行焙烧,Co物种容易还原,并可较好分散,催化剂具有较高的催化活性和重质烃选择性。较高温度下焙烧,Co物种和载体间的相互作用增强,形成难还原的铝酸钴化合物,同时氧化钴晶粒聚集或烧结,Co物种的还原程度下降,催化剂CO加氢活性降低,重质烃选择性下降。在原料气n(H₂)∶n(CO)=2.0、483 K、1.5 MPa和800 h^-1条件下,未焙烧、673 K和923 K焙烧的催化剂上进行F-T合成反应,CO的转化率分别为80.27%、78.41%和61.14%,重质烃的选择性C₅⁺分别为88.54%、88.57%和77.95%。较低焙烧温度有利于反应速率的提高和重质烃的合成,较高焙烧温度使CO加氢活性下降,有利于低碳烃的生成。     

草酸二甲酯加氢制乙二醇Cu/SiO_2催化剂失活研究

采用沉积-沉淀法制备Cu/SiO_2催化剂,研究Cu/SiO_2催化剂在草酸二甲酯制乙二醇反应中的活性及稳定性。采用XRD、TG、SEM和EDS等对催化剂进行表征,分析催化剂的失活原因。结果表明,催化剂表面积炭和活性组分铜的烧结是造成催化剂失活的主要原因。在高空速1.5 h~(-1)下,对催化剂进行寿命考察,结果表明,运行350 h,草酸二甲酯转化率维持95%以上,乙二醇选择性下降至约60%。     

分子筛固载双金属Fenton催化剂的制备及其反应性能

采用离子交换法,将Fe2+和Cu2+负载在NaY分子筛上,制备了Fe-Cu-Y非均相Fenton催化剂。比较了具有不同Fe/Cu摩尔比的催化剂对苯酚的催化氧化性能。结果显示,当催化剂的Fe/Cu摩尔比为2.40时,其催化反应速率最快,反应2 h后苯酚降解率达99.07%,并且该催化剂稳定性较高,可循环使用。在催化剂的焙烧温度试验中,通过BET、SEM、XRD表征及活性测定发现,提高焙烧温度使得催化剂比表面积减小、催化活性降低,700℃焙烧还会造成催化剂的烧结。该非均相Fenton体系对苯酚的降解反应在60 min内符合准1级反应动力学,其表观活化能为47.56 kJ/mol。     

焙烧温度对CuO/ZrO_2催化剂催化草酸酯加氢性能的影响

采用乙酸络合法一锅制备催化剂前驱体,再经过不同温度焙烧制得CuO/ZrO_2催化剂,用于草酸二甲酯(DMO)加氢制乙二醇(EG)。利用SEM、XRD和化学吸附等对催化剂进行表征与活性评价,结果表明,焙烧温度影响催化剂的微观结构和催化活性:低温焙烧所得催化剂表面CuO颗粒分布均匀且粒径较小,所以易还原且催化性能较好;而高温焙烧所得催化剂表面颗粒发生团聚且Cu物种聚集,使得表面Cu质量分数远大于体相浓度且粒径变大,导致催化性能减弱; 550℃焙烧所得催化剂的催化性能最好,在液时空速为0.5 h~(-1)时,DMO转化率约为97.7%,EG选择性高达95.3%。     

草酸二甲酯加氢制乙二醇Cu/SiO2催化剂工业应用常见问题及分析

针对草酸二甲酯加氢制乙二醇Cu/SiO_2催化剂在工业应用中易发生粉化和活性降低的问题,对Cu/SiO_2催化剂的理化性能和工艺操作条件进行比对和分析,结果发现:催化剂机械强度低、草酸二甲酯进料水含量高、系统压力波动大和热冲击是Cu/SiO_2催化剂发生粉化的主要原因;催化剂老化和烧结、循环氢气纯度、氢酯摩尔比和反应温度对Cu/SiO_2催化剂的活性具有较大的影响。     

Ni/SiO2催化剂的制备条件对催化间二硝基苯加氢反应性能的影响

将Ni/SiO₂催化剂应用于间二硝基苯加氢反应中,考察了该催化剂制备过程中焙烧温度和还原温度对其催化性能的影响,并通过BET、XRD、TEM、TPR等方法对催化剂进行了表征.结果表明,在实验研究范围内,随着焙烧温度的提高,Ni/SiO₂催化剂比表面积降低,NiO与载体SiO₂之间的相互作用逐渐增强,催化剂的还原温度明显提高,活性组分Ni的晶粒度增大,焙烧温度为773 K时催化剂具有最佳的催化反应性能,此时活性组分Ni以高分散状态存在.催化剂的还原温度对Ni/SiO₂催化剂的结构和催化性能影响显著,当还原温度较低时,活性组分还原不完全,催化剂活性较低;而还原温度太高会使活性组分烧结,导致催化剂活性明显降低;还原温度为723 K时催化剂表现出最佳的活性和选择性.     

焙烧温度对Co—Ru—ZrO2／Y—Al2O3 F—T合成催化剂性能的影响

采用浸渍法制备钴基催化剂，考察了催化剂焙烧温度对其F—T合成反应性能和产物分布的影响。制备催化剂时，不对催化剂进行焙烧，Co物种容易还原，并可较好分散，催化剂具有较高的催化活性和重质烃选择性。较高温度下焙烧，Co物种和载体间的相互作用增强，形成难还原的铝酸钴化合物，同时氧化钴晶粒聚集或烧结，Co物种的还原程度下降，催化剂CO加氢活性降低，重质烃选择性下降。在原料气n（H2）：n（CO）=2．0、483K、1．5MPa和800h^-1条件下，未焙烧、673K和923K焙烧的催化剂上进行F—T合成反应，CO的转化率分别为80．27％、78．41％和61．14％，重质烃的选择性C5^＋分别为88．54％、88．57％和77．95％。较低焙烧温度有利于反应速率的提高和重质烃的合成，较高焙烧温度使CO加氢活性下降，有利于低碳烃的生成。     

CO2加氢一步制二甲醚展望

CO₂加氢制二甲醚（DME）是有潜力实现CO₂资源化利用的重要途径之一。与光、电催化相比,CO₂的非均相催化转化具有转化效率高等优点,但目前CO₂加氢一步制备DME催化剂的反应活性较低、稳定性较差。本文在简要介绍CO₂加氢一步制DME的铜基双功能催化剂、复合氧化物和氮化镓催化剂的基础上,重点总结了活性中心结构和反应机理的研究进展。对于铜基双功能催化剂,CO₂加氢经甲醇中间体合成DME,其中还原态铜（Cu⁰、Cu⁺及Cu ^δ+,0<δ<2）是其催化活性中心,且还原态铜的分散度及稳定性、固体酸的性质和酸性位分布以及两类活性中心的耦合效应是决定DME收率和催化剂稳定性的关键因素。与此相反,DME是氮化镓催化CO₂加氢的初级产物。这与铜基双功能催化剂有着本质区别,属新催化剂体系。在此基础上,文章对CO₂加氢制DME的可能研究方向进行了展望,认为“二甲醚经济”更具发展潜力。     

Studies of Cu-ZSM-5 by X-ray absorption spectroscopy and its application for the oxidation of benzene to phenol by air

The oxidation of benzene to phenol has been successfully carried out in air over Cu-ZSM-5 at moderate temperatures. Several parameters such as Cu loading, calcination temperature and co-exchanged metal ions influence the nature of the catalyst. At low Cu loadings, the catalyst is more selective to phenol while at high Cu loadings CO₂ is the major product. In situ H₂-TPR XAFS studies reveal that at low Cu loadings, Cu exists as isolated pentacoordinated ions, with 4 equatorial oxygens at 1.94 Å and a more distant axial oxygen at 2.34 Å. At higher loadings, monomeric as well as dimeric Cu species exist, with a Cu–Cu distance of 2.92 Å. This suggests that the isolated Cu sites are the active sites responsible for phenol formation. When the catalyst was calcined at 450 °C, the activity peaked in the first hour and then slowly deactivated, but when the calcination temperature was increased to 850 °C, the activity slowly increased until it reached a plateau. Analysis of the XANES region during in situ H₂-TPR shows that at lower calcination temperatures two reduction peaks are present, corresponding to Cu²⁺ → Cu⁺ and Cu⁺ → Cu⁰. At high calcination temperatures, only a small fraction of the Cu undergoes the two-step reduction and most of the Cu remains in the +2 state. Slow deactivation of the catalyst calcined at 450 °C is due to migration of the Cu ions to inaccessible sites in the zeolite; at high calcination temperatures the Cu is tightly bound to the framework and is unable to migrate. EXAFS analysis of the sample calcined at 850 °C reveals two Cu–Si(Al) scattering paths at 2.83 Å. Doping the catalyst with other metals, in particular Ag and Pd, further improves the activity and selectivity of the reaction. The addition of water to the reaction increases the selectivity of the reaction by displacing the product from the active site.     

Insight into the promotional mechanism of Cu modification towards wide-temperature NH3-SCR performance of NbCe catalyst

A simple strategy of Cu modification was proposed to broaden the operation temperature window for NbCe catalyst. The best catalyst Cu_0.010/Nb₁Ce₃ presented over 90% NO conversion in a wide temperature range of 200-400 ℃ and exhibited an excellent H₂O or/and SO₂ resistance at 275 ℃. To understand the promotional mechanism of Cu modification, the correlation among the “activity-structure-property” were tried to establish systematically. Cu species highly dispersed on NbCe catalyst to serve as the active component. The strong interaction among Cu, Nb and Ce promoted the emergence of NbO₄ and induced more Brønsted acid sites. And Cu modification obviously enhanced the redox behavior of the NbCe catalyst. Besides, EPR probed the Cu species exited in the form of monomeric and dimeric Cu²⁺, the isolated Cu²⁺ acted as catalytic active sites to promote the reaction: Cu²⁺-NO₃^-+NO(g) → Cu²⁺-NO₂^-+NO₂(g). Then the generated NO₂ would accelerate the fast-SCR reaction process and thus facilitated the low-temperature deNO efficiency. Moreover, surface nitrates became unstable and easy to decompose after Cu modification, thus providing additional adsorption and activation sites for NH₃, and ensuring the improvement of catalytic activity at high temperature. Since the NH₃-SCR reaction followed by E-R reaction pathway efficaciously over Cu_0.010/Nb₁Ce₃ catalyst, the excellent H₂O and SO₂ resistance was as expected.     

溶胶-凝胶法制备草酸二甲酯加氢Cu/SiO2催化剂及性能

以正硅酸乙酯为硅源,采用溶胶-凝胶法制备草酸二甲酯加氢合成乙二醇的Cu/SiO₂催化剂,并考察老化时间对Cu/SiO₂催化剂活性与结构的影响。用N2物理吸附、XRD、FT-IR和H₂-TPR等技术对Cu/SiO₂催化剂性能与结构进行表征。结果表明,溶胶-凝胶法制备的Cu/SiO₂催化剂中有层状硅酸铜形成,铜物种均匀分布在载体SiO₂上,易被还原,活性较高。合理的老化时间可抑制SiO₂对催化剂表面活性位的包覆,提高活性。在200 ℃、2.0 MPa、氢酯物质的量比60∶1、草酸二甲酯空速1.0 h^-1和老化时间1.5 h的条件下,草酸二甲酯转化率达99.51%,乙二醇选择性93.60%。
     

Active sites in Cu/ZnO/ZrO2 catalysts for methanol synthesis from CO/H2

Among various Cu/ZnO/ZrO₂ catalysts with the Cu/Zn ratio of 3/7, the one with 15 wt.% of ZrO₂ obtains the best activity for methanol synthesis by hydrogenation of CO. The TPR, TPO and XPS analyses reveal that a new copper oxide phase is formed in the calcined Cu/ZnO/ZrO₂ catalysts by the dissolution of zirconium ions in copper oxide. In addition, the Cu/ZnO/ZrO₂ catalyst with 15 wt.% of ZrO₂ turns out to contain the largest amount of the new copper oxide phase. When the Cu/ZnO/ZrO₂ catalysts is reduced, the Cu²⁺ species present in the ZrO₂ lattice is transformed to Cu⁺ species. This leads to the speculation that the addition of ZrO₂ to Cu/ZnO catalysts gives rise to the formation of Cu⁺ species, which is related to the methanol synthesis activity of Cu/ZnO/ZrO₂ catalyst in addition to Cu metal particles. Consequently, the ratio of Cu⁺/Cu⁰ is an important factor for the specific activity of Cu/ZnO/ZrO₂ catalyst for methanol synthesis.     

Enhanced synergy between Cu0 and Cu+ on nickel doped copper catalyst for gaseous acetic acid hydrogenation

As the substitution of common noble catalysts in the hydrogenation of carboxylic acid, a highly effective Cu-Ni/SiO₂ catalyst was prepared by a novel stepwise ammonia evaporation method. Its performance in the gas-phase hydrogenation of acetic acid was further examined. With the introduction of Ni dopant, more stable Cu^δ+ sites, which can adsorb more acetic acid, were formed due to the electron transfer from Cu to Ni. This makes more Cu⁰ sites available for hydrogen adsorption, which was suggested as the rate-determining step in acetic acid hydrogenation. A conversion of 99.6% was successfully achieved on this new Cu/SiO₂-0.5Ni catalyst, accompanied by the ethanol selectivity of 90%. The incorporation of nickel between copper nanoparticles enhances the synergistic effect between Cu⁰ and Cu⁺. It also helps mitigate the aggregation of copper nanoparticles due to the Ostwald ripening effect induced by acetic acid and enhance the stability of copper catalyst in the conversion of carboxylic acid.     

Characterization and NO decomposition activity of Cu-MFI zeolite in relation to redox behavior

The redox behavior and states of Cu ions in Cu ion-exchanged MFI (Cu(n)-MFI, n: exchange level) have been investigated by means of temperature-programmed desorption (TPD) of oxygen, diffuse reflectance (DR) UV–VIS spectroscopy and Cu⁺ photoluminescence (PL) spectroscopy. TPD chromatograms of oxygen from Cu(n)-MFI were characterized by the appearance of three desorption peaks: (below 200°C), β (300–500°C) and γ (above 500°C). It has been suggested that and β oxygen are extra-lattice oxygen adsorbed on Cu ions, while γ oxygen is lattice oxygen coordinated to Cu ions. The Cu⁺ emission was tremendously reduced once the catalyst contacted with O₂ and NO at elevated temperatures such as 500°C, and it was almost invisible under the working state of the catalyst, suggesting that PL-active Cu⁺ ions are not real active sites under the working state. The desorption of β oxygen was intimately related to the creation of active centers for the NO decomposition reaction. DR measurements showed that the desorption of β oxygen caused tetragonal Cu²⁺ to decrease and trigonal Cu²⁺ to increase simultaneously. It has been proposed that both Cu²⁺ and Cu⁺ are involved in the NO decomposition catalysis over Cu-MFI under the working state.     

Comparative study of Au/ZrO2 catalysts in CO oxidation and 1,3-butadiene hydrogenation

This work investigates the effects of Au³⁺/Au⁰ ratio or distribution of gold oxidation states in Au/ZrO₂ catalysts of different gold loadings (0.01–0.76% Au) on CO oxidation and 1,3-butadiene hydrogenation by regulating the temperature of catalyst calcination (393–673 K) and pre-reduction with hydrogen (473–523 K). The catalysts were prepared by deposition–precipitation and were characterized with elemental analysis, nitrogen adsorption/desorption, TEM, XPS and TPR. The catalytic data showed that the exposed metallic Au⁰ atoms at the surface of Au particles were not the only catalytic sites for the two reactions, isolated Au³⁺ ions at the surface of ZrO₂, such as those in the catalysts containing no more than 0.08% Au were more active by TOF. For 0.76% Au/ZrO₂ catalysts having coexisting Au³⁺ and Au⁰, the catalytic activity changed differently with varying the Au³⁺/Au⁰ ratio in the two reactions. The highest activity for the CO oxidation reaction was observed over the catalyst of Au³⁺/Au⁰ = 0.33. However, catalyst with a higher Au³⁺/Au⁰ ratio showed always a higher activity for the hydrogenation reaction; co-existance of Au⁰ with Au³⁺ ions lowered the catalyst activity. Moreover, the coexisting Au particles changed the product selectivity of 1,3-butadiene hydrogenation to favor the formation of more trans-2-butene and butane. It is thus suggested that for better control of the catalytic performance of Au catalyst the effect of Au³⁺/Au⁰ ratio on catalytic reactions should be investigated in combination with the particle size effect of Au.     

合成气经二甲醚羰基化及乙酸甲酯加氢制无水乙醇的研究进展

合成气经二甲醚羰基化及乙酸甲酯加氢路线制无水乙醇技术因具有诸多优点而备受市场关注。本文综述了该工艺的核心反应机理和最近研究进展。主要探讨了丝光沸石8元环与12元环对羰基化反应的作用。阐明了如何通过调变丝光沸石8元环与12元环的活性位来提高羰基化催化剂的活性与稳定性。评述了铜纳米粒子的粒径、分散度以及Cu⁺与Cu⁰的分布等特点对铜基催化剂加氢催化活性的影响。提高乙醇选择性与催化剂稳定性是该研究的重点与难点。指出羰基化催化剂的优化重点是调变丝光沸石的孔道结构,加氢催化剂的发展方向是构建高分散度的铜纳米粒子,并在反应过程中保持稳定。