Highly active and selective Cu/SiO2 catalysts prepared by the urea hydrolysis method in dimethyl oxalate hydrogenation

Cu/SiO₂ catalysts have been successfully prepared via urea hydrolysis method. The catalysts have been systematically characterized by X-ray diffraction, high-resolution transmission electron microscopy, N₂-physisorption and H₂ temperature-programmed reduction. The results demonstrated the presence of copper nanoparticles and their high dispersion on the SiO₂ support. Catalysts with different copper loadings were prepared, and their performances in the hydrogenation of dimethyl oxalate to ethylene glycol were studied. A 100% conversion of dimethyl oxalate and maximum 98% selectivity of ethylene glycol were reached with 15.6 wt.% copper loading at 200 °C and 2 MPa. Furthermore, under the same reaction conditions, the catalyst can maintain the selectivity of 90% when the reduction temperature reduced from 350 °C to 200 °C. The high activity and selectivity over the catalyst may be ascribed to the homogenously distribution of copper nanoparticles on the large surface.     

草酸二甲酯气相选择性加氢铜基催化剂研究进展

乙二醇是重要的化工原料,广泛应用于各种行业。煤经草酸二甲酯加氢制乙二醇符合我国"富煤少油"能源特点,具有良好的发展前景。对于草酸二甲酯气相选择性加氢合成乙二醇反应中催化剂的开发是实现该路线工业化的关键。重点介绍Cu基催化剂非均相气相加氢的研究进展,包括Cu基催化剂的活性中心、载体以及助剂,展望草酸二甲酯加氢Cu基催化剂的研究方向。     

Highly efficient mesostructured Ag/SBA-15 catalysts for the chemoselective synthesis of methyl glycolate by dimethyl oxalate hydrogenation

Ag/SBA-15 catalyst is found to exhibit excellent catalytic activity and long-term stability for the chemoselective hydrogenation of dimethyl oxalate to methyl glycolate. The size of Ag crystallites, which is markedly affected by the Ag loading levels and catalyst pretreatment conditions, is a key factor determining the reaction rate of the structure-sensitive hydrogenation but hardly influenced the product distribution. The best catalytic hydrogenation activity is obtained over the Ag/SBA-15 catalyst with an average Ag crystallite size of around 3.9 nm.     

高效稳定的铜镍催化剂在草酸二甲酯加氢中的应用

为了探索高效、稳定的草酸二甲酯（DMO）加氢制乙醇酸甲酯（MG）催化剂,采用水热合成法制备Cu-Ni/SiO₂催化剂,探索了不同Cu：Ni摩尔比对于催化剂活性的影响。通过XRD、TEM和XPS等表征,结果表明：利用二氧化硅微球作载体,铜镍物种的分散更加均匀。并且调变不同的Cu：Ni摩尔比,对Cu⁺在催化剂中的比例有一定的影响,从而影响乙醇酸甲酯的收率。在氢酯比为150、反应压力2 MPa、反应温度200℃和液时空速为0.5 h^-1的反应条件下,Cu：Ni摩尔比为1：1时的催化剂Cu₁Ni₁/SiO₂表现出了最好的催化性能,草酸二甲酯的转化率达到90%,乙醇酸甲酯的选择性达到了80%,催化剂能稳定运行100 h。上述结果可为研制催化活性高、选择性强、寿命长、易于生产乙醇酸甲酯的催化剂提供一定的参考。     

焙烧温度对MgO修饰Cu/ZnO催化剂结构及催化草酸二甲酯加氢反应研究

采用共沉淀法制备了系列掺杂Mg2+离子的Cu-Mg/ZnO[n(Cu)∶n(Zn)=5∶4]催化剂,并用N2吸附-脱附、XRD和H2-TPR等对催化剂进行表征,考察焙烧温度对催化剂结构及其催化草酸二甲酯加氢反应性能的影响。结果表明,经350℃焙烧所得Cu-Mg/ZnO-c350催化剂具有较大的比表面积,发达的介孔结构,较高的Cu物种分散性和较多的表面Cu0活性位;而较高的焙烧温度导致催化剂中纳米粒子聚集烧结,降低催化剂比表面积、孔径尺度和表面Cu0活性物种数量。适宜反应条件,Cu-Mg/ZnO-c350催化剂催化草酸二甲酯气相加氢反应转化率为100%,乙二醇收率为95%。此外,较强的金属-载体作用力抑制铜活性物种的抗烧结能力,赋予其优异的稳定性。     

草酸二甲酯加氢制乙醇酸甲酯催化剂的研究进展

实现合成气经草酸酯加氢制乙醇酸酯的C₁工业路线关键在于高性能催化剂的开发,而目前国内外在这方面的研究还处于基础阶段。本文对草酸二甲酯加氢制乙醇酸甲酯催化剂的研究进展进行了概述,包括液相加氢和气相加氢。着重阐述了气相加氢催化剂稳定性和选择性的影响因素,介绍了相应催化剂的结构组成及合成方法,并初步探讨了加氢反应机理。最后,综合分析了草酸二甲酯加氢制乙醇酸甲酯催化剂在现在或将来要面临的实际问题。这些将为我国开发出具有自主知识产权的催化剂及其合成工艺提供有益参考。     

共沉淀法制备Cu/ZnO催化剂用于1,4-丁二醇合成吡咯

采用共沉淀法制备的Cu/ZnO催化剂成功应用于1,4-丁二醇合成吡咯的反应,利用气质、红外光谱对产物进行定性和定量分析,同时采用XRD、H2-TPR、N2O分解对Cu/ZnO催化剂的成分Cu0和ZnO的作用进行分析。实验研究表明,Cu0是该反应的催化活性中心,ZnO起到了分散和稳定铜颗粒的作用,这种作用是由于在催化剂制备过程中形成了CuZn(OH)2CO3和(CuZn)5(OH)6(CO3)2这两种前体导致的。尽管Cu0是该反应的催化活性中心,Cu/ZnO催化剂的催化活性与Cu0的比表面积不呈线性关系,该反应具有晶面敏感性。在常压、280 ℃、1,4-丁二醇的空速为0.46 h?1、氨醇摩尔比为1.1∶1条件下对催化剂进行评价,Cu/Zn摩尔比为1∶1时1,4-丁二醇的转化率为100%,吡咯有较佳的选择性为58%。     

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%。
     

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。     

Total oxidation of propane over Cu-Mn mixed oxide catalysts prepared by co-precipitation method

The catalytic activity of Cu-Mn mixed oxides with varying Cu/Mn ratios prepared by co-precipitation method was examined for the total oxidation of propane. The nature and phase of the metal oxide species formed were characterized by various methods such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H₂ temperature-programmed reduction (TPR) as well as BET surface area measurement. The co-precipitation method provides highly interdispersed copper and manganese metallic elements forming Cu-Mn mixed oxide of spinel structure (Cu_1.5 Mn_1.5O₄). Besides the spinel-type Cu-Mn mixed oxide, CuO or Mn₂O₃ phases could be formed depending on the Cu/Mn molar ratio of their precursors. The catalytic activity of Cu-Mn mixed oxide catalyst for propane oxidation was much higher than those of single metal oxides of CuO and Mn₂O₃. The higher catalytic activity likely originates from a synergic effect of spinel-type Cu-Mn mixed oxide and CuO. The easier reducibility and BET surface area seems to be partially responsible for the high activity of Cu-Mn mixed oxide for total oxidation of propane.     

Highly active PtRu catalysts supported on carbon nanotubes prepared by modified impregnation method for methanol electro-oxidation

A simple and rapid synthesis method (denoted as modified impregnation method, MI) for PtRu/CNTs (MI) and PtRu/C (MI) was presented. PtRu/CNTs (MI) and PtRu/C (MI) catalysts were characterized by transmission electron microscopy (TEM) and X-ray diffractometry. It was shown that Pt-Ru particles with small average size (2.7 nm) were uniformly dispersed on carbon supports (carbon nanotubes and carbon black) and displayed the characteristic diffraction peaks of Pt face-centered cubic structure. Cyclic voltammetry and chronoamperometry showed that the Pt-Ru/CNTs (MI) catalyst exhibited better methanol oxidation activities than Pt-Ru/C (MI) catalyst and commercial Pt-Ru/C (E-TEK) catalyst. The single cells with Pt-Ru/CNTs (MI) catalyst exhibited a power density of 61 mW/cm², about 27% higher than those single cells with commercial Pt-Ru/C (E-TEK) catalyst.     

草酸二甲酯加氢制乙醇酸甲酯反应网络分析及其多相加氢催化剂研究进展

乙醇酸甲酯（MG）官能团丰富,是一种重要的精细化工中间体,而且经过缩聚反应可制得新一代可生物降解材料聚乙醇酸。采用合成气经草酸二甲酯（DMO）加氢路线可实现MG的规模化制备,而该技术工业化的关键是高性能加氢催化剂的开发,当前DMO加氢制MG催化剂正处于工业化前期阶段。本文分析了DMO加氢反应网络及各特征反应的热力学特点,重点概述了DMO多相加氢制MG催化剂的研究进展,包括铜基催化剂、银基催化剂、非铜/银基催化剂等,基于网络特点分析了各催化剂的研究重点及存在的难题,并从反应工艺控制、催化剂载体设计、助剂及活性组分选择等角度提出了改善工业化催化剂开发及性能的思路,建议近期将改性复合载体负载的铜基催化剂,或以银、镍等为第二助剂的复合铜基催化剂作为重点攻关方向,远期将新型非贵金属体系作为储备方向,期望能为开发我国自主知识产权的工业化催化剂提供有益参考。     

Polymer-supported catalysts—selective hydrogenation of acid chlorides over palladium/polyamide

The catalytic behaviour of palladium supported on aromatic polyamides was studied in the liquid phase hydrogenation of benzoyl chloride at 1 atm total pressure and between 348 and 408 K. The specific activity of the catalysts as a function of palladium concentration was found to increase with metal loading. It is suggested that palladium in a metallic state is the active site for the acid chloride hydrogenation. A decrease in the reaction rate has been observed at the highest temperatures indicating that under these conditions the availability of hydrogen becomes the rate determining step. Results on the liquid phase hydrogenation of acyl- and aroyl-chlorides are reported. No strong influence of the nature of the substituents was observed on reaction parameters.     

Characterizations of Ru/ZnO catalysts with different Ru contents for selective hydrogenation of crotonaldehyde

Ru catalysts supported on ZnO with different Ru contents were prepared by an impregnation method and were applied to the vapor-phase selective hydrogenation of crotonaldehyde. The catalysts were characterized by X-ray powder diffraction (XRD), NH₃ temperature-programmed desorption (NH₃-TPD), transmission electron microscopy (TEM) and temperature-programmed oxidation (TPO). It was found that with increasing Ru contents in the Ru/ZnO catalysts, the activity (TOF), surface acidity amount and deactivation rate increased and the selectivity to crotyl alcohol increased first and then decreased. The 3Ru/ZnO catalyst showed the highest selectivity to crotyl alcohol (up to 88.0%) for the hydrogenation of crotonaldehyde. The initial TOF values of the catalysts depended on the strength of surface acidity and the Ru particle sizes. The more Lewis acid sites made catalysts deactivate more easily. It was assumed that the deactivation was due to the formation of organic compounds deposition and poison effect of CO strongly adsorbed on the Ru atoms.     

强静电吸附法制备PdZnx/Al2O3催化1,4-丁炔二醇选择加氢

针对1,4-丁炔二醇选择加氢反应特性,以强静电吸附法可控地制备了一系列Pd、Zn不同物质的量比的PdZnx/Al2O3双金属催化剂,并探究Zn的引入对催化加氢性能的影响.研究发现,少量Zn的添加能够保持催化剂在较高活性的情况下,大幅度改善其对中间产物1,4-丁烯二醇的选择性.其中,PdZn2/Al2O3催化剂表现出较高的催化活性和顺式-1,4-丁烯二醇的选择性.反应在50℃、1 MPa的条件下进行,1,4-丁炔二醇在接触时间为6 gcat·h/mol时的转化率为91％,顺式-1,4-丁烯二醇的选择性可达到86％.结合程序升温还原与X射线电子衍射光谱分析发现,前驱体经400℃焙烧和400℃还原处理后形成了PdZn双金属催化剂.Zn原子的掺入有效调变了Pd活性位点的几何效应和电子效应,抑制了中间产物的过渡加氢.     

静电纺丝法制备高活性多孔Ni/SiO2甲烷化催化剂

以三嵌段共聚物P123为模板剂,采用静电纺丝法制备了多孔Ni/SiO₂催化剂,考察其在CO甲烷化中的催化性能。采用N₂物理吸脱附测试、扫描电子显微镜（SEM）、X射线衍射（XRD）、H₂-程序升温还原（H₂-TPR）、透射电子显微镜（TEM）、热重分析（TGA）对催化剂的结构性质进行表征。结果表明,静电纺丝法制备的多孔Ni/SiO₂催化剂活性组分Ni在SiO₂载体纤维上高度分散,比表面积大,Ni颗粒尺寸小,金属与载体相互作用强,在CO甲烷化反应中表现出优异的催化活性和稳定性。在温度450℃,压力0.1 MPa,质量空速15000 ml/（g·h）条件下,多孔Ni/SiO₂催化剂CO转化率最高可达96.4%,CH₄选择性可达86.4%。此方法为工业上制备高催化活性且无须二次成型的甲烷化催化剂提供了新思路。     

草酸酯加氢铜基催化剂关键技术与理论研究进展

合成气经草酸酯加氢制乙二醇工艺是非石油路线合成大宗化学品的新兴路线。在我国贫油、少气、煤炭相对丰富的能源结构条件下,该工艺路线的研究具有重要的现实意义和战略意义。本文着重介绍了草酸酯加氢制乙二醇铜基催化剂的研究进展。系统讨论了催化剂载体、助剂对活性和选择性的影响规律,以及催化剂的结构与价态的形成机制及其对催化性能的影响,并对草酸酯加氢制乙二醇催化剂中的内扩散问题以及催化剂成型进行综述和分析。此外,还对该草酸酯加氢反应放大和工程化进展进行了简单介绍。提出具有较高加氢活性与机械强度的新型催化剂研究是草酸酯加氢催化剂研究的重要课题,而异型催化剂的研究则有可能解决催化剂床层阻力大这一工程化难题。此外也提出制备高温稳定的铜基催化剂是今后的重要研究方向。     

Methanol synthesis over Cu/ZnO catalysts prepared by ball milling

Cu/ZnO catalysts (with a Cu/Zn atomic ratio of 30/70) have been prepared by high intensity mechanical mixing of copper and zinc oxide powder in air and under vacuum. During milling in vacuum gradual amorphisation of the constituents occurs, as evidenced by broadening of the Cu⁰ and ZnO diffraction peaks in XRD, but the two original phases remain. The result of such treatment is a catalyst with low BET area and low Cu metal surface area. Consequently, the activity of the vacuum milled samples in batch methanol production from synthesis gas (CO/CO₂/H₂=20/5/75) at 50 bar and 250°C is low. Milling in air leads to oxidation of the copper metal phase and much higher BET surface area and, after reduction, Cu metal surface area. Prolonged milling times in air result in more than 90% Cu²⁺ formation as evidenced by TPR. Activity in methanol synthesis for the air milled samples is comparable to a conventional Cu/ZnO catalyst prepared by coprecipitation. It is concluded that high intensity ball milling at ambient conditions is a promising method to prepare mixed oxide catalysts or catalyst precursors. This revised version was published online in July 2006 with corrections to the Cover Date.     

Highly active Fischer–Tropsch synthesis Co/SiO2 catalysts prepared from microwave irradiation

Studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) as well as energy-diffusive X-ray spectroscopy (EDX), a highly active Co/SiO₂ catalyst which was prepared through microwave irradiation showed more uniform and better dispersion of the Co particles within the catalyst pellets, compared to that prepared by the conventional heating method. The Fischer–Tropsch (FT) synthesis activity of the microwave-irradiated catalyst was greater than that of the conventional heating one. Not only did the catalytic activity depend on the particle distribution, but also the irradiative time. The longer irradiative time increased the catalytic activity. It was shown that the irradiative time of 14 min was an optimum. It was found that cobalt distributed uniformly inside the whole catalyst pellet prepared by the microwave irradiation. On the contrary, cobalt concentration at the outer surface, with agglomerated form, was greater than that at the center or inner part of the catalyst pellet made by the conventional heating method. Higher dispersion state of the supported cobalt, as also proved by XRD, realized at the microwave irradiated catalyst determined its improved FT activity.     

The relationship between the structure and catalytic performance Cu/ZnO/ZrO2 catalysts for hydrogenation of dimethyl 1,4-cyclohexane dicarboxylate

The gas-phase hydrogenation of dimethyl 1,4-cyclohexane dicarboxylate to 1,4-cyclohexane dimethanol (CHDM) was conducted on well-dispersed supported Cu/ZnO/ZrO₂ catalysts. The results indicated that the structure and catalytic performance of resulting copper-based catalysts were profoundly affected by the addition of zirconium. Moreover, the as-synthesized catalyst with 35.0 wt.% ZrO₂ component was found to exhibit superior catalytic performance with a high CHDM yield of 96.8% to other catalysts, which should be mainly attributed to the significant dispersion effect of ZrO₂ on the copper-containing species resulting in a higher metallic copper surface area as well as a larger number of Cu⁺ species.