铜基甲醇合成催化剂失活原因的探讨

采用加压微型反应器和化学分析、原子吸收光谱法、X 射线荧光分析、X 射线衍射峰宽化法和其它分析方法对工业使用前后的铜基甲醇合成催化剂M K101 进行了分析和讨论。探讨了该催化剂的失活原因。     

Role of ZnO in methanol synthesis on copper catalysts

The varied results obtained by different groups concerning synergy between ZnO and Cu metal in methanol synthesis catalysts are shown to be a result of different experimental test conditions. It is suggested that synergy, when it occurs, arises from H spillover from ZnO to Cu metal. This revised version was published online in July 2006 with corrections to the Cover Date.     

The role of metal oxides in promoting a copper catalyst for methanol synthesis

The coverage of oxygen formed on the surface of catalysts during methanol synthesis from CO₂ has been measured for copper-based catalysts including various metal oxides using a method called reactive frontal chromatography (RFC). An excellent correlation between the specific activity for methanol synthesis and the oxygen coverage () was obtained, where the activity increased linearly with oxygen coverage at<0.16 and then decreased at>0.18. The results strongly indicate that the support effect or addition of metal oxides revealed in methanol synthesis over copper catalysts is ascribed to the ratio of Cu⁺ to Cu⁰ on the surface of copper particles.     

The role of surface oxygen on copper metal in catalysts for the synthesis of methanol

Discrepancies in experimental measurements of adsorbed oxygen coverage on copper metal surfaces in working Cu/ZnO/Al₂O₃ catalysts are interpreted in terms of two types of adsorbed oxygen. The first, O(a), is identical with that observed in studies of single‐crystal copper surfaces. The second, O^*(a), not seen in single‐crystal studies, is more strongly bonded to the metal surface. It is suggested that the adsorption sites of O^*(a) contain Zn as well as Cu, from surface α‐brass (copper/zinc alloy) formation during catalyst reduction. Earlier experimental results on O(a) coverages on various supported copper catalysts are re‐assessed. Only catalysts containing Zn (or Ga) gave abnormally high coverages: with other supports, basic or acidic, O(a) coverages are less than ∼0.1. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of titania on zirconia promoted Cu/SiO2 catalysts for methanol synthesis from CO/H2 and CO2/H2

The effects of adding mixtures of titania and zirconia on the methanol synthesis activity and selectivity of Cu/SiO₂ were investigated. The synthesis of methanol from both CO/H₂ and CO₂/H₂ mixtures was examined at 0.65 MPa and temperatures between 448 and 573 K. For CO hydrogenation, the addition of ZrO₂ alone increased the methanol synthesis activity of Cu/SiO₂ by up to three-fold. Substitution of a portion of the ZrO₂ by TiO₂ decreased the methanol synthesis activity of the catalyst relative to that observed when only ZrO₂ is added. ZrO₂ addition also enhanced the methane synthesis activity by as much as seven fold. In the case of CO₂ hydrogenation, the maximum methanol synthesis activity is achieved when a 50/50 wt% mixture of ZrO₂ and TiO₂ is added to Cu/SiO₂. Neither the presence of the oxide additive nor its composition had any effect on the activity of the reverse water–gas-shift reaction, which suggests that this reaction proceeds only on Cu. The observed effects of ZrO₂ and TiO₂ on the catalytic activity of methanol synthesis from CO and CO₂, and methane synthesis from CO, are interpreted in terms of the strength and concentration of acidic and basic groups on the surface of the dispersed oxide.     

工业生产中Pd/C催化剂失活原因研究

采用ICP。XRD。SEM。EDX比表面测定。S含量测定等测试手段对仪征化纤公司化工厂1997年2月至1999年9月使用的4批加氢催化剂进行了全面的分析,找出了4批催化剂失活原因分别为Pd流失。S中毒。催化剂破碎。并根据具体情况提出了延长Pd/C催化剂使用寿命的方法及措施。     

The active site for methanol synthesis on a Cu/ZnO/SiO2 catalyst

This note rectifies serious omissions from the references included in a recent paper by Fujitani et al. concerned with methanol synthesis over Cu/SiO₂ containing ZnO. This revised version was published online in July 2006 with corrections to the Cover Date.     

The influence of zinc ions discharged in a non-aqueous cell on a copper catalyst on the rate of cyclohexanol dehydrogenation reaction

Results of studies on the influence of a copper catalyst modification with zinc ions on the activity in the reaction of cyclohexanol dehydrogenation are presented. The modification has been performed by electrochemical discharging-insertion of zinc ions on a copper electrode in a non-aqueous cell. It has been demonstrated that the catalyst activity depends on the amount of discharged zinc ions as well as on the nature and concentration of the electrolyte. In the case of zinc ions discharged from a solution of ZnCl₂ in propylene carbonate, the yield of cyclohexanone increased up to five times and using Zn(BF₄)₂ in dimethylformamide almost twenty times. The activity of the system in the competing reaction of dehydration was low, hence the selectivity in the dehydrogenation reaction was high.     

An in situ high pressure FT-IR study of CO2/H2 interactions with model ZnO/SiO2, Cu/SiO2 and Cu/ZnO/SiO2 methanol synthesis catalysts

In situ FT-IR spectroscopy allows the methanol synthesis reaction to be investigated under actual industrial conditions of 503 K and 10 MPa. On Cu/SiO₂ catalyst formate species were initially formed which were subsequently hydrogenated to methanol. During the reaction a steady state concentration of formate species persisted on the copper. Additionally, a small quantity of gaseous methane was produced. In contrast, the reaction of CO₂ and H₂ on ZnO/SiO₂ catalyst only resulted in the formation of zinc formate species: no methanol was detected. The interaction of CO₂ and H₂ with Cu/ZnO/SiO₂ catalyst gave formate species on both copper and zinc oxide. Methanol was again formed by the hydrogenation of copper formate species. Steady-state concentrations of copper formate existed under actual industrial reaction conditions, and copper formate is the pivotal intermediate for methanol synthesis. Collation of these results with previous data on copper-based methanol synthesis catalysts allowed the formulation of a reaction mechanism.     

On the mechanism of the methanol synthesis involving a catalyst based on zirconia support

The nature of the pivotal intermediate during the synthesis of methanol from CO₂/H₂, in the presence of ZnO/ZrO₂ aerogel catalyst is envisaged. The kinetic studies performed using in situ FTIR spectroscopy of the species formed on the surface of the catalyst in the absence and in the presence of hydrogen show that the initial reactive adsorbed species formed from C0₂ gas is the unidentate carbonate species. Its hydrogenation into the formate species is much faster than the hydrogenation of the formate species into methoxyl species. The comparison is based on a quantitative measurement of the rate constant of the hydrogenation of the various species. The results explain that during the C0₂/H₂ reaction only formate and methoxyl species are observed.     

含CO2合成气低温合成甲醇的研究

以含CO₂的合成气为原料,Cu-Zn基催化剂,醇溶剂,低温、低压（443 K、3.0 MPa）下合成甲醇。考察了时间、溶剂和催化剂对反应的影响。结果表明,随着反应时间的增加,碳的总转化率、甲醇选择性及收率均逐渐增加;醇溶剂参与反应,但并不被消耗,起到助催化作用,且2-丁醇溶剂表现出较高的反应活性;ZnO、Y₂O₃、La₂O₃、MgO和Al₂O₃作为载体制得的Cu/M_xO_y催化剂,Cu/ZnO呈现出较高的反应活性;稀土元素La作为助剂,能提高Cu-Zn基催化剂的活性,当使用n(Cu)∶n(Zn+La)=1∶1,且n(Zn)∶n(La)=3∶2的Cu/ZnO/La2O3催化剂进行甲醇合成反应时,碳总转化率、甲醇的选择性和收率均高于Cu/ZnO催化剂。     

助剂二氧化硅对CO2加氢制备甲醇CuO-ZnO-Al2O3-ZrO2催化剂性能的影响

采用共沉淀法制备了一系列CuO-ZnO-Al₂O₃-ZrO₂(CZAZ)催化剂,用于二氧化碳加氢合成甲醇。通过加入少量的助剂二氧化硅得到了一系列CZAZ/SiO₂改性催化剂。采用XRD、BET、H₂-TPR、NH₃-TPD以及CO₂-TPD等技术进行表征,研究了助剂二氧化硅含量对催化剂的物理化学性质以及组织结构的影响。结果表明,助剂二氧化硅的含量对催化剂的组织结构具有较大的影响。同时评价了该组催化剂参与二氧化碳加氢合成甲醇反应的催化性能。测试结果表明,采用助剂二氧化硅质量分数为4%的改性催化剂,表现出较为优良的催化活性。助剂二氧化硅促进了活性组分氧化铜的分散,并且经过二氧化硅改性的CZAZ催化剂具有更大的比表面积,这些因素都对该催化剂在二氧化碳加氢合成甲醇方面的良好表现起到重要作用。     

含锰铜基甲醇催化剂的性能及其结构研究

用一步并流共沉淀法制备了CuO/ZnO/Al₂O₃和CuO/ZnO/Al₂O₃/MnO₂两种甲醇合成催化剂。通过测试它们的初活性及耐热后的活性可知, 含锰的催化剂CuO/ZnO/Al₂O₃/MnO₂具有较好的热稳定性。 利用XRD 和SEM 等实验手段, 对催化剂的结构和形貌进行了考察。 并研究了反应条件对催化剂活性的影响。     

Evidence for the migration of ZnOx in a Cu/ZnO methanol synthesis catalyst

The behavior and role of ZnO in Cu/ZnO catalysts for the hydrogenations of CO and CO₂ were studied using XRD, TEM coupled with EDX, TPD and FT-IR. As the reduction temperature increased, the specific activity for the hydrogenation of CO₂ increased, whereas the activity for the hydrogenation of CO decreased. The EDX and XRD results definitely showed that ZnO _x (x = 0–1) moieties migrate onto the Cu surface and dissolve into the Cu particle forming a Cu-Zn alloy when the Cu/ZnO catalysts were reduced at high temperatures above 600 K. The content of Zn dissolved in the Cu particles increased with reduction temperature and reached 18% at a reduction temperature of 723 K. The CO-TPD and FT-IR results suggested the presence of Cu⁺ sites formed in the vicinity of ZnO _x on the Cu surface, where the Cu⁺ species were regarded as an active catalytic component for methanol synthesis.     

美罗培南合成用钯炭催化剂的失活及再生研究

采用物理吸附、X射线衍射、扫描电镜、X射线能谱及等离子体发射光谱法对在美罗培南合成过程中失活的Pd/C催化剂比表面积、孔容、孔径、钯粒径形貌、表面元素及钯含量的变化进行分析,对催化剂的失活原因及再生方法进行研究。结果表明,催化剂在反应过程中吸附体系物质对钯活性中心的覆盖包裹及金属钯的少量流失是催化剂失活的主要原因。以30%四氢呋喃水溶液在超声条件下洗涤可以部分去除催化剂表面沉积的有机物,同时补加质量分数30%催化剂时,再次使用时效果较好。     

Cu/Zn比对CuO/ZnO/ZrO_2催化CO_2加氢合成甲醇性能的影响

研究了不同Cu/Zn摩尔比对CO2加氢合成甲醇催化性能的影响。采用草酸凝胶共沉淀法制备了一系列不同Cu/Zn摩尔比的Cu O/Zn O/Zr O2催化剂,考察不同温度及Cu/Zn摩尔比对催化性能的影响,并结合X射线衍射(XRD)、N2物理吸附、程序升温还原(H2-TPR)和程序升温脱附(H2/CO2-TPD)技术对催化剂的结构和性质进行表征。结果表明:适宜的Cu/Zn摩尔比可以提高催化剂的反应性能。在513 K,2.0 MPa,n(H2)/n(CO2)=3/1和GHSV=4 800 h-1反应条件下,当R(Cu/Zn)=4时,Cu O/Zn O/Zr O2催化剂反应性能最好,CO2转化率高达17.8%,甲醇选择性高达67.8%。     

Creation of the active site for methanol synthesis on a Cu/SiO2 catalyst

The effect of ZnO/SiO₂ in a physical mixture of Cu/SiO₂ and ZnO/SiO₂ on methanol synthesis from CO₂ and H₂ was studied to clarify the role of ZnO in Cu/ZnO-based catalysts. An active Cu/SiO₂ was prepared by the following procedure: the Cu/SiO₂ and ZnO/SiO₂ catalysts with a different SiO₂ particle size were mixed and reduced with H₂ at 523-723 K, and the Cu/SiO₂ was then separated from the mixture using a sieve. The methanol synthesis activity of the Cu/SiO₂ catalyst increased with the reduction temperature and was in fairly good agreement with that previously obtained for the physical mixture of Cu/SiO₂ and ZnO/SiO₂. These results indicated that the active site for methanol synthesis was created on the Cu/SiO₂ upon reduction of the physical mixture with H₂. It was also found that ZnO itself had no promotional effect on the methanol synthesis activity except for the role of ZnO to create the active site. The active site created on the Cu/SiO₂ catalyst was found not to promote the formation of formate from CO₂ and H₂ on the Cu surface based on in situ FT-IR measurements. A special formate species unstable at 523 K with an OCO asymmetric peak at ~1585 cm^-1 was considered to be adsorbed on the active site. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis of ethylene carbonate from urea and ethylene glycol over zinc/iron oxide catalyst

BACKGROUND: Ethylene carbonate (EC) was synthesised via urea and ethylene glycol (EG) over zinc/iron oxide catalyst. By so doing, the by‐product, EG, generated in the process of producing dimethyl carbonate by the transesterification route was converted back to the raw material, EC. The reaction mechanism of EC synthesis was also investigated by means of gas chromatography/mass spectrometry and in situ Fourier transform infrared/attenuated total reflection spectroscopy. RESULTS: Suitable conditions for the preparation of zinc/iron oxide catalyst were as follows: zinc acetate and iron nitrate as precursors, Zn/Fe molar ratio 8:1, calcination temperature 350 °C and calcination time 4 h. Characterisation by X‐ray diffraction revealed two different crystal phases: ZnO and ZnFe₂O₄. The highest yield of EC (66.1%) was obtained under the following conditions: reaction temperature 150 °C, reaction time 2.5 h, catalyst weight percentage 1.5% and urea/EG molar ratio 1:8. The study of the reaction mechanism revealed that the reaction for the synthesis of EC proceeded in two steps. CONCLUSION: The synergistic effect of ZnO and ZnFe₂O₄ promoted the catalytic performance of zinc/iron oxide. Copyright © 2008 Society of Chemical Industry     

ＣeＯ２对Cu-ＺnＯ催化剂性质和CO２加氢反应性能的影响

运用活性评价、ＸＲＤ、ＴＰＲ、ＣＯ_２-ＴＰＤ和积炭测定手段,探讨了CeＯ_２对Cu-ＺnＯ催化剂性质和CO_２加氢反应性能的影响。结果表明,催化剂经CeＯ_２改性后,CuＯ晶粒明显长大,致使催化剂还原难度增加;有利于CO歧化反应进行,使催化剂上积炭量增加;CO_２吸附量减少,CO_２加氢生成甲醇的活性增加。