Role of ZnO in Cu/ZnO/Al2O3 catalyst for hydrogenolysis of butyl butyrate

For hydrogenolysis of butyl butyrate (BB), a series of Cu/ZnO/Al₂O₃ catalysts with different metal compositions were prepared, and characterized by N₂O chemisorption for measuring Cu surface area and by chromatographic experiment for determining the heat of BB adsorption. As a result, the presence of ZnO in Cu-based catalysts was found to enhance the catalytic activity of Cu due to dual function of ZnO. The Cu surface area was linearly correlated with the butanol productivity, demonstrating that ZnO exerts the structural function in Cu/ZnO/Al₂O₃ catalysts. Additionally, the role of ZnO as a chemical contributor was revealed such that its presence leads to lower activation energy of the surface reaction, thus resulting in higher Cu catalytic activity obtained at a low temperature such as 200 °C. Consequently, optimizing the Cu/Zn ratio in Cu/ZnO/Al₂O₃ catalyst is required to tune its structural and chemical characteristics of Cu metals, and thus to obtain a higher activity on the hydrogenolysis reaction.     

Cu/ZnO/Al_2O_3催化剂用于醋酸仲丁酯加氢制备仲丁醇联产乙醇

采用固定床反应器,研究共沉淀法制备的Cu/ZnO/Al_2O_3催化剂用于醋酸仲丁酯催化加氢制备仲丁醇联产乙醇的催化性能,并考察反应温度、氢酯物质的量比、反应压力和空速对反应的影响。结果表明,Cu/ZnO/Al_2O_3催化剂表现出优良的催化性能,在反应温度210℃、氢酯物质的量比15、反应压力4.0MPa和空速1.0h-1条件下,醋酸仲丁酯转化率大于99%,仲丁醇选择性大于99%,乙醇选择性大于97%。推测Cu/ZnO/Al_2O_3催化剂上醋酸仲丁酯加氢制备仲丁醇联产乙醇的反应网络,仲丁醇与乙醇的脱氢反应和脱水反应、烯烃饱和加氢反应和酯交换反应是该体系在Cu/ZnO/Al_2O_3催化剂上存在的主要副反应。     

CO removal from reformed fuel over Cu/ZnO/Al2O3 catalysts prepared by impregnation and coprecipitation methods

A composition of Cu/ZnO/Al₂O₃ catalysts prepared by the impregnation method was optimized for water gas shift reaction (WGSR) coupled with CO oxidation in the reformed gas. The optimum composition of the impregnated catalyst for high WGSR activity was 5 wt.% Cu/5 wt.% ZnO/Al₂O₃. The optimum loading amounts of Cu and ZnO in the impregnated catalyst were smaller than those in the coprecipitated catalyst. Its catalytic activity above 200 °C was comparable to that of the conventional coprecipitated Cu/ZnO/Al₂O₃ catalyst. However, the activity of the impregnated Cu/ZnO/Al₂O₃ catalysts was significantly lowered at 150 °C, whereas no deactivation was observed for the coprecipitated catalyst at the same temperature. It was found that deactivation occurred over impregnated catalysts with H₂O and/or O₂ in the reaction gas; it prevented CO adsorption on the surface.     

改进的二步共沉淀法制备Cu/ZnO/Al2O3甲醇合成催化剂

采用改进的二步共沉淀法制备了Cu/ZnO/Al₂O₃甲醇合成催化剂。用XRD、SEM和BET等手段对催化剂结构和形貌进行了表征。采用流动固定床微型反应器在5.0 MPa和空速5 000 h^-1条件下,考察了其催化合成气合成甲醇的活性,并在同一条件下用一种工业催化剂做对比测试。结果表明,改进的二步法制备的甲醇合成催化剂结晶度较低,基本以无定形状态的固溶体形式存在,铜锌之间的协同作用大,催化剂粒度较小,尺寸分布较均匀,比表面积较大,催化剂单位面积活性达98.54 mg·m^-2。     

Dynamical Changes in Cu/ZnO/Al2O3 Catalysts

A combination of various transient and steady-state kinetic experiments was used to provide evidence for dynamical changes in a Cu/ZnO/Al₂O₃ catalyst of industrial interest. From these it can be deduced that the reversible structural alterations strongly depend on the reaction conditions as well as on the pretreatment. The pretreatment was found to induce changes in the morphology of the metallic Cu particles to some extent, and surface alloying under more severe reducing conditions.     

机械研磨燃烧法制备Cu/ZnO/Al2O3甲醇合成催化剂

引言Cu/ZnO/Al2O3催化剂近年来广泛应用于低压甲醇合成、二甲醚合成和水煤气变换等领域[1-2],该催化体系具有活性高、使用寿命长、反应温度及     

Effect of preparation methods on the hydrocracking performance of NiMo/Al2O3 catalysts

In this work, NiMo catalysts with various contents of MoO_3 were prepared through incipient wetness impregnation by a two-step method(NM-x A) and one-pot method(NM-xB). The catalysts were then characterized by XRD, XPS, NH_3-TPD, H_2-TPR, HR-TEM, and N2 adsorption–desorption technologies.The performance of the NiMo/Al_2O_3 catalysts was investigated by hydrocracking low-temperature coal tar. When the MoO_3 content was 15 wt%, the interaction between Ni species and Al_2O_3 on the NM-15 B catalyst was stronger than that on the NM-15 A catalyst, resulting in the poor performance of the former.When the MoO_3 content was 20 wt%, MoO_3 agglomerated on the surface of the NM-20 A catalyst, leading to decreased number of active sites and specific surface area and reduced catalytic performance. The increase in the number of MoS_2 stack layers strengthened the interaction between Ni and Mo species of the NM-20 B catalyst and consequently improved its catalytic performance. When the MoO_3 content reached 25 wt%, the active metals agglomerated on the surface of the NiMo catalysts, thereby directly decreasing the number of active sites. In conclusion, the two-step method is suitable for preparing catalysts with large pore diameter and low MoO_3 content loading, and the one-pot method is more appropriate for preparing catalysts with large specific surface area and high MoO_3 content. Moreover, the NMx A catalysts had larger average pore diameter than the NM-xB catalysts and exhibited improved desulfurization performance.     

助剂和制备方法对V2O5/Al2O3催化性能的影响

用浸渍法制备了负载型MxOy-V2O5/Al2O3催化剂,同时考察了不同的制备方法对MoO3-V2O5/Al2O3催化剂的性能影响。用BET、H2-TPR、TPD平衡法等考察了催化剂的比表面积、氧化还原性能、表面氧脱附性能,结果表明,添加变价助剂Mo、Fe和Cr氧化物会增加供氧数目,提高α-蒎烯转化率。MoO3-V2O5/Al2O3催化剂表面O 2-和O-物种较多,活性也较好,桃金娘烯醛收率较高。MoO3-V2O5/Al2O3催化剂的制备方法影响其催化性能,表面化学改性法制备的催化剂表面具有较多O2-和O-物种,有利于催化剂的活性提高,α-蒎烯的转化率达88.9%,桃金娘烯醛的收率为79.1%。     

ZnO对CuO-ZnO/Al2O3催化剂催化甘油氢解性能的影响

以氧化铝为载体,采用浸渍法制备了负载型CuO-ZnO/Al2O3催化剂,通过XRD、XPS、TPR手段表征催化剂上CuO和ZnO的分布和化学形态。结果表明,CuO-ZnO/Al2O3催化剂催化甘油氢解反应中,CuO是活性组分,ZnO的引入可以降低CuO与载体氧化铝的相互作用强度,有利于CuO的还原,提高催化剂甘油氢解活性;催化剂表面呈缺电子状态的Cu物种是甘油氢解的活性中心。当活性组分CuO质量分数为12%,n(Cu)∶n(Zn)=1∶1.5时,CuO-ZnO/Al2O3催化剂催化甘油氢解活性最高,甘油转化率可达97.82%,对1,2-丙二醇选择性达94%。     

Flame-made Cu/ZnO/Al2O3 catalyst for dimethyl ether production

For the single step synthesis of dimethyl ether (DME) from synthesis gas a Cu/ZnO/Al₂O₃-catalyst has been prepared using flame-spray pyrolysis. The resulting powder was co-mixed with γ-alumina to give an admixed system for DME production. The flame-made catalyst was analyzed using the BET method, in situ XRD, N₂O decomposition, TPR and XPS. These studies unraveled that the catalyst exhibited a high Cu surface area including good contact with zinc oxide and alumina as well as small Cu particles resulting in high catalytic activity and product selectivity, also in comparison to a commercially available catalyst.     

An EXAFS study of Cu/ZnO and Cu/ZnO-Al2O3 methanol synthesis catalysts

Cu K-absorption edge and EXAFS measurements on binary Cu/ZnO and ternary Cu/ ZnO-Al₂O₃ catalysts of varying compositions on reduction with hydrogen at 523 K, show the presence of Cu microclusters and a species of Cu¹⁺ dissolved in ZnO apart from metallic Cu and Cu₂O. The proportions of different phases critically depend on the heating rate especially for catalysts of higher Cu content. Accordingly, hydrogen reduction with a heating rate of 10 K/min predominantly yields the metal species (>50%), while a slower heating rate of 0.8 K/min enhances the proportion of the Cu¹⁺ species ( 60%). Reduced Cu/ZnO-Al₂O₃ catalysts show the presence of metallic Cu (upto 20%) mostly in the form of microclusters and Cu¹⁺ in ZnO as the major phase ( 60%). The addition of alumina to the Cu/ZnO catalyst seems to favour the formation of Cu¹⁺/ZnO species.     

Hydrogenolysis of Dimethyl Maleate on Cu/ZnO/Al2O3 Catalysts

The gas‐phase hydrogenolysis of dimethyl maleate at 10 bar and 513 K was investigated over a series of co‐precipitated Cu/ZnO/Al₂O₃ catalysts. High copper surface areas were obtained with a molar Al content of 5 % in the catalysts. Upon variation of composition at fixed alumina content, copper surface areas increased until the molar ratio exceeded Cu/Zn = 2:1. At the given reaction conditions, dimethyl maleate was completely converted to dimethyl succinate, which further reacted to methanol, γ‐butyrolactone, tetrahydrofuran, and water over all catalysts. Initial deactivation of catalysts was mainly caused by a loss of copper surface area. The catalyst with a molar Cu/Zn ratio of 1:2 was found to be most active and stable under reaction conditions.     

Activity and stability of Cu/ZnO/Al2O3 catalyst promoted with B2O3 for methanol synthesis

The addition of B₂O₃ to a Cu/ZnO/Al₂O₃ catalyst increased the activity of the catalyst for methanol synthesis after an induction period during the reaction. The stability of the B₂O₃-containing Cu/ZnO/Al₂O₃ catalyst was greatly improved by the addition of a small amount of colloidal silica to the catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

The origin of particle size effects in supported metal catalysts: Propane hydrogenolysis on Ru/Al2O3 catalysts

The kinetics of the hydrogenolysis of propane on Ru/Al₂O₃ catalysts differing in particle size have been analysed according to a classical rate equation which supposes the reactive species to be a dehydrogenated form of the alkane. With small ruthenium particles there is a sharp maximum in rate as hydrogen pressure is increased; with large particles the peak is broader and at higher hydrogen pressures. Published results showing the latter to give higher turnover frequencies are only valid at high hydrogen: alkane ratios. Ethane selectivity (S₂) is almost independent of hydrogen pressure on small particles, but on large particles it increases markedly as the hydrogen pressure is raised. The results are interpreted by supposing hydrogen chemisorption to be strong on small ruthenium particles, and weaker on large ones; effects of temperature on selectivities are also explained in this way. The geometric basis of structure-sensitivity is thereby called into question.     

Low-temperature water-gas shift reaction over Mn-promoted Cu/Al2O3 catalysts

Water-gas-shift reaction was carried our over a series of Mn-promoted Cu/Al₂O₃ catalysts in the temperature range of 448–533 K. The catalysts were characterized suitably by various techniques. The catalyst containing 8.55 wt% Mn was found to be the most active one among five catalysts tested. A maximum CO conversion of 90% was obtained over this catalyst at 513 K with a CO space-time of 5.33 h. The catalysts were found to be structure sensitive for the low-temperature water-gas shift reaction. A detailed kinetic study was performed for the reaction under investigation over the best catalyst. The kinetic data were fitted to two different models and the redox model was found to the better one than the other. From the estimated kinetic constant, the activation energy was determined to be 81 kJ/mol for the water-gas shift reaction in the temperature range of 448–463 K.     

A new method of low-temperature methanol synthesis on Cu/ZnO/Al2O3 catalysts from CO/CO2/H2

A new synthesis method of low-temperature methanol proceeded on Cu/ZnO/Al₂O₃ catalysts from CO/CO₂/H₂ using 2-butanol as promoters. The Cu/ZnO/Al₂O₃ catalysts were prepared by co-impregnation of r-Al₂O₃ with an aqueous solution of copper nitrate and zinc nitrate. The total carbon turnover frequency (TOF), the yield and selectivity of methanol were the highest by using the Cu/ZnO/Al₂O₃ catalyst with copper loading of 5% and the Zn/Cu molar ratio of 1/1, which precursor were not calcined, and reduced at 493 K. The activity of the catalysts increased due to the presence of the CuO/ZnO phase in the oxidized form of impregnation Cu/ZnO/Al₂O₃ catalysts. The active sites of the Cu/ZnO/Al₂O₃ catalyst for methanol synthesis are not only metallic Cu but also special sites such as the Cu–Zn site, i.e. metallic Cu and the Cu–Zn site work cooperatively to catalyze the methanol synthesis reaction.     

Thermogravimetric study on pyrolysis of biomass with Cu/Al2O3 catalysts

The Cu/Al₂O₃ catalysts of three different compositions (10, 20 and 30 wt.% Cu loading), have been investigated with regard to their catalytic effects on pyrolysis of paper biomass species (up to 800 °C) by thermogravimetric analysis (TGA) experiments. The results show that catalysts made devolatilization at lower (below 200 °C) and middle temperature (200–400 °C) regions in the pyrolysis of the biomass species, and the temperature reduction effects follow the order: 30 > 20 > 10 wt.% copper loading. Although the catalysts with 10 and 20 wt.% copper have shown almost similar activity, whereas dehydration reaction was enhanced almost 40% in the presence of 30 wt.% copper-loaded catalyst. At the same time, the amount of residue at the end of the reaction also decreased with increase in the copper loading from 10 to 30 wt.%. At higher temperatures (above 400 °C), the catalyst with greater copper loaded worked more nicely possibly due to the enhancement of the depolymerization reaction over dehydration of cellulose in presence of more basic catalysts. The catalysts were characterized by using X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis and scanning electron microscopy (SEM). XRD results show the formation of CuAl₂O₄ spinel and Cu₂O phase in the catalysts.     

Glycerol Hydrogenolysis to 1,2-Propanediol by Cu/ZnO/Al2O3 Catalysts

The effect of preparation methods on the Cu/ZnO/Al₂O₃ catalyst structure and catalytic activity on liquid glycerol hydrogenolysis to 1,2-propanediol has been investigated. The physicochemical properties of the catalysts were characterized by BET, XRD, TG/DTA, NH₃-TPD and TPR. The experimental results showed that the catalyst prepared by an oxalate gel–coprecipitation had the highest activity. At 200 °C and 400 psi hydrogen pressure, the glycerol conversion and 1,2-propanediol selectivity catalyzed by the Cu/ZnO/Al₂O₃ catalyst prepared via oxalate gel–coprecipitation were 92.3 and 94.5 % respectively. It was found that the 1,2-propanediol selectivity was dependent on hydrogen pressure and the un-desired by-products were mainly due to the side reactions caused by the presence of the intermediate acetol.     

甘油氢解Cu/Cr催化剂制备方法对性能的影响

Cu/Cr催化剂由于Cu对C—C键氢解活性很低,对C—O键氢解活性很高而成为甘油氢解制1,2-丙二醇效果最好的固体催化剂。采用5种方法制备了Cu/Cr催化剂,并用于甘油的催化氢解反应,发现Cu/Cr催化剂的制备方式极大地影响着其对甘油的催化氢解性能。以5种方法制备的Cu/Cr催化剂中,对甘油的催化氢解性能依次是:铜氨络合沉淀法Adkins法碳酸钠沉淀法硅藻土浸渍法干混法。运用XRD、TG、BET、FTIR、TPR等表征手段对制备的催化剂结构进行了表征,详细分析了不同方式制备的催化剂的结构差异,将催化剂的结构表征结果与催化反应性能进行关联分析和讨论,并从理论上解释了催化剂结构差异和催化氢解性能的关系。     

Glycerol Hydrogenolysis to 1,2-Propanediol by Cu/ZnO/Al2O3 Catalysts

The effect of preparation methods on the Cu/ZnO/Al₂O₃ catalyst structure and catalytic activity on liquid glycerol hydrogenolysis to 1,2-propanediol has been investigated. The physicochemical properties of the catalysts were characterized by BET, XRD, TG/DTA, NH₃-TPD and TPR. The experimental results showed that the catalyst prepared by an oxalate gel–coprecipitation had the highest activity. At 200 °C and 400 psi hydrogen pressure, the glycerol conversion and 1,2-propanediol selectivity catalyzed by the Cu/ZnO/Al₂O₃ catalyst prepared via oxalate gel–coprecipitation were 92.3 and 94.5 % respectively. It was found that the 1,2-propanediol selectivity was dependent on hydrogen pressure and the un-desired by-products were mainly due to the side reactions caused by the presence of the intermediate acetol.