Characterization and catalytic properties of the CuO/SiO2 catalysts prepared by precipitation-gel method in the hydrogenolysis of glycerol to 1,2-propanediol: Effect of residual sodium

The effect of residual sodium on the CuO/SiO₂ catalysts prepared by precipitation-gel (PG) method has been investigated in correlation with the detailed characteristics of active component performance and catalytic performance in glycerol hydrogenolysis. Characterization of the catalysts showed that the residual sodium had a negative effect on the chemical–physical properties of the catalysts, such as the BET surface area, the dispersion of copper, and the reducibility of Cu²⁺ species as well as the adsorbility of reactant molecules. As a consequence, the conversion and selectivity of the catalysts in glycerol reactions generally decreased with increasing sodium content. The leaching of sodium from catalyst surface as a base could, however, on the one hand, weakly promote the activity of the catalyst, and on the other hand, could help retard the leaching of the active copper component and reduce the deactivation rate of the catalyst. The glycerol hydrogenolysis reaction is supposed to be a structure-sensitive reaction, in which copper particle sizes lower than a critical limit or those that did not fulfill a certain ensemble requirement were not active for glycerol reaction. Such details explained the lower TOFs of the catalysts with much smaller sizes. A certain amount of sodium is deduced to be needed for CuO/SiO₂ catalyst to exhibit both high catalytic activity and good stability. In addition, a reaction mechanism based on the effect of sodium on the activity and selectivity in glycerol hydrogenolysis has been proposed.     

The Promotion Effect of Cr on Copper Catalyst in Hydrogenolysis of Glycerol to Propylene Glycol

Binary Cu/Cr catalysts, containing various molar ratios of copper to chromium, were synthesized and their catalytic activities were examined for the hydrogenolysis of glycerol to propylene glycol. When catalyst containing Cu and Cr ratio of 1:2, it was mainly composed of CuCr₂O₄ phase. And it was found to have the highest catalytic activity in this reaction, due to its favorable reduction properties.     

Gas‐Phase Hydrogenolysis of Glycerol Catalyzed by Cu/MOx Catalysts

The catalytic activities of Cu/MO_x (MO_x = Al₂O₃, TiO₂, and ZnO) catalysts in the gas‐phase hydrogenolysis of glycerol were studied at 180–300 °C under 0.1 MPa of H₂. Cu/MO_x (MO_x = Al₂O₃, TiO₂, and ZnO) catalysts were prepared by the incipient wetness impregnation method. After reduction, CuO species were converted to metallic copper (Cu⁰). Cu/Al₂O₃ catalysts with high acidity, high specific surface areas and small metallic copper size favored the formation of 1,2‐propanediol with a maximum selectivity of 87.9 % at complete conversion of glycerol and a low reaction temperature of 180 °C, and favored the formation of ethylene glycol and monohydric alcohols at high reaction temperature of 300 °C. Cu/TiO₂ and Cu/ZnO catalysts exhibited high catalytic activity toward the formation of hydroxyacetone with a selectivity of approx. 90 % in a wide range of reaction temperature.     

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%。     

Methane combustion over copper chromite catalysts

A study of the activity and durability of two different copper chromite catalysts in methane combustion is presented. The catalysts, a massive (CAT-E) and a supported (CAT-I) copper chromite, were characterized by different techniques in order to investigate morphological properties (N₂ adsorption), crystalline structure (X-ray diffraction, XRD) and surface composition (X-ray photoelectron spectroscopy, XPS). Among the different crystalline phases identified, CuCr₂O₄ spinel represented the common phase in both the catalysts. The Cr^VI/Cr^III surface ratio was almost the same for the two catalysts, while the Cu^II/Cu^I surface ratio was much higher on the massive catalyst than on the supported one. The activity for CH₄ combustion was studied in the temperature range 300-700°C at constant CH₄:air ratio of 1:30 and constant methane content, 1.2%. The activity was higher for CAT-I and CAT-E showed better stability. A kinetic study from the catalytic data, collected at different contact times in the interval 0.047-0.315 s as a function of temperature, provided a value of about 110 kJ/mol for the activation energy. This value was obtained for various degrees of methane converted for the two catalysts. The reaction rates were between 10^-3 and 10^-4 (mol_CH4)_conv/(g h) in the temperature interval 550-700°C, for both the catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Effect of ZnAl2O4 on the Performance of Cu/ZnxAlyOx+1.5y Supported Catalysts in Steam Reforming of Methanol

This paper demonstrates the benefit of using spinel (ZnAl₂O₄) as a support for copper catalysts in hydrogen generation. We have investigated the influence of catalyst pre-treatment, support composition and copper content on the physicochemical and catalytic properties of copper catalysts supported on Zn_xAl_yO_x+1.5y in the methanol steam reforming. The physicochemical properties of the catalysts were examined by X-ray diffraction, temperature-programmed reduction, specific surface area and porosity, X-ray photoelectron spectroscopy, FTIR and chemisorption methods. The reduced copper catalysts showed higher conversion of methanol and higher hydrogen production. We also found that the presence of Cu⁺ and Cu⁰ species on the catalyst surface strongly influences the reaction yield and hydrogen production. FTIR measurements performed for copper catalysts confirmed that increasing of aluminium content in the case of catalytic systems caused the growth of adsorbed species on the catalyst surface.     

The selective catalytic reduction activity of Cu/MCM-41 catalysts prepared by using the Cu2+–MCM-41 mesoporous materials with copper ions in the framework as precursors

The Cu²⁺–MCM-41 mesoporous materials with different loadings of copper species in the framework have been prepared by hydrothermal method and characterized by using various physico-chemical methods combined with the selective catalytic reduction of NO by NH₃. It has been shown that the particle size of metallic copper formed after hydrogen reduction is much smaller than that in the supported catalysts prepared by impregnation method, and that the SCR activity of catalyst increases obviously with the increase of Cu content to 10 wt.% because of its higher dispersion of copper metal in the mesoporous catalyst even at higher Cu loading.     

负载型CuO/γ-Al2O3催化剂结构与催化甘油氢解性能

采用浸渍法制备了CuO/γ-Al2O3催化剂,通过BET、XRD、XPS和TPR方法表征催化剂上CuO的分布与化学形态,结合固定床催化甘油氢解制备1,2-丙二醇试验.结果表明,催化剂表面高度分散缺电子状态的Cu物种是甘油氢解制备1,2-丙二醇的活性中心.采用浸渍法制备的铜基催化剂具有较好的甘油氢解制备1,2-丙二醇性能...     

Effect of activation temperature on the surface copper particles and catalytic properties of Cu–Ni–Mg–Al oxides from hydrotalcite-like precursors

The Cu–Ni–Mg–Al oxides catalysts for furfural hydrogenation were prepared from the hydrotalcite-like precursors, and the effect of activation temperature on the Cu⁰ particles and catalytic properties of the catalyst was thoroughly investigated. The catalyst activated by H₂ at 300 °C was found to exhibit the best catalytic activity, due to the presence of the smallest Cu⁰ particles with a high dispersion. Moreover, the bigger Cu⁰ particles were active for furfuralcohol hydrogenolysis to 2-methylfuran in the liquid-phase (ethanolic solution), and the hydrogenation of the furan ring of furfuralcohol and 2-methylfuran on Cu⁰ particles was easily achieved in the vapour-phase.     

Comparative Study on Catalytic Performances for Low-temperature CO Oxidation of Cu–Ce–O and Cu–Co–Ce–O Catalysts

Two series of Cu–Ce–O and Cu–Co–Ce–O catalysts were prepared by co-precipitation method. The prepared catalysts were characterized by XRD, IR, TPR, XPS, BET and ICP-AES. The catalytic activities of the catalysts for low-temperature CO oxidation were evaluated through a microreactor-GC system. TPR results indicate that the addition of cobalt to the Cu–Ce–O can increase the dispersion of copper oxide, and the interaction between cobalt and copper can enhance the reducibility of each other. XPS analysis show that Ce⁴⁺, Cu²⁺, along with Co₃O₄, are present on the surface of Cu_0.4Co_0.6Ce₄ catalyst. The Co/Cu atomic ratio and the calcination temperature have significant effect on the activities of the catalysts. Compared with Cu₁Ce₄ catalyst, the Cu_0.4Co_0.6Ce₄ catalyst has better activity and thermal stability.     

Active species of copper chromite catalyst in C–O hydrogenolysis of 5-methylfurfuryl alcohol

The active sites of copper chromite catalyst, CuCr₂O₄·CuO, were investigated for the condensed-phase hydrogenolysis of 5-methylfurfuryl alcohol to 2,5-dimethylfuran at 220 °C. The bulk and surface features of the catalyst were characterized by XRD, H₂-TPR, N₂ adsorption, CO chemisorption, N₂O titration, NH₃-TPD, XPS, and AES. Maxima of both of the potential active species, Cu⁰ and Cu⁺, occurred after reduction in H₂ at 300 °C compared to 240 and 360 °C. These Cu⁰ and Cu⁺ maxima also coincided with the highest specific rate of reaction based on the surface area of the reduced catalyst. The trends of Cu⁰ and Cu⁺ observed by N₂O titration and CO chemisorption were also observed qualitatively by AES. Correlations between activity and the possible active species suggested that Cu⁰ was primarily responsible for the activity of the catalysts.     

Cu/SiO2 catalyst prepared by electroless method

Cu/SiO₂ catalysts prepared by an electroless deposition method were investigated and compared with those by an impregnation method. Copper contents varied from 5% to 15% and SiO₂ was used as support. All catalysts were characterized by BET, DSC, SEM and TPR and tested by an n-butanol dehydrogenation reaction for activities and stabilities. BET analysis showed that the catalysts prepared by the two methods present larger average pore size and less surface area than those of the fresh SiO₂, indicating that smaller pores may get blocked during the course of preparation. This blockage is more severe in the impregnation method. SEM photos showed that the electroless method produces smaller copper crystals than the impregnated method. The reaction activity was found to be in the order of the calcined electroless copper catalyst>the fresh electroless copper catalyst>impregnated copper catalyst. © 1998 Society of Chemical Industry     

Influence of Support Preparation Methods on Structure and Catalytic Activity of Co/TiO2-SiO2 for Fischer–Tropsch Synthesis

TiO₂-SiO₂ supports were prepared by various methods including precipitation, impregnation, hydrolysis-reflux and sol–gel, and then cobalt was impregnated on those supports. The properties of various catalysts were characterized by N₂ physisorption, XRD, XPS and TPR. The introduction of TiO₂ led to stronger Co-support interaction, accompanying with the variation of dispersion and reduction degree of cobalt. The catalytic test for F-T synthesis revealed that the addition of TiO₂ improved the performance of catalysts prepared by precipitation, impregnation and hydrolysis-reflux, but had a negative effect with sol–gel method.     

Hydrogenolysis of glycerol to 1,2‐propanediol catalyzed by Cu‐H4SiW12O40/Al2O3 in liquid phase

BACKGROUND: Crude glycerol will increase to over 400 million L year^?1, and the market is likely to become saturated due to the limited demand for glycerol. The main aim of this work is to develop a novel process for the sustainable conversion of glycerol to 1,2‐propanediol (l,2‐PD). RESULTS: Cu‐H₄SiW₁₂O₄₀/Al₂O₃ catalysts with different H₄SiW₁₂O₄₀ (STA) loadings were prepared for the hydrogenolysis of glycerol to produce l,2‐PD in liquid phase. At 513 K, 6 MPa and LHSV of 0.9 h^?1 in 10% (w/w) glycerol aqueous solutions, the catalyst with 5% (w/w) STA showed the best performance with 90.1% of glycerol conversion and 89.7% selectivity to l,2‐PD. More important, both the initial glycerol conversion and l,2‐PD selectivity were maintained over 250 h. CONCLUSION: l,2‐PD can be continuously produced with high yields via the liquid phase hydrogenolysis of glycerol over Cu‐H₄SiW₁₂O₄₀/Al₂O₃. Furthermore, the characterization indicated that catalyst acidity could be greatly modified by STA, which promoted Cu reducibility. It was also found that hydrogenolysis could be favored by a bi‐functional catalyst with the appropriate amount of both acid and metal sites. Copyright © 2010 Society of Chemical Industry     

Influence of Zirconia Promoter on Catalytic Properties of Cu–Cr–Si Catalysts for Methanol Synthesis at High CO Conversion in Slurry Phase

The low-temperature methanol synthesis was studied using novel Cu–Cr–Si catalysts promoted by zirconia at 115 °C and 3.0 MPa in slurry phase. Zirconia addition improved significantly the catalytic performance. From the characteristic results, copper and chromium were enriched on the catalyst surface and more Cu⁺ cations were stabilized by the zirconia promotion.     

Comparison of normal and reverse precipitation methods in the preparation of Cu/ZnO/Al2O3 catalysts for hydrogenolysis of butyl butyrate

For the hydrogenolysis of butyl butyrate into butanol, Cu/ZnO/Al₂O₃ catalysts are prepared using normal precipitation (NP) and reverse precipitation (RP) methods. The activity trends of NP-series and RP-series catalysts are different as a function of the Cu/Zn ratio. Through several characterization techniques, the major differences between both series of catalyst samples are caused by the high-temperature carbonate (HT-CO₃) present in the precursor phase. The butanol productivity of RP-series catalysts is thus found to be associated with the HT-CO₃ amount in precursor and calcined samples, while it shows a linear relationship with the copper surface area.     

Waste-free Soft Reactive Grinding Synthesis of High-Surface-Area Copper–Manganese Spinel Oxide Catalysts Highly Effective for Methanol Steam Reforming

Cu–Mn spinel oxides with a high specific surface area were prepared by a simple and waste-free soft reactive grinding (SRG) technique involving the use of clean precursor salts as the starting materials. The samples were characterized by means of N₂ adsorption, X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature-programmed reduction (H₂-TPR). The results show that the catalysts obtained from the SRG route exhibited much higher catalytic activity in methanol steam reforming as compared to their wet-chemically synthesized counterparts prepared by conventional coprecipitation. The superior performance of the SRG-derived Cu–Mn materials was attributed to the favorable formation of Cu_1.5Mn_1.5O₄ spinel phase leading to the creation of much smaller copper nanoparticles with enhanced stability in the working catalyst.     

Steam reforming of methanol using Cu-ZnO catalysts supported on nanoparticle alumina

Methanol steam reforming was studied over several catalysts made by deposition of copper and zinc precursors onto nanoparticle alumina. The results were compared to those of a commercially available copper, zinc oxide and alumina catalyst. Temperature programmed reduction, BET surface area measurements, and N₂O decomposition were used to characterize the catalyst surfaces. XRD was used to study the bulk structure of the catalysts, and XPS was used to determine the chemical states of the surface species. The nanoparticle-supported catalysts achieved similar conversions as the commercial reference catalyst but at slightly higher temperatures. However, the nanoparticle-supported catalysts also exhibited a significantly lower CO selectivity at a given temperature and space time than the reference catalyst. Furthermore, the turnover frequencies of the nanoparticle-supported catalysts were higher than that of the commercial catalyst, which means that the activity of the surface copper is higher. It was determined that high alumina concentrations ultimately decrease catalytic activity as well as promote undesirable CH₂O formation. The lower catalytic activity may be due to strong Cu-Al₂O₃ interactions, which result in Cu species which are not easily reduced. Furthermore, the acidity of the alumina support appears to promote CH₂O formation, which at low Cu concentrations is not reformed to CO₂ and H₂. The CO levels present in this study are above what can be explained by the reverse water-gas-shift (WGS) reaction. While coking is not a significant deactivation pathway, migration of ZnO to the surface of the catalyst (or of Cu to the bulk of the catalyst) does explain the permanent loss of catalytic activity. Cu₂O is present on the spent nanoparticle catalysts and it is likely that the Cu⁺/Cu⁰ ratio is of importance both for the catalytic activity and the CO selectivity.     

Steam reforming of methanol using Cu-ZnO catalysts supported on nanoparticle alumina

Methanol steam reforming was studied over several catalysts made by deposition of copper and zinc precursors onto nanoparticle alumina. The results were compared to those of a commercially available copper, zinc oxide and alumina catalyst. Temperature programmed reduction, BET surface area measurements, and N₂O decomposition were used to characterize the catalyst surfaces. XRD was used to study the bulk structure of the catalysts, and XPS was used to determine the chemical states of the surface species. The nanoparticle-supported catalysts achieved similar conversions as the commercial reference catalyst but at slightly higher temperatures. However, the nanoparticle-supported catalysts also exhibited a significantly lower CO selectivity at a given temperature and space time than the reference catalyst. Furthermore, the turnover frequencies of the nanoparticle-supported catalysts were higher than that of the commercial catalyst, which means that the activity of the surface copper is higher. It was determined that high alumina concentrations ultimately decrease catalytic activity as well as promote undesirable CH₂O formation. The lower catalytic activity may be due to strong Cu-Al₂O₃ interactions, which result in Cu species which are not easily reduced. Furthermore, the acidity of the alumina support appears to promote CH₂O formation, which at low Cu concentrations is not reformed to CO₂ and H₂. The CO levels present in this study are above what can be explained by the reverse water-gas-shift (WGS) reaction. While coking is not a significant deactivation pathway, migration of ZnO to the surface of the catalyst (or of Cu to the bulk of the catalyst) does explain the permanent loss of catalytic activity. Cu₂O is present on the spent nanoparticle catalysts and it is likely that the Cu⁺/Cu⁰ ratio is of importance both for the catalytic activity and the CO selectivity.     

Catalyst Preparation Using Supercritical Carbon Dioxide: Preparation of Rh/FSM-16 Catalysts and Their Catalytic Performances in Butane Hydrogenolysis Reaction

Supported Rh catalysts on FSM-16 were prepared by treating FSM-16, impregnated with [Rh(OAc)₂]₂ in supercritical carbon dioxide at 398 K and 30.3 MPa, followed by calcination and hydrogen reduction. The resulting Rh/FSM-16 catalysts were characterized by CO chemisorption, XRD, TEM, FTIR and EXAFS, and catalytic performances of the Rh/FSM-16 were tested in butane hydrogenolysis reaction. It is demonstrated that highly dispersed Rh particles are obtained by the supercritical CO₂ treatment. In the hydrogenolysis reactions, the supercritical CO₂-treated catalyst showed higher conversions and ethane formation.