Hydrogenation of carbon dioxide over metal catalysts prepared using microemulsion

This paper relates to a novel preparation method of metal supported catalysts using microemulsions. The size distribution of metal particles in the catalysts, thus, prepared was appreciably narrow and the average particle size was much smaller than that of the conventional catalyst prepared from impregnation. It was found that the particle size could be controlled by the conditions of microemulsions regardless of metal content. The Rh, Pd and Pt catalysts prepared from microemulsions were found to exhibit a much higher activity for the hydrogenation of carbon dioxide than those from impregnation.     

Preparation of spherical AlN powders by combined microemulsion method and carbothermal method

In this study, a two-step strategy for the preparation of micron-sized spherical aluminium nitride (AlN) powder by the combined micro-emulsion method in conjunction with the carbothermal reduction nitridation (CRN) route was designed. The spherical AlN powder with perfect dispersibility was prepared after a heat treatment at 1550 °C for 2 h in flowing N₂. The effects of the aluminium fluoride (AlF₃) content, reaction temperature and the introduction of yttrium oxide (Y₂O₃) on the nitridation ratio and on the morphology of granules, in particular, were investigated by XRD analysis and SEM. Additionally, the promotion mechanism of AlF₃ and Y₂O₃ on the nitridation reaction was also discussed. Specifically, one of the underlying formation mechanisms of the spherical granules with the aid of AlF₃ and Y₂O₃, and suggestions on the selection of additives for the CRN synthesis of spherical AlN powder were logically proposed.     

微乳法制备Pd-Cu双金属催化剂

选择Cu为助剂,采用微乳法分别优选具有较好稳定性的Cu和Pd微乳液体系,并将Cu和Pd依次负载于Al_2O_3载体上,经干燥、活化和还原制备了Pd-Cu/Al_2O_3催化剂。采用原位IR、CO化学吸附和HRTEM等对催化剂进行表征,结果表明,与常规溶液负载法制备的Pd-Ag/Al_2O_3催化剂相比,采用微乳法降低了催化剂表面酸性,提高了活性组分Pd分散度,Pd粒径分布更为均匀。在750 mL加氢反应器中,采用C_2后加氢原料对催化剂性能进行评价,结果表明,与常规溶液负载法相比,微乳法制备的催化剂在反应温度低4℃条件下,乙炔转化率相当,选择性高9.9个百分点,绿油生成量较低。微乳法制备Pd-Cu双金属催化剂具有良好的工业应用前景。     

Solvent free liquid phase oxidation of benzyl alcohol using Au supported catalysts prepared using a sol immobilization technique

Solvent free oxidation of benzyl alcohol was investigated in the absence of a base using Au catalysts prepared by sol immobilization on titania and carbon supports. Comparison between the Au supported catalysts revealed that activity and distribution of products was dependent on the nature of support and heat treatment. Specifically, heat pre-treatment of the Au catalysts has a beneficial effect in terms of activity, but is detrimental in terms of selectivity to the benzaldehyde. We conclude that sol immobilization is a suitable technique for preparing gold catalysts with small particle size and narrow particle size distributions and very high activity and selectivity for benzyl alcohol oxidation.     

Preparation of polymeric macroporous hydrogels for the immobilization of enzymes using an emulsion-gelation method

Novel polymeric macroporous hydrogels were developed to entrap and immobilize lipase. Poly(ethylene glycol) methyl ether acrylate hydrogel was used as the support. The emulsion-gelation method using oil-in-water emulsions was used to simultaneously synthesize the hydrogels and entrap lipase in the randomly distributed, non-interconnected, sphere-like macropores, which were several micrometers in diameter. The lipase, immobilized within the macroporous hydrogel, successfully catalyzed the hydrolysis of triacetin without leakage of lipase or loss of activity during repeated use. The macroporous hydrogel-immobilized lipase exhibited higher activity than the lipase immobilized within a non-porous hydrogel, which indicates entrapment of lipase in the macropores without interference from the polymer and excellent diffusional permeability of macroporous hydrogel to substrate/product species.     

微乳法制备纳米催化剂研究进展

微乳法作为制备纳米微粒的有效方法,具有操作简单、制备粒子尺寸均匀、颗粒大小及形状可控等优点,在纳米催化剂制备领域具有广阔的应用前景。综述了近年来采用微乳法制备纳米催化剂的研究状况,尤其是对利用微乳法制备金属纳米粒子、金属氧化物及负载型金属催化剂进行了综述。     

Nanostructured Pt-M/C (M = Fe and Co) catalysts prepared by a microemulsion method for oxygen reduction in proton exchange membrane fuel cells

Nanostructured Pt-M/C (M = Fe and Co) catalysts have been synthesized by a microemulsion method and a high-temperature route. They have been characterized by cyclic voltammetry in 1 M H₂SO₄ and for oxygen reduction in proton exchange membrane fuel cells (PEMFC). The Pt-M alloy catalysts synthesized by the microemulsion method show higher electrochemical active surface area than those prepared by the high-temperature route, and some of them exhibit improved catalytic activity towards oxygen reduction compared to pure Pt. Among the various alloy catalysts investigated, the Pt-Co/C catalyst prepared by the microemulsion method shows the best performance with the maximum catalytic activity and minimum polarization loss. Mild heat treatment of the catalysts prepared by the microemulsion method at moderate temperatures (200 °C) in reducing atmosphere is found to improve the catalytic activity due to a cleaning of the surface and an increase in the electrochemical surface area.     

Catalytic selective reduction of NO with propylene over Cu-Al2O3 catalysts: influence of catalyst preparation method

NO reduction to N₂ by C₃H₆ was investigated and compared over Cu-Al₂O₃ catalysts prepared by four different methods, namely, the conventional impregnation, co-precipitation, evaporation of a mixed aqueous solution, and xerogel methods. It was found that the catalyst preparation method as well as the Cu content exerts a significant influence on catalyst activity. For the catalysts prepared by the first three preparation methods, with the increase of Cu content from 5 to 15 wt%, the maximum NO reduction conversion decreased slightly, but the temperature for the maximum NO reduction also decreased. For the xerogel Cu-Al₂O₃, there was a significant decrease in NO reduction conversion with the increase of Cu content from 5 to 10 wt%. In the absence of water vapour, the Cu-Al₂O₃ catalyst prepared by the impregnation method exhibited the highest activity toward NO reduction. The purity of alumina support was found to be a crucial factor to the activity of the Cu-Al₂O₃ catalyst prepared by impregnation. In the presence of water vapour, a substantial decrease in NO conversion was observed for the Cu-Al₂O₃ catalysts prepared by the first three methods, especially for the impregnated Cu-Al₂O₃ catalyst. In contrast, the presence of water vapour showed only a minor influence on the xerogel 5 wt% Cu-Al₂O₃ and it showed the highest activity for NO reduction in the presence of 20% water vapour. The xerogel 5 wt% Cu-Al₂O₃ catalyst was also found to be less affected by a 5 wt% sulfate deposition than the Cu-Al₂O₃ catalysts prepared by other methods.     

Synthesis and properties of carbon nanospheres grown by CVD using Kaolin supported transition metal catalysts

Carbon spheres with diameters between 400 and 2000 nm were synthesized in large quantities by catalytic chemical vapor deposition (CCVD) method using Kaolin supported transition metal salts (M=Fe, Co, Ni, etc.) as catalysts. The reaction conditions for the synthesis of carbon spheres in different sizes are described. The reactivity of the carbon spheres in various organic solvents is discussed. The as-synthesized carbon spheres are composed of unclosed graphene layers with the interlayer distances 0.33-0.35 nm. These carbon spheres have been characterized by SEM, TEM, HRTEM, XRD, Raman, ESR and SQUID magnetization techniques. From the ESR and SQUID the metallic nature of the carbon spheres is described.     

Selective hydrogenation of cinnamaldehyde using Pd catalysts supported on Mg/Al mixed oxides: Influence of the Pd incorporation method

A series of hydrotalcite‐like compounds was synthesized by varying Mg/Al molar ratio with values of 2, 3, and 4. After thermal treatment at 823 K, the corresponding mixed oxides were obtained and used as catalytic supports. The incorporation of a Pd metallic phase (0.5 g/g loading), was carried out by two methods: 1) in situ vapour phase thermal decomposition, and 2) impregnation by organic method. Fresh and calcined samples were characterized by XRD and N₂ sorption experiments. The basic and metal functions were analyzed by CO₂‐TPD and H₂‐TPR. The Pd‐support interaction was studied by FTIR spectroscopy using CO as a probe molecule while the morphology of Pd nanoparticles on the catalysts was studied by SEM, HRTEM, and theoretical simulation using the Fast Fourier Transform (FFT) method. Finally, the catalytic activity results showed a higher conversion towards hydrocinnamaldehyde in the cinnamaldehyde hydrogenation reaction for the catalysts prepared by vapour phase thermal decomposition, compared with those prepared by organic method, showing the significant dependence on the catalytic activity and the Pd incorporation method.     

K–V–Ca catalysts supported on porous alumina ceramic substrate for soot combustion: Preparation and characterization

The KCl, KNO₃, CaCl₂, Ca(NO₃)₂, V–Ca and K–V–Ca catalysts supported on alumina ceramic substrates have been prepared. X-ray diffraction and thermogravimetry/differential scanning calorimetry were used to characterize the catalysts, and their catalytic activities were evaluated by a soot oxidation reaction using the temperature-programmed reaction system. The catalytic activity of KNO₃ is higher than KCl, and the catalytic activity of Ca(NO₃)₂ is as much as that of CaCl₂. The catalyst containing a higher KNO₃ content exhibits CO₂ adsorption, whereas higher CaCl₂ and Ca(NO₃)₂ content can restrain the adsorption of CO₂. The K–V–Ca catalyst with a molar ratio of 6:1:1 had the lowest soot onset combustion temperature. The melting and oxidation–reduction of KNO₃, oxygen content of catalyst surface, and formation of some eutectic phase may be the key factors in improving catalytic activity of catalysts.     

混浆法制备甲烷氧化偶联催化剂及其表面形貌研究

采用混浆法制备了甲烷氧化偶联（OCM）催化剂，并考察了焙烧温度、焙烧时间、分解温度等对制备结果的影响。结果表明,分解温度是制备过程的主要影响因素；当分解温度在550 ℃左右时，OCM反应收率最高。对催化剂进行了BET和SEM测试，结果表明,分解温度能改变催化剂比表面积，在530 ℃左右时，比表面积最大。     

Preparation of ultrafine metal particles supported on alumina by pyrolysis of polymer complex/alumina composites

Ultrafine metal particles supported on alumina were prepared by pyrolysis of poly(vinylferrocene) (Poly(VFc))/alumina or sodium polyacrylate-Pd(II) (Poly(AANa)-Pd(II))/alumina precursors at 800 ～ 1200°C. α-Fe particles produced on k-Al₂O₃ was obtained by pyrolysis of the mixture of Poly(VFc)/alumina(5/5) at 1000°C. Crystalline Pd supported on alumina was also obtained from Poly(AANa)-Pd(II)/alumina precursor. The size of metal particles formed increased with increasing mixing ratio of polymer complex with alumina. © 1994 John Wiley & Sons, Inc.     

氧化铝负载Co-Mo双金属氧化物的共沉淀制备

采用双溶剂体系(硝酸铝和硝酸钴的乙醇溶液与钼酸铵的碳酸铵水溶液)共沉淀制备了氧化铝负载Co-Mo双金属氧化物。研究了双溶剂体系中乙醇和水的体积比对共沉淀的影响,考察了老化时间对氧化物结构参数的影响,研究了焙烧温度对氧化物还原性能的影响。结果表明:乙醇和水体积比对钼酸根离子的沉淀有重要影响,为了保证钼酸根离子的完全沉淀,乙醇的体积要随着MoO3负载量的增加而提高;随着老化时间的增加,氧化物的比表面积先增加后下降,6 h老化的样品具有最大的比表面积;低温焙烧制得的氧化物较容易还原。     

Preparation of alumina supported molybdena catalysts by new slurry impregnation method: MoO3/Al2O3 sulfide hydrodesulfurization catalyst

A new slurry impregnation method (SIM) of the preparation of a catalyst or catalyst precursor MoO₃/Al₂O₃ is described. Aqueous slurry of powdered MoO₃ is mixed with alumina extradátes and the mixture is refluxed. A low solubility of MoO₃ is sufficient for transport of MoO₃ from powder form via solution to the surface of the support. The catalysts were tested by hydrodesulfurization of thiophene at 1.6 MPa and 280–400°C. Their activity was similar to the activity of industrial and laboratory MoO₃/Al₂O₃ samples prepared by conventional impregnation with solution of ammonium heptamolybdate. The advantage of the SIM method is that calcination, producing nitrogeneous waste gases, is not required and that all deposited molybdenum species are adsorbed and not precipitated.     

Effect of support on hydrogen production by auto-thermal reforming of ethanol over supported nickel catalysts

Nickel catalysts supported on various supports such as ZnO, MgO, ZrO₂, TiO₂, and Al₂O₃ were prepared by an impregnation method to investigate the effect of support on catalytic performance in hydrogen production by auto-thermal reforming of ethanol. Among the supported catalysts, the Ni/ZrO₂ and Ni/TiO₂ catalysts showed better catalytic performance than the other catalysts. The electronic structure of nickel species supported on ZrO₂ and TiO₂ was favorably modified for the reaction, and thus, the reducibility of nickel species supported on ZrO₂ and TiO₂ was increased due to the weak interaction between nickel and support. On the other hand, the Ni/MgO and Ni/ZnO catalysts exhibited poor catalytic performance in the auto-thermal reforming of ethanol due to the formation of a solid solution phase.     

微乳法制备Fe-DMC催化剂用于CO_2与环氧丙烷聚合

采用微乳法制备了铁锌双金属氰化物(Fe-DMC)催化剂,改变破乳时间获得不同形态的Fe-DMC催化剂。破乳时间为4h时制备的Fe-DMC催化剂催化CO2与环氧丙烷(PO)共聚合,在80℃,4MPa条件下,所制共聚物中CO2固定率为44%,脂肪族PPCP的摩尔分数为99%,且共聚物数均分子量达9.20×104,相对分子质量分布仅为1.03,均优于用沉淀法制备的Fe-DMC催化剂催化CO2与PO共聚合。当破乳时间增加到9h,产物中出现大量的环状碳酸酯,数均分子量下降,且相对分子质量分布增大。     

Microencapsulation of caffeic acid and its release using a w/o/w double emulsion method: Assessment of formulation parameters

Caffeic acid (CAF)has numerous health benefits mainly due to its antioxidant, antibacterial and fungicide properties. However, its incorporation in skin care products as anti-aging and the photoprotective agent is still limited due to its solubility and stability in oily matrices or solutions balanced with the skin pH. In this research, CAF–ethyl cellulose (EC) microparticles were produced by water-in-oil-water double emulsion solvent evaporation encapsulation technique using a biocompatible polymer, EC, as a coating material and a surfactant, polyvinyl alcohol, as a stabilizer of the double emulsion. The study assessed the influence of formulation parameters as the solubility of the polymer in organic solvents and the polymer concentration on microparticles final characteristics. CAF–EC microparticles were characterized by product yield, encapsulation efficiency, mean particle size, particle size distribution and polydispersity and imaged by scanning light microscopy. In vitro release profiles were obtained in water and octanol to mimic oily based and water-based matrices balanced with the skin pH. In vitro release kinetics studies were carried out to investigate the release pattern of CAF in simulated cosmetic formulations. Both the product yield and the encapsulation efficiency were found to be dependent on the solubility of the polymer in the organic phase. The product yield was mainly affected by operational factors such as the sticking and the agglomeration of the polymer to the walls and the magnet stirring during microparticles hardening and results from the encapsulation efficiency revealed that an increase of the polymer concentration led to an increase of the encapsulation efficiency. The usage of a water-soluble solvent contributed to a decrease in the mean particle size and reduction of polydispersity with higher polymer concentrations. The polymer concentration, the polymer solubility in the organic phase and the amount of CAF entrapped shown to affect the release in water, whereas the release in octanol was mainly independent of the amount of CAF entrapped in EC microparticles. The double emulsion solvent evaporation technique and the assessment of the selected formulation conditions have given significant and innovative insights on the microencapsulation of bioactive ingredients for cosmetics formulations.     

Preparation and characterization of high metal content Pt-Ru alloy catalysts on various carbon blacks for DMFCs

High metal content Pt-Ru alloy catalysts (80 and 90 wt.%) with various carbons were prepared by the colloidal method without increasing particle size. As increasing the specific areas of supporting materials, catalysts exhibited homogeneous dispersions. The 90 wt.% Pt-Ru/Ketjen Black showed the best performance as the anode catalyst in unit cell and the 80 wt.% Pt-Ru/Ketjen Black in electrochemical experiments. This difference comes from types of electrolytes, i.e. liquid and solid.