Ethanol to Acetaldehyde Conversion under Thermal and Microwave Heating of ZnO-CuO-SiO2 Modified with WC Nanoparticles

The nonoxidative conversion of ethanol to acetaldehyde under thermal and microwave heating was studied on mixed oxide ZnO-CuO-SiO₂ catalysts modified with additives of tungsten carbide nanoparticles. The results revealed that the WC-modified catalyst exhibited superior activity and selectivity under microwave heating conditions. It is assumed that when microwave heating is used, hot zones can appear at the contact points of WC nanoparticles and active centers of the mixed oxide ZnO-CuO-SiO₂ catalyst, which intensively absorb microwave energy, allowing the more efficient formation of acetaldehyde at moderate temperatures. Thermodynamic calculations of equilibrium concentrations of reagents and products allowed us to identify the optimal conditions for effective acetaldehyde production. The initial catalyst and the catalyst prepared by the coprecipitation of the oxides with the addition of WC were characterized by physicochemical methods (TPR-H₂, XRD, DRIFTS of adsorbed CO). The active centers of the oxide catalyst can be Cu⁺ cations.     

Metal oxide-modified ZnO/SiO <Subscript>2</Subscript> catalysts for cyclo-dehydrogenation of ethylenediamine with propyleneglycol to 2-methylpyrazine

Metal oxide-modified ZnO /SiO2 catalysts were studied for the cyclo-dehydrogenation of ethylenediamine with propyleneglycol to 2-methylpyrazine at 633 K. The ZnO/SiO₂ catalyst showed fairly good ethylenediamine conversion and quantitative propyleneglycol conversion with about 60 mol% of 2-methylpyrazine selectivity, which is due to the existence of large amount of unconverted intermediate, 2-methylpiperazine. Metal oxide (CuO, NiO, Co₃O₄)-modified ZnO/SiO₂ catalysts were prepared to facilitate the dehydrogenation of 2-methylpiperazine to 2-methylpyrazine. About 82 mol% of 2-methylpyrazine selectivity was achieved on CuO and Co₃O₄ modified ZnO/SiO₂ catalysts, with significant increases of pyrazine selectivity. The catalytic properties of the metal oxidemodified ZnO/SiO₂ catalysts, pretreated with hydrogen gas as in the cyclo-dehydrogenation, were compared using the well-known probe reaction, the dehydrogenation/ dehydration of cyclohexanol to cyclohexanone or phenol/cyclohexene. The selectivities of pyrazine in the cyclo-dehydrogenation on the metal oxide-modified ZnO/SiO₂ catalysts were correlated with the phenol selectivities of the probe reaction. It is proposed that the metallic site of catalyst is responsible for the formation of pyrazine from ethylenediamine dimerization. The improved 2-methylpyrazine yield on CuO/ZnO/SiO₂ catalyst was explained by the proper adjustment of catalytic properties, which could be differentiated by the phenol selectivity in the cyclohexanol probe reaction. Thus, the large enhancement of 2-methylpiperazine dehydrogenation to 2-methylpyrazine and the suppression of excess pyrazine formation are supposed to occur on the metallic Cu formed in situ during the reaction during the cyclo-dehydrogenation of ethylenediamine with propyleneglycol.     

Catalytic dehydrogenation of ethanol into acetaldehyde and isobutanol using mono- and multicomponent copper catalysts

The purpose of this work was to investigate biomass-derived ethanol dehydrogenation into acetaldehyde using several mono- and multicomponent (CuO, ZnO and Cr₂O₃)-containing catalysts supported on industrial size Al₂O₃ beads. The catalysts, prepared with either solution combustion or incipient wetness method, were characterized by using various physico-chemical methods, such as EDXA, SEM-EDXA, TEM, XRD, XPS, pyridine adsorption desorption FTIR, and ζ-potential measurements. The results revealed that the multicomponent catalysts exhibited superior activity compared to the metal oxide catalysts containing only one metal oxide. In addition, the most selective catalyst towards acetaldehyde formation, with 50% selectivity at 55% conversion of ethanol at 300 °C and WHSV 1 h^?1 was CuOCr₂O₃/Al₂O₃ prepared by using the solution combustion method, indicating that this inexpensive and rapid catalyst preparation method is promising for other applications.     

Role of preparation parameters of Cu–Zn mixed oxide catalyst in solvent free glycerol carbonylation with urea

Solvent-free carbonylation of glycerol with urea to glycerol carbonate (GC) was achieved over heterogeneous Cu–Zn mixed oxide catalyst. Cu–Zn catalysts with different ratios of Cu:Zn were prepared using co-precipitation (CP) and oxalate gel (OG) methods. As compared to CuO–ZnO(2:1) catalyst prepared by oxalate gel (OG) method, much higher conversion of glycerol and highest selectivity towards glycerol carbonate (GC) was achieved with CuO–ZnO_CP(2:1) catalyst. Physicochemical properties of prepared catalysts were investigated by using XRD, FT-IR, BET, TPD of CO₂ and NH₃ and TEM techniques. The effect of stoichiometric ratio of Cu/Zn, calcination temperature of CuO–ZnO catalysts and effect of reaction parameters such as molar ratio of substrates, time and temperature on glycerol conversion to GC were critically studied. Cu/Zn of 2:1 ratio, glycerol–urea 1:1 molar ratio, 145 ​°C reaction temperatures were found to be optimized reaction conditions to achieve highest glycerol conversion of 86% and complete selectivity towards GC. The continuous expel of NH₃ from reaction the mixture avoided formation of ammonia complex with CuO–ZnO catalyst. As a result of this, CuO–ZnO catalyst could be recycled up to three times without losing its initial activity.     

微波辐射对TiO2制备及其光催化氧化乙醛性能的影响

采用微波辐射与常规加热法由TiO₂溶胶制备出TiO₂催化剂，采用高频低功率微波-光催化装置考察了微波对两种催化剂上CH₃CHO光催化氧化转化率和产物分布的影响。结果表明，微波干燥制备的TiO₂晶体比普通加热制备的TiO₂晶体对乙醛有更高的光催化活性和更强的氧化能力，且它们对乙醛光催化氧化的途径不同，前者的初始中间体为甲醛和甲酸，后者的初始中间体却为乙酸。还发现，微波辐射对两种样品上乙醛的光催化转化率有不同的影响，对微波辐射法所制样品的影响比对常规加热法所制样品的影响显著。微波辐射通过场效应可加速光催化初始中间体的转化，但它不改变光催化反应的途径，反应途径取决于光催化剂的特性。     

Improvement in the light conversion efficiency of silicon solar cell by spin coating of CuO,ZnO nanoparticles and CuO/ZnO mixed metal nanocomposite material

Synthesis of pure Zinc oxide (ZnO), Copper oxide (CuO) nanoparticles (NPs) and their (ZnO/CuO) nanocomposites (NCs) in 1:1 M ratio were successfully prepared by co-precipitation method. The structural properties of the as synthesized nanoparticles and nanocomposite materials were investigated using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) techniques. Optical band-gap studies were done using UV–Visible absorption spectroscopy. Photovoltaic properties of pure ZnO NPs, CuO NPs and ZnO/CuO NCs coated over a single-crystalline silicon solar cell were carried out to compare improvement of light-conversion efficiency in coated solar cell. The maximum light conversion efficiencies were found to be of 8.02% for CuO (3 mg/ml concentration) and 7.28% for ZnO NPs (3 mg/ml concentration), whereas that of mixed metal nanocomposite CuO/ZnO NCs was found to be 7.62%. at very low concentration of 1 mg/ml. This indicates with low concentration of mixed metal NCs an improvement in light efficiency can be obtained. The enhancement in efficiency could be due to formation of p - n heterojunction by CuO/ZnO NCs composites which enhances the number of electrons and holes participating in conduction on the surface.     

Preparation and characterization of CuO/SiO2 and NiO/SiO2 with bimodal pore structure by sol-gel method

CuO/SiO₂ and NiO/SiO₂ with bimodal pore structure were prepared by sol-gel reactions of Tetra-methoxysilane (TMOS) and the respective metal nitrate in the presence of poly (ethylene oxide) (PEO) with an average molecular weight of 10 000 and the catalyst of acetic acid. In this process, the interconnected macroporous morphology was formed when transitional structures of spinodal decomposition were frozen by the sol-gel transition of silica. The addition of copper and nickel into the silica-PEO system had a negligible effect on the morphology formation. In gel formation, it was found that NiO crystalline sizes in the samples increased with decreasing Si/Ni molar ratio. It was considered that PEO interacted with both silica and nickel cations. In the CuO/SiO₂ with the presence of PEO_, CuO crystalline sizes were larger than those of NiO/SiO_2. It was considered that there was no obvious interaction between the Cu cation and PEO, most of the copper ions in wet silica gel were present in the outer solution. They easily aggregated as copper salts in the drying process of wet gel and decomposed into CuO particles in heating. While in the CuO/SiO₂ with the absence of PEO, the Cu was selectively entrapped as small particles in the gel skeleton due to the interaction between Cu aqua complex and silica gel network.     

Evaluation of polymeric nanocomposites for the detection of toxic gas analytes

Four different metal oxide nanoparticles, copper oxide (CuO), aluminum oxide (Al₂O₃), nickel oxide (NiO), and titanium dioxide (TiO₂), were added to poly (2,5-dimethyl aniline) (P25DMA) during synthesis to create different polymer nanocomposites. These polymer nanocomposites were evaluated as potential sensing materials for six different gas analytes (acetaldehyde, acetone, benzene, ethanol, formaldehyde, and methanol). It was found that CuO did not incorporate into the P25DMA and only a small percentage of Al₂O₃ was incorporated. However, both NiO and TiO₂ were incorporated into the P25DMA at the same concentration as during the synthesis step. Overall, the type of metal oxide significantly affected the morphology of the sensing material and the amount of each analyte sorbed. For example, P25DMA doped with 5 wt% Al₂O₃ had high selectivity towards ethanol, whereas P25DMA doped with 20 wt% TiO₂ sorbed the most ethanol. However, P25DMA doped with 20 wt% TiO₂ also sorbed a high amount of formaldehyde, making P25DMA doped with 20 wt% TiO₂ less selective than P25DMA doped with 5 wt% Al₂O₃ towards ethanol with respect to formaldehyde.     

Microcalorimetric and infrared studies of ethanol and acetaldehyde adsorption to investigate the ethanol steam reforming on supported cobalt catalysts

Microcalorimetric and infrared studies of ethanol and acetaldehyde adsorption were carried out on fresh and deactivated ZnO-supported cobalt catalysts (Co/ZnO and Co/ZnO(d), respectively) as well as on ZnO support alone. The results were used to analyze the catalytic behavior of these materials for ethanol and acetaldehyde steam-reforming reactions. The Co/ZnO(d) sample contained extensive carbon deposition as shown by Raman spectroscopy and transmission electron microscopy. On fresh Co/ZnO, the adsorption energetics of ethanol and acetaldehyde (an intermediate in the ethanol reforming reaction) were similar. Under steam-reforming conditions at low conversion values of ethanol, acetaldehyde was selectively yielded. The presence of surface acetate species was shown from IR spectra following acetaldehyde adsorption. Besides that, the Co/ZnO catalyst was active and showed a high selectivity toward the reforming products, H2 and CO2, when the steam reforming of acetaldehyde was carried out at low conversion values. In contrast, on the deactivated sample, the strongest adsorption sites of ethanol have disappeared, and acetaldehyde was adsorbed with higher energy with respect to ethanol, resulting in the blockage of the active sites; a poorer catalytic performance in both ethanol and acetaldehyde steam-reforming reactions is observed. The presence of acetate species after adsorption of acetaldehyde on Co/ZnO(d) was not shown. The polymerization of acetaldehyde over Co/ZnO(d) was related to the decomposition of acetaldehyde under reforming conditions to give CO and CH4.     

Direct Catalytic Conversion of Ethanol to C5+ Ketones: Role of Pd–Zn Alloy on Catalytic Activity and Stability

Ethanol can be used as a platform molecule for synthesizing valuable chemicals and fuel precursors. Direct synthesis of C₅₊ ketones, building blocks for lubricants and hydrocarbon fuels, from ethanol was achieved over a stable Pd‐promoted ZnO‐ZrO₂ catalyst. The sequence of reaction steps involved in the C₅₊ ketone formation from ethanol was determined. The key reaction steps were found to be the in situ generation of the acetone intermediate and the cross‐aldol condensation between the reaction intermediates acetaldehyde and acetone. The formation of a Pd–Zn alloy in situ was identified to be the critical factor in maintaining high yield to the C₅₊ ketones and the stability of the catalyst. A yield of >70 % to C₅₊ ketones was achieved over a 0.1 % Pd‐ZnO‐ZrO₂ mixed oxide catalyst, and the catalyst was demonstrated to be stable beyond 2000 hours on stream without any catalyst deactivation.     

Effect of mechanically mixed ZnO on the evolution of pore structure of SiO2 upon thermal treatment

N₂ adsorption at 77 K was used to follow the change in the pore structure of silica (mesoporous) produced on heating at 300 and 600?C in the presence of different contents of mechanically mixed ZnO (15–85 mol%). Heating of pure silica at 300?C caused pore narrowing. This proceeded differently in the presence of ZnO, the pore system being split into two ranges of limited sizes. The pore widening effect upon heating silica at 600?C was greatly reduced upon the addition of ZnO, to the extent of the evolution of some micropores at low levels of ZnO. At both heating temperatures, the composition 30% ZnO represented a transient state through the flux of pore system change. The IR spectra indicated that at this composition the silica particles are more oblate. The pore structure variations due to heating at the examined temperatures correlated with the solid-state reactions that take place at 1000?C, where the spinel Zn₂SiO₄ is detected.     

PROBING STUDY OF Rh CATALYSTS ON DIFFERENT SUPPORTS IN CO HYDROGENATION

Rh catalysts on SiO₂ and CeO₂ were studied in CO hydrogenation by adding probing molecules during the reaction. The results demonstrate that alkanes were not formed through the oxygen-containing intermediates, e.g. methanol, ethanol or acetaldehyde. Ethanol and acetaldehyde were not produced through the formation of methanol. Acetaldehyde was not formed through ethanol dehydrogenation, however, ethanol was formed through the hydrogenation of acetaldehyde and CeO₂ itself can catalyze the hydrogenation of acetaldehyde.     

快速制备高掺杂CuO/SiO2复合气凝胶

通过环氧丙烷预反应法, 以乙腈为溶剂快速制备了高掺杂的氧化铜/二氧化硅复合气凝胶. 在典型的合成过程中, 将正硅酸甲酯(TMOS)、乙腈、去离子水和环氧丙烷混合进行预反应, 然后将该溶液与氯化铜的乙腈-水溶液混合并添加环氧丙烷, 在35℃烘箱中静置0.5 h 后转化为湿凝胶, 再经过CO₂超临界流体干燥和热处理即可获得黑色块状CuO/SiO₂复合气凝胶. 最终气凝胶样品密度约为180 mg·cm^-3, 比表面积高达625 m2·g^-1, 平均掺杂比为19.91%±2.42% (Cu:Si 摩尔比), 压缩模量为1.639 MPa, 具有成型性好、分散均匀等优点,是良好的背光源靶材料. 本论文还通过对比实验对凝胶化过程的机理进行分析, 结果表明, 通过改变溶剂和采用环氧丙烷预催化均衡了两种不同前驱体的反应速率, 实现了共凝胶的目的. 此外, 该方法还有望为其它金属氧化物/二氧化硅复合气凝胶的制备提供新思路.     

Preparation of nitrogen doped zinc oxide nanoparticles and thin films by colloidal route and low temperature nitridation process

Nitrogen doped zinc oxide (ZnO) nanoparticles have been synthesized using a colloidal route and low temperature nitridation process. Based on these results, 200 nm thick transparent ZnO thin films have been prepared by dip-coating on SiO₂ substrate from a ZnO colloidal solution. Zinc peroxide (ZnO₂) thin film was then obtained after the chemical conversion of a ZnO colloidal thin film by H₂O₂ solution. Finally, a nitrogen doped ZnO nanocrystalline thin film (ZnO:N) was obtained by ammonolysis at 250 °C. All the films have been characterized by scanning electron microscopy, X-ray diffraction, X-Ray photoelectron spectroscopy and UV–Visible transmittance spectroscopy.     

Copper-catalyzed rearrangement of oximes into primary amides

The atom-efficient and cost-effective rearrangement of oximes into primary amides is catalyzed by simple copper salts. The use of homogeneous Cu(OAc)₂ (1-2 mol %) was found to be effective for this transformation at 80 °C. The reaction was successful with either conventional or microwave heating. CuO and CuO/ZnO on activated carbon provided a competent reuseable heterogeneous catalyst which could be used in a batch process or in flow. Copper salts are much cheaper than the precious metals previously used for this rearrangement, and the reaction conditions are milder than those reported.     

Thermal degradation study of tetrabromobisphenol A under the presence metal oxide: Comparison of bromine fixation ability

Thermal degradation of mixture of tetrabromobisphenol A (TBBA) and metal oxide (ZnO, Fe₂O₃, La₂O₃, CaO and CuO) has been studied under inert atmosphere. The formation of hydrogen bromide and brominated organic compounds is observed for pyrolysis of TBBA. The addition of metal oxide gives rise to considerable suppression of HBr as well as brominated organic compounds. The suppression owes to the bromination of oxides. The influence of oxide on thermal degradation of TBBA is discussed with emphasis on the conversion of bromine.     

ZnO与骨架NiMo物理混合用于丙三醇催化重整-氢解制1,2-丙二醇

以骨架NiMo以及与氧化物物理混合, 考察了其在连续固定床反应器中无外加氢气条件下的丙三醇一锅法重整-氢解制1,2-丙二醇(1,2-PDO)的性能.研究发现, 骨架NiMo自身催化活性高, 但对1,2-PDO的选择性一般.当将其与MgO, SiO₂, Al₂O₃, HZSM-5, TiO₂, ZrO₂或CeO₂机械混合时, 丙三醇转化率和1,2-PDO选择性均发生下降.但当与ZnO物理混合时, 催化活性和选择性均有所提高, 1,2-PDO得率可达52.0%, 优于贵金属催化剂在该一锅法反应中得到的结果.物理混合的ZnO与骨架NiMo之间这种独特的协同作用, 归因于重整过程中产生的CO₂在ZnO上发生化学吸附, 原位增强了ZnO的路易斯酸性.这不仅促进了丙三醇在ZnO上脱水生成中间产物丙酮醇, 也促进了丙酮醇在骨架NiMo上加氢生成1,2-PDO.     

Preparation of ZrO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> mixed oxide by combination of sol–gel and alcohol-aqueous heating method and its application in tetrahydrofuran polymerization

Without using any acid or base catalyst, complexing agent or zirconium alkoxides, ZrO₂–SiO₂ mixed oxide with the ZrO₂ content of 50 mol% was prepared by combination of sol–gel and alcohol-aqueous heating method using zirconyl nitrate and tetraethoxysilane as starting materials. The structural and surface acidic properties were characterized by FT-IR, XRD, NH₃-TPD and pyridine adsorption FTIR. Compared with another mixed oxide with the same ZrO₂ content prepared by mechanical grinding, the obtained ZrO₂–SiO₂ mixed oxide was homogeneously mixed in molecular level. The existed Zr–O–Si hetero-linkages strongly retarded the ZrO₂ particle growth. The obtained mixed oxide maintained amorphous phase until it was calcined at 1,173 K for 3 h when crystallization of tetragonal zirconia took place. NH₃-TPD and pyridine adsorption FTIR showed that both Brønsted and Lewis acidity were largely developed in the mixed oxide and most of the acidic sites belonged to the medium acidity. Because of the existence of abundant medium acidity, the mixed oxide showed catalytic activity for tetrahydrofuran polymerization. Furthermore, the produced poly tetramethylene ether glycol had moderate average molecular weight around 2,000. Neither the pure oxides nor the mixed oxide prepared by the mechanical grinding presented catalytic activity for this reaction.     

Fabrication and characterization of composition-gradient CuO/SiO2 composite aerogel

With tetramethoxysilane as the silica precursor, CuCl₂·2H₂O as the copper–oxide precursor, acetonitrile as the solvent and gelled by PO via a sol–gel process, the CuO/SiO₂ composite aerogel was fabricated. By adjusting the amount of CuCl₂·2H₂O, CuO/SiO₂ composite aerogels with different molar ratio of Cu/Si such as 1, 5, 10, 20, 30 and 35 % was prepared. Finally, via a self-built device and sol-co-gelation technic, a continuous formation process was developed to fabricate the composition-gradient CuO/SiO₂ composite aerogel. Density of these aerogels was about 200 mg/cm³, the composition-gradient CuO/SiO₂ composite aerogel was cylindrical and about 2.5 cm in height. Scanning electron microscope was used to characterize its microstructure at different position. X-ray diffraction, energy dispersive spectrometer and Fourier transform infrared spectrometer were used to characterize its composition and composition distribution, the results showed that the cylindrical CuO/SiO₂ composite aerogel’s molar ratio of Cu/Si changed from 31.06 to 4.43 % as the measure point from the bottom up, the whole sample displayed obvious composition-gradient.     

Effective hydrodeoxygenation bio-oil via natural zeolite supported transition metal oxide catalyst

Bio-oil from biomass pyrolysis is promising to be used as a sustainable biofuel and high-value-added chemical. However, the presence of high acid, water, and oxygenate causes corrosive properties, low higher heating value (HHV), and instability of the bio-oil component. Therefore, refining the bio-oil is essential to improve its quality. In this study, we introduced natural zeolite (HZ) impregnated with transition metal oxide (TMO) to refine the bio-oil using the hydrodeoxygenation method (HDO) at various catalyst ratios and temperatures. We find that ZnO/HZ 5% wt. shows the best catalytic performance, with the conversion of organic phase reaching ～ 50%. The refined bio-oil from Fe₂O₃, ZnO, and CuO has high-quality physicochemical properties with carbon, oxygen, water level, and HHV values are 37–52%, 40–53%, 8–27%, and 17–21 MJ/kg, respectively. This result represents a high catalytic performance for the hydrodeoxygenation process of bio-oil using natural zeolite-based transition metal oxide for better and low-cost biofuel production.