Novel metal oxide nanocomposite of Au/CuO–ZnO for recyclable catalytic aerobic oxidation of alcohols in water

Synthesis of Palladium and Copper Nanoparticles Supported on TiO2 for Oxidation Solvent-Free Aerobic Oxidation of Benzyl Alcohol

The use of metal oxides as supports for palladium and copper (Pd–Cu) nanoalloys constitutes a new horizon for improving new active catalysts in very important reactions. From the literatures, Pd-based bimetallic nanostructures have great properties and active catalytic performance. In this work, nanostructures of titanium dioxide (TiO2) were used as supports for Pd–Cu nanoparticles catalysts. Palladium and copper were deposited on these supports using the sol-immobilisation method. The composite nanoalloys were characterized using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The catalyst was evaluated for the oxidation of benzyl alcohol. The effect of the Cu–Pd ratio using sol-immobilization methods supported on TiO2 was investigated. The results show that monometallic Cu/TiO2 was observed to have a low activity. However, as soon as the catalyst contained any palladium, the activity increased with a significant increase in the selectivity towards isomerization products. The influence of support and temperature were investigated. Furthermore, the catalyst reusability was also tested for oxidation of benzyl alcohol reactions, by repeatedly performing the same reaction using the recovered catalyst. The Pd–Cu/TiO2 catalyst displayed better reusability even after several reactions

Batch Preparation of CuO/ZnO-Loaded Nanofiber Membranes for Photocatalytic Degradation of Organic Dyes

Composite nanofiber membranes (CNFMs) loaded with CuO/ZnO (CZCNFMs) have important applications in a series of organic and industrial catalytic reactions because of nanoeffects of the nanofibers and the peculiar performances of semiconductor oxides. In this work, CZCNFMs with different mass ratios of Cu to Zn were successfully fabricated in batches using modified bubble electrospinning (MBE), a heat treatment method, and a hydrothermal method. The influences of the mass ratio of Cu to Zn on the morphologies, structures, and properties of the CNFMs were studied, and the obtained CNFMs with different mass ratios of Cu to Zn were applied to the photodegradation of methyl orange (MO) and methylene blue (MB). The results showed that when the mass ratio of Cu to Zn was 5:5, the fabricated CNFM had better morphology, structure, and mechanical properties and had the best degradation effects on MO and MB. In addition, the principal active substances produced during the photodegradation of MO were defined by free radical capture experiments, and the influences of the pH value of the MO solution on the photocatalytic activity of the CNFMs with the optimal mass ratio of 5:5 were discussed.

Selective Catalytic Oxidation of Benzyl Alcohol to Benzaldehyde by Nitrates

In this paper, ferric nitrate was used to oxidize benzyl alcohol in a mild condition and demonstrated its better performance compared to HNO₃. In the reaction, the conversion rate and product selectivity could be both as high as 95% in N₂ atmosphere, while the benzaldehyde yield also reached 85% in air. Similar to Fe(NO₃)₃·9H₂O, the other metallic nitrates such as Al(NO₃)₃·9H₂O and Cu(NO₃)₂·3H₂O could also oxidize the benzyl alcohol with high activity. The applicability of Fe(NO₃)₃·9H₂O for other benzylic alcohol was also investigated, and the reaction condition was optimized at the same time. The results showed the Fe(NO₃)₃·9H₂O would be more conducive in oxidizing benzyl alcohol under the anaerobic condition. The experiments in N₂ or O₂ atmospheres were conducted separately to study the catalytic mechanism of Fe(NO₃)₃. The results showed the co-existence of Fe³⁺ and NO3- will generate high activity, while either was with negligible oxidation property. The cyclic transformation of Fe³⁺ and Fe²⁺ provided the catalytic action to the benzyl alcohol oxidation. The role of NO3- was also an oxidant, by providing HNO₂ in anaerobic condition, while NO3- would be regenerated from NO in aerobic condition. O₂ did not oxidize the benzyl alcohol conversion directly, while it could still be beneficial to the procedure by eliminating the unwelcome NO and simultaneously reinforcing the circulation of Fe²⁺ and Fe³⁺, which therefore forms a green cyclic oxidation. Hence, the benzyl alcohol oxidation was suggested in an air atmosphere for efficiency and the need of green synthesis.

Synergistic Effect in Au-Cu Bimetallic Catalysts for the Valorization of Lignin-Derived Compounds

The selective oxidation of veratryl alcohol as lignin-derived compound was studied under mild conditions, using Au-Cu catalysts synthesized from pre-formed nanoparticles with different Au:Cu molar ratios. Bimetallic catalysts show higher activity compared to monometallic counterparts, highlighting a clear synergistic effect. By comparing the physico-chemical surface properties of catalysts supported on carbon and Al2O3, we were able to establish a strong support effect, with alumina-based catalysts being more active than carbon-supported ones. Moreover, TEM and X-ray photoelectron spectroscopy (XPS) analyses showed a different composition of nanoparticles (NPs) and metal exposure, and we established that Au is the active phase of the reaction. The co-presence of Au and Cu species, and their different interaction with the support, enabled obtaining more than 70% conversion of veratryl alcohol to veratryl aldehyde as a unique product. Moreover, the Au1Cu1 supported on alumina catalyst was recovered by filtration and reused without significant loss of activity and selectivity up to four times.

Synthesis and Comparative Catalytic Study of Zirconia-MnCO3 or -Mn2O3 for the Oxidation of Benzylic Alcohols

We report on the synthesis of the zirconia-manganese carbonate ZrO_x(x   %)-MnCO₃ catalyst (where x=1-7) that, upon calcination at 500 °C, is converted to zirconia-manganese oxide ZrO_x(x   %)-Mn₂O₃ . We also present a comparative study of the catalytic performance of the both catalysts for the oxidation of benzylic alcohol to corresponding aldehydes by using molecular oxygen as the oxidizing agent. ZrO_x(x   %)-MnCO₃ was prepared through co-precipitation by varying the amounts of Zr(NO₃)₄ (w/w %) in Mn(NO₃)₂. The morphology, composition, and crystallinity of the as-synthesized product and the catalysts prepared upon calcination were studied by using scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and powder X-ray diffraction. The surface areas of the catalysts [133.58 m² g^-1 for ZrO_x(1 %)-MnCO₃ and 17.48 m² g^-1 for ZrO_x(1 %)-Mn₂O₃ ] were determined by using the Brunauer-Emmett-Teller method, and the thermal stability was assessed by using thermal gravimetric analysis. The catalyst with composition ZrO_x(1 %)-MnCO₃ pre-calcined at 300 °C exhibited excellent specific activity (48.00 mmolg^-1 h^-1) with complete conversion within approximately 5 min and catalyst cyclability up to six times without any significant loss in activity. The specific activity, turnover number and turnover frequency achieved is the highest so far (to the best of our knowledge) compared to the previously reported catalysts used for the oxidation of benzyl alcohol. The catalyst showed selectivity for aromatic alcohols over aliphatic alcohols.

Eu-Based MOF/graphene oxide composite: a novel photocatalyst for the oxidation of benzyl alcohol using water as oxygen source

An Eu-based MOF/graphene oxide composite is an efficient photocatalyst for the oxidation of benzyl alcohol using water as an oxygen source.

Synthesis, Characterization, and Relative Study on the Catalytic Activity of Zinc Oxide Nanoparticles Doped MnCO3, –MnO2, and –Mn2O3 Nanocomposites for Aerial Oxidation of Alcohols

Zinc oxide nanoparticles doped manganese carbonate catalysts [X% ZnOx–MnCO3] (where X = 0–7) were prepared via a facile and straightforward coprecipitation procedure, which upon different calcination treatments yields different manganese oxides, that is, [X% ZnOx–MnO2] and [X% ZnOx–Mn2O3]. A comparative catalytic study was conducted to evaluate the catalytic efficiency between carbonates and oxides for the selective oxidation of secondary alcohols to corresponding ketones using molecular oxygen as a green oxidizing agent without using any additives or bases. The prepared catalysts were characterized by different techniques such as SEM, EDX, XRD, TEM, TGA, BET, and FTIR spectroscopy. The 1% ZnOx–MnCO3 calcined at 300°C exhibited the best catalytic performance and possessed highest surface area, suggesting that the calcination temperature and surface area play a significant role in the alcohol oxidation. The 1% ZnOx–MnCO3 catalyst exhibited superior catalytic performance and selectivity in the aerial oxidation of 1-phenylethanol, where 100% alcohol conversion and more than 99% product selectivity were obtained in only 5 min with superior specific activity (48 mmol·g−1·h−1) and 390.6 turnover frequency (TOF). The specific activity obtained is the highest so far (to the best of our knowledge) compared to the catalysts already reported in the literatures used for the oxidation of 1-phenylethanol. It was found that ZnOx nanoparticles play an essential role in enhancing the catalytic efficiency for the selective oxidation of alcohols. The scope of the oxidation process is extended to different types of alcohols. A variety of primary, benzylic, aliphatic, allylic, and heteroaromatic alcohols were selectively oxidized into their corresponding carbonyls with 100% convertibility without overoxidation to the carboxylic acids under base-free conditions.

Electrochemical Water Oxidation of Ultrathin Cobalt Oxide-Based Catalyst Supported onto Aligned ZnO Nanorods

A stable and durable electrochemical water oxidation catalyst based on CoO functionalized ZnO nanorods (NRs) is introduced. ZnO NRs were grown on fluorine-doped tin oxide (FTO) by using a low-temperature chemical solution method and were functionalized with cobalt oxide by electrochemical deposition. The electrochemical water oxidation performance of cobalt oxide functionalized ZnO NRs was studied under alkaline (pH = 10) conditions. From these studies, it is noticed that cobalt oxide functionalized ZnO NRs show electrocatalytic activity toward water oxidation with current density on the order of several mA cm(-2). Further, 30 s CoO deposited ZnO nanorods exhibited excellent galvanostatic stability at a current density of 1 mA cm(-2) and potentiostatic stability at 1.25 V vs Ag/AgCl over an electrolysis period of 1 h.

Aerobic flow oxidation of alcohols in water catalyzed by platinum nanoparticles dispersed in an amphiphilic polymer

Various alcohols were aerobically oxidized in an aqueous solution in a continuous-flow reactor containing a platinum nanoparticles dispersed in a polystyrene–poly(ethylene glycol) resin to give the corresponding carbonyl compounds in up to 99% yield.

A highly efficient, ligand-free and recyclable SBA-15 supported Cu2O catalyzed cyanation of aryl iodides with potassium hexacyanoferrate(ii)

SBA-15 supported Cu₂O nanoparticles (Cu₂O/SBA-15) have been fabricated and characterized. The Cu₂O/SBA-15 nanoparticles can effectively catalyze cyanation of aryl iodides using non-toxic K₄[Fe(CN)₆] as a cyanide source.