Catalytic Performance of Co3O4 on Different Activated Carbon Supports in the Benzyl Alcohol Oxidation

Radical-driven selective oxidation of benzyl alcohol on MnCoOx catalysts with no oxidant other than air in reactor

Mn reinforced Co3O4 catalysts (MnCoOx) were prepared by a facile solid phase mixed foaming method with an in-situ heating enhancement for the formation of spinel phase mixed oxide species, and studied in the selective oxidation of benzyl alcohol just the air in reactor as oxygen donor. It was found that the MnCoOx catalysts are composed of relatively minimal spinel MnCo2O4 mixed oxide and massive Co3O4 to form MnCo2O4-Co3O4 oxide pair. The micro-domains of MnCo2O4-Co3O4 oxide pair present two redox couples of Mn3+/Mn2+ and Co3+/Co2+ instead of the single one of Co3+/Co2+ in Co3O4, and then dramatically enhance the formation of superoxide radicals (•O2-) species from the O2 in air, which can efficiently initiate the conversion of benzyl alcohol to benzaldehyde in a Fenton-like processes. With no oxidant other than air in reactor, the interaction between MnCo2O4 and Co3O4 in MnCoOx catalysts leads to a benzyl alcohol conversion up to 98 % with a 100 % benzaldehyde selectivity at atmospheric pressure while single component Co3O4 can only present a benzyl alcohol conversion at 37 %. This embodiment of highly efficient heterogeneous selective oxidation just with air as oxidant provides a probability for developing a low-cost and super-facile radical-induced selective oxidation process for alcohols.

Vapour phase hydrogenation of cinnamaldehyde using cobalt supported inside and outside hollow carbon spheres

The hydrogenation of cinnamaldehyde is usually performed in the liquid phase in batch mode. In this study, a vapour phase flow system has been used to evaluate the use of cobalt catalysts supported inside and outside hollow carbon spheres (HCSs). The influence of temperature, hydrogen flow rate, and catalyst mass on the hydrogenation reaction was investigated. The catalysts generally showed modest conversion to the required products, hydrocinnamaldehyde, 3-phenyl propanol, cinnamyl alcohol, together with formation of various decomposition products. The data revealed that the Co@HCS showed better conversion and product selectivity compared with the Co/HCS. The catalysts with smaller particle sizes (ca. 6 nm) were more efficient than those with larger particles (30–40 nm). An increase in reaction temperature (200–300 °C) resulted in a lower cinnamaldehyde conversion and a poor product selectivity. TPR studies revealed that the Co@HCSs had a stronger metal-support interaction than the Co/HCSs catalysts. Catalyst recycling studies revealed that only the Co/HCSs could be regenerated (four cycles) and post reaction analysis of the catalysts revealed that this was due to HCS pore blockage and not Co sintering.

Oxidation of Benzyl Alcohol Using Cobalt Oxide Supported Inside and Outside Hollow Carbon Spheres

Cobalt oxide nanoparticles (6 nm) supported both inside and outside of hollow carbon spheres (HCSs) were synthesized by using two different polymer templates. The oxidation of benzyl alcohol was used as a model reaction to evaluate the catalysts. PXRD studies indicated that the Co oxidation state varied for the different catalysts due to reduction of the Co by the carbon, and a metal oxidation step prior to the benzyl alcohol oxidation enhanced the catalytic activity. The metal loading influenced the catalytic efficiency, and the activity decreased with increasing metal loading, possibly due to pore filling effects. The catalysts showed similar activity and selectivity (to benzaldehyde) whether placed inside or outside the HCS (63 % selectivity at 50 % conversion). No poisoning was observed due to product build up in the HCS.

Hydrogenation of 4-nitrochlorobenzene catalysed by cobalt nanoparticles supported on nitrogen-doped activated carbon

The hydrogenation of nitroarenes to produce the corresponding amines using dihydrogen as reducing agent has an important industrial role, since it allows to obtain important added-value products.

A Highly Efficient Bifunctional Catalyst CoOx/tri-g-C3N4 for One-Pot Aerobic Oxidation–Knoevenagel Condensation Reaction

A highly efficient bifunctional catalyst of an s-triazine-based carbon-nitride-supported cobalt oxide is developed for the aerobic oxidation–Knoevenagel condensation tandem reaction of benzyl alcohol and malononitrile, whereby 96.4% benzyl alcohol conversion with nearly 100% selectivity towards benzylmalononitrile can be obtained in 6 h at 80 °C. The excellent catalytic performance derives from the high basicity of carbon nitride and strong redox ability of Co species induced by carbon nitride. The catalyst is also quite stable and can be reused without any regeneration treatment, whose product yield is only an 11.5% reduction after four runs.

Recent Developments for Aluminum–Air Batteries

Abstract

Environmental concerns such as climate change due to rapid population growth are becoming increasingly serious and require amelioration. One solution is to create large capacity batteries that can be applied in electricity-based applications to lessen dependence on petroleum. Here, aluminum–air batteries are considered to be promising for next-generation energy storage applications due to a high theoretical energy density of 8.1 kWh kg−1 that is significantly larger than that of the current lithium-ion batteries. Based on this, this review will present the fundamentals and challenges involved in the fabrication of aluminum–air batteries in terms of individual components, including aluminum anodes, electrolytes and air cathodes. In addition, this review will discuss the possibility of creating rechargeable aluminum–air batteries.

Graphic Abstract

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.

Heterogeneous Bimetallic Cu–Ni Nanoparticle-Supported Catalysts in the Selective Oxidation of Benzyl Alcohol to Benzaldehyde

Three bimetallic Cu–Ni nanoparticle-supported catalysts were synthesized by co-immobilization followed by H2 reduction. A chromium(III) terephthalate metal organic framework (MIL-101), titanium dioxide (TiO2), and carbon (C) with different properties (acidity and Brunauer–Emmett–Teller surface area) were selected as supports for studying the effect of the support nature on the catalytic activity and selectivity in the oxidation of benzyl alcohol. The physicochemical properties of the Cu–Ni-supported catalysts were characterized by XRD, NH3-TPD, nitrogen adsorption/desorption, TEM, EDS, XPS, and ICP-OES. Bimetallic Cu–Ni nanoparticles were highly dispersed on the support. The catalytic activities of CuNi/MIL-101, CuNi/TiO2, and CuNi/C were tested in the selective oxidation of benzyl alcohol to benzaldehyde in the presence of molecular oxygen under mild reaction conditions. The highest benzaldehyde yields were achieved with CuNi/TiO2, CuNi/MIL-101, and CuNi/C catalysts at 100 °C within 4 h under 5, 3, and 3 bar of O2, respectively. The bimetallic Cu–Ni-supported catalysts possessed two types of catalytic active sites: acid sites and bimetallic Cu–Ni nanoparticles. The CuNi/MIL-101 catalyst possessed a high number of acid sites and exhibited high yield during selective benzyl alcohol oxidation to benzaldehyde. Importantly, the catalysts exhibited a high functional group (electron-donating and electron-withdrawing groups) tolerance. Cu–Ni-supported catalysts with an Cu:Ni mole ratio of 1:1 exhibited the highest yield of 47% for the selective oxidation of benzyl alcohol to benzaldehyde. Reusability and leaching experiment results exhibited that CuNi/MIL-101 showed better stability than CuNi/TiO2 and CuNi/C catalysts due to the large porous cavities of MIL-101 support; these cavities can be used to trap bimetallic Cu–Ni nanoparticles and inhibit nanoparticle leaching.

CeFe-Based Bead Nanocomposites as Catalysts for Oxidation of Ethylbenzene Reaction

Oxides with good catalytic performances and more selectivity to valuable chemicals attract numerous research interests for the oxidation of hydrocarbon fuels. Taking advantage of the nanocasting route, CeFe-based nanocomposites were prepared and characterized to achieve superior stability in the oxidation of cyclic compounds. Adding a third metal (Me = Ni2+, Mn2+/Mn3+ or Co2+/Co3+) to the CeFe-based oxide helped the formation of Ce3+/Ce4+, Fe2+/Fe3+ and active couples in the ternary nanocomposites. The solids having a spherical morphology and good textural properties enabled the formation of promising ternary oxide catalysts for the oxidation of ethylbenzene compared with those of binary and single monoxide nanocomposites. The close contact among the Ce3+/Ce4+ and Fe2+/Fe3+ pairs with Ni2+ species provided the formation of a highly stable CeFeNi catalyst with enhanced performance in the oxidation of cyclic compounds such as ethylbenzene, styrene and benzyl alcohol substrates.

Effect of Ce Doping of a Co/Al2O3 Catalyst on Hydrogen Production via Propane Steam Reforming

We synthesized cerium-doped cobalt-alumina (CoxCey/Al2O3) catalysts for the propane steam reforming (PSR) reaction. Adding cerium introduces oxygen vacancies, and the oxygen transfer capacity of the Ce promoter favors CO to CO2 conversion during PSR, inhibiting coke deposition and promoting hydrogen production. The best PSR activity was achieved at 700 °C using the Co0.85Ce0.15/Al2O3 catalyst, which showed 100% propane (C3H8) conversion and about 75% H2 selectivity, and 6% CO, 5% CO2, and 4% CH4 were obtained. In contrast, the H2 selectivity of the base catalyst, Co/Al2O3, is 64%. The origin of the difference in activity was the lower C3H8 gas desorption temperature of the Co0.85Ce0.15/Al2O3 catalyst compared to that of the Co/Al2O3 catalyst; thus, the PSR occurred at low temperatures. Furthermore, more CO was adsorbed on the Co0.85Ce0.15/Al2O3 catalyst, and subsequently, desorbed as CO2. The activation energy for water desorption from the Co0.85Ce0.15/Al2O3 catalyst was 266.96 kJ/mol, higher than that from Co/Al2O3. Furthermore, the water introduced during the reaction probably reacted with CO on the Co0.85Ce0.15/Al2O3 catalyst, increasing CO2 generation. Finally, we propose a mechanism involving the Co0.85Ce0.15/Al2O3 catalyst, wherein propane is reformed on CoxCey sites, forming H2, and CO, followed by the conversion of CO to CO2 by water on CeO2 sites.