Elsevier

Molecular Catalysis

Volume 448, April 2018, Pages 63-70
Molecular Catalysis

Investigation of hollow bimetal oxide nanomaterial and their catalytic activity for selective oxidation of alcohol

https://doi.org/10.1016/j.mcat.2018.01.028Get rights and content

Highlights

  • In this study, the metal (Co and Fe) oxide hollow nanoparticles was successfully prepared using a favorable chemical method.

  • This Non-noble Metal magnetic material application procedure is in accordance with the principles of sustainable and green chemistry.

  • The catalysts exhibit excellent the aerobic oxidation reaction activity and high stability.

  • Oxidation state metal is the major phase when the reaction temperature is 120 °C.

Abstract

The aerobic oxidation procedure utilized sustainable non-noble-metal catalysts has been a long-standing objective in laboratory and industrial research. The synthesized hollow bimetal oxide nanoparticles catalysts (HNPs) as a stable and efficient catalyst, which was applied to the selective oxidation of alcohols with molecular oxygen as oxidant, is reported. The catalytic performance of Co3O4/Fe3O4@C HNPs was tested via selective aerobic oxidation catalytic reaction of cinnamyl alcohol in the liquid phase. The results prove that the Co3O4/Fe3O4@C HNPs exhibit ∼ 90% yield for alcohol oxidation, which can be conveniently separated and recycled from reaction system by an external magnetism. Forthrmore, the catalyst can be reutilized for at least 5 runs without a distinct activity reduction. A feasible reaction mechnism over the bimetal catalyst for the alcohol oxidation was proposed. The surface effect between metal oxide nanoparticle and carbon support, and relatively high and easy reducibility grant favorable catalytic activity of Co3O4/Fe3O4@C HNPs. This make the Co3O4/Fe3O4@C HNPs a very significant catalyst for aerobic catalytic oxidation reaction of alcohols in the liquid phase for industrial manufacture.

Introduction

Selective aerobic oxidation of alcohol to the corresponding aldehyde or ketone has turned out to be a very pivotal reaction process in the current of laboratory and chemical industry. Utilization of corresponding products as diverse intermediates for synthesis of key fine chemicals is emerging as a complementary alternative the current energetically inefficient and/or environmentally unfriendly multi-step reactions such as pharmaceuticals, agrochemicals and ploymers [[1], [2]]. Traditionally, many toxic stoichiometric oxidative regents are performed for this oxidation process, which fabricate a lot of waste and pollutants, and are unsanctioned in viewpoint of green and environmental chemistry [3]. From both green and substainable standpoints, there are a strongly moving toward searching and developing the environmental-friendly and green oxidant in this chemosynthesis, such as the air or O2 being the ideal oxidant from the enviromental point of view [4]. Since these oxidants are readily securable, inexpensive, vast pollution-free natural gas, and water is the main byproduct, that catalytic process is industrially promising alternatives for available alcohol oxidation [5].

In recent years, noble metal nanoparticles have shown a high activity to effect alcohol oxidation using molecular oxygen under moderate temperatures and pressures [[1], [2], [3]]. The heterogeneous precious metal catalysts have been abundantly employed in aerobic oxidation catalysis reaction of alcohols owing to their perfect catalytic property [6], for example, many efficient catalysts based on gold [[7], [8]], palladium [[9], [10]], and platinum [[8], [11]], have been extensively reported and obtained a good result. However, these catalysts possess obvious drawbacks used in practical application, which are expensive cost, limited availability and toxic properties [[12], [13]]. Therefore, considering the drawbacks of noble metal catalysts, it would be still desirable to develop non-noble metal catalysts to affect alcohol oxidation. Moreover, a more significant shortcoming with some of these catalysts in solid-liquid state reaction using molecular oxygen as the oxidant are sensitive for the deactivation of alcohol oxidation due to substrates overoxidation, and a basic condition is needed to activate and enhance catalyst for reaction process [[14], [15], [16]].

Based on the reports of the above, and considered the past study of the non-noble metal and non-noble oxides due to their properties such as non-toxicity, lower cost, fine chemical stability and environmentally friendly [[17], [18], [19], [20], [21], [22]], for example CoxOy [23], FexOy [24], MnxOy [[25], [26], [27], [28]], CeOx [29], VOx [22], and many bimetal oxides, including Co2Mn3O8 [30], Co-Mn-Al complex oxides [31], Co-Mn oxides [32], Mo-Fe bimetal oxides [33] and others. Meanwhile, cobalt oxide and iron oxide are excellent catalyst for dehydrogenation [[24], [34], [35]], CO oxidation [36], CO2 conversion [37], alcohol oxidation reaction [38], and others. carbon materials due to low density, abundants surface functional grounps, well-diffusion performances and higher specific surface area, are a widely-applied support for plentiful catalytic nanoparticles, and hollow nanoparticles with low density, higher surface-to-volume, their prospective applications in catalysis and others based on nanoscale Kirdendall effect are also proven to be fascinating catalytic support for numerous reaction [[39], [40]]. In addtion, the experiments have demonstrated that the iron oxide and carbon support have special interaction, the negatively charged surface oxygen functional groups of the carbon support serve as strongly active sites for anchoring positively charged Fe3+ ions and lead to high dispersion of iron oxide species. These oxygen functional groups also provide a suitable coordinate environment to increase the electron density of iron centres and form efficient active sites for the oxidation of alcohols with molecular oxygen [41].

Herein, considering the previous reported catalysts employed in basic condition and expensive cost limited availability, the catalytic property of the Co3O4/Fe3O4@C HNPs catalysts was employed in the selective oxidation of alcohol with molecular oxygen in the liquid phase, which shows >95% alcohol conversion and ∼ 90% aldehyde yield without any promoter (eg., NaOH). In addition, the catalyst can be reused after at least 5 runs with a good activity and recycled with external magnetic. This catalyst is a useful and a meaningful candidate for aerobic catalytic oxidation reaction of alcohols in the liquid phase system.

Section snippets

Reagents and chemicals

All reagents and chemicals were analytical grade and used as received without any further purification. Ferric (Ⅲ) nitrate nonahydrate (Fe (NO3)3·9H2O, 98.5%) was purchased from Chengdu Kelong Chemical Reagents Co., Ltd. Cobalt (Ⅱ) nitrate hexhydrate (Co(NO3)2·6H2O, 99.0%) was purchased from Shanghai Zhongqin Chemical Reagents Co., Ltd. Sodium hydroxide (NaOH, 96.0%) was purchased Chemical Reagents Manufacturing Co., Ltd. Sodium oleate (C17H33COONa or NaOA, 99.5%) was purchased from Tianjin

Characterizations catalyst

To characterize and prove the morphology of Co3O4/Fe3O4 HNPs@C, the TEM, HRTEM-mapping and EDX were carried out. Fig. 1a presents a typical TEM image of Co3O4/Fe3O4 HNPs@C, which clearly exhibits a hollow structure metal oxide nanoparticles of the catalyst, and the sample of Co3O4/Fe3O4 HNPs@C was successfully obtained. Fig. 1b showed a part of a HNSs with HRTEM and the corresponding morphology sketch. It was observed that the shell of a thin layer of Co3O4/Fe3O4 HNPs. The EDX spectrum of the Co

Conclusion

In summary, a functional bimetal oxide hollow nonacomposite (Co3O4/Fe3O4@C) has been designed and synthezied by a favorable method. Co3O4/Fe3O4@C is a reasonable catalyst for aerobic oxidation carried out in heterogeneous reaction process with the liquid phase. The results demonstrated that the catalyst can be used as a substitute for the noble-metals-based catalyst to realize the alcohol oxidation process. the investigation of reaction process proved that the surface effect between metal oxide

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