Elsevier

Catalysis Communications

Volume 118, 5 January 2019, Pages 65-69
Catalysis Communications

Short communication
Mechanochemically modified aluminosilicates for efficient oxidation of vanillyl alcohol

https://doi.org/10.1016/j.catcom.2018.09.017Get rights and content

Highlights

  • Simple mechanochemical synthesis of Fe2O3/Al-SBA-15.

  • Efficient oxidation of vanillyl alcohol to vanillin.

  • Highly active oxidation catalysts (>99% conversion, 88% selectivity).

  • Stable mechanochemical systems with almost full initial activity after ten reuses.

Abstract

A mechanochemical protocol was applied to the synthesis of a magnetic material based on iron oxide nanoparticles and Al-SBA-15. Full characterization of the prepared Fe2O3/Al-SBA-15 evidenced the effective functionalization of the aluminosilicate surface. Particularly, TEM analysis revealed that the mechanochemical protocol did not considerable affect the hexagonal ordered structure of Al-SBA-15. DRIFT experiments of Fe2O3/Al-SBA-15 showed interesting acidic properties, which can be further associated to a good catalytic performance. The catalytic behavior of the prepared material was tested in the oxidation of vanillyl alcohol to vanillin, displaying an excellent activity and selectivity. The material resulted to be highly stable in the aforementioned reaction, without considerable decrease of conversion after 10 reuse cycles.

Introduction

Mechanochemistry has emerged as an outstanding methodology for the preparation of metal oxides and related materials with potential catalytic applications [1]. Besides the advantages from an environmental point of view, mechanical stress can induce defects in the crystal structure, which can result on a superior catalytic performance [[2], [3], [4]]. Several oxides, have been obtained employing the aforementioned technique, such as ZnO, TiO2, SnO2, among others [[5], [6], [7], [8]]. Notably, iron oxides nanoparticles (NPs) have become an interesting case to study due their wide range of applications, including not just catalysis but also biomedicine [9], magnetic resonance imaging [10], and energy storage [11]. Noticeably, maghemite phase in γ-Fe2O3 confers outstanding magnetic features as catalytic systems, making possible an easier recovery and reusability. It is also worth to mention that iron oxide NPs possesses non-toxic characteristics and can give rise to cost-effective sustainable processes [12,13].

The catalytic activity of iron oxide supported on mesoporous materials, such as MCM-41, MCM-48 and SBA-15, has been a great deal of attention in recent years [14]. Such supports can provide high surface areas and contribute to the stabilization of NPs, facilitating both dispersion and particle size control. The incorporation of aluminum in SBA-15 has been broadly described since it can result in a mesoporous structure with acidic properties, offering additional possibilities for its application in catalytic processes [15].

Iron oxide based catalysts have been extensively applied to alkylation reactions, as well as both selective and total oxidation reactions of alcohol functionalized compounds. Particularly, oxidation of vanillin alcohol to produce vanillin has a remarkable economic interest [16]. The latest molecule is one of the most popular flavoring compound used in food and cosmetic production, as well as in chemical industry. Conventional procedures to obtain vanillin involve petro-based intermediates and non-environmentally friendly protocols. Therefore, alternative methodologies employing isoeugenol and vanillyl alcohol, which are lignin derived compounds, and several catalytic systems have been investigated [[17], [18], [19], [20]]. Nonetheless, finding a good balance between conversion and selectivity is still one of the main challenges that face vanillin synthesis.

Taken into account these remarks, herein we have prepared a magnetically separable iron oxide functionalized aluminum-silicate (Fe2O3/Al-SBA-15), with noticeable surface area, employing a mechanochemical methodology. The catalytic performance of Fe2O3/Al-SBA-15 mesoporous material toward vanillin production was investigated in order to propose an alternative procedure with enhanced conversion and selectivity.

Section snippets

Experimental

Reagents were purchased from Sigma-Aldrich and employed without further purification.

Results and discussion

In the present work, the surface of a mesoporous material (Al-SBA-15) has been modified with iron oxide magnetic nanoparticles, employing a dry-milling approach. The proposed protocol resulted to be effective for the preparation of such catalytic systems, confirming that mechanochemistry represents a sustainable and outstanding methodology to synthesize advanced nanomaterials (Scheme 1). The employed propionic acid gives rise to an iron propionate complex, which subsequently resulted in the

Conclusions

In sumary we have prepared a magnetically separable catalyst based on iron oxide and a mesoporous aluminosilicate by a mechanochemical protocol. Besides the advantages from an enviromental point of view, the employed methodology resulted to be effective for the successful functionalization of the Al-SBA-15 surface, without significant damage of the nanostrutured arquitecture. The synthezised catalytic system displayed outstanding results, in terms of conversion and selectivity for the

Acknowledgments

Rafael Luque gratefully acknowledges support from MINECO under project CTQ2016-78289-P, co-financed with FEDER funds. Ana Franco gratefully acknowledged MINECO for the provision of a FPI contract (REF BES-2017-081560) associated with the project CTQ2016-78289. Daily Rodriguez-Padron also gratefully acknowledge MINECO for providing a research contract under the same project. Farveh Saberi gratefully acknowledges Sistan and Baluchestan University of Iran for the financial support of the research

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