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Benign-by-design Orange peel-templated nanocatalysts for continuous flow conversion of levulinic acid to N-heterocycles Daily Rodríguez-Padrón, Alain Rafael Puente Santiago, Alina Mariana Balu, Antonio A. Romero, Mario J. Muñoz Batista, and Rafael Luque ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b03896 • Publication Date (Web): 09 Nov 2018 Downloaded from http://pubs.acs.org on November 9, 2018
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Benign-by-design
Orange
peel-templated
nanocatalysts for continuous flow conversion of levulinic acid to N-heterocycles Daily Rodríguez-Padrón,a Alain R. Puente-Santiago.a Alina M. Balu,a Antonio A. Romero,a Mario J. Muñoz-Batista,a* and Rafael Luquea,b* aDepartamento
de Química Orgánica, Universidad de Córdoba, Campus de Rabanales, Edificio
Marie Curie (C-3), Ctra Nnal IV-A, Km 396, E14014, Cordoba, Spain. bPeoples
Friendship University of Russia (RUDN University), 6 Miklukho-Maklaya Str.,
117198, Moscow, Russia * M.j.M-B
[email protected] ,
[email protected]; R.L.
[email protected] Abstract In this work, two different strategies have been employed to explore the potential valorization of biomass waste. A TiO2 based sample was prepared by a dry-milling strategy, involving orange peel valorization towards nanostructured materials. Subsequently ruthenium deposition was accomplished by a chemical reduction method to obtain different ruthenium loadings on the titania support. The prepared catalysts were characterized using a multi-technique approach in terms of chemical, structural and morphological properties. Levulinic acid, a typical model molecule associated with lignocellulosic biomass, was subsequently converted into N-
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heterocycles in a continuous flow reactor. The prepared Ru-TiO2 systems exhibited outstanding catalytic performance in terms of conversion and selectivity in comparition with Ru/P25 and Ru/C catalytic references. Maximum activity (79% conversion, 85 % selectivity to 1-ethyl-2(ethylideneamino)-5-methylpyrrolidin-2-ol) was achieved for the sample containing 3 wt. % Ru, homogeneously deposited on the titania surface. The obtained results were interpreted with help of a complete post-reaction characterization analysis of the most active sample. KEYWORDS. Biomass, Levulinic acid, N-heterocycles, Continuous flow reaction, Orange peel, Titania-based catalysts, Ruthenium
Introduction Biomass valorization recently emerged as an alternative for the production of fuels, chemicals and materials.1–5 Particularly, biomass-derived chemicals have been a green source to generate starting compounds towards sustainable Nitrogen heterocycles (N-heterocycles) production.6 Nheterocycles represent an attractive family of organic compounds which are present in many of the most demanded chemicals in modern society.7 Their unique ability to be used as biomimetics as well as active pharmacophores makes them valuable compounds towards the design of a myriad of chemicals such as photocatalysts, dyes, agrochemical compounds, polymers and pharmaceutical compounds.8–11 In this remark various approaches have been developed for the preparation of N-heterocycles. Yan et al. have developed an easy one-pot synthetic protocol to generate pyrrole molecules from waste shrimp shells derived compounds with significant yields.12 Furthermore, Xu et al. have reported an innovative method to directly transform different lignocellulose biomass in a number of heterocycles including pyrroles, pyridines and indoles using commercial zeolites as catalysts
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via thermocatalytic conversion and ammonization approach.13 Recently, a one-step synthesis from glucose of N-heterocycles products via an efficient ammonium catalytic system was successfully achieved using tungsten-based catalysts.14 Among the most promising platform molecules towards biomass valorization is levulinic acid (LA), accessible from lignocellulosic biomass via simple hydrolysis.1,15–17 LA has been employed to produce valuable N-substituted pyrrolidones by a catalytic reductive amination process followed by subsequent cyclization.18–20 However, the majority of the synthetic procedures to obtain N-heterocycles usually employs compounds derived from limited resources derived from crude oil using complex multistepprocesses.21,22 Additionally, the most employed catalysts for these reactions are those with excellent π-Lewis acidity like palladium, copper and transition-metal complexes, which lead to undesirable drawbacks such as poor recyclability of catalysts, long reaction times, harsh reaction conditions, toxic organic solvents, among others.23–26 It is worth to point out that approaches towards the synthetic studies of N-heterocyclic compounds have also been commonly carried out in batch conditions, keeping significant limitations for their direct application at large scale production. Consequently, finding new synthetic pathways for N-heterocycles through the development of sustainable heterogeneous catalysts, together with the application of flow chemistry desirably offers advantages such as facile scale-up, energy safety, well-defined flows, enhance heat and mass transfer. Ultimately, a number of attempts have been directed to the design of heterogeneous catalysts employing a green strategy (benign-by-design). Significant breakthroughs have been achieved by our research group taking into account the advantages of mechanochemical processes including short reaction times and the possibility of avoiding circumventing solvent issues.27,28 In this
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regard, our research group have developed various nanomaterials, employing biomass-derived residues as sacrificial templates.27–30 In this work, biomass valorization was applied towards both chemicals and materials preparation. Titania based catalytic systems were prepared employing orange peel as sacrificial template and utilized in the conversion of levulinic acid, a biomass derived molecule, resulting in attractive nitrogen-heterocycle compounds.
Experimental Synthesis of TiO2-based nanocatalysts Prior to the preparation of the titania based catalyst, orange peel residues were firstly milled in a ball mill (Emax ball mill model, Retsch), at 900 rpm for 10 min (Figure S1). The preparation of TiO2 was then carried out by a mechanochemical protocol, employing a 2:1 metal precursor (titanium isopropoxide)/sacrificial template (orange peel) ratio, in a Retsch PM100 ball mill (125 mL reaction chamber and eighteen 10 mm stainless steel balls). Subsequently, the material was oven-dried at 100 °C for 24 h, and finally calcined at 500 °C for 2h. In a second step, Ru was deposited onto the TiO2 nanomaterial by a chemical deposition method using RuCl3•xH2O. The titania was firstly suspended in deionized water for 30 min, followed by adding the proper quantity of RuCl3•xH2O, in order to prepare three catalysts with 1, 2 and 3 wt. % of Ru, respectively. A hydrazine solution was then added with the consequent ruthenium deposition (Ru/hydrazine molar ratio 1/3). The obtained mixture was stirred for 30 min and the final solids were filtered, washed with deionized water and dried at 100 °C. Material characterization
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XRD analysis was performed in the Bruker D8 Advance Diffractometer with the LynxEye detector. The XRD patterns were recorded in a 2θ scan range from 10° to 70°. Bruker Diffracplus Eva software, supported by Power Diffraction File database, was used for phase identification. N2 adsorption-desorption measurements were performed in the Micromeritics ASAP 2000 equipment. The samples were previously degassed for 24 h under vacuum (p
