Elsevier

Molecular Catalysis

Volume 440, October 2017, Pages 148-157
Molecular Catalysis

Aerobic oxidation of primary amines into corresponding nitriles over MnxCe1-xOs catalysts prepared by co-impregnation method

https://doi.org/10.1016/j.mcat.2017.07.017Get rights and content

Highlights

  • Mixed oxides without noble metals are prepared via co-precipitation method.

  • Good yields were obtained for oxidation of amines to corresponding nitriles at nMn/nCe = 2.

  • MnxCe1-xOs solid solution was formed very well when the Mn/Ce atomic mole ratio was 2:1.

  • The mobility of oxygen species to the surface can be facilitated due to the formation of Mn0.67Ce0.33Os solid solution.

  • A possible reaction pathway for the aerobic oxidation of amines was proposed.

Abstract

Mn-Ce mixed oxides, synthesized by co-impregnation method, have been used in the catalytic oxidation of primary amines to corresponding nitriles. The effects of Mn/Ce molar ratio on the structure and catalytic properties were investigated, and the results showed the MnxCe1-xOs mixed oxides exhibited higher catalytic activity than MnOx or CeO2. It was found that favorable selectivity and the best conversions for benzylic, heterocyclic, and aliphatic primary amines were obtained when the Mn/Ce atomic mole ratio was 2:1 (denoted as Mn0.67Ce0.33Os). These materials have been investigated using XRD, FT-IR, SEM, HRTEM, XPS, DR-UV–vis, H2-TPR, and EPR techniques. XRD results showed that the samples did not appear any diffraction of manganese oxides. SEM images showed that the nanoparticles of the mixed oxides can be uniformly distributed than MnOx or CeO2. HRTEM micrographs exhibited that Mn-Ce mixed oxides were all exposed (111) and (220) planes corresponding to CeO2, and Mn0.67Ce0.33Os catalyst had the highest mutual solubility, thus this catalyst could have the stronger interaction than other Mn-Ce mixed oxides, which was in accordance with XPS, H2-TPR, and EPR analysis. XPS studies confirmed that the highest concentration of Ce3+ was obtained at the surface of Mn0.67Ce0.33Os sample, this situation provides a basis for the formation and stabilization of oxygen vacancies, and it is beneficial for oxidation reaction, which is in consistent with DR-UV–vis results. In addition, XPS data also showed that Mn0.67Ce0.33Os sample provided the most adsorbed oxygen species, this suggested that the mobility and availability of the active oxygen species were enhanced. This conclusion also can be drawn from H2-TPR analysis. EPR studies further supported the formation of Mn0.67Ce0.33Os solid solution. Based on the above analysis, the excellent catalytic performance should be attributed to the formation of a solid solution with the incorporation of Mnx+ into the CeO2 cubic fluorite lattice, this reduces the formation energy of oxygen vacancies and enhances the mobility of active oxygen species from the bulk to the catalyst surface.

Graphical abstract

Mn-Ce mixed oxides catalysts with different Mn/Ce molar ratio were prepared and used in the oxidation of primary amines to corresponding nitriles. The formation of Mn0.67Ce0.33Os solid solution between CeO2 and MnOx can greatly reduce the formation energy of oxygen defects and facilitate the mobility of oxygen species from the bulk to the surface, this leads to the Mn0.67Ce0.33Os sample showing the best catalytic performance.

  1. Download : Download full-size image

Introduction

Nitriles are important industrial intermediates, used to produce various polymers [1]. Nitriles are generally prepared by either nucleophilic substitution of halogenated hydrocarbon with cyanide ions, ammonia oxidation, or the Sandmeyer reaction [2]. These traditional methods usually require dangerous chemical reagents and stringent reaction conditions. This has motivated the exploration of new strategies to produce these commodities. Various methods have been developed for the synthesis of nitrile derivatives, the most direct of which is aerobic oxidation of amines [3]. Recently, the conversion of amines to nitriles has attracted the attention of researchers, several favorable results have been obtained. Metal-based oxidants [4] and noble metal catalysts such as Ru [5], [6] and Au [7] have been reported, these processes often lead to the production of wastes. Although the addition of noble metal can improve the reaction activity, their high costs may limit their application. It is more reasonable to use molecular oxygen as sole oxidant from the consideration of green and sustainable chemistry [8].

A redox transformation between Ce3+ and Ce4+ in ceria and the high mobility of absorbed oxygen enables the formation of oxygen vacancies [9]. This promotes the activation and transportation of oxygen species, and leads to the high oxygen storage capacity of ceria [10]. Many reports have shown that adding a second metal to the ceria can effectively improve its activity in oxidation reactions [11], [12]. The incorporation of manganese has been shown to improve the thermal stability as well as redox properties due to the formation of an efficient redox couple [13]. Synergistic interactions between MnOx and CeO2 can supply more active oxygen species [14], making Mn-Ce mixed oxides very attractive in various catalytic applications, such as hydrocarbons oxidation, combustion of volatile organic compounds and CO oxidation [14], [15], [16].

Herein, we have synthesized Mn-Ce mixed oxides catalysts, as well as the singular oxides via a co-impregnation method. We have investigated their catalytic performances for the oxidation of benzylamine, and obtained the most active catalyst Mn0.67Ce0.33Ox. This catalyst has achieved excellent catalytic results in the oxidation of several kinds of amines to corresponding nitriles. As far as we all know, it is the first time to report the aerobic oxidation of primary amines into corresponding nitriles over Mn-Ce mixed oxides.

Section snippets

Materials and methods

Ce (NO3)3·6H2O, Mn (CH3COO)2·4H2O, and Na2CO3, were purchased from Aladdin Industrial Corporation. Mn-Ce mixed oxides with different Mn/Ce mole ratios were prepared (respectively as 1:2, 1:1 and 2:1) through a modified co-impregnation method [11], [17]. In a typical procedure, a certain amount of Ce(NO3)3·6H2O and Mn(CH3COO)2·4H2O was dissolved in 20 ml H2O and titrated to pH 10 with 1 M Na2CO3, and the solution was stirred at room temperature for 40 min. The resulting solids were filtered, washed

Optimization of reaction conditions

The oxidation of benzylamine was chosen as a model reaction to determine the optimal reaction conditions (Table 1). Firstly, the reactions were performed over various catalysts in acetonitrile solvent (Table 1, entries 1–5). Mn0.67Ce0.33Os gave the highest conversion and 100% benzonitrile selectivity with 0.5 h (Table 1, entry 5). In addition, both the MnOx and CeO2 exhibited poor activity on benzylamine even with 1 h (Table 1, entries 1 and 2). Higher conversion was observed using oxygen as

Conclusions

A series of Mn-Ce mixed oxides, pure MnOx, and CeO2 were prepared by a co-impregnation method and used in the aerobic oxidation of primary amines to the corresponding nitriles, which has achieved favorable conversion and selectivity. Mn-Ce mixed oxides exhibited better catalytic activity than MnOx or CeO2. When the mole ratio of Mn/Ce was 2:1, the catalytic activity of Mn-Ce mixed oxides showed the best catalytic performance, this catalyst can be used for five times without any loss of

Acknowledgements

This work is financially supported by the National Natural Science Foundation of China (21303085), the Natural Science Foundation of Jiangsu Province (BK20130901, BK20130930), the Program to Cultivate Outstanding Young Key Teachers of Nanjing Normal University, Postgraduate Research & Practice Innovation Program of Jiangsu Province (KYCX17-1087) and the Priority Academic Program Development of Jiangsu Higher Education Institutions.

References (58)

  • T.G. Clarke et al.

    Tetrahedron Lett.

    (1968)
  • P.T. Anastas et al.

    Catal. Today

    (2000)
  • P. Fornasiero et al.

    J. Catal.

    (1998)
  • Y. Liao et al.

    Catal. Today

    (2013)
  • X. Liu et al.

    J. Rare Earths

    (2009)
  • D. Delimaris et al.

    Appl. Catal. B: Environ.

    (2008)
  • P. Venkataswamy et al.

    Catal. B: Environ.

    (2015)
  • M. Abecassis-Wolfovich et al.

    J. Catal.

    (2007)
  • P. Sudarsanam et al.

    Appl. Catal. B: Environ.

    (2016)
  • Z. Wang et al.

    Appl. Catal. B: Environ.

    (2013)
  • S.M. Mousavi et al.

    Mater. Chem. Phys.

    (2014)
  • H. Mai et al.

    Appl. Surf. Sci.

    (2011)
  • R.C.R. Neto et al.

    Appl. Catal. A: Gen.

    (2013)
  • D. Andreescu et al.

    Colloids Surf. A: Physicochem. Eng. Asp.

    (2006)
  • E. Finocchio et al.

    Catal. Today

    (2001)
  • C.M. Julien et al.

    Spectrochim. Acta Part A: Mol. Biomol. Spectrosc.

    (2004)
  • D. Terribile et al.

    J. Catal.

    (1998)
  • H. Li et al.

    J. Rare Earth

    (2010)
  • Y. Liu et al.

    J. Catal.

    (2014)
  • G. Picasso et al.

    Chem. Eng. J.

    (2007)
  • L. Lamaita et al.

    Catal. Today

    (2005)
  • A. Bensalem et al.

    Appl. Catal. A: Gen.

    (1995)
  • K.N. Rao et al.

    Catal. Commun.

    (2010)
  • Q. Tang et al.

    Microporous Mesoporous Mater.

    (2010)
  • E. Aneggi et al.

    J. Alloys Compd.

    (2006)
  • Tana et al.

    Catal. Today

    (2009)
  • X. Tang et al.

    Chem. Eng. J.

    (2006)
  • V.D. Makwana et al.

    J. Catal.

    (2002)
  • M.T. Schümperli et al.

    ACS Catal.

    (2012)
  • Cited by (16)

    • Solvent-free toluene aerobic selective oxidation over Co(OH)<inf>2</inf>/Cr<inf>2</inf>O<inf>3</inf>:The effect of calcination temperature on product selectivity

      2022, Applied Catalysis A: General
      Citation Excerpt :

      We can clearly see the change of crystal plane before and after calcination. As shown in Fig. 5a, uncalcined catalyst shows only one lattice fringe with a lattice spacing of 0.25 nm, corresponding to the crystal plane of Cr2O3 [34,35]. The catalyst calcined at 500 °C showed a lattice with a lattice spacing of 0.43 nm, which is determined to be the crystal plane [36] of Co3O4, thus further confirms that Co(OH)2 after calcination at 500 °C is transformed into Co3O4 completely.

    • Controllable synthesis of novel nanoporous manganese oxide catalysts for the direct synthesis of imines from alcohols and amines

      2019, Chinese Journal of Chemical Engineering
      Citation Excerpt :

      The peak at 529.8 eV corresponded to the lattice oxygen atoms (O2−, denoted as Olatt); the peak at 531.3 eV was attributed to the surface adsorbed oxygen species (O2−, O22−, O−, denoted as Oads); the small peak at 533.0 eV was attributed to the adsorbed OH groups, molecular water and carbonate species (denoted as Osuf) [25,34]. M-350 and M-400 had the more adsorbed oxygen species (Table 2), implying the better catalytic activity for the organic oxidative reactions due to the mobility and availability of the surface adsorbed oxygen species [35]. By comparing Table 2, it was found that the higher the (Mn3+ + Mn4+)/Mn2+ ratio, the higher the content of surface adsorbed oxygen species was.

    • Rational design of CrO<inf>x</inf>/LaSrMnCoO<inf>6</inf> composite catalysts with superior chlorine tolerance and stability for 1,2-dichloroethane deep destruction

      2019, Applied Catalysis A: General
      Citation Excerpt :

      The appearance of Mn3O4 peaks in the LSMC samples can be contributed to the interaction between CrOx and LSMC, which results in the exposure of the Mn3O4 crystal phase. FTIR was also used to prove the formation of doped oxides as the vibration frequencies of metal-oxygen bonds are sensitive to be detected [36]. As displayed in Fig. S1, the broad band at around 600 cm–1 is assigned to the stretching vibration of O CO functional group in plane and out of plane bending modes [37].

    • Melamine-Schiff base/manganese complex with denritic structure: An efficient catalyst for oxidation of alcohols and one-pot synthesis of nitriles

      2018, Journal of Colloid and Interface Science
      Citation Excerpt :

      Some methods have been reported for the one-pot conversion of alcohols to nitriles including the treatment of H5IO6/KI [16], NaIO4/KI [17], Ni2+/S2O82–/OH– [18], MnO2/MgSO4 [19], 1,3-diiodo-5,5-dimethylhydantoin or I2 [20], KI or I2/tert-butyl hydroperoxide (TBHP) [21], Ru(OH)x/Al2O3/air [22], trichloroisocyanuric acid [23], copper salts/(2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)/O2 [15], I2 or t-BuOCl/TEMPO [24] with ammonia as a nitrogen source. Oxidative conversion of primary amines into the corresponding nitriles has also been studied well using MnxCe1−xOs [25], Pb(OAc)4 [26], AgO [27], cobalt peroxide [28], Co3O4-based catalysts [29], Cu/ N,N′-dimethylethylendiamine (DMEDA)/TEMPO [30], Cu(I) or Cu(II) with oxygen [31], RuCl3 and related Ru reagents [32], Ru/activated carbon [33] and trichloroisocyanuric acid with TEMPO [7]. However, most of applied catalysts for the oxidation of benzylamines to benzonitriles suffer from lack of selectivity due to various oxidation products (Scheme 1a).

    View all citing articles on Scopus
    View full text