A study of the oxidehydration of 1,2-propanediol to propanoic acid with bifunctional catalysts

https://doi.org/10.1016/j.apcata.2019.05.036Get rights and content

Highlights

  • 1,2-propanediol undergoes oxidehydration to propionic acid.

  • Hexagonal tungsten bronzes can perform the reaction with moderate selectivity.

  • Parallel reactions of dioxolanes formation lower the selectivity to propionic acid.

  • The main undesired reaction is the oxidative cleavage of reactant and propionaldehyde.

  • Catalyst acidity is needed but is responsible for by-products formation.

Abstract

The gas-phase oxidehydration (ODH) of 1,2-propanediol to propionic acid has been studied as an intermediate step in the multi-step transformation of bio-sourced glycerol into methylmethacrylate. The reaction involves the dehydration of 1,2-propanediol into propionaldehyde, which occurs in the presence of acid active sites, and a second step of oxidation of the aldehyde to the carboxylic acid. The two reactions were carried out using a cascade strategy and multifunctional catalysts, made of W-Nb-O, W-V-O and W-Mo-V-O hexagonal tungsten bronzes, the same systems which are also active and selective in the ODH of glycerol into acrylic acid. Despite the similarities of reactions involved, the ODH of 1,2-propanediol turned out to be less selective than glycerol ODH, with best yield to propanoic acid no higher than 13%, mainly because of the parallel reaction of oxidative cleavage, occurring on the reactant itself, which led to the formation of C1-C2 compounds.

Introduction

Propanediols (PD) are interesting bio-based building blocks for the synthesis of a variety of chemicals [[1], [2], [3]]. Both 1,2-PD and 1,3-PD can be obtained from biomass, e.g., by sugar fermentation or by chemo-catalytic hydrodeoxygenation (HDO) of glycerol or lactic acid [[4], [5], [6], [7], [8], [9], [10]]. In the latter case, various catalytic systems are known to catalyse efficiently the HDO to 1,2-PD, whereas the synthesis of 1,3-PD is more challenging, requiring catalysts based on Rh(Ir)/Re in order to achieve acceptable selectivity.

Amongst the various compounds which can be synthesized from 1,2-PD, eg, propionaldehyde (PAL) by dehydration [[11], [12], [13], [14]], propanol [15], pyruvaldehyde [16], and propanoic acid (PAC) [[17], [18], [19]], the latter might be the intermediate for the synthesis of bio-based methacrylic acid (MAA) and methylmethacrylate (MMA), the monomer for polymethylmethacrylate [[20], [21], [22]]. The glycerol-to-MAA pathway would thus include the steps shown in Scheme 1.

The second step (i.e., the acid-catalysed dehydration of 1,2-PD) and the third step (the oxidation of PAL to PAC) may be carried out with a one-pot process by using a single but bifunctional catalyst, showing both acid and oxidizing properties [[23], [24], [25]].

Indeed, it is well-know that on acidic catalysts, 1,2-PD can also transform into acetone and allylic alcohol, depending on which hydroxyl group is involved into the dehydration process [11,13,26]. Referring to literature, it is interesting to note that PAL generally is the main dehydration product with most of the acid materials so far studied for 1,2-PD dehydration. The latter behavior was explained by Zhang et al [11] on the basis of the mechanism reported in Scheme 2.

1,2-Diols are known to undergo the pinacol rearrangement to give the corresponding aldehyde [27], hence the authors proposed that protonation of either of the hydroxyl groups and rearrangement can generate three different reactive carbenium intermediates which yield acetone, PAL and allyl alcohol, respectively. The secondary carbenium ion, leading to PAL, is the more stable thus it is expected to have the higher concentration. Despite this, acid/base features of the catalysts might considerably influence 1,2-PD conversion [26].

In previous works, we reported about the reactivity of hexagonal tungsten bronzes (HTBs) for the oxidehydration (ODH) of glycerol to acrylic acid, with intermediate formation of acrolein [[28], [29], [30], [31], [32], [33], [34]]. The glycerol-to-acrylic acid reaction is supposed to be similar to 1,2-PD-to-propanoic acid, because of the similar molecules and reaction steps involved, and HTB oxides appear to possess the proper acid properties to perform the selective dehydration of 1,2-PD to PAL, both in terms of acid strength and type of acid sites, where the preponderance of Brønsted sites was proved to be beneficial for the reaction. Here we report about the use of HTBs for the ODH of 1,2-PD to PAC, via intermediate formation of PAL.

Section snippets

Catalyst preparation

W-V-O, W-Nb-O and W-Mo-V-O catalysts, with hexagonal tungsten bronze structure (HTB), were prepared hydrothermally at 175 °C for 48 h, according to a previously reported preparation procedure [[28], [29], [30]]. The catalysts precursors were finally heat-treated at 600 °C for 3 h in an inert atmosphere. They will be named as WV-1, WNb-2 and WMoV-3, respectively.

A Mo-V-W-O catalyst, with Mo/V/W molar ratio of 8/2/0.5, was prepared by coprecipitation from an aqueous solution (with ammonium

Physico-chemical characteristics of catalysts

Table 1 summarizes the characteristics of catalysts used. They showed surface area in the range of 9 to 40 m2 g−1, depending on the composition and the catalyst preparation procedure.

The tungsten-based metal oxides (i.e. WV-1, WNb-2 and WVMo-3) showed the typical XRD diffraction patterns of the hexagonal tungsten bronze (HTB) phase (JCPDS: 85–2460) (Fig. 1, patterns a to c) [30,31].

The MoVW-4 sample presented diffraction peaks similar to those reported previously for catalysts presenting a Mo5O

Conclusions

Hexagonal tunsgten bronzes (HTBs) were tested as catalysts for the oxidehydration of 1,2-propanediol into propionic acid, via intermediate formation of propionaldehyde; the latter is an intermediate compound in the multi-step transformation of glycerol into methylmethacrylate. Mixed metal HTBs containing W, V and Mo were active in the reaction, but the best propionic acid yield achieved was no higher than 13%. In fact, even though the acid properties of the HTB allowed to efficiently catalyse

References (41)

  • R.D. Cortright et al.

    Appl. Catal. B

    (2002)
  • D. Sun et al.

    Appl. Catal. B

    (2016)
  • D. Zhang et al.

    Appl. Catal. A Gen.

    (2011)
  • D. Sun et al.

    Appl. Catal. A Gen.

    (2016)
  • K. Mori et al.

    Appl. Catal. A Gen.

    (2009)
  • M. Ai et al.

    Appl. Catal. A Gen.

    (2003)
  • J. Machek et al.

    Stud. Surf. Sci. Catal.

    (1994)
  • M. Ai

    Appl. Catal. Al

    (2005)
  • M. Ai

    Catal. Today

    (2006)
  • G. Busca et al.

    Catal. Today

    (1996)
  • L.Z. Tao et al.

    Catal. Today

    (2014)
  • B. Török et al.

    J. Mol. Catal. A Chem.

    (1996)
  • A. Chieregato et al.

    Catal. Today

    (2012)
  • A. Chieregato et al.

    Appl. Catal. B

    (2014)
  • A. Chieregato et al.

    Coord. Chem. Rev.

    (2015)
  • S. Knobl et al.

    J. Catal.

    (2003)
  • S. Solmi et al.

    Appl. Catal. A Gen.

    (2018)
  • P. Concepcion et al.

    Appl. Catal. A Gen.

    (2004)
  • M. Baldi et al.

    Appl. Catal. A Gen.

    (1998)
  • M.A. Peluso et al.

    Appl. Catal. B

    (2008)
  • Cited by (8)

    • Reactivity of vanadyl pyrophosphate catalyst in ethanol ammoxidation and β-picoline oxidation: Advantages and limitations of bi-functionality

      2021, Applied Catalysis A: General
      Citation Excerpt :

      Multifunctionality in heterogeneous catalysts is a fundamental trait useful for performing complex transformations [1], and this is especially important in oxidation catalysts for the transformation of organic substrates [2,3].

    View all citing articles on Scopus
    View full text