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IFPEN takes its inspiration from the living world to “dope” the transformation of materials

November 2017

In recent years, there has been a growing interest among the scientific community in the concept of bio-inspiration, particularly in the field of materials synthesis.

It is for this reason that IFPEN organized a scientific conference on the theme in 2016Sustainable Materials Inspired by the Living world for Energy [SMILE 2016]. The conference included a session dedicated to catalytic materials and IFPEN is pursuing research in this disruptive field with a view to improving the performance of refining catalysts.

For example, post-doctoral research has been conducted examining hydrotreatment catalysts prepared using bio-polymers and, in particular, a precursor from the catecholamine family (L-Dopamine). The proposed concept was to use bio-polymers to modify the interaction between the active phase precursors Mo and Co and the catalyst supports (Al2O3, SiO2, etc.). For some supports (Al2O3, TiO2), this interaction is generally too strong, while for others (SiO2) it is too weak, leading in both cases to non-optimized active phases.

According to the literature, since functional groups of bio-polymers are liable to interact with the surface of the support as well as with molecular species of Mo and Co, in the impregnation solution, interactions of a different nature could be envisaged. Moreover, polymers can also modify genesis, the growth of MoS2 layers and their self-assembly (stacking, spacing), as well as the incorporation of the Co promoter in the layers, during the sulfurization step.

Dopamine is a bio-molecule that possesses a number of very interesting properties: thanks to these catechol and amine functional groups*:

  • it is capable of generating bonds with the surface of almost all solids;
      
  • it polymerizes spontaneously via an oxidative polymerization mechanism, when the pH is high (> 7.5);
      
  • it can also form macromolecules by self-assembly (hydrogen bonds).

A polydopamine coating was applied to the alumina surface, following a specially developed protocol, and the spectroscopic and textural characteristics confirmed the formation of a homogeneous layer[1]. Polymerization took place spontaneously, thanks to the basic behavior of the alumina in these pH conditions, increasing its value to close to 8.

This (poly-)dopamine “carpet” generates different interactions with the metallic precursors of Mo and Co to form complexes with hydroxyls of the polydopamine.

Following sulfurization, the presence of dopamine improves the dispersion of the MoS2 layers and limit their sintering at high temperatures, particularly when the surface density of Mo is high. The catalytic activity increases significantly compared to a preparation without dopamine (see Figure). Selective hydrodesulfurization tests demonstrated a very significant selectivity gain, once again suggesting that the properties of the sulfur phase and/or the support were modified.

                                          Click on the picture to enlarge it

The idea of modifying the support using dopamine was extended to silica[2]. With SiO2, although the degree of dopamine polymerization is lower than with alumina, a highly beneficial effect is once more observed on the activity during selective hydrodesulfurization (HDS) with no loss of selectivity. It is suggested that dopamine generates new adsorption sites for Mo, thereby improving dispersion compared to non-modified silica, which barely interacts with metallic precursors. In addition, the characterization of sulfurized catalysts confirmed a reduction in stacking of the layers with no length reduction.

* The coexistence of catechol and amine functions is used in nature, notably by mussels to adhere to various surfaces in wet conditions.

Publications

  1. “Efficient CoMoS Catalysts Supported on Bio-Inspired Polymer Coated Alumina for Hydrotreating Reactions”, Rajesh Munirathinam, Dorothée Laurenti, Gerhard D. Pirngruber, Denis Uzio ; Chemistry Select Volume 2, Issue 8 (2017) 2373–2382.
    >> https://hal.archives-ouvertes.fr/hal-01519804/
          
  2. “Do happy catalyst supports work better ? Surface coating of silica and titania supports with (poly)dopamine and their application in hydrotreating”. Rajesh Munirathinam, Dorothée Laurenti, Denis Uzio, Gerhard D. Pirngruber ; Applied Catalysis A, General 544 (2017) 116–125
    >> DOI: 10.1016/j.apcata.2017.07.008

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