The great interest of shifting towards biodiesel from vegetable oils or waste fats results in a tremendous increase of glycerol production as an inevitable by-product. This waste sparked the need for glycerol valorization to justify biodiesel as alternative for diesel from petroleum. Our research efforts are to partially electro-oxidize glycerol into value-added chemicals in order to make biodiesel production more environmentally benign with added financial benefits. The primary objective of this project is the identification of an active and stable electro-catalyst that can affect the selective electrooxidation of glycerol to value-added products without C-C-C bond cleavage leads to the formation of a large number of high value-added chemicals [1]. The control of catalyst selectivity and activity could be achieved through formulation of novel, nanostructured electrocatalysts [2]. Nickel is an attractive material for glycerol electrooxidation in alkaline media [3, 4], due to its natural abundance and good stability in alkaline media. Designing nanostructured 3D Ni electrodes could enhance the catalytic activity of Ni, whereas its selectivity could be altered by addition of small amounts of the second metal [5].

Monometallic Ni nanoparticles were synthesized using modified polyol method. Change of NaOH concentration resulted in the variation of Ni nanoparticles (NPs) shape: triangular NiNPs were synthesized at lower concentrations while Ni NPs of urchin-like structure were fabricated at higher NaOH concentration. Bi-metallic Ni_xPd_x-1 (x=95,90 and 80 at.%) were also synthesized by hydrazine reduction in the presence of ethylene glycol. The synthesised nanoparticles were characterized by XRD, SEM, TEM, EDS mapping and HAADF imaging. In this work, electro-oxidation of glycerol reaction (GEOR) is investigated in detail on mono- and bimetallic Ni nanoparticles in alkaline medium. In order to better understand the role of the nickel surface on GEOR, electrochemical measurements have been carried out on synthesized unsupported nickel nanoparticles using different electrochemical tests such as cyclic voltammetry (CV), chronoamperometry (CA) and linear sweep voltammetry (LSV). Results indicated that the Ni was able to catalyze the GEOR at the NiOOH surface, well known as the active species. Ni₈₀Pd₂₀ displays the highest activity toward glycerol electro-oxidation. Chronoamperommetry coupled with in-situ polarization modulation infrared-reflection absorption spectroscopy (PM-IRRAS) for the simultaneous analysis of products on the Ni surface and in the bulk solution showed that the main reaction products on Ni surface are glyceraldehyde, carbonyl, carboxylate ions and some carbon dioxide.

The correlation of electrocatalytic activity and selectivity with nanoparticle shape, size, surface and bulk composition, as well as structure of Ni-based nanoparticles will be discussed in terms of mass activities and product distribution during GEOR.

References

1. Behr, J. Eilting, K. Irawadi, J. Leschinski, F. Lindner, Green Chemistry 10 (2008) 13.
2. M. Simoes, S. Baranton, C. Coutanceau, Applied Catalysis B: Environmental110 (2011) 40.
3. M.S.E. Houache, E. Cossar, S. Ntais, E.A. Baranova, J. Power Sources 375 (2018) 310.
4. V.L. Oliveira, C. Morais, K. Servat, T.W. Napporn, G. Tremiliosi-Filho, K.B. Kokoh, Electrochim.Acta. 117 (2014) 255.
5. M. Simoes, S. Baranton, C. Coutanceau, ChemSusChem 5 (2012) 2106.