Electro-oxidation of renewable glycerol to value added chemicals over phosphorous-doped Pt/MCNTs nanoparticles

Abstract

In the present work, Pt/MCNTs and P-dopedPt/MCNTs catalysts were synthesized via hydrothermal method and utilized for glycerol oxidation reaction (GOR). The catalysts were physio-chemically characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction, field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) to investigate pore size, pore volume, structure and morphology of the catalysts. A remarkable reduction in BET surface area was found for P-dopedPt/MNCTs which 1.56 time less than the sole MNCTs is confirming the incorporation of phosphorous into the pore channels of Pt/MCNT. The TEM analysis of P-dopedPt/MCNTS demonstrated the uniform distribution of Pt nanoparticles over multiwalled carbon nanotubes with an average particle size of 6.23 nm. The activity and stability of the catalysts were analysed for GOR using cyclic voltammetry (CV) and chronoamperometry (CA). The CV testing showed the higher current density for P-doped Pt/MCNTs (28.33 A/m2) which is 2 times higher than the Pt/MCNTs (14.20 A/m2) current density. The synthesized products were analysed by high performance liquid chromatography (HPLC) analysis which demonstrated the selective synthesis of tartronic acid as a major product with maximum yield. It was found that the P-dopedPt/MCNTs have higher selectivity for tartronic acid and glyceric acid as compared to its counterpart.

Towards the electrocatalytic oxidation of sugar alcohols, saccharides and polysaccharides

“…46 Several other studies performed at 0.5-1.0 M KOH have shown that Pt is highly selective toward the formation of TA. 98,142,143 In the case of Pt/CNT in 0.5 M KOH at 0.7 V vs RHE, up to 75-95% TA was found over a 2 hour time frame, 142 while over a P-doped Pt/MWCNT catalyst in 0.5 M KOH at 0.73 V, near equimolar amounts of TA and GLA were detected, both accounting for 90% of the final products. 143 These results show that dicarboxylic acids (TA) are only produced under highly alkaline conditions, as was also shown for Au electrodes at pH ≥ 14.3.…”

“…98,142,143 In the case of Pt/CNT in 0.5 M KOH at 0.7 V vs RHE, up to 75-95% TA was found over a 2 hour time frame, 142 while over a P-doped Pt/MWCNT catalyst in 0.5 M KOH at 0.73 V, near equimolar amounts of TA and GLA were detected, both accounting for 90% of the final products. 143 These results show that dicarboxylic acids (TA) are only produced under highly alkaline conditions, as was also shown for Au electrodes at pH ≥ 14.3. 90,92 At 1.0 M KOH, Ferreira et al showed for a Pt/C catalyst that higher current densities (90 mA cm -2 ) and hence higher overpotentials, promoted C-C cleavage reactions, whereas lower current densities (60 mA cm -2 ) and overpotentials promoted the formation of TA and reduced the C-C cleavage.…”

“…98 Doping the Pt/MCNT with P improved the stability of the catalyst, without affecting the catalyst selectivity. 143 The increased activity was ascribed to the reduction of the accumulation of carbonaceous intermediates and an increase in the local hydroxyl concentration. 143 In summary, the electrocatalytic oxidation of sugar alcohols under acidic and neutral conditions is substantially faster on Pt than on Au.…”

“…143 The increased activity was ascribed to the reduction of the accumulation of carbonaceous intermediates and an increase in the local hydroxyl concentration. 143 In summary, the electrocatalytic oxidation of sugar alcohols under acidic and neutral conditions is substantially faster on Pt than on Au. The use of non-equilibrated Pt surfaces can be used to improve the catalyst activity further.…”

“…TA was previously only formed through electrocatalytic reactions at pH ≥ 13.7 on Au and Pt electrodes. 90,92,98,142,143 It was argued that the high selectivity toward TA can be attributed to the high selectivity of Pd(100) toward the electrocatalytic oxidation of the primary alcohol group (section 2.4, Scheme 2.3). 145 In the second case, at pH = 13.7 after 2h electrolysis, GALD is the main product regardless of the potential applied (55-60% at 0.6 ≤ E ≤ 1.2 V), followed by a 30% of oxalate and 5-10% of glycerate.…”