Selective Electrocatalytic Oxidation of Biorenewable Polyols (Ethylene Glycohol, 1,2-propanediol, glycerol and mesoerythritol)

Exploring sustainable and cost-effective catalytic processes for production of value-added chemicals from biomass compounds is in urgent need to replace petrochemical feedstocks. However, the complexity of these highly-functionalized biomass compounds always leads to difficulty in limiting oxidation or reduction to the target functional group without affecting the rest. Tuning catalyst function and improving catalytic reaction process to produce target product with high selectivity (yield) remains one of the grand catalysis research challenges, because higher selectivity means greater atom economy, better resource utilization, and higher energy efficiency.
We have focused our research in aqueous phase electrocatalytic selective oxidation of biorenewable polyols since 2009, and we found the leading role of potential on controlling product selectivity - as what we called   "potential-regulated electrocatalytic oxidation".
With the support from a NSF grant (CBET 1159448, 1501124 2011-2015), we have acquired new insights into the role of the electrochemical potential on the alcohol groups over Au nanoparticle catalysts. Through combining a self-designed on-line sample collection off-line HPLC analysis system, three-electrode half cell, electrolysis cells and fuel cell, we have found potential-regulated pathways for electrocatalytic oxidation of polyols (e.g. glycerol, ethylene glycol), and achieved cogeneration of valuable chemicals and electrical energy. We discovered that the degree of glycerol oxidation on Au nanoparticles can be tuned with anode potential to produce tartronate (oxidizing two primary alcohol group, ≥ 0.35 V vs. RHE), mesoxalate (oxidizing three alcohol groups, ≥ 0.45 V vs. RHE), or glycolate (breaking C-C bond, ≥ 0.9 V vs. RHE) under studied MEA and operation conditions; and we successfully achieved cogeneration of electricity and tartronate with high yield of 68% at low anode potential (e.g. <0.45 V vs. RHE) or mesoxalate with high selectivity of 45% at relative high anode potential (e.g. 0.5-0.65 Vvs. RHE), over Au nanoparticle anode catalysts in anion exchange membrane fuel cells. With carbon nanotube supported Au catalyst (Au/CNT), we demonstrated glycerol can be electro-oxidized to glycolate with a high selectivity of 85% at high potential of 1.6 V vs. RHE under ambient conditions (room temperature and atmosphere pressure). Our work provides a new strategy for the targeted transformation of biorenewable compounds with poly-alcohol or multi-functional groups into valuable chemicals via electrode potential tuning. The mains results are summarized in the above figure. 

We collaborated with Dr. Michael Janik from Penn State to combine theoretical DFT computation with experimental studies to study selective electrocatalytic oxidation of 1,2 propanediol and relevant oxidation intermediates. We found pyryvate is dominant product on Au catalyst, while lactate is the major product on Pt/C. DFT helped to identify the most favorable reaction intermediates and provided new insights into the likely reaction pathways.   
We further extended our research to bimetallic catalysts and 4 carbon-chain polyol, including PdAg bimetallic catalysts for alcohol (ethanol, ethylene glycerol, glycerol and mesoerythritol) oxidation, PdAu bimetallic catalysts for 5-hydroxymethylfurfural (one hydroxyl one aldehyde group); and we obtained insights into the different role of Pd and Au (Ag), and potential-regulated electrocatalytic polyol oxidation. More importantly, with the new understanding we developed high performance and low cost direct alcohol fuel cell technologies.  

Sponsors: NSF-CBET 1159448, NSF-CBET1501124
US20170263945A1Fuel-cell system and method of generating energy from crude fuel
Selected publications:
    Au catalysts for glycerol oxidation and  electro-oxidation research methods: 
* Zhiyong Zhang, et al, Electrocatalytic oxidation of glycerol on Pt/C in anion exchange membrane fuel cell: Cogeneration of electricity and valuable chemicals, Applied Catalysis B Environmental, 2012, 119, 40-48.Full PDF
* Zhiyong Zhang, et al., Supported gold nanoparticles as anode catalyst for anion exchange membrane – direct glycerol fuel cell (AEM-DGFC), International Journal of Hydrogen Energy, 2012, 37, 9393-9401. Full text PDF
* Le Xin, et al., Simultaneous generation of mesoxalic acid and electricity from glycerol on Au anode catalyst in anion exchange membrane fuel cells, ChemCatChem, 2012, 4, 110-1114. Full text PDF
* Zhiyong Zhang, et al, Selective electro-oxidation of glycerol to glycolate on carbon nanotube supported gold catalyst, Green Chemistry, 2012,14, 2150-2152. Full text PDF
* Le Xin, et al, Electrocatalytic oxidation of ethylene glycol (EG) on supported Pt and Au catalysts: Reaction pathway investigation in three-electrode cell and fuel cell reactors, Applied Catalysis B Environmental, 2012, 125, 85-94. Full text PDF
* Zhiyong Zhang, et al., Selective electro-oxidation of glycerol to tartronate or mesoxalate on Au nanoparticle catalyst via electrode potential tuning, Applied Catalysis B Environmental, 2014, 147, 871-878. Full text PDF
* Ji Qi, Le Xin, et al., Electrocatalytic Selective oxidation of glycerol to tartronate on Au/C anode catalysts in anion exchange membrane fuel cells with electricity cogeneration, Applied Catalysis B Environmental, 2014, 154-155,360-368. Full text PDF
    Combined DFT and experimental study:
*    David J. Chadderdon, Le Xin, Ji Qi, Brian Brady, Julie A. Miller, Kai Sun, Michael J. Janik*, and Wenzhen Li*, Selective Oxidation of 1,2-Propanediol in Alkaline Anion-Exchange Membrane Electrocatalytic Flow Reactors: Experimental and DFT Investigations. ACS Catalysis, 2015, 5, 6926-6936. DOI: 10.1021/acscatal.5b01085
   Bimetallic catalysts:
* David J. Chadderdon, Le Xin, Ji Qi, Yang Qiu, Phani Krishna, Karren L. More, Wenzhen Li*, Electrocatalytic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid on Supported Au and Pd Bimetallic Nanoparticles, Green Chemistry, 2014, 2014,16, 3778-3786.  Full text PDF
* Ji Qi, Neeva Benipal, Changhai Liang, Wenzhen Li*, PdAg/CNT Catalyzed Alcohol Oxidation Reaction for High-Performance Anion Exchange Membrane Direct Alcohol Fuel Cell (Alcohol = Methanol, Ethanol, Ethylene Glycol and Glycerol), Applied Catalysis B: Environmental, 2016,199, 494–503. DOI: 10.1016/j.apcatb.2016.06.055
* Neeva Benipal, Ji Qi, Qi Liu, Wenzhen Li, Carbon Nanotube Supported PdAg Nanoparticles for Electrocatalytic Oxidation of Glycerol in Anion Exchange Membrane Fuel Cells, Applied Catalysis B: Environmental, 2017, 210, 121–130. DOI: 10.1016/j.apcatb.2017.02.082
*   Neeva Benipal, Ji Qi, Ryan F. McSweeney, Changhai Liang, Wenzhen Li, Electrocatalytic oxidation of meso-erythritol in anion-exchange membrane alkaline fuel cell on PdAg/CNT catalyst, Journal of Power Sources, 2017, 375, 345–350. DOI: 10.1016/j.jpowsour.2017.06.082
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