Supporting Information

Transcription

1 Electronic Supplementary Material (ESI) for Green Chemistry. This journal is The Royal Society of Chemistry 217 Transmittance (arbitrary units) Supporting Information A Switchable Route to Valuable Commodity Chemicals from Glycerol via Electrocatalytic Oxidation with an Earth Abundant Metal Oxidation Catalyst Chun Ho Lam, Aaron J. Bloomfield, Paul T. Anastas* Center for Green Chemistry and Green Engineering, Yale University, New Haven, CT 6511 USA Department of Chemistry, Yale University, New Haven, CT 6511 USA 1. Synthesis of the Co-DPPE catalyst A 5-mL thick-walled Pyrex round-bottom flask equipped with a sidearm that could be sealed with a Teflon valve was used as the reaction vessel (pictured at right). In a glovebox filled with dry nitrogen gas, the reaction vessel was charged with dicobalt octacarbonyl (13.1 g, 38.3 mmol) and 1,2-bis(diphenylphosphino)ethane (15.2 g, 38.3 mmol), and a Teflon-coated magnetic stirbar. The Teflon valve was closed, the sidearm was sealed with a rubber septum, and the reaction vessel was removed from the glovebox. The septum was pierced a needle connected to an oil bubbler, and the reaction vessel was placed over a magnetic stirplate set to ca. 2 rpm. Then the valve was opened, and 275 ml xylenes (sparged with dry N 2 for one hour immediately beforehand) was added quickly by cannula over the course of 9 minutes. As soon as the solvent was added, the reaction began to evolve carbon monoxide gas. (WARNING: a substantial amount of carbon monoxide gas is released at this point--be sure that the flask is properly vented to prevent over-pressurization, and that the gas is vented through an oil bubbler into the back of a fume hood to prevent inhalation of the toxic gas!) The reaction mixture was stirred at ambient temperature during the course of the solvent addition, and then for an additional 4 minutes (until bubbling ceased). The Teflon valve was sealed and the reaction vessel was transferred to a 16 C oil bath on a magnetic stirplate, behind a large blast shield. (WARNING: heating a sealed glass vessel must be done behind appropriate shielding. Performing this experiment using a different temperature, scale, reaction vessel, or modifying any other parameters may be dangerous!) The reaction was stirred at ca. 2 rpm for 9 minutes at 16 C, then allowed to cool to ambient temperature. Once the reaction vessel had reached ambient temperature, the contents were transferred to a 1 ml glass beaker. The reaction vessel was rinsed with two 5 ml portions of xylenes, which were combined with the reaction mixture in the beaker. A large Teflon-coated magnetic stirbar was added, and the mixture was stirred vigorously open to the air for 7 days. The resulting suspension was transferred to 8 5-mL Falcon tubes, using ethyl acetate to rinse the beaker and fill each Falcon tube to the 4 ml mark. The tubes were closed and centrifuged (4 at a time) for 3 minutes at 25 rpm. Then the dark supernatant was discarded, and the tubes were refilled with ethyl acetate up to the 4 ml mark. Then the tubes were resealed and shaken vigorously by hand to re-suspend the precipitate, before being centrifuged again. Each tube was centrifuged a total of 1 times, each time decanting and discarding the supernatant before refilling with fresh ethyl acetate and re-suspending the precipitate. After the 1 th centrifugation, the nearly colorless supernatant was decanted and discarded, and the remaining solids were allowed to air-dry for 1 hours. The resulting paste was then transferred to two glass petri dishes and allowed to air dry until a constant mass was achieved. The product was a fine, light brown powder (21.8 g, 81.5 % yield based on mass of Co incorporated). Analysis by FT-IR (Figure S1) and elemental analysis indicated identity and purity, by comparison to previously reported spectrum and composition Figure S1: FT-IR spectrum of the Co-DPPE catalyst Wavenumber (cm 1 ) 4.4 4

2 Elemental analysis shows 17.1% Co; 8.3% P (ICP-MS) 44.8% C, 4.7% H (CHN) balance assumed to be O (25.1%), and by EDX measurements: 14% Co, 7% P, 22% O, 53% C, balance assumed to be H (4%) (probably over-estimated C content due to background) 2. Selectivity Equation Derivation Selectivity of a product was calculated based on dividing the quantity of carbon of the product of interests by the total carbons from all quantified products. S X (%) = n[x] n TA [TA] + n GA [GA] + n LA [LA] + n GoA [GoA] + n OA [OA] + n FA [FA] 1% where n is the number of carbons of product x, and [x] the concentration of any detectable products. Others: TA: Tartronic Acid, GA: Glyceric Acid, LA: Lactic Acid, GoA: Glycolic Acid, OA: Oxalic Acid, and FA: Formic Acid. In the case for lactic acid: S L.A. (%) = 3[L. A. ] n TA [TA] + n GA [GA] + n LA [LA] + n GoA [GoA] + n OA [OA] + n FA [FA] 1% [L. A. ] S L.A. (%) = n x [x] 1% 3 3. Industrial Crude Glycerol Extraction and Pretreatment: Industrial crude glycerol (Greenleaf Biofuels, LLC) is highly viscous and lacks the conductivity necessary for electrocatalytic reaction. Direct electrocatalytic upgrading would be difficult. Therefore, we herein report a simple pretreatment method that can glycerol efficiently from its crude mixture. 1 g of industrial crude glycerol (Figure S2a) was dissolved in 5 ml of 5 mm sulfuric acid. The mixture was filtered in vacuo through a glass fiber filter (Reeve Angel, USA) twice to remove insoluble organic residues before adding 2 g of sodium hydroxide to create a final concentration of 1. M (Figure S2b). The solution was kept at room temperature until use as shown in Figure S2b. The extracted glycerol was inspected with HPLC-RI for its purity, and only glycerol was found. Figure S2: (a, Left) Crude glycerol from Greenleaf Biofuels. LLC, stored at 4 o C until use. (b, Right) Extracted and filtered glycerol from crude glycerol and is stored at room temperature until use.

3 Product Distribution (mm) Product Distribution (mm) 4. Formic acid Production from Various Conditions Applied Current (ma) Applied Current (ma) Figure S3: (a, Left) Production of formic acid from different current settings, and is complimentary to figure 1 in the manuscript. (b, Right) Production of formic acid from different current settings, and is complimentary to figure 3 in the manuscript. Due to the large concentration difference, graphical data related to formic acid are presented in the ESI to improve clarify of the figures in the manuscript. 5. Procedures for ICP-MS Analysis 2 ml of reaction sample was mixed with 25 ml of aqua regia, solution was stirred for 1 hours and was diluted with 2% nitric acid to 1 liter. Measurements were quantified against external standards of cobalt solution using 1% scandium as internal standard. Detection limit was 1 partper-billion (ppb). Table S1: ICP-MS quantification of cobalt from reaction electrolyte (5 ml) using the same anode repeatedly Trial [Co] in the reaction electrolyte (ppb) Amount of Co leached out from electrode 1 st use ppb.87 µg 2 nd use ppb.29 µg 3 rd use B.D.L. - 4 th use B.D.L. - Pt mesh anode (control) B.D.L. - Note: B.D.L.: Below detection limit, ppb: parts-per-billion = µg L Galvanometric Electrolysis of Glycerol in Divided Cell Anion Exchange membrane (AEM) was purchased from commercial vendor (Membrane International, New Jersey), and was activated in 5% sodium chloride aqueous solution for 12 hours. Activated AEMs were washed and stored in deionized water until use. Working electrode was prepared same way reported in the experimental procedures, and a nickel strip was used as the counter electrode. Both compartments were filled with 1 ml of 1M NaOH, and 24 mg (266 mm) of glycerol was added to the anode compartment. Exposure area for both electrodes were doubled to 2.25 cm 2 (from the standard trials of 1.13 cm 2 ) to compensate for the increase in reaction volume. Electrolysis was performed at 6 C for 15 hours at current density of 1.8 ma cm -2. Samples were taken from both compartments and analysed with analytical techniques reported in the experimental procedure. Table S2: Production distribution (mm) of electrolysis performed in divided cell. Abbreviation: Fara. (%): percent of faradaic efficiency and S-LA (%): Selectivity towards lactic acid Compartment Oxalic Tartronic Glyceric Glycolic Lactic Glycerol Formic Fara. (%) S-LA (%) Anode Cathode

4 Anodic Voltage vs. Hg/HgO (mv) Anodic Voltage vs. Hg/HgO (mv) 7. Control experiment with a Platinum Mesh Electrode Control experiment using platinum mesh working electrode. Reaction was performed with standard procedure described in the experimental section. Table S3: Production distribution (mm) of electrolysis performed using different working electrode in an undivided cell. Abbreviation: Fara. (%): percent of faradaic efficiency and S-LA (%): Selectivity towards lactic acid. Electrode Glycerol int. Current Density Fara. S-LA (mm) (ma cm -2 Oxalic Tartronic Glyceric Glycolic Lactic Glycerol Formic ) (%) (%) Pt mesh * Co-DPPE *Note: current density (ma cm -2 ) is estimated based on geometric area of the Pt mesh electrode (mesh number = 1) 8. Working Electrode Potential Determination and Tafel Studies: Working electrode potential determination: Both experiments were performed in conventional setups using the pre-cut FTO loading with 35 µg cm -2 of Co-DPPE catalyst, and an equal size nickel strip as working and counter electrodes, respectively. A Hg/HgO electrode was used as the reference electrode was placed closely to the working electrode during the reaction. During the reaction run, potential difference between the working and reference electrode was recorded every.2 seconds until the end of the reaction Time (h) Figure S4: Working potential of glycerol oxidation to lactic acid. Reaction was performed with 22 mm of glycerol in 1.M NaOH at 1.8 ma cm -2 at 6 o C for 15 hours Time (h) Figure S5: Working potential glycerol oxidation to glyceric acid. Reaction was performed with 22 mm glycerol in.5m NaOH at 8.8 ma cm -2 at room temperature for 3 hours. Tafel Studies: Stock electrolyte solutions A (.5 M NaOH), B (1. M NaOH), C (.5 M NaOH and 22 mm glycerol), and D (1. M NaOH and 22 mm glycerol) were prepared. Solutions A and C were used as electrolyte for experiments at 23 C while solutions B and D were used as electrolyte for experiments at 6 C. A Pine Bipotentiostat (Model AFCBP1) was used in a three electrode mode. For each experiment a fresh nickel foil electrode was used as the counter electrode, a fresh FTO/glass electrode (1.2 cm x 1.2 cm) with or without 35 µg cm -2 catalyst deposited on the surface as the working electrode, and a Hg/HgO reference electrode. The electrodes were arranged as in the previously described galvanostatic experiments. At each temperature, four experiments were performed: using a bare FTO electrode in electrolyte containing no glycerol (A or C), using a bare FTO electrode in electrolyte containing glycerol (B or D), using a catalyst-laden FTO electrode in electrolyte containing no glycerol (A or C), and using a catalyst-laden FTO electrode in electrolyte containing glycerol (B or D). For experiments at room temperature (23 C): The solution was stirred vigorously and the potential of the working electrode was increased monotonically in 5 mv increments from 3 mv to 12 mv vs Hg/HgO, remaining at each potential for 3 seconds, and recording the current

5 log j (ma cm -2 ) every three seconds. Current density was determined at each potential by averaging the measured current during the last 24 seconds of each 3- second run, and dividing by geometric area of submerged working electrode. (See Table S2 and Figure S5) For experiments at 6 C: An external oil bath with temperature kept at 6 C was used to regulate the temperature of the electrolytic cell. The same procedure for experiments performed at 23 C (described above) was preceded by a 3-minute period with the working electrode held at 3 mv vs Hg/HgO for temperature equilibration, and only potentials up to 9 mv (inclusive) were studied. (See Table S3 and Figure S6) Table S4: Log 1 (current density) in ma cm -2 from experiments performed at 23 C (potential expressed in mv vs Hg/HgO)..5 M NaOH at 23 C Potential No cat. No G No cat. w/g Cat. No G Cat w/g log j = 1.34 log j = mv dec -1 Cat w/g 157 mv dec -1 Cat. No G mv dec -1 No cat. w/g 96 mv dec -1-2 No cat. No G Applied Potential (mv vs Hg/HgO) Figure S6: Tafel plot of 22 mm glycerol oxidation in.5 M NaOH at room temperature (23 C)

6 log j (ma cm -2 ) Table S5: Log 1 (current density) in ma cm -2 from experiments performed at 6 C (potential expressed in mv vs Hg/HgO). 1. M NaOH at 6 C Potential No cat. No G No cat. w/g Cat. No G Cat w/g log j = mv dec Cat w/g 131 mv dec mv dec -1 Cat. No G No cat. w/g -2 log j = mv dec -1 No cat. No G Applied Potential (mv vs Hg/HgO) Figure S7: Tafel plot of 22 mm glycerol oxidation in 1. M NaOH at 6 C 9. References 1. Bloomfield, A. J.; Sheehan, S. W.; Collom, S. L.; Anastas, P. T., Performance Enhancement for Electrolytic Systems through the Application of a Cobalt-based Heterogeneous Water Oxidation Catalyst. ACS Sustainable Chem. Eng. 215, 3 (6), Bloomfield, A. J.; Sheehan, S. W.; Collom, S. L.; Crabtree, R. H.; Anastas, P. T., A heterogeneous water oxidation catalyst from dicobalt octacarbonyl and 1,2-bis(diphenylphosphino)ethane. New J. Chem. 214, 38 (4),