A switchable route to valuable commodity chemicals from glycerol via electrocatalytic oxidation with an earth abundant metal oxidation catalyst

Article abstract of DOI:10.1039/c7gc00371d

Electrocatalytic upgrading of glycerol to value-added commodity is demonstrated using an ultralow loading of a cobalt-based oxidation catalyst at 16 μg cm^-2. Reactions take place under ambient conditions in an aqueous environment, while generating H₂ as a byproduct. Selectivity towards two major products, lactic acid and glyceric acid, can be controlled via simple variation of reaction conditions. The system is scalable and functions well even in the presence of methanol, an impurity commonly found in the industrial bio-diesel waste stream. Industrial glycerol waste from a local bio-diesel plant was also shown to be upgradable after a simple aqueous pretreatment.

Full text of DOI:10.1039/c7gc00371d

View Article Online
View Journal
Green
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: C. H. Lam, A. J.
Bloomfield and P. Anastas, Green Chem., 2017, DOI: 10.1039/C7GC00371D.
This is an Accepted Manuscript, which has been through the
Volume 18 Number
7 7 April 2016 Pages 1821–2242
Royal Society of Chemistry peer review process and has been
accepted for publication.
Green
Chemistry
Accepted Manuscripts are published online shortly after
Cutting-edge research for a greener sustainable future
www.rsc.org/greenchem
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1463-9262
CRITICAL REVIEW
G. Chatel et al.
Heterogeneous catalytic oxidation for lignin valorization into valuable
chemicals: what results? What limitations? What trends?
rsc.li/green-chem

Please do not adjust margins
Page 1 of 11
Green Chemistry
View Article Online
DOI: 10.1039/C7GC00371D
Green Chemistry
ARTICLE
A Switchable Route to Valuable Commodity Chemicals from
Glycerol via Electrocatalytic Oxidation with an Earth Abundant
Metal Oxidation Catalyst
Received 00th January 20xx,
Accepted 00th January 20xx
Chun Ho Lama, Aaron J. Bloomfieldb, and Paul T. Anastas*a,b
DOI: 10.1039/x0xx00000x
Electrocatalytic upgrading of glycerol to value-added commodity is demonstrated using an ultralow loading of
cobalt-based oxidation catalyst at 16 µg cm-2. Reactions take place under ambient conditions in aqeuous
environment, while generating H2 as byproduct. Selectivity towards two major products, lactic acid and glyceric
acid, can be controlled via simple variation of reaction conditions. The system is scalable and functions well
even in the presence of methanol, an impurity commonly found in industrial bio-diesel waste stream. Industrial
glycerol waste from a local bio-diesel plant was also shown to be upgradable after a simple aqueous
pretreatment.
www.rsc.org/
27800,000 tons per year globally, and is expected to rise in the
28future.23 Commercially available lactic acid is produced
1Introduction
29through
a
multi-step anaerobic fermentation of
Homo-26-29
or hetero-catalytic
30carbohydrates.23-25
2
3
4
5
6
7
8
9
As renewable fuel production increases while society seeks
fossil fuel replacements, there is a surplus of by-products
from generating biodiesel, such as glycerol (a by-product
from triglyceride transesterification). Glycerol, named as
one of the top twelve platform chemicals,1 has excellent
potential to be transformed to satisfy shortages in other
chemicals. Recent publications have demonstrated the
heterogeneous transformation of glycerol into a variety of
31transformation of glycerol to lactic acid has been heavily
32sought after in recent years. Beyond lactic acid, glyceric acid
33is another chemical with growing interest. Its D-isomer,
34recently commercialized, is known to be an anti-cirrhosis
31
35agent.30,
Furthermore, glyceric acid is also readily
36oxidizable to tartronic, hydroxypyruvic, and mesoxalic acid,
37all of which have significant medicinal and industrial
38values.15, 17 A recent report on poly(glyceric acid carbonate)
39shows that the polymer exhibits an improved cell
40cytotoxicity profile and excellent biodegradability compared
41to polyacrylic acid.32 However, the current scheme makes
42use of acrylate as the starting material, raising sustainability
43questions as the production of glyceric acid, and
44subsequently poly(glyceric acid carbonate) continues to
45increase.
10commodity chemicals including lactic acid,2-5 methyl
11lactate,6 glyceric acid,7 dihydroxyacetone (DHA),8
12pyridine,9, 10 propylene glycol,11-14 and many others that are
13noted in recent reviews.15-19 However, many of these
14transformations typically require the use of a stoichiometric
15oxidant, pressurized vessels and/or precious metals. While
16precious metals are known to be resilient against oxidative
17dissolution, their use challenges the notion of sustainability.
18Further, recent reports have demonstrated that while earth
19abundant metal oxides can be viable catalysts for lactic acid
46Driven by the Principles of Green Chemistry33-35 and a
47growing supply of renewable electricity, we explored
48electrocatalysis as a novel alternative to conventional
49hydrothermal upgrading of glycerol to lactic acid.24
20production via glycerol, these processes also require high
21pressure and temperature,
22challenges.
20-22
also posing sustainability
50Compared to
a
batch type pressurized system,
23Lactic acid has long been recognized as an important
24platform chemical in the bio-based chemical economy.23 For
25example, production of polylactic acid (PLA) from lactic
26acid, one of its best developed applications, has reached
51electrocatalysis has several features that appeal to the green
52chemist. First, it typically operates at atmospheric pressure,
53below the boiling point of the electrolyte, which is water in
54most cases. Second, its heterogeneous nature allows facile
55separation of products from the catalyst, making it adaptable
56for flow style, high volume production. Third,
57electrocatalysis achieves redox conversion with electricity,
58effectively bridging the gap between renewable and
59chemical bond energy. Considering that the high- energy
60cost of hydrothermal catalysis is usually paid with fossil
61energy, electrocatalysis is promising as a more efficient and
a.School of Forestry and Environmental Studies, Center for Green Chemistry and
Green Engineering, Yale University, New Haven Connecticut 06511 USA. E-mail:
paul.anastas@yale.edu; Tel.: +1 203-432-5215
b.Department of Chemistry, Yale University, 225 Prospect Street, New Haven,
Connecticut 06520 USA
† Details of any supplementary information available. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 2017
Green Chem., 2017, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 2 of 11
ARTICLE
Green Chemistry
62sustainable practice by reducing the overall energy demand,
63and subsequent adverse impacts. As such, electrocatalysis
64has gained interest in recent years.36-43 Although
65electrocatalytic oxidation of glycerol has been previously
66investigated by several authors,44-47 all of them employed
67working electrodes that are made of precious materials such
68as gold, palladium, platinum, or doped-diamond. While these
69studies were useful in understanding the redox behaviour of
70glycerol, these rare metal electrodes are less attractive when
71considered for larger scale application. Thus, we developed
72and evaluated a scalable strategy that employs a cobalt-based
73oxidative catalyst, bypassing the need for precious metals.
74Further, the presence of the cobalt catalyst improves the
75selectivity and reduces the energy requirement for lactic acid
76formation.48
105possible after a simple pre-treatment with dilute aqueous
View Article Online
DOI: 10.1039/C7GC00371D
106acid.
107Experimental
108Electrode Preparations
109All reagents were used as received. The Co-DPPE catalyst
110was prepared according to procedures documented in
111previously reported literature49, 50 (a detailed description of
112catalyst synthesis and yield are reported in the ESI.) The
113deposition of Co-DPPE catalyst on a fluorine-tin-oxide
114(FTO) electrode (Aldrich, USA) was achieved as follows:
1155.4 mg of the catalyst was suspended in 15 mL of ethyl
116acetate and then sonicated for 30-minute prior to use. One
117aliquot of 0.1 mL of the catalyst solution, measured by
118mechanical pipette, was applied on the surface of a FTO
119electrode (1.5 x 1.5 cm) to give a loading density of 16 µg
120cm-2. After ethyl acetate evaporated, half of the FTO
121electrode was submerged in the reaction electrolyte
122(exposure area: 1.13 cm2). A nickel metal strip with the same
123exposure area was used as cathode (counter electrode) for the
124reaction. Unless specified otherwise, all reactions were
125performed under galvanostatic conditions using a D.C.
126power supply (B&K Precision 1739) in 5.0 mL of
127electrolyte, stirred at 200 rpm, and reaction time was set to
128deliver one equivalent of electrons assuming reaction
129proceeds with perfect Faradaic efficiency to form lactic acid.
130Reactions error bars were calculated from results of
131triplicates. All reaction samples were frozen until analysed.
77If oxidation of glycerol to glyceraldehyde can be achieved
78electrocatalytically in an alkaline environment, then the
79subsequent conversion of glyceraldehyde to lactic acid could
80take place in-situ to afford lactic acid in a one-pot, two-step
81reaction sequence as shown in Eq. 1. In addition to glycerol
82oxidation, hydroxide anion is expected to undergo oxidation
83to form water and O2 in the strong alkaline environment (Eq.
842). On the cathode (the counter electrode), where reduction
85takes place, water is reduced to form hydroxide anions and
86hydrogen gas (Eq. 3). Combination of Eq. 1-3 yields the net
87reaction that shows glycerol oxidation using only water as a
88reagent and generating O2 and H2 as by-products (Eq. 4).
89
90
Anode (Working Electrode)
132Analysis
Eq. 1
133All samples were analysed by high performance liquid
134chromatography equipped with photodiode array detector
135and reflective index detector (Shimadzu) using HPX-87H
136column (Aminex, Bio-Rad) at 50.0 °C. Eluent was 5 mM
137sulfuric acid in water running isocratically at 0.6 ml min-1.
138All samples were diluted in half with 20 mM of propylene
139glycol (internal standards) prior to analysis. Control
140experiments showed propylene glycol was not formed in any
141tested conditions.
Eq. 2
Cathode (Counter Electrode)
Eq. 3
Overall Reaction:
Eq. 4
91
92Note: reactants and products are drawn in their neutral forms to improve clarity.
142Results and Discussion
93
143Towards Selective Production of Lactic Acid
94In this work, we report a switchable selective process to
95convert glycerol to different products, lactic and glyceric
96acid, using a nanoparticulate material formed from dicobalt
97octacarbonyl and 1,2-bis(diphenylphosphino)ethane (Co-
98DPPE) as the electrocatalyst.49, 50 This catalyst works well in
99an alkaline environment, and can withstand the presence of
100methanol. In addition to the aforementioned merits of green
101chemistry and system robustness, selectivity between the
102major products, lactic or glyceric acid, can be controlled by
103simple alterations of reaction conditions. Transformation of
104crude industrial glycerol waste to desired products was also
144Selectivity towards the formation of lactic acid was
145systematically investigated by changing three parameters:
146alkalinity, current density, and temperature. Five products:
147lactic acid, glyceric acid, glycolic acid, oxalic acid, and
148formic acid were formed consistently in variable amounts
149depending on system conditions, while traces of tartronic
150acid were occasionally detected, as shown in Scheme 1.
151From Table 1, it appears that strong alkalinity and high
152temperature favour lactic acid production. Although 3.0 M
153NaOH(aq) gave the highest selectivity for lactic acid (S-L.A.),
2 | Green Chem., 2017, 00, 1-3
This journal is © The Royal Society of Chemistry 2017
Please do not adjust margins

Page 3 of 11
Green Chemistry
Please do not adjust margins
Green Chemistry
ARTICLE
154the modest 5% increase in S-L.A. was not sufficient to
155warrant the extreme alkalinity (entries 3 and 4).
194but dropped noticeably when the current density reached
View Article Online
19544.2 mA cm-2. Based on the slightlyDlOoIw: 1e0r.10c3a9r/bCo7nGCb0a0la37n1cDe
196shown in Figure 2, it is possible that formic acid was
197oxidized to CO2.
156Furthermore, similar enhancement was observed by
157lowering the current density further to 13.3 mA cm-2, a
158preferable strategy to increasing alkalinity for optimizing
159lactic acid selectivity. To further understand the role of
160current in relation to lactic acid’s selectivity, a series of
161experiments with variable current settings were conducted
162with the other two parameters, temperature and alkalinity,
163held constant at 60 °C, and 1.0 M NaOH(aq), respectively.
50
45
40
35
30
25
20
15
10
5
Oxalic
Glycolic
Glyceric
Lactic
164
165Scheme 1: Reaction scheme of electrocatalytic oxidation of glycerol to value-
added products
0
44.2 22.1 13.3
8.8
4.4
1.8
1.3
Current Density (mA cm-2)
166
198
199Figure 1: Production distribution in different current (working electrode area: 1.13
200cm2). All reactions were performed in 250 (±10) mM of glycerol dissolved in 5 mL
201of 1 M NaOH(aq) at 60 (±3) °C. Note: remaining glycerol and formic acid are not
202shown here for clarity (See ESI, figure S3a). Reaction time courses varied to
203normalize charge delivery.
167Table 1: Preliminary experiments exploring the effect on various parameters on
168selectivity towards lactic acid. Note: electrode working area: 1.13 cm2, reaction
169times were varied to ensure net charge passed was the same for all reactions.
170Legend: C Bal.: carbon balance, and S-L.A.: lactic acid’s selectivity
Current
NaOH(aq) Temp. C Bal.
Conv.
(%)
S-L.A.
(%)
Density
(mA cm-2)
44.2
44.2
22.1
22.1
22.1
13.3
13.3
(M)
(°C)
(%)
120%
100%
1
2
3
4
5
6
7
1.0
1.0
1.0
3.0
0.5
1.0
1.0
RT
60
60
60
60
60
40
78
91
82
75
96
67
83
31
27
32
34
15
42
34
7
8
S-G.A.
S-L.A.
C Bal. (%)
% Fara.
80%
60%
32
37
15
34
16
40%
20%
0%
171
44.2
22.1
13.3
8.8
4.4
1.8
1.3
Current Density (mA cm-2)
172As shown in Figure 1, formation of lactic acid increases as
173the current drops until current density j = 1.8 mA cm-2
174(current = 2.0 mA). The data suggest that slower oxidation
175rates favour lactic acid formation. Interestingly, lactic acid
176production drops for current densities below 1.8 mA cm-2,
177perhaps due to the lack of anodic potential to oxidize the
178glycerol efficiently. Glyceric acid, on the other hand,
179displays an opposite trend and is formed with greater
180selectivity with increasing current density. Control
181experiments show that glyceric acid was not converted to
182lactic acid under experimental conditions, and only traces of
183pyruvic acid was observed if lactic acid was subjected to
184reaction conditions alone. The amount of glycolic acid
185appears to be constant throughout all current settings; its
186steady state nature suggests its role as an intermediate
187chemical of the overall reaction pathway. Less oxalic acid
188was found at the higher current setting as expected, as it is
189known to be oxidizable to CO2 at higher applied potential or
190current.51 Approximately 50 mM of formic acid was also
191observed in the reaction, but was omitted from Figure 1 for
192clarity (See ESI, figure S3a). Interestingly, the amount of
193formic acid increased steadily similar to that of glyceric acid
204
205Figure 2: Selectivity (%) to lactic (S-L.A.) and glyceric acid (S-G.A.), and Faradaic
206efficiency analysis (% Fara.) at different current density. All reactions were
207performed in 250 (±10) mM of glycerol dissolved in 1 M NaOH (aq) at 60 (±3) °C.
(푚표푙푃푟표푑 ×퐹 ×푛)
퐹. 퐸. (%) =
Eq. 5
퐶푡표푡푎푙
208where MolProd = moles of product formed. F = Faraday's constant, 96485 C mol-1, n
209= number of electrons per reaction, and Ctotal = total charge passed
210Eq. 5 calculates the Faradaic efficiency, which accounts for
211the amount of charge spent on glycerol oxidation. As
212expected, Faradaic efficiency is inversely related to current
213density, with more non-productive, competing side reactions
214(such as water oxidation or over-oxidation of organic
215species) at greater current densities. Another contributor,
216though less significant as evidenced by the consistency of the
217carbon balance, is that since oxalic acid is vulnerable to
218oxidization to CO2, the apparent losses in Faradaic efficiency
219may also be unaccounted current spent on forming CO2.
This journal is © The Royal Society of Chemistry 2017
Green Chem., 2017, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 4 of 11
ARTICLE
Green Chemistry
[푃푟표푑. ]
245Another series of variable current density experiments were
View Article Online
(
)
푆푃푟표푑. % =
×100%
DOI: 10.1039/C7GC00371D
246conducted in 0.5 M NaOH(aq) and room temperature to verify
Eq. 6
푛
3
푥 [푥]
∑
247the two proposed reaction pathways suggested above.
248Interestingly, it was found that the new conditions improved
249production of glyceric acid at the expense of lactic acid.
250Compared to Figure 2, selectivity of glyceric acid nearly
251doubled (32% to 58%; see j = 44.2 mA cm-2 on Figure 2 and
252Figure 4, respectively), suggesting both temperature and
253alkalinity were important to the selectivity switch. A small
254amount of lactic acid was still detected at j = 4.4 mA cm-2 as
255shown in Figure 3 and Figure 4, which was not surprising
256since low current promotes lactic acid production. We
257speculate that selectivity toward lactic acid is actually
258controlled kinetically through the oxidation rate. As
259mentioned above, glyceraldehyde can readily rearrange to
260lactic acid under ambient alkaline condition, and thus it is
261logical that low oxidation rate would give glyceraldehyde
262more time for the rearrangement (vide infra), while higher
263current would favour formation of glyceric acid, the direct
264oxidation production of glyceraldehyde.
220where [Prod.] is the concentration of the product of interest, nx is the number of
221carbons in the product x, and [x] the concentration of any detectable products.
222Selectivity for lactic and glyceric acid was calculated with
223Eq. 6. As shown in Figure 2, these products display opposite
224trends in behaviour: glyceric acid formation is favoured at
225high current while more lactic acid is favoured at low
226current, suggesting that the two products result from
227competing pathways. Knowing that both chemicals are
228readily obtainable from reactions of glyceraldehyde, and that
229glyceric acid is not a precursor to lactic acid, it appears that
230product selectivity reflects the fate of first-formed
231glyceraldehyde.
232Towards Selective Production of Glyceric Acid
40
35
30
265Based on Figure 4 alone, 22.1 mA cm-2 would have been
266assigned as the ideal current density based on selectivity or
267Faradaic efficiency. However, it was noticed that the
268electrolyte at those currents turned brown soon after
269prolonged electrolysis – a sign of corrosion that was not
270found in lower current settings. Also, the Faradaic
271efficiencies at those current settings were lower due to water
272competing for oxidation. Hence, 8.8 mA cm-2, the lowest
273current setting without formation of lactic acid, was chosen
274as the optimal current setting for glyceric acid production.
Lactic
Tartronic
Oxalic
Glycolic
Glyceric
25
20
15
10
5
0
44.2
22.1
13.3
8.8
4.4
Current Density (mA cm-2)
233
275Tafel Plot Studies
234Figure 3: Product distribution in different current (working electrode area: 1.13
235cm2). All reactions were performed in 250 (±10) mM of glycerol dissolved in 0.5 M
236NaOH(aq) at 20 (±3) °C, and stirred at 200 rpm. Note: reaction durations vary based
237on the current setting to ensure the same amount of charge (C) is passed through
238for all reactions. Remaining glycerol and formic acid are not shown here for clarity
239(See ESI, figure S3b).
276In order to better understand the role of the catalyst and the
277extent of competing water oxidation reactions under the
278optimized conditions for both lactic acid and glyceric acid,
279Tafel plots were generated using a 3-electrode setup.
280Experiments relevant to lactic acid production (Figure 5a)
281were run with 1.0 M NaOH(aq) and at 60 °C over a potential
282range of 300–900 mV with respect to the Hg/HgO reference
283electrode (1.33–1.73 V vs. RHE). Control experiments
284revealed that the averaged optimal current density for lactic
285production (j = 1.8 mA cm-2) corresponded to a working
286potential of 558 ± 40 mV vs. Hg/HgO (See ESI). In
287experiments performed with the catalyst at a potential of 550
288mV vs. Hg/HgO, the current density was over 100 times
289greater in the presence of glycerol than without glycerol
290(Figure 5a), indicating that the current is generated almost
291exclusively from Faradaic reaction of glycerol, which is
292consistent with the near-unity Faradaic yields of lactic acid
293produced under optimal conditions. Overpotentials for both
294glycerol and water oxidation reactions are substantially
295decreased by the presence of the catalyst, supporting the
296notion that the Co-DPPE catalyst is critical to the energy
297efficiency of the process.
100%
80%
S-G.A.
S-L.A.
% Fara.
C Bal. (%)
60%
40%
20%
0%
44.2
22.1
13.3
8.8
4.4
Current Density (mA cm-2)
240
241Figure 4: Selectivity (%) to lactic (S-L.A.) and glyceric acid (S-G.A.), and Faradaic
242efficiency analysis (% Fara.) at different current density. All reactions were
243performed in 250 (±10) mM of glycerol dissolved in 0.5 M NaOH (aq) at 20 (±3) °C,
244and stirred at 200 rpm.
298Experiments performed in 0.5 M NaOH(aq) at 25 °C (Figure
2995b) indicated a significant amount of water oxidation as a
300side reaction at the higher applied potential of 1100 mV,
4 | Green Chem., 2017, 00, 1-3
This journal is © The Royal Society of Chemistry 2017
Please do not adjust margins

Page 5 of 11
Green Chemistry
Please do not adjust margins
Green Chemistry
ARTICLE
301which is the optimized working potential for glyceric acid
302production. At this potential, the presence of glycerol results
303in current densities nearly identical to those measured in the
304absence of glycerol, which is in agreement with the observed
305Faradaic efficiency for glyceric acid production from Figure
3064.
307In the absence of catalyst, there is a clear change in the nature
308of the electrochemical reactions when the oxidizing potential
309is increased above 900 mV in Figure 5b. At lower potentials
310glycerol oxidation proceeds, and begins to plateau around
311700 mV, before the current density increases again as water
312oxidation becomes a significant competing reaction. In the
313presence of catalyst, this transition is less apparent, but can
314be inferred by comparison of current density in the presence
315and absence of glycerol. At high potentials, the glycerol-free
316current densities surpass those observed in the presence of
317glycerol, most likely due to the increased viscosity of the
318glycerol solution, which is more significant with reduced
319ionic strength and lower temperature.
335mechanisms. However, analysis of the product distributions
View Article Online
DOI: 10.1039/C7GC00371D
336in Figure 1-4 indicated production of glyceric acid across a
337wide range of current densities (and therefore potentials).
338The product distributions also indicated the pathways to
339glyceric acid exist across the range of examined potentials,
340and it does not suggest that there is a sudden change in
341selectivity at the increased potential. The mechanism of
342water oxidation appears to be different in the presence of
343catalyst vs. in the absence of catalyst (FTO alone). At room
344temperature, the Tafel slope changes from 157 mV decade-1
345in the absence of catalyst, to 59 mV decade-1in the presence
346of catalyst, while at 60 °C, the shift is less dramatic, only
347changing from 69 to 64 mV decade-1 (see ESI). Because of
348the much shallower slopes, and competing water oxidation
349reaction, this analysis is not as clear cut for glycerol
350oxidation. However, it is possible that there is a similar
351change in mechanism for glycerol as well.
352Mechanistic Insight
Glycerol
Formic
2
250
200
150
100
50
200
150
100
50
log j = 0.68
1.5
1
0.5
0
0
0
0
6
12 18 24 30 36 42 48
Time (h)
0
6
12 18 24 30 36 42 48
Time (h)
-0.5
-1
Cat w/G
Cat. No G
No cat. w/G
No cat. No G
log j = -1.61
Lactic
Glyceric
80
60
40
20
0
10
-1.5
-2
8
6
4
2
0
300
500
700
900
Applied Potential (mV vs Hg/HgO)
320
2
1.5
1
0
6
12 18 24 30 36 42 48
Time (h)
0
6
12 18 24 30 36 42 48
Time (h)
log j = 1.34
Oxalic
Glycolic
40
30
20
10
0
12
10
8
6
4
log j = 1.27
0.5
0
-0.5
-1
2
0
Cat w/G
Cat. No G
No cat. w/G
No cat. No G
0
6
12 18 24 30 36 42 48
Time (h)
0
6
12 18 24 30 36 42 48
Time (h)
-1.5
-2
353
Glycerol Converted
C Bal. (%)
% Fara
S-L.A.
300
500
700
900
1100
100%
80%
60%
40%
20%
0%
Applied Potential (mV vs Hg/HgO)
321
322Figure 5a and b: Tafel plot studies of 220 mM under optimized conditions for lactic
323(top, a) and glyceric acid (bottom, b) production. Working electrode area is roughly
3240.70 cm2, Cat.: with catalyst, No cat.: with catalyst, w/G: with glycerol, No G: no
325glycerol.
326The presence of glycerol consistently improves the current
327output at any voltage setting under reaction conditions that
328are not limited by mass transfer. This indicates that at low
329potentials glycerol is directly oxidized at the anode rather
330than anodic production of hydroxy radical (• OH) or other
331oxidizing species which subsequently react with the
332glycerol. At higher potentials, where current densities are
333similar in the presence or absence of glycerol, we cannot rule
334out the possibility of other contributing or even dominant
0
1
2
3
4
5
6
8
10
24
48
Time (h)
354
355Figure 6: A 48-hour kinetic experiment of electrocatalytic oxidation of glycerol,
356each substrate is expressed individually to improve clarity. Reaction was performed
357in 20 ml of 251 mM of glycerol in 1 M NaOH(aq) at 60 °C at 1.8 mA cm-2, and stirred
358at 400 rpm.
This journal is © The Royal Society of Chemistry 2017
Green Chem., 2017, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 6 of 11
ARTICLE
Green Chemistry
359In a 48-hour kinetic experiment shown in Figure 6,
360concentrations of lactic and formic acids increase steadily for
361the first 24 hours, and begin to level off afterwards. Similar
362trends are observed for glyceric and glycolic acid but their
363level-off behaviours are more apparent. Oxalic acid is not
364detected until the 5th hour, and its late stage appearance
365confirms its role as an end product before it becomes CO2.
366Also, oxalic acid shows no signs of reaching plateau,
367suggesting its conversion to CO2 may be a slow step.
368S-L.A. remains constant throughout the reaction, which
369suggests its formation might be independent from other
370products. Faradaic efficiency (% Fara.) of organic
371transformation starts from zero and peaks at the 8th hour. The
372trend is unexpected as it is more common for Faradaic
373efficiency to start high and then exhibit an exponential decay
374behaviour.52
View Article Online
DOI: 10.1039/C7GC00371D
413
414Scheme 2: proposed mechanism of electrochemically oxidation of glycerol to
415various products. Detected products are framed. All chemicals were drawn in their
416neutral states for clarity purposes.
417Glycerol did not react in the absence of current, which
418indicates electrocatalytic oxidation is imperative in the
419whole reaction scheme. Also, no DHA but traces of
420glyceraldehyde were detected occasionally suggesting
421glyceraldehyde might be the only initial product from
422glycerol oxidation, and the dehydration must have taken
423place rapidly tautomerization could take place. The rapid
424rearrangement step was confirmed by subjecting
425glyceraldehyde and DHA each to the experimental
426conditions individually. Shortly after introduction of the
427sodium hydroxide electrolyte, both reaction mediums
428changed colour from colourless to yellow to dark brown,
429suggesting the occurrence of aldol condensation. In both
430cases, the starting material was converted completely,
431producing a small amount of lactic acid and significant
432amounts of oligomeric condensation products. Therefore, in
433a retrospect, the healthy carbon balance shown in Figure 2
434and Figure 4 serves as a preliminary indicator showing
435rearrangement to lactic acid must have occurred rapidly
436before condensation could take place. TEMPO-mediated
437oxidation of glycerol, through a single electron transfer
438mechanism, was known to form DHA and beta-
439hydroxypyruvic acid (β-HPA) at prolonged reaction time55.
440However, the absence of β-HPA in our control experiment
441was perhaps due to the rapid rearrangement to lactic acid and
442condensation of DHA. Therefore, we found the control
443experiment of DHA formation remained inconclusive.
4441,2-Propanediol was not observed in the product mixture,
445suggesting the 2-oxopropanal reacted with the hydroxide
446anion before hydrogenation on the cathode.11 Also, a control
447experiment conducted in a divided cell using an anion
448exchange membrane did not affect formation of lactic acid,
449confirming the counter electrode played no direct role for the
450chemical transformation (see ESI, Table S2). In another
451control experiment with a platinum working electrode, the
452selectivity towards lactic acid was significantly lower, along
453with more glyceric and formic acid formed. The result
454suggested platinum favoured over-oxidized products
455compared to the Co-DPPE catalyst. The Faradaic efficiency
456was also lower with the platinum working electrode,
457showing the water oxidation has consumed part of the
458faradaic electrons. It could also be due to the loss of CO2,
375The slow initial rise in Faradaic efficiency may reflect the
376fact that formation of glyceraldehyde from glycerol is
377thermodynamically uphill, and thus the system initially may
378prefer water splitting in preference to oxidizing glycerol. As
379the reaction progresses, more readily oxidizable products
380such as glyceraldehyde, glyceric acid and tartronic acid are
381formed, leading to a steady rise in Faradaic efficiency. The
382drop in both carbon balance (C. Bal %) and Faradaic
383efficiency at later stages is likely due to the escape of CO2.
384Since CO2 was not captured in the experiment, its carbon
385count and the electrons that were spent on its formation were
386essentially lost. Another possible reason is that as the
387reactant concentration falls, electrode voltage rises and splits
388water to generate enough Faradaic reactions to maintain the
389pre-designated current setting. Last but not least, it is also
390possible that oxidized products such as oxalic acid, could be
391reduced back to glycolic acid at the cathode, as confirmed by
392control experiment, and lowered Faradaic efficiency. These
393scenarios are consistent with various experimental
394observations and control experiments, and thus it is not
395inconceivable that they all contributed to the decline.
396Piecing together all the mechanistic fragments, we postulate
397formation of lactic acid begins with glycerol oxidization to
398glyceraldehyde, which dehydrates to form
2-
399hydroxypropenal, which tautomerizes, and then goes
400through a benzilic acid rearrangement to form lactic acid as
401shown in Scheme 2.53 Instead of rearranging to lactic acid,
402glyceraldehyde can be further oxidized to glyceric acid.
403Further, oxidization at the 3-carbon leads to tartronic acid,
404which can decarboxylate to become glycolic acid. Glycolic
405acid can be then oxidized to oxalic acid. Further oxidation of
406oxalic acid leads to CO2 as shown in Scheme 2. Attempts
407were made to quantify the CO2 released, but the effort was
408complicated by the mixture of H2 and O2 evolving from both
409electrodes, as well as the high solubility of CO2 in alkaline
410medium. When oxalic acid is subjected to the reaction
411conditions, traces of glycolic acid were detected confirming
412it was reducible electrocatalytically.54
6 | Green Chem., 2017, 00, 1-3
This journal is © The Royal Society of Chemistry 2017
Please do not adjust margins

Page 7 of 11
Green Chemistry
Please do not adjust margins
Green Chemistry
ARTICLE
459which electrons are not accounted for, resulted from oxalic
460acid oxidization (see ESI, Table S3).
515shown in Figure 7, as it favours over-oxidized products,
View Article Online
DOI: 10.1039/C7GC00371D
516turning glyceraldehyde to glyceric acid instead of allowing
461Coupled with observations from other control experiments,
462it appears that once glyceraldehyde is dehydrated, it enters a
463chemically rapid pathway to become lactic acid. If
464glyceraldehyde is oxidized before reacting with base, it
465enters the detour and becomes glyceric acid, which
466eventually becomes formic acid or CO2 as confirmed by
467control experiments. Based on our findings, we conclude that
468the dehydration step between glyceraldehyde and 2-
469hydroxypropenal was the critical step to favour selectivity
470for lactic acid. This explains why elevated temperature and
471high alkalinity favour lactic acid production, while the
472opposite conditions favour glyceric acid. Although the
473current setting plays no direct role in the dehydration step, it
474determines the oxidation rate, and the time window in which
475glyceraldehyde dehydrates before being oxidized. At low
476current, glyceraldehyde has more time to undergo
477dehydration to 2-hydroxypropenal, while higher current
478leads to oxidation to glyceric acid. These mechanistic
479insights guide the manipulation of product distribution by
480simple variation of reaction conditions.
517to rearrange to lactic acid.
Oxalic Glycolic Lactic Glyceric
Oxalic Glycolic Lactic Glyceric
40
40
20
20
0
0
1st
2nd 3rd
4th
32 µg 16 µg 8 µg No cat.
518
519Figure 7: (a, left) Comparison of product distribution from a recycled electrode, and
520(b, right) an electrodes loaded with different amount of catalyst (right)
60
Blank (FTO)
Before reaction (6x cat. loading)
After NaOH treatment overnight
After reaction (6x cat. loading)
50
40
30
20
10
0
481Catalyst Recyclability
0
0.2
0.4
0.6
0.8
1
Voltage (vs. Ag/AgCl)
-10
482Catalyst durability was examined by recycling the working
483electrode multiple times under standard reaction conditions.
484Post-reaction electrolytes analysed by ICP-MS revealed 0.87
485µg and 0.29 µg of Co were found in the electrolyte after the
4861st and 2nd experiment, respectively (note: 40.5 µg of catalyst
487was applied on the surface of the working electrode, and 16.8
488% of which was Co, which yields 6.8 µg). For the remaining
489two runs, Co concentration was below detectable levels.
490Seeing that the detected amount from the 2nd run was almost
491half of that of the first, we speculated that catalyst losses
492might follow an exponential decay pattern. To probe this
493hypothesis, electrodes loaded with different amounts of
494catalyst, 32 µg, 16 µg, 8 µg and no catalyst, were examined.
495Surprisingly, the overall product distribution between the
496two sets of experiments matched reasonably well, as shown
497in Figure 7.
521
522Figure 8: Cyclic Voltammetry analysis (scan rate = 50 mV s-1) of working electrode
523before and after 15 hours of electrolysis with 6x catalyst loading under standard
524reaction condition: constant current electrolysis at 2 mA (current density j = 1.8 mA
525cm-2) at 60 °C in 1.0 M aqueous sodium hydroxide solution.
526To further probe the catalyst durability, a separate electrode
527overloaded with six times of the normal amount was
528examined in its pre- and post- reaction with cyclic
529voltammetry (CV). In another experiment, 25 mg of the Co-
530DPPE catalyst was treated with 1 M NaOH(aq) at 60 °C for
53124 hours, and then examined with CV. As shown in Figure 8
532the overpotential for water oxidation did not change
533significantly, which confirms the catalyst’s robustness in the
534described experimental conditions.
498However, the differences in product distribution arising from
499varying catalyst loading was unexpected. Production of
500glycolic and formic acid was almost constant throughout the
501four trials, while glyceric and oxalic acid exhibited rising and
502declining trends, respectively, as the catalyst loading
503decreased. Lactic acid, unlike the other four products,
504reached the highest amount when the electrode was used for
505the 2nd time, or the surface was loaded with 16 µg of catalyst.
506The shift in product selectivity most likely resulted from the
507change in working potential which results from the catalyst
508dislodgement. As Figure 5a and b show, the presence of
509catalyst significantly decreases the overpotential required to
510maintain a given current density. Therefore, under constant
511current electrolysis, the electrode without catalyst must
512operate at a higher working potential to support the required
513faradaic current. This higher working potential is responsible
514for the shift in selectivity from lactic to glyceric acid as
535Influence of Methanol and Application on Crude Glycerol
536Transesterification using methanol is broadly practiced in the
537bio-diesel industry and so methanol impurity is therefore
538generally found in the glycerol waste stream. Thus, the two
539optimized conditions for lactic acid and glyceric acid
540production were examined in the presence of methanol,
541which are denoted as LA-M and GA-M, respectively.
542Interestingly, lactic acid production was not hindered by the
543presence of methanol, but its selectivity dropped as a result
544of accumulation of other products. Comparing trial LA and
545LA-M, the lowered yield of oxalic acid and conversion of
54641% of the methanol to formic acid suggests that methanol
547obstructs the oxidation path from glyceric to oxalic acid, but
548not that of glycerol to glyceraldehyde. We attribute the
549preferences to the differences in surface concentration of
550these reactants rather than their chemical properties, because
This journal is © The Royal Society of Chemistry 2017
Green Chem., 2017, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 8 of 11
ARTICLE
Green Chemistry
551both glycerol and methanol are at
a
much higher
591actual waste stream into a set of valuable products under mild
View Article Online
DOI: 10.1039/C7GC00371D
592conditions is highly encouraging, especially when knowing
552concentration than that of glyceric acid. When reaction was
553performed at a larger volume, 20 ml (trial LA*), selectivity
554toward both reaction products remained essentially
555unchanged, showing that the system is likely scalable.
556At room temperature and higher currents, the reaction
557produced lactic acid-free products as expected. More
558importantly, methanol had no noticeable impact on product
559distributions. Given that only 7% of methanol was oxidized,
560it is safe to conclude that methanol is more vulnerable at
561elevated temperature, which is in agreement with other
562oxidative studies conducted on well-defined precious metal
563surfaces.56 The lower alkalinity could also be a contributing
564factor since the pKa of methanol is higher than any of the
565organic acids present (the pKa of glycerol and methanol are
56614.15 and 15.54, respectively57). As such, the unionized
567methanol may not be as attractive to the positively charged
568anode, and thus not as competitive for oxidation.
593formic acid could be useful for other renewable feedstocks,
594such as lignin, processing.58
595Conclusion and Outlook
596We have described a mild electrocatalytic system to convert
597glycerol to lactic and glyceric acid with tuneable selectivity
598between the desired products via alteration of the system
599conditions. Under atmospheric pressure, lactic acid can be
600made at 60 °C at a relatively low current density (j = 1.8 mA
601cm-2), while glyceric acid can be made at room temperature
602at higher current density of (j = 8.8 mA cm-2). The system
603also functions well in the presence of methanol, and more
604importantly, is able to convert crude industrial glycerol to
605desired and anticipated products. Such robustness and
606flexibility could be advantageous in large-scale
607manufacturing where setup alternations are costly and
608burdensome.
609Compared to the present route for lactic acid production
610through anaerobic fermentation of carbohydrate, this
611glycerol upgrading protocol is simpler: 1) it can operate in a
612one-pot setting or in the presence of a separator if needed;
613and 2) the Co-DPPE catalyst can be prepared in large
614quantity and is easy to apply and handle. However, even
615though crude glycerol can be obtained for low to no cost as
616a (waste) byproduct from biodiesel production, the use of 1
617M sodium hydroxide demands a cost-effective neutralization
618scheme. While the necessary neutralization of the final
619effluent is beyond the scope of this paper, there are
620approaches that relay on abundant and inexpensive waste
621materials that could be explored.59-61 The outcomes
622presented here by no means represent a standalone operation.
623However, the robust, simple upgrading strategy to convert
624crude glycerol waste into other useful commodity chemicals
625could be the important piece to the sustainable bio-refinery
626picture when integrated appropriately.
569
570Table 2: Constant current electrolysis of 5 ml of glycerol under optimized
571conditions in the presence of 0%, 10% (v./v.) of methanol (-M), and pre-
572treated industrial crude glycerol (-C). *reaction volume was 20 ml. **reaction
573was also performed in 20 ml and medium was same as that of LA-C but
diluted in half with deionized water. N.F.: Not Found
LA
LA-M
LA*
LA-C*
GA
GA-M
GA*
GA.C**
Reaction Settings
Current density
(mA cm-2)
1.8
8.8
Temperature (°C)
NaOH(aq) (M)
Reaction time (hour)
MeOH (%)
Initial MeOH (M)
Final MeOH (M)
Decrease of MeOH (%)
Initial glycerol (mM)
Products Yield (mM)
Oxalic
60
1.0
20
0.5
15
48
-
-
-
-
24
N.F.
-
-
-
3
6
6
-
-
-
-
10
2.44
1.43
41
-
-
-
-
10
2.47
2.30
7
-
-
-
-
N.F.
-
-
-
243
232
266
135
238
229
229
64
5.8
-
2.5
0.7
22.7
-
21.4
0.9
2.8
0.9
14.3
8.7
-
0.7
12.1
8.6
0
0.8
43.9
29.2
-
-
-
Tartronic
Glyceric
Glycolic
Lactic
Glycerol (remain)
Formic
3.8
9.4
22.4
157.2
50.2
12.4
13.7
22.6
153.7
83.7
12.8
14.8
66.4
49.2
12.9
12.8
32.1
20.3
93.3
10.8
14.9
-
-
-
169.5
21.9
167.6
24.3
87.7
145.4
10.1
43.9
143.4
Analytics (%)
Carbon balance
Conversion
87
35
105
34
78
82
94
85
84
29
85
27
72
69
71
84
Selectivity (%)
Lactic (S-L.A.)
Glyceric (S-G.A.)
43
7
31
17
44
8
32
13
-
48
-
46
-
47
-
31
574
627Although electrochemistry enables reaction transformations
628under mild condition, it does so at the expense of a long
629reaction time. The current setting, which corresponds to
630reaction rate, is often limited by the presence of oxidizable
631solvent, water in this case. However, this phenomenon can
632potentially be circumvented by the ongoing development of
575Under the optimized conditions, the pre-treated crude
576glycerol (see ESI for the pre-treatment procedures) was
577converted to the anticipated products. Formic acid was
578formed predominantly in both LA-C and GA-C trials,
579respectively, and contributed to the drop in selectivity by
58010% and 18% compared to those run with pure glycerol.
581While the prolonged electrolysis was predominantly
582responsible for the large increase in formic acid similar to the
58348-hour trial, it is difficult to rule out the possibility that the
584aqueous soluble organics could be contributing to the formic
585acid population. It is worth pointing out that the glyceric and
586glycolic product population were surprisingly similar
587between the LA-M and LA-C trials, which indicates perhaps
588that methanol might be a good model substrate to study
589influences of impurities. Although the drop in selectivity
590deserves further improvements, being able to upgrade an
633high surface area electrodes among the electro-organic62, 63
,
634photovoltaic64, and electrical energy storage communities65.
635It is also worth noting that the Co-DPPE catalyst can be
636synthesized on multi-gram scale.50 We report the preparation
637of 20g (see ESI for experimental details), which can
638potentially cover more than 120 m2 electrode area based on
639the optimized loading at 16 µg cm-2. Furthermore, under
640optimized conditions, the faradaic efficiency of near unity
641suggests that the electrons were almost exclusively spent on
642glycerol transformation as opposed to side reactions, such as
643water oxidation forming oxygen gas. This can be particularly
644helpful in avoiding interfacial supersaturation66, a common
8 | Green Chem., 2017, 00, 1-3
This journal is © The Royal Society of Chemistry 2017
Please do not adjust margins

Page 9 of 11
Green Chemistry
Please do not adjust margins
Green Chemistry
ARTICLE
645phenomenon where dissolved or evolving gases obstruct the
646substrate of interest from reaching the electrode surface.
647Coupled with the many developed industrial electrochemical
648processes67, this simple, highly flexible protocol could be
649easily adapted into a different setup without elaborated
650modifications.
View Article Online
DOI: 10.1039/C7GC00371D
692Abbreviations
693S-L.A.: Selectivity towards lactic acid, S-G.A.: Selectivity
694towards glyceric acid, % Fara: Faradaic efficiency expressed
695in percentage, MolProd: moles of product formed, F: faraday's
696constant = 96485 C mol-1, n: number of electrons per
697reaction, Ctotal: total charge passed, Cat. w/G: loaded with
698Co-DPPE catalyst and solution contains glycerol, Cat. No G:
699loaded with Co-DPPE catalyst and solution does not contain
700glycerol, No cat. w/G: no Co-DPPE catalyst and solution
701contains glycerol, No cat. w/G: no Co-DPPE catalyst and
702solution does not contain glycerol.
651In addition to lactic and glyceric acid production, it is also
652worth mentioning that all components, glycolic, oxalic, and
653formic acid, found in the product mixture are commonly used
654in the cosmetic industry. In fact, the alpha hydroxy acids (aka
655AHA, lactic and glycolic acid), and oxalic acid are
656commonly used together as skin care exfoliating agents.68
657The use of Co-DPPE catalyst eliminates the need for
658precious metals to withstand the anodic oxidative
659environment, and only traces of catalyst are needed for
660preparation. Unfortunately, some of the fine, powdery
661catalyst shed from the flat FTO surface over long reaction
662time, but a search for porous conductive material is currently
663underway to improve catalyst immobilization. Furthermore,
664both computational and spectroscopic efforts are underway
665to elucidate the active catalyst structure which will be critical
666to understanding glycerol adsorption and improving
667selectivity further. These studies will be discussed in future
668reports.
669Finally, this work raises awareness on the use of
670electrochemistry for catalytic chemical transformation as
671well-aligned with the Principles of Green Chemistry. As
672discussed in the introduction, electrochemistry avoids the
673needs of energy-demanding conditions (heat and pressure)
674with small voltage input, and more importantly, it represents
675a strategy that bridges the gap between renewable energy and
676chemical production. The use of the cobalt-based oxidative
677catalyst bypasses the need for precious metal catalyst, and
678demonstrates oxidation can be achieved using water
679electrocatalytically.
703Notes and references
7041. T. Werpy, G. Petersen, A. Aden, J. Bozell, J. Holladay, J. White, A. Manheim, D.
705
706
707
Eliot, L. Lasure and S. Jones, Top Value Added Chemicals From Biomass.
Volume 1 - Results of Screening for Potential Candidates From Sugars and
Synthesis Gas, DEPARTMENT OF ENERGY WASHINGTON DC, 2004.
7082. F. L. Marques, A. C. Oliveira, J. Mendes Filho, E. Rodríguez-Castellón, C. L.
709
Cavalcante Jr and R. S. Vieira, Fuel Process. Technol., 2015, 138, 228-235.
7103. R. K. P. Purushothaman, J. van Haveren, D. S. van Es, I. Melián-Cabrera, J. D.
Meeldijk and H. J. Heeres, Appl. Catal., B, 2014, 147, 92-100.
7124. J. Xu, H. Zhang, Y. Zhao, B. Yu, S. Chen, Y. Li, L. Hao and Z. Liu, Green Chem.,
2013, 15, 1520-1525.
7145. T. Komanoya, A. Suzuki, K. Nakajima, M. Kitano, K. Kamata and M. Hara,
ChemCatChem, 2016, 8, 1094-1099.
7166. R. K. Pazhavelikkakath Purushothaman, J. van Haveren, I. Melián-Cabrera, E. R.
H. van Eck and H. J. Heeres, ChemSusChem, 2014, 7, 1140-1147.
7187. C. H. Zhou, J. N. Beltramini, C. X. Lin, Z. P. Xu, G. Q. Lu and A. Tanksale, Catal.
Sci. Technol., 2011, 1, 111-122.
7208. W. Hu, D. Knight, B. Lowry and A. Varma, Ind. Eng. Chem. Res., 2010, 49,
10876-10882.
7229. L. Xu, Z. Han, Q. Yao, J. Deng, Y. Zhang, Y. Fu and Q. Guo, Green Chem., 2015,
17, 2426-2435.
711
713
715
717
719
721
723
72410. Y. Zhang, X. Yan, B. Niu and J. Zhao, Green Chem., 2016, 18, 3139-3151.
72511. N. D. Kim, J. R. Park, D. S. Park, B. K. Kwak and J. Yi, Green Chem., 2012, 14,
726
2638-2646.
72712. C. Pendem, P. Gupta, N. Chaudhary, S. Singh, J. Kumar, T. Sasaki, A. Datta and
728
R. Bal, Green Chem., 2012, 14, 3107-3113.
72913. J. Zhou, J. Zhang, X. Guo, J. Mao and S. Zhang, Green Chem., 2012, 14, 156-163.
73014. F. Cai and G. Xiao, Catal. Sci. Technol., 2016, DOI: 10.1039/C6CY00116E.
73115. C.-H. Zhou, J. N. Beltramini, Y.-X. Fan and G. Q. Lu, Chem. Soc. Rev., 2008, 37,
732
527-549.
73316. J. ten Dam and U. Hanefeld, ChemSusChem, 2011, 4, 1017-1034.
680Acknowledgements
73417. B. Katryniok, H. Kimura, E. Skrzynska, J.-S. Girardon, P. Fongarland, M. Capron,
735
736
R. Ducoulombier, N. Mimura, S. Paul and F. Dumeignil, Green Chem., 2011, 13,
1960-1979.
681CHL would like to express his deepest appreciation to the
682Donnelley Foundation for his fellowship support. Special
683thanks goes to Prof. Ned Jackson, Prof. Julie Zimmerman,
684and Prof. Crabtree’s group members for the equipment
685support as well as intellectual input. PTA thanks QAFCO for
686financial support.
73718. Y. Nakagawa and K. Tomishige, Catal. Sci. Technol., 2011, 1, 179-190.
73819. M. Crocker, Journal.
73920. L. Chen, S. Ren and X. P. Ye, Fuel Process. Technol., 2014, 120, 40-47.
74021. D. Roy, B. Subramaniam and R. V. Chaudhari, ACS Catal., 2011, 1, 548-551.
74122. G.-Y. Yang, Y.-H. Ke, H.-F. Ren, C.-L. Liu, R.-Z. Yang and W.-S. Dong, Chem. Eng.
742
J., 2016, 283, 759-767.
74323. M. Dusselier, P. Van Wouwe, A. Dewaele, E. Makshina and B. F. Sels, Energy
Environ. Sci.,, 2013, 6, 1415-1442.
74524. P. Mäki-Arvela, I. L. Simakova, T. Salmi and D. Y. Murzin, Chemical Reviews,
2014, 114, 1909-1971.
74725. R. Datta and M. Henry, Journal of Chemical Technology & Biotechnology, 2006,
81, 1119-1129.
74926. L. S. Sharninghausen, J. Campos, M. G. Manas and R. H. Crabtree, Nat Commun,
2014, 5.
75127. Z. Lu, I. Demianets, R. Hamze, N. J. Terrile and T. J. Williams, ACS Catal., 2016,
6, 2014-2017.
75328. Y. Li, M. Nielsen, B. Li, P. H. Dixneuf, H. Junge and M. Beller, Green Chem., 2015,
17, 193-198.
75529. L. S. Sharninghausen, B. Q. Mercado, R. H. Crabtree and N. Hazari, Chem.
Commun. (Cambridge, U. K.), 2015, 51, 16201-16204.
75730. H. Habe, T. Fukuoka, D. Kitamoto and K. Sakaki, Appl. Microbiol. Biotechnol.,
2009, 84, 445-452.
75931. M. Pagliaro, M. Rossi and R. S. o. Chemistry, The Future of Glycerol: New Uses
of a Versatile Raw Material, Royal Society of Chemistry, 2008.
744
746
748
750
752
754
756
758
760
687Associated Content
688Materials and preparation procedures. These materials are
689free of charge via internet at http://pubs.rsc.org
690Corresponding Author
691paul.anastas@yale.edu
This journal is © The Royal Society of Chemistry 2017
Green Chem., 2017, 00, 1-3 | 9
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 10 of 11
ARTICLE
Green Chemistry
76132. H. Zhang, X. Lin, S. Chin and M. W. Grinstaff, J. Am. Chem. Soc., 2015, 137,
12660-12666.
76333. P. T. Anastas and J. C. Warner, Green Chemistry: Theory and Practice, Oxford
University Press, 1998.
76534. P. T. Anastas, T. C. Williamson, D. Hjeresen and J. J. Breen, Environ. Sci.
Technol., 1999, 33, 116A-119A.
76735. P. T. Anastas, L. G. Heine and T. C. Williamson, in Green Chemical Syntheses
and Processes, American Chemical Society, 2000, vol. 767, ch. 1, pp. 1-6.
76936. H. L. Chum and M. M. Baizer, The electrochemistry of biomass and derived
materials, American Chemical Society, 1985.
77137. Z. Li, M. Garedew, C. H. Lam, J. E. Jackson, D. J. Miller and C. M. Saffron, Green
Chem., 2012, 14, 2540-2549.
77338. Z. Li, S. Kelkar, L. Raycraft, M. Garedew, J. E. Jackson, D. J. Miller and C. M.
Saffron, Green Chem., 2014, 16, 844-852.
77539. S. K. Green, J. Lee, H. J. Kim, G. A. Tompsett, W. B. Kim and G. W. Huber, Green
Chem., 2013, 15, 1869-1879.
View Article Online
DOI: 10.1039/C7GC00371D
762
764
766
768
770
772
774
776
77740. J. J. Roylance and K.-S. Choi, Green Chem., 2016, 18, 2956-2960.
77841. Y. Qiu, L. Xin, D. J. Chadderdon, J. Qi, C. Liang and W. Li, Green Chem., 2014,
779
16, 1305-1315.
78042. J. J. Roylance, T. W. Kim and K.-S. Choi, ACS Catal., 2016, 6, 1840-1847.
78143. K. J. Carroll, T. Burger, L. Langenegger, S. Chavez, S. T. Hunt, Y. Román-Leshkov
782
783
and F. R. Brushett, ChemSusChem, 2016, DOI: 10.1002/cssc.201600290, n/a-
n/a.
78444. S. Lee, H. J. Kim, E. J. Lim, Y. Kim, Y. Noh, G. W. Huber and W. B. Kim, Green
785
Chem., 2016, 18, 2877-2887.
78645. G. Yildiz and F. Kadirgan, J. Electrochem. Soc., 1994, 141, 725-730.
78746. Y. Kwon, Y. Birdja, I. Spanos, P. Rodriguez and M. T. M. Koper, ACS Catal., 2012,
788
2, 759-764.
78947. S. Lux, P. Stehring and M. Siebenhofer, Sep. Sci. Technol., 2010, 45, 1921-1927.
79048. All reactions are performed in alkaline and neutral medium, and thus all
791
792
793
products are expected to be present in deprotonated form such as lactate and
glycerate. However, nonmenclature of their neutral forms such as lactic acid
and glyceric acid will be used interchangibly for the sake of discussion.
79449. A. J. Bloomfield, S. W. Sheehan, S. L. Collom, R. H. Crabtree and P. T. Anastas,
795
New J. Chem., 2014, 38, 1540-1545.
79650. A. J. Bloomfield, S. W. Sheehan, S. L. Collom and P. T. Anastas, ACS Sustainable
Chem. Eng., 2015, 3, 1234-1240.
797
79851. M. Ferreira, M. F. Pinto, O. S. G. P. Soares, M. F. R. Pereira, J. J. M. Ó rfão, J. L.
799
800
Figueiredo, I. C. Neves, A. M. Fonseca and P. Parpot, Electrochim. Acta, 2012,
60, 278-286.
80152. C. H. Lam, C. B. Lowe, Z. Li, K. N. Longe, J. T. Rayburn, M. A. Caldwell, C. E.
802
803
Houdek, J. B. Maguire, C. M. Saffron, D. J. Miller and J. E. Jackson, Green Chem.,
2015, 17, 601-609.
80453. H. Kishida, F. Jin, Z. Zhou, T. Moriya and H. Enomoto, Chem. Lett., 2005, 34,
805
1560-1561.
80654. S. Kitano, M. Yamauchi, S. Hata, R. Watanabe and M. Sadakiyo, Green Chem.,
2016, DOI: 10.1039/C6GC01135G.
80855. R. Ciriminna, G. Palmisano, C. D. Pina, M. Rossi and M. Pagliaro, Tetrahedron
Lett., 2006, 47, 6993-6995.
81056. H. A. Gasteiger, N. Marković, P. N. Ross and E. J. Cairns, J. Electrochem. Soc.,
1994, 141, 1795-1803.
807
809
811
81257. in Applications of Ion Chromatography for Pharmaceutical and Biological
813
814
Products, John Wiley & Sons, Inc., 2012, DOI: 10.1002/9781118147009.app2,
pp. 455-456.
81558. A. Rahimi, A. Ulbrich, J. J. Coon and S. S. Stahl, Nature, 2014, 515, 249-252.
81659. S. Khaitan, D. A. Dzombak and G. V. Lowry, Environmental Engineering Science,
817
2008, 26, 431-440.
81860. I. Doye and J. Duchesne, Applied Geochemistry, 2003, 18, 1197-1213.
81961. R. C. Sahu, R. K. Patel and B. C. Ray, Journal of Hazardous Materials, 2010, 179,
820
28-34.
82162. C. H. Lam, C. B. Lowe, Z. Li, K. N. Longe, J. T. Rayburn, M. A. Caldwell, C. E.
822
823
Houdek, J. B. Maguire, C. M. Saffron, D. J. Miller and J. E. Jackson, Green Chem.,
2015, 17, 601-609.
82463. A. Cyr, F. Chiltz, P. Jeanson, A. Martel, L. Brossard, J. Lessard and H. Menard,
825
Can. J. Chem., 2000, 78, 307-315.
82664. W. Li, J. Liu and D. Y. Zhao, Nat. Rev. Mater., 2016, 1, 17.
82765. G. Wang, L. Zhang and J. Zhang, Chemical Society Reviews, 2012, 41, 797-828.
82866. H. Vogt, Journal of Applied Electrochemistry, 1993, 23, 1323-1325.
82967. G. G. Botte, The Electrochemical Society Interface, 2014, 23, 49-55.
83068. Alpha Hydroxy Acids, http://www.cosmeticsinfo.org/alpha-hydroxy-acids,
831
832
(accessed 19th June, 2016).
10 | Green Chem., 2017, 00, 1-3
This journal is © The Royal Society of Chemistry 2017
Please do not adjust margins

Page 11 of 11
Green Chemistry
View Article Online
DOI: 10.1039/C7GC00371D
A switchable mild electrocatalytic protocols to transform glycerol, a byproduct of biodiesel
production, into either lactic or glyceric acid.