Using a Nitrophenol Cocktail Screen to Improve Catalyst Down-selection

Article abstract of DOI:10.1002/cphc.202000400

The catalytic reduction of 4-nitrophenol (4NP) with excess NaBH₄ is the benchmark model for quantifying catalytic activity of nanoparticles. Although broadly useful, the reaction can be very selective. This can lead to false positives and negatives when utilized for catalyst down-selection from a broader materials candidate pool. We report a multi-nitrophenol cocktail screening methodology incorporating 4NP and other amino-nitrophenols, utilizing Ag, Au, Pt, and Pd nanoparticles on carbon support. The reduction of the cocktail proceeds with no deleterious side reactions on the time-scale tested. The resulting kinetic rates provide an improved correlation of relative catalyst activity when compared to performance with other reducible moieties (e. g. azo bonds), or when compared to solely 4NP screening.

Full text of DOI:10.1002/cphc.202000400

Accepted Article
Title: Using a Nitrophenol Cocktail Screen to Improve Catalyst Down-
selection
Authors: Titel Jurca, Lorianne R. Shultz, Lin Hu, and Xiaofeng Feng
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To be cited as: ChemPhysChem 10.1002/cphc.202000400
Link to VoR: https://doi.org/10.1002/cphc.202000400
0
1/2020

ChemPhysChem
10.1002/cphc.202000400
COMMUNICATION
Using a Nitrophenol Cocktail Screen to Improve Catalyst Down-
selection
Lorianne R. Shultz,[a],[b] Lin Hu,[b],[c] Xiaofeng Feng,[b],[d] and Titel Jurca*[a],[b],[e]
[
a]
L. R. Shultz, Prof. T. Jurca
Department of Chemistry
University of Central Florida
Orlando, Florida, 32816 (USA)
E-mail: Titel.Jurca@ucf.edu
L. R. Shultz, L. Hu, Prof. X. Feng, Prof. T. Jurca
Renewable Energy and Chemical Transformations Cluster
University of Central Florida
Orlando, Florida, 32816 (USA)
L. Hu,
Department of Materials Science and Engineering
University of Central Florida
Orlando, Florida, 32816 (USA)
Prof. X. Feng
[b]
[c]
[d]
[e]
Department of Physics
University of Central Florida
Orlando, Florida, 32816 (USA)
Prof. T. Jurca
NanoScience Technology Center
University of Central Florida
Orlando, Florida, 32826 (USA)
Supporting information for this article is given via a link at the end of the document.
Abstract: The catalytic reduction of 4-nitrophenol (4NP) with excess
NaBH is the benchmark model for quantifying catalytic activity of
by certain catalysts at an appropriate pH.[13] Subsequent
adsorption and reaction of 4-nitrophenolate (4NP*), the resulting
4
nanoparticles. Although broadly useful, the reaction can be very
selective. This can lead to false positives and negatives when
4
product of 4NP and NaBH , with the surface leads to the
hydrogenated product 4-aminophenolate (4AP*). Its broad
application is due to the ease and accuracy of extracting kinetic
data via UV-Vis spectroscopic monitoring of the λmax = 400 nm
peak of 4NP*. Catalyst performance is quantified in terms of the
apparent rate constant kapp (eq. 1), derived from the slope of
utilized for catalyst down-selection from
a broader materials
candidate pool. We report a multi-nitrophenol cocktail screening
methodology incorporating 4NP and other amino-nitrophenols,
utilizing Ag, Au, Pt, and Pd nanoparticles supported on carbon
support. The reduction of the cocktail proceeds with no deleterious
side reactions on the time-scale tested. The resulting kinetic rates
provide an improved correlation of relative catalyst activity when
compared to performance with other reducible moieties (e.g. azo
bonds), or when compared to solely 4NP screening.
ln(C/C
0
) as a function of time; C/C
0
is obtained from the
), collected after an
absorbance for 4NP* at λmax = 400 nm (A/A
0
induction period. This operates under the assumption that the
adsorption of 4NP* onto the catalyst surface is the rate limiting
step.[7]
(
1)
Para-, or 4-nitrophenol (4NP), and more broadly, compounds in
the nitroaromatic family are widely used in the fabrication of
pharmaceuticals, explosives, pesticides, pigments and dyes.[1]
As a result, they have become a very common anthropogenic
pollutant in aqueous industrial effluent. While many
nitroaromatics display acute toxicity, are mutagenic and either
potential or established carcinogens,[2] their reduction products,
aniline-derivatives, are typically less toxic, commercially
important synthetic intermediates. For example, the reduction
product of 4NP is 4-aminophenol (4AP), a useful component for
the synthesis of dyes, agrochemicals, and pharmaceuticals.[3]
Concomitantly, due to its simplicity and reliability, the 4NP →
4
AP reduction process has also become one of the most widely
4 2
Scheme 1. General scheme for 4NP reduction with excess NaBH in H O.
used probe reaction systems for heterogeneous catalyst
development.[
4-12]
4
When conducted in water with significant excess of NaBH as
The near universal use of this model reaction can, when applied
properly, provide a unifying point of comparison when designing
new heterogeneous catalysts and is thus extremely valuable.[
Another common use of the 4NP screen is for down-selection of
the H-source, the reaction is commonly described in terms of the
Langmuir-Hinshelwood model as a pseudo-first order process.[7]
The system entails the delivery of H to the catalyst surface via
4 2
NaBH hydrolysis, which also produces H that can be activated
14]
1
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ChemPhysChem
10.1002/cphc.202000400
COMMUNICATION
heterogeneous catalysts from a larger candidate pool, typically
synthesized under variably parameterized synthetic protocols.
The most active material for 4NP reduction is typically promoted
to an expanded substrate scope, then subjected to further
analysis; a typical process flow is illustrated in Fig. 1. From our
previous studies where all catalyst candidates were promoted to
an expanded substrate scope, it became evident that the 4NP
reduction does not always select the best catalyst.[15,16] It is not
surprising that different catalysts, whether they have a disparate
chemical constitution via similar preparative routes, or a similar
constitution via different preparative routes, exhibit distinct
selectivities. However, it does call into question the
prognosticating ability, and suitability of the ubiquitous 4NP
reaction for catalyst down-selection. The broader utility of the
4
maxima (vide infra). All catalysts promote hydrolysis of NaBH to
some degree[17] (Scheme 1) which leads to a turbid solution,
resulting in artificially increased baseline absorbance (up to ~1
a.u.); this is most pronounced for Pd@C and Pt@C. To enable
data extraction under these conditions, spectra were normalized
to the baseline, and kapp was assigned to the initial few data
2
points prior to significant noise from H evolution. Further details
are provided in the Supporting Information.
4
NP reaction is thus not being refuted.
Figure 1. Illustrated flow-chart for catalyst down-selection using the 4NP →
4AP* reaction.
In our prior report we screened a series of carbon-supported
<
10 nm precious metal nanoparticles; (w/w % by ICP-MS)
Au@C (6.8 ± 0.9%), Ag@C (23.5 ± 0.4%), Pt@C (27.8 ± 1.5%),
and Pd@C (13.5 ± 1.9%) (Fig. S1). All catalysts were first
utilized for reduction of 4NP, then a series of variably substituted
aminonitrophenols (ANPs): 4-amino,3-nitrophenol (4A3NP), 2-
amino,5-nitrophenol (2A5NP), 4-amino,2-nitrophenol (4A2NP).
Finally, two common azo dyes methyl red (MR) and methyl
orange (MO) were reduced under similar conditions, and the
Scheme 2. Catalytic reduction of (A) nitrophenol cocktail and (B) azo dyes MO
and MR and azobenzene (AB) by metal nanoparticles in DIW with excess
NaBH . MO and MR reduction has been previously reported in ref. 15.
4
2
reduction of -NO and -N=N- groups reduction was analyzed.
The cocktail results in a cumulative bimodal peak in the visible
region with a maximum at λmax = 400 nm, and a shoulder at λ =
00 nm (Fig. 2). To obtain kapp for the cocktail, the decrease in
absorbance intensity of both the maxima (400 nm) and shoulder
500 nm) were monitored, and the values across both observed
peaks were averaged (kavg); this is done to ensure that rate is
not biased towards the main constituents of each peak (i.e.
NP* and 2A5NP* at 400 nm, and 4A2NP* and 4A3NP* at 500
nm) (Fig. S2). When normalized to %metal content, Kavg values
Ultimately, we found that reaction rates varied greatly among
both the nitrophenols and the azo dyes, and 4NP offered low
predictability. However, averaging weight normalized rates (K =
5
-1 -1
min g ; g of metal) across all individual nitrophenol trials led to
a closer match for catalyst performance against azo groups.[15]
Nonetheless, a cumbersome multi-step process is not attractive
for rapid screening of multiple candidates. Herein we report the
succesful application of a “cocktail“ of the aforementioned 4NP
and ANPs which allows rapid single run screening. We compare
the results to previously screened MO and MR as well as
azobenzene (AB) and methylene blue (MB).[15]
(
4
-
1
-1
-1 -1
yield 1659.6 ± 40.5 min g (Ag@C), 9131.1 ± 1684.2 min g
-1 -1
(
Au@C), 3740.9 ± 313.5 min g (Pt@C), and 11407.4 ± 2260.3
-1 -1
min g (Pd@C) (Table 1). In all instances, the reaction traces
remained identical and led to the emergence of a peak at λmax
02 nm (Fig. 2). Critical to the employment of the cocktail is the
To ensure a direct comparison, where possible, reactions
were conducted under identical conditions to our prior report: in-
situ (1 cm path length quartz UV cell) in 3 mL of deionized water
=
3
necessity for limiting competing side reactions between the
individual components (both reagents and products). To
demonstrate lack of side reactions, individual reagent and
product spectra from 0.39 μmol solutions were plotted. Next,
spectral deconvolution (OriginPro 2020, Peak Deconvolution
App) was carried out for the reagent components which
constitute the bimodal peak, and for the product components
which constitute the monomodal peak. The calculated peak
centers, areas, and full width at half max were then fed back into
the deconvolution software, where it was used to generate the
(
DIW), with excess NaBH
comprised of 0.39 μmol of each component; 4NP, 4A3NP,
A5NP, 4A2NP (Scheme 2A). AB and MB screening was
conducted with 0.39 μmol and 0.083 μmol of reagents
respectively (Scheme 2B), with AB in a 2:1 H O:EtOH solution
to aid solubility. After recording a t absorbance, 1 mg of catalyst
4
. The nitrophenol cocktail was
2
2
0
was added and stirred gently for ~2 s. The reactions were
allowed to proceed without further intervention and monitored at
fixed intervals by the decreasing absorbance at the defined
2
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ChemPhysChem
10.1002/cphc.202000400
COMMUNICATION
cumulative peak and compared to the experimental trace from
the cocktail (Fig. S4 and S5). Notably, cumulative peak shapes
offer a very good fit to experimental spectra. Slight differences in
the intensity (reagents experimental shows higher intensity) and
spectral shifting (products experimental blue shifts 2 nm) arise
from changes in molar absorptivity due to different
environmental conditions (single component vs cocktail) and
Ag@C and Pt@C and emphatically promotes only Pd@C, the
cocktail screen highlights significant performance from Au@C
and reduced, but notable activity from Pt@C.
1
00
25
Azo avg.
4NP
NP cocktail
20
15
10
5
0
5
[
1
NaBH
4
] in solution after reduction of 0.39 μmol of substrate vs
80
.56 μmol.[18] Ultimately, the spectral components point to no
-
persistent unexpected products within the timescale measured.
-10
60
40
20
0
-15
20
-
Au@C Ag@C
Pt@C
Pd@C
Au@C
Ag@C
Pt@C
Pd@C
Figure 3. Comparison of normalized K values across all catalysts tested for
the 4NP and cocktail screens, compared to the average for azo substrates AB,
MO and MR (see Tables 1 and S2).
Extending the reaction screening to the reduction of
[
21]
methylene blue (MB) to leucomethylene blue (LMB) reveals a
limitation for the predictability of the cocktail screening (Fig. 3).
In situ monitoring of the decreased in absorbance at λmax = 663
Figure 2. UV-Vis spectra for the catalytic reduction of a nitrophenol cocktail by
-1
nm revealed very high kapp for both Pt@C and Pd@C (2.75 min ,
4
(A) Ag@C, (B) Au@C, (C) Pd@C, and (D) Pt@C in DIW with excess NaBH .
and 4.75 min-1 respectively) commensurate with rapid
[
22]
decoloration. Notably, the solutions were very turbid due to the
rapid and continuous evolution of H from NaBH hydrolysis
2
4
To expand the scope of azo-substrates, reduction of AB was
(
Scheme 1). Conversely, Ag@C and Au@C yielded lower kapp
conducted under slightly modified conditions to accomodate
solubility (vide supra). In this instance, all catalysts showed
selectivity towards the partial reduction to hydrazobenzene
values (0.16 min-1 and 0.19 min-1 respectively), and most
importantly, maintained an equilibrium between MB and LMB,
with a gradual shift towards MB as the NaBH concentration
4
decreased (Fig. S9 and S10). Solution turbidity in both cases
was substantially lower, which allows the reversal of the
(
HAB) instead of the anticipated aniline (Scheme 2). In situ
monitoring followed the decrease in absorbance at λmax = 322
nm (trans-AB) with product peaks appearing at λmax = 244 nm
and λmax = 288 nm, consistent with HAB (Fig. S6 and S7).[19,20]
Normalization to %metal content yielded high K values across
2
reduction to occur by interaction with dissolved O ; a common
phenomenon with MB reduction.[
23,24]
We postulate that the rapid
2 2
generation of H by Pt@C and Pd@C serves to purge O from
-1 -1
the board: 10808.5 ± 183.7 min g (Ag@C), 24411.8 ± 3173.5
the system, circumventing the redox equilibrium. In this instance,
this secondary process interferes with the accurate assesment
of reduction rate and provides poor correlation to the cocktail
screening protocol.
-
1
-1
-1 -1
min g (Au@C), 13484.4 ± 728.2 min g (Pt@C), and 12592.6
±
-1 -1
1762.9 min g (Pd@C) (Table 1). This similarity in selectivity
across all four catalysts facilitates the azo reduction comparison.
To compare the predictivity of catalyst performance for the
4
NP screen and the nitrophenol cocktail screen as applied
towards azo bond reduction, K was normalized across each
substrate set and represented as a percentage value for each
catalyst. This creates three subsets for visual comparison, i.e.
4
NP, cocktail, and Azo avg, the latter being the average
performance across AB, and the previously reported MO and
MR reductions (Tables 1 and S2). A graphical representation is
depicted in Figure 3. Notably, the inset illustrates the % +/- for
over and underrepresentation. Clearly, the 4NP screen
dramatically overestimates the peformance of Pd@C and
similarly underestimates that of Pt@C. By contrast, the cocktail
screen yields a tighter grouping, more closely resembling the
broader average performance of the catalysts tested. For
example, whereas the 4NP screen immediately discounts both
Figure 3. Catalytic reduction of methylene blue (MB) by metal nanoparticles in
DIW with excess NaBH
changes.
4
. (inset) Picture of a solution denoting associated color
3
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ChemPhysChem
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COMMUNICATION
Table 1. summary of mass normalized reaction rates (K)
aMO
aMR
AB
a4NP
cocktail
cocktail
cocktail
Catalyst
-
1
-1
-1 -1
-1 -1
-1 -1
1
-1 -1
2
-1 -1
-1 -1
K (min g )
K (min g )
K (min g )
K (min g )
K (min g )
K (min g )
K
avg (min g )
Ag@C
Au@C
Pt@C
Pd@C
2311.9 ± 226.6
2285.4 ± 498.8
6628.8 ± 122.9
6339.6 ± 483.4
8363.7 ± 212.9
10808.5 ± 183.7
24411.8 ± 3173.5
13484.4 ± 728.2
12592.6 ± 1762.9
3608.06 ± 376.2
14648.86 ± 1011.4
3219.08 ± 233.9
33451.73 ± 1244.8
1361.7 ± 23.1
1957.5 ± 33.3
1659.6 ± 40.5
7282.6 ± 860.1
4718.1 ± 144.9
27147.8 ± 1974.9
8394.7 ± 1091.3
2050.4 ± 110.7
10962.9 ± 1534.8
9867.5 ± 1282.8
5431.7 ± 293.3
11851.9 ± 1658.3
9131.1 ± 1684.2
3740.9 ± 313.5
11407.4 ± 2260.3
[
a] values reported in ref. 15
In summary we have shown additional reactivity for our
previously reported catalyst set; namely reduction of methylene
blue which is enhanced by solution turbidity via complementary
[5]
[6]
[7]
S. Gu, S. Wunder, Y. Lu, M. Ballauf, R. Fenger, K. Rademann, B.
Jaquet, A. Zaccone, J. Phys. Chem. C. 2014, 118, 18618-18625.
M. Nasrollahzadeh, Z. Nezafat, M. G. Gorab, M. Sajjadi, Mol. Catal.
2020, 484, 110758.
2 4
H generation from NaBH hydrolysis, and selective azobenzene
semihydrogenation. Most importantly, we have endeavored to
develop a cocktail screening methodology which overcomes the
catalyst specificity of the 4NP reduction reaction, with the hope
of improving catalyst down-selection. The example presented
herein is a proof of concept that multiple nitrophenols can be
reduced in concert without deleterious side reactions, and their
overall rate similarly logged by facile UV-Vis measurement and
kinetic interpretation. The result thereof appears to yield an
improved understanding of relative catalyst performance when
compared, inherently, to a broader nitrophenol substrate scope,
and to azo bonds. Our ongoing focus is on the discovery of
improved reagent cocktails, and an expansion of the
comparative library of reducible moieties beyond azo functional
groups. The ultimate goal is the development of a “tool box“ of
screening protocols for accurate catalyst down-selection.
(a) T. Aditya, A. Pal, T. Pal, Chem. Commun. 2015, 51, 9410-9431; (b)
N. Pradhan, A. Pal, T. Pal, Colloids surf., A., 2002, 196, 247-257 (c) J.
Strachan, C. Barnett, A. F. Masters, T. Maschmeyer, ACS Catal. 2020,
1
0, 5516-5521.
P. Zhao, X. Feng, D. Huang, G. Yang, D. Astruc, Coord. Chem. Rev.
015, 287, 114-136.
[
[
8]
9]
2
P. Hervés, M. Pérez-Lorenzo, L. M. Liz-Marzán, J. Dzubiella, Y. Lu, M.
Ballauff, Chem. Soc. Rev. 2012, 41, 5577-5587.
[
[
[
10] N. C. Antonels, R. Meijboom, Langmuir 2013, 29, 13433-13442.
11] S. Wunder, Y. Lu, M. Albrecht, M. Ballauf, ACS Catal. 2011, 1, 908-916.
12] S. Wunder, F. Polzer, Y. Lu, Y. Mei, M. Ballauf, J. Phys. Chem. C 2010,
114, 8814-8820.
[13] R. Grzeschik, D. Schäfer, T. Holtum, S. Küpper, A. Hoffmann, S.
Schlücker, J. Phys. Chem. C. 2020, 124, 2939-2944.
[
14] (a) N. E. Larm, N. Bhawawet, J. A. Thon, G. A. Baker, New. J. Chem.,
2019, 43, 17932-17936; (b) U. I. Kramm, R. Marschall, M. Rose,
ChemCatChem, 2019, 11, 2563-2574.
[
[
15] L. R. Shultz, L. Hu, K. Preradovic, M. J. Beazley, X. Feng, T. Jurca,
ChemCatChem, 2019, 11, 2590-2595.
Acknowledgements
16] L. R. Shultz, B. McCullough, W. J. Newsome, H. Ali, T. E. Shaw, K. O.
Davis, F. J. Uribe-Romo, M. Baudelet, T. Jurca, Molecules, 2020, 25,
This work was supported by the Departments of Chemistry and
Physics, College of Science, and the FCI at the University of
Central Florida. A. P. Sattelberger, UCF, is thanked for helpful
discussions.
89.
[
17] (a) H. I. Schlesinger, H. C. Brown, A. E. Finholt, J. R. Gilbreath, H. R.
Hoekstra, E. K. Hyde, J. Am. Chem. Soc. 1953, 75, 215-219; (b) R.
Retnamma, A. Q. Novais, C. M. Rangel, Int. J. Hydrogen Energ. 2011,
36, 9772-9790.
[18] M. F. Vitha, Spectroscopy Principles and Instrumentation, 2019, Wiley,
NJ, USA
Keywords: nitrophenol • heterogeneous catalysis •
[
19] C. Tosi, Spectrochimica Acta, 1966, 22, 399-402.
20] (a) Y. Shiraishi, M. Katayama, M. Hashimoto, T. Hirai, Chem. Commun.
nanoparticles • catalytic hydrogenation • catalyst screening
[
2
018, 54, 452-455; (b) H. Abdullah, D.-H. Kuo, N. S. Gultom, Catal. Sci.
[
1]
(a) S. Yi, W.-Q. Zhuang, B. Wu, S. Tiong-Lee, J-H. Tay, Environ. Sci.
Technol. 2006, 40, 2396-2401; (b) M. R. H. Podeh, S. K. Bhattacharya,
M. Qu, Water Res. 1995, 29, 391-399; (c) J. Xia, G. He, L. Zhang, X.
Sun, X. Wang, Appl. Catal., B 2016, 180, 408-415; (d) S. Yu, J. Hu, J.
Wang, J. Hazard. Mater. 2010, 177, 1061-1067.
Technol. 2019, 9, 2651-2663.
[
21] (a) S. Du, Z. Liao, Z. Qin, F. Zuo, Z. Li, Catal. Commun. 2015, 72, 86-
9
0; (b) S. Hemmati, L. Mehrazin, H. Ghorban, S. H. Garakani, T. H.
Mobaraki, P. Mohammadi, H. Veisi, RSC Adv. 2018, 8, 21020-21028;
c) N. R. Jana, T. K. Sau, T. Pal, J. Phys. Chem. B. 1999, 103, 115-121.
(
[
[
2]
3]
(a) K.-S. Ju, R. E. Parales, Microbiol. Mol. Biol. Rev. 2010, 74, 250-272;
[
[
[
22] C. Corredor, M. D. Borysiak, J. Wolfer, P. Westerhoff, J. D. Posner,
(
b) H. Zhao, C.-H. Kong, Chem. Eng. J. 2018, 339, 424-431; (c) M. Sun,
D. D. Reible, G. V. Lowry, K. B. Gregory, Environ. Sci. Technol. 2012,
6, 6174-6181.
(a) R. S. Downing, P. J. Kunkeler, H. van Bekkum, Catal. Today 1997,
7, 121-136; (b) G. Wegener, M. Brandt, L. Duda, J. Hofmann, B.
Environ. Sci. Technol. 2015, 49, 3611-3618.
23] X. Bi, H. Ma, P. Westerhoff, Environ. Sci. Technol. 2018, 52, 13289-
4
13297.
24] A similar O
2
-mediated reversible reaction between nitrosophenol and
3
nitrophenol is proposed to occur during the induction period prior to
rapid reduction: (a) J. Strachan, C. Barnett, A. F. Masters, T.
Maschmeyer, ACS Catal. 2020, 10, 5516-5521; (b) E. Menumerov, R. A.
Hughes, S. Neretina, Nano Lett. 2016, 16, 7791-7797; (c) R. D. Neal, Y.
Inoue, R. A. Hughes, S. Neretina, J. Phys. Chem. C. 2019, 123, 12894-
Klesczewski, D. Koch, R.-J. Kumpf, H. Orzesek, H.-G. Pirkl, C. Six, C.
Steinlein, M. Weisbeck, Appl. Catal., A 2001, 221, 303-335; (c) K.
Nomura, J. Mol. Catal. A: Chem. 1998, 130, 1-28; (d) M. Espinosa
Bosch, A. J. Ruiz Sánchez, F. Sánchez Rojas, C. Bosh Ojeda, J.
Pharm. Biomed. Anal. 2006, 42, 291-321.
12901.
[
4]
Z. Xiong, H. Zhang, W. Zhang, B. Lai, G. Yao, Chem. Eng. J. 2019, 359,
13-31.
4
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Entry for the Table of Contents
Catalytic reduction of 4-nitrophenol is the benchmark model for testing catalytic activity of nanoparticles. A single molecule probe is
however prone to disparate selectivity leading to false rankings for catalyst down-selection. We report a facile multi-nitrophenol
cocktail screening method. When tested with noble metal nanoparticles, the cocktail approach provides improved ranking of relative
catalyst activity when compared to reduction of azo bonds.
5
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