Iron Oxychloride as an Efficient Catalyst for Selective Hydroxylation of Benzene to Phenol

Article abstract of DOI:10.1021/acscatal.8b03590

Selective hydroxylation of benzene is a felicitous strategy for the production of phenol that is deemed to be an alternative to conventional processes. Thus, the development of a durable and highly efficient catalyst for the selective hydroxylation of benzene should be a key topic. In this work, FeOCl was prepared by a chemical vapor transition method and characterized using various techniques including XRD, TEM, Raman spectroscopy, N₂ adsorption-desorption, DLS, and TGA. The prepared FeOCl was applied as a heterogeneous catalyst in benzene hydroxylation, and the reaction conditions were optimized. The acquired data manifested that FeOCl has shown superiority over the other reported catalysts utilized in benzene hydroxylation. The superiority of FeOCl is attributed to the facile self-redox potential of FeOCl and its remarkable ability for the production of an overwhelming amount of hydroxyl radicals in a short period of time. The catalyst recovery and reuse test showed that FeOCl is able to endure the harsh conditions of benzene hydroxylation for four runs. The mechanism of benzene hydroxylation using FeOCl as a catalyst in the presence of hydrogen peroxide as an oxidant was also illustrated.

Full text of DOI:10.1021/acscatal.8b03590

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Article
Iron oxychloride as an efficient catalyst for
selective hydroxylation of benzene to phenol
Ahmed E. ElMetwally, Ghada Eshaq, Fatma Z. Yehia, Ahmed M. Al-Sabagh, and Søren Kegnæs
ACS Catal., Just Accepted Manuscript • Publication Date (Web): 09 Oct 2018
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Iron oxychloride as an efficient catalyst for selective hydroxylation
of benzene to phenol
Ahmed E. ElMetwally*, a, Ghada Eshaq a, Fatma Z. Yehia a, Ahmed M. Al-Sabagh b, Søren
Kegnæs c
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a
Petrochemicals department, Egyptian Petroleum Research Institute, Nasr City, Cairo 11727, Egypt
b
Petroleum applications department, Egyptian Petroleum Research Institute, Nasr City, Cairo 11727, Egypt
c
DTU Chemistry, Technical University of Denmark, Kemitorvet 207, DK-2800 Kgs. Lyngby, Denmark
ABSTRACT
Selective hydroxylation of benzene is a felicitous strategy for the production of phenol that
is deemed an alternative route for conventional processes. Thus, the development of a durable and
highly efficient catalyst for the selective hydroxylation of benzene should be the key topic. In this
work, FeOCl was prepared by chemical vapor transition method and characterized using various
techniques including XRD, TEM, Raman spectroscopy, N2 adsorption–desorption, DLS and TGA.
The prepared FeOCl was applied as heterogeneous catalyst in benzene hydroxylation and the
reaction conditions were optimized. The acquired data manifested that FeOCl has shown
superiority over the other reported catalysts utilized in benzene hydroxylation. The superiority of
FeOCl is attributed to the facile self-redox potential of FeOCl and its remarkable ability for the
production of an overwhelming amount of hydroxyl radicals in a short period of time. The catalyst
recovery and reusing test showed that FeOCl is able to endure the harsh conditions of benzene
hydroxylation for four runs. The mechanism of benzene hydroxylation using FeOCl as a catalyst
in the presence of hydrogen peroxide as an oxidant was also illustrated.
Keywords: benzene; phenol; hydroxylation; catalysis; oxychloride
*corresponding author: Tel: +201115025588, Fax: +20222747433
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E-mail address: ahmed_ezzatt@msn.com
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INTRODUCTION
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Phenol is deemed as one of the most indispensable organic compound that is used
extensively in various chemical and petrochemical industries. Phenol is also used as an
intermediate in the production of phenol derivatives and phenolic resins. Cumene process is
commonly used for the production of nearly 90% of phenol produced throughout the globe, where
propylene and benzene are used as starting materials with acetone as a side product.1-2 Cumene
process comprises three consecutive stages and suffers from various drawbacks including
excessive energy consumption and the generation of hazardous intermediate such as cumene
hydroperoxide. In spite of the economic importance for the production of acetone, the demand for
phenol is still rising as the global demand for phenol is currently being driven by an increasing
demand of its various derivatives.1, 3 Consequently, the production of phenol from the direct
oxidation of benzene has attracted much attention to overcome the drawbacks encountered with
cumene process.4-6
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Recently, great efforts have been made to develop the catalytic system of the direct
oxidation of benzene to phenol especially when the hydrogen peroxide is used as an oxidant.7
During this tenure, several catalysts including palladium membrane, modified titanium silicalite,
titanium-mesoporous molecular sieves, vanadium-substituted polyoxometalates, activated carbon,
cerium promoted V-g-C3N4 and vanadium-containing mesoporous carbon have been explored.8-22
Among these explored catalysts, iron-based catalysts have shown supremacy over the other tested
catalysts in different aspects including the cost, abundance, environmental friendliness and low
toxicity.
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Previous studies reported that iron-based catalysts were highly efficient and selective when
used as catalysts in different oxidative processes and particularly the challenging processes.23-25
Wang et al. 26 reported that a high phenol yield from benzene hydroxylation can be achieved over
two Fe-based metal–organic frameworks catalysts using hydrogen peroxide as an oxidant.
Jourshabani et al. 27 studied the effect of using Fe-supported cage like mesoporous silica in benzene
hydroxylation to phenol using H2O2 as an oxidant. Baykan and Oztas,28 reported the synthesis of
phenol via the direct hydroxylation of benzene over iron phosphate. Carneiro and Silva, 29 studied
the direct hydroxylation of benzene to phenol using hydrogen peroxide in the presence of Fe(III)
Schiff base complex as a catalyst. Recently, iron ferrite was reported to be an efficient catalyst for
the selective hydroxylation of benzene to phenol under mild conditions in the presence of hydrogen
peroxide as an oxidant.30 Although the examined catalysts were efficient and selective in benzene
hydroxylation, the phenol yield did not reach its climax as this process still demand more
development. Thus, exploring a catalyst that is able to enhance the phenol yield remains a major
goal. Such catalyst will be able to minimize the production of different byproducts while
maintaining a high phenol yield.
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Iron oxychloride (FeOCl) is a ternary layered material that have distinguished layered
framework and unrivaled chemical stability. The layers of this distinguishable layered framework
are attached together by van der Waals interaction, which makes FeOCl able to host organic
compounds.31 The charge transfers between the host organic compound and FeOCl may change
iron oxidation state from +3 to +2.32 Studies revealed that hosting an organic compound within
FeOCl layered framework was responsible for the in situ reduction of one fourth of Fe3+ to Fe2+.32-
33 FeOCl has been employed as a catalyst in the degradation of some persistent organic compound
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and found to have fabulous activity, which is attributed to the extraordinary structural
configuration of its atoms and also for its reducible electronic characteristics.34
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We believe that this is the first article that uses FeOCl as a heterogeneous catalyst in benzene
hydroxylation to phenol. Herein, FeOCl was prepared using chemical vapor transition method and
characterized using XRD, TEM, Raman spectroscopy, N2- sorption, DLS and TGA analysis.
FeOCl was examined in benzene hydroxylation and the reaction conditions were optimized to
fulfil the maximum phenol yield. Finally, the reaction mechanism of benzene hydroxylation using
FeOCl was illustrated.
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EXPERIMENTAL
Materials
Anhydrous iron (III) chloride and ethylene glycol were supplied from Sigma–Aldrich. Benzene
and ammonia solution (30%) were supplied from Merck. Hydrogen Peroxide (30 %) was supplied
from PanReac AppliChem. Acetic Acid (70-80% w/w) was supplied from Fisher Scientific.
Preparation of FeOCl
First, α-Fe2O3 was prepared by dissolving certain amount of anhydrous ferric chloride in
aqueous solution containing 80% ethylene glycol. Ferric ions were precipitated by adding 3 M
ammonia solution under stirring at 50ºC and kept at this temperature for 30 min. The formed slurry
was aged for 12 h and then the resultant precipitate was separated by centrifugation, washed by
deionized water and dried at 100ºC overnight. Second, FeOCl was prepared by chemical vapor
transition method from the prepared Fe2O3 according to the procedure reported in.34 In particular,
the prepared α-Fe2O3 was mixed with anhydrous ferric chloride in ratio of 1:1.3. The resultant
mixture was sealed in an evacuated glass vessel and kept in a muffle furnace for 48 h at 380ºC.
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The obtained sample was washed successively with acetone to get rid of the unreacted ferric
chloride and eventually dried at 100 ºC for 6 h.
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Characterization
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A JEOL JEM-2100 operating at 200 kV was used to obtain the TEM images of the sample.
The hydrodynamic diameter was characterized using dynamic light scattering (DLS) analysis
on a Malvern Zetasizer Nano (Malvern Instruments Ltd., Worcestershire, UK). XRD analysis was
performed to identify and confirm the phase of the prepared sample using a Philips powder
diffractometer using Cu Kα radiation. The analysis was carried out at a scanning speed of 2º θ/min
and 2θ step of 0.02º. The Raman spectra of the prepared sample was obtained using a Bruker
Optics Raman spectrometer operating at room temperature with an exciting lines of 532 nm. TGA
analysis was conducted at rate of 10°C min-1 under nitrogen atmosphere on a SDT Q600, TA
Instruments. A NOVA 3200 system instrument was used to obtain the surface texture parameters
by nitrogen sorption at -195.85°C.
Catalytic activity
The reaction was carried out in a 25 mL two necked flask equipped with a condenser. The
reaction temperature was adjusted by immersing the flask in a thermally controlled oil bath. In
each run, benzene (0.9 mL) and 70% acetic acid (1 mL) were fed into the two necked flask
followed by the addition of a particular amount of FeOCl. Thereafter, certain amount of 30%
hydrogen peroxide was introduced to the reaction medium. The catalytic activity was evaluated
at different reaction temperature in the range of 30-80°C and at different reaction time in the range
of 0.5-6 h. When the reaction was complete, the catalyst was separated by centrifugation and the
liquid product was collected to be analyzed. An Agilent 7890 GC equipped with HP-5 capillary
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column (5%-Phenyl)-methylpolysiloxane (30 m, 0.25 µm and 0.32 mm) and flame ionization
detector. The phenol selectivity was obtained as the molar ratio of the produced phenol to the
converted benzene while the phenol yield was obtained as the molar ratio of the produced phenol
to the initial benzene. p-benzoquinone selectivity was obtained as the molar ratio of the produced
p-benzoquinone to the converted benzene.35
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Results and Discussion
Catalyst characterization
The TEM micrograph of the prepared sample reveals that catalyst has a stone-like
morphology with a size in the range of 40–50 nm as displayed in Figure 1.
Dynamic light scattering technique was conducted to screen the size distribution of the
prepared FeOCl. The obtained data reveal that the diameter range of FeOCl is 50 nm as displayed
in Figure 1.
The phase of the prepared FeOCl sample was identified and confirmed using the obtained
XRD pattern presented in Figure 1. The phase of the prepared FeOCl is confirmed by matching
the obtained pattern with the FeOCl reference code (01-072-0619). The obtained data manifest
that the prepared FeOCl has an orthorhombic structure with a crystallite size of 50 nm that was
calculated using Scherrer equation, which is in consistence with the data observed in the TEM
micrograph and DLS analysis.
The Raman spectrum of the prepared FeOCl (Figure 1) exhibits band at 216 cm-1 that can be
ascribed to Fe−Cl stretching modes while the bands appear at 285 cm-1 and 400 cm-1 can be
ascribed to Fe−O stretching modes.
The acquired N2 sorption isotherm of the prepared FeOCl reveals that the sample can be
categorized to Type II as shown in Figure 1. The isotherm of FeOCl exhibits an initial knee, which
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is attributed to the monolayer formation. It should be mentioned that the region observed for the
onset of multilayer formation is usually recognized with initial concaved portion followed by a
hoist that ascribed to multilayer formation. It is obvious that the FeOCl isotherm exhibits an H3
hysteresis that extends P/Po = 0.15. These characteristics can be ascribed to the existence of fragile
narrow pores that imploded during the formation of monolayer leading to the formation of an open
texture with a slit shape where a limited numbers of multilayer is formed.36-37 The value of specific
surface area calculated using BET equation for FeOCl is 17.11 m2g-1, and the total pore volume
(Vp) taken at P/Po = 0.95, is 0.034, mL g-1. The BJH calculation method was used to obtain the
pore size distribution curves as shown in Figure 1. The pore size distribution curve of iron
oxychloride implies the presence of a sharp peak with a climax centered at 19 Å and broad peak
with a climax centered at 46 Å.
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The thermal stability analysis was carried out prior to the catalytic testing to make sure the
catalyst is able to endure the reaction temperature of benzene hydroxylation. It also provides a
preliminary survey whether the reusability of the employed catalyst is possible or not. The TGA
analysis of the prepared FeOCl (Figure 1) reveals that the catalyst endures the examined
temperature range without any obvious transformational change. Thus, it can be inferred that the
employed catalyst is thermally stable within the range of the tested reaction temperature of benzene
hydroxylation.
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Figure 1. (a) TEM image of FeOCl. (b) DLS of FeOCl (c) XRD pattern of FeOCl. (d) Raman
spectrum of FeOCl. (e#) N2 adsorption-desorption isotherm of FeOCl (e*) pore size distribution
curve of FeOCl. (f) TGA curve of FeOCl.
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The catalytic activity of FeOCl in benzene hydroxylation
Impact of reaction time
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The impact of reaction time is a very important parameter that gives us a wide view on the
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catalytic performance of the catalyst. When the phenol yield becomes steady or decreases this
means that either the radical chain reaction is brought to an end or the generated phenol is further
oxidized. The impact of reaction time on benzene hydroxylation was tested in the 0.5-6 h range as
presented in Figure 2 and Table S1. The obtained data reveal that the phenol yield is directly
proportional to the reaction time reaching a climax with a value of 43.5% after 4 h of benzene
hydroxylation and beyond this time the phenol yield slightly decreases. Consequently, the use of
elongated time of benzene hydroxylation has a negative impact on the phenol yield because the
produced phenol undergoes further oxidation. Thus, it can be inferred that beyond 4 h of benzene
hydroxylation a significant portion of the generated radical species tends to oxidize the produced
phenol molecules instead of attacking benzene molecules. This explanation agrees well with the
data obtained for phenol selectivity upon increasing the reaction time, which reveals a slight
decrease in the phenol selectivity due to the production of p-Benzoquinone (Table S2 and Figure
S1) as a side product. p-Benzoquinone is a stable side product produced as result of hydroquinone
oxidation.
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Phenol yield
Phenol selectivity
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Time (h)
Figure 2. Impact of reaction time. Reaction conditions: Benzene (0.9 mL), FeOCl (0.1 g),
benzene: H2O2 (1:1), acetic acid (1 mL) and 60°C.
Compared to the previously reported data (Table S3), a maximum phenol yield of 43.5 %
in only 4h of benzene hydroxylation highlights the high efficacy of FeOCl. This high efficacy can
be attributed to the unique ability of FeOCl for the production of a high amount of hydroxyl
radicals in a short period of time. This ability can be ascribed to the substantial structure of FeOCl
where its polar surface and specifically the 020 plane is overstuffed with a huge number of
unsaturated Fe atoms.38 Compared to water, the hydrogen peroxide molecules have more affinity
to the polarized plan of iron oxychloride.34 These Fe atoms were uniformly arranged on this plan
with a O−Fe−Cl configuration.
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Compared to α-FeOOH, FeOCl is able to increase the production of hydroxyl radicals from
hydrogen peroxide with a yield 100 times higher than that produced in the presence of α-FeOOH.34
Moreover, the Fe3+ ions of the iron oxychloride are susceptible to be reduced to Fe2+ ions upon
their reaction or intercalation with different species, which makes clear that FeOCl is distinguished
by facile self-redox properties. The Fe2+ ions are able to catalyze the production of hydroxyl
radicals from hydrogen peroxide with a rate 1000-10000 times higher than that produced in the
presence of Fe3+ ions.39 A partial reduction could occur as a result of the electron-charge transition
from hydrogen peroxide to FeOCl upon the adsorption of hydrogen peroxide and organic
molecules over the FeOCl surface.
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II
FeOCl + H2O2 ↔ Fe1- n IIIFen + HOO• +H+
(1)
(2)
≡ FeII +H2O2 ↔ ≡ FeIII + HO• + OH-
Thus, the efficacy of FeOCl in benzene hydroxylation can be attributed to unique features of FeOCl
and the matchless configuration.
Impact of catalyst dosage
To find out the most suitable catalyst dosage on phenol yield, benzene hydroxylation
reaction was carried out using different catalyst doses in the 0.05-0.25 g range as displayed in
Figure 3. The results show that the phenol yield increases with increasing the catalyst dosage and
it reaches a maximum value at a catalyst dosage of 0.1 g and beyond this amount the phenol yield
decreases. It is clear that increasing the catalyst dosage has a positive impact on the phenol yield
because of increasing the number of active sites that leads to a massive increase in the amount of
hydroxyl radicals. However, the addition of an excessive amount of catalyst has a negative impact
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on the phenol yield because of the agglomeration of the catalyst particles that block the active sites.
This blockage prevents the benzene molecules from reaching the active sites that are rich with
highly active hydroxyl radicals and consequently the hydroxyl radicals tend to scavenge each other
instead of attacking the benzene molecules.
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Phenol selectivity
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weight of the catalyst (g)
Figure 3. Impact of catalyst dosage. Reaction conditions: Benzene (0.9 mL), benzene: H2O2
(1:1), acetic acid (1 mL), 60°C and 4 h.
Impact of benzene:H2O2 molar ratio
To maximize the yield of phenol using FeOCl as a catalyst, we carefully optimized the
benzene to hydrogen peroxide ratio as the addition of an excessive amount of hydrogen peroxide
may have a negative impact on the oxidation process. Thus, it is highly recommended to carefully
adjust the concentration of hydrogen peroxide to fulfil a maximum phenol yield. The impact of
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benzene:H2O2 molar ratio on the hydroxylation of phenol was examined in the range from 1:0.5
to 1:2 as displayed in Figure 4. The obtained results reveal that the phenol yield is directly
proportional to the benzene:H2O2 molar ratio, peaking at the molar ratio 1:1 and beyond this ratio
the phenol yield declines.
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Phenol yield
Phenol selectivity
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1:0.5
1:0.7
1:1
1:1.5
1:2
Benzene: H2O2 molar ratio
Figure 4. Impact of benzene:H2O2 molar ratio. Reaction conditions: Benzene (0.9 mL), FeOCl
(0.1 g), acetic acid (1 mL), 60°C and 4h.
It should be noted that the maximum H2O2 efficiency was detected at the molar ratio 1:1 in
the presence of FeOCl as a catalyst as presented in Figure S2. The enhancement of the phenol yield
upon increasing the benzene:H2O2 molar ratio is attributed to the presence of a considerable
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amount of H2O2 that produces higher amounts of hydroxyl radicals. However, the decline of the
phenol yield upon the use of higher concentration of hydrogen peroxide is attributed to the
presence of an overwhelming amount of H2O2 that scavenges the produced hydroxyl radicals with
a rate, k = 2.7 x107 M-1s-1. The reaction of H2O2 with hydroxyl radicals gives rise to hydroperoxyl
radicals. The generated hydroperoxyl radicals also reacts with hydroxyl radicals (k = 6 x109 M-1s-
1) and consequently more hydroxyl radicals will be lost as presented in the following equations.40-43
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•
H2O2 +•OH→H2O+HO2
(3)
(4)
•
HO2 + •OH→H2O+ O2
Another explanation or the decline of the phenol yield upon using an excessive concentration of
H2O2 is the further of oxidation of the produced phenol to p-Benzoquinone. This explanation is
supported by the decline of phenol selectivity upon increasing the benzene:H2O2 molar ratio. Thus,
the produced radicals are involved in phenol oxidation instead of attacking the benzene molecules.
Impact of reaction temperature
The impact of reaction temperature on benzene hydroxylation was examined in the 30-
80°C range to find out the lowest temperature that provides the maximum phenol yield as displayed
in Figure 5. The adjustment of the reaction temperature in a catalytic system that contains hydrogen
peroxide as an oxidant is a quite intricate operation. The use of elevated temperature leads to the
decomposition of hydrogen peroxide into water and oxygen and consequently a great portion of
the hydrogen peroxide will be lost. Screening the reaction temperature reveals that the phenol yield
is directly proportional to the reaction reaching its climax at 60°C, and beyond this temperature
the phenol yield decreases. It can be argued that increasing the reaction temperature reduces the
mass transfer limitation of hydroxyl radicals and thus the rate of the reaction between the benzene
molecule and hydroxyl radicals is significantly enhanced. Furthermore, the oxidation rate of the
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organic compounds is greatly enhanced upon using elevated temperature .44 However, the use of
excessively elevated temperature such as 80°C has a negative impact on the phenol yield as the
hydrogen peroxide is thermally decomposed into oxygen and water.
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Phenol yield
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Phenol selectivity
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Temperature (°C)
Figure 5. Impact of reaction temperature. Reaction conditions: Benzene (0.9 mL), FeOCl (0.1 g),
benzene: H2O2 (1:1), acetic acid (1 mL) and 4h.
FeOCl recovery and reuse
To check out the durability of the FeOCl in benzene hydroxylation, several experiments were
carried out using the recovered FeOCl using the same employed conditions. FeOCl was recovered
by centrifugation after each catalytic run, washed with ethanol and then dried at 120°C for 6 h.
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The obtained results manifest that there is only a negligible decrease in the phenol yield after the
fourth run using FeOCl catalyst under the same condition as displayed in Table S4. Thus, it can be
inferred that the employed FeOCl is able to endure the harsh reaction condition of the benzene
hydroxylation reaction. The phase of the recovered catalyst was investigated using XRD analysis
to make sure that the catalyst did not suffer from any phase transformation during the catalytic
activity and the obtained XRD patterns of the fresh and recovered catalyst is displayed in Figure
S3. The obtained XRD pattern of the recovered catalyst reveals that did not undergo any phase
transformation during benzene hydroxylation, however, a slight decrease in the peaks intensity
was only observed.
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Insight into the mechanism of benzene hydroxylation using FeOCl
As mentioned previously the efficacy of FeOCl in benzene hydroxylation is attributed to
the unique ability of FeOCl for the production of a high amount of hydroxyl radicals in a short
period of time and this process takes place via several successive steps. First, the facile self-redox
potential of FeOCl fosters the prompt reduction of Fe3+ to Fe2+ upon the reaction with hydrogen
peroxide (Scheme 1), which finally produces hydroperoxyl radical.45 The generated Fe2+ then
reacts with hydrogen peroxide to produce hydroxyl radical and to eventually accomplish the redox
cycle comprising the Fe2+/ Fe3+ pair. It is to be noted that this redox cycle is deemed the essence
of the homogeneous Fenton reaction where the reduction ferric ions to ferrous ions is the rate
determining step that controls the reaction rate.46
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Scheme 1. Illustration of benzene hydroxylation mechanism using FeOCl
Moreover, FeOCl enhances the production of hydroxyl radicals by dodging the undesirable
oxidation of Fe2+ to Fe4+. It has been reported that Fe4+ could be formed as a result of the reaction
of hydrogen peroxide and Fe2+ without producing hydroxyl radicals and thus this reaction was
considered unfavorable.47 It should be mentioned that the existence of such reaction is reason that
lies behind the inefficiency of a homogeneous Fenton catalyst at neutral pH. Dodging such
undesirable pathway directs the reaction between hydrogen peroxide and Fe2+ toward the
production of hydroxyl radicals. The exposure of a huge number of unsaturated iron atoms over
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the plane (020) is considered the driving force for the prompt reduction of Fe3+ to Fe2+ and dodging
the undesirable oxidation of Fe2+ to Fe4+ to produce hydroxyl radical.45 These exposed atoms can
act as an active center for the activation of hydrogen peroxide. Moreover, the coordination of
chlorine and oxygen boosts the reduction potential of the exposed iron atoms. Thus, electron
transfer takes place more efficiently from the hydrogen peroxide molecule during the reduction of
Fe3+ to Fe2+ and homolytic cleavage of hydrogen peroxide.48
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In particular, the produced hydroxyl radical attack the benzene molecule to produce
benzene-OH-adduct as presented in scheme 1. Next, benzene-OH-adduct produces phenol by
losing hydrogen. On another hand, the generated hydroperoxyl radicals may also attack the
benzene molecule to produce benzene-OOH-adduct. Thereafter, hydrogen peroxide reacts with the
benzene-OOH-adduct that gives rise to a benzene-hydrogen-transferred OOH-adduct, which
finally produces phenol by losing water molecule.49-50
CONCLUSIONS
In conclusion, selective hydroxylation of benzene to produce phenol with a high phenol
yield (43.5%) and high selectivity (100%) has been fulfilled after only 4h of hydroxylation using
FeOCl in the presence of hydrogen peroxide as an oxidant. The exposure of a huge number of
unsaturated iron atoms over the polar surface of FeOCl is considered the driving force for the
prompt reduction of Fe3+ to Fe2+ and dodging the undesirable oxidation of Fe2+ to Fe4+ to produce
considerable amount of hydroxyl radicals. The present work offers a felicitous strategy that can be
an alternative for conventional processes concerned with the selective hydroxylation of benzene.
ASSOCIATED CONTENT
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The Supporting Information is available free of charge on the ASC Publications website. Effects
of reaction conditions on the selectivity and yield of phenol. Effects of reaction conditions on the
selectivity of p-benzoquinone. Comparison between phenol selectivity and p-benzoquinone
selectivity. Hydrogen peroxide efficiency. Comparison of catalytic activities with other catalysts
for benzene hydroxylation. Reusability of FeOCl in benzene hydroxylation. XRD pattern of fresh
and recovered catalyst.
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