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Journal Article•DOI•

Manganese oxides at different oxidation states for heterogeneous activation of peroxymonosulfate for phenol degradation in aqueous solutions

Edy Saputra1, Edy Saputra2, Syaifullah Muhammad3, Syaifullah Muhammad2, Hongqi Sun2, Ha Ming Ang2, Moses O. Tadé2, Shaobin Wang2 •
Riau University1, Curtin University2, Syiah Kuala University3
01 Oct 2013-Applied Catalysis B-environmental (elsevier)-Vol. 142, pp 729-735
TL;DR: A series of manganese oxides (MnO, MnO2, Mn2O3 and Mn3O4) were synthesized and tested in heterogeneous activation of peroxymonosulfate (PMS) for phenol degradation in aqueous solutions as discussed by the authors.
Abstract: A series of manganese oxides (MnO, MnO2, Mn2O3 and Mn3O4) were synthesized and tested in heterogeneous activation of peroxymonosulfate (PMS) for phenol degradation in aqueous solutions. Their properties were characterized by several techniques such as X-ray diffraction (XRD), thermogravimetric-differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), and N2 adsorption/desorption isotherms. Catalytic activities of Mn oxides were found to be closely related to the chemical states of Mn. Mn2O3 is highly effective in heterogeneous activation of PMS to produce sulfate radicals for phenol degradation compared with other catalysts (MnO, MnO2, and Mn3O4). The activity shows an order of Mn2O3 > MnO > Mn3O4 > MnO2. Mn2O3 could completely remove phenol in 60 min at the conditions of 25 mg/L phenol, 0.4 g/L catalyst, 2 g/L PMS, and 25 °C. After heat regeneration, the activity could be fully recovered. A pseudo first order model would fit to phenol degradation kinetics and activation energy was obtained as 11.4 kJ/mol.

Summary (2 min read)

Jump to: [1. Introduction] – [2.1. Preparation of Mn catalysts] – [2.2. Characterization of catalysts] – [2.3. Kinetic study of phenol oxidation] – [3.1. Characterization of manganese oxide catalysts] – [3.2. Preliminary study of phenol oxidation on Mn-oxide catalysts] – [3.4. Reactivity of spent α-Mn2O3 catalyst and reusability] and [4. Conclusions]

1. Introduction

  • Over the last decades, water treatment plays an important role in their lives, because of fresh water crisis and the increasing awareness of human health and ecological systems as a result of industrial waste pollution.
  • The organics in wastewaters from chemical and related industries cannot be well treated by conventional processes due to degradation of these pollutants being very slow or ineffective and not environmentally compatible [4, 5].
  • Heterogeneous catalytic oxidation systems have recently attracted much interest due to easily recovery and reuse of the catalysts [8].
  • Moreover, they found that catalytic activity was influenced significantly by pH. Saputra et al. [26] reported the oxidative removal of phenol from water by MnO2 and studied the factors influencing the reactions.

2.1. Preparation of Mn catalysts

  • A manganese dioxide (MnO2) was purchased from Sigma-Aldrich Company and used without further treatment.
  • Another catalyst (MnO) was obtained by a two-step method.
  • First, MnCO3 was synthesized by a hydrothermal method [27] and then calcination was made.
  • Typically, KMnO4 (3 mmol) and an equal amount of glucose were put into distilled water at room temperature to form a homogeneous solution, which was transferred into a 45 mL Teflon-lined autoclave.
  • The autoclave was sealed and maintained at 150 oC for 10 h, and was then cooled down to room temperature naturally.

2.2. Characterization of catalysts

  • Catalysts were characterized by X-ray diffraction (XRD), N2 adsorption/desorption isotherm, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA).
  • N2 adsorption/desorption was measured using a Micromeritics Tristar 3000 to obtain pore volume and the Brunauer-Emmett-Teller (BET) specific surface area.
  • The external morphology and chemical compositions of the samples were observed on a ZEISS NEON 40EsB scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (SEM-EDS).

2.3. Kinetic study of phenol oxidation

  • The catalytic oxidation of phenol was carried out in a 1 L glass beaker containing 25-100 ppm of phenol solutions (500 mL), which was attached to a stand and dipped in a water bath with a temperature controller.
  • The reaction was carried on for 120 min and at a fixed time interval, 0.5 mL of solution sample was taken from the mixture using a syringe with a filter of 0.45 µm and then mixed with 0.5 mL methanol to quench the reaction.
  • For selected samples, total organic carbon (TOC) was obtained using a Shimadzu TOC-5000 CE analyzer.
  • For recycled catalyst tests, two regeneration methods were used.
  • One is simple washing treatment and the other is high-temperature calcination.

3.1. Characterization of manganese oxide catalysts

  • MnO2 and MnCO3 were studied by TGA under air and argon atmosphere, respectively (Fig. 1).
  • For MnCO3, TGA pattern in Fig.1B shows 10% weight loss below 350 oC, which corresponds to a loss of water, organic and trace amount of carbon dioxide, and another 29% weight loss at around 450 oC corresponds to loss of carbon dioxide from MnCO3 lattice resulting in the phase transformation to MnO.
  • The four samples present different crystalline peaks.

3.2. Preliminary study of phenol oxidation on Mn-oxide catalysts

  • Adsorption tests showed that Mn oxides presented minor adsorption of phenol, giving less than 10% in 120 min, which is due to low surface area[26].
  • The results also showed that about 90%, 66.4%, and 61.5% of phenol removal were obtained for MnO-PMS, Mn3O4-PMS and MnO2-PMS, respectively, within 120 min. Anipsitakis and Dionysiou [20] studied Mn2+ for activation of H2O2 and PMS to found that Mn2+ could activate H2O2 and PMS to produce hydroxyl radicals and SRs, respectively, although the rate of reaction was still low.
  • Mn oxides at different oxidation states can activate peroxymonosulfate to produce SRs (SO4- and SO5-) for phenol degradation as shown in the following equations.
  • Phenol degradation efficiency decreased with increasing phenol concentration.

3.4. Reactivity of spent α-Mn2O3 catalyst and reusability

  • After heat treatment at 500 oC for 1 hour, the activity of α-Mn2O3 was fully recovered and complete degradation of phenol can be achieved at 120 min as the same as the first use.
  • Deactivation of α-Mn2O3 could be attributed to intermediate deposition on the surface and chemical phase change[38].
  • XRD analysis showed that no phase change occurred after reaction.
  • This suggests that the intermediate deposits on the catalyst surface plays important role for catalyst deactivation and they can be removed by heat treatment.

4. Conclusions

  • Different oxidation states of manganese oxide were synthesized and tested for catalytic oxidation of phenolic contaminants with PMS.
  • Kinetic studies showed that the phenol degradation followed first order reaction and activation energy of Mn2O3 were obtained to be 11.4 kJ/mol.

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NOTICE: This is the author’s version of a work that was accepted for
publication in Applied Catalysis B: Environmental. Changes resulting
from the publishing process, such as peer review, editing, corrections,
structural formatting and other quality control mechanisms may not
be reflected in this document. Changes may have been made to this
work since it was submitted for publication. A definitive version was
subsequently published in Applied Catalysis B: Environmental,
Volumes 142–143, October–November 2013, Pages 729–735.
http://doi.org/10.1016/j.apcatb.2013.06.004
Manganese oxides at different oxidation states for heterogeneous activation of
peroxymonosulfate for phenol degradation in aqueous solutions
Edy Saputra
1,2
, Syaifullah Muhammad
1,3
, Hongqi Sun
1
, Ha-Ming Ang
1
, Moses O. Tadé
1
, Shaobin
Wang
1,
*
1
Department of Chemical Engineering and CRC for Contamination Assessment and Remediation of
the Environment (CRC-CARE), Curtin University, GPO Box U1987, Perth, WA 6845, Australia
2
Department of Chemical Engineering, Riau University, Pekanbaru 28293, Indonesia
3
Department of Chemical Engineering, Syiah Kuala University, Banda Aceh, Indonesia
Abstract
A series of manganese oxides (MnO, MnO
2
, Mn
2
O
3
and Mn
3
O
4
) were synthesized and tested in
heterogeneous activation of peroxymonosulfate (PMS) for phenol degradation in aqueous solutions.
Their properties were characterized by several techniques such as X-ray diffraction (XRD),
thermogravimetric analysis (TGA),
scanning electron microscopy (SEM), and N
2
adsorption/desorption isotherms. Catalytic activities of Mn oxides were found to be closely related
to the chemical states of Mn. Mn
2
O
3
is highly effective in heterogeneous activation of PMS to
produce sulfate radicals for phenol degradation compared with other catalysts (MnO, MnO
2
, and
Mn
3
O
4
). The activity shows an order of Mn
2
O
3
> MnO > Mn
3
O
4
> MnO
2
. Mn
2
O
3
could completely
remove phenol in 60 min at the conditions of 25 ppm phenol, 0.4 g/L catalyst, 2 g/L PMS, and 25
o
C. After heat regeneration, the activity could be fully recovered. A pseudo first order model would
fit to phenol degradation kinetics and activation energy was obtained as 11.4 kJ/mol.
Key words: Mn oxides, peroxymonosulfate activation, advanced oxidation, phenol degradation
*Correspondence author. Email: Shaobin.wang@curtin.edu.au
2
1. Introduction
Over the last decades, water treatment plays an important role in our lives, because of fresh water
crisis and the increasing awareness of human health and ecological systems as a result of industrial
waste pollution. Industrial activities generate large amounts of organic hazardous substances
discharged into the environment. The organic wastes can be found in many industries as by-
products such as petroleum refining, petrochemical, pharmaceutical, plastic, pesticides, chemical
industries, agrochemicals, and pulp and paper industries [1, 2]. The organic pollutants e.g. phenol,
are toxic and cause considerable damage and threat to the ecosystem in water bodies and to the
human health even at low concentrations[3]. It is important to dispose of wastewater in a proper
way in order to comply with environmental regulations. However, the organics in wastewaters from
chemical and related industries cannot be well treated by conventional processes due to degradation
of these pollutants being very slow or ineffective and not environmentally compatible [4, 5]. The
most promising method for degradation of organic pollutants in wastewater is advanced oxidation
processes (AOPs). AOPs are based on generation and utilization of reactive species, such as
hydroxyl radicals (HO•) that have a high standard oxidation potential and react none selectively [6,
7]. Heterogeneous catalytic oxidation systems have recently attracted much interest due to easily
recovery and reuse of the catalysts [8].
Lately, manganese oxides
,
such as MnO, MnO
2
, Mn
2
O
3
and Mn
3
O
4
,
have attracted much attention
due to their physical and chemical properties for being used as catalysts, adsorbents,
supercapacitors, and battery materials [9-15]. Kim and Shim [16] have conducted a study on the
catalytic combustion of aromatic hydrocarbons (benzene and toluene) on manganese oxides. The
results indicated that the catalysts showed high activity in the oxidation of hydrocarbons at
temperatures below 300
o
C. Furthermore, the reactivity of catalysts exhibited an order of Mn
3
O
4
>
Mn
2
O
3
> MnO
2
, which was correlated with oxygen mobility on the catalysts. Ramesh et al. [17]
have studied CO oxidation over a series of manganese oxide catalysts and found that Mn
2
O
3
is the
best catalyst, with the sequence of catalytic activity as MnO ≤ MnO
2
< Mn
2
O
3
. Santos et al. [18]
reported the synthesis of manganese oxide nanoparticles for ethyl acetate oxidation. Complete
oxidation of ethyl acetate was achieved at temperature below 300
o
C. However, few investigations
have been conducted in the activity of a series of manganese oxides at different valence states in
water treatment.
In the most of previous investigations in water treatment, MnO
x
was usually used for Fenton-like
reaction for production of hydroxyl radicals from H
2
O
2
and oxidation of organic compounds.
Recently, sulfate radicals (SRs) produced by Co
2+
/oxone(peroxymonosulfate, PMS) or Ru
3+
/oxone
3
have attracted intense attention in degradation of organic compounds for water treatment [19, 20].
However, Co
2+
or Ru
3+
may generate secondary pollution [21-23]. Therefore, alternative metal such
as Fe
2+
, has been proposed by Zazo et al. [24]. They found that Fe
2+
/H
2
O
2
have a high catalytic
activity for degradation of phenol. In contrary, a recent study by Watts et al. [25] revealed that
Mn
2+
/H
2
O
2
was significantly more reactive than Fe
2+
/H
2
O
2
. Moreover, they found that catalytic
activity was influenced significantly by pH. Saputra et al. [26] reported the oxidative removal of
phenol from water by MnO
2
and studied the factors influencing the reactions. They found that
MnO
2
exhibited as a promising chemical agent under certain conditions for phenol removal from
wastewater. However, no further investigation has been reported for solid MnO
x
for the activation
of PMS to generate SRs.
In this research, we investigate the performance of a series of manganese oxides at varying valence
states for heterogeneous generation of SRs for chemical mineralization of phenol in the solution.
These catalysts will be an alternative for heterogeneous AOP. Several key parameters in the kinetic
study such as phenol concentration, catalyst loading, PMS concentration and temperature were
investigated. Regeneration of used catalysts was also investigated.
2. Experimental methods
2.1. Preparation of Mn catalysts
A manganese dioxide (MnO
2
) was purchased from Sigma-Aldrich Company and used without
further treatment. Mn
2
O
3
was obtained by treating the MnO
2
at 550
o
C in air for 5 h. In addition,
MnO
2
was calcined at 950
o
C in air for 2 h to get Mn
3
O
4
. Another catalyst (MnO) was obtained by a
two-step method. First, MnCO
3
was synthesized by a hydrothermal method [27] and then
calcination was made. Typically, KMnO
4
(3 mmol) and an equal amount of glucose were put into
distilled water at room temperature to form a homogeneous solution, which was transferred into a
45 mL Teflon-lined autoclave. The autoclave was sealed and maintained at 150
o
C for 10 h, and
was then cooled down to room temperature naturally. The resulted solid product (MnCO
3
) was
filtered, washed with distilled water and dried in air at 100
o
C overnight. Finally, MnO catalyst was
obtained by calcination of MnCO
3
at 500
o
C under argon flow at the rate 60 mL/min for 2 h.
2.2. Characterization of catalysts
Catalysts were characterized by X-ray diffraction (XRD), N
2
adsorption/desorption isotherm,
scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). XRD patterns were
obtained on a Bruker D8 (Bruker-AXS, Karlsruhe, Germany) diffractometer using filtered Cu Kα
4
radiation source (λ = 1.54178 Å), with accelerating voltage 40 kV, current 30 mA and scanned at 2θ
from 5 to 70
o
. N
2
adsorption/desorption was measured using a Micromeritics Tristar 3000 to obtain
pore volume and the Brunauer-Emmett-Teller (BET) specific surface area. Prior to measurement
the samples were degased at 120
o
C for 5 h under vacuum condition. The external morphology and
chemical compositions of the samples were observed on a ZEISS NEON 40EsB scanning electron
microscope (SEM) equipped with an energy dispersive spectrometer (SEM-EDS).
2.3. Kinetic study of phenol oxidation
The catalytic oxidation of phenol was carried out in a 1 L glass beaker containing 25-100 ppm of
phenol solutions (500 mL), which was attached to a stand and dipped in a water bath with a
temperature controller. The reaction mixture was stirred constantly at 400 rpm to maintain a
homogenous solution. A fixed amount of peroxymonosulfate (using Oxone, Dupont’s triple salt,
2KHSO
5
•KHSO
4
•K
2
SO
4
(PMS), Sigma-Aldrich) was added into the solution and allowed to
dissolve completely before reaction. Further, a fixed amount of catalyst was added into the reactor
to start the oxidation reaction of phenol. The reaction was carried on for 120 min and at a fixed time
interval, 0.5 mL of solution sample was taken from the mixture using a syringe with a filter of 0.45
µm and then mixed with 0.5 mL methanol to quench the reaction. Concentration of phenol was
analyzed using a HPLC with a UV detector at wavelength of 270 nm. The column used was C-18
with a mobile phase of 30% acetonitrile and 70% ultrapure water. For selected samples, total
organic carbon (TOC) was obtained using a Shimadzu TOC-5000 CE analyzer. For the
measurement of TOC, 5 mL solutions were extracted at a fixed interval and quenched with 5 mL of
3 M sodium nitrite solution and then analyzed on the TOC analyzer.
For recycled catalyst tests, two regeneration methods were used. One is simple washing treatment
and the other is high-temperature calcination. In general, Mn oxides were collected by filtration
after reaction, washing with water and drying at 80 ºC overnight for reuse test. Some dried samples
were further calcined at 500 ºC in air for 1 h and then reused for test again.
3. Result and discussion
3.1. Characterization of manganese oxide catalysts
MnO
2
and MnCO
3
were studied by TGA under air and argon atmosphere, respectively (Fig. 1). The
TGA pattern of MnO
2
(Fig. 1A) shows 5% weight loss below 300
o
C, which corresponds to a loss
of surface adsorbed water, organic and trace amount of oxygen. At around 550
o
C, weight loss of
about 8% corresponds to the loss of oxygen from MnO
2
lattice resulting in the phase transformation
Citations
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Generation of sulfate radical through heterogeneous catalysis for organic contaminants removal: Current development, challenges and prospects

[...]

Wen-Da Oh1, Zhili Dong1, Teik-Thye Lim1•
Nanyang Technological University1
05 Oct 2016-Applied Catalysis B-environmental
TL;DR: In this paper, the authors provide a state-of-the-art review on the development in heterogeneous catalysts including single metal, mixed metal, and nonmetal carbon catalysts for organic contaminants removal, with particular focus on peroxymonosulfate (PMS) activation.
Abstract: Sulfate radical-based advanced oxidation processes (SR-AOPs) employing heterogeneous catalysts to generate sulfate radical (SO4 −) from peroxymonosulfate (PMS) and persulfate (PS) have been extensively employed for organic contaminant removal in water. This article aims to provide a state–of–the–art review on the recent development in heterogeneous catalysts including single metal, mixed metal, and nonmetal carbon catalysts for organic contaminants removal, with particular focus on PMS activation. The hybrid heterogeneous catalyst/PMS systems integrated with other advanced oxidation technologies is also discussed. Several strategies for the identification of principal reactive radicals in SO4 −–oxidation systems are evaluated, namely (i) use of chemical probe or spin trapping agent coupled with analytical tools, and (ii) competitive kinetic approach using selective radical scavengers. The main challenges and mitigation strategies pertinent to the SR-AOPs are identified, which include (i) possible formation of oxyanions and disinfection byproducts, and (ii) dealing with sulfate produced and residual PMS. Potential future applications and research direction of SR-AOPs are proposed. These include (i) novel reactor design for heterogeneous catalytic system based on batch or continuous flow (e.g. completely mixed or plug flow) reactor configuration with catalyst recovery, and (ii) catalytic ceramic membrane incorporating SR-AOPs.

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15 Feb 2017-Chemical Engineering Journal
TL;DR: A literature review on environmental application of peroxymonosulfate (PMS) in degradation of contaminants to clarify the performance of PMS is carried out in this paper, which describes the PMS usage in remediation of environmental pollutants with focus on the different methods of activation and the effect of main operational parameters on PMS-based processes.

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Persulfate-Based Advanced Oxidation: Critical Assessment of Opportunities and Roadblocks.

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Jaesang Lee1, Urs von Gunten2, Urs von Gunten3, Jae-Hong Kim4•
Korea University1, École Polytechnique Fédérale de Lausanne2, Swiss Federal Institute of Aquatic Science and Technology3, Yale University4
17 Mar 2020-Environmental Science & Technology
TL;DR: This Critical Review comparatively examines the activation mechanisms of peroxymonosulfate and peroxydisulfates and the formation pathways of oxidizing species and the impacts of water parameters and constituents such as pH, background organic matter, halide, phosphate, and carbonate on persulfate-driven chemistry.
Abstract: Reports that promote persulfate-based advanced oxidation process (AOP) as a viable alternative to hydrogen peroxide-based processes have been rapidly accumulating in recent water treatment literature. Various strategies to activate peroxide bonds in persulfate precursors have been proposed and the capacity to degrade a wide range of organic pollutants has been demonstrated. Compared to traditional AOPs in which hydroxyl radical serves as the main oxidant, persulfate-based AOPs have been claimed to involve different in situ generated oxidants such as sulfate radical and singlet oxygen as well as nonradical oxidation pathways. However, there exist controversial observations and interpretations around some of these claims, challenging robust scientific progress of this technology toward practical use. This Critical Review comparatively examines the activation mechanisms of peroxymonosulfate and peroxydisulfate and the formation pathways of oxidizing species. Properties of the main oxidizing species are scrutinized and the role of singlet oxygen is debated. In addition, the impacts of water parameters and constituents such as pH, background organic matter, halide, phosphate, and carbonate on persulfate-driven chemistry are discussed. The opportunity for niche applications is also presented, emphasizing the need for parallel efforts to remove currently prevalent knowledge roadblocks.

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Sulfate radicals induced from peroxymonosulfate by magnetic ferrospinel MFe2O4 (M = Co, Cu, Mn, and Zn) as heterogeneous catalysts in the water

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Harbin Engineering University1, Harbin Institute of Technology2
01 Apr 2015-Applied Catalysis B-environmental
TL;DR: In this paper, the mechanism of different catalysts in the catalytic peroxymonosulfate (PMS) solution was illustrated, and the results showed that the incorporation of CoFe 2 O 4 had the highest catalytic performance in PMS oxidation for DBP degradation.
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TL;DR: One-dimension manganese dioxides (α- and β-MnO2) were discovered as effective PDS activators among the diverse manganes oxides for selective degradation of organic contaminants in wastewater and provides a novel catalytic system for selective removal of organic contamination in wastewater.
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18 Sep 2003-Environmental Science & Technology
TL;DR: The advantage of Co/PMS compared to the traditional Fenton Reagent is attributed primarily to the oxidizing strength of the radicals formed, since sulfate radicals are stronger oxidants than hydroxyl and the thermodynamics of the transition-metal-oxidant coupling.
Abstract: A highly efficient advanced oxidation process for the destruction of organic contaminants in water is reported. The technology is based on the cobalt-mediated decomposition of peroxymonosulfate that leads to the formation of very strong oxidizing species (sulfate radicals) in the aqueous phase. The system is a modification of the Fenton Reagent, since an oxidant is coupled with a transition metal in a similar manner. Sulfate radicals were identified with quenching studies using specific alcohols. The study was primarily focused on comparing the cobalt/peroxymonosulfate (Co/PMS) reagent with the traditional Fenton Reagent [Fe(II)/H2O2] in the dark, at the pH range 2.0-9.0 with and without the presence of buffers such as phosphate and carbonate. Three model contaminants that show diversity in structure were tested: 2,4-dichlorophenol, atrazine, and naphthalene. Cobalt/peroxymonosulfate was consistently proven to be more efficient than the Fenton Reagent for the degradation of 2,4-dichlorophenol and atrazine, at all the conditions tested. At high pH values, where the efficiency of the Fenton Reagent was diminished, the reactivity of the Co/PMS system was sustained at high values. When naphthalene was treated with the two oxidizing systems in comparison, the Fenton Reagent demonstrated higher degradation efficiencies than cobalt/peroxymonosulfate at acidic pH, but, at higher pH (neutral), the latter was proven much more effective. The extent of mineralization, as total organic carbon removed,was also monitored, and again the Co/PMS reagent demonstrated higher efficiencies than the Fenton Reagent. Cobalt showed true catalytic activity in the overall process, since extremely low concentrations (in the range of microg/L) were sufficient for the decomposition of the oxidant and thus the radical generation. The advantage of Co/PMS compared to the traditional Fenton Reagent is attributed primarily to the oxidizing strength of the radicals formed, since sulfate radicals are stronger oxidants than hydroxyl and the thermodynamics of the transition-metal-oxidant coupling.

1,390 citations

Journal Article•DOI•
Catalytic combustion of VOCs over a series of manganese oxide catalysts

[...]

Sang Chai Kim1, Wang Geun Shim2•
Mokpo National University1, Chonnam National University2
01 Aug 2010-Applied Catalysis B-environmental
TL;DR: In this paper, the authors used the Brunauer Emmett Teller (BET), temperature programmed reduction (TPR), X-ray diffraction (XRD) and Xray photoelectron spectroscopy (XPS) to study catalytic combustion of volatile organic compounds (VOCs): benzene and toluene.
Abstract: Catalytic combustion of volatile organic compounds (VOCs: benzene and toluene) was studied over manganese oxide catalysts (Mn3O4, Mn2O3 and MnO2) and over the promoted manganese oxide catalysts with alkaline metal and alkaline earth metal. Their properties and performance were characterized by using the Brunauer Emmett Teller (BET), temperature programmed reduction (TPR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The sequence of catalytic activity was as follows: Mn3O4 > Mn2O3 > MnO2, which was correlated with the oxygen mobility on the catalyst. Each addition of potassium (K), calcium (Ca) and magnesium (Mg) to Mn3O4 catalyst enhanced the catalytic activity of Mn3O4 catalyst. Accordingly, K, Ca and Mg seemed to act as promoters, and the promoting effect might be ascribed to the defect-oxide or a hydroxyl-like group. A mutual inhibitory effect was observed between benzene and toluene in the binary mixture. In addition, the order of catalytic activity with respect to VOC molecules for single compound is benzene > toluene, and the binary mixture showed the opposite order of toluene > benzene.

602 citations

Journal Article•DOI•
Effect of Phase Structure of MnO2 Nanorod Catalyst on the Activity for CO Oxidation

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Shuhui Liang1, Fei Teng1, G. Bulgan1, Ruilong Zong1, Yongfa Zhu1 •
Tsinghua University1
18 Mar 2008-Journal of Physical Chemistry C
TL;DR: In this paper, the catalytic properties of the α-, β-, γ-, and δ-MnO2 nanorods were evaluated for CO oxidation, and the effects of phase structures on the catalysts were investigated.
Abstract: The α-, β-, γ-, and δ-MnO2 nanorods were synthesized by the hydrothermal method. Their catalytic properties for CO oxidation were evaluated, and the effects of phase structures on the activities of the MnO2 nanorods were investigated. The activities of the catalysts decreased in the order of α- ≈ δ- > γ- > β-MnO2. The mechanism of CO oxidation over the MnO2 nanorods was suggested as follows. The adsorbed CO was oxidized by the lattice oxygen, and the MnO2 nanorods were partly reduced to Mn2O3 and Mn3O4. Then, Mn2O3 and Mn3O4 were oxidized to MnO2 by gaseous oxygen. CO chemisorption, the Mn−O bond strength of the MnO2, and the transformation of intermediate oxides Mn2O3 and Mn3O4 into MnO2 can significantly influence the activity of the MnO2 nanorods. The activity for CO oxidation was mainly predominated by the crystal phase and channel structure of the MnO2 nanorods.

576 citations

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Frequently Asked Questions (1)
Q1. What are the contributions mentioned in the paper "Manganese oxides at different oxidation states for heterogeneous activation of peroxymonosulfate for phenol degradation in aqueous solutions" ?

In this paper, a series of manganese oxides ( MnO, MnO2, Mn2O3 and Mn3O4 ) were synthesized and tested in heterogeneous activation of peroxymonosulfate ( PMS ) for phenol degradation in aqueous solutions.