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A maghemite supported palladium catalyst was prepared and tested in nitrobenzene hydrogenation. The catalyst support was made by a newly developed combined technique, where sonochemical treatment and combustion have been used. As a first step, maghemite nanoparticles were synthesized. Iron(II) citrate was treated in polyethylene glycol by high-intensity ultrasound cavitation to get a homogeneous dispersion, then the product was combusted. The produced powder contained maghemite nanoparticles with 21.8 nm average particle size. In the second step of catalyst preparation, the magnetic nanoparticles were dispersed in the ethanolic solution of palladium(II) nitrate. The necessary energy for the reduction of Pd2+ ions was achieved in the “hot spots” by acoustic cavitation, thus catalytically active palladium was formed. The prepared maghemite supported Pd catalyst have been tested in nitrobenzene hydrogenation at three different temperatures (283 K, 293 K and 303 K) and constant pressure (20 bar). At 293 K and 303 K, the conversion and selectivity of nitrobenzene was above 99% and 96%, respectively. However, the selectivity was only 73% at 273 K because the intermediate species (azoxybenzene and nitrosobenzene) have not been transformed to aniline. All in all, the prepared catalyst is successfully applied in nitrobenzene hydrogenation and easily separable from the reaction media.
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Reaction Kinetics, Mechanisms and Catalysis (2020) 129:107–116
1 3
Catalytic activity ofmaghemite supported palladium
catalyst innitrobenzene hydrogenation
ViktóriaHajdu1· ÁdámPrekob1· GáborMuránszky1· IstvánKocserha2·
ZoltánKónya3· BélaFiser1,4· BélaViskolcz1· LászlóVanyorek1
Received: 29 October 2019 / Accepted: 31 December 2019 / Published online: 9 January 2020
© The Author(s) 2020
A maghemite supported palladium catalyst was prepared and tested in nitroben-
zene hydrogenation. The catalyst support was made by a newly developed com-
bined technique, where sonochemical treatment and combustion have been used. As
a first step, maghemite nanoparticles were synthesized. Iron(II) citrate was treated
in polyethylene glycol by high-intensity ultrasound cavitation to get a homogene-
ous dispersion, then the product was combusted. The produced powder contained
maghemite nanoparticles with 21.8 nm average particle size. In the second step
of catalyst preparation, the magnetic nanoparticles were dispersed in the ethanolic
solution of palladium(II) nitrate. The necessary energy for the reduction of Pd2+
ions was achieved in the “hot spots” by acoustic cavitation, thus catalytically active
palladium was formed. The prepared maghemite supported Pd catalyst have been
tested in nitrobenzene hydrogenation at three different temperatures (283K, 293K
and 303K) and constant pressure (20bar). At 293K and 303K, the conversion
and selectivity of nitrobenzene was above 99% and 96%, respectively. However, the
selectivity was only 73% at 273K because the intermediate species (azoxybenzene
and nitrosobenzene) have not been transformed to aniline. All in all, the prepared
catalyst is successfully applied in nitrobenzene hydrogenation and easily separable
from the reaction media.
Keywords Magnetic catalyst· Selectivity· Nitrobenzene· Aniline
Several different complex catalysts have been successfully applied in the hydro-
genation of nitro groups, such as carbon (C), silica (SiO2) or alumina (Al2O3) sup-
ported Pd, Pt, Ru, Rh, Ni, Fe or bimetallic systems [113]. The easy handling and
* László Vanyorek
Extended author information available on the last page of the article
Reaction Kinetics, Mechanisms and Catalysis (2020) 129:107–116
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separability are very important properties for the catalysts. These can be improved
by introducing magnetic features (e.g. magnetic catalyst supports), which will allow
the easy and efficient removal of the catalysts after the reactions. For this reason,
magnetic systems have been widely used in various applications. Magnetite (Fe3O4)/
silica composite catalyst was used for esterification of palmitic acid with metha-
nol [14]. Pd, Pr–Cu and Pr6O11 decorated Fe3O4/SiO2 catalyzed the reduction of
2,4-dinitrophenylhydrazine, 4-nitrophenol and chromium(VI) ions, Mizoroki–Heck
coupling reaction, and the catalytic ozonation of acetochlor [1517]. Magnetite/
carbon support was applied in Suzuki–Miyaura cross-coupling of 4-iodotoluene
and phenylboronic acid and aniline synthesis by palladium [18, 19]. By magnetite/
alumina supported Pd catalyst the hydrogenation of nitrate in water and 4-nitro-
phenol can be achieved [20, 21]. Magnetic iron oxides can be combined with dif-
ferent layered double hydroxides (Fe3O4-LDH), complex magnesium silicates
(Fe3O4-sepiolite) and hydroxyapatite (γ-Fe2O3-HAP) to use as a support for Pd and
these catalytic systems can be applied to catalyze the Heck reaction between iodo-
benzene and styrene, and the reduction of nitroarenes and nitrobenzene [2224].
Magnetite itself is also a promising catalyst support as it was proved by the applica-
bility of Ag/Fe3O4, Ag–Ni/Fe3O4, Pd/Fe3O4 and Rh/Fe3O4 systems in the synthesis
of 3,4-dihydropyrimidinones. 2,4-dihydropyrano[2,3-c]pyrazoles, and the hydro-
genation of soybean oil and nitroarenes [2528]. The two main components of the
catalysts mentioned above are the support and the catalytically active metal. The
catalysts are prepared through several steps, including the activation of metal, within
which metal (e.g. palladium ions) ions or their complex ions are reduced to the cata-
lytically active form (e.g. Pd0). In the case of Pd ions, the activation (reduction) can
be done on the supports in aqueous solution by molecular hydrogen (6atm, 75°C)
or by using NaBH4 in ethanol but the ethylene glycol is also efficient [21, 24, 29].
In our work, a simplified reduction step was applied during the catalyst produc-
tion (palladium(II) nitrate to Pd0) by applying alcohol and acoustic cavitation. The
high energy of the ultrasonic treatment in liquids generates acoustic cavitation,
which leads to the formation of micro vapor-bubbles. The collapse of the formed
bubbles leads to „hot spots” where intense local heating (~ 5000K), high pressure
(~ 1000atm), enormous heating and cooling rates (> 109K/s) and liquid jet streams
(~ 400km/h) appear in a small volume [30]. The energy in the „hot spots” can cover
the needs of the reduction of metal ions to metals in the presence of a reducing agent
[3136]. By using of ultrasonic cavitation, palladium nanoparticles were deposited
on the surface of maghemite in methanol phase. Owing to the magnetic properties
of the maghemite, this is a remarkable catalyst support in liquid phase hydrogena-
tion because the catalyst easily separated from the reaction media by magnetic field.
Iron(III) citrate hydrate (FeC6H5O7H2O, PanReac AppliChem) as precursor and
polyethylene glycol (PEG400, Sigma Aldrich) were applied for the synthesis of
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Reaction Kinetics, Mechanisms and Catalysis (2020) 129:107–116
maghemite. Palladium(II) nitrate dihydrate (Pd(NO3)22H2O, Merck) and absolute
ethanol (VWR) was used to synthesize catalytically active palladium.
Application ofmaghemite supported palladium catalyst
Maghemite nanoparticles, as catalyst supports were synthesized by a combustion
method. 3.5 g iron(III) citrate hydrate was dispersed in 20g polyethylene glycol
(PEG 400, Sigma Aldrich) by using a Hielscher Ultrasound tip homogenizer. The
iron precursor containing dispersion was heated up and burned at 500°C in a calcin-
ing furnace for two hours.
The before-synthetized maghemite was applied for catalyst preparation by using
a Hielscher Ultrasound tip homogenizer (UIP1000hDT). The palladium precursor
(0.125g) was solved in 50ml abs. ethanol, and 1.00g maghemite was added to the
solution. The ethanolic dispersion was sonicated by using the homogenizer (115W,
19.43kHz) for 2min. Then, the catalyst was removed from the dispersion with a Nd
magnet, washed with ethanol, and dried at 105°C overnight.
Characterization techniques ofthenanoparticles
Maghemite and palladium nanoparticles were examined by using high-resolution
transmission electron microscopy (HRTEM, FEI Technai G2 electron microscope,
200kV). The samples were prepared by dropping their aqueous suspension on 300
mesh copper grids (Ted Pella Inc.). The diameters of the nanoparticles were meas-
ured on the HRTEM images, based on the original scale bar by using the ImageJ
software. X-ray diffraction (XRD) measurements were used to identify and quantify
the crystalline phases, by applying a Rigaku Miniflex II diffractometer with Cu Kα
radiation source (30kV, 15mA). The palladium content was determined with a Var-
ian 720 ES inductively coupled optical emission spectrometer (ICP-OES), by using
a Merck Certipur ICP multi-element standard IV.
Catalytic tests
The catalytic hydrogenation was carried out in a Büchi Uster Picoclave reactor, in a
200ml stainless steel vessel with heating jacket. The hydrogen pressure was 20bar
and the reactions were carried at 283 K, 293 K and 323 K. Sampling took place
after the beginning of hydrogenation at 5, 10, 15, 20, 30, 60, 120, 180, and 240min.
The initial concentration of nitrobenzene was 0.125moldm−3 in methanol. The total
amount of the solution was 150ml and 0.2g catalyst was used during each test. Ani-
line formation was followed by applying Agilent 7890A gas chromatograph coupled
with Agilent 5975C Mass Selective detector. Analytical standards (aniline, nitroben-
zene, nitrosobenzene, azoxybenzene, dicyclohexylamine, o-toluidine, cyclohexy-
lamine and n-methylaniline) were provided by Dr. Ehrenstorfer and Sigma Aldrich.
The efficiency of the catalytic hydrogenation was compared by calculating the con-
version (X%) of nitrobenzene based on the following equation (Eq.1):
Reaction Kinetics, Mechanisms and Catalysis (2020) 129:107–116
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The selectivity (S%) of the catalyst was calculated as follows (Eq.2):
re naniline and nnitrobenzene are the corresponding chemical amounts of the compounds.
By assuming that the process is a first order reaction, based on the initial and
measured nitrobenzene concentrations (c0 and ck, mol/dm3), the reaction rate con-
stant (k) was calculated at different temperatures by non-linear regression (Fig.4)
according to the following (Eq.3):
Results anddiscussion
Surface morphology andphase composition ofthecatalyst
The reduction of palladium ions to elemental Pd have been confirmed by XRD
measurements (Fig.1a). Reflections at 40° and 48.8° 2θ degrees were identified on
the XRD pattern, which are attributed to the Pd(111) and Pd(200) phases (Fig.1a,
red line). Other reflections were also identified such as the peaks at 24.1°, 30.3°,
35.7°, 43.3°, 54°, 57.3° and 63° 2θ degrees, which are assigned to the presence of
(210), (220),(100), (400), (422), (511) and (400) planes of maghemite (γ-Fe2O3)
crystalline phase. The average size of the maghemite particles was found to be
21.8nm (Fig.1b). Palladium nanoparticles were deposited onto the surface of the
maghemite crystals. The palladium deposition onto the surface of the maghemite led
to the aggregation of the magnetic particles, the size of the nanocomposite aggre-
gates are between 70–200nm. The palladium particles on the maghemite aggregates
initial n
Fig. 1 XRD pattern of the maghemite (blue line) and Pd/maghemite catalyst (red line) (a) HRTEM
image and size distribution of maghemite (b) and Pd/maghemite (c)
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Reaction Kinetics, Mechanisms and Catalysis (2020) 129:107–116
are smaller than 8nm (the average size is 4.5nm) (Fig.1c). The formation of palla-
dium nanoparticles can be explained by the reduction effect of the appearing .CH2R
radicals. These reactive species generated by the ultrasonic treatment through the
reaction of .OH radicals and ethanol [37, 38].
Catalytic activity ofthemagnetic Pd catalyst
The prepared magnetic Pd catalyst was tested in nitrobenzene hydrogenation. The
maximum conversions were reached after 80min at 293K and 303K (Fig.2a). At
283K the reaction is slower, but the total amount of nitrobenzene was transformed
to aniline. The aniline selectivity was high, 97% and 96.7% at 293K and 303K,
respectively (Fig.2b). The catalytic activity was tested through five cycles at 303K
and 20bar hydrogen pressure, while the reaction time was 80min. The catalyst was
not regenerated between the cycles, only washed with methanol. The activity started
to decrease from the third cycle, which indicates that the regeneration of the catalyst
is necessary (Fig.2c).
The selectivity was lower, only 73.8%, at 283K which can be explained by the
low reaction rate, and the persistence of the intermediates which are not converted
to aniline (Fig.3a). At 283K, azoxybenzene and nitrosobenzene have been detected
during the reactions, which indicates that, the hydrogenation process follows the
Haber mechanism [3842]. At higher temperatures the intermediates transformed
to aniline (Fig.3b and c). The catalyst was very selective towards the formation of
aniline, by-products have not been detected. All in all, the prepared maghemite sup-
ported palladium catalyst at 303K reaction temperature and 20bar hydrogen pres-
sure can be applied effectively for aniline synthesis.
The reaction rate constants (k) at different temperatures were calculated based
on the measured nitrobenzene concentrations by using non-linear regression [43]
(Fig.4; Table1).
Fig. 2 Conversion of nitrobenzene vs time of hydrogenation (a) and aniline selectivity (b) at various
temperatures (283, 293 and 303K). Aniline yield vs number of cycles at 20bar pressure and 303K, after
80min of hydrogenation
Reaction Kinetics, Mechanisms and Catalysis (2020) 129:107–116
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Maghemite supported palladium catalyst was prepared. The maghemite catalyst
support was made by a newly developed combined technique, where sonochemical
Fig. 3 Concentration of the intermediates vs time of hydrogenation, at 283 K (a), 293 K (b) and
303K(c) at 20bar pressure
Fig. 4 Concentration of nitrobenzene vs time of hydrogenation
Table 1 Reaction rate constants
of nitrobenzene hydrogenation Temperature (K) 283 293 303
Reaction rate constant (s−1)1.73 × 10–2 4.09 × 10–2 5.10 × 10–2
SD 7.76 × 10–4 2.99 × 10–3 3.83 × 10–3
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Reaction Kinetics, Mechanisms and Catalysis (2020) 129:107–116
treatment and combustion have been used. This procedure leads to nanoparticles
with smaller crystalline size (21.8nm) and high adsorption capability. The catalyst
is in an active form immediately after the production of the Pd/maghemite nano-
composite, as the sonochemical treatment initiated the involvement of the disper-
sion media in the reduction of palladium ions to elemental palladium particles (Pd0).
In this sense, the catalyst does not require further post-treatments, and it does not
need to be reduced under a hydrogen atmosphere, therefore the catalyst preparation
method is simplified. The synthesized magnetic catalyst was efficiently applied in
nitrobenzene hydrogenation at 293K and 303K and the conversion was more than
99% in both case. The catalyst was selective towards aniline, and the selectivity was
97.0% and 96.7% at 293K and 303K, respectively. By-products were not detected
during the reaction. All in all, a simple method has been designed for magnetic cata-
lyst production. The achieved catalytic system is easily separable from the reaction
media, thanks to its magnetic property and successfully applicable in nitrobenzene
Acknowledgements Open access funding provided by University of Miskolc (ME). This research was
supported by the European Union and the Hungarian State, co-financed by the European Regional Devel-
opment Fund in the framework of the GINOP-2.3.4–15-2016–00004 project, aimed to promote the coop-
eration between the higher education and the industry. The EFOP-3.6.1-16-2016-00014 project is also
gratefully acknowledged due to support our work.
Compliance with ethical standards
Conict of interest On behalf of all authors, the corresponding author states that there is no conflict of
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Reaction Kinetics, Mechanisms and Catalysis (2020) 129:107–116
1 3
ViktóriaHajdu1· ÁdámPrekob1· GáborMuránszky1· IstvánKocserha2·
ZoltánKónya3· BélaFiser1,4· BélaViskolcz1· LászlóVanyorek1
Viktória Hajdu
Ádám Prekob
Gábor Muránszky
István Kocserha
Zoltán Kónya
Béla Fiser
Béla Viskolcz
1 Institute ofChemistry, University ofMiskolc, 3515Miskolc-Egyetemváros, Hungary
2 Institute ofCermics andPolymer Engineering, University ofMiskolc,
3515Miskolc-Egyetemváros, Hungary
3 Department ofApplied andEnvironmental Chemistry, University ofSzeged, Rerrich Béla sq. 1,
6720Szeged, Hungary
4 Ferenc Rákóczi II. Transcarpathian Hungarian Institute, Beregszász, Transcarpathia90200,
... Conventional catalyst preparation processes usually consist of several steps including post-treatment to activate the catalysts, which can be avoided by using a sonochemical method [28,29]. By applying sonochemical treatment, an active catalyst can be achieved in only one step [28,29]. ...
... Conventional catalyst preparation processes usually consist of several steps including post-treatment to activate the catalysts, which can be avoided by using a sonochemical method [28,29]. By applying sonochemical treatment, an active catalyst can be achieved in only one step [28,29]. The intense ultrasonic irradiation-(sonication) induced sound waves initiate cycles of high and low pressure in the liquid medium. ...
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The catalytic hydrogenation of 2,4-dinitrotoluene (DNT) to 2,4-toluenediamine (TDA) is a key step in the production of polyurethanes; therefore, the development of efficient hydrogenation catalysts for industrial use is of paramount importance. In the present study, chromium(IV) oxide nanowires were decorated by palladium and platinum nanoparticles in a one-step, simple, and fast preparation method to yield highly efficient hydrogenation catalysts for immediate use. The nanoparticles were deposited onto the surface of CrO2 nanowires by using ultrasonic cavitation and ethanol as a reduction agent. Beneficially, the catalyst became catalytically active right at the end of the preparation and no further treatment was necessary. The activity of the Pd-and Pt-decorated CrO2 catalysts were compared in the hydrogenation of 2,4-dinitrotoluene (DNT). Both catalysts have shown high activity in the hydrogenation tests. The DNT conversion exceeded 98% in both cases, whereas the 2,4-toluenediamine (TDA) yields were 99.7 n/n% and 98.8 n/n%, with the Pd/CrO2 and Pt/CrO2, respectively, at 333 K and 20 bar H2 pressure. In the case of the Pt/CrO2 catalyst, 304.08 mol of TDA formed with 1 mol Pt after 1 h hydrogenation. Activation energies were also calculated to be approximately 24 kJ•mol −1. Besides their immediate applicability, our catalysts were well dispersible in the reaction medium (methanolic solution of DNT). Moreover, because of their magnetic behavior, the catalysts were easy to handle and remove from the reaction media by using a magnetic field.
... The supports made of magnetic materials are promising vectors for the post-process operations. The application of magnetic materials as a support in catalytically active composites is a novel approach in the development of heterogeneous catalysts [14][15][16][17][18][19][20]. Magnetic supports allow for simple and efficient separation of a catalyst from the reaction mixture. ...
... Hajdu et al. [14] reported a high-performance catalyst composed of nanosized maghemite and metallic palladium. In their case, the high nitrobenzene synthesis yield was obtained at a lower temperature in comparison to our material (97 % at 20 • C). ...
A novel easy-to-prepare magnetic catalyst, composed of palladium nanoparticles supported on surface-oxidized carbon-encapsulated iron nanoparticles, has been synthesized. The synthesis involved the reduction of palladium precursor in the presence of magnetic core-shell nanomaterial. The size of the palladium nanoparticles distributed over the support does not exceed 15 nm. The catalytic performance of this composite material was tested in hydrogenation of seven various nitro compounds to the respective amino derivatives. The composite exhibits excellent catalytic activity and can be easily separated from the reaction mixture after the reaction. The determined reaction yields were above 90 % and this value was not worsened even after ten cycles, for the case of hydrogenation of nitrobenzene. Importantly, the method is chromatography-free and employs the ammonium formate as a hydrogen source, which makes the herein presented protocol safer in comparison with the previously reported reductions in which highly dangerous gaseous hydrogen was used.
... It is a difficult job to compare our results with others in literature. For better comparison, the same parameters and Pd content were used in two of our earlier papers [35,40]. Comparing to our 5 wt% Pd N-doped carbon nanotube/zeolite composite catalyst the cellulose based catalyst provided higher specific surface area (15 m 2 /g for zeolite composite, 289,70 m 2 /g for carbonized cellulose) and fibrous structure with low porosity for faster mass transport [40]. ...
... In case of our 5 wt% Pd/maghemite magnetic catalyst, the preparation was more complex (including a combustion step), more reagents were necessary, and was more difficult to handle due to its powder form [35]. ...
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Carbonized cellulose catalyst support was prepared and decorated with 5 wt% Pd nanoparticles using an impregnation method. According to the SEM images, the carbonized cellulose catalyst support kept its original fibrous structure with an average diameter of 200 nm, owing to the carbonization of the cellulose fibers. The surface of the formed carbon fibers is richly coated by palladium with even coverage. The particles can be divided into two groups within which the average diameter is either 5 nm, or 20–70 nm. TGA method was used to measure the amount of the remained carbon, which was 31.71 wt%. The FTIR spectrum shows the presence of oxygen containing functional groups on the surface of the support, which are hydroxyl groups. XRD method was used to determine the phases of Pd on the support where elemental Pd was detected which confirms the success of the activation step. The catalyst was tested in nitrobenzene hydrogenation in methanolic solution as a model reaction for nitroarene hydrogenation, meanwhile the temperature dependence of the reaction was also examined. Catalytic tests were carried out at four different temperatures (283–323 K) and constant hydrogen pressure (20 bar). The highest conversion (>99%) has been reached at 303 K and 20 bar. The corresponding activation energy was calculated by non-linear regression based on Arrhenius plot, and it was 24.16 ± 0.8 kJ/mol. All in all, the granulated cellulose beads are ideal starting points for carbon based catalyst supports.
... The author ascribed this drastic drop to the lack of a catalyst regeneration step between consecutive runs. [68] Other magnetic Pd catalysts include Fe 3 O 4 @SiO 2 @polysalophen-Pd(II) which incorporated the Pd(II) complex onto the magnetite surface to achieve 76% conversion of 4-nitrophenol (4-NP) with 96% selectivity for 4-aminophenol (4-AP). The magnetic Pd-complex was also investigated for the reduction of other nitro benzenes such as nitrobenzene, 1,3-dinitrobenzene and 4-methyl-1-nitrobenzene that achieved yields of 96%, 98% and 90%, respectively. ...
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The increase in population and industrial activities has resulted in harmful pollutants in our water sources that cause a concern for our future health and environmental well-being. These pollutants include pharmaceuticals, nitroarenes, synthetic dyes, oil and heavy metals that can be toxic, carcinogenic and lead to multiple organ failure. Conventional methods used to remove these toxins are of high cost, poor recyclability and low efficiency. Therefore, it is important to find suitable methods to purify industrial and household wastewater. Nanoparticles possess useful characteristics such as high surface-to-volume ratio, high optical absorption coefficient and tunable band edges for optimized catalytic capability. Magnetite NPs in specific have proven great efficiency in the removal and degradation of such pollutants as it is affordable, recyclable and easy to remove in the presence of an external magnetic field. Surface functionalization of these magnetic NPs is seen as an excellent bridge between homogeneous and heterogeneous catalysis. A metal catalyst immobilized on the surface of these magnetic nanoparticles (MNPs) affords customization and optimization of their properties for targeted applications. This study briefly discusses the synthesis of the magnetic core and different immobilization methods used to secure a metal catalyst onto its surface. This is followed by a detailed discussion where these metal catalysts immobilized on MNPs are used to improve its absorption and degradation capabilities in wastewater treatment.
... Palladium catalysts on activated carbon are the main types, although their separation from the reaction medium is difficult and time-consuming due to their very small (several 10-100 nm) particle size. The use of magnetic materials as catalyst supports is a novel approach in the hydrogenation of NB [21][22][23][24]. Magnetic materials allow easy and efficient separation of the catalyst using an external magnet or magnetic field, avoiding complicated and time-consuming additional separation operations such as filtration and centrifugation [25]. ...
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Aniline (AN) is one of the most important compounds in the chemical industry and is prepared by the catalytic hydrogenation of nitrobenzene (NB). The development of novel, multi-functional catalysts which are easily recoverable from the reaction mixture is, therefore, of paramount importance. Compared to conventional filtration, magnetic separation is favored because it is cheaper and more facile. For satisfying these requirements, we developed manganese ferrite (MnFe2O4)-supported, magnetically separable palladium catalysts with high catalytic activity in the hydrogenation of nitrobenzene to aniline. In addition to high NB conversion and AN yield, remarkable aniline selectivity (above 96 n/n%) was achieved. Surprisingly, the magnetic support alone also shows moderate catalytic activity even without noble metals, and thus, up to 94 n/n% nitrobenzene conversion, along with 47 n/n% aniline yield, are attainable. After adding palladium nanoparticles to the support, the combined catalytic activity of the two nanomaterials yielded a fast, efficient, and highly selective catalyst. During the test of the Pd/MnFe2O4 catalyst in NB hydrogenation, no by-products were detected, and consequently, above 96 n/n% aniline yield and 96 n/n% selectivity were achieved. The activity of the Pd/MnFe2O4 catalyst was not particularly sensitive to the hydrogena-tion temperature, and reuse tests indicate its applicability in at least four cycles without regenera-tion. The remarkable catalytic activity and other favorable properties can make our catalyst potentially applicable to both NB hydrogenation and other similar or slightly different reactions.
... CNTs are well-known supporter catalysts in metal NPs such as Ru, Pt, Rh, Ni, Fe, and Pd to improve the catalytic activity and selectivity of the NPs in a variety of chemical reactions to attributed metal-support interaction and mass transfer (Hashemi et al. 2016). Maghemite-supported palladium NPs was prepared by Hajdu et al. (2020) for catalytic hydrogenation of nitrobenzene derivatives. The Pd NPs exhibited 99% conversion of aniline in all cases without forming byproducts and the nanocatalyst was recovered using a magnet for subsequent use without any post-treatment. ...
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Designing and building an ideal catalyst for organic reactions is needed to increase the efciency, reaction conditions, and to reduce its environmental impacts. The growth of nanotechnology is realized in the production of various nano-level catalysts for diferent applications. The as-synthesized nanocatalysts are easily manipulated to a desired shape and size with a high surface area to volume ratio, which is their critical property of the interaction of the nanomaterials with the substrates. These days, a vast array of catalysts (nanocatalysts) such as metals, metal oxides, magnetic, and alloyed/mixed nanocatalysts are applied in organic reactions to synthesize important chemicals in industries and pharmaceutical sectors with a high yield, selectivity, and reusability via reduction/hydrogenation, oxidation, condensation, C–C coupling, cyclization, and more. Consequently, this present review highlights the application of various nanocatalysts in organic reactions by combining certain proposed reaction mechanisms that have shown the impact of nanoparticles on the reactions. The factors influencing nanocatalyst performances are also discussed. Finally, the conclusion and future prospects are conveyed
This review provides an overview of the synthetic methods used for the preparation of monometallic Pd and Pt metal nanoparticles (NPs) supported on iron oxide and bimetallic Pd-Fe and Pt-Fe systems. The use of iron as a support or as a modifier leads to a change in electronic density on the noble metal, which in turn affects the catalyst activity. In particular, when iron oxide is used as a support the noble metal tends to donate electrons to the support. On the contrary, bimetallic noble metal-Fe NPs show a charge transfer from iron to the noble metal. This behavior occurs both when iron is in contact or strictly closed to the noble metal NPs. The synthetic approach used for the synthesis influences the physico-chemical properties of the final material, thus a focus on the synthetic procedures and the catalyst characterization are provided to elucidate the key factors that influence the exceptional catalytic performances of these materials. Pd-Fe, Pt-Fe bimetallic NPs were selected as representative systems due to their broad use in heterogeneous oxidation and hydrogenation catalytic reactions.
Maghemite particles were synthesized by using a combined combustion method and sonochemical step. Maghemite was used as carrier to prepare supported Pt and Pd catalysts after deposition via a sonochemical step. The catalysts were immediately ready to be used (metals were catalytically active) for the 2,4-dinitrotoluene hydrogenation to produce 2,4-toluenediamine. The most active catalysts were the Pd/maghemite and bimetallic Pd-Pt/maghemite. The catalysts were easily separable after reaction due to their magnetic properties.
Cobalt, copper, and nickel ferrite spinel nanoparticles have been synthesized by using a combination of sonochemical treatment and combustion. The magnetic nanoparticles have been used as supports to prepare ~4 wt% palladium catalysts. The ferrites were dispersed in an ethanolic solution of Pd(II) nitrate by ultrasonication. The palladium ions were reduced to metallic Pd nanoparticles, which were then attached to the surface of the different metal oxide supports. Thus, three different catalysts (Pd/CoFe2O4, Pd/CuFe2O4, Pd/NiFe2O4) were made and tested in the hydrogenation of 2,4-dinitrotoluene (DNT). A possible reaction mechanism, including the detected species, has been envisaged based on the results. The highest 2,4-diaminotoluene (TDA) yield (99 n/n%) has been achieved by using the Pd/NiFe2O4 catalyst. Furthermore, the TDA yield was also reasonable (84.2 n/n%) when the Pd/CoFe2O4 catalyst was used. In this case, complete and easy recovery of the catalyst from the reaction medium is ensured, as the ferrite support is fully magnetic. Thus, the catalyst is very well suited for applicationy in the hydrogenation of DNT or other aromatic nitro compounds.
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The solvent-free selective hydrogenation of nitrobenzene was carried out using a supported AuPd nanoparticles catalyst, prepared by the modified impregnation method (MIm), as efficient catalyst >99% yield of aniline (AN) was obtained after 15 h at 90 °C, 3 bar H2 that can be used without any further purification or separation, therefore reducing cost and energy input. Supported AuPd nanoparticles catalyst, prepared by MIm, was found to be active and stable even after four recycle experiments, whereas the same catalyst prepared by SIm was deactivated during the recycle experiments. The most effective catalyst was tested for the chemoselective hydrogenation of 4-chloronitrobenzene (CNB) to 4-chloroaniline (CAN). The activation energy of CNB to CAN was found to be 25 kJ mol−1, while that of CNB to AN was found to be 31 kJ mol−1. Based on this, the yield of CAN was maximized (92%) by the lowering the reaction temperature to 25 °C.
This study intends to design and prepare a new magnetic copper catalyst and its activity was assessed by carbon-carbon coupling reactions. For this purpose, 1-[3-(trimethoxysilyl) propyl] urea (TMSPU), hydrazine and CuI were used sequentially to modify Fe3O4@SiO2 core-shell magnetic nanoparticles to obtain an efficient magnetic transition metal catalyst. Various analytical techniques were used to characterize the catalyst to show that the achieved structure and its properties are well-suited for coupling reactions. Finally, Mizoroki-Heck and Ullmann coupling reactions were performed using Fe3O4@SiO2@PrNCu catalyst. The new catalyst offer simple synthetic procedure, convenient use for routine casework and low price. The Fe3O4@SiO2@PrNCu catalyst was easily separated by means of a permanent and ordinary magnet and the recovered catalyst was reused in six cycles without any significant loss of activity.
Fe 3 O 4 @SiO 2 microspheres were fabricated by a simple urea-assisted hydrothermal route. The spheres have a diameter of about 400 nm containing a dense magnetic core (150 nm) composed of individual magnetite nanoparticles (12 nm). The material was functionalized with different organosilanes containing electron-donor groups (APTES and APTDS). The materials were further used to stabilize Pd nanoparticles deposited on the microspheres surface, obtained by the in-situ reduction of Pd(NO 3 ) 2 . The catalysts were applied in the reduction of 4-nitrophenol using benign molecular H 2 as a reducing agent under mild reaction conditions (75 °C, PH 2 = 6 atm). The core-shell structures, dubbed Fe 3 O 4 @SiO 2 @-APTES-Pd and Fe 3 O 4 @SiO 2 @-APTDES-Pd were able to reduce p-nitrophenol to p-aminophenol in less than 7 min, and TOF as high as 533 h ⁻¹ was achieved. A single portion of each catalyst was also able to be reused several times in successive reaction batches, and the functionalization was crucial to obtain high catalytic activity. When comparing the activity of both catalysts, a single portion of Fe 3 O 4 @SiO 2 @-APTES-Pd could be used up to 22 times giving a total turnover number (TON) of 385 which is more than doubled compared to that obtained using the Fe 3 O 4 @SiO 2 @-APTDES-Pd catalyst. Another important result achieved in this study is the morphology of the core-shell (Fe 3 O 4 @SiO 2 ) microspheres (420 nm) obtained using a new coating methodology. The synthetic protocol uses urea as pH regulator to promote the hydrolysis of the shell precursor (TEOS) to SiO 2 . We found out that using urea instead of unfriendly alkaline reactants leads to the formation of regular core-shell Fe 3 O 4 @SiO 2 microspheres whereas the use of NaOH results in the formation of a random silica matrix containing magnetite nanoparticles.
In this study, a magnetically recyclable Pd catalyst was developed by using the novel support of iron-rich coal fly ash/silica ([email protected] 2 ) for highly efficient reduction of p-nitrophenol (p-NP). IRFA microspheres were coated with amorphous SiO 2 synthesized from non-magnetic coal fly ash (NMFA) and then loaded with Pd by impregnation method for the synthesis of Pd/[email protected] 2 . Various surface analyses demonstrated that amorphous SiO 2 was well deposited on the surface of IRFA, providing a unique three-dimensionally structured SiO 2 layer to suppress aggregation of IRFA and enhance dispersion of Pd nanoparticles. Pd/[email protected] 2 exhibited a significantly enhanced p-NP reduction than those of Pd/IRFA, Pd/Al 2 O 3 , and Pd/SiO 2 . Compared to other Pd- and metal-loaded catalysts, Pd/[email protected] 2 showed ˜4000× enhancements in k obs-p-NP /C M (L min ⁻¹ g M⁻¹ , M = precious metals) values and ˜3800× increases in price-normalized k obs-p-NP values, indicating that Pd/[email protected] 2 is a highly efficient and cost-effective alternative catalyst. The catalyst was successfully recycled five times without significant leaching of Pd, Si, and heavy metals because of the magnetic property of Pd/[email protected] 2 . The experimental results suggest the applicability of the surface-modified IRFA support for the development of novel magnetically recoverable catalysts without severe toxicity problems.
Multi-walled carbon nanotubes were filled or externally decorated with iron oxide nanoparticles to make them magnetically-recoverable. In the first case, the external surface was treated to be free of defects and oxygenated groups to favor internalization. A thermal decomposition route was followed in the second case. The formed nanoparticles were characterized and shown to consist in magnetite and/or maghemite. Moreover, when placed on the external surface of carbon nanotubes, they remained small and well-dispersed, leaving high proportion of free carbon surface for further functionalization. The intact sp ² carbon atoms were subsequently attacked by means of xanthate radical chemistry, followed by post-functionalization to graft a dipyridylamine ligand on the surface of both solids and pristine carbon nanotubes for comparison. Solids at each step of the syntheses were characterized by X-ray photoelectron spectroscopy (XPS). Palladium coordination onto the surface ligand was studied and the precursor [Pd(COD)Cl 2 ] complex gave the best results to afford CNT-supported molecular Pd(II) catalysts. XPS confirmed the +2 oxidation state of palladium on the carbon surface. The so-prepared magnetically-recoverable catalysts were successfully used in Suzuki-Miyaura cross-coupling catalytic application.
Clays are nontoxic, inexpensive, abundant, and have great potential as catalytic carriers because of their special structure, surface, and suitability for supporting transition metals. In this study, sepiolite was used as a ligand for the heterogenization of palladium chloride on Fe3O4 nanoparticle surface as a novel, high temperature stable, and recoverable green catalyst (Fe3O4@sepiolite-Pd²⁺). The catalytic activity of this system was tested in the reduction of nitroarene compounds and the Suzuki cross-coupling reaction. The catalyst structure was characterized using spectroscopic data and magnetic and thermal techniques such as Fourier transform infrared, scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction, vibrating sample magnetometer (VSM), and thermogravimetric analysis.
This report provides a description of the preparation and characterization of a Fe3O4@Ag- β-CD composite as a new magnetically recoverable catalyst for the synthesis of a number of biologically and pharmaceutically significant organic compounds in aqueous medium. The magnetic composite was characterized by TEM, EDS, XRD, VSM and FT-IR techniques. The result of the TEM analysis shows that the average size of Fe3O4@Ag-β-CD is less than 30 nm. Application of this hybrid material, as a catalyst, was studied efficiently in the one-pot multicomponent synthesis of 3,4- dihydropyrimidinone and 2,4-dihydropyrano[2,3-c]pyrazole derivatives. The main advantages of our method are simple isolation of products, easy recovery of the magnetic catalyst by an external magnet, reusability of the catalyst, and use of water as a green solvent.
Establishing a method of reduction of nitroarenes into corresponding amines in water without using flammable sodium borohydride or toxic hydrazine as hydrogen source, is quite challenging. Here, we show for the first time the propensity of sub-nanometric rhodium nanoparticles (< 1 nm) supported on ultra-small magnetic nanoparticles (8–10 nm), as reusable catalyst for the nitroarene reduction in aqueous medium using tetrahydroxydiboron (THDB) as reductant.
In this research, the performance of palladium catalyst coated on an efficient support, Fe3O4@Al2O3, was investigated for the removal of nitrate from groundwater in a catalytic chemical reduction process. The hydrogen gas was produced using an electrochemical cell with two graphite electrodes. The material characterization was performed using FE-SEM, TEM, XRD, and VSM analyses. The alumina coating had a considerable impact on the removal efficiency. An optimum rate of 8 wt% was selected for loading of palladium on the support. The Box-Behnken of response surface methodology was applied to optimize the reduction process and investigate effects of variables (time, nitrate concentration, and catalyst dosage) and their interactions on the response. Furthermore, the impact of current density as a parameter affecting the electrochemical production of hydrogen gas was investigated. A quadratic model with the maximum removal efficiency of 96% and N2 selectivity of 95% was obtained at an initial nitrate concentration of 150 mg L⁻¹, catalyst dosage of 2 g L⁻¹, and reaction time of 90 min. Moreover, using the catalyst dosage of 1.3 g L⁻¹, the nitrate concentration decreased from 150 mg L⁻¹ to the maximum contaminant level (MCL) of 50 mg L⁻¹ after the reaction time of 30 min, pH 7, and a current density of 25 mA cm⁻². The investigation of catalyst performance after three cycles of the regeneration showed that the catalyst regeneration was successful.