Nickel hydroxide/cobalt-ferrite magnetic nanocatalyst for alcohol oxidation

Article abstract of DOI:10.1021/co500031b

A magnetically separable, active nickel hydroxide (Bronsted base) coated nanocobalt ferrite catalyst has been developed for oxidation of alcohols. High surface area was achieved by tuning the particle size with surfactant. The surface area of 120.94 m² g^-1 has been achieved for the coated nanocobalt ferrite. Improved catalytic activity and selectivity were obtained by synergistic effect of transition metal hydroxide (basic hydroxide) on nanocobalt ferrite. The nanocatalyst oxidizes primary and secondary alcohols efficiently (87%) to corresponding carbonyls in good yields.

Full text of DOI:10.1021/co500031b

Research Article
pubs.acs.org/acscombsci
Nickel Hydroxide/Cobalt−Ferrite Magnetic Nanocatalyst for Alcohol
Oxidation
Pooja B. Bhat,† Fawad Inam,‡ and Badekai Ramachandra Bhat*,†
†Catalysis and Materials Chemistry Laboratory, Department of Chemistry, National Institute of Technology Karnataka,
Srinivasanagar, Surathkal, Mangalore-575025, Karnataka, India
‡Faculty of Engineering and Environment, Northumbria University, Newcastle upon Tyne, NE1 8ST, United Kingdom
S
* Supporting Information
ABSTRACT: A magnetically separable, active nickel hydrox-
ide (Brønsted base) coated nanocobalt ferrite catalyst has been
developed for oxidation of alcohols. High surface area was
achieved by tuning the particle size with surfactant. The
surface area of 120.94 m2 g−1 has been achieved for the coated
nanocobalt ferrite. Improved catalytic activity and selectivity
were obtained by synergistic effect of transition metal
hydroxide (basic hydroxide) on nanocobalt ferrite. The
nanocatalyst oxidizes primary and secondary alcohols
efficiently (87%) to corresponding carbonyls in good yields.
KEYWORDS: nano cobalt ferrite, transition metal hydroxide, high surface area, alcohol oxidation
INTRODUCTION
RESULTS AND DISCUSSION
■
■
Heterogeneously catalyzed selective oxidation of alcohols to
aldehydes presents a great challenge in the fine chemical
industry. The facile recovery and reuse of the nanoparticles
have received increasing attention in catalysis.1 In recent years,
nanostructured spinel ferrite have aroused as potential applicant
for catalysis with combination of green oxidants.2 Therefore,
researchers have employed magnetic nanoparticles as recyclable
support matrix with superior catalytic activity. Recent studies
explore that high catalytic activity can be harnessed by tuning
the particle size of the catalyst in heterogeneous selective
aerobic oxidation of alcohols.3
Chemical modification of spinel ferrite with different
transition metal ion leads to products with variable surface
area.4 Among the ferrites, cobalt substituted spinel ferrite are
attractive candidates because of their strong anisotropy, high
coercivity, moderate saturation magnetization, good mechanical
and excellent chemical stabilities at higher temperature.5,6
Rapid electron exchange between tetrahedral and octahedral
sites of spinel containing transition metal ion enhances its
catalytic activity.7 The catalytic activity of cobalt ferrite has been
reported for Knoevenagel condensation reaction and aerobic
oxidation of cyclohexane to cyclohexanol.8,9Gawande et al.
reported inexpensive magnetic Co−Fe2O4 nanocatalyst as
viable alternative for oxidation of alcohols to carbonyl
compounds with excellent yield using TBHP (tert-butyl
hydroperoxide) as oxidant.10
Characterization of the Catalyst. The amount of nickel
in the catalyst was determined to be 3 w% by Atomic
Absorption Spectroscopy (AAS). The FTIR spectrum of the
catalyst exhibited intense band at 3400 and 570 cm−1
corresponding to −OH stretch and Fe−O stretch, respectively,
as observed in Figure 1A. The band in the region of 1040 cm−1
assigned to Si−O stretching, evidently confirms the aminosilane
functionalization of the catalyst.11 The appearance of
absorption peak at 340 nm in the UV−vis spectra of the
catalyst further confirms silane adsorption as shown in Figure
1B.
The patterns of X-ray powder diffractograms of the catalyst
(Figure 2) showed three major diffraction peaks (JCPDS 22-
1086): 35.0, 57.2, and 62.0 indexed as (311), (511), and (440),
respectively.
The crystallite size present in solids was calculated from the
main diffraction lines of these phases using Scherer equation
(1)
D = 0.9λ/B cos θ
where B is the full wave half width maximum (fwhm) of the
diffraction peak at 2θ recorded using X-rays of wavelength λ =
1.514 Å.
Average crystallite size of 20 nm was observed. The
compositional analysis show the respective elements present
in the catalyst as observed in Figure 3.
In this study, we report the synthesis of nickel hydroxide
coated cobalt ferrite nanocatalyst for the oxidation of alcohols
under mild condition with H2O2 as terminal oxidant.
Received: February 24, 2014
Revised: July 9, 2014
Published: July 30, 2014
© 2014 American Chemical Society
397
dx.doi.org/10.1021/co500031b | ACS Comb. Sci. 2014, 16, 397−402

ACS Combinatorial Science
Research Article
Figure 1. (A) FTIR spectra and (B) UV−vis spectra of the catalyst.
The surface morphology of the catalyst shows that magnetic
nanoparticles were formed having dimensions less than 100 nm
(Figure 4). Uniform sized nanoparticles with different
morphology were obtained by using 3-aminopropyltriethox-
ysilane (APTES) as a surfactant. TEM micrographs exhibited
dispersion of nickel hydroxide on the spherical and flake shaped
ferrites with a smoothened surface. The hydroxide coating on
the nanocobalt ferrite is indicated by yellow circle (Figure 5).
The surfactant added forms an envelope on the magnetic
nanoparticles and prevents it from further agglomeration.
Hydroxide coating is observed as a thin dispersed layer on the
surface of the nanoparticles. Average crystallite size observed in
FESEM is comparable with the obtained TEM results. The
corresponding selected area electron diffraction (SAED)
pattern shows the well-defined rings and spots, characteristic
of the cubic structure of nanocrystalline CoFe2O4 in nickel
hydroxide-coated CoFe2O4 catalyst.
Figure 2. XRD pattern of cobalt ferrite.
The BET specific surface area of the catalyst was determined
over the relative pressure ranging from 0.05 to 0.3. The
Figure 3. Energy dispersive X-ray (EDX) analysis of the catalyst.
398
dx.doi.org/10.1021/co500031b | ACS Comb. Sci. 2014, 16, 397−402

ACS Combinatorial Science
Research Article
Figure 4. FESEM image of (A) naked CoFe2O4, (B) CoFe2O4: APTES (1:1), (C) CoFe2O4: APTES (1:0.5).
coordinating ability.13,14 Product selective liquid phase
oxidation of alcohols by different bases has been carried out
with synthesized catalyst as shown in Figure 7. The oxidation of
benzyl alcohol to benzaldehyde was used as a model reaction. It
is clear that bases, such as KOH, pyridine are prone to form
acids, while maximum conversion to aldehyde is observed by
the synthesized transition metal hydroxide constituted
CoFe2O4@ APTES@ Ni(OH)2 catalyst.
In this study, optimization of the reaction conditions of
alcohol conversion by the synthesized catalyst was carried out
under the influence of solvent, temperature, alcohol/oxidant
molar ratio, and length of the reaction time. Among the various
solvents, acetone, acetonitrile, dichloromethane, and methanol,
the activity of nano catalyst with H2O2 gave a good yield in
acetonitrile medium. Product analysis was done at regular
intervals of time under similar reaction conditions to study the
effect of time on the activity (Figure 8). It was observed that
the gas chromatography (GC) yield remained constant after a
reaction time of 7 h. The effect of the concentration of catalyst
in oxidation of alcohols with respect to model substrate showed
significant conversion for 0.01 g of catalyst which revealed the
catalytic role of transition metal hydroxide coated nanocobalt
ferrite.
Reduction in dimension of the catalyst offers higher surface
area with higher number of coordination sites and surface
vacancies which are responsible for the higher catalyst activity.
GC conversion of 87% on model substrate was observed for the
synthesized catalyst. Oxidation reaction was extended to a
variety of alcohols using the optimized reaction conditions. The
results for the oxidation of a variety of alcohols are summarized
in Table 1. Aromatic substituent was found to be more reactive
than aliphatic alcohols which can be attributed to its
delocalization. Similarly electron donating groups were found
Figure 5. TEM image of the catalyst showing nanoflakes and
nanoparticles enveloped by a hydroxide layer (circled). Inset shows
SAED image of the catalyst.
obtained belong to type IV according to IUPAC classification12
and exhibited hysteresis loop with BET surface area 120.94 m2
g−1 (Figure 6A). These hysteresis loops are characteristic of
mesoporous solid. BJH approach was used to calculate pore size
distribution for all the samples. The mean pore radius of the
investigated cobalt ferrite samples was in the range of 3−5 nm
which confirms the nature of the prepared system as
mesoporous solid. Figure 6B evidently showed narrow pore
size distribution.
The magnetization measurements determined by a vibrating
sample magnetometer (VSM) showed ferromagnetism and
hysterisis loop with coercivity (Hc) of 515.51G.
Catalytic Oxidation of Alcohols. Oxidation of alcohols
can be accelerated with base as a cocatalyst due to its high
399
dx.doi.org/10.1021/co500031b | ACS Comb. Sci. 2014, 16, 397−402

ACS Combinatorial Science
Research Article
Figure 6. (A) Nitrogen sorption isotherm and (B) BJH pore size distribution of the catalyst.
reaction. Among the various alcohols studied here, phenyl-
ethanol showed maximum conversion with GC yield of 99.5%.
Heterogeneous Catalysis and Reusability. Magnetic
catalysts can be easily recovered after the reaction and can be
reused (Figure 9) without the significant loss of the catalytic
activity and selectivity. After the reaction, catalyst was removed
from the reaction mixture by magnet, dried at 80 °C and
reused. Atomic absorption spectroscopy was carried out on the
synthesized CoFe2O4@ APTES@ Ni(OH)2 catalyst to verify
whether the observed oxidation of alcohols was caused by the
synthesized catalyst or because of the leached nickel species.
Catalyst media was separated by magnet around 50%
conversion and the oxidation reaction was continued with the
filtrate in the same condition. The separated catalyst media was
subjected to AAS. Clearly, the filtrate obtained after the
reaction had nickel concentration 0.2 w% compared to 3 w% of
CoFe2O4@APTES@Ni(OH)2 catalyst. This confirmed that the
catalyst is heterogeneous in nature. Furthur heterogeneity of
the catalyst was confirmed by mercury drop test.15
Figure 7. Product selectivity of the catalyst CoFe2O4@APTES treated
with [1] KOH (0.25 mmol), [2] pyridine (0.25 mmol), and [3]
Cs(CO3)2 (0.25 mmol) and [4] without base and [5] synthesized
catalyst.
In conclusion, high surface area of cobalt ferrite with variable
catalytic activity can be achieved with lower amount of
surfactant. The high surface area of 120.94 m2 g−1 has been
achieved for nickel hydroxide coated nanocobalt ferrite.
Coordinatively unsaturated metal centers (Lewis acid) with
transition metal hydroxide sites (Brønsted base) can provide
outstanding catalytic performance in oxidation of alcohols. The
synthesized magnetic nanocatalyst provides efficient and
environment friendly method for oxidation of aromatic alcohols
to corresponding carbonyls with high yield. Hence, this catalyst
is a viable alternative for oxidation of alcohols.
EXPERIMENTAL PROCEDURES
■
The FTIR spectra was measured on JASCO FTIR-4200 (KBr
technique). The flame atomic absorption spectroscopy (FAAS)
measurements was recorded on GBC 932-PLUS. The UV−vis
spectra were recorded in Analytikjena SPECORD S600.
Powder X-ray Diffraction (XRD) measurements were per-
formed on JEOL JDX 8P diffractometer. Surface morphology
and composition was studied by Field Emission Gun Scanning
Electron Microscopy (FEG-SEM) JSM-7600F, Transmission
Figure 8. Effect of time on the catalyst.
to slow down the oxidation reaction, whereas electron
withdrawing groups were found to accelerate the oxidation
400
dx.doi.org/10.1021/co500031b | ACS Comb. Sci. 2014, 16, 397−402

ACS Combinatorial Science
Research Article
Table 1. Catalytic Activity for Alcohol Oxidation Catalyzed by CoFe2O4@APTES@Ni(OH)2
*
Substrate (1.0 mmol); catalyst (Ni: 3 w%); oxidant (H2O2, 30%, 10 mmol) acetonitrile (3.0 mL). Conversion and selectivity were determined by
GC. Average of GC 3 trials.
Electron Microscope (TEM) Philips CM200. Surface area and
pore size distribution were studied by Gemini V2.00 surface
analyzer. All magnetic properties were determined by Lake-
shore VSM 7410 Vibrating Sample Magnetometer at room
temperature. The reaction product analysis was carried out
using Gas Chromatography (GC) (Shimadzu 2014, Japan),
siloxane Restek capillary column (30 m length and 0.25 mm
diameter) and Flame Ionization Detector. Column temperature
was increased at the rate of 10 °C/min and nitrogen was used
as the carrier gas.
401
dx.doi.org/10.1021/co500031b | ACS Comb. Sci. 2014, 16, 397−402

ACS Combinatorial Science
Research Article
REFERENCES
■
(1) Gill, C. S.; Price, B. A.; Jones, C. W. Sulfonic acid-functionalized
silica-coated magnetic nanoparticle catalysts. J. Catal. 2007, 251, 145−
152.
(2) Shi, F.; Tse, M. K.; Pohl, M. M.; Bruckner, A.; Zhang, S.; Beller,
M. Tuning catalytic activity between homogeneous and heterogeneous
catalysis: Improved activity and selectivity of free nano-Fe2O3 in
selective oxidations. Angew. Chem. 2007, 119, 9022−9024.
(3) Shi, F.; Tse, M. K.; Pohl, M. M.; Radnik, J.; Bruckner, A.; Zhang,
S.; Beller, M. Nano-iron oxide-catalyzed selective oxidations of
alcohols and olefins with hydrogen peroxide. J. Mol. Catal. A: Chem.
2008, 292, 28−35.
(4) Khan, A.; Smirniotis, P. G. Relationship between temperature-
programmed reduction profile and activity of modified ferrite-based
catalysts for WGS reaction. J. Mol. Catal. A: Chem. 2008, 280, 43−51.
(5) Pang, X.; Fu, W.; Yang, H.; Zhu, H.; Xu, J.; Li, X.; Zou, G.
Preparation and characterization of hollow glass microspheres coated
by CoFe2O4 nanoparticles using urea as precipitator via coprecipitation
method. Mater. Res. Bull. 2009, 44, 360−363.
Figure 9. Magnetically separable catalyst: (a) before magnetization
and (b) after magnetization.
(6) Soler, M. A. G.; Lima, E. C. D.; Silva, S. W.; Melo, T. F. O.;
Pimenta, A. C. M.; Sinnecker, J. P.; Azevedo, R. B.; Garg, V. K.;
Oliveira, A. C.; Novak, M. A.; Morais, P. C. Aging investigation of
cobalt ferrite nanoparticles in low pH magnetic fluid. Langmuir. 2007,
23, 9611−9617.
(7) Mohapatra, S.; Rout, S. R.; Panda, A. B. One-pot synthesis of
uniform and spherically assembled functionalized MFe2O4 (M = Co,
Mn, Ni) nanoparticles. Colloids Surf., A 2011, 384, 453−460.
(8) Senapati, K. K.; Roy, K. S.; Borgohain, C.; Phukan, P. Palladium
nanoparticle supported on cobalt ferrite: An efficient magnetically
separable catalyst for ligand free Suzuki coupling. J. Mol. Catal. A:
Chem. 2012, 352, 128−134.
Synthesis of CoFe2O4@APTES. Magnetic CoFe2O4 were
prepared by coprecipitation technique. The detailed synthesis
and optimization were reported elsewhere.16,17 Purified
CoFe2O4 were modified with 3-aminopropyltriethoxysilane
(APTES). One gram of CoFe2O4 nanoparticles were treated
with 0.5 g of APTES in the presence of toluene at 80 °C for 6 h
in argon atmosphere. After 1 h of aging, the resultant were
centrifuged and dried at 80 °C.
Synthesis of CoFe2O4@APTES@Ni (OH)2. The synthe-
sized CoFe2O4 were vigorously stirred with aqueous solution of
NiCl2.7H2O for 24h at room temperature with pH >13.2. The
nickel hydroxide functionalized CoFe2O4 was washed with
deionized water, ethanol, and dried at 80 °C.
Oxidation Reaction. All reactions were carried out on a
glass reactor (∼50 mL) in which benzyl alcohol (1 mmol),
nanocatalyst (0.01 g), and acetonitrile (3 mL) were added,
respectively. H2O2 (30 wt % in water, 10.0 mmol) was added as
oxidant and the reaction mixture was vigorously stirred at 80
°C. The aliquots of the reaction mixture were used for product
analysis at regular interval by gas chromatography technique.
The retention times for various compounds were determined
by injecting pure compounds under identical GC conditions.
(9) Tong, J.; Bo, L.; Li, Z.; Lei, Z.; Xia, C. Magnetic CoFe2O4
nanocrystal: A novel and efficient heterogeneous catalyst for aerobic
oxidation of cyclohexane. J. Mol. Catal. A: Chem. 2009, 307, 58−63.
(10) Gawande, M. B.; Rathi, A.; Nogueria, I. D.; Ghumman, C. A. A.;
Bundaleski, N.; Teodoro, O. M. N. D.; Branco, P. S. A Recyclable
Ferrite−Co Magnetic Nanocatalyst for the Oxidation of Alcohols to
Carbonyl Compounds. ChemPlusChem. 2012, 77, 1−7.
(11) Phan, N. T. S.; Jones, C. W. Highly accessible catalytic sites on
recyclable organosilane-functionalized magnetic nanoparticles:An
alternative to functionalized porous silica catalysts. J. Mol. Catal. A:
Chem. 2006, 253, 123−131.
(12) Sing, K. S. W.; Everett, D. H.; Haul, R. A. W.; Moscou, L.;
Pierotti, R. A.; Rouquerol, J.; Siemieniewska, T. Pure Appl. Chem.
1985, 57, 603−619.
(13) Zhu, J.; Figueiredo, J. L.; Faria, J. L. Au/activated-carbon
catalysts for selective oxidation of alcohols with molecular oxygen
under atmospheric pressure: Role of basicity. Catal. Commun. 2008, 9,
2395−2397.
ASSOCIATED CONTENT
■
S
* Supporting Information
(14) Yamaguchi, K.; Kim, J. W.; He, J.; Mizuno, N. Aerobic alcohol
oxidation catalyzed by supported ruthenium hydroxides. J. Catal. 2009,
268, 343−349.
Detailed information about optimization of the catalyst and its
magnetic reusability is attached, so as to facilitate the
understanding of magnetically retrievable catalyst. This material
is available free of charge via the Internet at http://pubs.acs.org.
(15) Sheldon, R. A.; Wallau, M.; Arends, I. W. C. E.; Schuchardt, U.
Heterogeneous catalysts for liquid-phase oxidations: Philosophers’
stones or Trojan horses? Acc. Chem. Res. 1998, 31, 485−493.
(16) Shobaky, G. A.; Turky, A.; Mostafa, N. Y.; Mohamed, S. K.
Effect of preparation conditions on physicochemical, surface and
catalytic properties of cobalt ferrite prepared by coprecipitation. J.
Alloys Compd. 2010, 493, 415−422.
(17) Qu, Y.; Yang, H.; Yang, N.; Fan, Y.; Zhu, H.; Zou, G. The effect
of reaction temperature on the particle size, structure and magnetic
properties of coprecipitated CoFe2O4 nanoparticles. Mater. Lett. 2006,
60, 3548−3552.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: brchandra@gmail.com. Fax: +91 824-2474033. Tel:
+91 824-2474000, ext. 3204.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
P.B.B. thanks NITK, Surathkal, for research fellowship, and IIT
Bombay, CRNTS, for FESEM and TEM analysis. We also
thank NIT Trichy for BET surface area analysis.
402
dx.doi.org/10.1021/co500031b | ACS Comb. Sci. 2014, 16, 397−402