G. Singh et al.
Molecular Catalysis 500 (2021) 111339
n-octane and supercritical CO2 have also been used for liquid phase FAL
hydrogenation[37]. A comparative evaluation of the solvent types for
the liquid phase FAL hydrogenation will be of much more importance to
give direction to future research work[38]. Moreover, according to the
principle of green chemistry, these organic solvents can create negative
effects on living organisms. Therefore, water was also used as a green
solvent in this work, and its performance is compared with organic
solvents. Operational variables such as reaction temperature, H2 pres-
sure, reaction time, and catalyst dose and reactant concentration also
instigate major effects. In this work, to the best of our knowledge, a
comprehensive study was made for the first time to show the effect of
different solvents and discussed the role of solvent on conversion and
selectivity in FAL hydrogenation reaction over the best catalyst selected
from a screening of various catalysts.
CZAl) and calcined in a muffle furnace. The catalyst was heated to 350
◦C at heating rate 1 ◦C/min and aged at the same temperature for 6 h.
The obtained sample was black in color. Other catalysts such as CZ, CA,
CZCr, CZCr, CZAlLa, CZAlZa, CZAlTi, CZMgAl, and CZZr were prepared
following a similar procedure.
Two supported catalysts Cu(10 wt%)/hydrotalcite and Pd(3 wt
%)/activated carbon were prepared using the incipient wetness
impregnation method. In a typical process of synthesizing Cu/hydro-
talcite, the required amount of copper nitrate hexahydrate precursor
was dissolved in 10 mL of deionized water in a round bottom flask to
which 2 g of hydrotalcite (HT) was added. The sample was kept at 80 ◦C
under constant stirring until the complete water evaporated. The cata-
lyst sample was further washed with an excess of water, dried at 100 ◦C
for 12 h. Subsequently, the dried powder was calcined in a muffle
furnace for 4 h at 550 ◦C to obtain the powder of Cu/MgO-Al2O3 par-
ticles. A similar process was followed to prepare Pd(3 wt%)/activated
carbon. Commercial CuCrO3 catalyst was also used for hydrogenation of
FAL and designated by the code of CCr.
In this paper, several Cu/Zn/X-Y [X-Y = Al2O3, Al2O3-ZrO2, Al2O3-
TiO2, Al2O3-MgO, La2O3, hydrotalcite (without Zn)] were synthesized.
Two supported catalysts Pd/Activated carbon, and Cu/ Hydrotalcite was
also synthesized and tested for comparative evaluation of catalysts. The
performance of these catalysts was examined and compared in terms of
catalyst activity and stability for the chemoselective hydrogenation of
FAL to FA. Furthermore, the effect of several solvents, including protic,
aprotic polar, and aprotic apolar was investigated over the Cu/Zn/Y/Z
catalyst system. The chemistry has been discussed considering sol-
vatochromic solvent parameters such as hydrogen bond acceptance
2.3. Catalyst characterization
The crystallinity of the samples was analyzed from X-ray diffraction
(XRD) pattern recorded on the ROTO AXRD benchtop system using
monochromatic Cu-Kα radiation (λ = 1.542 Å) at 40 kV and 40 mA. The
capability (β), hydrogen bond acceptance capability (α), and the polar-
XRD patterns of all the samples were recorded in the 2θ range of 20◦-80◦
with a 0.04 step size. The average crystallite size (T) was calculated
using the Scherrer formula (eq. 1):
izability/polarity index (П*). The effects of different operating condi-
tions (temperature, time, H2 pressure, reactant concentration, and
catalyst weight) were measured on conversion, selectivity, and FA yield.
Moreover, the long term stability of catalyst and kinetics of the hydro-
genation reaction were examined due to their importance from an in-
dustrial point of view.
0.9λ
β cosθ
T =
(1)
Where K (dimensionless shape factor) = 0.9, λ = X-ray wavelength, θ =
Bragg angle and β = line broadening at the half-maximum intensity
(FWHM). The textural properties of all samples were evaluated by N2
sorption measurements at ꢀ 196 ◦C using Micromeritics ASAP 2020
Surface area and Porosity analyzer. Before the analysis, the degas-
ification of the samples was carried out at 240 ◦C for 6 h. The BET model
was fitted to isotherms between relative pressure ranges (P/P0 = 0.05-
0.3) to determine the specific surface area of samples. Total pore vol-
ume was estimated using N2 adsorption data of isotherm at relative
pressure P/P0 = 0.99. The average pore size was determined using the
Barrett-Joyner-Halenda (BJH) method. Temperature programmed
reduction (TPR) analysis was carried out to check the reducibility of the
synthesized material. TPR experiments were conducted in a Micro-
meritics, AutoChem II 2920 instrument connected with a thermal con-
ductivity detector (TCD). The analysis was carried out in the
temperature range of 40-900 ◦C with an increment of 10 ◦C per minute
using Helium as a carrier gas. The microstructure of the sample was
analyzed using a high-resolution transmission electron microscope JEOL
JEM 2100. First, the sample was dispersed into ethanol and then
mounted on a lacey carbon formvar coated copper grid. Elemental
analysis of the synthesized samples was carried out by energy-dispersive
X-ray spectroscopy (EDX). Thermal gravimetric analysis (TGA) analysis
of the samples was performed in the air on a Perkin Elmer TGA 8000
thermal analyzer maintaining a flow rate of 30 mL/min and heating rate
of 20 ◦C/min.
2. Experimental
2.1. Materials
Copper nitrate trihydrate salt (Aldrich, Germany) was used as a
copper source in all the catalysts. The reactant furfural [chemical for-
mula = C5H4O2, M.W. = 96.09 g/mol] was sourced from TCI Japan and
used without additional purification. Other chemicals used were zinc
nitrate hexahydrate (Aldrich, Germany), nitric acid (SD fine Chemicals,
India), magnesium nitrate hexahydrate (Aldrich, Germany), aluminum
nitrate nonahydrate (Aldrich, Germany), lanthanum trinitrate hydrate
(Aldrich, Germany), zirconium oxynitrate hydrate (Aldrich, Germany)
and sodium carbonate (Rankem, India). The chemical composition of
the prepared catalysts is given in Table 1.
2.2. Catalyst preparation
Different catalysts were prepared using co-precipitation and wet-
impregnation method [39]. Cu/Zn/X-Y catalysts were synthesized
using the co-precipitation method under semi-batch reaction conditions.
In a typical process of preparing CZAl samples, two solutions A and B
were prepared. The solution A containing metal ions (1 M) was prepared
by dissolving copper nitrate trihydrate, zinc nitrate hexahydrate, and
aluminum nitrate in 290 ml of distilled water with 7.5 ml of concen-
trated nitric acid. Solution B (1.6 M) containing sodium carbonate was
prepared to adjust the pH. Solution A was introduced slowly by a peri-
staltic pump in a container holding 400 ml of distilled water at T =65 ◦C,
and a constant pH = 6.5 was maintained by controlling the flow of so-
lution B. The mixture was stirred continuously to keep uniform condi-
tion throughout precipitation in the semi-batch reactor. After
completion of the controlled pH precipitation process, the suspension
was aged for 90 min under the same condition, filtered, washed with
deionized water until pH is neutral, and dried overnight at 100 ◦C. The
dried powder (green in color) was grinded to obtain fine powder (fresh
2.4. Catalyst activity
All batch experiments were carried out in a 25 ml Parr reactor
equipped with a heating system, pressure gauge, and overhead stirrer
(Fig. 1). Prior to every reaction, all Cu-based catalysts were reduced at
300 ◦C for 2 h. The reaction solution of FAL of desired concentration was
freshly prepared in HPLC grade water, and catalytic hydrogenation of
this solution was performed with continuous stirring at 700 RPM. In
each experiment, the 15 mL solution was taken, and the desired amount
3
Singh, Gurmeet
