Pore Size Architecture of Hexagonal Mesoporous Carbon Nitride (HMCN) for Metal-Free Synthesis of p-Hydroxycinnamic Acid

Article abstract of DOI:10.1007/s10562-018-2373-9

Abstract: The nanochannels of hexagonal mesoporous carbon nitride (HMCN) base catalytic materials were architected with diameter of 4.7, 5.9, and 7.1?nm using SBA-15 hard templates and these catalysts were represented as HMCN (4.7), HMCN (5.9), and HMCN (7.1), respectively. These materials were characterized by XRD, N₂ sorption, FESEM, EDAX, HRTEM, FTIR and DR UV–Vis spectroscopy. The influence of HMCN catalysts with different pore sizes on p-hydroxycinnamic acid synthesis was investigated in metal/pyridine-free reaction conditions. The catalytic experimental results of HMCN (5.9) catalyst with optimum pore diameter of 5.9?nm showed an excellent catalytic performance of 94.5% p-hydroxybenzaldehyde conversion with 100% p-hydroxycinnamic acid selectivity within 60?min in comparison with other two catalysts, namely HMCN (4.7) and HMCN (7.1).

Full text of DOI:10.1007/s10562-018-2373-9

Catalysis Letters
https://doi.org/10.1007/s10562-018-2373-9
Pore Size Architecture of Hexagonal Mesoporous Carbon Nitride
(HMCN) for Metal-Free Synthesis of p-Hydroxycinnamic Acid
P. Elamathi1 · G. Chandrasekar1
Received: 5 December 2017 / Accepted: 25 March 2018
© Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
The nanochannels of hexagonal mesoporous carbon nitride (HMCN) base catalytic materials were architected with diameter
of 4.7, 5.9, and 7.1 nm using SBA-15 hard templates and these catalysts were represented as HMCN (4.7), HMCN (5.9), and
HMCN (7.1), respectively. These materials were characterized by XRD, N2 sorption, FESEM, EDAX, HRTEM, FTIR and
DR UV–Vis spectroscopy. The influence of HMCN catalysts with different pore sizes on p-hydroxycinnamic acid synthesis
was investigated in metal/pyridine-free reaction conditions. The catalytic experimental results of HMCN (5.9) catalyst with
optimum pore diameter of 5.9 nm showed an excellent catalytic performance of 94.5% p-hydroxybenzaldehyde conversion
with 100% p-hydroxycinnamic acid selectivity within 60 min in comparison with other two catalysts, namely HMCN (4.7)
and HMCN (7.1).
Graphical Abstract
Keywords HMCN · Pore size · Knoevenagel–Doebner condensation · Heterogeneous catalysis · Metal-free base catalyst
1 Introduction
Electronic supplementary material The online version of this
p-Hydroxycinnamic acid (p-coumaric acid) is a very impor-
article (https://doi.org/10.1007/s10562-018-2373-9) contains
tant ingredient for the synthesis of several drugs and phar-
maceuticals as they find their direct applications in anti-
tuberculosis, anti-inflammatory, anti-cancer, anti-oxidant,
anti-microbial, hepatoprotective, CNS depressant, anti-
bacterial, anti-fungal, anti-malarial, and UV rays absorbent
supplementary material, which is available to authorized users.
* G. Chandrasekar
gc_sekar78@yahoo.co.in
1
Chemistry Division, School of Advanced Sciences, VIT
University Chennai Campus, Chennai, Tamil Nadu, India
Vol.:(0123456789)
1 3

P. Elamathi, G. Chandrasekar
[1–5]. Traditionally the p-hydroxycinnamic acid is synthe-
sised by Knoevenagel–Doebner reactions using homogene-
ous base catalysts like aniline, pyridine, hexamethylenetet-
ramine, tri-ethylamine, ammonia and piperidine [6–8], etc.
But these catalysts have their own disadvantages of hazard-
ousness, carcinogenic, and unrecoverable from the reaction
mixture, because of homogeneous nature. Solid heteroge-
neous base catalysts such as metal oxides, metal–organic
frameworks (MOF), magnetic supports, silica, and polymers
have been employed in Knoevenagel–Doebner reaction
[9–12] to solve the catalyst recovery issues. Nevertheless
these solid catalysts possess drawbacks like low stability
(MOF), lack of structural variability (magnetic nanopar-
ticles) or restrictions to reuse (polymers). Hence there is
a huge demand in the catalyst preparation to design an
environment friendly, efficient, and economical way for
p-hydroxycinnamic acid synthesis.
yield of 91%, 100% selectivity and maximum p-hydroxy-
benzaldehyde conversion of 94.5% at 60 min compare to
other two catalysts, namely HMCN (4.7) and HMCN (7.1).
These findings provide insight into the design and develop-
ment of HMCN catalytic materials with suitable pore size
for a wide range of product for the selective catalytic organic
transformations.
2 Experimental
2.1 Synthesis of SBA‑15 Templates and HMCN
Catalysts
Mesoporous SBA-15 silica template was synthesised by
employing optimized procedure with a molar gel composi-
tion of TEOS: 0.016 P123: 12.6 HCl: 167 H2O at different
aging temperature of 100, 120, and 150 °C [20]. The solid
product obtained from aging process was filtered, washed
with deionized water then calcined at 550 °C for 36 h.
HMCN catalysts were prepared using SBA-15 templates
with different pore diameters. In a typical synthesis, 0.5 g
of SBA-15 was added to a mixture of EDA (2.2 g) and CTC
(5.4 g) in RB flask. The resultant mixture was refluxed and
stirred at 90 °C for 6 h. Then the mixture was dried for 24 h
and ground into fine powder. The composite powdered mate-
rial was pyrolysis at 800 °C in an inert atmosphere for 5 h.
HMCN materials were obtained after the removal of silica
templates by HF and were labelled as HMCN (x), where x
indicates the pore diameter of the materials [21].
Hexagonal mesoporous carbon nitride (HMCN) opened
a new avenue in the field of catalysis and material science
owing to its significant properties such as large specific
surface area, uniform pore size distribution, high specific
pore volume, hydrophobic nature, and high chemical and
mechanical stability [13–16]. Very recently HMCN materi-
als are used in base catalytic organic transformations with
promising results [17–19]. The great problem in the porous
material catalysis is that a catalytic material with similar
pore size might not be applicable for different reactants with
different molecular sizes. Hence, the architecture on the pore
size of HMCN will facilitates the reactants with different
molecular sizes to access the basic sites inside the pores of
HMCN catalysts.
So herein we report for the first time an efficient envi-
ronment friendly HMCN catalytic system by architecting
the pores with different pore sizes of 4.7, 5.9, and 7.1 nm
(Scheme 1) for the synthesis of p-hydroxycinnamic acid
from p-hydroxybenzaldehyde and malonic acid in pyridine-
free, metal-free, and environmental friendly conditions.
The influence of pore sizes in the HMCN base catalysts was
investigated in the p-hydroxycinnamic acid synthesis and
the experimental results reveal that HMCN (5.9) showed
a better catalytic performance with high product isolated
2.2 Characterisation
XRD patterns of HMCN samples were recorded on a pow-
der X-ray diffractometer (Rigaku, Smart lab, Japan) using
Cu Kα (λ=1.54 Å) radiation. Nitrogen sorption isotherms
were measured in Quantachrome (Autosorb 1 sorption ana-
lyzer, USA). FESEM images were recorded Hitachi S-4800-
TWIN. Transmission electron microscopy was conducted
using a FEI-Tecnai G2 20 S-TWIN electron microscope
operated at an accelerating voltage of 200 kV. UV–Vis
Scheme 1 Synthesis of p-hydroxycinnamic acid using HMCN catalyst
1 3

Pore Size Architecture of Hexagonal Mesoporous Carbon Nitride (HMCN) for Metal-Free Synthesis…
diffused reflectance spectroscopy was performed on a PER-
KIN ELMER LAMDA 35, USA, double beam spectrometer
in the range of 200–800 nm in ambient conditions. 1H NMR
and 13C NMR spectra were recorded on Bruker (AVANCE
III, 400 MHz) spectrometer using TMS as an internal stand-
ard. LCMS spectrums were recorded using Agilent 1290
series, Mass 6150 quadru pole LCMS.
recrystallization. Product was confirmed by NMR analysis
(ESI).
3 Results and Discussion
Powder XRD pattern of (a) SBA-15 templates and (b)
HMCN materials are shown in Fig. 1. The XRD pattern (a)
of SBA-15 templates showed a characteristic peaks due to
(100), (110), and (200) reflections due to p6mm symmetry.
The XRD pattern (b) of HMCN samples showed a character-
istic intense peak at 2ϴ value of 0.97 due to (100) reflection
and two higher order peaks due to (110) and (200) reflec-
tions below 2ϴ value of 2. This clearly indicates the persis-
tence of hexagonal structure having p6mm symmetry in the
HMCN samples. The XRD peaks of SBA-15 samples shift
towards 2ϴ values as the aging temperature increases from
100 to 150 °C. This confirms that as the aging temperature
increases the unit cell constant and d-space value increases.
The same trend was observed in the HMCN replica materi-
als synthesised from the corresponding SBA-15 templates
(Table 1). This result firmly confirms that HMCN samples
have an ordered structure and the replication process from
SBA-15 template to HMCN is very much successful. The
high angle XRD pattern of HMCN (5.9) sample (Fig. 1b,
inset) showed a broad peak at 2ϴ value of 24.8 and a weak
peak at 44 due to (002) and (100) reflections, respectively.
This is similar to the XRD pattern of graphitic CN obtained
from turbostratic graphite-like stacking of the conjugated
aromatic CN units [20].
2.3 Synthesis of p‑Hydroxycinnamic Acid
The catalytic performance of HMCN samples was tested
on the synthesis of p-hydroxycinnamic acid in Knoev-
enagel–Doebner reaction under toluene (10 ml) azeo-
tropic reflux condition (105 °C) by taking 1:2 mol ratio of
p-hydroxybenzaldehyde (0.0040 mol) and malonic acid
(0.0081 mol) with 200 mg of HMCN base catalyst. The cata-
lytic reactions were studied with different reaction conditions
such as reaction time, catalyst amount, pore size of the cata-
lyst, and reaction cycle. The reaction mixture were collected,
filtered using syringe filter and analysed by gas chromatog-
raphy (Thermo Scientific TRACE1300, USA) equipped
with DB-5 capillary column (30 m×0.32 mm×1 µm film
thickness) and flame ionization detector using nitrogen
carrier gas using n-decane as internal standard. The per-
formance of HMCN catalysts is evaluated quantitatively
by the conversion of p-hydroxybenzaldehyde (conversion
%), and the selectivity to p-hydroxycinnamic acid (selectiv-
ity %) obtained at the selected conditions. Herein, conver-
sion (%) = ((initial peak area of reactant − final peak area
of reactant)/initial peak area of reactant)×100; selectivity
(%)=(relative peak area of specific product/sum of relative
peak area of the all products) × 100. After completion of
reaction, the catalyst was recovered by filtration and washed
with methanol and hexane. The reaction product p-hydrox-
ycinnamic acid was obtained after the toluene removal
by a rotary evaporator and purified by absolute ethanol
Nitrogen adsorption isotherms (a) and pore size distri-
butions (b) of HMCN samples are shown in Fig. 2 and the
textural properties are shown in Table 1. Nitrogen adsorption
isotherms (a) of HMCN samples exhibit type IV adsorption
isotherm with H1 hysteresis loop, which revealed a narrow
pore size distribution present in the HMCN materials. The
Fig. 1 Powder XRD patterns
of a SBA-15 templates and b
HMCN catalysts
1 3

P. Elamathi, G. Chandrasekar
Table 1 Physicochemical property of different SBA-15 and HMCN samples
S. no. Samples
Catalyst C/N mole Catalyst C/N mole
S
BET (m2/g) Vp (cm3/g) Dp (nm) ao (nm) d100 (nm) Total amount of
ratio in synthetic
gel
ratio in sample by
EDAX
nitrogen (mmol/g)
by EDAX
1
2
3
4
5
6
SBA-15 (9.0)
–
–
–
1.48
1.48
1.48
–
–
–
2.22
2.22
2.25
895
653
395
509
389
379
1.20
1.20
1.10
0.51
0.55
0.64
9.0
10.5
11.3
4.7
5.9
7.1
10.3
10.9
11
9.8
10.3
10.7
8.9
9.4
9.5
8.5
8.9
9.3
–
–
–
4.92
4.90
4.78
SBA-15 (10.5)
SBA-15 (11.3)
HMCN (4.7)
HMCN (5.9)
HMCN (7.1)
The SBET, Dp, and Vp values of SBA-15 are based on the literature (see Ref. [20])
SBET specific surface area, Vp pore volume, Dp pore diameter, ao unit cell constant was calculated as, ao =2×d100/√3
Fig. 2 a Nitrogen adsorption
isotherms and b pore size distri-
butions of HMCN catalysts
pore diameter of HMCN catalysts prepared using SBA-15
templates synthesised at different temperatures increased
from 4.7 to 7.1 nm. A shift in the position of capillary con-
densation step of N2 adsorption isotherms of HMCN sam-
ples was observed from low P/P0 (relative pressure) to high
P/P0 value. This indicates a huge expansion in the pore size
of HMCN replica materials as the synthesis temperature
of corresponding SBA-15 templates increases. This is in
consistent with increase in unit-cell constants and d-space
values observed from the XRD patterns of HMCN samples
in Fig. 1b [21]. A decrease in specific surface area from 509
to 379 m2/g and increase in specific pore volume from 0.5
to 0.64 cm3/g and pore diameter from 4.7 to 7.1 nm of the
HMCN replica materials were observed as increase in the
aging temperature of SBA-15 templates used. The change in
Fig. 3 UV–Vis diffused reflectance spectra of HMCN catalysts
the pore diameter of the HMCN materials upon increasing
the pore diameter of the SBA-15 template is clearly evident
from their BJH adsorption pore size distribution (Fig. 2b).
Diffused reflectance UV–Vis spectra (Fig. 3) of HMCN
samples exhibited a strong absorbance at ca. 330 nm due to
π→π* electronic transition of aromatic 1,3,5-triazine and
n→π* non-bonding electronic transition of nitrogen atoms
[22]. FT-IR spectra (Fig. 4) of HMCN samples show three
predominant broad bands at ca. 1222, 1571 and 3354 cm−1
1 3

Pore Size Architecture of Hexagonal Mesoporous Carbon Nitride (HMCN) for Metal-Free Synthesis…
due to aromatic C–N stretching bands, aromatic ring modes
and N–H stretching in the aromatic ring, respectively [20].
The FESEM–EDAX mapping of carbon and nitrogen ele-
mental analysis of HMCN (5.9) sample is shown in Fig. 5.
FESEM image (a) of HMCN (5.9) sample showed aggre-
gates of warm like regular rod-shaped particles of ca. 2 µm
sizes with co-existence of ca. 0.5 µm particle size. EDAX
analysis of HMCN (5.9) sample is provided in Table 1.
EDAX results showed that the final product of HMCN cata-
lyst has a higher C/N mole ratio than the actual mole ratio
used in the synthesis. This is due to the low thermodynamic
stability of nitrogen in the carbon matrix and the nitrogen
prefers to stay as nitrogen molecule at high temperature.
Elemental mapping analysis (b) and (c) of HMCN (5.9) sam-
ple clearly demonstrates that N is homogeneously distributed
in the carbon matrix within the HMCN composites.
HRTEM measurement was used to further examine the
structural order and morphology of the HMCN materi-
als with different pore diameters and it is shown in Fig. 6.
HRTEM images of (a) HMCN (4.7), (b) HMCN (5.9), and
(c) HMCN (7.1) samples show a linear array of mesopores
arranged in regular tubular channels. The HRTEM analysis
Fig. 4 FTIR spectra of HMCN catalysts
Fig. 5 a FESEM image of HMCN (5.9) and EDAX element mapping of b carbon and c nitrogen
Fig. 6 HRTEM images of HMCN samples a HMCN (4.7), b HMCN (5.9), and c HMCN (7.1)
1 3

P. Elamathi, G. Chandrasekar
of HMCN samples prepared from SBA-15 synthesised at
100, 120, and 150 °C showed that the width of mesopore
tubular channels are ca. 7.4, 8.3, and 8.9 nm, respectively.
Electronic structure calculations on p-hydroxybenzal-
dehyde and p-hydroxycinnamic acid were performed using
Gaussian 03W, version 6 with basis set of 6-31++g (d, p)
by density functional theory method with B3LYP hybrid
functional. The molecular geometry was viewed through
Gauss view 3.0. The lowest energy molecular dimension
of p-hydroxybenzaldehyde and p-hydroxycinnamic acid
was calculated using three dimensional coordinates and
it was found that these molecules exists as planar struc-
ture with the dimensions of 0.430 nm × 0.696 nm and
0.431 nm×0.976 nm, respectively. It is interesting that the
pore sizes of HMCN catalysts synthesised for this study are
greater than the molecular dimensions of p-hydroxybenza-
ldehyde and p-hydroxycinnamic acid. Hence the catalytic
conversion of p-hydroxybenzaldehyde to p-hydroxycinnamic
acid is undoubtedly formed inside the pores of HMCN
catalysts rather than on the external surface. The mini-
mum energy conformation of p-hydroxybenzaldehyde and
p-hydroxycinnamic acid with different pore sizes of HMCN
catalysts are depicted in Scheme 2.
time viz., 5, 10, 15, 30, 60, 90, 120, 150, and 180 min using
200 mg of HMCN (4.7), HMCN (5.9), and HMCN (7.1)
catalysts and they are shown in Fig. 7a–c, respectively.
The isolated yield of p-hydroxycinnamic acid synthesised
using HMCN catalysts was shown in Fig. 8. The three cata-
lysts namely HMCN (4.7), HMCN (5.9), and HMCN (7.1)
showed p-hydroxybenzaldehyde conversion of 79.8, 94.5,
and 91.7%, with selectivity to p-hydroxycinnamic acid of
96.3, 100, and 100%, respectively at 60 min. Since HMCN
(4.7) catalyst has smaller pore diameter of 4.7 nm than
HMCN (5.9) and HMCN (7.1), it experience a greater dif-
fusion constrain for the reactants to enter into the HMCN
(4.7) nanochannels to meet the active sites to get convert into
products and the formed product to diffuse out of the chan-
nels. This is the reason for the lower conversion (79.8%) and
selectivity (96.3%) and isolated yield (55%) for HMCN (4.7)
catalyst than HMCN (5.9) and HMCN (7.1). But HMCN
(5.9) has the pore size of 5.9 nm with 20.3% greater in pore
dimension than HMCN (4.7). The size tuned pores with
5.9 nm, facilitates the faster diffusion of the reactants with
less diffusion constrains to adsorb on the active sites to get
converted into product and the product formed can easily
diffused out. This is the reason for high conversion (94.5%),
product selectivity (100%) and isolated yield (91%) within
60 min for HMCN (5.9) compare to HMCN (4.7) and this
The effect of catalysts pore size on the synthesis of
p-hydroxycinnamic acid was studied at different reaction
Scheme 2 The minimum
energy conformation structure
of p-hydroxybenzaldehyde,
p-hydroxycinnamic acid and
pore size illustrations of HMCN
(4.7), HMCN (5.9) and HMCN
(7.1) catalysts
1 3

Pore Size Architecture of Hexagonal Mesoporous Carbon Nitride (HMCN) for Metal-Free Synthesis…
Fig. 7 Effect of reaction time
in the synthesis p-hydroxycin-
namic acid on a HMCN (4.7),
b HMCN (5.9), and c HMCN
(7.1) catalyst
The pore diameter of HMCN (7.1) catalyst with 7.1 nm is
of 33.8 and 16.9% higher than the pore diameter of HMCN
(4.7) and HMCN (5.9), respectively. Hence more number
of reactant molecules can enter into the pores without any
diffusion constrains. But at the same time, some of the mol-
ecules can be diffused out of the HMCN (7.1) nanochan-
nels without adsorption on the active sites, results decrease
in p-hydroxybenzaldehyde conversion (91.7%) compare to
HMCN (5.9) base catalyst. From this study it is confirmed
that the HMCN (5.9) catalyst would be the best choice for
high p-hydroxybenzaldehyde conversion with high selectiv-
ity to p-hydroxycinnamic acid.
The effect of catalyst amount of HMCN (5.9) on the
synthesis of p-hydroxycinnamic acid was studied at 60 min
using different catalyst amount viz., 50, 100, 200, 300, and
400 mg and the corresponding product yield was shown
in Fig. 9. Initially the yield of p-hydroxycinnamic acid is
increased gradually from 55 to 91% as increase in the cata-
lyst amount from 50 to 200 mg due to the increase of active
basic sites on the catalyst surface in the reaction medium.
But there is no increase in the product yield was observed,
even after increase in the catalyst amount to 300, 400 mg.
Hence from this study, it is observed that 200 mg of HMCN
Fig. 8 Effect of pore diameter of different HMCN catalysts on the
yield of p-hydroxycinnamic acid
new HMCN (5.9) catalytic reaction system provides much
faster reaction rate with high p-hydroxybenzaldehyde con-
version with high selectivity to p-hydroxycinnamic acid
compare to the earlier reports (Table 2).
1 3

P. Elamathi, G. Chandrasekar
Table 2 Comparison of various
base catalysts used for the
synthesis of p-hydroxycinnamic
acid via Knoevenagel–Doebner
reaction
Entry
Catalytic system
Yield (%)a
Time (h)
References
1
Diamino-functionalised MCM-41
Amino-functionalized mesoporous silica
Pyridine:piperidine
Pyridine:piperidine
Pyridine:piperidine
85–90
75–85
99
97
0.25
3
3
0.03
5
[23]
[24]
[25]
[26]
2
3b
4c
5
75–85
[27]
6
HMCN (5.9)
91 (100% selectivity)
1
Present work
Our reaction conditions: p-hydroxybenzaldehyde (0.0040 mol), malonic acid (0.0081 mol), HMCN (5.9)
(200 mg), toluene (10 ml), reflux temperature
aIsolated yield
bUltrasound assisted
cMicrowave assisted
Fig. 9 Effect of catalyst amount on the synthesis p-hydroxycinnamic
acid over HMCN (5.9) catalyst
(5.9) catalyst would be the optimum amount to convert
p-hydroxybenzaldehyde to p-hydroxycinnamic acid. No
reaction product was observed in the absence of catalyst
under identical conditions. It clearly reveals the importance
of the basic active sites of HMCN catalysts in the Knoev-
enagel type of reactions.
Scheme 3 Schematic wall structure of HMCN
having suitable pore size makes more opportunity for the
reactants to access the active sites of HMCN catalysts.
The formation mechanism of p-hydroxycinnamic acid
is illustrated in Scheme 4. At first the acidic proton from
the active methylene group of malonic acid is abstracted by
the Lewis basic sites of carbon nitride. Then the produced
compound (I) undergo nucleophilic attack to the carbonyl
carbon of compound (II) to form oxyanion (III). The oxy-
anion abstract H+ from the protonated Lewis basic site of
HMCN catalyst produces compound (IV) and the catalyst
is regenerated. The compound IV leads to the formation of
p-hydroxycinnamic acid with the elimination of water and
CO2.
On the basis of the structure, physicochemical proper-
ties, and catalytic testing results of the HMCN materials,
the excellent catalytic performance of HMCN is attributed
to the following two factors. On the one hand, the combina-
tions of Brönsted and Lewis active basic centres (Scheme 3)
of HMCN catalysts catalyse the Knoevenagel–Doebner type
condensation reaction more effectively [20]. On the other
hand, the unique surface textural properties of HMCN mate-
rial play a key role to obtain an excellent catalytic activ-
ity with high selectivity to p-hydroxycinnamic acid. The
uniform pore channel with optimum pore size (5.9 nm) of
HMCN material facilitates the easy diffusion of reactants
and products elution from the nanochannels, which reduces
the internal mass transfer resistance. Hence HMCN catalysts
The HMCN (5.9) catalyst recycle test was conducted after
the separation of catalyst from the reaction mixture by filtra-
tion, and washing first with toluene and then with methanol
1 3

Pore Size Architecture of Hexagonal Mesoporous Carbon Nitride (HMCN) for Metal-Free Synthesis…
Scheme 4 The formation mechanism of p-hydroxycinnamic acid
and dried at 100 °C. The recovered catalyst was reused for
the next reaction run in order to study the catalyst lifetime
and stability. It was observed that conversion of p-hydroxy-
benzaldehyde and selectivity to p-hydroxycinnamic acid is
not much affected even after six cycles as shown in Fig. 10.
p-hydroxycinnamic acid synthesis was investigated in a non-
conventional metal-free, pyridine-free, eco-friendly reaction
conditions. HMCN (4.7), HMCN (5.9), and HMCN (7.1)
showed p-hydroxybenzaldehyde conversion of 79.8, 94.5,
and 91.7%, with selectivity to p-hydroxycinnamic acid of
96.3, 100, and 100%, respectively at 60 min. The low cata-
lytic performance of HMCN (4.7) than HMCN (5.9) and
HMCN (7.1) catalysts is due to the smaller pore diameter
of 4.7 nm, experiences greater diffusion constrain for the
reactants to enter into nanochannels. The high catalytic per-
formance of HMCN (5.9) catalyst with 94.5% p-hydroxy-
benzaldehyde conversion and 100% p-hydroxycinnamic acid
selectivity compare to other catalysts is due to easy diffusion
4 Conclusions
The size of nanochannels of HMCN catalytic materials were
architected with the diameter of 4.7, 5.9, and 7.1 nm using
SBA-15 hard templates synthesised at different tempera-
tures. The influence pore diameter of HMCN catalysts on
1 3

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of p-hydroxybenzaldehyde into HMCN nanochannels with
suitable pore size of 5.9 nm. The low catalytic performance
of HMCN (7.1) catalyst compare to HMCN (5.9) is due to
the large pore size of 7.1 nm, facilitates reactants to diffuse
much faster rate and some of them can easily diffusion out
without adsorb on the reactive sites. These findings suggest
that the methodology adopted here could also offer many
opportunities for the synthesis of organic molecules with dif-
ferent molecular sizes such as paraffins, aromatics, vitamins
and amino acids.
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