Applied Catalysis A: General 382 (2010) 115–121
Applied Catalysis A: General
The heterogenation of melamine and its catalytic activity
Farook Adam∗, Kasim Mohammed Hello, Hasnah Osman
School of Chemical Sciences, University Sains Malaysia, 11800 Penang, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history:
The immobilization of melamine (Mela) onto silica extracted from rice husk ash (RHA) has been done
via 3-chloropropyltriethoxysiline (CPTES). The resulting catalyst was designated as RHAPrMela. The
melamine loading on the silica was found to be ca. 65.74%. The 29Si MAS NMR showed the presence
of T2, T3, Q3 and Q4 silicon centers. The 13C MAS NMR showed that RHAPrMela had three chemical shifts
at 14.83, 31.17 and 52.24 ppm, consistent with the three carbon atoms, and two chemical shifts at 161.52
and 169.67 ppm with double spinning side bands, indicating that the three carbon atoms in melamine
ring are not equivalent in RHAPrMela. The catalytic potential of RHAPrMela was tested for the esterifica-
tion of acetic acid with several alcohols. A conversion of 73% was achieved with 100% selectivity for the
respective esters. The catalyst was easily regenerated and could be reused many times without loss of
catalytic activity.
Received 11 November 2009
Received in revised form 4 April 2010
Accepted 22 April 2010
Available online 29 April 2010
Keywords:
Surface modification
Silica surface
Sol–gel technique
Melamine
© 2010 Elsevier B.V. All rights reserved.
Esterification
1. Introduction
melamine molecule, which we thought could be put to beneficial
use.
The important rule in the design of any heterogeneous cata-
lyst should be its ease of synthesis. The cost should be low and
the catalyst recoverable, hence reusable and environment friendly.
In this respect, a simple one-pot synthesis developed by Adam et
al. [1] allowed the immobilization of 3-chloropropyltriethoxysiline
(CPTES) onto silica extracted from rice husk ash (RHA). These hybrid
organic–inorganic materials with an organic functionality as part of
the solid network have important and unique properties and many
possible applications due to the high surface area and the presence
of the organic end group, CH2–Cl. We had recently reported the
synthesis of a saccharine-silica (RHAC-Sac) catalyst by nucleophilic
substitution of the chlorine atom of the CH2–Cl end group with sac-
charine. This catalyst was shown to be an excellent heterogeneous
catalyst for the esterification of acetic acid with ethanol [2].
Melamine (1,3,5-triazine–2,4,6-triamine) is a chemical interme-
and has several industrial uses. Since it became commercially avail-
able in the late 1930s, it has been used in a wide range of products,
i.e. in combination with formaldehyde to produce melamine resin
as a durable thermosetting plastic, and melamine foam as a poly-
meric cleaning product [4]. However, it must be acknowledged that
the recent misuse of melamine in tainted infant milk powder raised
people’s awareness of its many possibilities. It also raised our inter-
est due to the presence of a high number of heteroatoms in the
It is the objective of the current study to incorporate the
melamine molecules onto RHA to produce a hybrid with a
silica–melamine architecture that could give beneficial catalytic
properties. The melamine immobilized catalyst (RHAPrMela) was
used as a heterogeneous catalyst for the esterification of several
alcohols with acetic acid. To the best of our knowledge, the use of
melamine as a homogeneous or a heterogeneous catalyst has not
been reported.
Sodium hydroxide (Systerm, 99%), nitric acid (Systerm, 65%),
CPTES (Sigma–Aldrich, 95%), toluene (J.T. Baker, 99.8%), absolute
ethanol (HmbG Chemical, 99.74%), 1-propanol and 1-butanol (R&M
Chemical, 99.5%), benzyl alcohol (Unilab, 97%), tert-butanol (Merck,
99%), 2-propanol (Unvasol, 99%), acetic acid (Systerm, 99.5%), tri-
ethylamine (R&M Chemical, 99%), melamine (Acros Organics, 99%).
The rice husk (RH) was collected from a rice mill in Penang,
Malaysia. All other chemicals used were AR grade or of high purity
and were used directly without further purification.
2.2. Extraction and modification of silica from RHA
2.2.1. Sources of silica
The rice husk ash (RHA) was chosen as the source of amorphous
silica as it was available in abundance. The silica was extracted from
rice husk according to a reported method [5,6].
∗
Corresponding author. Tel.: +60 4 6533567; fax: +60 4 6574854.
0926-860X/$ – see front matter © 2010 Elsevier B.V. All rights reserved.