RSC Advances
PAPER
Nano metal oxides as efficient catalysts for
selective synthesis of 1-methoxy-2-propanol from
Cite this: RSC Adv., 2018, 8, 4478
methanol and propylene oxide†
*
*
and Shuying Zang
Jiawei Zhang, Qinghai Cai,
Jingxiang Zhao
Nano metal oxides such as Fe2O3, Fe3O4, CuO, NiO, ZnO and SnO2 were prepared and characterized using
XRD, SEM and TEM analysis. These as-prepared metal oxide materials were used as catalysts for the
etherification of methanol with propylene oxide (PO). The results showed that a-Fe2O3 exhibited
outstanding catalytic performance with 97.7% conversion and 83.0% selectivity to MP-2 at 160 ꢀC for
8 h. Furthermore, the relationship between the catalytic activity or selectivity and surface basicity or
energy gap was investigated. This catalyst could be easily recovered and reused due to its
heterogeneous catalytic nature.
Received 7th December 2017
Accepted 10th January 2018
DOI: 10.1039/c7ra13119d
rsc.li/rsc-advances
reaction. The simply prepared Fe2O3 catalyst, which is inex-
pensive and environmentally benign, demonstrated excellent
Introduction
catalytic performance for the synthesis of MP-2. The results are
disclosed herein.
Glycol ethers are considered to be important chemicals that
combine the best solvency features of alcohols and ethers for
synthesizing organic compounds.1 They are widely used as
industrial solvents for coating materials, printing ink, dyeing
leather etc. Due to the low toxicity of propylene glycol ether, it is
expected to be a safe substitute for toxic ethylene glycol ether.
Although there are several methods for synthesizing propylene
glycol ether, the propylene oxide route is the most convenient
and industrially feasible in terms of atom-economy and energy-
efficiency. In this method, the epoxide ring of propylene oxide
may open at the C–O bond and react with alcohols to form
propylene glycol ether, catalyzed by acid or base catalysts. These
catalysts include earlier homogeneous acids or bases, such as
NaOH, alcoholic sodium, H2SO4 and BF3 etc.,2,3 and later solid
acids or bases, e.g. acidic zeolites,4 Mg/Al hydrotalcite,5 Zn–Mg–
Al oxides,1 MgO6 and amine-modied porous silica7 etc. Very
recently, brucite-layer materials,8 Al2O3/MgO,9 and basic and
acidic ionic liquids10,11 have been developed as highly efficient
catalysts for the selective synthesis of propylene glycol ether.
Because there is much research interest in developing envi-
ronmentally benign catalysis, we wish to report the preparation
of nano metal oxides using a simple method, and highlight
their catalytic performance for the synthesis of
1-methoxymethane-2-propanol (MP-2) via an atom–economic
Experimental
Preparation of the catalysts
Iron oxide was prepared using the following procedure.12 30 mL
of FeCl3 aqueous solution (1 mol Lꢁ1), 2.5 g of urea and 2 mL of
polyethylene glycol (PEG-400) as a dispersant were added to
a three-necked ask tted with a reux condenser and an
electric heater. Ammonia solution (28%) was added dropwise to
the mixed solution to maintain a pH of 3.7 to afford Fe(OH)3.
Thereaer, the reactor was heated to 80 ꢀC and aged at this
temperature for 8 h. The mixed solution was then ultrasonically
treated at room temperature for 20 min, followed by ltration to
remove the ltrate. The obtained solid was washed with
deionized water and anhydrous ethanol. Thereaer, it was dried
at 100 ꢀC for 12 h, and then calcined at 500 ꢀC for 2 h in a muffle
furnace to afford nano-iron oxide. Other oxides, such as CuO,
ZnO, NiO and SnO2, were prepared with the same method to
that of iron oxide, using CuSO4, ZnSO4, NiCl and SnCl4 aqueous
solutions as precursors. However, the pH values for precipita-
tion of Cu(OH)2, Zn(OH)2, Ni(OH)2 and Sn(OH)4 were adjusted
to 4.7, 6.0, 7.2 and 2.5, respectively. Fe3O4 was prepared
according to the literature.13
Key Lab of Remote Sensing Monitoring of Geographic Environment, College of
Heilongjiang Province, School of Chemistry and Chemical Engineering, Harbin
Normal University, No. 1 Shida Road Limin development Zone, Harbin 150025, P.
R. China. E-mail: Zsy6311@163.com; caiqinghai@yahoo.com; Fax: +86-451-
88060580; Tel: +86-451-88060580
Catalyst characterization
XRD of the sample was performed on a Bruker-D8 Advance X-ray
diffractometer with Cu Ka radiation (40 kV and 36 mA). TEM
measurements were taken on a JEM-2100 electron microscope
(JEOL Japan) with an acceleration voltage of 200 kV. The
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c7ra13119d
4478 | RSC Adv., 2018, 8, 4478–4482
This journal is © The Royal Society of Chemistry 2018