LETTER
▌1405
lSeteterlenium-Doped TiO2 as an Efficient Photocatalyst for the Oxidation of Tetra-
hydrofuran to γ-Butyrolactone Using Hydrogen Peroxide as Oxidant
Selenium-Doped TiO2 as Efficient Photocatalyst
Patnam Padmalatha, Praveen K. Khatri, Suman L. Jain*
Chemical Sciences Division, CSIR-Indian Institute of Petroleum, Mohkampur, Dehradun-248005, India
Fax +91(135)2660202; E-mail: suman@iip.res.in
Received: 08.01.2013; Accepted after revision: 25.04.2013
γ-Butyrolactone (GBL) is a highly useful commodity of
Abstract: Selenium-doped TiO2 has been used for the first time as
great industrial interest which find extensive applications,
efficient photocatalyst for the oxidation of tetrahydrofuran by using
for example, as a dye solvent, as a spinning solvent for
synthetic fibers, and as intermediate for the synthesis of
hydrogen peroxide as oxidant, affording γ-butyrolactone (GBL) in
excellent yield with higher selectivity. TiO2-doped with selenium
showed greater visible absorption and exhibited superior photocat- solvents like pyrrolidone and N-methyl pyrrolidone
alytic activity than undoped TiO2. The prepared catalyst was sub-
jected to reflux in Millipore water in order to remove the surface-
bound selenium species. After this treatment, the catalyst did not
1940s by Reppes, from acetylene and formaldehyde to
show any leaching and showed efficient recycling with consistent
catalytic efficiency.
(NMP), which have lower environmental impact than
chlorinated ones. The first GBL synthesis was appeared in
give 1,4-butanediol (BDO) and then GBL by dehydroge-
nation. However, this process is associated with draw-
Key words: photocatalysis, selenium-doped titania, oxidation,
backs including the fluctuating prices of the raw materials
THF
as well as the hazards and environmental impact associat-
ed with the use of both acetylene and formaldehyde. The
commercial process for the synthesis of GBL involves the
TiO2 and its derivatives are known as efficient photocata-
liquid-phase hydrogenation of maleic acid/anhydride or
lysts and have been extensively used for air and water pu-
succinic acid/anhydride with hydrogen over a metallic
rification and self-cleaning of the surfaces.1 Owing to its
catalyst. This process has certain limitations, such as low-
low cost, reliability, strong oxidization power, environ-
er product yield, deactivation of the catalyst, and higher
mental nontoxicity, high stability, and chemical/biologi-
reaction temperature and pressure. Another approach for
cal inertness TiO2 has found enormous applications as
the synthesis of GBL involves the cyclization of 1,4-bu-
photocatalyst and catalyst support for developing a num-
tanediol, which have been known for a long time.16,17
A
ber of potential photocatalytic reactions and processes.
Additionally, it can be used as antibacterial agent because
of its strong oxidation activity and super hydrophilicity.
Recently, photocatalytic TiO2-based materials have been
shown to exhibit good efficiency in the visible-light spec-
trum and are gaining considerable interest. One promising
approach for enhancing the photocatalytic activity of TiO2
is the deposition or doping of another metal or nonmetal
atom either to the surface of commercial TiO2 or in the
crystal lattice. In general, these modified TiO2-based ma-
terials have shown remarkable visible-light absorbance
with enhanced photocatalytic activity. However, in some
cases the doping affects the thermal stability of the cata-
lyst and also photocatalytic activity depends on the con-
tent of the deposited element and method of preparation.
Recently, doping of nonmetal elements with flexible oxi-
dation states have emerged to be potential candidates for
enhancing the photocatalytic activity of TiO2.2–14 In this
regard, modification of TiO2 with iodine is well studied,14
however, enhanced solar activity of the TiO2 photocata-
lyst by doping of selenium(IV) ions has recently been
studied by Gurkan et al.15
disadvantage of this process is that the 1,4-butanediol
used has to be extra pure which comprises a complicated
multistage distillation for the removal of low- and/or high-
boiling constituents, including water. An alternative ap-
proach for the synthesis of GBL involves the oxidation of
THF with brominated oxidizing agents.18–20 The use of
toxic bromine is undesirable from environmental view-
points. Subsequently, other oxidizing agents including ru-
thenium tetraoxide, peroxophosphoric acid, and calcium
hypochlorite have also been used for the oxidation of tet-
rahydrofuran.21,22 Very recently, Bhaumik et al. reported
the oxidation of cyclic ethers such as tetrahydrofuran by
using TS-1 as catalyst and hydrogen peroxide as oxi-
dant.23
Herein, we report the photocatalytic oxidation of tetrahy-
drofuran (THF) by using selenium(IV)-doped TiO2 as
photocatalyst and hydrogen peroxide as oxidant under
mild reaction conditions. Selenium-doped TiO2 was pre-
pared from selenium dioxide and titanium(IV) butoxide
by following the literature procedure.24–26 For comparison
purposes, undoped TiO2 was also synthesized by follow-
ing a similar procedure without the selenium source. The
prepared samples were calcined at 450 °C prior to use.
The X-ray powder diffraction of the selenium(IV)-doped
titania and undoped TiO2 are presented in Figure 1.
SYNLETT 2013, 24, 1405–1409
Advanced online publication: 06.06.2013
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DOI: 10.1055/s-0033-1338859; Art ID: ST-2013-B0027-L
© Georg Thieme Verlag Stuttgart · New York