光とメタンの有効利用：Ce-Ti 共担持光触媒による直接メタンカップリング

光とメタンの有効利用：Ce-Ti 共担持光触媒による直接メタンカップリング反応
Utilization of methane and light energy: Doubly loaded cerium and titanium oxides
on silica as photocatalyst for direct methane coupling
レニユリアティ 1・伊藤秀章 2・吉田寿雄 2
Leny Yuliati1, Hideaki Itoh2, Hisao Yoshida2
1
Graduate School of Engineering, Nagoya University, 2EcoTopia Science Institute, Nagoya University
〒464-8603 名古屋市千種区不老町, 1 名古屋大学大学院工学研究科, 2 名古屋大学エコトピア科学研究所
Tel: 052-789-5859, Fax: 052-789-5859, E-mail: [email protected]
Introduction
Direct methane coupling to produce mainly ethane
and hydrogen, 2CH4 → C2H6 + H2, has been reported
to proceed photocatalytically at room temperature.
The highly dispersed metal oxides on silica support
have been proposed as suitable photocatalysts for the
reaction.1-4 However, it is difficult to obtain highly
dispersed system with high loading amount due to the
aggregation of the loaded metal oxides. In the
present study, we prepared a new photocatalyst, i.e.,
two kinds of metal oxides coexisting on silica support,
and tested its photoactivity for the reaction.
Experimental
Ce(x)/SiO2 and Ti(x)/SiO2 samples were prepared
by impregnation method, followed by calcination in a
flow of air at 773 K for 5 h. Number in parentheses
shows Ce or Ti content in the sample (mol %). The
sample
was
prepared
by
Ce(x)/Ti(y)/SiO2
impregnation of Ti(y)/SiO2 with an aqueous solution
of Ce(NO3)3, followed by another calcination in a
flow of air at 773 K for 5 h.
The photoreactions were performed similarly to the
previous studies.1-4 The sample was pretreated with
O2 for 1 h, followed by evacuation for 1 h at 1073 K.
Results and discussion
Ce(0.1)/Ti(0.1)/SiO2 showed two absorption bands
around 220 nm and 265 nm due to the presence of
highly dispersed tetrahedral titanium oxide species
and highly dispersed cerium oxide on silica support,
respectively (Fig.1). This result was in agreement
with XANES spectra that confirmed the presence of
tetrahedral Ti(IV) species and highly dispersed
Ce(III) as the main species.
Kubelka-Munk function
A new design of photocatalyst, doubly loaded cerium and titanium oxides on silica, was performed. In the
present method, both highly dispersed cerium and titanium oxides species were obtained on silica. The
photoactivity of the present sample was almost close to the sum of photoactivities over each supported metal
oxide of equivalent loading amount, suggesting that both highly dispersed metal oxide on silica would act as
photoactive sites for the direct methane coupling.
(a)
2
(b)
(c)
1
0
200
300
400
500
Wavelength / nm
Fig. 1 DR UV-Vis spectra of (a) Ti(0,1)/SiO2, (b)
Ce(0.1)/SiO2, and (c) Ce(0.1)/Ti(0.1)/SiO2 samples.
As shown in Table 1 the activity of Ce(0.2)/SiO2
was slightly lower than Ce(0.1)/SiO2 (entry 1 and 2),
suggesting that the higher loading did not result in the
higher photoactivity. The Ce(0.1)/Ti(0.1)/SiO2
showed higher activity than Ce(0.1)/SiO2 and
Ti(0.1)/SiO2, almost close to the sum of activities
over Ce(0.1)/SiO2 and Ti(0.1)/SiO2 as shown in Table
1 (entry 1,3, and 4). This shows that the present
method enabled the formation of each highly
dispersed metal oxide on silica support that acted as
photoactive sites for the reaction.
Table 1 Results of photocatalytically direct methane coupling
Total yield
Entry
Sample
H2 (exp)/
H2 (theory)a
/ 10-2 C%
1
Ce(0.1)/SiO2
7.5
2.0
2
Ce(0.2)/SiO2
7.0
1.3
3
Ti(0.1)/SiO2
5.3
1.2
4
Ce(0.1)/Ti(0.1)/SiO2
11.7
1.1
a
H2 calculated from hydrocarbons products.
Ref:
1) H. Yoshida, et al., Phys. Chem. Chem. Phys., 4, 2459,
(2002).
2) H. Yoshida, et al., J. Photochem. Photobiol. A, 160, 47,
(2003).
3) L. Yuliati, et al., Phys. Chem. Chem. Phys., 7, 195, (2005).
4) L. Yuliati, et al., Chem. Commun., 4824, (2005).

Download Report