X. Fang, et al.
CatalysisCommunications125(2019)48–51
obtained rather good results, but their catalyst system are Fe-based
catalyst and K2Ti6O13, which is lack of comparability to some extent.
Our group also did some work on concentrating light reactor using Xe
lamp as the light source and obtained some interesting results. [19,20]
However, due to the power limits, it cannot raise the reaction tem-
perature efficiently.
In this manuscript, a concentrating solar light reactor system was set
up with a large Fresnel lens (diameter = 1 m). It can effectively raise
light intensity, reaction temperature as well as the pressure of CO2 and
H2O of the reactor system. The CO2 photoreduction behavior was then
investigated in the reactor system. To make comparable results, the
most common catalyst P25 was used. The results show that CO2 pho-
toreduction performance are greatly improved and reaction rates of
hydrocarbons are boosted up to very high values.
catalyst was prepared to be disc shape and put into the reactor. A k-type
thermocouple is passed through a hole on the reactor wall and touched
the upper surface of the catalyst to measure the temperature. Then the
reactor was sealed and cleaned with nitrogen (99.999%) for half an
hour to remove the impurity gas. Next, it was continuously replaced
and saturated with CO2 gas (99.999%) for at least 30 min, and the
pressure of the reactor was regulated to 0.1 MPa. 2.0 mL of H2O was
then charged into the reactor. The reaction was operated in batch
mode. The gas products were analyzed by a gas chromatograph
(GC2014, Shimadzu) equipped with an HT-PLOT Q capillary column
(30m × 0.32mm × 20μm), FID detector. The hydrocarbons are de-
termined by external standard method. A standard curve of CH4 was
first obtained. The reaction rate of CO2 RPs and CO2 conversion are
calculated according to the equations:
nC
i
rCI (μmol·g−1·h−1) =
2. Experimental
(w ×time)
(2)
t.
nCH + 2nC H + 2nC H + 2nC H
2.1. Catalyst preparation and characterization
4
2
2
2
4
2 6
XCO2 (%) =
× 100%
nCO
(3)
2
P25 TiO2 was purchased from Degussa. The powder were calcined
in a muffle furnace at a rate of 2 °C·min−1 up to 400 °C and held at this
temperature for 2 h to remove the organic impurities.
where nC is the mole of hydrocarbons (CH4, C2H2, C2H4 and C2H6)
i
yielded in the system, and wt. is the catalyst weight.
In order to investigate the structure and crystallinity, powder X-ray
diffraction (XRD, X'Pert PRO) was performed. The scanning rate was
0.02o min−1 from 20o to 80o. Ultraviolet–visible absorption spectra of
the samples were collected with an UV–Vis-NIR spectrophotometer
(UV–vis, UV-2600). Field emission scanning electron microscope (FE-
SEM, Hitachi S-4700) measurements were used to disclose the
morphologies. Specific surface area was measured by a 3flex physical
adsorption apparatus.
3. Results and discussions
The catalyst characterization results can be seen in Fig.S1-S3 and
Table S1, which confirms the catalyst is a typical P25 TiO2. Blank ex-
periments have been performed to exclude the probable misleading of
The tests on the large concentrating solar light reactor system show
the effect of reaction condition intensification on the CO2 photo-
reduction. Fig. 2 first displays a typical products distribution of CO2
photoreduction under concentration ratio (CR) 800. Compared to most
of the reports, it can be seen that besides CH4, more type of products are
detected. [6,7] C2H2, C2H4, C2H6 and C3H6 can be observed clearly,
which were further confirmed by MS (Seen in Fig.S4 and S5). Then
calculated by external standard method, the maximum CH4 reaction
rate reaches 3157.2 μmol·g−1·h−1 at concentration ratio of 800 after
half an hour reaction, as shown in Table 1; at the same time, the C2H4
reaction rate reaches 511.6 μmol·g−1·h−1, and the C2H6 reaction rate
reaches 1346.0 μmol·g−1·h−1. Considering all the products are form
CO2 reduction, the total CO2 reduction rate achieves about
5715 μmol·g−1·h−1, which is larger than all the values recently re-
ported. [21] At other concentration ratios, the reaction rates of
2.2. Illustration of reactor system and catalytic tests
The CO2 photoreduction with H2O reaction was performed in a self-
made concentrating light reactor system, as shown in Fig. 1. The system
contains a reactor, a Fresnel lens and an auto tracing system. The lens
(diameter = 1 m, PMMA material) was purchased from Mylens Co.,
Shenzhen. Detailed description of the reactor can be seen in Ref. [19].
The auto tracing system contains a motor, a controller and a sensor,
which is used to keep the solar lights perpendicular to the lens and the
catalyst. The catalyst amount is about 0.05 g. Before reaction, the
Fig. 2. A typical gas chromatogram map of CO2 reduction products distribu-
tion.
100 mL batch reactor, initial reactants contains 0.1 MPa CO2 and 2 mL H2O,
concentration ratio 800, temperature 531.5 °C, pressure 1.0 MPa. Concentration
ratio is defined as the ratio of Fresnel lens area to catalyst disc area.(The same
below).
Fig. 1. The concentrating reactor system. 1. Concentrating mirror; 2. Reactor;
3. Sensor for tracing sun; 4. Controller. 5. Motor.
49