**2.3 CO2 reduction experiment**

**Figure 1** [27, 28] shows the experimental set-up of the reactor composing of stainless tube (100 mm (*H*.) 50 mm (*I*.*D*.)), Cu/TiO2 film coated on netlike glass disc (50 mm (*D*.) 1 mm (*t*.)) located on the Teflon cylinder (50 mm (*H*.) 50 mm (*D*.)), a quartz glass disc (84 mm (*D*.) 10 mm (*t*.)), a sharp cut filter cutting off the light whose wavelength is below 400 nm (SCF-49.5C-42 L, SIGMA KOKI CO. LTD.), a 150 W Xe lamp (L2175, Hamamatsu Photonics K. K.), mass flow controller, and CO2 gas cylinder. The volume of reactor to charge CO2 is 1.3 <sup>10</sup><sup>4</sup> <sup>m</sup><sup>3</sup> . The light of Xe lamp which is located inside the stainless tube illuminates Cu/TiO2 film coated on the netlike glass disc through the sharp cut filter and the quartz glass disc that are at the top of the stainless tube. The wavelength of light from Xe lamp is ranged from 185 to 2000 nm. Since the sharp cut filter can remove UV components of the light from the Xe lamp, the wavelength of light from Xe lamp is ranged from 401 to 2000 nm with the filter. **Figure 2** [29] shows the performance of the sharp cut filter to cut off the wavelength is below 400 nm. The

#### **Figure 1.**

*Schematic drawing of CO2 reduction experimental set-up (left: CO2/H2/H2O system; right: CO2/NH3/H2O system).*

Cu/TiO2 film coated on netlike glass disc [28]. EPMA analysis was carried out for SEM images taken by 1500 times magnification. In EPMA image, the concentration of each element in observation area is indicated by the different colors. Light colors, for example, white, pink, and red indicate that the amount of element is large, while

From these figures, it can be observed that TiO2 film was coated on netlike glass fiber. During firing process, the temperature profile of TiO2 solution adhered on the netlike glass disc was not even due to the different thermal conductivities of Ti and SiO2. Their thermal conductivities of Ti and SiO2 at 600 K are 19.4 and 1.8 W/(mK) [30], respectively. Due to thermal expansion and shrinkage around netlike glass fiber, it can be considered that thermal crack is formed on the TiO2 film.

In addition, it is observed from **Figure 4** that nanosized Cu particles are loaded

To evaluate the amount of loaded Cu within TiO2 film quantitatively, the obser-

dark colors like black and blue indicate that the amount of element is small.

*CO2 Reduction Characteristics of Cu/TiO2 with Various Reductants*

*DOI: http://dx.doi.org/10.5772/intechopen.93105*

on TiO2 uniformly, resulted from that the pulse arc plasma method can emit

vation area, which is the center of netlike glass disc, of diameter of 300 μm is analyzed by EPMA. The ratio of Cu to Ti is counted by averaging the data obtained in this area. As a result, the weight percentages of elements of Cu and Ti in the Cu/

nanosized Cu particles.

**Figure 3.**

**Figure 4.**

**79**

TiO2 film are 0.6 and 99.4 wt%, respectively.

*SEM image of Cu/TiO2 film coated on netlike glass disc.*

*EPMA image of Cu/TiO2 film coated on netlike glass disc.*

**Figure 2.** *Light transmittance data of sharp cut filter.*

average light intensity of Xe lamp without and with the sharp cut filter is 58.2 and 33.8 mW/cm<sup>2</sup> , respectively.

In the CO2 reduction experiment with H2 and H2O, CO2 gas with the purity of 99.9 vol% which were controlled by mass flow controller was mixed in the buffer chamber and introduced into the reactor which was pre-vacuumed by a vacuum pump. The mixing ratio of CO2 and H2 was confirmed by TCD gas chromatograph (Micro GC CP4900, GL Science) before introducing into the reactor. After confirming the mixing ratio of CO2 and H2, the distilled water was injected into the reactor through a gas sampling tap by syringe and Xe lamp illumination was turned on the same time. The amount of injected water was measured and controlled by the syringe. The injected water vaporized completely in the reactor. The molar ratio of CO2/H2/H2O was set at 1:1:1, 1:0.5:1, 1:1:0.5, 1:0.5:0.5. Due to the heat of Xe lamp, the temperature in reactor was attained at 343 K within an hour and kept an approximately 343 K during the experiment.

In the CO2 reduction experiment with NH3 and H2O, after purging the reactor with CO2 gas of 99.9 vol% purity introduced in the reactor, which was pre-vacuumed by a vacuum pump, for 15 minutes, the valves located at the inlet and the outlet of reactor were closed. After confirming the pressure and gas temperature in the reactor at 0.1 MPa and 298 K, respectively, the NH3 aqueous solution (NH3; 50 vol%), which was changed according to the planed molar ratio, was injected into the reactor through gas sampling tap, and Xe lamp illumination was turned on the same time. The NH3 aqueous solution injected was vaporized completely in the reactor. Due to the heat of Xe lamp, the temperature in the reactor was attained at 343 K within an hour and kept at approximately 343 K during the experiment. The molar ratio of CO2/ NH3/H2O was set at 1:1:1, 1:0.5:1, 1:1:0.5, 1:0.5:0.5, 3:2:3, 3:8:12, respectively. The gas in the reactor was sampled every 24 hours during the experiment. The gas samples were analyzed by FID gas chromatograph (GC353B, GL Science). Minimum resolution of FID gas chromatograph and methanizer is 1 ppmV.

## **3. Results and discussion**
