Photon Factory Activity Report 2022 #40 (2023)

BL-9C, BL-12C, AR-NW10A/2021G546

Investigation of stable Ag–Ni–ZrO2 photocatalyst for sustainable
photocatalytic CO2 reduction into fuels
Rento Ishii, Tomoki Oyumi, and Yasuo Izumi*
Department of Chemistry, Graduate School of Science, Chiba University, Yayoi 1-33, Inage-ku
Chiba 263-8522, Japan
1. Introduction
To create a new carbon neutral cycle, Ni–ZrO2
photocatalyst was investigated to convert CO2 intomethane [1]. The Ni nanoparticles need to be metallic(valence zero) for the best performance, methane
formation rate of 0.98 mmol h−1 gcat−1. However, a few
nanometers Ni particles easily oxidized in air and are
difficult to handle in practical applications. In thisproposal, secondary metal was deposited to Ni–ZrO2 andthe Ni0 site was tried to be stable for the sustainableapplication for CO2 photocatalytic reduction into fuels.

2. Experimental section
Ni–ZrO2 photocatalyst was prepared via liquid phasereduction method from Ni(NO3)2 [1]. Then, Ag wasdeposited on Ni–ZrO2 photoelectrochemically. Namely,Ag(NO3) ethanol solution (50 mmol L−1) was mixed with
Ni–ZrO2 powder and irradiated under UV–visible lightfor 3–6 h. The suspension was filtered and dried at 373 K.
The amount ratio of Ni: Ag used was 1: 10.

3. Results and Discussion
The normalized XANES spectra for Ag–Ni–ZrO2
photocatalysts that were irradiated under UV–visible lightfor 3 h and 6 h were compared to those of Ni metal andNiO standard samples (Figure 1). Apparently, Ni sites
were oxidized to NiO during drying of Ni0–ZrO2 sample
obtained via liquid phase reduction. Because the NiII sites
were not reduced under the irradiation of UV–visible
light immersed in Ag+ ethanol solution, we reduced Ag–Ni–ZrO2 photocatalysts under H2 at 723 K (Figure 1).
Alternatively, we performed photoelectrochemical
deposition of Ag+ on Ni–ZrO2 without contact to air
during the later stage than liquid phase reduction. In suchpreparation, Ni sites remained metallic Ni0 (data notshown).
In this report, the Debye–Waller factor changes for
Ag–Ni–ZrO2 photocatalysts reduced under H2 at 723 K
were monitored by Ni K-edge EXAFS under theirradiation of UV–visible light at beamline (Figure 2).
Clearly, Ni sites were quickly warmed by light energy
and reached thermal equilibrium while the temperaturevery quickly dropped to room temperature when the UV–
visible light was turned off (Figure 2).

Figure 1. Normalized Ni K-edge XANES spectra for Ag–Ni–ZrO2 photocatalysts that were irradiated under UV–visible lightfor 3 h and 6 h and the one irradiated under UV–visible light for
6 h was further reduced under H2 at 723 K in comparison tostandard spectra for Ni metal and NiO.

Figure 2. Time course of Co K-edge EXAFS Fourier transformfor Ag–Ni–ZrO2 photocatalysts that were irradiated under UV–visible light for 6 h and then reduced under H2 at 723 K (A)under UV–visible light irradiation at beamline and (B) UV–visible light off.

Reference[1] Zhang, H.; Itoi, T.; Konishi, T.; Izumi, Y. Efficient andSelective Interplay Revealed: CO2 Reduction to CO overZrO2 by Light with Further Reduction to Methane over Ni0

Photon Factory Activity Report 2022 #40 (2023)

by Heat Converted from Light. Angew. Chem. Int. Ed. 2021,60, 9045–9054.

* yizumi@faculty.chiba-u.jp