This study monitored 13CO2 conversion to exclude the conversion of adventitious C and clarified dual photocatalytic roles of UV-visible light: charge separation at the band gap (BG) and heat via localized surface plasmon resonance (LSPR). Photocatalytic tests were performed under 2.3 kPa of 13CO2 and 21.7 kPa of H2 using ZrO2 or Ag-ZrO2 irradiated by UV-visible light. The selective CO generation rate was maximum: 0.57 μmol h-1 gcat-1 when the Ag content was 5.0 wt%. 8.6% of 12CO was mixed in the products derived from 12CO2 preadsorbed from air as demonstrated by 13CO2 exchange experiment. In comparison to photocatalytic test irradiated under full UV-visible light, the CO formation rate decreased to the 30% and 2% when the excitation light was filtered to be λ &gt; 320 nm and λ &gt; 580 nm respectively, i.e. UV light of λ &lt; 248 nm to separate the charges at the BG of ZrO2 and UV-visible light of 330 &lt; λ &lt; 580 nm to induce LSPR of Ag, respectively, played exclusive photocatalytic roles to convert CO2 into CO. The Ag was metallic state and the temperature (T) was monitored for Ag-ZrO2 irradiated by UV-visible light using Ag K-edge EXAFS. In the time course, the Ag-Ag coordination number negligibly changed whereas the Debye-Waller factor gradually increased and suddenly dropped when the UV-visible light was turned off (Figure 1A, B). Based on the EXAFS curve-fit analyses and bulk and surface Debye T (225 and 155 K, respectively), the T of Ag sites were evaluated (Figure 1B). The T reached 392 K at 90 min, suggesting the LSPR transformed into heat. Bicarbonate species were observed as peaks at 1624, 1429, and 1222 cm-1 over ZrO2 in FTIR, that was effectively reduced to CO by charge separation in ZrO2 and heat on Ag to supply activated H (Scheme 1c, d) both derived from light.

Dual photocatalytic roles of light: charge separation at the band gap and heat via localized surface plasmon resonance to photoconvert CO2 into CO over siliver-zirconium oxide

2019 Spring National Meeting

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