Table 3. Effects of Dopant M on Photocatalytic CO2 Reduction Using Rh–Ru/NaTaO3:Ma.
| entry | photocatalyst | surface step structure | cocatalyst | rates
of gas evolution under UV/μmol h–1 |
CH4 select % | amounts
of evolved gases/μmol (9 h) |
stored O2 ratio % | e–/h+ | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| H2 | CO | CH4 | O2 | H2 | CO | CH4 | O2 | stored O2 | |||||||
| 1 | NaTaO3 | absent | none | 139 | 0.10 | 0 | 65 | 0 | 1186 | 1.02 | 0 | 527 | 0 | 0 | 1.1 |
| 2 | NaTaO3 | absent | Rh–Ru | 20 | 0.03 | 0.11 | 8 | 2.15 | 222 | 0.23 | 0.82 | 79 | 7 | 8.1 | 1.3 |
| 3 | NaTaO3:Ca(1%) | incomplete | none | 233 | 0.09 | 0.01 | 115 | 0.02 | 1951 | 0.08 | 0.97 | 960 | 0 | 0 | 1.0 |
| 4 | NaTaO3:Ca(1%) | incomplete | Rh–Ru | 44 | 0.01 | 0.8 | 12 | 6.78 | 312 | 0.1 | 3.9 | 84 | 82 | 49.4 | 1.0 |
| 5 | NaTaO3:Sr(0.5%) | absent | Rh–Ru | 39 | 0.01 | 0.81 | 11 | 7.67 | 319 | 0.1 | 3.8 | 85 | 48 | 36.1 | 1.3 |
| 6 | NaTaO3:Sr(1%) | incomplete | none | 350 | 0.12 | 0 | 177 | 0 | 3118 | 1.29 | 0 | 1564 | 0 | 0 | 1.0 |
| 7 | NaTaO3:Sr(1%) | incomplete | Rh–Ru | 54 | 0 | 1.44 | 14 | 9.64 | 443 | 0.08 | 9.10 | 130 | 44 | 25.3 | 1.4 |
| 8 | NaTaO3:Sr(2%) | complete | Rh–Ru | 41 | 0.01 | 1.3 | 12 | 11.25 | 351 | 0.05 | 6.77 | 77 | 79 | 50.6 | 1.2 |
| 9 | NaTaO3:Sr(5%) | complete | Rh–Ru | 33 | 0.01 | 1.1 | 9 | 11.76 | 299 | 0.05 | 6.49 | 70 | 86 | 55.1 | 1.0 |
| 10 | NaTaO3:Ba(1%) | incomplete | none | 233 | 0.04 | 0 | 114 | 0 | 2105 | 0.95 | 0 | 1015 | 0 | 0 | 1.0 |
| 11 | NaTaO3:Ba(1%) | incomplete | Rh–Ru | 12 | 0.01 | 0.23 | 4 | 7.12 | 150 | 0.15 | 1.4 | 36 | 26 | 41.9 | 1.3 |
| 12 | NaTaO3:La(1%) | complete | none | 483 | 0.09 | 0 | 228 | 0 | 4362 | 1.04 | 0 | 2094 | 0 | 0 | 1.04 |
| 13 | NaTaO3:La(1%) | complete | Rh–Ru | 52 | 0.01 | 0.5 | 15 | 3.7 | 419 | 0.12 | 4.33 | 131 | 73 | 35.7 | 1.05 |
a
Photocatalyst: 1.5 g, cocatalyst: Ru (0.375 wt %) and Rh (0.5 wt %) loaded by a liquid phase reduction, solution: water without any additives (350 mL, pH 4–5), flow gas: CO2 (1 atm, 30 mL min–1), light source: 400 W high pressure Hg lamp, cell: inner-irradiation quartz cell, and total irradiation time: 9 h. Rates of gas evolution were estimated after an induction period of UV irradiation. CH4 selectivity was calculated using the rates of gas evolution. e–/h+ was calculated from amounts of evolved gases including stored O2.