Table 2. Effect of Loading Amounts of Rh–Ru Cocatalysts on Photocatalytic CO₂ Reduction Using NaTaO₃:Sr(1%)^a.

entry	loaded Rh/μmol (wt %)	loaded Ru/μmol (wt %)	Rh/Ru	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	0	0		350	0.12	0	177	0	3118	1.29	0	1564	0	0	1.0
2	0	54.9 (0.375)		1339	0.20	0.04	737	0.01	10 603	2.31	0.36	5761	242	4.0	0.9
3	72.9 (0.5)	0		129	0.02	0.07	60	0.22	1171	0.44	0.76	557	62	10.0	0.9
4	72.9 (0.5)	37.2 (0.25)	1.96	60	0	0.72	17	4.58	434	trace	4.02	119	89	42.9	1.1
5	29.8 (0.2)	22.5 (0.15)	1.32	75	0.01	0.50	25	2.60	568	0.09	4.11	177	100	36.1	1.1
6	44.2 (0.3)	32.3 (0.225)	1.37	74	0.01	0.65	24	3.39	519	0.09	4.73	163	66	28.8	1.2
7	72.0 (0.5)	55.1 (0.375)	1.31	54	0	1.44	14	9.64	443	0.08	9.10	130	44	25.3	1.4
8	101.8 (0.6)	76.5 (0.45)	1.33	44	0	1.26	10	10.28	340	trace	7.06	80	61	43.3	1.3
9	144.8 (1)	110.6 (0.75)	1.31	41	0	1.01	9.8	8.97	404	trace	4.43	100	60	37.5	1.3
10	363.9 (2.5)	271.1 (1.87)	1.34	75	0.02	0.23	19	1.21	1046	0.31	1.77	245	89	26.6	1.6
11	72.6 (0.5)	74.0 (0.5)	0.98	54	trace	1.00	14	6.90	423	0.09	4.84	118	64	35.2	1.2
12	72.8 (0.5)	110.0 (0.75)	0.66	61	trace	0.66	15	4.15	393	0.06	2.76	93	72	43.6	1.2
13	30.1 (0.2)	56.2 (0.375)	0.54	835	0.03	0.26	394	0.12	4694	0.19	1.40	2105	139	6.2	1.0

^aPhotocatalyst: 1.5 g, cocatalyst: a liquid phase reduction (loaded amounts (/μmol) was determined by XRF), 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 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.