Table 2. Catalytic hydrogenation of carbon dioxide to formic acid in different solvent mixtures.

Entry	Solvent	H2O (%)	Solvent (%)	HCOOH (M)	TON
1	H2O	100	—	0.11	40
2	[BMIM][BF4]	50	50	0.15	54
3	[BMIM][tos]	52	48	0.19	69
4	[BMIM][tos]	40	60	0.10	36
5	[BMIM][BF4]	20	80	0.14	51
6	[BMIM][BF4]	10	90	0.12	43
7	THF	50	50	0.095	34
8	DMSO	50	50	0.34	123
9	DMSO	20	80	0.98	355
10	DMSO	10	90	1.31	475

THF, tetrahydrofuran.

Reaction conditions: [RuCl₂(PTA)₄] (2.76 mM), P(total)=100 bar, P(H₂)/P(CO₂) ratio of 1, t=50 °C, reaction time 120 h, solvent (2 ml containing DSS, 0.0130 M), average values of several (two to three) measurements for each cycle, reproducibility is±15%.