Catalytic Generation of Hydrogen with Titanium Citrate and a Macrocyclic Cobalt Complex
Hydrogen evolution from acidic aqueous solutions of TiIIIcitrate is strongly catalyzed by Co(dmgBF{sub 2}){sub 2}. The reaction generates an intermediate with maximum absorbance at 770 nm. The slow disappearance of this intermediate takes place simultaneously with the generation of H{sub 2} in a process that was most efficient at pH 1.6 (turnover number 53). The loss of the catalytic activity is caused by the loss of the macrocyclic ligand and formation of Co{sub aq}{sup 2+}. Control experiments implicate Co{sup III} as the most likely oxidation state responsible for catalyst destruction, and thus provide indirect evidence for the involvement of Co{sup III} in the catalytic cycle. Taken together, the data suggest that hydrogen generation takes place at least in part by the H{sup +}/HCo{sup III}(dmgBF{sub 2}){sub 2} route. Incitrate-containing solutions at 7 {le} pH {le} 8, the protonation of Co{sup I}(dmgBF{sub 2}){sub 2}{sup -} to yield HCo{sup III}(dmgBF{sub 2}){sub 2} has a rate constant k{sub H} = 1.4 x 10{sup 6} M{sup -1} s{sup -1}. This reaction is about ten times slower in the absence of citrate.
- Research Organization:
- Ames Lab., Ames, IA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- DE-AC02-07CH11358
- OSTI ID:
- 983657
- Report Number(s):
- IS-J 7535; TRN: US201014%%864
- Journal Information:
- European Journal of Inorganic Chemistry, Vol. 2010, Issue 17
- Country of Publication:
- United States
- Language:
- English
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