Mechanism of CO₂ and H⁺ Reduction by Ni(cyclam)⁺ in Aqueous Solution. A Pulse and Continuous Radiolysis Study

Abstract

The reduction of CO 2 and H + by Ni(cyclam) + in aqueous solution was found to proceed by the reduction of Ni(cyclam)(CO 2 ) + or Ni(cyclam)(H) 2+ by Ni(cyclam) + . At ambient temperature the rate constants for the bimolecular reactions are 1.6 × 10 8 and 7.2 × 10 7 M -1 s -1 , respectively. Continuous γ-radiolysis studies have demonstrated nearly quantitative formation of CO from two Ni(cyclam) + at pH 5.2 under 1 atm of CO 2 and in the presence of formate. Under the same conditions, but at low CO 2 concentration, the reduction of protons was found to compete with CO 2 reduction.

Reduction of CO2 to CO at Low Overpotential in Neutral Aqueous Solution by a Ni(cyclam) Complex Attached to Poly(allylamine)

“…The percentages of C, H, and N obtained from elemental analysis of Ni(cyclam)-PALA were 33.24 %, 6.21 %, and 12.31 %, respectively. UV/vis spectra ( Figure S4) of [Ni(cyclam)(pyCHO)](ClO 4 ) 2 and Ni(cyclam)-PALA displayed four transition bands, corresponding to 3 A 2g to 3 T 2g (680 nm), 3 A 2g to 3 T 1g (450 nm), and 3 A 2g to 3 T 1g (330 nm) transitions [5] for a d 8 metal ion in an octahedral environment (the bands at ca. An FTIR spectrum of the polymer (Figure S2) showed an C=N stretching vibration at 1606 cm À1 , proving Schiff's base condensation with the nickel complex.…”

“…The rather broad aromatic peak indicates that the motions of these aromatic protons are slow, due to them being attached to the polymer backbone. UV/vis spectra ( Figure S4) of [Ni(cyclam)(pyCHO)](ClO 4 ) 2 and Ni(cyclam)-PALA displayed four transition bands, corresponding to 3 A 2g to 3 T 2g (680 nm), 3 A 2g to 3 T 1g (450 nm), and 3 A 2g to 3 T 1g (330 nm) transitions [5] for a d 8 metal ion in an octahedral environment (the bands at ca. 270 nm are due to charge-transfer transitions), suggesting axial coordination of 4-pyridine.…”

Application of Pulse Radiolysis to Mechanistic Investigations of Catalysis Relevant to Artificial Photosynthesis

“…[42] [Ni(cyclam)] 2 + (cyclam = 1,4,8,11-tetraazacyclotetradecane) is an efficient andselective electrocatalyst for the electrochemical reduction of CO 2 in acidic (pH 4) aqueouss olution,e specially with am ercury pool electrode, as shown by Beley et al in 1984. [43] Although it is known that mercury-adsorbed [Ni I (cyclam)] + is an active catalystf or CO 2 reduction in water, Kelly et al [39,44] tried to produce [Ni(cyclam)(CO 2 )] + through the reduction of [Ni(cyclam)] 2 + by e aq À or CO 2 C À ,f ollowed by CO 2 addition in aqueous solution containing CO 2 .A ss hown in Figure13, they found that the resulting intensity of the [Ni(cyclam)] + spectrum( l max = 380 nm) exhibitedasmalll inear decrease with [CO 2 ], which indicated the presenceo fa ne quilibrium, as shown in Equation (31). Assuming that the CO 2 adduct does not have any significant absorption in the l = 300-700 nm region, the K CO 2 for Equation (31) was estimated to be 16 m À1 (see Ta ble 3).…”

Diaqua[(1R,2S,4R,8R,9S,11R)-2,9-dimethyl-1,4,8,11-tetraazacyclotetradecane]nickel(II) dichloride dihydrate

“…For uses of the title compound, see: Kimura et al (1992); Liang et al (2002); Burrows et al (1992Burrows et al ( , 1988; Kelly et al (1999); Churchard et al (2010). For the synthesis of the ligand, see: Beck & Lang (2003); Beck et al (1998.…”