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To improve their CO2 absorption capacity, alkali-based sorbents prepared by impregnation and wet mixing method of potassium carbonate on supports such as activated carbon and MgO (KACI30, KACP30, KMgI30, and KMgP30), were investigated in a fixed bed reactor (C02 absorption at 50-100 degrees C and regeneration at 150-400 degrees C). Total CO2 capture capacities of KMgI30-500 and KMgP30-500 were 178.6 and 197.6 mg CO2/g sorbent, respectively, in the presence of 11 vol % H2O even at 50 degrees C. The large amount of CO2 capture capacity of KMgP30-500 and KMgI30-500 could be explained by the fact that MgO itself, as well as K2CO3, could absorb CO2 in the presence of water vapor even at low temperatures. In particular, water vapor plays an important role in the CO2 absorption of MgO and KMgI30-500 even at low temperatures below 60 degrees C, in marked contrast to MgO and CaO which can absorb CO2 at high temperatures. The CO2 capture capacity of the KMgI30-300 sorbent, however, was less than that of KMgI30-500 due to the formation of Mg(OH)2 which did not absorb CO2. MgO based-sorbents promoted with K2CO3 after CO2 absorption formed new structures such as K2Mg(CO3)2 and K2Mg(CO3)2 x 4(H2O), unlike KACI30 which showed only the KHCO3 crystal structure. The new Mg-based sorbents promoted with K2CO3 showed excellent characteristics in that it could satisfy a large amount of CO2 absorption at low temperatures, a high CO2 absorption rate, and fast and complete regeneration.

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The spectroscopic properties, including emission spectra and lifetimes, absorption and diffuse reflectance spectra and excitation spectra, of the hexanuclear copper(1) and silver(1) clusters Cu6(mtc)6 (l), Ag6(mtc) (2), and Ag,(dt~)~ (3) (mtc = di-npropylmonothiocarbamate, dtc = di-n-propyldithiocarbamate) are reported. At room temperature 1 exhibits a strong single emission (e.g., in toluene A=, = 725 nm, T = 1.0 I S ) , while at 77 K each of these is a bright emitter (spectral properties: 1 in toluene,

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Reported are the photophysical properties of the copper(1) halide clusters Cu4X4(dpmp)4 with the bulky organic base 2-(diphenylmethy1)pyridine (X = I, Br, Cl) which have been shown by previous crystal structure determinations to have "cubanem-like Cu4X4 cores with very similar Cu-Cu distances (2.87-3.01 A). As solids at 77 K, these compounds each exhibit a strong, relatively long-lived emission band [Amaxem = 467, 487, and 505 nm; T = 18.1, 10.0, and 10.0 ps (for X = I, Br, and C1, respectively)], which is attributed to radiative decay from a halide to ligand charge transfer (XLCT) excited state. At higher temperatures, a weak shoulder appeared in the emission spectra for the Cu414(dpmp)4 and Cu4Br4(dpmp)4 solids (at -570 and -626 nm, respectively), and the relative intensities of these shoulders could be fit to the function A exp(-AE/RT), with AE = 990 f 370 cm-' for the appearance of this red emission in C~~B r~( d p m p )~.The excited state (ES) lifetimes observed for these shoulders were identical to those observed for the still dominant higher energy bands. In analogy to earlier results with the copper(1) iodide cluster C U~I~( P Y )~, this longer wavelength band was attributed to emission from a Cu4X4 core centered ES of mixed halide-to-copper charge transfer (XMCT) and metal centered "d-s" orbital parentage. The nature of such transitions in CuJ4L4 clusters is discussed with respect to the Cu-Cu distances in the ground state structures.

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