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In this contribution, we synthesized three model Cu-SSZ-13 catalysts with primarily ZCuOH, Z2Cu, and extraframework Cu x O y species and then measured their N2O formation rates during standard selective catalytic reduction (SCR). We first present evidence that the formation of extraframework Cu x O y species after sequential aqueous ion exchange and calcination correlates with the formation of Cu­(OH)2 precipitates during ion exchange. These Cu x O y species are not active for standard SCR, and unchanged apparent activation energies and reaction orders demonstrate that these Cu x O y species do not induce transport limitations to accessible Cu2+ active centers. During standard SCR, N2O formation rates on a per Cu basis were the fastest (and exhibited higher selectivities) on ZCuOH, followed by Z2Cu and then extraframework Cu x O y . Because N2O formation apparent activation energies were indistinguishable from the standard SCR apparent activation energies associated with the reduction-limited step, we posit that N2O is formed during the standard SCR reduction step. Additionally, using sulfur poisons to force the ZCuOH rate-limiting step to the oxidation half-cycle resulted in an unchanged N2O formation apparent activation energy, further supporting our hypothesis. These results suggest that utilizing Cu-SSZ-13 catalysts with higher fractions of Z2Cu active centers in commercial aftertreatment systems can lead to reduced N2O emissions.

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Irradiation (k [ 320 nm) of ferrocene in chloroform causes decomposition of chloroform and the accumulation of HCl, CCl 3 OOH, and C 2 Cl 6 . This appears to occur initially through a cycle in which (a) ferrocene is oxidized to ferrocenium and tetrachloroferrate ions, (b) FeCl 4 -undergoes photodissociation, and (c) ferrocenium reoxidizes the chloroferrate(II) species. On extended photolysis, the concentrations of CCl 3 OOH and FeCl 4 -build up and a competing cycle in which FeCl 4 -is restored through oxidation of the chloroferrate(II) species by CCl 3 OOH accelerates the decomposition rate.

Exposure of solutions of tetrabutylammonium chlorochromate in chloroform to UV or blue light causes decomposition of the chloroform and the buildup of HCl and peroxides in solution. The CrO(3)Cl(-) is converted during irradiation to CrO(2)Cl(2), which forms a suspension in the chloroform, and then to CrOCl(4)(-). CrO(2)Cl(2) does not by itself catalyze photodecomposition. The initial rate of HCl formation shows an apparently linear dependence on the incident light intensity and on the fraction of light absorbed by chlorochromate, but different values for the apparent quantum yield at 435 nm with high and low concentrations imply a nonlinear contribution to the rate. It is proposed that, at least initially, a cycle involving photoreduction of a Cr(vi) species and thermal reoxidation of Cr(v) by CCl(3)OOH produces radicals that initiate further decomposition.