Ozone decomposition kinetics on alumina: effects of ozone partial pressure, relative humidity and repeated oxidation cycles

[摘要] The room temperature kinetics of gas-phase ozone loss via heterogeneousinteractions with thin alumina films has been studied in real-time using 254nmabsorption spectroscopy to monitor ozone concentrations. The films wereprepared from dispersions of fine alumina powder in methanol and theirsurface areas were determined by an in situ procedure using adsorption of krypton at77K. The alumina was found to lose reactivity with increasing ozoneexposure. However, some of the lost reactivity could be recovered overtimescales of days in an environment free of water, ozone and carbondioxide. From multiple exposures of ozone to the same film, it was foundthat the number of active sites is large, greater than 1.4x10¹⁴active sites per cm² of surface area or comparable to the total numberof surface sites. The films maintain some reactivity at this point, which isconsistent with there being some degree of active site regeneration duringthe experiment and with ozone loss being catalytic to some degree. Theinitial uptake coefficients on fresh films were found to be inverselydependent on the ozone concentration, varying from roughly 10^-6 forozone concentrations of 10¹⁴ molecules/cm³ to 10^-5 at10¹³ molecules/cm³. The initial uptake coefficients were notdependent on the relative humidity, up to 75%, within the precision ofthe experiment. The reaction mechanism is discussed, as well as theimplications these results have for assessing the effect of mineral dust onatmospheric oxidant levels.

[学科分类] 大气科学