Emission Spectroscopic Studies of Plasma-Induced NO Decomposition and Water Splitting

Abstract

Plasma methods have been extensively used in materials processing and the abatement of air pollutants such as halogenated hydrocarbons, NO{sub x}, and SO{sub x}. Other plasma research areas include ozone formation, ammonia synthesis, and activation of CH{sub 4}, H{sub 2}O, and CO{sub 2}. NO decomposition and water splitting with ac (alternating current) power plasmas at atmospheric pressure have been studied using both quartz and metal reactors. Optical emission spectroscopic (OES) studies have been carried out by employing a CCD (charge-coupled device) detector to monitor the change of plasma species neat and in the presence of reactants and metal surfaces to provide mechanistic information. Selective features of energy transfer from excited helium species to reactant molecules have been observed. Energy transfer in nitrogen plasmas is nonselective, whereas in argon plasmas it is slightly selective. Energy efficiency of plasma-induced reactions is largely determined by the efficiency of energy transfer and catalytic effects of metal surfaces. A mechanism has been proposed on the basis of OES and activity data that comprise energy transfer from excited carrier gas species to reactant molecules and heterogeneous catalysis of metal electrodes involving adsorption and combination of intermediates (oxygen radicals) on metal surfaces.