Employing Optical Emission Spectroscopy to Elucidate the Impact of Titanium Dioxide in Plasma-Assisted Catalysis

Abstract

The roles of gas phase, gas–surface interface, and material properties of the catalyst must be understood to fully realize future applications of plasma-assisted catalysis (PAC) for pollution remediation. This requires understanding of fundamental processes contributing to plasma–catalyst synergy, including determination of molecular temperatures. Optical emission spectroscopy (OES) was employed for gas-phase processes in H2 and CH4 inductively coupled plasmas in the presence of catalytic TiO2. TiO2 introduction has a minimal effect on the rotational temperature of H2 [TR(H2)] in 100% H2 plasmas but reduces TR(H2) by ≤300 K in 100% CH4 plasmas. Time-resolved OES studies echo energy partitioning results and reveal further kinetic details on H2 formation and the impact of catalysts on gas-phase processes. Comprehensive analysis of the catalyst before and after plasma exposure reveals H2 plasmas act as etching systems whereas competing etching and deposition processes occur under some conditions in CH4 plasmas.