Characterizing the stability of ultra-thin metal oxide catalyst films in non-thermal plasma CO2 reduction reactions

The use of metal oxide catalysts to enhance plasma CO2 reduction has seen significant recent development towards processes to reduce greenhouse gas emissions and produce renewable chemical feedstocks. While plasma reactors are effective at producing the intended chemical transformations, the conditions can result in catalyst degradation. Atomic layer deposition (ALD) can be used to synthesize complex, hierarchically structured metal oxide plasma catalysts that, while active for plasma CO2 reduction, are potentially vulnerable to degradation due to their high surface area and nanoscopic thickness. In this work, we characterized the effects of extended non-thermal, glow discharge plasma exposure on ALD synthesized, ultra-thin film (<30 nm) TiO2 and ZnO catalysts. We used X-ray diffraction, reflectivity, and spectroscopy to compare films exposed to a CO2 plasma to ones exposed to an Ar plasma and to ones annealed in air. We found that the CO2 plasma exposure generated some surface reduction in TiO2 and increased surface roughening by a small amount, but did not initiate any phase changes or crystallite growth. The results suggest that ALD-deposited metal oxide films are robust to low pressure CO2 plasma exposure and are suitable as catalysts or catalyst supports in extended reactions.