Investigation of NO and NO₂ Transformation in a Non-Thermal Plasma-Assisted SCR System with Cu/Al₂O₃

¹ Department of Mechanical and Automotive Engineering Technology, Faculty of Engineering and Technology, King Mongkut’s University of Technology North Bangkok (Rayong Campus), 21120 Rayong, Thailand
² KMUTNB Techno Park, King Mongkut’s University of Technology North Bangkok, 10800 Bangkok, Thailand
³ College of Industrial Technology, King Mongkut’s University of Technology North Bangkok, 10800 Bangkok, Thailand
⁴ Research Centre for Combustion Technology and Alternative Energy (CTAE), Science and Technology Research Institute, King Mongkut’s University of Technology North Bangkok, 10800 Bangkok, Thailand

^* Corresponding author: punya.p@technopark.kmutnb.ac.th

Abstract

This research investigates a hybrid methodology for the abatement of low-temperature NO_x by amalgamating non-thermal plasma (NTP) with a Cu/Al₂O₃ catalyst under conditions that simulate diesel exhaust. A catalyst consisting of 2 wt% Cu-loaded γ-Al₂O₃ was synthesized through the technique of incipient wetness impregnation and subsequently characterized using X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS), thereby confirming the presence of metallic Cu⁰ and its uniform distribution. Plasma experiments were executed at input power levels of 20, 30, and 40 W. The results indicated that NTP in isolation effectively facilitated the oxidation of NO to NO₂, attributable to the generation of reactive species including O₃ and O*. Nevertheless, when this plasma treatment was employed in conjunction with the catalyst, both NO and NO₂ were concurrently eliminated via the rapid selective catalytic reduction (SCR) mechanism, resulting in substantially enhanced NO_x conversion rates. Further examination revealed that a reduction in the electrode gap resulted in an increase in electric field strength (E = V/d), which in turn amplified plasma reactivity. At a gap of 3 cm, the most significant NO_x reduction efficiency was attained due to improved NO oxidation and an optimal NO/NO₂ ratio entering the catalyst. In summary, this study elucidates that the efficacy of plasma-catalytic systems is influenced not solely by plasma power but also by the geometrical configuration of the reactor. These findings offer essential insights for the design of energy-efficient systems aimed at low-temperature NO_x control.