Real-time monitoring of N2O production in a catalytic reaction process using mid-infrared quantum cascade laser

Highlights: • Real-time tracking N₂O production during a catalytic reduction of NO by CO over a Pt/SiO₂ catalyst using QCL. • This work allows for experimental investigation of conversion efficiencies of NO to N₂, N₂O and NO₂ through the catalytic reaction. • Optimal catalytic reaction conditions for zero N₂O production is obtained. In the context of climate change mitigation, reuse of carbon dioxide (CO₂) represents an alternative with important applications in chemical industry and power generation. For this purpose, CO₂ must be purified. Combustion processes lead to high amounts of CO₂ but still with impurities and also accompanied by toxic gases (mainly NO and CO). A catalytic reduction process of NO (to N₂) while oxidizing CO into CO₂ is a promising method to purify the CO₂. However, nitrous oxide (N₂O) with a global warming potential of 300 times greater than CO₂ may be a by-product from this process. It is therefore necessary to optimize the chemical reaction conditions to minimize N₂O production. A room-temperature continuous-wave (CW) external cavity quantum cascade laser (EC-QCL)-based optical sensor was developed for real-time monitoring N₂O production during the whole catalytic reaction process. A well-isolated N₂O absorption line, located at 1261.0598 cm⁻¹, of the ν₁ fundamental vibrational band was selected for sensitive and selective measurement of N₂O concentration by direct absorption spectroscopy. Using a modified-Herriot multi-pass cell with an effective path-length of 50 m, the limit of detection (1σ) of 32.3 ppbv was obtained in 12 s with 1.1% relative uncertainty in measurement precision. N₂O productions through the catalytic reduction of NO by CO over Pt/SiO₂ catalyst under different temperatures were investigated. High N₂O production of up to ∼6.1 ppmv at 190 °C was observed. The optimal reaction conditions for zero N₂O production were found at a temperature higher than 340 °C where 47% of NO was converted to N₂.