Catalytic reduction of NOx by CO using monolith corrugated cylindrical Cu-Cr-based catalysts prepared by plasma spray coating

Abstract

The present work is dedicated to the investigation of NOx removal from flue gases, in particular to NOx catalytic reduction by CO using monolith corrugated cylindrical Cu-Cr-based catalysts prepared by plasma spray coating technique. X-ray photoelectron spectroscopy was conducted to provide comprehensive information about oxidation states and chemical forms of main active components of the catalysts prepared. Investigation of NOx catalytic reduction was carried out under different initial oxygen concentrations (0.0–0.1%, 0.6–0.7% and 1.2–1.3%) and gas flow velocities (0.1, 0.3 and 1.0 m/s) using different amount of catalysts and providing different residence time in the range of 0.1–3 s. The NOx conversion achieved at 0.0–0.1% oxygen concentration was 50%, 75% and 88% for the residence time of 1 s, 2 s and 3 s. The corresponding NOx conversion observed at the O2 concentration of 0.6–0.7% was 37%, 60% and 70%. However, investigated Cu-Cr-based catalysts were found as ineffective at initial oxygen concentrations higher than 1% regardless the residence time. The dependence of NOx conversion on residence time in general was represented by logarithmic regression and can be described by the following formula y = 23.962 ln(x) + 56.575, where “y” is NOx conversion degree (%) and “x” denotes the residence time. It was demonstrated that NOx conversion efficiency decreases along with increasing the gas flow velocity, which can be explained by reduction of residence time of a gas flow inside the catalysts. However, the obtained results revealed that using different gas flow velocities and providing the same residence time by changing the amount of catalysts, different NOx conversion was observed. In particular the degree of NOx reduction obtained at the gas flow velocity of 1 m/s was much lower than that achieved by applying lower gas flow velocity (0.3 m/s) regardless the residence time was the same. The negligible NOx reduction was found for all cases when the gas flow velocity of 1 m/s was used. Therefore, it was supposed that the gas flow velocity of 1 m/s does not ensure the required mass transfer between the gas components and catalyst’s surface inhibiting the catalytic reaction to take place and resulting in extremely low NOx conversion.