Catalytic reduction of NO x by CO using monolith corrugated cylindrical Cu-Cr-based catalysts prepared by plasma spray coating

The present work is dedicated to the investigation of NO x removal from flue gases, in particular to NO x 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 NO x 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 NO x 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 NO x conversion observed at the O 2 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 NO x 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 NO x conversion degree (%) and “x” denotes the residence time. It was demonstrated that NO x 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 NO x conversion was observed. In particular the degree of NO x 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 NO x 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 NO x conversion.