A simulated rotary reactor for NOx reduction by carbon monoxide over Fe/ZSM-5 catalysts

Abstract

Carbon monoxide could be used to reduce NOx to N2 over zeolite catalysts. But the NOx reduction efficiency is highly inhibited by oxygen present in the flue gas. In this research, a rotary reactor was proposed for the treatment of NOx in oxygen-rich flue gases. In the proposed rotary reactor, an adsorption zone and a reduction zone were configured in such a way that the flue gas stream, containing NOx and oxygen, and the reducing gas stream, containing CO, are introduced into the reactor separately. Loaded catalysts were rotated between the two zones to adsorb NOx from the flue gas in the adsorption zone and then reduce the adsorbed NOx by CO in the reduction zone. The performance of the rotary reactor was investigated in a fixed bed reactor loaded with Fe/ZSM-5 catalysts synthesized in the lab, and the dynamic adsorption-reduction process was simulated by switching the inlet gas stream. The results showed that the simulated rotary reactor could well remove and reduce NOx from oxygen containing flue gases. NOx removal efficiencies were very stable in the investigated temperature range, i.e., 250–400°C. Higher CO concentration could significantly enhance both NOx removal and reduction efficiencies. The amount of CO slipping into the adsorption zone was very low even though CO is in great excess. In order to explore the reaction mechanism, in situ DRIFT study was performed. It was found that CO could occupy the active Fe sites, promoting NOx desorption and the subsequence NOx removal in the adsorption stage. But the active intermediates for NOx reduction is not effectively formed during CO purging, resulting in a lower NOx reduction efficiency.