Adsorptive removal of trace NO from a CO2 stream over transition-metal-oxide-modified HZSM-5

This study investigates the adsorption performance of a number of absorbents prepared by incipient wetness impregnation of 3.85 wt% Fe, Co, Ni, Mn, Co and Ce oxides on HZSM-5 for the removal of trace NO (150–200 ppm) from a CO₂ stream to produce food-grade CO₂. The adsorbents were characterized using X-ray diffraction, X-ray fluorescence, and N₂ adsorption with their performances evaluated in a fixed-bed flow system. The investigations revealed NO removal of better than 0.1 ppm from the CO₂ stream. The breakthrough capacities of the adsorbents for NO removal in the presence of O₂ were found to significantly increase. The converse was observed in the case of NO adsorption selectivity. Co/HZSM-5(25) was found to be the best adsorbent under all the conditions tested producing CO₂ purities of better than 99.9999%. This is significantly higher than for Fe–Mn mixed oxides, claimed to be the best NO adsorbent reported in the literature for CO₂ purification.