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.