Effect of morphology and simultaneous sulfation on Fe doped CeO2 for selective catalytic reduction of NO with NH3

Researchers have been developing novel environment-friendly NH3-SCR catalysts for controlling NOx emission from fossil fuel combustion. Fe doped CeO2 catalysts with nanorod, nanocube and nanopolyhedron shape were synthesized and sulfation was conducted on porous nanorod simultaneously. Their NOx conversions were in sequence of sulfated porous nanorod (S-FeCeOx) > nanorod (R-FeCeOx) > nanopolyhedron (P-FeCeOx) > nanocube (C-FeCeOx) and presented distinct morphology dependence. S-FeCeOx catalyst possessed above 95 % NOx conversion and nearly 100 % N2 selectivity in very high gas hourly space velocity of 240, 000 mL·g−1·h−1 at 275–400 °C. The sequence of BET specific surface area was: P-FeCeOx > R-FeCeOx > S-FeCeOx > C-FeCeOx and thus the change of physical adsorption capacity may be not the main reason for high SCR catalytic activity of S-FeCeOx and R-FeCeOx. Fe doping and sulfation induced porous nanorod shape with preferentially exposed {110} faces, most oxygen vacancy defect sites and highest surface chemisorbed oxygen ratio, which contributed to the highest NOx conversion of S-FeCeOx. Fe doping mainly increased strong acid sites, and surface sulfate species significantly increased Brønsted acid sites promoting NH3 adsorption and suppressed NOx adsorption on S-FeCeOx catalyst, beneficial to both high NOx conversion and low N2O formation on it. R-FeCeOx catalyst mainly followed Langmuir-Hinshelwood mechanism, while SCR reaction mechanism was changed by sulfation and S-FeCeOx catalyst mainly followed Eley-Rideal mechanism.