Investigation of NO dissociation and reduction by H 2 on nanosized W 2N surface with transient-response techniques

Abstract

Nanosized W 2N was prepared by NH 3-temperature-programmed reaction and characterized by XRD, transmission electron microscopy (TEM), BET, X-ray photoelectron spectroscopic (XPS) and temperature-programmed desorption (TPD) techniques. Transient-response experiments were applied in order to improve understanding of the mechanism of NO reduction with H 2 on W 2N surface. Switches of He into 1% NO/0–7% H 2/He gas streams on W 2N surface were performed at 500 °C. The 1% NO/He step-response experiment showed that NO dissociation in the absence of H 2 was not effective on W 2N surface because the surface oxygen from dissociated NO was strongly bond to the catalyst surface, poisoning the NO dissociation sites and inhibiting further NO dissociation. In the 1% NO/1–7% H 2/He step-response experiments, N 2, NH 3, H 2O and N 2O (little or none) were detected as reaction products. The formation of H 2O on the catalyst surface was the most crucial step for NO dissociation to proceed and that it depended on the NO:H 2 ratio in the reaction mixture. Reasonable NO:H 2 ratio of 1:5 in feed gas was determined to keep the catalyst surface sites active for the catalytic dissociation of NO. Reaction pathways explaining the reduction of NO with H 2 were proposed.