Role of NO and SO in mercury oxidation over a LaO/FeO catalyst with high thermal stability.

In this study, the thermal stability of a ferric oxide catalyst for mercury oxidation was found to be considerably promoted by doping with LaO. The catalysts doped with LaO maintained a higher surface area when subjected to high-temperature calcination, with lower average pore size and a narrower pore size distribution. X-ray diffraction (XRD) results revealed that LaO doping hinders the growth of catalyst particles and crystallization of the material at high temperatures. Both NO and SO inhibited Hg oxidation over the LaO/FeO catalyst. Fourier transform infrared (FTIR) spectra revealed that SO reacts with O over the catalysts to form several species that are inert for mercury oxidation, such as SO, HSO, or other related species; these inert species cover the catalyst surface and consequently decrease Hg oxidation capacity. In addition, NO or SO competed with Hg for active sites on the LaO/FeO catalyst and hindered the adsorption of mercury, thereby inhibiting subsequent Hg oxidation. Hg oxidation on the LaO/FeO catalyst mainly followed the Eley-Rideal mechanism. Moreover, the inhibition effects of NO and SO were at least partially reversible, and the catalytic activity was temporarily restored after eliminating NO or SO.