An investigation of the thermal stability and sulphur tolerance of Ag/γ-Al2O3 catalysts for the SCR of NOx with hydrocarbons and hydrogen

• Published in: Applied catalysis. B, Environmental Vol. 70; no. 1-4; pp. 36 - 44
• Main Authors: Breen, J.P., Burch, R., Hardacre, C., Hill, C.J., Krutzsch, B., Bandl-Konrad, B., Jobson, E., Cider, L., Blakeman, P.G., Peace, L.J., Twigg, M.V., Preis, M., Gottschling, M.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 31.01.2007
• Subjects: Ag/γ-Al2O3; Ageing; EXAFS; Octane; SCR-NOx; Silver; Sulphur tolerance; Toluene; XRD; Octane; Silver; Toluene; Sulphur tolerance; Ageing; Ag/γ-Al2O3; XRD; EXAFS; SCR-NOx
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2006.05.005

The sulphur tolerance and thermal stability of a 2wt% Ag/γ-Al2O3 catalyst was investigated for the H2-promoted SCR of NOx with octane and toluene. The aged catalyst was characterised by XRD and EXAFS analysis. It was found that the effect of ageing was a function of the gas mix and temperature of ageing. At high temperatures (800°C) the catalyst deactivated regardless of the reaction mix. EXAFS analysis showed that this was associated with the Ag particles on the surface of the catalyst becoming more ordered. At 600 and 700°C, the deactivating effect of ageing was much less pronounced for the catalyst in the H2-promoted octane-SCR reaction and ageing at 600°C resulted in an enhancement in activity for the reaction in the absence of H2. For the toluene+H2-SCR reaction the catalyst deactivated at each ageing temperature. The effect of addition of low levels of sulphur (1ppm SO2) to the feed was very much dependent on the reaction temperature. There was little deactivation of the catalyst at low temperatures (≤235°C), severe deactivation at intermediate temperatures (305 and 400°C) and activation of the catalyst at high temperatures (>500°C). The results can be explained by the activity of the catalyst for the oxidation of SO2 to SO3 and the relative stability of silver and aluminium sulphates. The catalyst could be almost fully regenerated by a combination of heating and the presence of hydrogen in the regeneration mix. The catalyst could not be regenerated in the absence of hydrogen.