IN-SITU DIFFUSE-REFLECTANCE FTIR STUDY OF THE SELECTIVE CATALYTIC REDUCTION OF NO BY NH3 OVER VANADIA-TITANIA AEROGELS

Selective catalytic reduction of NO by NH3 (SCR) on high surface area (BET > 180 m2 g-1 vanadia-titania aerogels with 5, 10, and 20 wt% of vanadia, has been investigated by diffuse reflectance FTIR spectroscopy coupled with mass spectrometry under reaction conditions and by temperature-programmed desorption of preadsorbed NH3 and NO. The SCR activity of these catalysts increases with the vanadia loading. This behaviour is reflected by the temperatures necessary to reach 50% NO conversion under standard conditions, which decreased in the sequence 5% V2O5, 545 K; 10% V2O5, 470 K; 20% V2O5, 440 K. A similarly prepared high surface area (182 m2 g-1) titania aerogel does not exhibit significant NO conversion in this temperature range. On pure titania aerogel, mainly Lewis-bound ammonia is observed subsequent to NH3 adsorption at ambient temperature. In contrast, it is shown that Bronsted-bound ammonia, characterized by bands at 1660 and 1414 cm-1, is involved in the SCR reaction. The SCR activities correlate with the fraction of Bronsted-bound ammonia which significantly increases with the vanadia loading of the aerogel samples. (C) 1994 Academic Press, Inc.