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 v anadia, has been investigated by diffuse reflectance FTIR spectroscopy coupled with mass spectrometry under reaction conditions and by tempe rature-programmed desorption of preadsorbed NH3 and NO. The SCR activi ty of these catalysts increases with the vanadia loading. This behavio ur is reflected by the temperatures necessary to reach 50% NO conversi on under standard conditions, which decreased in the sequence 5% V2O5, 545 K; 10% V2O5, 470 K; 20% V2O5, 440 K. A similarly prepared high su rface area (182 m2 g-1) titania aerogel does not exhibit significant N O conversion in this temperature range. On pure titania aerogel, mainl y Lewis-bound ammonia is observed subsequent to NH3 adsorption at ambi ent 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-b ound ammonia which significantly increases with the vanadia loading of the aerogel samples. (C) 1994 Academic Press, Inc.