Characterisation and acid properties of some modified combustion catalysts: Pt/alumina with barium and Pt/zirconia with yttrium

Platinum was deposited on alumina and zirconia, subjected or not to additio n of barium or yttrium, respectively. Surface acidic properties were probed by ammonia adsorption followed by FT-IR spectroscopy and temperature-progr ammed desorption (TPD) using an original inductive set-up for fast heating of the sample. The Pt/alumina sample exhibits 0.34 acid site per nm(2). The addition of ba rium (14.8 wt%) to this catalyst neutralises the hydroxyl groups located at the surface of alumina and therefore leads to the complete eradication of Lewis acid sites. Considering the Pt/zirconia sample, the nature and density of surface acid sites are very close to what was determined for Pt/alumina. No Bronsted aci dity is detected and additions of 2.03 and 3.42 wt% yttrium lead to a conco mitant decrease of the number (and of the strength) of the acid sites in or der to reach densities of 0.16 and 0.10 per nm(2), respectively. (C) 2000 E lsevier Science B.V. All rights reserved.