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

Platinum was deposited on alumina and zirconia, subjected or not to addition of barium or yttrium, respectively. Surface acidic properties were probed by ammonia adsorption followed by FT-IR spectroscopy and temperature-programmed desorption (TPD) using an original inductive set-up for fast heating of the sample. The Pt/alumina sample exhibits 0.34 acid site per nm2. The addition of barium (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 Brönsted acidity is detected and additions of 2.03 and 3.42 wt% yttrium lead to a concomitant decrease of the number (and of the strength) of the acid sites in order to reach densities of 0.16 and 0.10 per nm2, respectively.