Heats of Adsorption of Linear NO Species on a Pt/Al2O3 Catalyst Using in Situ Infrared Spectroscopy under Adsorption Equilibrium

The adsorption of 1% NO/He on a reduced 2.9% Pt/Al2O3 catalyst is studied at several adsorption temperatures Ta in the range 300–680 K using in situ FTIR spectroscopy. At 300 K several adsorbed NO species are formed on the Pt particles and on the support leading to numerous IR bands in the range 1850–1200 cm−1. After a short duration of the adsorption, two main IR bands are detected at 1764 and 1710 cm−1 assigned to two linear NO species (denoted by L) on defect and terrace sites of the Pt particles, respectively. The IR band at 1710 cm−1 is not modified with the duration of the adsorption at 300 K while that at 1764 cm−1 progressively decreases. Several IR bands are detected in the range 1650–1200 cm−1 mainly due to the formation of nitrite and nitrate-adsorbed species on the support. The increase in Ta from 300 to 540 K leads to a strong decrease in the IR band at 1710 cm−1 while that at 1764 cm−1 increases and shifts to 1778 cm−1. For higher adsorption temperatures (Ta