Heat of adsorption and reaction activation energies of surface species measured by infrared spectroscopy

COLLINS, S. E.; BALTANÁS, M. A.; BONIVARDI, A. L.

Cuarnavaca, Mexico

Simposio; Fourth San Luis Conference in Surface Science, Interfaces and Cataysis; 2007

Pan-American Advances Studies Institute

The temperature-programmed adsorption equilibrium of CO at 4 kPa on Pd/SiO2 and of CO2 at 101 kPa on g-Ga2O3 was studied by infrared spectroscopy between 298 and 723 K. The coverage evolution (q) of each adsorbed species as a function of the adsorption temperature was measured by normalizing the IR absorption bands. The Temkin model was used to fit the experimental q vs. T data of each surface species and to obtain the initial (q = 0) and final (q = 1) isobaric heats of adsorption of COL and COB on palladium and of HCO3-, b-CO3=, br-CO3= and CO2- on gallia. The reactive adsorption of CO (101 kPa) on gamma gallia was also studied. CO reacts with surface OH groups to give formate species from 448 K. These formate species are further decomposed to CO2(g) and Ga-H species from 573 K onward. The whole process was modeled by considering the rate of reaction for each elementary step. Thus, the activation energy of the reactive adsorption of CO and of the formate decomposition on g-Ga2O3 were calculated.