Methanol synthesis from CO2/H2 using Ga2O3–Pd/silica catalysts: Kinetic modeling

D.L. CHIAVASSA; S.E. COLLINS; A.L. BONIVARDI; M.A. BALTANÁS

CHEMICAL ENGINEERING JOURNAL

ELSEVIER SCIENCE SA

Año: 2009 vol. 150 p. 204 - 212

1385-8947

The synthesis of methanol from CO2/H2 on a Ga2O3–Pd/silica catalyst, together with the reverse watergas shift reaction, was modeled for a wide range of temperatures (508–538 K), pressures (1–4MPa),compositions (H2/CO2 = 1, 3 and 6) and space velocity conditions. The kinetic information was combinedwith relevant spectroscopic (FT-IR) data. The rate determining steps (rds) of the reactions werethe hydrogenation of the formate intermediate, and its decomposition on the gallia surface, respectively.A competitive adsorption mechanism, where adsorbed atomic hydrogen occupies the same active sitesas other oxygenated surface intermediates on the gallia, was found as the most satisfactory, in terms ofphysicochemical significance of the parameter estimates. Minimal residualswere foundwhenconsideringas kinetically relevant the simultaneous surface occupancy by formate, methylenebisoxy, hydroxyl andatomic hydrogen intermediates.The deleterious impact of CO for certain process conditions, such as high conversion and/or ternaryH2/CO2/CO mixture feeds, was also studied. In these cases, CO competes with H2 on the Pd crystallites,severely limiting the availability of atomic hydrogen to the gallia surface. Using the steady-stateapproximation, the supply and demand of atomic hydrogen were then balanced to find the best modelinterpretation of the observed reactivity.