The Role of Formate Groups in the Mechanism of Methanol Synthesis from H2/CO2 over a Pd/Ga2O3 Catalyst

SEBASTIÁN E. COLLINS; MIGUEL A. BALTANÁS; ADRIAN L. BONIVARDI

Toledo, España

Congreso; Second International Congress in Operando Spectroscopy (Operando II); 2006

To understand the mechanism of methanol synthesis from CO2 hydrogenation, we previously performed infrared in-situ temperature programmed reaction experiments using H2 and CO2 (323-723 K, 0.1 MPa) over a model Pd/Ga2O3 catalyst. A  bifunctional scheme was proposed, where: i) carbon dioxide chemisorbs (weakly) on the galia surface as (bi)carbonate species, which are stepwise hydrogenated to monodentate and bidentate formate species (m-HCOO and b-HCOO, resp.), methylenebisoxy (H2COO), methoxy (CH3O) and, finally methanol, and ii) Pd provides surface atomic hydrogen for CO2 reduction by spillover. Now, the role of the formate groups in the methanol synthesis was investigated by infrared spectroscopy using a high pressure infrared reactor. A reaction mixture (H2/CO2 = 3/1) was flowed through the reactor at 523 K and 0.1 MPa or 0.7 MPa and the gaseous products were analyzed by gas chromatography. Our results suggest that methoxy/methanol formation from H2/CO2 takes place as a consequence of the m-HCOO hydrogenation and, also, that b-HCOO behaves more likely as a spectator.