The role of Pd–Ga bimetallic particles in the bifunctional mechanism of selective methanol synthesis via CO2 hydrogenation on a Pd/Ga2O3 catalyst

Abstract

The effect of palladium?gallia interaction in Pd(1 wt.%)/b-Ga 2 O 3 during selective methanol synthesis byCO 2 hydrogenation was studied. A detailed quasi-in situ transmission electron microscopy analysis of theas-prepared H 2 -reduced catalyst, without exposing it to air, showed that Ga?Pd bimetallic (nano)parti-cles were formed under a reductive atmosphere at or above 523 K. However, these particles were unsta-ble; upon air exposure, a dramatic and extensive encapsulation of the metallic crystallites by Ga 2 O 3occurred. In addition, the function of the bimetallic particles in the mechanism of methanol synthesiswas investigated by in situ infrared spectroscopy at 0.7 MPa. The results confirmed those of previousstudies in which the stepwise hydrogenation of (bi)carbonate to formate and then to methoxy groupson the Ga 2 O 3 surface took place via a bifunctional pathway. In this pathway, the role of the Ga?Pd bime-tallic crystallites was to provide atomic hydrogen, via spillover, to the oxidic surface and to hamper bothCH 3 OH decomposition and CO production.