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H. Lorenz, S. Penner, W. Jochum, C. Rameshan, B. Klötzer:
"Pd/Ga₂O₃ methanol steam reforming catalysts: Part II. Catalytic selectivity";
Applied Catalysis A: General, 358 (2009), 203 - 210.

Structure, morphology and composition of two Pd/Ga₂O₃ methanol steam reforming catalysts were correlated with the associated activity and selectivity changes in the methanol steam reforming reaction and linked to studies on pure Ga₂O₃ supports. For both systems, that are, a Pd/Ga₂O₃ thin film model catalyst and a powder-supported Pd catalyst, we identified a temperature range in which the reduction with hydrogen yields a single Pd-Ga bimetallic on a reduced oxide support, which in turn suppresses methanol dehydrogenation and results in a high CO₂-selectivity in methanol steam reforming. For the thin film catalyst, this included the Pd₅Ga₂ bimetallic present after reduction in the temperature range 523-600 K, for the powder-supported catalyst, Pd₂Ga, formed after reduction between 523 and 773 K, was found to account for the high CO₂-selectivity. In contrast to studies on the corresponding Pd/ZnO catalysts, sintering and metal decoration by reduced GaOx species will additionally have to be considered for discussions about structure-activity correlations in Pd/Ga₂O₃ thin film model catalysts. Reduction at 673 K causes catalyst deacti-vation and loss of CO₂-selectivity due to encapsulation of catalytically active bimetallic particles by mobile GaOx species and hampers oxidative catalyst regeneration. No such behavior has been observed for the powder-supported catalyst. This difference in catalytic activity and selectivity between the two catalysts is interpreted in terms of their different (bi-) metallic - oxide contact area.
Formic acid formation has been observed on pure Pd/Ga₂O₃ supports, which yields additional CO by formic acid decarbonylation. For the CO₂-selective methanol steam reforming reaction over a Pd-Ga bimetallic particle, formic acid is not a gas phase species, which indicates a preferen-tial decarboxylation pathway of adsorbed formate species at low temperatures.

Catalysis, CO2 selectivity, methanol dehydrogenation, CO, Ga2O3, reduction, Pd-Ga alloys, Formic Acid

http://dx.doi.org/10.1016/j.apcata.2009.02.027