A set of different Pd/Ga2O3 catalysts has been tested as suitable CO2-selective catalysts in methanol steam reforming, formaldehyde steam reforming and formic acid decomposition. Special focus was put on two different polymorphic forms of Ga2O3, namely alpha-Ga2O3 and gamma-Ga2O3 and their comparison to the use of the more common beta-Ga2O3 as oxide support of small Pd particles. The formation of eventually CO2-selective intermetallic Pd-Ga phases started at around 523 K on both supports. Pd2Ga at low temperatures (between 523 K and 673 K) and generally PdGa at higher temperatures (at and above 673 K) were the only intermetallic phases observed. Both thermodynamically metastable oxide supports transformed into the stable beta-Ga2O3 structure at 873 K reduction temperature. In contrast to previous studies, a highly CO2-selective state in methanol steam reforming (CO2 selectivity > 70%) could be established on both catalysts after reduction at 673 K (alpha-Ga2O3) and 523 K (gamma-Ga2O3), where the active state of the catalysts can be characterised as Pd2Ga/alpha-Ga2O3 and Pd2Ga/gamma-Ga2O3, respectively. alpha-Ga2O3 itself is reasonably CO2-selective in methanol steam reforming (similar to 80%), although not very active. In contrast, the gamma-Ga2O3 polymorph is neither CO2-selective, nor active and resembles the behaviour of beta-Ga2O3. The high CO2-selectivity of alpha-Ga2O3 is explained in terms of a higher surface basicity alongside efficient decarboxylation of intermediary formed formic acid. As crucial parameters for the observed CO2-selectivity in methanol steam reforming, decarboxylation of formic acid and oxidation of formaldehyde proceeding efficiently via a low-temperature reaction channel over either oxide-supported Pd2Ga intermetallic catalysts were identified. (C) 2012 Elsevier B.V. All rights reserved.