Methanol steam reforming provides clean hydrogen by onboard production, which can directly be used for fuel cell applications-while using appropriate catalysts. InxPdy/In2O3 aerogels exhibit excellent CO2 selectivities of 99%. This is caused by the active participation of chemically bound oxygen from the material as proven by isotope-labeling experiments. In addition, the dynamic, temperature-dependent equilibrium between intermetallic and oxidic species has a strong impact on the catalytic properties of the material. Thus, the intermetallic compounds in close proximity to a supporting reducible oxide act as selectivity-decisive redox centers, enabling a Mars-van Krevelen mechanism, which is responsible for the excellent selectivity toward CO2.