CO2-reforming reactions have been studied in a plug-flow reactor with catalysts containing less than a monolayer of Rh, Ru, or Ir deposited from tetrametallic dodecacarbonyl clusters onto low surface area polycrystalline alpha-Al2O3, MgO, CeO2, La2O3, and TiO2. The catalytic reactions are studied in conditions at which the carbon formation quickly deactivates Ni-based catalysts but does not deactivate noble metal based materials. Diffuse-reflectance-infrared-Fourier-transform (DRIFT) spectroscopy and mass spectrometry experiments inside a high-temperature high-pressure (HTHP) chamber have cast light on molecular aspects of the CO2-reforming reaction which have been embodied in a reaction mechanism. The formation of highly reactive oxidic species from the dissociation of CO2 is showed, and their role in inhibiting the production of large carbon aggregates is discussed.