Selective Vapor-Phase Formic Acid Decomposition Over Carbon-Supported Rhenium Catalysts with Metallic, Carbide, and Oxide Rhenium Phases.

Formic acid is obtained as a byproduct of biomass pyrolysis and is used as a liquid organic hydrogen carrier due to its low decomposition temperature, enabling hydrogen production under mild conditions with noble metals. The decomposition of FA in the vapor phase using different rhenium phases (metal, carbide, and oxide) supported on graphite and carbon nanotubes was studied within a temperature range of 80-220 °C, in a fixed-bed reactor with a space velocity of 651 mL g_cat h^-1. The catalysts were characterized by N₂ adsorption-desorption, H₂-temperature-programmed reduction, transmission electron microscopy, temperature programmed desorption-ammonia, temperature programmed reaction-methanol, X-ray diffraction, and X-ray photoelectron spectroscopy. Graphite-supported catalysts achieved higher activity than carbon nanotube-supported ones, due to the higher rhenium dispersion on graphite. Catalytic reactions revealed that ReC/G exhibited superior performance at lower temperatures per active site, attributed to the rhenium carbide phase. High selectivity toward CO₂ was observed across all catalysts, except for ReOx/G at lower temperatures, where differences in active site characteristics likely influenced performance. ReC/G displayed the highest intrinsic activity, highlighting rhenium carbide as a more active phase than metallic or oxide rhenium.