Autothermal reforming of simulated and commercial fuels on zirconia-supported mono- and bimetallic noble metal catalysts

摘要

New energy sources are needed if energy supply and demand are to remain in balance. At the same time, the level of emissions needs to be reduced to minimise their contribution to the greenhouse effect. Renewable energy sources, and hydrogen (H2), have been attracting much attention, and more efficient technologies for energy recovery have been developed. Among these are fuel cells. H2 is not a source of energy but an energy carrier, which needs to be produced from a primary fuel (hydrocarbons, alcohols, water). Conventionally H2 is produced by steam reforming (SR) of natural gas. For mobile applications, however, a liquid fuel that is easy to deliver and safe to store is at present more feasible. Since the reaction enthalpy of SR increases markedly with the length of the hydrocarbon chain of the fuel, autothermal reforming (ATR), where endothermic SR is combined with exothermic partial oxidation (POX), is preferable to conventional SR. ATR of hydrocarbon fuels was investigated for the on-site production of H2-rich fuel gas suitable for solid oxide fuel cell (SOFC) applications. ATR of commercial fuels has to be carried out at high temperatures (700–900 °C) to achieve complete conversion of both the aliphatic and aromatic hydrocarbon fractions. With high temperature, however, thermal reactions of aliphatic hydrocarbons accelerate producing undesired compounds that also promote coke formation. These challenges can be overcome with active, selective and stable catalysts. ZrO2-supported mono- and bimetallic noble metal (Rh, Pd, Pt) catalysts were examined. Rh proved to be most active for SR, whereas Pt was active for oxidation reactions. The good features of these two metals were combined in the bimetallic catalysts where strong synergism exists between Rh and Pt. Catalytic performance was excellent, there were no side products and coke formation was suppressed. Furthermore, ATR of commercial low-sulfur diesel was successfully carried out on these bimetallic RhPt catalysts, which exhibited high thermal stability even in the presence of heterocyclic sulfur compounds.