Diesel fuel reforming using catalytic membrane reactors

Reactors incorporating porous membranes of yttria-stabilized zirconia combined with beds of perovskite oxidation catalysts are being developed to convert pump-grade, low-sulfur diesel fuel into synthesis gas. Purified mixtures of H2 and CO might be used to power solid-oxide fuel cells (SOFCs), or the hydrogen could be used as a reductant in diesel automotive pollution control devices. Air is transported into reactors through porous cylindrical reactor walls. A very high local partial pressure of oxygen is maintained near the inner reactor walls to thermodynamically disfavor formation of carbon on reactor surfaces, especially along the cool zones of the fuel feed. The reactor hot zone, which contains a bed of perovskite catalyst, is operated at or above 950 °C and under conditions which thermodynamically suppress formation of carbon. Perovskite catalysts, La0.5Sr0.5CoO3−δ and La0.5Sr0.5FeO3−δ, show tolerance to sulfur and high activity for reforming diesel fuel, the latter being more stable under reducing conditions. Under the appropriate thermodynamic conditions, cobalt and iron catalyze Fischer-Tropsch reactions in reverse, transforming hydrocarbons into hydrogen and carbon monoxide. The perovskite catalysts are designed to incorporate lattice vacancies, allowing high oxygen-anion mobility and oxidation of adsorbed carbonaceous materials from beneath. The perovskites are mixed electron-anion conductors also designed for high mobility of electrons required for electron transfer reactions. Platinum–rhodium wire gauze operated above 950 °C shows good tolerance to sulfur and high activity for oxidation of diesel fuel and is used as a baseline for comparison of activity of the perovskite catalysts. In excess oxygen, the perovskites catalyze the complete oxidation of diesel fuel into CO2 and water and are comparable in activity to that of the noble metals. Perovskite oxidation catalysts may find application in pollution control.