Mechanism of iron-catalyzed water vapour gasification of carbon

✍ Scribed by Günter Hermann; Klaus J. Hüttinger

• Publisher: Elsevier Science
• Year: 1986
• Tongue: English
• Weight: 730 KB
• Volume: 24
• Category: Article
• ISSN: 0008-6223
• DOI: 10.1016/0008-6223(86)90263-0

✦ Synopsis

The mechanism of iron-catalyzed water vapour gasification of carbon was studied by temperature programmed desorption measurements of carbon monoxide using a polyvinyl chloride coke (HTT 9OO"C), which was impregnated with iron sulphate (approx. 2 wt% Fe), pregasified in different hydrogen/water vapour atmospheres and quenched at 300 K . min' to temperatures between 500 and 300°C. or at 300 K . SC' to room temperature. Three carbon monoxide desorption peaks were detected (peak temperatures 550-600°C. 650-7OO"C, 800°C); they are ascribed to three iron-oxygen surface complexes of different stability. A steady state isothermal water vapour gasification catalyzed by iron is only possible above 700°C with the most stable ironoxygen surface complexes as intermediates. The results support an oxygen transfer mechanism, where the oxygen transfer from the iron to the carbon surface represents the rate-limiting step. The activation energy of iron-catalyzed water vapour gasification is higher than 360 kJ mol-' and therefore higher than that of noncatalyzed gasification (336 kJ mol-'). The activation energy is attributed to the oxygen transfer step. Acceleration of the gasification by iron at temperatures starting from 700°C may only be affected by a large increase in concentration of active sites for dissociation of water vapour, which represents the rate-limiting step of noncatalyzed gasification. Key WordsWater vapour, gasification. catalysis, iron, carbon monoxide desorption. oxygen transfer mechanism.