Stationary and transient kinetics of the high temperature water-gas shift reaction

✍ Scribed by Riitta L. Keiski; Tapio Salmi; Pekka Niemistö; Jorma Ainassaari; Veikko J. Pohjola

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 933 KB
• Volume: 137
• Category: Article
• ISSN: 0926-860X
• DOI: 10.1016/0926-860x(95)00315-0

✦ Synopsis

The high temperature water-gas shift reaction over an industrial Fe304-Cr20 3 catalyst was investigated by stationary and transient experiments in isothermal conditions and at elevated pressures. A new modular computer controlled catalyst evaluation unit which can be operated either as a plug flow tubular reactor (PFTR) or a gradientless reactor was used. The plug flow mode was used to produce kinetic data for power-law kinetic models and the gradientless reactor to generate kinetic data for classical kinetic models. Separate chemisorption of CO, CO 2, and H 2 were done at 293, 373, 473 and 623 or 673 K to study the importance of these components as surface intermediates in the shift reaction. In PFTR the kinetic experiments were performed at 3-5 bar and 573-633 K in two separate series during the slow decay of the catalyst activity. The age of the catalyst in these experimental series was 200-280 and 725-763 h, respectively. The transient experiments were performed in the gradientless reactor at 573-623 K and 5 bar the age of the catalyst being 200-870 h. According to the stationary studies, the reaction rate is strongly dependent on the CO concentration, weakly dependent on the H20 concentration and practically independent on the CO 2 and H 2 concentrations. The reaction orders with respect to CO and H20 were around 1 and 0.5. In transient experiments CO 2 was always liberated faster than H 2 when the catalyst pretreatment was done without water. During the pretreatment of the catalyst with H20/N 2, small amounts of H 2 were formed. The H20 pretreatment retarded the CO 2 response. Based on these results a reaction mechanism was proposed which consisted of CO adsorption and oxidation steps as well as of H20 adsorption, decomposition and H 2 formation steps. The rate determining steps were the CO oxidation and H 2 formation steps. Non-dissociative (CO, CO 2) and dissociative (H 2) adsorption were described with Langmuir isotherms.