Propene is one of basic substances used in industry. With the development of new methods of propene production, such as oxidative dehydrogenation, it takes kinetic data for finding optimal reaction conditions and modelling industrial reactors. Besides, the study of kinetics can give the information on the process mechanism. There are many works on kinetics of propane dehydrogenation in O2 presence but studies with CO2 as oxidant are few [1, 2]. The main difficulty of kinetics investigations is keeping of the catalyst activity at constant level for a long time. The catalysts prepared by direct hydrothermal synthesis embedding chromium and gallium species in the siliceous framework of MCM-41 are filled this requirement. The work is devoted to the kinetic study of propane dehydrogenation in CO2 presence in stationary (in the gradientless flow circulating system) and nonstationary (in the flow unit of small volume) conditions at 580-620oC and atmospheric pressure over the following catalysts: 1.0%(wt.)Cr-MCM-41 and 2.0%(wt.)Ga-MCM-41. Catalysts were investigated by DR-UV-Vis and IR-FTIR spectroscopy, XRD, TEM, BET, TPR. Ga is better embedded in siliceous framework of MCM-41 (data XRD, BET, TEM) and regular mesoporous structure of MCM-41 is retained at 2.0%(wt.)Ga in difference with the catalysts containing 2.0%(wt.)Cr. The initial partial pressures of propane and carbon dioxide are varied in the range of 0.15- 0.33 and 0.30-0.66 atm., respectively. Kinetic equations of propene and cracking products formation had power-rational forms over both the catalysts. It was shown that the adsorption capacity of the reaction components and their surface covering were different over studied catalysts. It was determined the role of CO2 in this process: CO2 took an active participation in reverse water-gas shift reaction and in oxidation of catalyst surface over chromium oxides catalysts, the main role of CO2 in propane dehydrogenation consisted in a decrease of coke deposition over gallium oxides catalysts prepared by hydrothermal synthesis as well as over precipitation on SiO2 gallium catalysts [3].
Kinetics of propane dehydrogenation in CO2 presence over chromium and gallium oxide catalysts based on MCM-41
BOTAVINA, Maria
2012-01-01
Abstract
Propene is one of basic substances used in industry. With the development of new methods of propene production, such as oxidative dehydrogenation, it takes kinetic data for finding optimal reaction conditions and modelling industrial reactors. Besides, the study of kinetics can give the information on the process mechanism. There are many works on kinetics of propane dehydrogenation in O2 presence but studies with CO2 as oxidant are few [1, 2]. The main difficulty of kinetics investigations is keeping of the catalyst activity at constant level for a long time. The catalysts prepared by direct hydrothermal synthesis embedding chromium and gallium species in the siliceous framework of MCM-41 are filled this requirement. The work is devoted to the kinetic study of propane dehydrogenation in CO2 presence in stationary (in the gradientless flow circulating system) and nonstationary (in the flow unit of small volume) conditions at 580-620oC and atmospheric pressure over the following catalysts: 1.0%(wt.)Cr-MCM-41 and 2.0%(wt.)Ga-MCM-41. Catalysts were investigated by DR-UV-Vis and IR-FTIR spectroscopy, XRD, TEM, BET, TPR. Ga is better embedded in siliceous framework of MCM-41 (data XRD, BET, TEM) and regular mesoporous structure of MCM-41 is retained at 2.0%(wt.)Ga in difference with the catalysts containing 2.0%(wt.)Cr. The initial partial pressures of propane and carbon dioxide are varied in the range of 0.15- 0.33 and 0.30-0.66 atm., respectively. Kinetic equations of propene and cracking products formation had power-rational forms over both the catalysts. It was shown that the adsorption capacity of the reaction components and their surface covering were different over studied catalysts. It was determined the role of CO2 in this process: CO2 took an active participation in reverse water-gas shift reaction and in oxidation of catalyst surface over chromium oxides catalysts, the main role of CO2 in propane dehydrogenation consisted in a decrease of coke deposition over gallium oxides catalysts prepared by hydrothermal synthesis as well as over precipitation on SiO2 gallium catalysts [3].
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