| Isobutane catalytic dehydrogenation has been considered as a promising route for direct conversion of abundant isobutane into high value-added chemical isobutene. This process, involving C-H bond activation and control dehydrogenation, is of great scientific significance and industrial interest in the petrochemical field.In this thesis, alumina supporters were successfully prepared by three different methods hydrothermal crystallization, sol-gel and solvent evaporation self-assembly to adjust the morphology and pore structure. The Cr2O3-K2O/γ-Al2O3 catalysts for isobutane catalytic dehydrogenation were prepared by the impregnation method with chromium oxygen species as the active component and alkali metal potassium as the additive. Effect of the operation conditions of temperature, feed flow velocity and particle size on the catalytic performance was investigated. The relevance between the morphology, pore structure and properties of the catalysts was studied in details by X-ray powder diffraction, transmission electron microscope, nitrogen physical adsorption desorption, hydrogen temperature program reduction, thermal gravity analysis and other characterization methods. The findings are as follow:1. Three kinds of controllable morphology γ-Al2O3 were synthesized through hydrothermal crystallization method by means of controlling the hydrothermal temperature. Over three kinds of morphology Cr-based catalysts, the conversion of isobutane were initially 42.4%,54.3% and 65.9%, then decreased rapidly to 35.0% after 500 min. The initial selectivity isobutene were 86.0%,89.0% and 81.9%, then decreased slowly to 83.0%after 500 min.2. Based on the traditional sol-gel method with H2O as the solvent, a further hydrolysis and condensation reaction with ethanol as the solvent was first proposed. Effect of the ethanol solvent on the particle size and morphology of products was studied. In comparison to the stone-like γ-Al2O3 prepared by the traditional sol-gel method, the flake γ-Al2O3 was prepared after the further solvent thermal reactioa With adding non-ionic three block copolymer P123, flake γ-Al2O3 aggregates (F-Al2O3-AS) with surface area 114.70 m2/g were prepared via sol-gel method. The construction of flake γ-Al2O3 aggregates reduced agglomeration effect, increased surface area and facilitated the kinetic transfer process. The research indicated that over the Cr2O3-K2O/F-Al2O3-AS catalyst, the conversion of isobutane was initially 67.5%and the selectivity of isobutene was 89.6%. After the reaction of 500 min, the conversion and selectivity was decreased to 30.0%and 80.0%, respectively.3. According to the above catalysts stability problem, ordered mesoporous structure was introduced. A thermal stability and ordered mesoporous γ-Al2O3 was synthesized via the improved low temperature hydrolysis condensation evaporation induced self-assembly strategy. The surface area was 296.50 m2/g. The mesoporous Cr2O3-K2O/meso-γ-Al2O3 catalyst exhibited significantly improvement of catalytic performance and stability in isobutane catalytic dehydro genation, which the conversion of isobutane reached up to 63.1% and the selectivity of isobutene reached up to 85.5%. Moreover, the conversion of isobutane and the selectivity of isobutene remained approximate 54.2% and 80.8% after 700 min. During the 700 min reaction, the Cr2O3-K2O/meso-γ-Al2O3 catalyst exhibited remarkably high isobutane conversion and isobutene yield increased by 10%～15%. Compared to the conventional catalyst, the Cr2O3-K2O/meso-γ-Al2O3 catalyst possessed the advantages of large specific surface area, highly dispersed active components, good diffusion and excellent coke-tolerance because of the introduction of mesoporous. |
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