(265h) Cobalt Oxide Supported on SiO2 Modified Al2O3 for Propane Dehydrogenation: High Cobalt Oxide Dispersion and Enhanced Selectivity

With the increasing demand for propylene, there is a need to seek for the cost-effective and energy efficient process for its production. Moreover, dehydrogenation is a promising process for the production of olefins in comparison with the steam cracking process. From the past few years, apart from the commercial catalyst (Pt-Sn/ Al₂O₃ and Cr₂O₃/ Al₂O₃) studied for the reaction, there is tremendous interest in other transition metal-based catalyst for dehydrogenation reaction. In this limelight, the cobalt-based catalyst has also attained great attention. From the prior art in the development of a cobalt-based catalyst for propane dehydrogenation, it has shown promising behavior however requires further improvisation for commercialization. The major challenge for this catalyst is the lower propylene selectivity and faster deactivation due to coke deposition. Therefore, this study aims at developing a highly selective and stable cobalt-based catalyst for propane dehydrogenation. The properties of support play a crucial role in changing the metal support interaction and also provides necessary acidic sides for the reaction. Gamma alumina offers a varying range of Lewis acidic center from strong to weak. Some of these sites also promote cracking reaction under the presence of hydrocarbon. Hence, modification of this acidic center possibly reduces the extra Lewis acidic center. In this study, a novel strategy is proposed where the alumina support was modified by doping different ratios of SiO₂ as support for cobalt. The catalyst was synthesized by a facile one-pot method using a structure directing agent. After the dehydrogenation reaction, the trend showed that an optimum percentage of SiO2 is required to achieve the highest selectivity and a deviation from which imposes a trade-off between conversion and selectivity. The Co/ SiO₂-Al₂O₃ (1:10) showed the highest propylene selectivity of 92% and propane conversion of 35 % at 600 ºC. The catalyst was tested for 12 hours of reaction, and the deactivation rate was lower as compared with only Al₂O₃. From XAS analysis, it was found that cobalt existed in a well-dispersed CoO form in the silica doped Al₂O₃ however a mixture of Co₃O₄, CoO and CoAl₂O₄ existed in Co/Al₂O₃. Other characterizations such as TPR , Uv-Vis ,XPS and in-situ DRIFTs were performed which indicated the unique role of doping SiO₂ in Al₂O₃ which improved the metal support interaction thereby enhancing both activity and stability. This elucidates the role of SiO₂ in the better dispersion of active cobalt oxide. Overall, this study demonstrates the possible route to improve the selectivity towards propylene via modification of support.