Development of advanced dehydrogenation catalyst for the production of light olefins

Abstract

Light olefins (e.g., ethylene, propylene, butene, butadiene) are important raw materials for the production of petrochemical products. In the petrochemical industry, they have been mainly produced by steam cracking and fluid catalytic cracking (FCC) of naphtha and other oil-based products. However, in the last decade, the increased availability of shale gas has shifted the reactant feedstock from petroleum-based naphtha to shale-based ethane. Although economical ethylene production has become possible, the ethane cracking mainly produces ethylene compared to naphtha cracking, which leads to supply-demand imbalance of C3–C4 olefins. Therefore, in recent years, extensive efforts have been performed to develop on-purpose production of C3–C4 olefins. In this thesis, the development of advanced catalysts for the dehydrogenation process as part of on-purpose production technology will be discussed. The researches had been conducted on the development of carbon-based catalysts for oxidative dehydrogenation and platinum-promoted gallium-doped alumina catalysts for direct dehydrogenation. The results revealed that carbon nanostructure was an important factor in determining the graphitic order and the density of catalytic active site, carbonyl group (C═O). It was also found that the catalytic activity and selectivity of individual active site (C═O) were dependent to their density on the carbon surface. Most carbon materials showed a trade-off relationship between activity and stability, because the carbons with high graphitic order possessed few active sites (C═O). However, the carbon material having the structure of ‘coin-stacking’ carbon layers exceptionally exhibited high catalytic activity and stability simultaneously. Another study investigated the catalytic interaction between Ga and Pt in Pt-promoted Ga-doped alumina catalyst during the propane dehydrogenation. It was found that C–H bond of propane was heterolytically dissociated on the gallium site, whereas platinum facilitates the recombination of hydrogen atoms accumulated on the catalyst surface. To maintain the catalytic interplay of Ga and Pt during the repeated reaction-regeneration cycles, Pt sintering should be suppressed by increasing support-metal interaction while preserving the metallic state, which is active toward H recombination. Atomically dispersed Ce3+ sites on the alumina surface effectively suppressed the sintering of metallic Pt0, exhibiting a significantly improved catalyst stability.