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Steam cracking of ethane, a non-catalytic thermochemical process, remains the dominant means of ethylene production. The severe reaction conditions and energy expenditure involved in this process incentivize the search for alternative reaction pathways and reactor designs which maximize ethylene yield while minimizing cost and energy input. Herein, we report a comparison of catalytic and non-catalytic non-oxidative dehydrogenation of ethane. We achieve ethylene yields as high as 67 % with an open tube quartz reactor without the use of a catalyst at residence times ~4 s. The open tube reactor design promotes simplicity, low cost, and negligible coke formation. Pristine quartzmore » tubes were most effective, since coke formation was detected when defects were introduced by scratching the surface of the quartz. Surprisingly, the addition of solids to the quartz tube, such as quartz sand, alumina powder, or even Pt-based intermetallic catalysts, led to lower ethylene yield. Pt alloy catalysts are effective at lower temperatures, such as at 575 °C, but conversion is limited due to thermodynamic constraints. When operated at industrially relevant temperatures, such as 700 °C and above, these catalysts were not stable in our tests, causing ethylene yield to drop below that of the open tube. Furthermore, these results suggest that future research on non-oxidative dehydrogenation should be directed at optimizing reactor designs to improve the conversion of ethane to ethylene, since this approach shows promise for decentralized production of ethylene from natural gas deposits.« less

Dopants enhance the catalytic properties of ceria. However, conventional techniques for synthesizing doped ceria have limitations in terms of structural homogeneity, surface area, and catalytic activity of the resulting oxide. Use of toxic and corrosive chemicals presents further challenges. The sol-gel method described in this work provides a facile approach for incorporating high concentrations of dopants in a uniform, high surface area structure, yielding excellent catalytic activity. Addition of polyvinylpyrrolidone (PVP) complexing agent prevents the segregation of cerium and dopant atoms during synthesis. Surface areas up to 179 m²/g are achieved, which represents a substantial improvement over doped ceria producedmore » through coprecipitation, solution combustion, or melt-synthesis methods. The resulting powders exhibit dramatically improved CO oxidation activity (T₉₀ = 132 °C for 3.2 wt% Cu-CeO₂ compared to 274 °C for a 2 wt% Pt-Al₂O₃ reference catalyst). First principles calculations suggest a Mars Van Krevelen mechanism, which is facilitated by dopants causing oxygen vacancies.« less

Metallic nickel is known to be an active, but not a selective hydrogenation catalyst for conversion of alkynes to alkenes. On the other hand, nickel oxide is not active. Recently, we have demonstrated that nickel doped into ceria provides an inexpensive catalyst for selective hydrogenation of acetylene in the presence of ethylene. Here, we evaluate various synthesis methods to achieve optimal selective hydrogenation performance. We examined incipient wetness impregnation, coprecipitation, solution combustion, and sol-gel synthesis to study how the method of preparation affects catalytic structure and behavior. Sol-gel synthesis, coprecipitation, and solution combustion synthesis methods favor nickel incorporation into themore » ceria lattice, while incipient wetness impregnation creates segregated nickel species on the ceria surface. For hydrogenation of acetylene, these nickel surface species lead to poor ethylene selectivity due to ethane and oligomer formation. However, when nickel is incorporated into the ceria lattice, ethane formation is prevented even while achieving 100 % conversion of acetylene. Coke formation is also significantly reduced on these catalysts compared to conventional nanoparticle counterparts. Finally, we conclude that sol-gel synthesis provides the optimal method for creating a uniform dopant distribution within the high surface area ceria.« less