Oxidative Dehydrogenation of Propane (ODHP) to Propylene

Dr. Kyriakidou’s group and Dr. Swihart’s group developed a new type of ODHP catalyst: boron-hyperdoped silicon with varied boron concentration (0 - 42 at.%) which was synthesized by laser pyrolysis and showed excellent C₃H₆ productivity.  The boron-hyperdoped silicon had a C₃H₆ productivity of > 0.94 g_C₃H₆g_cat^-1h^-1 at 450 °C, which is >6 times higher than the C₃H₆ productivity of commercial h-BN catalyst (0.16 g_C₃H₆g_cat^-1h^-1) under the same reaction conditions (Figure 1). 

    Propylene (C₃H₆) is one of the most important building blocks in the petrochemical industry.  It is used in the production of many industrial products, such as polypropylene, propylene oxide and isopropanol.  Propylene is traditionally produced by steam cracking and fluid catalytic cracking in petroleum refineries.  However, both technologies have low selectivity, high energy consumption and significant production of CO₂ emissions.  Direct production of C₃H₆ by the dehydrogenation of propane (C₃H₈) is currently of great interest in an effort to close the C₃H₆ supply and demand gap in the US.  The oxidative dehydrogenation of propane (ODHP) reactions have attracted extensive attention as they are more resistant to coke deposition compared to the non-oxidative DHP reactions and they are not limited by equilibrium.

            Traditional supported metal oxide catalysts, such as vanadium, molybdenum and chromium oxides have low C₃H₆ selectivities (<60%) and form significant amounts of over-oxidation byproducts (CO and CO₂; 20-50% CO_x selectivity).  Recently, boron containing catalysts showed great potential, especially the commercial hexagonal boron nitride (h-BN) that has excellent selectivity towards propylene (79%) and ethane (12%) with negligible CO_x (≤5%) formation.  However, h-BN had a C₃H₆ productivity of as low as 0.82 g_C₃H₆g_cat^-1h^-1 at 490 °C and required surface activation (oxidation and hydrolyzation) to obtain its reported activity. 

            Dr Kyriakidou’s group and Dr. Swihart’s group developed a series of boron-hyperdoped silicon catalysts synthesized by a laser pyrolysis process, with boron concentrations of 15, 25 and 42 at.% that were reported to be stable up to annealing temperatures of 600 °C.  Unlike traditional doping methods, where the dopant concentration is limited by its solid solubility, hyperdoping allows boron doping on silicon to exceed the solubility of boron (1.2 at.%) resulting to high boron concentrations.  This synthesis method facilitated the formation of boron enriched surface active sites that contribute to excellent C₃H₆ productivity under ODHP reaction conditions.  Fourier-transform infrared spectroscopy and B1s XPS spectra indicated the presence of BO_x and B-OH species in boron-hyperdoped silicon samples that can serve as the active sites for ODHP.

• J. Chen, P. Rohani, M.J. Lance, T.J. Toops, M.T. Swihart, E.A. Kyriakidou, “Boron-hyperdoped Silicon for the Selective Oxidative Dehydrogenation of Propane to Propylene.” Chemical Communications, DOI: 10.1039/D0CC02822C (2020).

• Junjie Chen (PhD)