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 gC₃H₆gcat-1h-1 at 450 °C, which is >6 times higher than the C3H6 productivity of commercial h-BN catalyst (0.16 gC₃H₆gcat-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% COx 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 COx (≤5%) formation. However, h-BN had a C3H6 productivity of as low as 0.82 gC₃H₆gcat-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 BOx and B-OH species in boron-hyperdoped silicon samples that can serve as the active sites for ODHP.