Catalytic oxidative cracking (COC) of hydrocarbons is a potential alternative to energy-intensive steam cracking, but the production of COx from metal oxide catalysts precludes industrial implementation. Recently, we discovered hexagonal boron nitride (hBN) is a catalyst for the selective oxidative dehydrogenation (ODH) of alkanes to their respective olefins. It was observed that lowering the partial pressure of O2 shifted the product distribution from ODH products to oxidative cracking products. As compared to previous literature catalysts, boron nitride suppresses the over-oxidation of the formed olefin to COx, making it a promising material for further study as an oxidative cracking catalyst. The oxidative cracking of n-butane to ethylene and propylene over hBN serves as a model system that can provide insight into the role of reactant partial pressures, temperature, and contact time. Varying the O2 partial pressure revealed a Langmuir adsorption-type dependence. Because feeds that are very lean in oxygen reduce the reaction rate, higher temperatures and longer contact times are required to achieve decent alkane conversion. Comparisons to the well-established Li/Dy2O3/MgO cracking catalyst reveal a similar oxygen-dependent product distribution and from this we can begin to elucidate a reaction mechanism. It is believed there is a combination of heterogeneous and homogeneous reactions occurring: reaction of the alkane with surface oxygen species yields alkyl radicals that propagate in the gas phase. Long-term stability of hBN under cracking conditions as well as low CO2 production makes hBN an industrially attractive catalyst.

Hexagonal boron nitride as a catalyst for the oxidative cracking of n-butane

2019 Spring National Meeting

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