Selective conversion of alkanes to value added products using heterogeneous catalysts is of great interest with the dramatic increasing availability of light alkanes from shale fracking. With the combination of surface science experiments and density functional theory calculations, we demonstrated that the stoichiometric terminated IrO2(110) can activate small alkanes (C1 – C3) below room temperatures. Alkanes strongly interact with the coordinatively unsaturated (cus) sites thereby adsorption on the cus sites which is consistent with adsorption behavior of alkanes on other transition metal oxides (PdO(101) and RuO2(110)). The surface oxygen (Obr) is highly active toward the dehydrogenation and oxidation of alkanes. As a result, adsorbed alkanes facilely undergo further dehydrogenations. In addition, IrO2(110) surface is found to be selective toward C2H4 formation during C2H6 temperature programmed reaction spectroscopy (TPRS) under ultrahigh vacuum conditions. With the combinations of TPRS experiment and DFT calculations, we found that that HObr generated by the dehydrogenation of C2Hx is inactive, and it prevents further dehydrogenations and oxidations of C2H6. As a result, formed C2H4 undergoes the desorption rather than the further dehydrogenation or oxidations which lead to the observed selectivity toward C2H4. We will discuss efforts to use DFT and microkinetic modeling to explore doping strategies of Obr sites to promote selectivity towards ethylene formation.

Low temperature selective alkane activation on IrO2(110) surfaces

ACS Spring 2022

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