Low-Temperature Nonoxidative Dehydrogenation of Short-Chain Alkanes over Copper(I) Mordenite via Chemical Looping.

We report selective low-temperature non-oxidative dehydrogenation of ethane and propane to ethylene and propylene via chemical looping using copper(I)-containing mordenite as active material. Combining Cu K-edge X-ray absorption spectroscopy, in situ infrared spectroscopy (FTIR), H/D kinetic isotope effect measurements, and density functional theory calculations, we show that the active sites for the dehydrogenation reaction are copper(I) cations hosted in zeolite framework, and the rate-limiting step is activation of the first C-H bond of alkane. The stoichiometric reaction between the gas-phase alkane and copper(I) cationic site results in the formation of a stable copper(I)-alkene π-complex and gaseous hydrogen. Complete saturation of copper(I) sites with alkenes can be attained at 573 K with a selectivity close to 100%. The strong binding of alkenes to copper(I) sites promotes the dehydrogenation reaction, enabling the yield of alkene more than 100 times greater than the gas-phase thermodynamic limit. Copper(I)-alkene complexes can be decomposed in a separate step by contact with water at near-ambient temperature, releasing alkenes into the gas phase, and the material can be regenerated without detectable loss of activity.