(338d) Microwave Enhanced CO2 Dehydrogenation of Ethane over Supported Transition Metal Carbides

CO₂ dehydrogenation of ethane (CO₂-DHE) over supported transition metal carbide (TMCs) catalysts consisting of molybdenum, iron, and cobalt were studied under thermal or microwave heating. Mo, Fe, and/or Co metals were loaded onto TiC, TiO_x, and CeO_x by wet impregnation method followed by carburization at 700^oC in a 10/90 CH₄/H₂ atmosphere to form the transition metal carbides, located on the surface of the support materials. Different metal loadings were investigated to illustrate the support/metal effects on catalytic activity and dielectric properties. The different supports, CeO_x, TiO_x, and TiC were tested to determine the effect of the microwave on different supports. The CeO_x is a commonly used/well-studied support that is often regarded for its Ce³⁺ and Ce⁴⁺ reactivity. Whereas, TiO_x is less commonly used, but shows promising aspects as a photocatalyst due to its semiconductor properties. Generally, TiO_x has an n-type semiconductor response, however, modification by metal doping often results in the more desired p-type semiconductor response. TiC is a less studied support for the CO₂ ethane dehydrogenation reaction but is a very good microwave absorber that exhibits good chemical stability and electrical conductivity.

Microwave heating was carried out in a 900-watt 2.45GHz solid-state microwave equipped with automatic tunning, pyrometer temperature measurement, and PID temperature control. A thermal imager was used to extract temperature distributions profiles of the catalyst beds. Thermal heating was carried out in a resistively heated tubular furnace controlled by PID. TPR, BET, TGA, XRD, Raman, and TEM were used to characterize the samples before and after the CO₂-DHE reaction. It was found that the microwave produced different effects based on the type of support. For the TiC supported samples exhibited higher microwave absorption and lower power requirements than TiO_x or CeO_x. The lower power requirements resulted in a higher ethylene/g-cat/watt ratio than that produced for the TiO_x supported samples. Thus, suggesting that the TiC is a more suitable catalyst support for microwave heating than the conventional TiO_x. This work draws attention to the importance of catalyst design for microwave enhanced reactions.