Unravelling the pathway for the dehydrogenation of n-butane to 1,3-butadiene using thermodynamics and DFT studies

Dehydrogenation of n-butane is one of the main on-purpose method for producing 1,3- butadiene. Thermodynamics studies revealed that reasonable yields of 1,3-butadiene can only be achieved at higher temperatures, while the formation of butene isomers are favored at lower temperatures, confirming that 1,3-butadiene is a secondary product. In the present study, NiO/Al₂O₃ and Ni-BiO_x/Al₂O₃ catalysts, having 10 and 20 wt% Ni and 10 and 30 wt% Bi loading were synthesized. Experimental testing using fixed bed reactor validated that the addition of BiO_x improved 1,3-butadiene selectivity from 20 % to 43 % with similar n-butane conversion, at 500 °C. Also, density functional theory (DFT) studies for n-butane adsorption on Ni (1 1 1) and Bi-Ni (1 1 1) surfaces confirmed that, the addition of Bi promoters to the Ni surface modifies the n-butane adsorption strength resulting in lower adsorption energies of −0.02 eV weaker than −0.36 eV on Ni (1 1 1) surfaces. The reaction pathways investigation for the successive dehydrogenation route of n-butane on the most stable structures of Ni (1 1 1) and Bi-Ni (1 1 1) surfaces revealed that 1-butene pathway via the formation of 1-butyl, is most favorable relative to the 2-butene pathway via 2-butyl formation. This is due to the higher activation barrier for the formation of 2-butene intermediate on both Ni (1 1 1) and Bi-Ni (1 1 1) surfaces.