Unusual Selectivity of Gold Catalysts for Hydrogenation of 1,3-Butadiene toward cis-2-Butene: A Joint Experimental and Theoretical Investigation

We report a combined experimental and theoretical investigation of the unusual catalytic properties of gold nanoparticles in the selective hydrogenation of 1,3-butadiene. It is found that nanogold catalysts exhibit a unique preference toward forming cis-2-butene compared to the trans isomer, and the ratio of cis/trans isomers is structure-sensitive in terms of the size of gold nanoparticles. Our density functional theory calculations show that the cis-1,3-butadiene can be preferably adsorbed at the edges and corners of gold nanoparticles as compared to the trans-1,3-butadiene. Moreover, the transition state calculations indicate that the isomerization of trans-butadiene to cis-butadiene is kinetically favorable, with rather low energy barriers. These unique properties of gold nanoparticles toward 1,3-butadiene adsorption are discussed based on orbital interaction analyses. It is found that Au-6s-based molecular orbitals prefer adsorption of cis-1,3-butadiene to the trans isomer due to spatial match. The catalytic selectivity of gold nanoparticles toward formation of cis-2-butene has been further corroborated by comparable investigations on silver and copper catalysts.