Tailoring the Selectivity of 1,3-Butadiene versus 1-Butene Adsorption on Pt(111) by Ultrathin Ionic Liquid Films
Leonhard Winter, Simon Trzeciak, Cynthia C. Fernández, Stephen Massicot, Timo Talwar, Florian Maier, Dirk Zahn, Hans‐Peter Steinrück
Abstract
The solid catalyst with ionic liquid layer (SCILL) concept is a promising approach to enhance the selectivity of hydrogenation reactions, like the selective hydrogenation of 1,3-butadiene to 1-butene using transition-metal catalysts. In this context, the adsorption dynamics of 1,3-butadiene and 1-butene were studied on Pt(111) modified with ultrathin layers of the ionic liquid (IL) 1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ([C 1 C 1 Im][Tf 2 N]). The sticking coefficients of the two hydrocarbons are measured using the direct method of King and Wells. Both olefins show pronounced precursor-mediated dynamics on clean Pt(111) and on the IL-modified surface. Increasing the IL coverage leads to an increased blocking of adsorption sites for the incoming olefins. Coadsorbed hydrogen does not significantly affect the precursor and site-blocking effects for 1,3-butadiene. Interestingly, a smaller IL amount is needed to prevent 1-butene adsorption compared to 1,3-butadiene adsorption, which is proposed to be directly related to the IL’s influence on selective hydrogenation in SCILL catalysis. Indeed, molecular dynamics simulations show IL film densification/relaxation as the key mechanism to allowing/excluding olefin adsorption on the metal. Being a function of IL coverage, the energy of film penetration is used to control the effective olefin adsorption energy and thus creates an operation regime for suppressing 1-butene while permitting 1,3-butadiene adsorption.