Tailoring the Selectivity of 1,3-Butadiene versus 1-Butene Adsorption on Pt(111) by Ultrathin Ionic Liquid Films

L Winter and S Trzeciak and C Fernández and S Massicot and T Talwar and F Maier and D Zahn and HP Steinrück, ACS CATALYSIS, 13, 10866-10877 (2023).

DOI: 10.1021/acscatal.3c02126

Thesolid catalyst with ionic liquid layer (SCILL) concept is apromising approach to enhance the selectivity of hydrogenation reactions,like the selective hydrogenation of 1,3-butadiene to 1-butene usingtransition- metal catalysts. In this context, the adsorption dynamicsof 1,3-butadiene and 1-butene were studied on Pt(111) modified withultrathin layers of the ionic liquid (IL) 1,3-dimethylimidazoliumbis(trifluoromethanesulfonyl)imide (C(1)C(1)ImTf2N). The sticking coefficients of the two hydrocarbons aremeasured using the direct method of King and Wells. Both olefins showpronounced precursor-mediated dynamics on clean Pt(111) and on theIL-modified surface. Increasing the IL coverage leads to an increasedblocking of adsorption sites for the incoming olefins. Coadsorbedhydrogen does not significantly affect the precursor and site- blockingeffects for 1,3-butadiene. Interestingly, a smaller IL amount is neededto prevent 1-butene adsorption compared to 1,3-butadiene adsorption,which is proposed to be directly related to the IL's influenceon selective hydrogenation in SCILL catalysis. Indeed, molecular dynamicssimulations show IL film densification/relaxation as the key mechanismto allowing/excluding olefin adsorption on the metal. Being a functionof IL coverage, the energy of film penetration is used to controlthe effective olefin adsorption energy and thus creates an operationregime for suppressing 1-butene while permitting 1,3-butadiene adsorption.

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