Tuning Nanoparticle Alloys to Enhance C-H Bond Activation for the Catalytic Dehydrogenation of Ethane

Tuning Nanoparticle Alloys to Enhance C-H Bond Activation for the Catalytic Dehydrogenation of Ethane

Viktor J. Cybulskis¹, James R. Gallagher², Han-Ting Tseng¹, Brandon Bukowski¹, Zhenwei Wu¹, Evan Wegener¹, A. Jeremy Kropf², Bruce Ravel³, Jeffrey Greeley¹, Fabio H. Ribeiro¹, Jeffrey T. Miller¹

¹  Chemical Engineering, Purdue University, West Lafayette, IN 47907, USA

²  Chemical Sciences and Engineering, Argonne National Laboratory, Argonne, IL 60439, USA

³  Materials Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA

Supported Pt catalysts are widely used in a number of industrial hydrocarbon processes, including hydrogenation, isomerization, naphtha reforming, and dehydrogenation reactions, due to their affinity for paraffinic C-H bonds [1]. While structure insensitive reactions, such as alkane dehydrogenation, can occur on isolated metal sites, larger nanoparticle ensembles are known to catalyze side reactions, such as cracking and hydrogenolysis [2]. Recent work by Childers et al. [3] has demonstrated that Zn addition to SiO₂-supported Pt catalysts enhances propylene selectivity during propane dehydrogenation by forming an intermetallic alloy that effectively isolates Pd surface sites via a geometric effect.

In the present study, we demonstrate how the addition of Zn to Pt/SiO₂ leads to near 100% ethylene selectivity during ethane dehydrogenation (EDH) at 600 ¡C by forming a high-symmetry Pt₁Zn₁ alloy with isolated Pt sites that effectively eliminate concomitant C-C bond cleavages. Kinetic measurements and in situ resonant inelastic X-ray scattering (RIXS) experiments indicate that Zn also modifies the electronic structure of Pt and increases the EDH turnover frequency (TOF) per exposed surface Pt by a factor of ten compared to monometallic Pt/SiO₂. The molecular level insight obtained from this study provides a model that suggests control of the geometric structure of the active sites affects alkene selectivity, while control of the promoter affects the adsorbate binding strength and TOF.

References:

[1]   J. J. H. B. Sattler, J. Ruiz-Martinez, E. Santillan-Jimenez, and B. M. Weckhuysen, Chem. Rev. 114 (2014) 10613.

[2]   M. Boudart, G. Djega-Mariadassou, Kinetics of Heterogeneous Catalytic Reactions, Princeton, 1984, pp. 155-193.

[3]   D.J. Childers, N.M. Schweitzer, S.M.K. Shahari, R.M. Rioux, J.T. Miller, R.J. Meyer, J. Catal. 318 (2014) 75.