Active, Selective, and Durable Catalyst for Alkane Dehydrogenation Based on a Well-Designed Trimetallic Alloy

Catalyst design based on a pseudobinary alloy concept was applied to develop a highly efficient catalytic system for alkane dehydrogenation. A series of Pt-based alloy catalysts supported on silica (Pt3M/SiO2, where M = Fe, Co, Cu, Zn, Ga, In, Sn, Pb) were prepared and tested for the dehydrogenation of methylcyclohexane, which has been an emerging topic in hydrogen carrier/production applications. Nanoparticulate intermetallic Pt3Fe exhibited high catalytic activity and durability. The Pt3Fe catalyst was further modified by substituting a part of the Fe with a series of metals (M = Co, Ni, Cu, Zn, Ga, In, Sn, Pb) to form a Pt-3(Fe-0.75,M-0.25) pseudobinary alloy. The partial substitution of Fe with Zn to form Pt-3(Fe0.75Zn0.25) resulted in outstandingly high catalytic activity, selectivity, and durability: a 2.7-fold higher turnover frequency (TOF) in comparison to that of Pt/SiO2 (the highest H-2 evolution rate ever reported), >99% toluene selectivity (methane concentration <500 ppm), and long-term durability with >99% MCH conversion for at least 50 h. A mechanistic study based on detailed characterization and theoretical calculations revealed that the Fe enhanced hydrogenation of CHx species (decoking) and Zn promoted toluene desorption by both ligand and ensemble effects. The adjacency of Pt, Fe, and Zn in at the atomic level allows construction of a multifunctional active site for effective C-H activation, decoking, and toluene desorption.