Researchers tune active sites of bimetallic catalysts with atomic precision

Bimetallic particles, composed of a noble metal and a base metal, exhibit unique catalytic properties in selective heterogeneous hydrogenations due to their distinct geometric and electronic structures. At the molecular level, effective and selective hydrogenation requires site-specific interactions where the active atoms on the catalyst particle selectively engage with the functional group targeted for transformation in the substrate. 

Reducing the particle to nanoscale atomic clusters and single-atom alloys enhances surface dispersion and improves the efficient utilization of noble metal atoms. These size reductions also simultaneously change the electronic structure of the active sites, which significantly impacts the intrinsic activity or product distributions. By precisely tuning the bonding structures of noble metal single atoms with the base metal host, reactants are flexibly accommodated and the electronic properties are fine-tuned to activate specific functional groups. However, the fabrication of such atomically precise active sites remains a challenge.

In a study published in Chem, a team led by Prof. SHEN Wenjie and Prof. LI Yong from the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences (CAS), collaborating with Prof. LI Weixue from University of Science and Technology of China of CAS and Prof. WANG Yuemin from Karlsruhe Institute of Technology in Germany, successfully regulated the atomic structure of active sites for hydrogenation reaction. 

Researchers first developed a method to densely populate and precisely position isolated Pt atoms in the form of Pt-Fe-Pt heterotrimer on α-Fe nanoparticles. The Pt-Fe-Pt heterotrimer was achieved by H₂-reduction of a Pt-Fe₂O₃ particle pair, where a 3.3 nm Pt particle sits on a 9.8 nm Fe₂O₃ particle. During the H₂ reduction, iron oxides were reduced to iron, facilitating dispersion of Pt particles into Pt-Fe-Pt heterotrimers on the surface of iron particles via surface alloying.

In addition, researchers uncovered the formation pathway and coordination environment of the Pt-Fe-Pt heterotrimer. In the gas-phase hydrogenation of crotonaldehyde, the Pt-Fe-Pt heterotrimer showed a preference for hydrogenated the C=O bond to produce crotyl alcohol rather than the conjugated C=C bond. The intrinsic hydrogenating rate increased by 35 times, effectively resolving the activity-selectivity trade-off in hydrogenation reactions.

Furthermore, researchers revealed a site-bond recognition pattern of the Pt-Fe-Pt heterotrimer. The left-end Pt atom anchored the C=C bond, while the central Fe atom activated the C=O bond, which was further hydrogenated by H atoms adsorbed on the right-end Pt atom.

"Our study quantifies the surface catalytic reaction at the molecular level and offers a strategy for tailoring active sites on bimetallic catalysts with atomic precision," said Prof. SHEN.