(308d) Structure, Stability, and Selective Hydrogenation Catalysis Using Ternary Intermetallics

Intermetallic catalysts combining late transition metals with semi-metals/metalloids can provide various well-defined active site electronic and geometric structures by tuning stoichiometry. The combination with a third element, forming a ternary intermetallic, can further tune catalytic properties. While binary intermetallic phase stability is well studied both experimentally and with electronic structure theory, the wide phase space of ternary systems has only been selectively probed. In this talk, we will discuss the use of ternary intermetallics to tune trade-offs in activity and selectivity for selective hydrogenation catalysis. Specific systems will be used to demonstrate the ability to combine density functional theory (DFT), synthesis, and catalytic testing to rationalize catalytic performance as composition is varied in Pd-Zn-M (where M= Cu, Ag, Au), Pd-In-M (where M= Cu, Ag), and Pd-Sb-M (where M= Au) materials.

Taking the ternary gamma brass Pd-Zn-M system as an example, (Figure 1), the hydrogenation selectivity and activity of the catalyst can be more finely adjusted through the introduction of a third element. This adjustment is attributed to the distinct contributions of the third element to influence both the electronic and geometric dynamics at the catalytic sites. A computational workflow including both DFT (Density Functional Theory) and CALPHAD (Calculation of Phase Diagrams) calculations, is used to evaluate the phase stability and distribution of element site occupancies in ternary systems. DFT is then used to determine the most stable surface facets and evaluate elementary reaction energies and barriers. Microkinetic modeling is then used for prediction of activity and selectivity in (partial) hydrogenation reactions and reconciled to experimentally observed apparent activation barriers and reaction orders using data science approaches. This collective set of tools demonstrates a successful workflow for designing and realizing selective hydrogenation catalysis using ternary intermetallics.