Kinetics of liquid-phase diphenylacetylene hydrogenation on “single-atom alloy” Pd-Ag catalyst: Experimental study and kinetic analysis

Catalytic performance of Pd₁Ag₃/Al₂O₃ single-atom alloy (SAA) catalyst was studied in liquid-phase hydrogenation of diphenylacetylene (DPA) and compared with the performance of the reference monometallic Pd/Al₂O₃. Formation of SAA structure in Pd₁Ag₃/Al₂O₃ was confirmed by FTIR CO technique. It was found that Pd₁Ag₃/Al₂O₃ single-atom alloy catalyst exhibits excellent selectivity in diphenylethene (stilbene) (ca. 98 %), which remains constant over a wide range of DPA conversions (0–95%), while over Pd/Al₂O₃ selectivity decreases steadily with the increase in DPA conversion. It is remarkable that the selectivity of Pd₁Ag₃/Al₂O₃ depends neither on hydrogen pressure (5–15 bar), nor on DPA concentration (0.0262 – 0.159 mol/l). In contrast, over the reference Pd/Al₂O₃ selectivity tends to decrease with increasing P(H₂) and decreasing DPA concentration. The proposed reaction network comprises hydrogenation of DPA in a parallel formation of cis and trans-stilbene with following hydrogenation to bibenzyl and direct formation of the latter from the initial DPA. The calculations clearly shows the capability of the kinetic model to describe the experimental dependencies for Pd₁Ag₃ single-atom catalyst in an excellent way with the degree of explanation equal to ca. 99 %.