# Beyond the Lindlar catalyst: highly-oxidized Pd single atoms as promoters for alkyne semi-hydrogenation

## TL;DR

A new catalyst design improves the selective hydrogenation of steroidal alkynes without using inhibitors, offering higher efficiency and sustainability.

## Contribution

A novel 'grafting-then-coordination' strategy creates a Pd/C–NH2 catalyst with tetravalent Pd single atoms and nanoparticles for efficient alkyne hydrogenation.

## Key findings

- The Pd/C–NH2 catalyst achieves 99% conversion and 97% selectivity in mifepristone hydrogenation.
- PdIV single atoms and nanoparticles work cooperatively to enable efficient hydrogenation without inhibitors.

## Abstract

The semi-hydrogenation of alkynes is crucial for the synthesis of steroid hormone drugs, yet conventional approaches relying on Pd surface poisoning additives sacrifice activity and sustainability for selectivity. Herein, we present a “grafting-then-coordination” strategy to construct a Pd/C–NH2 catalyst featuring coexisting tetravalent Pd single atoms (PdIV SAs) and Pd nanoparticles (NPs), which achieves inhibitor-free and highly efficient hydrogenation of steroidal alkynes. The Pd/C–NH2 catalyst, functionalized with 3-aminopropyltriethoxysilane (APTES), exhibits 99% conversion with 97% selectivity in the selective hydrogenation of mifepristone under 0.1 MPa at 25 °C, with a remarkable turnover frequency (TOF) of 3675 h−1, representing a 17-fold enhancement over the conventional Lindlar catalyst. Mechanistic studies reveal that the PdIV SAs are stabilized through Pd–N/O coordination by leveraging oxygen-containing groups of the support and amino groups of the ligand. The electron-deficient PdIV SAs adsorb mifepristone, mitigating substrate self-poisoning on Pd NPs, while Pd NPs activate H2 and promote hydrogen spillover to PdIV SAs, enabling hydrogenation via a dual-site cooperative mechanism. The stable PdIV SAs transform conventional poisoning sites into productive active centers, offering valuable insights for the rational design of advanced selective hydrogenation catalysts.

A “grafting-then-coordination” strategy was proposed to construct Pd/C-NH2 featuring coexisting tetravalent Pd single atoms (PdIV SAs) and Pd nanoparticles (Pd NPs), which achieves inhibitor-free, highly efficient hydrogenation of steroidal alkynes.