Control of the single atom/nanoparticle ratio in Pd/C catalysts to optimize the cooperative hydrogenation of alkenes

We recently reported (R. Castro Contreras, B. Guicheret, B. F. Machado, C. Rivera-Carcamo, M. A. Curiel Alvarez, B. Valdez Salas, M. Ruttert, T. Placke, A. Favre Reguillon, L. Vanoye, C. de Bellefon, R. Philippe and P. Serp, J. Catal., 2019, 372, 226-244) that a structure/activity correlation exists in Pd/C catalysts for myrcene hydrogenation, which integrates the Pd dispersion, and the surface concentration of oxygen groups and defects of the support. Here, through a combined experimental-theoretical study, we provide an explanation of the influence of these three structural characteristics of Pd/C catalysts for alkene hydrogenation. Highly dispersed Pd nanoparticles (Pd-NP) are necessary to activate dihydrogen. A high concentration of surface defects on the support is necessary to stabilize Pd single atoms (Pd-SA), which coexist with Pd-NP on Pd/C catalysts. A high concentration of oxygenated surface groups is also necessary on the support to allow hydrogen spillover. We demonstrate that such a combination allows cooperative catalysis to operate between Pd-NP and Pd-SA that involves the formation of Pd-SA-H species, which are much more active than Pd-NP-H for alkene hydrogenation but also isomerization. Importantly, we also report an efficient method to control the ratio between Pd-SA and Pd-NP in Pd/C catalysts of similar loadings and show that the control of this ratio allows the development of a new generation of stable and highly active catalysts integrating the ultra-rational use of precious metals in short supply. Indeed, for myrcene hydrogenation, activity variations of several orders of magnitude were measured as a function of the value of this ratio.

Automated summary

This study reveals a structure/activity correlation in Pd/C catalysts for alkene hydrogenation, showing that highly dispersed Pd nanoparticles, surface defects, and oxygenated groups on the support play crucial roles in the catalytic process. A combination of these structural characteristics allows cooperative catalysis between Pd-NP and Pd-SA, leading to the formation of highly active Pd-SA-H species for alkene hydrogenation and isomerization. Additionally, an efficient method to control the ratio between Pd-SA and Pd-NP in Pd/C catalysts has been developed, enabling the design of stable and highly active catalysts with a rational use of precious metals.