Adjustment of the Single Atom/Nanoparticle Ratio in Pd/CNT Catalysts for Phenylacetylene Selective Hydrogenation

Pd/C catalysts are widely used for hydrogenation reactions in the chemical industry. One of the reasons for their high activity is the ability of Pd nanoparticles (Pd-NP) to dissociate H-2 and promote H-spillover. Nevertheless, for selective hydrogenation unpromoted Pd/C catalysts show disappointing results. The use of supported Pd single atom (Pd-SA) catalysts permits to achieve high selectivity. However, Pd-SA show low activity because they have difficulty in activating H-2. A cooperative catalysis between Pd-NP and Pd-SA operates for the hydrogenation of alkenes thanks to the H-spillover, which makes it possible to obtain active isolated Pd-SA-H species. Here, we present experimental and computational results obtained for phenylacetylene hydrogenation on Pd/CNT catalysts showing different Pd-SA/Pd-NP ratios. Tuning this ratio allows doubling the activity while reaching high selectivity to styrene at high conversion. DFT calculations suggest that the first coordination sphere of Pd-SA has a pronounced effect on their reactivity.