Disclosing the Role of Gold on Palladium – Gold Alloyed Supported Catalysts in Formic Acid Decomposition

Herein, we report the synthesis of preformed bimetallic Pd-Au nanoparticles supported on carbon nanofibers with different Pd : Au atomic ratio (nominal molar ratio: 8–2, 6–4, 4–6, 2–8) and the corresponding Pd and Au monometallic catalysts by sol immobilization method. The obtained materials were characterized thoroughly by Transmission Electron Microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectroscopy (ICP-OES). The catalytic performances of the Pd-Au catalysts were evaluated in the aqueous phase dehydrogenation of formic acid (FA) at room temperature obtaining enhanced activity, stability and selectivity compared to the monometallic systems. In particular, Pd$_{6}$Au$_{4}$ and Pd$_{8}$Au$_{2}$ showed the best combination of catalytic properties, i. e., high selectivity to H$_{2}$ and improved catalytic stability. Density functional theory (DFT) calculations on Pd15, Au15 and Pd9Au6 clusters supported on a carbon sheet were then simulated to provide atomic level understanding to the beneficial effect of gold observed in the experimental results. Au$_{15}$ barely adsorb FA, while Pd$_{15}$ possesses an adsorption energy higher than Pd$_{9}$Au$_{6}$. Dehydrogenation and dehydration pathways were followed on all these models. For Pd9Au6, the most favourable route was the formation of carbon dioxide and hydrogen. Analysis of the electronic structures was also performed on the different models showing a stronger interaction between the bimetallic system and the support proving the alloy superior stability