Hydrogenation of CO2 to formate/formic acid over Pd/H-MOR

Pd/H-MOR exhibits superior catalytic activity and stability for CO 2 hydrogenation to formateover other Pd/Zeolites and M/H-MOR. • Brønsted acid sites at Pd-H-MOR interface polarize CO 2 , while highly dispersed Pd nanoparticles dissociate H 2 barrierlessly. • Low Si/Al ratio optimizes metal-support synergy and reducing apparent activation energy to HCOOH. • Bicarbonate identified as the key reaction intermediates by in-situ DRIFTS and DFT study. Catalytic hydrogenation is a promising route for CO 2 conversion, yet the highly efficient formation of formic acid remains challenging. Herein, Pd nanoparticles dispersed on mordenite (Pd/H-MOR) are reported as an efficient and stable catalyst for CO 2 hydrogenation to produce formates. Under optimized conditions, Pd/H-MOR achieved an intrinsic turnover number of 1828 and a turnover frequency of 914 h −1 at 120 °C, surpassing all the other prepared catalysts with different metal active sites and zeolite supports. The high activity arises from the co-effect of Pd and the H-MOR support: Pd sites dissociate H 2 into active hydrogen, while Brønsted acid sites enhance CO 2 adsorption via polarization and stabilize bicarbonate intermediates, which subsequently convert to formates. Density functional theory (DFT) results revealed that Pd/H-MOR lowers the activation barriers for both H 2 dissociation and CO 2 activation at the Pd-MOR interface and combined with in-situ DRIFTS, identifying surface bicarbonates as the key reactive intermediates en-route to formate formation. Comparatively, kinetic studies of Pd/H-MOR revealed a reduced apparent activation energy of 15.81 ± 0.79 kJmol −1 , reflecting strong metal-support interactions, while the observed R = k ∙ P CO 2 0.56 ∙ P H 2 0.62 $\mathrm{R}=\mathrm{k}\bullet {{{\mathrm{P}}_{\mathrm{CO}}}_2}^{0.56}\bullet {{{\mathrm{P}}_{\mathrm{H}}}_2}^{0.62}$ reaction orders indicate that the reaction rate is weakly dependent of H 2 and CO 2 pressures but strongly dependent on the nature of the metal and the zeolite support. This work highlights metal dispersion and support acidity as key factors for CO 2 hydrogenation. Download: Download high-res image (224KB) Download: Download full-size image