The theoretical insights on the mechanism for Fe-N4 improving the HCOOH dissociation on Pd13/Gra

The reaction mechanism of HCOOH dissociation on the Fe-N4-Gra supported Pd13 (Pd13/Fe-N-Gra) is systematically investigated by using the density functional method. For Pd13/Fe-N-Gra, the two possible active sites, i. e., the top site (T) and interface (synergy) site (S site), are all considered. The results show that, besides pathway via HCOO (HCOOH -> HCOO -> CO2), there is a new favorable channel (HCOOH -> COOH -> CO2) for producing the CO2, which is different from that of pure Pd (prefer HCOO pathway). More importantly, the new pathway at T site shows higher selectivity and activity for HCOOH dissociation to CO2, compared with the S site. Further analysis based on energy splitting method and electronic structure indicate that the higher electron transfer during the intermediate COOH dissociation brings the deformation of Pd13, which increases the selectivity for CO. In conclusion, the Fe-N4 can not directly act as the active center for the reaction, while it can effectively keep the number of active electrons in Pd13, especially for the T site, to keep high activity and selectivity for the HCOOH dissociation to CO2. Meanwhile, the results also propose that the effective method for reducing the adsorption of OH species at the interface site or fast release the OH species can further improve the catalytic activity and life of Pd13/Fe-N-Gra for HCOOH dissociation.