Biomass‐Engineered Defect‐Rich g‐C ₃ N ₄ Anchors Pd ²⁺ ‐Rich Ultrafine Particles for Highly Efficient Formic Acid Dehydrogenation

Formic acid (FA) is considered to be a safe and convenient hydrogen source; however, achieving controlled and efficient FA dehydrogenation under mild conditions using stable solid catalysts remains a significant challenge. Pd‐based catalysts have been extensively studied due to their superior catalytic activity to other metal catalysts. Most researchers primarily attribute the activity of these catalysts to Pd 0 sites while recognizing the potential contributions of Pd 2+ species, and this merits further systematic investigation. In this study, Pd active species were innovatively loaded onto a defect‐rich g‐C 3 N 4 support engineered with biomass carbon, resulting in an exceptionally high Pd 2+ /Pd 0 ratio and enabling hydrogen evolution under nonreductive conditions. A strong interaction between the pyridinic nitrogen in the defect‐rich g‐C 3 N 4 support and Pd yields a high surface proportion of Pd 2+ species. Combined with in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations, HCOO* is identified as the key intermediate, predominantly adopting a bidentate adsorption mode on Pd n + sites. DFT calculations further reveal that HCOO* can undergo C–H bond cleavage on both Pd 0 and Pd n + sites. The high proportion of Pd 2+ is a critical factor underlying this system's enhanced catalytic activity and selectivity. Furthermore, the abundant defect sites on the support effectively prevent active Pd sites from aggregating. The resulting ultrasmall Pd particles further improve the electronic environment of the anchored Pd sites, enhancing the catalytic performance. The turnover frequency of the as‐prepared Pd/CN‐nutshell 5:1 catalyst reaches 5758 h −1 , substantially higher than most previously reported results.