Electron density engineering in Pd/H-TiO2 catalysts for enhanced photocatalytic CO2 to formic acid

Photocatalytic reduction of CO 2 to formic acid (HCOOH) offers a sustainable pathway for carbon utilization, yet its efficiency is fundamentally limited by poor CO 2 adsorption and rapid electron-hole recombination in conventional photocatalysts. To address this challenge, a series of Pd-loaded hydrogenated TiO 2 catalysts (x wt%Pd/H-TiO 2 ) were developed through a synergistic hydrogen reduction-impregnation strategy, aiming to regulate the electron density of Pd active sites and enhance interfacial charge separation. Systematic characterization revealed that increasing Pd loading (0.6–1.4 wt%) effectively trapped photogenerated electrons, suppressing recombination losses and elevating electron density at Pd sites. Combined with optimized CO 2 adsorption capacity (0.178 mmol·g −1 ) and accelerated charge transfer, the 1.0 wt%Pd/H-TiO 2 catalyst achieved a HCOOH production rate of 14.14 mmol·g cat −1 ·h −1 under mild conditions (30 °C, 2.0 MPa, 4.57 mW·cm −2 ), outperforming most reported TiO 2 -based systems. Mechanistic studies further demonstrated a strong correlation between Pd-induced electronic effects and multi-electron CO 2 activation kinetics. This work provides a scalable catalyst design paradigm for balancing charge dynamics and surface reactivity in photocatalytic CO 2 valorization.