Study on the Gas-Chromic Character of Pd/TiO₂ for Fast Room-Temperature CO Detection

As a widely used support, TiO₂ has often been combined with Pd to form highly sensitive gas-chromic materials. Herein, we prepared a series of Pd/TiO₂ catalysts with different Pd content (from 0.1 to 5 wt.%) by the impregnation method for their utilization in fast room-temperature CO detection. The detection was simply based on visible color change when the Pd/TiO₂ was exposed to CO. The sample with 1 wt.% Pd/TiO₂ presented an excellent CO gasochromic character, associated with a maximum chromatic aberration value of 90 before and after CO exposure. Systematic catalyst characterizations of XPS, FT-IR, CO-TPD, and N₂ adsorption-desorption and density functional theory calculations for the CO adsorption and charge transfer over the Pd and PdO surfaces were further carried out. It was found that the interaction between CO and the Pd surface was strong, associated with a large adsorption energy of -1.99 eV and charge transfer of 0.196 e. The color change was caused by a reduction in Pd²⁺ to metallic Pd⁰ over the Pd/TiO₂ surface after CO exposure.