Crystal phase engineering of TiO2 regulates surface acid sites to enhance methane adsorption and promote photothermal catalytic non-oxidative coupling of methane

Crystal phase governs the formation of surface acid sites, including Ti 3+ sites, and methane adsorption on TiO 2 . • Localized surface acid sites ( e.g. , Ti 3+ ), rather than oxygen vacancies, are the dominant sites for CH 4 adsorption and activation. • Crystal phase engineering enhances photothermal methane coupling via interface regulation. Photothermal non-oxidative coupling of methane (NOCM) offers an attractive route for the direct conversion of methane into value-added C 2 hydrocarbons and hydrogen under relatively mild conditions. However, the catalytic performance is strongly limited by the inefficient adsorption and activation of methane over semiconductor supports. Herein, the crystal phase of TiO 2 was engineered to regulate the surface electronic structure and methane adsorption behavior of Pd/TiO 2 photocatalysts for photothermal NOCM. TiO 2 supports with anatase and rutile phases, denoted TiO 2 (A) and TiO 2 (R), were prepared by calcination, and subsequently loaded with Pd species by photodeposition. Among the investigated catalysts, Pd/TiO 2 (A)-500 exhibited the highest C 2 H 6 production rate of 112.4 μmol·g –1 ·h –1 at 150 °C under Xe lamp irradiation together with excellent catalytic stability. Photoelectrochemical characterization demonstrated that TiO 2 (A) significantly promoted the separation and transfer of photogenerated charge carriers. Although TiO 2 (R) possessed a higher concentration of oxygen vacancies, comprehensive state-of-the-art in situ spectral characteristics revealed substantially weaker methane adsorption due to the migration of vacancy-induced electrons into subsurface Ti sites, resulting in fewer surface acid sites, such as Ti 3+ sites. These also confirmed that the enhanced surface Ti 3+ species on TiO 2 (A) facilitated methane adsorption and activation, promoted the generation of · CH 3 intermediates, and consequently accelerated C C coupling toward ethane formation. This work reveals the decisive role of TiO 2 crystal phase in regulating methane adsorption and activation during photothermal NOCM, providing new insights into the rational design of semiconductor supports for efficient solar-driven methane valorization. Crystal phase engineering of TiO 2 regulates surface acid sites to enhance methane adsorption and promote photothermal catalytic non-oxidative coupling of methane Download: Download high-res image (253KB) Download: Download full-size image