Pt-TiO₂ Catalyst for Aqueous-Phase Water–Gas Shift Reaction Constructed by Utilizing Strong Metal–Support Interaction

Aqueous-phase water–gas shift reaction (AP-WGSR, CO (g) + H2O (l) = H2 (g) + CO2 (g)) refers to the reaction between gas-phase carbon monoxide and aqueous-phase water that produces gas-phase hydrogen and carbon dioxide. Its Gibbs free energy value is more negative, and therefore, the conversion of CO would be more complete compared with the traditional gas-phase water–gas shift reaction (CO (g) + H2O (g) = H2 (g) + CO2 (g)). Herein, Pt-TiO2 catalysts reduced at different temperatures for AP-WGSR are prepared and the relationship between the catalytic activity for AP-WGSR and the structure of Pt-TiO2 catalysts reduced at different temperatures was studied. Pt-TiO2 catalyst reduced at 600 °C (Pt-TiO2-600R) exhibits the best catalytic performance and accomplishes the objective of catalyzing AP-WGSR. The low-temperature H2 formation rate of Pt-TiO2-600R reaches 20.3 μmol gcat–1 s–1 (170 °C, CO partial pressure of 4.5 MPa), which is almost 17 times larger than that of the Pt-TiO2 catalyst reduced at 300 °C (Pt-TiO2-300R, 1.2 μmol gcat–1 s–1). In addition, the Pt-TiO2-600R catalyst is hydrothermally stable and the CO conversion remains stable over six consecutive reactions at 180 °C. Characterizations reveal that a strong metal–support interaction (SMSI) occurs on the Pt-TiO2 catalysts reduced at high temperatures. TiOx species cover the Pt particle, and oxygen vacancies are formed at the Pt-TiOx interface. Mechanism studies indicate that AP-WGSR undergoes a redox mechanism with low apparent activation energies on the Pt-TiO2 catalyst containing Pt partially covered by TiOx species and an associative mechanism with high apparent activation energies on the Pt-TiO2 catalyst containing bare Pt, respectively.