Dynamic Interplay between Particle Size and Strong Metal Support Interaction in Rh/TiO2 Tuning the Selectivity of CO2 Hydrogenation

Abstract

The regulation of selectivity in CO₂ hydrogenation is of great importance and has been intensively studied for the utilization of CO₂. The particle size and metal–support interaction are proven to be key factors influencing the selectivity of CO₂ hydrogenation. However, the dynamic structure evolution during real reaction conditions and their impact on the selectivity are still poorly understood. Here in this work, we reported the crystal-phase-mediated dynamic restructuring of the Rh/TiO₂ catalyst during reaction that strongly modulates the mutual interaction of dynamic size stability and strong metal–support interaction (SMSI) encapsulation of the Rh catalyst and thus the selectivity of CO₂ hydrogenation toward CO/CH₄. By utilizing state-of-the-art characterizations, the interplay between dynamic size distribution and SMSI of the Rh catalyst on TiO₂ was clearly elucidated. The selectivity of CO₂ hydrogenation was prone to the particle size in the low reaction temperature range (225–275 °C) while highly depending on SMSI at high reaction temperatures (350–400 °C). Remarkably, anatase TiO₂ promotes small Rh particles and strong SMSI at the low-temperature range, rutile TiO₂ facilitates large particles but high-temperature SMSI encapsulation, while the P25 phase favors large Rh particles without encapsulation. The in situ DRIFTS experiments further reveal that all Rh/TiO₂ catalysts follow the hydrogenation path via *HCOO as an intermediate, where the large Rh particle size facilitates deep hydrogenation of *HCOO to CH₄, whereas the TiO_x encapsulation favors the *HCOO decomposition to CO due to the suppressed H₂ activation. Our results provide dynamic insight for the restructuring of the active sites in the Rh/TiO₂ catalyst that tunes the selectivity of CO₂ hydrogenation and opens up a route for the rational design of supported metal catalysts based on their dynamic structures.