Metal-Oxide Nanotube Channel Microenvironment Inducing Strong Metal-Oxide Interplay: A Case Study with CO₂ Hydrogenation to Methanol

Nanoconfined architectures and interfacial electronic modulation are essential strategies for enhancing catalytic performance in multistep reactions. While carbon nanotubes (CNTs) are commonly used for confinement, their chemical inertness limits the formation of synergistic active sites and optimization of the reaction environment. Replacing CNTs with metal-oxide nanotubes offers significant improvements in electronic metal–support interaction (EMSI), tunable structure, mass transfer, and stability. Nevertheless, research on confinement effects in metal-oxide nanotubes remains underexplored. Herein, using the CO2 hydrogenation as the model reaction, we engineered two distinct palladium–titania nanotube configurations: Pd@TiO2 NTs (with Pd confined within nanotubes) and Pd/TiO2 NTs (with Pd deposited on external surfaces). Density functional theory (DFT) calculations reveal that Pd@TiO2 NTs exhibit enhanced EMSI, suppress the reverse water gas shift (RWGS) reaction, and promote methanol production more than Pd/TiO2 NTs. Consistently, experimental results show that Pd@TiO2 NTs achieve a 3.7-fold higher methanol selectivity and 2.4-fold higher CO2 conversion compared with Pd/TiO2 NTs. Moreover, Pd@TiO2 NTs also demonstrates a space–time yield of 0.56 mmol gcat–1 h–1, approximately 9 times higher than that of Pd/TiO2 NTs. This significant finding provides critical guidance for engineering spatially confined catalysts utilizing metal-oxide nanotubes in heterogeneous catalytic systems.