Ti-mediated reduction to construct the oxygen vacancy-rich Pt-TiO₂ catalysts for the hydrogen production of dodecahydro-N-ethylcarbazole

With the global energy structure transitioning towards decarbonization, hydrogen energy has emerged as a critical energy carrier due to its merits of zero carbon emissions and high energy density. As a candidate material for liquid organic hydrogen carrier (LOHC), it is necessary to develop efficient dehydrogenation catalysts of dodecahydro-N-ethylcarbazole (12H-NECZ) to overcome the challenges of low kinetics and selectivity. In this work, by the defect engineering strategy, a series of Pt-TiO₂ catalysts are synthesized via thermal reduction using titanium (Ti) as a reducing agent. The effects of various TiO₂:Ti molar ratios (5:1 to 8:1), annealing temperatures (550–850 °C), and Pt loadings on the structural and catalytic properties are systematically investigated. It is indicated that the 2.5Pt-7:1–650 catalyst exhibits optimal dehydrogenation efficiency, achieving 100 % conversion, 99.03 % selectivity of NECZ, and hydrogen release capacity of 5.77 wt% under 453 K and 101.325 kPa for 7 h. Various structural characterizations from XRD, H₂-TPR, ESR, and XPS analysis reveal that the oxygen vacancies and Ti³⁺ species are generated induced by the metallic Ti reduction. The interaction between Pt and TiO₂ facilitates the electron transfer from TiO₂ to Pt, optimizes the electronic state of Pt and promotes the C-H bond cleavage of benzene ring in adsorbed 12-NECZ molecules. Furthermore, the kinetic analysis for a three-step reaction pathway confirms the dehydrogenation of 4H-NECZ to NECZ is the rate-limiting step. The stability measurements suggest that 2.5Pt-7:1–650 maintains the hydrogen release amount of 5.64 wt% after 20 cycles at 453 K, demonstrating the potential applications for the NECZ/12-NECZ system. This study provides a novel strategy for designing high-performance LOHC dehydrogenation catalysts through defect engineering.