Low-cost, environmentally friendly, and highly efficient catalysts are urgently needed for the direct propane dehydrogenation (PDH) to propylene. Studies have shown that defective TiO2 obtained by in situ reduction shows excellent catalytic PDH performance. Doping metals in the lattice of TiO2 is a plausible method for tuning the vacancy content and electronic property. In this paper, doping with fifth period transition metals was screened using a computational method, followed by experimental synthesis to further improve the PDH activity of TiO2-based catalysts. The TiO2 (101) surface with doping metals was first studied to determine the positive effect on the vacancy formation. Then, the two disputed reaction paths, that is, the concerted and stepwise path, were compared extensively on all of the doping models. Step one is found to be more preferable for all. The microkinetic modeling was employed to obtain the turnover frequency (TOF), based on which the linear relationship is found for TOF and binding energy of dissociated H2 or co-adsorption energy of 2-propyl&H. The abovementioned screening process shows Ru-doped TiO2, which shows the highest PDH activity and is justified by experimental results.

No abstract

Propane direct dehydrogenation (PDH) is an attractive technology for propylene production that has received extensive attention. Molecular sieves with uniform porous structure, high thermal stability, and unique confinement capability have been proven to be ideal supports for well-dispersed active sites to generate efficient PDH performance. In this review, we describe the progress in the synthesis and PDH performance of metal-molecular sieve catalysts, including metal-mesoporous silica, metal-zeolite, and metal-hierarchical zeolite catalysts. The strategies in identifying and regulating active site microstructure and metalmolecular sieve interactions as well as their correlations with active site structure and PDH mechanism are introduced simultaneously. Finally, the current limitations and future opportunities of metal-molecular sieve materials in the PDH reaction are also discussed. This review is expected to provide some guidance for future catalyst design based on utilizing the molecular sieve's structural confinement to facilitate propane activation and active site stabilization.

Propane direct dehydrogenation (PDH) has received much attention. How to effectively catalyze inert C–H bond activation is of great significance for industrial development. Pt-based catalysts show excellent activity but are limited by their expensive price. Cr-based catalysts are scarcely applied owing to their high toxicity. V-based catalysts are appropriate candidates for their cheap price and low toxicity, but they suffer from high energy consumption. The photothermal synergy effect induced by nonradiative relaxation is expected to make the C–H bond activation and hydrogen coupling process easier compared to bare thermal catalysis. Herein, a set of V/TiO2 nanoscale catalysts were synthesized. The optimized 3 wt % V/TiO2 catalyst (hereafter simplified as 3V) has a particle size of ∼26 nm, achieving a propylene production rate of 342 μmol·g–1·h–1 at 500 °C with UV–vis light radiation, which is 9.2% higher compared with bare thermal conditions. In situ radiation X-ray photoelectron spectroscopy (XPS) shows that photon injection leads to more electron-deficient V atoms (Vδ+, 5 > δ > 3). The strengthened Lewis acidity enhances the C3H8 activation as revealed by kinetic evidence and in situ C3H8-DRIFT measurements. The calculated molecular orbital diagrams show that the V atoms decrease the energy gap between the highest occupied orbital (HOMO) of C3H8 and the lowest unoccupied orbital (LUMO) of the model catalyst. This work describes an efficient photothermal synergy approach, specifically the nonthermal effect for promoting propane dehydrogenation.

No abstract