Balancing kinetics behavior is a significant priority in chemical reactions especially involving two or more elementary steps. Propane dehydrogenation (PDH), usually involves a slower 2nd C-H activation step at a low temperature, resulting in heat waste for overcoming a higher energy barrier of the 2nd dehydrogenation. Herein, we develop one Photo-assisted Thermal PDH process (PTPDH) based on PtZn clusters encapsulated in porous MFI zeolite, which effectively balances the kinetic elementary steps via exciting the ground state electrons of the active sites to the positively charged -C 3 H 7 fragments, achieving a 23.4 % growth ratio (from 39.6 to 51.3 · 10 −8 mol·g −1 ·s −1 ) with the assistance of ∼5 suns light intensity at 400 °C. The comparison between the temperature-dependent and light intensity-dependent kinetic parameters confirmed that the non-thermal effect instead of the photo-to-thermal effect dominates the PTPDH process. Furthermore, the Lewis acidity-activity correlation experiments, in-situ radiation mass spectrometry and the H 2 co-feeds experiment indicate that the hot electrons instead of the holes play a more significant role in propylene production. Last, the in-situ Drifts-MS technique and DFT calculations demonstrate light radiation conduce to the electron transition from metal to the unpopulated electronic states of -C 3 H 7 fragments, while not conducing to the adsorbed C 3 H 8 molecule, thus selectively promoting the 2nd dehydrogenation process and achieving a balanced chemical kinetic condition. Our findings demonstrate that Photo-assisted Thermal PDH is a promising method for balancing the 1st and 2nd dehydrogenation processes.
Liming Xia,Bofeng Zhang,Gang Hou,Li Wang,Sibao Liu,Guozhu Liu
Structured catalysts coatings exhibit excellent performance on non-adiabatic gas–solid process, deriving from their enhanced heat and mass transfer properties. However, the coating catalysts prepared by traditional hydrothermal method of zeolite encapsulating noble metal are prone to spalling, especially under conditions of large flow rate and high temperature. Herein, we prepared PtZn clusters encapsulated in silicalite-1 zeolite coating on stainless steel with high bonding strength by an improved in situ growth method. The optimized catalyst exhibited ultra-thin, uniform, continuous, and high degree of crosslinking, thereby enhancing mass transfer and thermal stability. In propane dehydrogenation reaction, the optimized PtZn@S-1-R showed a high specific activity of 14.7 mol C 3 H 6 $$ {\mathrm{mol}}_{{\mathrm{C}}_3{\mathrm{H}}_6} $$ mol Pt −1 s −1 and a propylene selectivity above 99% at 600°C with a high weight hourly space velocity of 120 h −1 . The metal-encapsulated zeolite coating catalysts broaden the application avenue for heterogeneous catalysis with great application prospects.
危险品化学品经营许可证（带存储）