Dual-Cycle Mechanism Based Kinetic Model for DME-to-Olefin Synthesis on HZSM-5-Type Catalysts

A kinetic model for the olefins synthesis from dimethyl ether on zeolite HZSM‑5 based catalysts is developed. The model includes the reaction pathways for the synthesis of olefins from oxygenates in the olefinic and aromatic cycles according to modern concepts of the dual-cycle reaction mechanism. The kinetic parameters were determined for the time-stable hydrothermally treated catalysts of various activities Mg-HZSM-5/Al2O3, HZSM-5/Al2O3, and Zr-HZSM-5/Al2O3. The kinetic parameters determination and the solution of the ordinary differential equations system were carried out in the Python software environment. The preliminary estimation of the kinetic parameters was carried out using the Levenberg-Marquardt algorithm, and the parameters were refined using the genetic algorithm. It is shown that reactions activation energies for different catalysts are close, which indicates that the priority of the reaction paths on the studied catalysts is the same. Thus, the topology of the zeolite plays a leading role in the determination of the synthesis routes, rather than the nature of the modifying metal. The developed model fits the experimental data obtained in an isothermal reactor in the range of temperature 320–360 °C, specified contact time 0.1–3.6 h*gcat/gC with a relative error of less than 15%.

Selective E to Z isomerization of 1,3-Dienes Enabled by A Dinuclear Mechanism

The E/Z stereocontrol in a C=C bond is a fundamental issue in olefin synthesis. Although the thermodynamically more stable E geometry is readily addressable by thermal Z to E geometric isomerization through equilibrium, it has remained difficult to undergo thermal geometric isomerization to the reverse E to Z direction in a selective manner, because it requires kinetic trapping of Z-isomer with injection of chemical energy. Here we report that a dinuclear PdI−PdI complex mediates selective isomerization of E-1,3-diene to its Z-isomer without photoirradiation, where kinetic trapping is achieved through rational sequences of dinuclear elementary steps. The chemical energy required for the E to Z isomerization can be injected from an organic conjugate reaction through sharing of common Pd species.

Mobility and versatility of the liquid bismuth promoter in the working iron catalysts for light olefin synthesis from syngas

Localization and migration of highly mobile and extremely efficient bismuth promoter in iron Fischer–Tropsch catalysts were elucidated using in situ methods.