Realizing of ZSM-5 microspheres with enhanced catalytic properties prepared from iron ore tailings via solid-phase conversion method.

The comprehensive utilization of iron ore tailings (IOTs) not only resolved environmental problems but also brought huge economic benefits. In this study, the synthetic route presented herein provides a novel method for the synthesis of ZSM-5 microspheres from IOTs. The effects of Si/Al molar ratios and the pH of the precursor solution on the formation of zeolite was evaluated by various analytical methods. The catalytic performance of the catalyst prepared by the solid-phase conversion method (denoted as MP-ZSM-5) was evaluated by methanol-to-propylene (MTP) reaction. Compared with the zeolite catalyst that synthesized via the conventional hydrothermal method (denoted as HM-ZSM-5), MP-ZSM-5 not only prolongs catalytic lifetime from 18.7 to 36.0 h but also has higher selectivity for propylene by MP-ZSM-5 (43.7%) than that for HM-ZSM-5 (38.6%). In addition, Kissinger-Akahira-Sunose (KAS) model is applied to the TG result to study the template removal process kinetics. The average activation energy values required for the removal of CTAB and TPABr are 201.11 ± 13.42 and 326.88 ± 16.91 kJ∙mol-1, respectively. Furthermore, this result is well coupled with the model-free kinetic algorithms to determine the conversion and isoconversion of the TPABr and CTAB decomposition in ZSM-5, which serves as important guidelines for the industrial production process.

Molecular dynamics simulations of the initial oxidation process on ferritic Fe-Cr alloy surfaces.

Oxidation processes of metallic interconnects are crucial to the operation of solid oxide fuel cells (SOFCs), and ferritic Fe-Cr alloy is one of the most important metallic interconnect materials. Based on the ReaxFF reactive potential, the interaction of O2 molecules with three types of surfaces (100, 110, 111) of ferritic Fe-Cr alloy has been studied by classical molecular dynamics at constant O2 concentrations and temperatures. The initial oxidation process is systematically studied according to the analysis of O2 absorption rate, charge variations, charge distributions, mean squared distributions, and oxidation rate. The results reveal that it is easier and faster for the Cr atoms to lose electrons than for the Fe atoms during the oxidation process. The obtained oxidation rate of Cr atoms is larger and the formation of Cr2O3 takes precedence over that of FeO. And the thickness of oxidation layers of different surfaces could be determined quantitatively. We also find that the high O2 concentration accelerates the oxidation process and obviously increases the thickness of oxidation layers, while the temperature has a weaker effect on the oxidation process than the O2 concentration. Moreover, the (110) surface presents the best oxidation resistance compared to the other two surfaces. And the (110) surface is efficient in preventing Fe atoms from being oxidized. Here we explore the initial oxidation process of Fe-Cr alloy and the corresponding results could provide theoretical guides to the related experiments and applications as metallic interconnects.