期刊
CATALYSIS SCIENCE & TECHNOLOGY
卷 12, 期 17, 页码 5274-5280出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/d2cy00496h
关键词
-
资金
- Koch Technology Solutions Ltd
- EPSRC [EP/L016443/1]
This study investigated the influence of varying water/acetic acid ratios on the structure and coordination environment of Co/Mn/Br catalyst, suggesting tetrahedral Co2+ species form with 2 or 3 Br- ligands at low water content. EPR linewidth changes in Mn2+ signals were correlated with water content, showing variations in coordination sphere. Findings provide insight into the relationship between solvent composition and catalyst structure.
The industrially important para-xylene oxidation reaction, based on a Co/Mn/Br catalyst, operates in a water/acetic acid (H2O/AcOH) solvent system. The correct H2O/AcOH ratio of the solvent is crucial in controlling the reaction yields and selectivities. However, the influence of this variable solvent system on the catalyst structure and coordination environment is not well understood. Using UV-vis spectroscopy, we observed the formation of tetrahedral Co2+ species when the solvent composition was below 10 wt% H2O. These were considered to be tetrahedral Co2+ species with either 2 or 3 coordinating Br- ligands. The pronounced CW EPR linewidth changes observed in the Mn2+ signals revealed a strong correlation on the solvent H2O content. Detailed analysis revealed that these variations in the linewidth were attributed to the changing coordination sphere around the Mn2+ centres, with a maximum linewidth occurring at 8-10 wt% H2O. The narrow linewidths below 8 wt% H2O were found to result from substitution of H2O/AcOH ligands by Br, whereas above 8 wt% H2O a further narrowing of the linewidth was actually caused by greater amounts of H2O coordination. To confirm this, 3-pulse ESEEM measurements on the Mn2+ were conducted in the solvent compositions corresponding to 3, 8, 13.7 and 20 wt% H2O. The results showed a marked change in the number (n) of coordinated H2O molecules (ranging from n = 0, 0, 1.0 to 4.0 respectively for the 3-20 wt% H2O content). For the first time, these findings provide a crucial insight into the relationship between solvent composition and catalyst structure in this industrially important catalytic reaction.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据