Supported Molybdenum Catalysts for Deoxydehydration: An access to olefinic special and fine chemicals from diols and polyols
Final Report Abstract
This project focused on the meticulous design of catalysts to achieve varying surface densities of Mo atoms per nm2 on TiO2, generating isolated, oligomerized, and polymerized MoO 3 species. These surface densities ranged from 0.5 Mo to 4.5 Mo atoms per nm 2 on TiO2. Despite variations in Mo loading, there was only a marginal change in the specific surface area of the catalysts. The XRD analysis demonstrated that even at a high Mo loading of 4.0 wt%, no additional reflexes associated with MoO3 crystallites were observed, indicating highly dispersed MoOx species on TiO2. Raman spectra revealed a gradual shift in the Mo=O stretching band to higher Raman shifts with increasing Mo density, signifying MoOx oligomerization from isolated to 2D polymerized to MoO3 nano crystallites. The presence of Mo significantly influenced the acidity of the catalysts, with increasing Mo loading resulting in a gradual decrease in total acidity. NH 3-TPD profiles exhibited broad desorption peaks, reflecting acid sites of varying strengths, with stronger acid sites becoming dominant as Mo surface density increased. Pyridine-FTIR analysis confirmed the presence of Lewis acid sites on TiO 2, while Brønsted acid sites emerged at higher Mo loadings, intensifying with increasing MoOx surface density. The DODH reaction rates were inversely correlated with Mo surface density, with isolated MoO x species exhibiting the highest activity. Calcination had a notable impact on catalyst performance, enhancing 1,4-AHE conversion and selectivity to 2,5-DHF for the 0.5Mo catalyst but reducing selectivity for the 3.5Mo catalyst, primarily due to increased acidity. Although leaching was observable for 0.5Mo catalyst, the leached Mo species were non-selective for the DODH. Recycle studies revealed that the remaining unleached Mo species on the 0.5Mo catalyst maintained stability and selectivity over multiple runs, with the possibility of increasing acidity with regeneration involving calcination. The influence of calcination temperature on the 0.5Mo catalyst showed that the catalyst maintained its activity even at lower calcination temperatures. Different Mo precursors, including a cost-effective option, yielded equivalent levels of activity. Furthermore, the study explored the role of Mo oxidation states in catalytic activity, with 0.5Mo catalyst outperforming other Mo compounds. But, uncertainties regarding surface composition necessitate further analysis. In conclusion, this project provides valuable insights into the ideal geometric requirements (Mo surface density) and electronic configurations (oxidation states) of Mo species for optimal performance in the DODH reaction. These findings offer a solid foundation for future research and catalyst design in this field, contributing to a better understanding of catalyst design principles for DODH reactions.
Publications
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Zeolite‐Supported Rhenium Catalysts for the Deoxydehydration of 1,2‐Hexanediol to 1‐Hexene. ChemCatChem, 13(10), 2393-2397.
Meiners, Isabell; Louven, Yannik & Palkovits, Regina
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Influence and stability of the surface density of MoOx on TiO2 in deoxydehydration: structure–activity correlations. Catalysis Science & Technology, 13(4), 1087-1097.
Sebastian, Joby; Mebrahtu, Chalachew & Palkovits, Regina
