Roles of Oxygen Species in Low-Temperature Catalytic o-Xylene Oxidation on MOF-Derived Bouquetlike CeO₂

Abstract

To realize efficient low-temperature catalytic o-xylene oxidation, MOF-derived CeO2-X catalysts were prepared via the pyrolysis of MOF precursors with different ratios of cerium nitrate to trimesic acid. Among the synthesized catalysts, the bouquet like CeO2-1 exhibited the best activity with T 50 and T 90 of 156 and 198 °C and the lowest activation energy of 60.67 kJ·mol–1 (WHSV= 48 000 mL·g–1·h–1, o-xylene concentration = 500 ppm). o-Xylene was completely mineralized, and no change in conversion efficiency or CO2 yield was found at 5 vol % H2O for over 50 h. The rich active oxygen species (XPS: Osur/Olatt = 0.69) and abundant oxygen vacancies (Raman: I D/I F2g = 0.036) of CeO2-1 made crucial contribution to its superior catalytic activity. The O2-TPD and H2-TPR results confirmed that CeO2-1 had more surface active oxygen and better mobility of bulk oxygen. Moreover, the reaction routes under different atmospheres were probed through in situ DRIFTS, in which oxygen vacancy played a key role in promoting the adsorption and activation of molecular oxygen and facilitating the migration of the bulk lattice oxygen.

MOF-Derived CeO2 and CeZrOx Solid Solutions: Exploring Ce Reduction through FTIR and NEXAFS Spectroscopy

“…Notably, the H 2 O, ν(t-OH) or Ce 3+ band area which highlights surface cerium reduction under H 2 , showed that the reaction had already begun at RT. This is in line with cerium’s higher reducibility in the case of MOF-derived CeO 2 samples [ 26 , 27 , 28 , 29 ].…”

“…The increase in the onset temperature with the Zr content was related to the known higher stability of pure Zr-UiO-66 [ 58 ]. MOF calcination was then conducted at 450 °C to eliminate the organic components, in line with the temperatures range reported in the literature [ 26 , 27 , 28 , 29 ]. C100-UiO-66 calcination could have been conducted at lower temperature (≈350 °C); however, this would have induced an inhomogeneity in the samples’ thermal treatments.…”

“…On the contrary, direct precursor calcination has shown a great potential for the direct preparation of catalysts [ 18 , 19 , 20 , 21 , 22 ]. In the latter approach, promising results have been reported for direct calcination of metal–organic frameworks (MOFs) at moderate temperatures (300–500 °C) [ 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. Indeed, depending on the employed linkers, MOF synthesis can be very simple and cheap [ 30 ].…”

Shifts of the Rate-Limiting Step in Airlift Microbial Electrolysis Cells for Gaseous Propanethiol Degradation

“…At present, biological treatment is regarded as an emerging technology for VOSCs degradation as it has been proven to be adaptable to VOSCs waste gas conditions, including low concentration, large flow rate, high moisture, and the required degradation rate of PT. − Unfortunately, the biological control of VOSCs still meets the low removal load bottleneck, which results from their low solubility and biotoxicity . In other words, both the mass transfer and reaction steps involved in the biological treatment of VOSCs waste gas are still hindered.…”

Fabrication of Hierarchical Porous Metal Oxides by the HPMC-Assisted Gel Combustion Strategy: Incorporation of Nanoceria into Cookie-like Mn2O3 with Enhanced Oxidation Activity and Excellent Water Resistance

“…Compared to the mixed Cu–Mn oxide obtained by direct calcination of metal salt in open space, the ordered Cu–Mn oxide prepared by the hard template route showed a high surface area and a rich porous structure, further leading to much better activity in the catalytic removal of carcinogenic benzene. Besides, some new precursors like metal–organic frameworks (MOFs) have been applied as a self-sacrificing template for synthesizing porous nanostructures via pyrolysis of organic components, − where the obtained nanostructure with a high surface area and rich active species displayed much better low-temperature activity. However, it is still a great challenge to get the porous oxides on a large scale due to the complicated procedure of the templating approach and costly precursors like MOF components.…”