Selective Oxidation of Cyclohexane Using Ce_1−xMn_xO₂ Nanocatalysts

Abstract

The Ce1-xMnxO2 nanocatalysts (x = 0.25, 0.50 and 0.75 wt.%) were synthesized by sol-gel method. The catalysts were characterized using various techniques such as XRD, N2 sorption study, DRSUV-Vis, TPR, SEM and TEM. The incorporation of Mn ions into the ceria lattice was confirmed by XRD analysis. DRUV-Vis spectra confirm the presence of Ce3+ ions in the lattice of Ce1-xMnxO2. H2-TPR study revealed the oxygen storage capacity of the catalyst. The 3D flowerlike morphology of the nanocatalysts was confirmed from FESEM and HRTEM images. The catalytic activity was tested for the vapor phase oxidation of cyclohexane using air as an oxidant. The key reaction parameters were varied to study the stability, activity and selectivity of the catalysts. The study concluded that suitable amount of manganese content is essential for the selective oxidation of cyclohexane at low temperature and Ce0.25Mn0.75O2 is the most suitable catalyst for high conversion and selectivity under the given reaction conditions. The activity of the catalyst is correlated with the characterization results.

Low temperature vapor phase selective oxidation of ethylbenzene over Ce 1−x Mn x O 2 nanocubes

“…The manganese ions incorporated nanocubes (Ce 1-x Mn x O 2 ) are synthesized by precipitation method using urea as follows [37,38] A c c e p t e d M a n u s c r i p t 5 procedure reported earlier [31,36]. Further, MnO 2 catalyst is also synthesized by the same procedure using manganese acetate as the precursor.…”

“…However, pure ceria posses low thermal stability, and leads to low oxygen storage capacity. In-order to improve the thermal stability and catalytic behavior of the catalyst, the transition metals are incorporated into ceria lattice [31,32]. In addition to the well-known particle size effect would make it into better catalytic activity [33,34], also the oxygen storage capacity of the catalysts is closely related to its morphology and exposure active planes [35,36].…”

“…Since, incorporation of Mn n+ plays a vital role in the morphological change, which might be attributed to the preferential adsorption of anions on definite crystallographic planes leads to decrease the relative surface energy, and further control the dynamics of crystal growth process results in the specific surface morphology[36]. In our previous report, the authors successfully synthesized pure CeO 2 and manganese incorporated ceria nanoparticles (Ce 1-x Mn x O 2 ) with flowerlike morphology using nitrate salt as the precursor[31]. The current study includes the use of manganese acetate precursor which induced the morphological changes in Ce 1-x Mn x O 2 catalysts from flowerlike into cubic structure(Fig.…”

Selective oxidation of cyclohexane: Ce promotion of nanostructured manganese tungstate

“…A study of cyclohexane oxidation by air over unsupported Mn oxides showed the highest cyclohexane conversion was achieved for calcination at 400ºC, which was attributed to the higher surface Mn 4+ concentration promoting oxygen mobility and increased oxygen adsorption capacity [18]. The use of Mn containing mixed-metal oxides in oxidation reactions has been studied frequently in the literature [19][20][21][22][23].…”

“…Mixed metals of variable valency increases oxygen vacancies and enhances oxygen ion mobility. Of particular relevance to the present study are the use of nanostructured MnWO 4 in the oxidative dehydrogenation of propane to propene [20], and of MnCeO x solid solutions for cyclohexane selective oxidation [21,22]. MnWO 4 nanorods prepared by hydrothermal synthesis were found to present higher selectivity to propene than bulk Mn oxide, which was attributed to its unique surface structure containing defect-rich MnO x zigzag chains geometrically isolated by W 2 O 8 units.…”