Morphology-Controlled SmMn₂O₅ Nanocatalysts for Improved Acetone Degradation

Abstract

The SmMn 2 O 5 catalyst is considered as an excellent substitute for noble-metal and transition-metal oxide catalysts due to its unique crystal structure. In order to further improve its catalytic activity for acetone degradation, SmMn 2 O 5 nanocatalysts with four morphologies were synthesized by the hydrothermal method by adjusting the type of manganese source reagent, the content of mineralizing agent, and hydrothermal temperature. Among them, the SMO-NF catalyst prepared with Mn(NO 3 ) 2 as the manganese source, 10 mL of NaOH, and a hydrothermal temperature of 220 °C has a special flower morphology and can achieve 100% acetone conversion at 118 °C. Because of its thin and large "petal" morphology providing active sites and oxygen vacancies, the excellent catalytic performance of the SMO-NF catalyst is an important breakthrough in the field of acetone degradation. In addition, the highly stable crystalline phase, abundant surface reactive oxygen species, and excellent reducibility of the SMO-NF catalyst also lay the foundation for its high catalytic activity, water resistance, and stability. The SMO-NS catalyst with a spherical morphology can completely degrade acetone at 136 °C, and its activity is better than that of the SMO-CP catalyst prepared by the coprecipitation method and Pt/TiO 2 catalysts. The relationship between the formation process of SmMn 2 O 5 nanocatalysts with special morphology and its catalytic activity is discussed as well. The successful synthesis of the SMO-NF catalyst also opens up a way for the synthesis of the special morphology of acetone degradation nanocatalysts.

Nanoporous CeO2-Decorated Cu-SmMn2O5 Composite Mullite Oxide Catalyst for Toluene Oxidation

“…Raman spectroscopy was used to study the vibrational modes of the species on the catalyst surface to evaluate the strength of bonds. In Figure a, based on the previous studies, the peaks around 191–209 cm –1 are assigned to the symmetric stretching vibration mode of the Mn–Mn dimer, and the peaks at a higher Raman shift (>600 cm –1 ) are ascribed to the asymmetric stretching vibration mode of the Mn–O–Mn structure, in which the peaks at 613 and 677 cm –1 correspond to the vibration of the Mn 4+ –O bond and Mn 3+ –O bond, respectively. ,,, It is clear that the three peaks are all observed in the SMO sample, confirming the formation of the mullite structure. The Raman peak intensity is correlated with the crystallite size, and the sharp Raman peak usually means that the crystallite size increases. , Compared with the SMO sample, the weakened and broadened Raman peaks are observed in the SCMO-Cu-IE sample indicating a decrease in the crystallinity, which is consistent with the above XRD results.…”

“…The results of O 2 -TPD are shown in Figure b. According to the previous studies, the peaks below 400 °C are ascribed to surface-adsorbed oxygen species, the peaks between 400 and 600 °C are regarded as surface lattice oxygen species, and the peaks over 600 °C represent the bulk lattice oxygen species. , It is widely accepted that surface-adsorbed oxygen species are active in oxidizing small molecules. , There are nearly no peaks observed in the SMO sample due to the poor mobility of oxygen species even though the temperature reaches 800 °C, which is reported by the previous work of our group . Four main peaks representing the desorption of different oxygen species are observed in the SCMO-Cu-IE sample within the temperature range.…”

“…At the current stage, introducing oxygen vacancies into the crystal structure of mullite oxide serves as an efficient way to solve the above-mentioned problem. − Researchers have developed various strategies to create oxygen vacancies including elemental doping − and interfacial decoration. ,, For example, Shen et al reported that Cu ions were doped into the crystal lattice of SmMn 2 O 5 replacing Mn 3+ ions to form the Cu 2+ –O–Mn 4+ structure . This Cu doping with inequivalence successfully created a large number of oxygen vacancies and weakened the strength of the Mn–O bond, thus enhancing the redox ability to convert lattice oxygen into active oxygen species.…”