Oxygen vacancies enabled enhancement of catalytic property of Al reduced anatase TiO 2 in the decomposition of high concentration ozone

Checking the Efficiency of a Magnetic Graphene Oxide–Titania Material for Catalytic and Photocatalytic Ozonation Reactions in Water

An easily recoverable photo-catalyst in solid form has been synthesized and applied in catalytic ozonation in the presence of primidone. Maghemite, graphene oxide and titania (FeGOTi) constituted the solid. Additionally, titania (TiO2) and graphene oxide–titania (GOTi) catalysts were also tested for comparative reasons. The main characteristics of FeGOTi were 144 m2/g of surface area; a 1.29 Raman D and G band intensity ratio; a 26-emu g−1 magnetic moment; maghemite, anatase and brookite main crystalline forms; and a 1.83 eV band gap so the catalyst can absorb up to the visible red region (677 nm). Single ozonation, photolysis, photolytic ozonation (PhOz), catalytic ozonation (CatOz) and photocatalytic ozonation (PhCatOz) were applied to remove primidone. In the presence of ozone, the complete removal of primidone was experienced in less than 15 min. In terms of mineralization, the best catalyst was GOTi in the PhCatOz processes (100% mineralization in 2 h). Meanwhile, the FeGOTi catalyst was the most efficient in CatOz. FeGOTi led, in all cases, to the highest formation of HO radicals and the lowest ozone demand. The reuse of the FeGOTi catalyst led to some loss of mineralization efficacy after four runs, likely due to C deposition, the small lixiviation of graphene oxide and Fe oxidation.

Removal of VOCs by Ozone: n-Alkane Oxidation under Mild Conditions

Volatile organic compounds (VOCs) have a negative effect on both humans and the environment; therefore, it is crucial to minimize their emission. The conventional solution is the catalytic oxidation of VOCs by air; however, in some cases this method requires relatively high temperatures. Thus, the oxidation of short-chain alkanes, which demonstrate the lowest reactivity among VOCs, starts at 250–350 °C. This research deals with the ozone catalytic oxidation (OZCO) of alkanes at temperatures as low as 25–200 °C using an alumina-supported manganese oxide catalyst. Our data demonstrate that oxidation can be significantly accelerated in the presence of a small amount of O3. In particular, it was found that n-C4H10 can be readily oxidized by an air/O3 mixture over the Mn/Al2O3 catalyst at temperatures as low as 25 °C. According to the characterization data (SEM-EDX, XRD, H2-TPR, and XPS) the superior catalytic performance of the Mn/Al2O3 catalyst in OZCO stems from a high concentration of Mn2O3 species and oxygen vacancies.

Recent advances in catalytic decomposition of ozone

Ozone (O₃), as a harmful air pollutant, has been of wide concern. Safe, efficient, and economical O₃ removal methods urgently need to be developed. Catalytic decomposition is the most promising method for O₃ removal, especially at room temperature or even subzero temperatures. Great efforts have been made to develop high-efficiency catalysts for O₃ decomposition that can operate at low temperatures, high space velocity and high humidity. First, this review describes the general reaction mechanism of O₃ decomposition on noble metal and transition metal oxide catalysts. Then, progress on the O₃ decomposition performance of various catalysts in the past 30 years is summarized in detail. The main focus is the O₃ decomposition performance of manganese oxides, which are divided into supported manganese oxides and non-supported manganese oxides. Methods to improve the activity, stability, and humidity resistance of manganese oxide catalysts for O₃ decomposition are also summarized. The deactivation mechanisms of manganese oxides under dry and humid conditions are discussed. The O₃ decomposition performance of monolithic catalysts is also summarized from the perspective of industrial applications. Finally, the future development directions and prospects of O₃ catalytic decomposition technology are put forward.

Magneli-Phase Titanium Suboxide Nanocrystals as Highly Active Catalysts for Selective Acetalization of Furfural

Alongside TiO₂, Magneli-phase titanium suboxide having the composition of Ti_nO_2n-1 is a kind of attractive functional materials composed of titanium. However, there still remain problems to be overcome in the synthesis of titanium suboxide; the existing synthesis methods require high temperature typically over 1000 °C and/or postsynthesis purification. This study presents a novel approach to synthesis of titanium suboxide nanoparticles through solid-phase reaction of TiO₂ with TiH₂. Crystal phases of titanium suboxide were easily controlled by changing TiO₂/TiH₂ molar ratios in a TiO₂-TiH₂ mixed precursor, and a series of titanium suboxide nanoparticles including Ti₂O₃, Ti₃O₅, Ti₄O₇, and Ti₈O₁₅ were successfully obtained. The reaction of TiO₂ with TiH₂ proceeded at a relatively low temperature due to the high reactivity of TiH₂, giving titanium suboxide nanoparticles without any postsynthesis purification. Ti₂O₃ nanoparticles and TiO₂ were applied as solid acid catalysts for reaction of furfural with 2-propanol. Ti₂O₃ showed a high catalytic activity and high selectivity for acetalization of furfural, while TiO₂ showed only poor activity for transfer hydrogenation of furfural. The difference in catalytic properties is discussed in terms of the acid properties of Ti₂O₃ and TiO₂.

Unravelling the efficient catalytic performance of ozone decomposition over nitrogen-doped manganese oxide catalysts under high humidity

Nitrogen-doped Mn species, coated with a carbon layer of several nanometers in thickness, for enhanced water vapor resistance.

Solar light induced transformation mechanism of allyl alcohol to monocarbonyl and dicarbonyl compounds on different TiO2: A combined experimental and theoretical investigation

Enols are an important group of photochemical precursors of atmospheric carbonyl compounds. However, the transformation mechanism is not fully understood. In this study, the photo-induced transformation of a typical enol, allyl alcohol, to carbonyl compounds on TiO₂ (P25) and aluminum reduced TiO₂ (P25, rutile and anatase TiO₂) were investigated. Intermediate results confirmed that a total of seven carbonyl compounds, including four monocarbonyl compounds (acetone, glycolaldehyde, 1,3-dihydroxyacetone and acrolein) and three dicarbonyl compounds (glyoxal, methylglyoxal and dimethylglyoxal), were formed on studied TiO₂. This is the first time to report the transformation of allyl alcohol to dicarbonyl compounds on TiO₂. The same byproducts formation indicated negligible effects of reduction treatment and crystal phase to the composition of carbonyl intermediates. However, the relative content ratio of dicarbonyl compounds to monocarbonyl ones on reduced P25 is ca. 4.1 times higher than that on P25, suggesting reduction treatment significantly accelerated the transformation of allyl alcohol or monocarbonyl compounds to dicarbonyl ones. Furthermore, both rutile and anatase crystal phases were found beneficial for the dicarbonyl compounds generation within enough reaction time, especially for anatase. The enhanced ^•OH was responsible for all accelerations. Furthermore, the intermediate results together with quantum chemical calculations confirmed that ^•OH addition and O₂ oxidation preferred converting allyl alcohol to dicarbonyl compounds rather than monocarbonyl ones. The present work could provide a deep insight into the transformation of allyl alcohol to carbonyl compounds, and efficiently replenish atmospheric transformation fate of enols.

Oxygen Vacancies Induced by Transition Metal Doping in γ-MnO2 for Highly Efficient Ozone Decomposition

Transition metal (cerium and cobalt) doped γ-MnO₂ (M-γ-MnO₂, where M represents Ce, Co) catalysts were successfully synthesized and characterized. Cerium-doped γ-MnO₂ materials showed ozone (O₃) conversion of 96% for 40 ppm of O₃ under relative humidity (RH) of 65% and space velocity of 840 L g^-1 h^-1 after 6 h at room temperature, which is far superior to the performance of the Co-γ-MnO₂ (55%) and γ-MnO₂ (38%) catalysts. Under space velocity of 840 L g^-1 h^-1, the conversion of ozone over the Ce-γ-MnO₂ catalyst under RH = 65% and dry conditions within 96 h was 60% and 100%, respectively, indicating that it is a promising material for ozone decomposition. XRD and HRTEM data suggested that Ce-γ-MnO₂ formed mixed crystals consisting of α-MnO₂ and γ-MnO₂ with specific surface area increased from 74 m²/g to 120 m²/g compared to undoped γ-MnO₂, thus more surface defects were introduced. H₂-TPR, O₂-TPD, XPS, Raman, and EXAFS confirmed that Ce-γ-MnO₂ exhibited more surface oxygen vacancies and surface defects, which play a key role during the decomposition of ozone. This study provides important insights for developing improved catalysts for gaseous ozone decomposition and promoting the performance of manganese oxide for practical ozone elimination.