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A set of mono-metallic nanoparticles catalysts, including palladium, platinum, and gold supported on titania, were prepared via the sol-immobilization technique, and evaluated for the total oxidation of propane as a model reaction of volatile organic compounds (VOCs) oxidation, which is a wide-ranging group of organic pollutants that contribute to serious atmospheric problems. The results showed that 1 wt.% Pt/TiO2 was the most active catalyst toward CO2, as the catalyst was very active, and the complete conversion of propane was achieved with full selectivity toward CO2. The effect of the support type was investigated through the immobilization of platinum nanoparticles on CeO2 and γ-Al2O3. The results indicated that the catalytic activity follows the order 1% Pt/TiO2 > 1% Pt/CeO2 > 1% Pt/Al2O3. For the Pt/TiO2 catalyst, the influence of the calcination temperature and metal loading on the catalytic activity was investigated. There is a slight increase in the Pt particle size when raising the calcination temperature from 300 °C to 500 °C, which enhances the catalytic activity of 1% Pt/TiO2 at 500 °C. Furthermore, increasing the metal loading from 0.1 to 1 wt.% enhances the catalytic activity as a result of the increase in particle size. Different characterization techniques were utilized, including XRD, TEM, XPS, and MP-AES, to determine the structure-activity relationship, and together they indicate that the catalytic activity is influenced more by the particle size of Pt nanoparticles than by the oxidation state. [ABSTRACT FROM AUTHOR]

[Display omitted] • Oxygen vacancies and acidity of La-Mn perovskite can be adjusted by Ca doping. • La 0.9 Ca 0.1 MnO 3 shows excellent activity and stability under harsh operation conditions. • Adsorbed oxygen species play an important role in C-C cleavage of intermediates. • Catalyst acidity determines the yield of N-containing byproducts. It is of great significance to design catalysts with high activity, N 2 selectivity and stability for nitrogen-containing volatile organic compound (NVOC) catalytic purification. Meanwhile, the role of oxygen species in NVOC catalytic oxidation is still ambiguous. Herein, the oxygen species of La-Mn perovskite catalysts were engineered by doping Ca in La site to elucidate their role in catalytic n-butylamine oxidation. Results demonstrate that La 0.9 Ca 0.1 MnO 3 exhibits the highest activity owing to its abundant adsorbed oxygen species and high surface area, achieving 100 % n-butylamine conversion (500 ppm; GHSV=60,000 mL g−1h−1) at 200 °C with N 2 selectivity of ca. 95 %. More adsorbed oxygen species generated due to Ca doping accelerates the oxidation rate and C-C cleavage of alcohol and acetate intermediates, resulting in higher CO 2 yield. Meanwhile, Ca-doping also modifies the acidity of catalysts, which affects the adsorption/desorption process of alkaline substances and yield of nitrogen-containing products. In addition, La 0.9 Ca 0.1 MnO 3 shows superior stability, high water and SO 2 resistance, and acceptable activity for other common NVOCs, demonstrating a promising catalyst for NVOC oxidation even under harsh operation conditions. Furthermore, the toxic effect of pollutant or products during n-butylamine catalytic oxidation on the growth of Chlorella Vulgaris was investigated and results suggest that catalytic oxidation is an environmentally friendly method for NVOC purification. This work sheds light on the relationships among oxygen species, catalyst acidity, and n-butylamine catalytic oxidation, which expand the understanding of rational design of efficient catalyst for NVOC oxidation. [ABSTRACT FROM AUTHOR]

Reactivity loss by intermediates aggregation and water vapor inhibition are two major and longstanding challenges for the noble-metal-based catalysts in oxygenated volatile organic compounds (OVOCs) oxidation. Herein, the core-shell Pd@CoO Janus sites are creatively designed and stabilized over the HSAPO-34 support. Quasi in situ XPS spectra reveal that the strong interactions in Pd@CoO Janus sites promote the charge redistribution and electron back-donation through Pd-O-Co coordination. Therefore, abundant positively charged Pd2+ sites are formed and oxygen species transformation is facilitated, which significantly promote the low-temperature efficiency of acetone oxidation. Furthermore, the Pd@CoO/HSAPO-34 catalyst facilitates H 2 O molecules dissociation and produce reactive OH Ter and OH Tri species, which considerably promotes the rapid decomposition of aldehyde intermediate via attacked CH 2 O* group, ensuring low-temperature oxidation of acetone. This work provides valuable guidance to develop specific catalysts with functional active sites for rationally utilizing H 2 O molecules to improve low-temperature performance and modulate reaction pathways during OVOCs oxidation. [Display omitted] • Thermal-depolymerization was employed to synthesize the Pd@CoO Janus sites. • Charge redistribution through Pd-O-Co coordination facilitates reactant activation. • Positively charged Pd2+ and activated Co-O coordination promote acetone oxidation. • Pd@CoO/HSAPO-34 catalyst facilitates the dissociation of H 2 O molecules. • Surface OH Tri and OH Ter groups accelerate aldehyde intermediate degradation. [ABSTRACT FROM AUTHOR]

The efficient catalytic oxidation of nitrogen-containing volatile organic compounds remains a big challenge due to unmanaged production of harmful byproducts. Herein, a series of Cu-Mn modified hierarchical SAPO-34 zeolite catalysts with different pore structures were synthesized for n-butylamine oxidation. The physicochemical properties and catalytic performance of catalysts were investigated and analyzed in detail. Among them, CuMn/S-1 shows the highest activity (T 90 = 279 °C, GHSV = 12,000 h−1), which is attributed to its higher porosity, higher surface acidity and superior reducibility. Meanwhile, it is found that the hierarchical structure and mesopore play an important role in improvement of N 2 selectivity. Meanwhile, CuMn/S-1 also exhibits high stability and water resistance. The catalytic mechanism of n-butylamine on CuMn/SAPO-34 was investigated by in situ DRIFTS, showing that propanol, methanol and acetate are the main intermediates. [Display omitted] • A series of Cu-Mn modified hierarchical SAPO-34 zeolite catalysts were prepared. • CuMn/S-1 shows the excellent n-butylamine oxidation activity and high N 2 selectivity. • Acidity and reducibility are the key factors determining catalytic activity in low/high temperature, respectively. • The hierarchical structure and acidity have effects on N 2 selectivity. [ABSTRACT FROM AUTHOR]

[Display omitted] • A series of transition metal cordierite-based monolithic catalysts were prepared. • Mn/Al 2 O 3 /COR shows excellent ethyl acetate (EA) oxidation activity and water resistance. • Surface oxygen species (O β) play vital roles in EA activation and intermediate generation. • Low content water vapor (≤1 vol%) promotes EA activation and ethanol formation. • Water vapor leads to the decline of O β and formation of large-size hard coke. The reduction and control of VOCs from anthropogenic sources becomes a research hotspot due to their tremendous environment hazards. Fabricating efficient and applicable noble-metal-free monolithic catalysts is still a great challenge for industrial VOC economical removal. In this work, cordierite-based honeycomb monolithic catalysts (M/Al 2 O 3 /COR; M = Cr, Mn, Fe, Co, Ni and Cu) were synthesized by a versatile and scalable wash-coating method and adopted for ethyl acetate (EA) catalytic oxidation. Mn/Al 2 O 3 /COR possesses remarkable activity with 90% of ethyl acetate (EA) oxidized at 236 °C owing to abundant surface active oxygen species. Moreover, excellent stability and water resistance of Mn/Al 2 O 3 /COR were observed during long-term successive reaction. In situ DRIFTS results reveal that the decomposition of EA to ethanol is the main pathway under humid conditions, and the presence of low content water vapor (≤1 vol%) promotes EA conversion ascribed to the presence of abundant OH derived from H 2 O dissociation; however, further increasing of water concentration inhibits EA conversion. The adsorption of OH over oxygen vacancies inhibits the generation of surface oxygen species and blocks further oxidation of intermediates to form acetate, leading to the reduction of CO 2 yield and formation of coke aggregates. This work will provide instructive and feasible references for designing of VOC oxidation catalysts under practical reaction conditions. [ABSTRACT FROM AUTHOR]

• Rod-, sheet-, and cube-like Co 3 O 4 with different exposing crystal facets were synthesized. • Rod-like Co 3 O 4 with (110) facet exhibits the highest catalytic activity in propane oxidation. • Co 3 O 4 with exposed (110) facet has more lattice defects and low coordination Co atoms. • (110) facet of Co 3 O 4 has the lowest formation energy of oxygen vacancy. • Lewis acid-base pairs and surface oxygen vacancy promote oxygen and propane activation. Low-temperature degradation of short chain alkane is one of the greatest challenges of volatile organic compound purification. Here, rod-, sheet-, and cube-like Co 3 O 4 (Co 3 O 4 -R, Co 3 O 4 -S, and Co 3 O 4 -C) with predominantly exposed (110), (111), and (100) facets respectively were fabricated. Co 3 O 4 -R presents excellent activity achieving 90 % of propane oxidized at just 195 °C owing to large amounts of lattice defects, oxygen vacancies and low coordinated Co atoms. Theoretical calculation reveals that Co 3 O 4 -R has the lowest formation energy of oxygen vacancy on (110) facet (E vo (110) =1.7 eV), which has a higher activation capacity for oxygen due to the largest O 2 adsorption energy (−1.30 eV) and thus accelerates propane oxidation. Moreover, largest amount of lewis acid-base pairs existed in Co 3 O 4 -R polarizes substrate electron distribution and therefore accelerates the activation of C–H bonds. Electrophilic oxygen species (O 2 2− or O−) caused the degradation of carbon skeleton and formed carboxylate intermediates before mineralized to CO 2. [ABSTRACT FROM AUTHOR]

• Hierarchical Al 2 O 3 -pm and ZnO-pm microspheres are prepared by a hydrothermal method. • Pd/Al 2 O 3 -pm and Pd/ZnO-pm show excellent EA oxidation activity and CO 2 yield. • Pd dispersion is enhanced by high surface area and developed porosity of supports. • Mechanisms of EA oxidation over Pd/Al 2 O 3 -pm and Pd/ZnO-pm were elucidated. • Pd availability is obviously enhanced by using Al 2 O 3 -pm and ZnO-pm coatings. Developing economical and active materials is of great significance for VOC purification. Here, hierarchical porous Al 2 O 3 and ZnO microspheres (Al 2 O 3 -pm and ZnO-pm) were synthesized by a facile hydrothermal strategy. The urchin-like Al 2 O 3 -pm and flower-like ZnO-pm possess high specific surface area (especially; external surface area) obviously boost the dispersion of Pd with 29.3 % and 30.1 % over Pd/Al 2 O 3 -pm and Pd/ZnO-pm, respectively, over 3.4 times higher than those of commercial Al 2 O 3 - and ZnO-supported counterparts. Pd/Al 2 O 3 -pm possesses excellent activity and CO 2 yield in ethyl acetate (EA) degradation, with TOF reaches 7.76 × 10−3 s−1 at 160 °C under GHSV of 50,000 h-1. Moreover, Pd/Al 2 O 3 -pm exhibits satisfied performance in EA-contained binary VOCs oxidation and has high long-term stability under both dry and humid conditions. Both Pd sites and Brønsted acid sites participated in reaction process and initially react with EA to form ethylene and ethanol, respectively. Larger amount Brønsted acid sites over Pd/Al 2 O 3 -pm promote ethanol formation and C-C cleavage, resulting in different CO 2 yields and EA activation mechanisms. The coating greatly enhances Pd dispersion over Pd supported monolithic catalyst, endowing its desired activity and stability even with a much lower Pd loading. This work promotes the potential application of noble-metal-based monolithic materials in VOC degradation. [ABSTRACT FROM AUTHOR]