An investigation on catalytic performance and reaction mechanism of RuMn/meso-TiO2 derived from RuMn intermetallic compounds for methyl ethyl ketone oxidation

Acid-etched spinel CoMn2O4 with highly active surface lattice oxygen species for significant improvement of catalytic performance of VOCs oxidation

PdPtVOx/CeO2−ZrO2: Highly efficient catalysts with good sulfur dioxide-poisoning reversibility for the oxidative removal of ethylbenzene

Surface lattice oxygen activation via Zr4+ cations substituting on A2+ sites of MnCr2O4 forming ZrxMn1−xCr2O4 catalysts for enhanced NH3-SCR performance

Kinetic and mechanistic studies were conducted on the isoprene oxidation products methacrolein, methyl vinyl ketone, methacrylic and acrylic acid reacting with hydroxyl and nitrate radicals and sulfate radical anions in aqueous solution by use of the laser flash photolysis technique and a reversed-rate method for kinetics. High-performance liquid chromatography/mass spectrometry was applied for product analysis. The kinetic investigations show the highest reactivity of the hydroxyl radical followed by sulfate and nitrate radicals. For methacrolein and methyl vinyl ketone the following rate constants have been determined at 298 K: k(OH+methacrolein) = (9.4 ± 0.7) × 10(9) M(-1) s(-1), k(OH+methyl vinyl ketone) = (7.3 ± 0.5) × 10(9) M(-1) s(-1), k(NO3+methacrolein) = (4.0 ± 1.0) × 10(7) M(-1) s(-1), k(NO3+methyl vinyl ketone) = (9.7 ± 3.4) × 10(6) M(-1) s(-1), k(SO4(-)+methacrolein) = (9.9 ± 4.9) × 10(7) M(-1) s(-1) and k(SO4(-)+methyl vinyl ketone) = (1.0 ± 0.2) × 10(8) M(-1) s(-1). Temperature and pH dependencies of the reactions of OH, NO3 and SO4(-) with methacrolein, methyl vinyl ketone, methacrylic and acrylic acid as well as Arrhenius parameters have been obtained and discussed. Product studies were performed on the OH radical induced oxidation of methacrolein and methyl vinyl ketone. In the reaction of methacrolein + OH methylglyoxal and hydroxyacetone were identified as first oxidation products with yields of 0.099 and 0.162. Methylglyoxal was primarily produced in the oxidation of methyl vinyl ketone with a yield of 0.052. For both precursor compounds the formation of glycolaldehyde was observed for the first time with yields of 0.051 and 0.111 in the oxidation of methacrolein and methyl vinyl ketone, respectively. Furthermore, highly functionalised C4 compounds were determined from the oxidation of both precursor compounds, but for the first time for methyl vinyl ketone. Reaction schemes were developed based on known peroxyl radical reaction mechanisms. The aqueous phase conversion of the first generation isoprene oxidation products can potentially contribute to tropospheric aqueous phase budgets of important carbonyl and dicarbonyl components which are expected to be conducive to the formation of aqSOA.

The development of efficient and stable catalysts is of great importance for the elimination of volatile organic pollutants (VOCs). In this work, AuPdx nanoparticles (NPs) were loaded on TiO2 through the electrostatic adsorption approach to generate the yAuPdx/TiO2 (i.e., 0.35AuPd0.46/TiO2, 0.34AuPd2.09/TiO2, and 0.37AuPd2.72/TiO2; x and y are Pd/Au molar ratio and AuPdx loading, respectively; x = 0.46–2.72; and y = 0.34–0.37 wt%) catalysts, and their catalytic activities for the oxidation of ethyl acetate were determined. The results showed that the 0.37AuPd2.72/TiO2 sample exhibited the best activity (T50% = 217 °C and T90% = 239 °C at SV = 40,000 mL/(g h), Ea = 37 kJ/mol, specific reaction rate at 220 °C = 113.8 µmol/(gPd s), and turnover frequency (TOFNoble metal) at 220 °C = 109.7 × 10−3 s−1). The high catalytic performance of the 0.37AuPd2.72/TiO2 sample was attributed to the good dispersion of AuPd2.72 NPs, the strong redox ability, the large ethyl acetate adsorption capacity, and the strong interaction between AuPdx and TiO2. Acetaldehyde, ethanol, and acetic acid are the main intermediates in the oxidation of ethyl acetate, and the loading of AuPdx NPs effectively reduces the formation of the toxic by-product acetaldehyde. The oxidation of ethyl acetate over the 0.34AuPd2.09/TiO2 sample might occur via the pathway of ethyl acetate → ethanol → acetic acid → acetate → CO2 and H2O. We believe that the obtained results may provide a useful idea for the design of bimetallic catalysts under industrial conditions and for understanding the VOCs oxidation mechanisms.

In the removal of volatile organic compounds (VOCs), Co3O4 catalysts with various morphologies are highly efficient due to rich active sites such as Co3+, adsorbed oxygen, and surface lattice oxygen species. It is worthwhile further disclosing the crucial roles and reaction mechanism of these active sites. The facile and uniform metal–organic framework (MOF) derivation method was selected to synthesize Co3O4 catalysts with different shapes for the catalytic oxidation of o-xylene: rod-like Co3O4-R exhibited a lower T90% of 270 °C, superior stability, and water resistance compared with spherical Co3O4-S. The enhanced catalytic performance of Co3O4-R probably originated from its more active surface lattice oxygen, namely, twofold-coordinate lattice oxygen (O2f), on exposed (220) planes, which gave rise to larger CO2 generation as revealed by HR-TEM, O2-TPD, and o-xylene-TPD. In situ DRIFTS study also showed that Co3O4-R adsorbed and oxidized more o-xylene via surface O2f, forming intermediates including alkoxide, carboxylate, and anhydride species and leaving oxygen vacancy. After the introduction of gaseous oxygen, the disappearance of intermediates occurred more rapidly on Co3O4-R owing to the good oxygen mobility. The lower formation energy of oxygen vacancy (EOv, 2.61 eV) and higher adsorption energy of oxygen (Eads,O2, −1.71 eV) on Co3O4-R theoretically confirmed the easier oxygen vacancy formation and gaseous oxygen replenishment on Co3O4-R due to the existence of active O2f on the surface. Therefore, the role of surface O2f in oxygen vacancy formation and gaseous oxygen replenishment crucially contributed to the enhanced catalytic oxidation of o-xylene over MOF-derived Co3O4 catalysts with different shapes. This study might shed light on the thorough understanding of active oxygen species in VOC catalytic oxidation and the preparation of efficient catalysts with various morphologies.

Controllable hydrogen release from NH3BH3 hydrolysis over Ru ultrafine particles stabilized on agriculture waste-derived carbon

Oxidation of ketones over metal oxide catalysts: I. Catalytic synthesis of biacetyl from methyl ethyl ketone

Three-dimensional (3D) ordered mesoporous Ag/Co3O4 and K–Ag/Co3O4 catalysts were successfully prepared on the basis of 3D-Co3O4. All catalysts possess 3D mesoporous structures, which are not affected due to Ag and K addition. Ag nanoparticles, uniformly dispersed and supported on the polycrystalline wall of K–Ag/Co3O4, provide sufficient active sites for HCHO oxidation reaction. 1.7% K–Ag/Co3O4 has turnover frequencies (TOFs) of 0.22 s–1 at 60 °C and 2.62 s–1 at 100 °C, and its HCHO conversion at room temperature is 55% (HCHO 100 ppm and GHSV 30000 h–1). The addition of K+ ions obviously promotes the catalytic performance for HCHO oxidation due to surface OH– species provided by K+ ions and more abundant Ag(111) active faces, Co3+ cations and surface lattice oxygen (O2–) species generated by stronger interaction between Ag and Co and anion lattice defects. Ag(111) faces, Co3+ ions, and O2– are active species. Combined with TOFs, at low temperature (<80 °C), the HCHO catalytic activity on K–Ag/Co3O4 catalyst largely depends on the surface OH– species at the perimeter of the Ag(111) facets; at relatively high temperature (>80 °C), the surface OH– species are consumed and replaced quickly, and their supplement relies on the migration of O2– species from 3D-Co3O4 support. The pathway of reaction for HCHO oxidation on the K–Ag/Co3O4 follows the HCHO → CHOO– + OH– → CO2 + H2O route.

Diacetyl synthesis by the direct partial oxidation of methyl ethyl ketone over vanadium oxide catalysts

Catalytic performance and moisture and sulfur dioxide resistance are important for a catalyst used for the oxidation of volatile organic compounds (VOCs). Supported noble metals are active for VOC oxidation, but they are easily deactivated by water and sulfur dioxide. Hence, it is highly desired to develop a catalyst with high performance and good moisture and sulfur dioxide resistance in the oxidation of VOCs. In this work, we first adopted the hydrothermal method to synthesize a V2O5-TiO2 composite support, and then employed the polyvinyl alcohol (PVA)-protecting NaBH4 reduction strategy to fabricate xPdPty/V2O5-TiO2 catalysts (x and y are the PdPty loading (0.41, 0.46, and 0.49 wt%) and Pt/Pd molar ratio (2.10, 0.85, and 0.44), respectively; the corresponding catalysts are denoted as 0.46PdPt2.10/V2O5-TiO2, 0.41PdPt0.85/V2O5-TiO2, and 0.49PdPt0.44/V2O5-TiO2). Among all the samples, 0.46PdPt2.10/V2O5-TiO2 exhibited the best catalytic activity for toluene oxidation (T50% = 220 °C and T90% = 245 °C at a space velocity of 40,000 mL/(g h), apparent activation energy (Ea) = 45 kJ/mol), specific reaction rate at 230 °C = 98.6 μmol/(gPt s), and turnover frequency (TOFNoble metal) at 230 °C = 142.2 × 10−3 s−1. The good catalytic performance of 0.46PdPt2.10/V2O5-TiO2 was associated with its well-dispersed PdPt2.10 nanoparticles, high adsorbed oxygen species concentration, good redox ability, large toluene adsorption capacity, and strong interaction between PdPty and V2O5-TiO2. No significant changes in toluene conversion were detected when 5.0 vol% H2O or 50 ppm SO2 was introduced to the reaction system. According to the characterization results, we can realize that vanadium is the main site for SO2 adsorption while PdO is the secondary site for SO2 adsorption, which protects the active Pt site from being poisoned by SO2, thus making the 0.46PdPt2.10/V2O5TiO2 catalyst show good sulfur dioxide resistance.

Catalytic performance and SO2 resistance of zirconia-supported platinum-palladium bimetallic nanoparticles for methane combustion

Mesoporous Si-WO3-supported Pt catalysts with high catalytic performance and excellent water resistance for toluene oxidation

Methacrolein (MAC) and methyl vinyl ketone (MVK), two major first‐generation products in the oxidation of isoprene, play important roles in tropospheric chemistry. However, little is known about their heterogeneous fate. Here we investigated the heterogeneous reactions of MAC and MVK on particles of silicon dioxide (SiO2), the major constituent of mineral dust in the troposphere, under simulated tropospheric conditions. We first investigated the adsorption and desorption processes. It was found that MAC and MVK molecules were adsorbed onto the surface of SiO2 particles by van der Waals forces and hydrogen bonding forces in a non‐reactive state, and the presence of water vapor did not result in the formation of new substances but could decrease the adsorption ability by consuming isolated hydroxyl groups on the surface of SiO2 particles. The initial adsorption and desorption rates, initial uptake coefficients, and adsorption concentrations at equilibrium were determined at different relative humidities. Notably, in the desorption process, a considerable amount of MAC or MVK molecules remained on SiO2 particles in dry air but were almost completely desorbed in high‐humid air. We also investigated the heterogeneous ozonolysis of MAC and MVK adsorbed onto SiO2 particles, determining product yields at different relative humidities. The heterogeneous ozonolysis of MAC and MVK adsorbed onto SiO2 particles yielded formaldehyde and methylglyoxal as the major secondary carbonyl products and formic acid and acetic acid as the major organic acid products, as in their gas‐phase ozonolysis. However, the yield of two major organic peroxides, methyl hydroperoxide and hydroxymethyl hydroperoxide, was much greater in their heterogeneous ozonolysis than in their gas‐phase ozonolysis. The mechanisms of heterogeneous ozonolysis of MAC and MVK onto the SiO2 surface are deduced.

Investigation on isobaric vapor–liquid equilibrium for acetic acid + water + methyl ethyl ketone + isopropyl acetate