Selective Conversion of Ethane to Ethene via Oxidative Dehydrogenation Over Ca-doped ThO2 Using CO2 as Oxidant

Ca-doped ThO2, synthesized by solution combustion method was tested for dehydrogenation of ethane with CO2. Doping ThO2 with Ca resulted in the creation of oxide ion vacancies and an increased conversion of ethane compared to pure ThO2. On Th0.75Ca0.25O2 selectivity to ethene was 97 at 46% ethane conversion at 725°C. Well-known reference catalysts like 5%Cr/TS-1 or OMS-2 showed significantly lower selectivity, but the former was more active under the same condition

Feasibility of Methyl Mercaptane as Probe Molecule for Supported Gold Nanoparticle Surface Area Determination

Gold nanoparticles supported on TiO2 were probed by adsorption of methyl mercaptane (MM), and the process was quantified gravimetrically. This method allowed discrimination between weakly adsorbed (physisorbed) and strongly bound (chemisorbed) methyl mercaptane. Strong adsorption of MM occured on exposed Au faces, while low-temperature pre-treatment (30 °C) completely suppressed adsorption of MM on the TiO2 support. The thus obtained high selectivity of MM adsorption on Au enabled characterization of the gold surface area and the resulting values are comparable with other noble metal systems of similar average particle size. The estimated adsorption stoichiometry indicates that the entire Au surface is probed

Selective Conversion of Ethane to Ethene via Oxidative Dehydrogenation Over Ca-doped ThO2 Using CO2 as Oxidant

ISSN:1022-5528ISSN:1572-902

Increasing the Brønsted acidity of flame-derived silica/alumina up to zeolitic strength

Silica/alumina was prepared in milliseconds by flame-spray pyrolysis (see picture) with a homogeneous composition and at super-high calcination temperatures. This solid acid has tunable acidity ranging from weak or moderate to strong Brønsted acidity. This unique property makes this material versatile for desired industrial applications.6 page(s

Oxidative coupling of methane over Ca- and alkali metal-doped ThO₂

Th₀.₈Ca₀.₂O₂₋δ and Na/K dispersed Th₀.₈Ca₀.₂O₂₋δ catalysts, synthesized by the citric acid gel method, have been tested concerning their efficiency in the oxidative coupling of methane. The structural properties of the catalysts were characterized by BET, XRD, Raman, TEM, TPD, and EPR techniques. The presence of oxide ion vacancies due to Ca ion incorporation into ThO₂ lattice was evidenced by Raman spectroscopy. EPR revealed the formation of radical oxygen in the Ca-doped ThO₂ sample after oxygen treatment at 500 °C. Th₀.₈Ca₀.₂O₂₋δ showed high catalytic activity reaching about 24% methane conversion (rate: 2.3 mol g⁻¹ h⁻¹) at 56% selectivity toward Cn₊ products at 600°C, whose performance is comparable to that of the well known Sr doped La₂O₃ catalyst. Other reference catalysts like 1.9%Mn-4%Na₂WO₄/SiO₂ and 5%Li/MgO showed considerably lower activity under these conditions. The high catalytic activity and selectivity of the Ca-doped sample is likely due to formation of stable active Ȯ⁻ species in the oxide ion vacancy site in the lattice.10 page(s

Tuning the support acidity of flame-made Pd/SiO₂-Al₂O₃ catalysts for chemoselective hydrogenation

Palladium nanoparticles on silica-alumina (Pd/SA) with tunable surface acidity were prepared by single-step flame spray pyrolysis and tested for the chemoselective hydrogenation of acetophenone under solvent-free conditions in a stirred autoclave at 50 bar. Quantitative solid-state NMR spectroscopy of the catalysts with different Si/Al ratio revealed that the concentration of Brønsted acid sites in these catalysts increases with increasing aluminum content up to 70 at%. The support acidity directly influenced the electronic properties of the Pd nanoparticles as proved by DRIFT spectroscopy with CO as probe molecule. Pd/SA with 15 at% aluminum (Pd/SA-15) exhibited excellent chemoselectivity for CO bond hydrogenation of acetophenone. At 170 °C and 50 bar H₂, acetophenone was converted to ethylbenzene with a selectivity of 99.9%. Beside 0.1% 1-phenylethanol, no other by products were detected. Further enhancement of the support acidity in catalysts with higher Al content resulted in higher reaction rate (TOF) and in additional products originating from the competitive hydrogenation of the aromatic ring.9 page(s

SrO·Al₂O₃ mixed oxides : a promising class of catalysts for oxidative coupling of methane

Varying the composition of Sr-Al oxides, mixed as well as single phase compounds were prepared and characterized extensively by XRD, NMR, TEM, EPR, XPS, and TPD. Depending on synthesis method and precursors, Sr/Al-based materials with different crystalline phases (e.g., Sr₃Al₄O₉·2H₂O, double perovskite, SrAl₄O₇, SrAl₂O₄, and SrCO₃) were obtained. Apart from these crystalline phases, several other species were present, as identified by solid state NMR and TG-MS. The ratio of tetrahedrally to octahedrally coordinated Al (AlIV/AlVI) in the Sr/Al mixed oxides increased from 0.5 (pure alumina) to 5.2 in Sr/Al = 1.25, as determined by solid state NMR. The performance of these catalysts in the oxidative coupling of methane depended on the AlIV/AlVI ratio, both activity as well as C₂₊ selectivity increased with increasing Sr-content. The catalyst with a Sr/Al ratio of 1.25 showed a performance comparable to the well-known catalyst 1.9%Mn-4%Na₂WO₄/SiO₂ under the conditions used (810°C, CH₄:O₂=108:22, GHSV∼26,000L/kg cat h).13 page(s