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Highly active and stable spinel-oxide supported gold catalyst for gas-phase selective aerobic oxidation of cyclohexanol to cyclohexanone

\u3cp\u3eHighly dispersed gold nanoparticles supported on Cu-doped spinel oxides were prepared by a simple deposition-precipitation method. The results indicate that Au/MgCuCr\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e catalyst is very efficient for gas-phase oxidation of cyclohexanol to cyclohexanone, giving 69.5% and 86.4% yield of cyclohexanone at 260 °C and 300 °C, respectively. Deactivation was not observed in a 100 h stability test. This excellent performance can be correlated with the highly stable gold nanoparticles in the reaction deriving from the strong gold-support interaction and efficient Au–Cu synergy.\u3c/p\u3

Gas-phase selective oxidation of cyclohexanol to cyclohexanone over Au/Mg\u3csub\u3e1-x\u3c/sub\u3eCu\u3csub\u3ex\u3c/sub\u3eCr\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e catalysts:On the role of Cu doping

\u3cp\u3eThe industrial production of cyclohexanone from cyclohexanol would benefit from a selective oxidation catalyst. Herein, Cu doping of MgCr\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e supports for gold nanoparticles active in gas-phase oxidation of cyclohexanol was investigated. Mg\u3csub\u3e1-x\u3c/sub\u3eCu\u3csub\u3ex\u3c/sub\u3eCr\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e exhibited spinel structures (x ≤ 0.25: MgCr\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e; x = 1: CuCr\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e) onto which 3–4 nm gold nanoparticles could be dispersed. Cu doping led to higher activity. During reaction, surface Cu\u3csup\u3e2+\u3c/sup\u3e was reduced to Cu\u3csup\u3e0\u3c/sup\u3e, resulting in Au–Cu alloy formation. At low temperature, low-Cu-content catalysts (x ≤ 0.1) showed higher activity than high-Cu-content catalysts, likely because the Au–Cu alloy with highly diluted Cu was more active for the dehydrogenation step of cyclohexanol. However, Au/Mg\u3csub\u3e0.99\u3c/sub\u3eCu\u3csub\u3e0.01\u3c/sub\u3eCr\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e and Au/Mg\u3csub\u3e0.9\u3c/sub\u3eCu\u3csub\u3e0.1\u3c/sub\u3eCr\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e showed lower cyclohexanol conversion at high temperature than samples with high Cu content, because O\u3csub\u3e2\u3c/sub\u3e activation involving Cu becomes rate-limiting. Stable cyclohexanol conversion and cyclohexanone selectivity were 99.1% and 90.2% (space-time yield of 266 g\u3csub\u3eKetone\u3c/sub\u3e g\u3csub\u3eAu\u3c/sub\u3e \u3csup\u3e−1\u3c/sup\u3e h\u3csup\u3e−1\u3c/sup\u3e) for Au/Mg\u3csub\u3e0.25\u3c/sub\u3eCu\u3csub\u3e0.75\u3c/sub\u3eCr\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e at 300 °C.\u3c/p\u3

Why Clays Swell

The particularly difficult subject of predicting the swelling behavior of clay minerals is addressed by a combination of mol. dynamics and Monte Carlo sampling techniques. The introduced algorithm essentially mimics the exptl. detn. of the water adsorption isotherm and quant. predicts clay swelling for a montmorillonite-type clay including such details as the occurrence of hydrated states and hysteresis. Furthermore, important insights into the underlying mechanism of clay swelling from the one-layer to the two-layer hydrate are derived. It turns out that, for this case, clay swelling proceeds via the migration of counterions that are initially bound to the mineral surface to the central interlayer plane where they become fully hydrated. The extent of clay swelling strongly depends on the charge locus. This information appears to be transferable to other clay types. [on SciFinder (R)

A model compound (methyl oleate, oleic acid, triolein) study of triglycerides hydrodeoxygenation over alumina-supported NiMo sulfide

We studied hydrodeoxygenation of model compounds for vegetable oil into diesel-range hydrocarbons on a sulfided NiMo/γ-Al2O3 catalyst under trickle-flow conditions. Methyl oleate (methyl ester of oleic acid, a C18 fatty acid with one unsaturated bond in the chain) represented the C18 alkyl esters in natural fats, oils and greases. The effect of temperature and pressure on activity and product distribution (mainly C17 and C18 hydrocarbons) were studied. Hydrolysis of the methyl ester results in fatty acid intermediates, which are converted by direct hydrodeoxygenation to C18 hydrocarbons or decarbonated (by decarbonylation or decarboxylation) to C17 hydrocarbons. Reactant inhibition is more pronounced for the former route. The reaction is hardly inhibited by H2S, H2O, CO and tetralin solvent. H2S and to a lesser extent H2O increase the C17/C18 hydrocarbon ratio, because they inhibit direct hydrodeoxygenation more than decarbonation. The catalyst surface contains different sites for direct hydrodeoxygenation and decarbonation reactions. During methyl oleate HDO, the catalyst slowly deactivated, mainly due to blocking of Lewis acid sites of the alumina support that catalyze methyl oleate hydrolysis. The catalyst was much more active in the HDO of triolein (glyceryl trioleate, representative triglyceride model compound) than in methyl oleate HDO, to be attributed to very facile hydrolysis of triglycerides. Although the overall kinetics of methyl oleate and triolein HDO were similar, our results show that the catalyst and H2S play a much more important role in the hydrolysis of methyl oleate than in hydrolysis of triglycerides

A real support effect on the hydrodeoxygenation of methyl oleate by sulfided NiMo catalysts

The effect of the support on the catalytic performance of sulfided NiMo in the hydrodeoxygenation of methyl oleate as a model compound for triglyceride upgrading to green diesel was investigated. NiMo sulfides were prepared by impregnation and sulfidation on activated carbon, silica, γ-alumina and amorphous silica-alumina (ASA). High sulfidation degrees were obtained in all cases. Despite the use of a chelating agent to minimize metal-support interactions, the support had a significant influence on the morphology of the active phase (MoS2 dispersion and stacking). All catalysts convert methyl oleate to C17 and C18 olefins and paraffins. Initially, NiMo/Al2O3 and NiMo/ASA displayed the highest overall HDO activity, but these catalysts deactivated slowly during the week on stream. Finally, they exhibited similar activity as NiMo/SiO2. NiMo/C and NiMo/SiO2 did not deactivate. The NiMo/C catalyst was appreciably more active than the others after prolonged reaction. The high initial and then deactivating performance of NiMo/Al2O3 and NiMo/ASA is due to the Lewis acidity of surface Al species active in methyl oleate hydrolysis. It has earlier been demonstrated that deposition of heavy products on the alumina surface deactivates these sites. SiO2 lacks such sites, resulting in lower catalytic performance. The NiMo/C support is more active in methyl oleate hydrolysis. This can be either due to intrinsically higher activity of the metal sulfide on carbon or to acidic surface groups. Besides, the reaction data show that the C18 hydrocarbons selectivity for NiMo/SiO2 and NiMo/C was substantially higher than for the other two catalysts. Clearly, the support has a significant influence on the performance of NiMo sulfide in methyl oleate HDO. The use of activated carbon as the support presents high and stable HDO activity of methyl oleate with good C18 hydrocarbons selectivity