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Applied Catalysis A, General (v.314, #2)
Carbided Y zeolite-supported molybdenum: On the genesis of the active species, activity and stability in benzene hydrogenation by A.S. Rocha; V. Teixeira da Silva; A.C. Faro Jr. (pp. 137-147).
The properties of molybdenum catalysts prepared by temperature-programmed decomposition of Mo(CO)6 adsorbed on de-aluminated Y zeolites were studied as a function of the silica–alumina ratios and sodium contents of the zeolite supports. The effect of the gas stream during activation was also studied.The catalysts were tested in benzene hydrogenation, and the catalysts and zeolite supports were characterized by several methods, including temperature-programmed decomposition of adsorbed n-propylamine, N2 adsorption and29Si NMR.The highest hydrogenation activity was obtained with the catalysts activated under a 20% (v/v) CH4/H2 gas mixture using temperature programming up to 923K. Activity increased with decreasing protonic acidity of the zeolite support. Catalyst stability increased in the same direction due to production of alkylation products in the more acidic zeolites.
Keywords: Benzene hydrogenation; Molybdenum carbide; Molybdenum hexacarbonyl; Y zeolite
Hydrophobic, solid acid catalysts for production of biofuels and lubricants by P.S. Sreeprasanth; R. Srivastava; D. Srinivas; P. Ratnasamy (pp. 148-159).
A novel application of Fe–Zn double-metal cyanide (DMC) complexes as solid acid catalysts in the preparation of fatty acid alkyl esters (biodiesel/biolubricants) from vegetable oils is reported. Unlike the homogeneous or other solid catalysts (like ZnO-Al2O3, for example), the Fe–Zn DMC catalysts are highly active even for the simultaneous transesterification of triglycerides and esterification of the free fatty acids present in unrefined and waste cooking oils as well as non-edible oils. They are also tolerant of water, probably, due to their surface hydrophobicity. ▪A novel application of Fe–Zn double-metal cyanide (DMC) complexes as solid catalysts in the preparation of fatty acid alkyl esters (biodiesel/biolubricants) from vegetable oils is reported. The catalysts are hydrophobic (no H2O adsorption at reaction temperatures) and contain only Lewis acidic sites (NH3 and pyridine adsorption). Brönsted acid sites are absent (absence of 1546 and 1639cm−1 bands on adsorption of pyridine). Basic sites are also absent (no CO2 adsorption). Unlike the homogeneous or other solid catalysts (like ZnO–Al2O3, for example), the Fe–Zn, DMC catalysts are highly active even for the simultaneous transesterification of triglycerides and esterification of the free fatty acids (FFA) present in unrefined and waste cooking oils as well as non-edible oils. They are also tolerant of water, probably, due to their surface hydrophobicity. A relationship between the transesterification activity and the concentration of strong Lewis acid sites has been observed. Coordinatively unsaturated Zn2+ ions in the structure of the Fe–Zn complex are the probable active sites.
Keywords: Transesterification of vegetable oils; Alcoholysis of vegetable oils; Esterification of free fatty acids; Fatty acid alkyl esters; Fatty acid methyl esters; Biodiesel; Biolubricants; Double-metal cyanides (DMC); Solid Fe–Zn catalysts
Stabilization effect of phosphorus on steamed H-MFI zeolites by G. Caeiro; P. Magnoux; J.M. Lopes; F. Ramôa Ribeiro; S.M.C. Menezes; A.F. Costa; H.S. Cerqueira (pp. 160-171).
The effect of the introduction of phosphorus on H-MFI zeolite before and after hydrothermal treatment was studied. The samples were characterized by XRF, nitrogen adsorption,27Al and31P MAS NMR, n-propylamine temperature-programmed decomposition, n-hexane cracking and vacuum gasoil cracking. Results showed that P stabilizes the MFI zeolite structure by preventing the segregation of the framework Al atoms during the steaming treatment. Although there is an optimum phosphorus content, its effect on the selectivity towards light olefins will depend on the severity of the steaming treatment, i.e., with more severe treatment the stabilization is more evident. NMR results evidenced the presence of several types of aluminium and phosphorus species. Besides the classical framework tetracoordinated Al, which is the main responsible for the acidity of the samples, another tetrahedral aluminium probably in a distorted environment also seems to be active in n-hexane cracking, besides favouring the light olefins production during gasoil cracking.
Keywords: MFI zeolite; Cracking; Phosporus; NMR; n; -Hexane; Acidity; Active site
Evaluation of the sodium effect on the physicochemical properties of Mo/SnO2 catalysts by Isaque Cardoso da Silva; Lucia G. Appel; Silvana Braun (pp. 172-178).
The effect of sodium addition on the physicochemical properties of Mo/SnO2 catalysts was studied. The catalysts were prepared by precipitation using aqueous solution of ammonium heptamolybdate in two Mo amounts (5.5 and 14.5% (wt)); afterwards they were impregnated with sodium ion (1% wt). The solids were characterized by nitrogen adsorption, X-ray diffraction, UV–vis diffuse reflectance spectroscopy, FTIR, and FTIR of adsorbed pyridine in order to evaluate changes on Mo species and textural and acidic properties. The results have shown that Mo/SnO2 samples present dispersed isolated tetrahedral Mo species. The addition of sodium ion to Mo/SnO2 catalysts promotes the transformation of dispersed isolated tetrahedral Mo species into dispersed two-dimensional polymolybdates and also causes changes in textural and acidic properties of these Mo/SnO2 catalysts.
Keywords: Molybdenum; Tin oxide; Lewis; Brønsted; Pyridine
Decomposition of water in the separate evolution of hydrogen and oxygen using visible light-responsive TiO2 thin film photocatalysts: Effect of the work function of the substrates on the yield of the reaction by Masaaki Kitano; Koichiro Tsujimaru; Masakazu Anpo (pp. 179-183).
The development of visible light-responsive TiO2 thin films (vis-TiO2) was successfully carried out by applying a radio-frequency magnetron sputtering (RF-MS) deposition method. The Pt-loaded vis-TiO2 thin films clearly showed high potential for the decomposition of water into H2 and O2 by the evolution of H2 from methanol/water as well as O2 from a silver nitrate/water system under both UV and visible light irradiation ( λ≥420nm). These thin films were found to decompose pure water into H2 and O2 stoichiometrically under light irradiation of wavelengths longer than 390nm. Next, a novel TiO2 thin film photocatalyst was prepared on various metal substrates such as Al, Fe, Pd, Pt, Ti and Zr, while nanoparticles of Pt were deposited on the other side of these substrates. The reaction rate was revealed to increase with a decrease in the work function ( ϕ) of the substrate. Moreover, the separate evolution of H2 and O2 could be successfully achieved under solar light irradiation by applying these thin film photocatalysts in an H-type glass container consisting of two water phases separated by a TiO2 thin film and proton-exchange membrane.
Keywords: Photocatalytic decomposition of water; Hydrogen production; Titanium oxide photocatalyst; Separate evolution of hydrogen and oxygen; Visible light; Solar light
Catalytic cracking and coking of (cyclo)alkane/1-octene mixtures on an equilibrium catalyst by R. Quintana-Solórzano; J.W. Thybaut; G.B. Marin (pp. 184-199).
N-decane and n-butylcyclohexane admixed with 1-octene are cracked in the presence of coke formation on an equilibrium catalyst in an oscillating microbalance TEOM® reactor. ▪Catalytic cracking of n-decane and n-butylcyclohexane spiked with 1-octene to promote coke formation has been performed in a temperature range 693–753K and (cyclo)alkane inlet partial pressure in the range 13.3–26.6kPa in an oscillating microbalance reactor on a commercial REUSY (rare earth-modified ultrastable Y zeolite) equilibrium catalyst. The catalyst is severely deactivated during the first minutes of the reaction, while the catalyst activity becomes practically asymptotic at long times on stream. The cracking of n-decane/1-octene mainly yields alkanes and alkenes, while that of n-butylcyclohexane/1-octene leads to alkanes, alkenes, cycloalkanes and aromatics. The coke selectivity increases with (cyclo)alkane conversion but decreases with temperature. It is significantly higher for n-decane/1-octene compared with n-butylcyclohexane/1-octene for a given (cyclo)alkane conversion. When cracking n-decane/1-octene, coke was associated to the formation of bulky oligomers formed via alkylation of (branched) C8+ alkylcarbenium ions with alkenes. Fed with n-butylcyclohexane, the conversion of 1-octene to coke proceeds via a more complicated mechanism involving alkenylcarbenium ions and ultimately aromatics. At the observed coke levels, coke formation negatively affects the rate of protolysis, hydride transfer and beta-scission as well as coking. At identical (cyclo)alkane conversions, however, the product distributions are not affected by the coke content of the catalyst except for typical protolysis products. The latter increases with coke content at a given conversion.
Keywords: Catalytic cracking; (Cyclo)alkanes; Alkenes; Hydride transfer; Coke; Coke content; Deactivation
Infiltration and immobilization of catalyst particles into the confined space of microstructured reactors via layer-by-layer self-assembly by H. Qiu; L. Bednarova; W.Y. Lee (pp. 200-207).
Layer-by-layer (LbL) self-assembly was explored as a new coating method for assembling, infiltrating, and immobilizing catalyst particles in the confined space of microstructured reactors. One layer of negatively charged ∼3μm Pd/Na–Al(Si)O catalyst particles was electrostatically deposited on Si, SiC, and stainless steel substrates. The substrates were made to be positively charged by applying a ∼20nm-thick polyelectrolyte multilayer (PEM). The PEM and particle deposition steps were repeated to build a four-layer catalyst particle assembly. Surface coverage, microstructural morphology, and uniformity of the four-layer catalyst particle assembly prepared on the flat Si surface and on the skeleton surface inside the cellular SiC structure with ∼400μm interconnected cells were similar, demonstrating the non-line-of-sight infiltration attribute of the LbL self-assembly technique. The four-layer assembly deposited on the inner wall of the stainless capillary tube with a 780μm inner diameter was mechanically stable under a water flow rate up to 10ml/min over a pH range of 3–11. Scotch tape peeling evaluation suggested that failure locations during peeling were mostly within the catalyst particle assembly, but near the assembly-PEM interface region. The study of catalyst performance in the hydrogenation of acetylene showed that activity and selectivity of the catalyst particles were not affected by the LbL self-assembly procedures.
Keywords: Layer-by-layer self-assembly; Multilayer particle assembly; Microstructured reactors or microreactors; Catalyst coating; Infiltration and immobilization; Hydrogenation of acetylene
Kinetics of ruthenium(III)-catalysed oxidation of paracetamol by diperiodatonickelate(IV) in aqueous alkaline medium (stopped flow technique) by R.M. Mulla; H.M. Gurubasavaraj; S.T. Nandibewoor (pp. 208-215).
The kinetics of ruthenium(III)-catalysed oxidation of paracetamol by diperiodatonickelate(IV) (DPN) in aqueous alkaline medium at a constant ionic strength of 1.0moldm−3 was studied spectrophotometrically using a rapid kinetic accessory. The reaction exhibits 1:2 stoichiometry (DPN:paracetamol). The reaction shows first order dependence on [DPN] and [ruthenium(III)] and (apparent) less than unit order in both [paracetamol] and [alkali] under the experimental conditions. However, the order in [paracetamol] and [alkali] changes from first order to zero order as the concentrations change from lower to higher concentrations. Addition of periodate has a retarding effect on the reaction. The effects of added products, ionic strength and dielectric constant of the reaction medium have been investigated. The main products were identified by spot test, IR and NMR. A mechanism involving the monoperiodatonickelate(IV) (MPN) as the reactive species of the oxidant has been proposed. The active species of ruthenium(III) is understood as [Ru(H2O)5OH]2+. The reaction constants involved in the different steps of mechanism are calculated. The activation parameters with respect to the slow step of the mechanism are computed and discussed and thermodynamic quantities are also calculated.
Keywords: Kinetics; DPN; Oxidation; Paracetamol; Ruthenium(III) catalysis
Manganese(III) porphyrin-encapsulated Ti,Si-mesoporous molecular sieves as heterogeneous catalysts for the epoxidation of alkenes by A. Kalilur Rahiman; K. Rajesh; K. Shanmuga Bharathi; S. Sreedaran; V. Narayanan (pp. 216-225).
The cationic manganese-porphyrin, [ meso-tetrakis(4-trimethylammoniophenyl)porphyrinato]manganese(III) pentachloride (MnTAPP) was encapsulated on well-defined pores of titanium substituted mesoporous materials; the synthesized composites provided good catalytic activity and epoxide selectivity. These heterogeneous catalysts were re-used successively under the same reaction conditions. ▪The mesoporous molecular sieves containing different amounts of titanium were synthesized using cetyltrimethylammonium bromide (CTAB) as the structure-directing agent and tetraethyl orthotitanate (TEOT) as the source of titanium. The heterogeneous catalysts were obtained by encapsulating cationic manganese-porphyrin, [ meso-tetrakis(4-trimethylammoniophenyl)porphyrinato]manganese(III) pentachloride (MnTAPP) into the titanium-substituted mesoporous molecular sieves. Both the type of catalysts, i.e., supported and unsupported were characterized by FTIR, TGA, low-angle X-ray diffraction, nitrogen adsorption isotherm, scanning electron microscopy and DRUV–vis spectroscopy. A combined study on the characterization and catalytic performance of MnTAPP supported systems suggests the successful encapsulation of MnTAPP inside the mesoporous molecular sieves. The catalytic activity of the manganese(III) porphyrin-encapsulated materials was tested in the epoxidation of cyclohexene and styrene using iodosylbenzene (PhIO) as oxygen source. When compared to the homogeneous system, the manganese(III) porphyrin-encapsulated materials show higher activity for the epoxidation reactions. The activity and selectivity of these heterogeneous catalysts were also compared with a heterogeneous catalyst containing no titanium and with unsupported molecular sieves. The former shows lower activity than the heterogeneous catalyst prepared by encapsulating MnTAPP onto titanium-substituted molecular sieves, whereas the latter was inactive in the oxidation of both cyclohexene and styrene. The selectivity of these heterogeneous catalysts does not change appreciably after three times of reusing, but their catalytic activity decreases marginally. The decrease in the activity may be due to some leaching and/or decomposition of MnTAPP complex under the reaction conditions.
Keywords: Ti-MCM-41; Manganese(III) porphyrin; Heterogeneous catalysts; Cyclohexene; Styrene; Epoxidation
Gas phase alkylation of 2-hydroxypyridine with methanol over hydrothermally synthesised zinc aluminate by Hanna Grabowska; Mirosław Zawadzki; Ludwik Syper (pp. 226-232).
The gas phase alkylation of 2-hydroxypyridine with methanol at atmospheric pressure, over ZnAl2O4, prepared via hydrothermal route, is reported. The catalyst was characterised by XRD, HRTEM, DTA-TG, BET surface area measurements, pore-size analysis and surface acidity. The catalyst indicates high selectivity (over 95%) in the reaction of methanol with 2-hydroxypyridine leading to N-methyl-2-pyridone and its activity does not change substantially in the temperature range of 325–340°C.
Keywords: 2-Hydroxypyridine; Zinc aluminate; Gas phase methylation; N; -Methyl-2-pyridone
Boron nitride supported PtFe catalysts for selective hydrogenation of crotonaldehyde by Jeffrey C.S. Wu; Tai-Shin Cheng; Chao-Ling Lai (pp. 233-239).
The selective hydrogenation of crotonaldehyde was studied using boron nitride (BN) supported PtFe catalyst. A higher selectivity of crotyl alcohol than butyraldehyde was obtained, although butyraldehyde is thermodynamic favorable in the hydrogenation. The catalyst, PtFe/BN, was prepared by co-incipient wetness method. The metal loadings were 1.1wt.% Pt and Fe ranging 0.1–0.6wt.%. Commercial catalyst supports, graphite and γ-Al2O3, were also used to compare with BN. The higher iron content, the higher the crotyl alcohol selectivity was, while the activity was depressed. PtFe/γ-Al2O3 gave the lowest selectivity of crotyl alcohol. PtFe/graphite had the product selectivities similar to PtFe/BN, but its activity was lower than that of PtFe/BN. A maximum yield of crotyl alcohol was found at 0.2wt.% Fe (molar ratio Fe/Pt=0.64) on PtFe/BN catalysts at 100°C. XRD revealed that PtFe alloy was formed on PtFe/BN during H2 reduction at 300°C. The improvement of selectivity toward crotyl alcohol was attributed to the easier formation of PtFe alloy particle on BN surface than on γ-Al2O3. The Fe2+ on PtFe alloy polarizes the CO bond of crotonaldehyde and the nearby Pto supplies the absorbed hydrogen to conduct the hydrogenation of the CO bond, instead of the CC bond. Therefore, both activity and the selectivity toward crotyl alcohol were enhanced appreciably.
Keywords: PtFe catalyst; Boron nitride; Selective hydrogenation; Crotonaldehyde
Kinetics of the reaction of toluene with benzyl alcohol over sulfated zirconia by Silvia A. Ardizzone; Paolo Beltrame; Giovanni Zuretti (pp. 240-247).
The title process includes: (i) conversion of benzyl alcohol to dibenzylether; (ii) benzylation of toluene by benzyl alcohol; (iii) benzylation of toluene by dibenzylether. The three reactions were studied in a slurry batch reactor, using cyclohexane as solvent and sulfated zirconia as solid acid catalyst. Runs were carried out at 60–75°C on and (i) and at 35–55°C on (ii), while reaction (iii) was studied separately at 55°C only. Reaction (iii) takes place only after complete reaction of the alcohol in (i) and (ii), and does not produce benzyl alcohol. Benzyl alcohol is confirmed to be preferentially adsorbed on the catalyst with respect to dibenzylether. The final products are the isomers of benzyltoluene and dibenzyltoluenes, and small amounts of unidentified byproducts. The kinetic results were interpreted by Langmuir–Hinshelwood models, one for (i)+(ii), the other for (iii). The main kinetic and adsorption coefficients involved in the reactions were evaluated.
Keywords: Activation energy; Benzyltoluene; Dibenzylether; Solid acid catalysts; Sulfated zirconia
Hydroisomerization of C6–C8 n-alkanes, cyclohexane and benzene over palladium and platinum beta catalysts agglomerated with bentonite by Paula Sánchez; Fernando Dorado; María Jesús Ramos; Rubí Romero; Vicente Jiménez; José Luis Valverde (pp. 248-255).
Hydroisomerization of three linear alkanes ( n-hexane, n-heptane and n-octane), cyclohexane and benzene was studied over two bifunctional catalysts based on beta zeolite agglomerated with bentonite, and as the metallic functions, palladium and platinum. In both catalysts, the reactivity of n-alkanes increased with the chain length due to enhanced adsorption properties. n-Octane was converted in a major extent than both n-heptane and n-hexane. However, the presence of cracking processes was more evident when the former was fed to the reactor. The conversion of cyclohexane (cC6) was clearly temperature dependent. In fact, the selectivity towards the dehydrogenation to benzene increased with increasing reaction temperatures. The conversion of benzene dropped as the temperature was increased. The higher hydrogenating capacity of platinum was the responsible of the higher benzene conversion values obtained with the platinum catalyst.The influence of each individual alkane on the catalytic activity of the others was studied by examining the reactivity of binary and ternary mixtures of alkanes in the hydroisomerization reaction. The inhibition by cyclohexane was higher due to its well known preferential adsorption over the zeolite. The simultaneous hydroisomerization of benzene and two linear alkanes favoured the partial conversion of the latter, but not the selectivity towards alkane isomers.
Keywords: Hydroisomerization; Binder; Beta zeolite; Cyclohexane; Benzene