Applied Catalysis A, General (v.206, #1)
Novel α-nitroketonate nickel(II) complexes as homogeneous catalysts for ethylene oligomerization by Carlo Carlini; Mario Marchionna; Anna Maria Raspolli Galletti; Glauco Sbrana (1-12).
The oxidative addition of α-nitroacetophenone (naph) to bis(cyclooctadienyl)nickel(0) [Ni(cod)2], in the presence or not of tricyclohexylphosphine (PCy3) was proven to give the η1,η2-cyclooctenyl)(naph)nickel(II) complex (III). When this reaction was carried out in the presence of PCy3, further addition of methylalumoxane (MAO) or trialkylaluminium compounds afforded the corresponding alkyl(PCy3)(naph)nickel(II) complex. This was also obtained by an alternative synthetic procedure involving the addition of a trialkylaluminium to the equimolar adduct of Ni(naph)2 with PCy3. When the above complexes, independently of the synthetic procedure adopted, were generated in situ by using MAO as a co-catalyst (Al/Ni=100), they resulted in being active in ethylene oligomerization. Whereas in the absence of PCy3, they gave mainly linear C4–C6 oligomers with turnover frequencies (TOFs) in the 4000–8000 h−1 range, the presence of the phosphine ancillary ligand not only produced a remarkable increase in activity (TOF=26,000–41,000 h−1) but also afforded a completely different distribution of oligomers, mainly branched C6–C13 products being obtained.
Keywords: α-Nitroacetophenone; α-Nitroacetophenonate/nickel complexes; Ethylene oligomerization; Homogeneous catalysts; Organoaluminium co-catalysts;
Ozone decomposition, benzene and CO oxidation over NiMnO3-ilmenite and NiMn2O4-spinel catalysts by D. Mehandjiev; A. Naydenov; G. Ivanov (13-18).
The catalytic activities of NiMnO3 and NiMn2O4 during heterogeneous catalytic decomposition of ozone and ozone-catalytic oxidation (OZCO) of benzene at low temperatures (20–80°C) have been investigated. The sensitivity of the two oxides towards strong catalytic poisons, such as nitrogen oxides, during the decomposition of ozone has also been estimated. On the basis of the experimental results obtained it is concluded that the NiMnO3 and NiMn2O4 obtained have a high activity with respect to the reactions of ozone decomposition and CO and CH oxidation in the presence of ozone at temperatures close to the room temperature. The sample with an ilmenite structure shows, in all cases, a higher catalytic activity. The surface oxygen of NiMnO3 is more reactive at room temperature than is the case of NiMn2O4. The hypothesis according to which when the two metal cations are in octahedral coordination the catalyst activity is higher and the stability towards catalytic poisons is enhanced has proved to be correct. It should be noted that a catalyst has been synthesized which is able to decompose ozone at room temperature and to activate the organic molecule to a degree permitting catalytic oxidation by ozone at room temperature. In addition, this catalyst shows a relatively high stability with respect to poisoning by nitrogen oxides.
Keywords: Ozone decomposition; Ozone-catalytic oxidation; Catalytic poisons; Nickel-manganese oxides;
Selective dichlorocyclopropanation of dicyclopentadiene under controlled phase transfer catalysis conditions by Joseph Paul Jayachandran; Maw-Ling Wang (19-28).
The kinetics of selective dichlorocyclopropanation of dicyclopentadiene has been studied under controlled phase transfer catalysis conditions using aqueous sodium hydroxide as the base and 2-benzilidine-N,N,N,N′,N′,N′-hexaethylpropane-1,3-diammonium dibromide (Dq-Br) as a new phase transfer reagent. The reaction was carried out at 40°C under pseudo-first order conditions by employing aqueous sodium hydroxide and chloroform in excess and was monitored by gas chromatography. The effect of various experimental parameters on the rate of the reaction has been studied; based on the experimental results, a suitable mechanism is proposed.
Keywords: Dichlorocyclopropanation; Dicyclopentadiene; Phase transfer catalysis;
Effect of Fischer–Tropsch synthesis on the microstructure of Fe–Co-based metal/spinel composite materials by F. Tihay; G. Pourroy; M. Richard-Plouet; A.C. Roger; A. Kiennemann (29-42).
Fe–Co-based metal/oxide composite materials (Co0.73 0Fe0.27 0)0.82 [Co0.35Fe2.65O4], (Co0.95 0Fe0.05 0)0.62 [Co0.31Fe2.69O4] and (Co0.90 0Fe0.10 0) [Co0.10Fe2.90O4] were prepared to be used in Fischer–Tropsch (F–T) synthesis in view of producing light alkenes. The metal is an iron–cobalt alloy of bcc structure in the former and of fcc structure in the two latter and the oxide, a cobalt containing magnetite. The metal, obtained directly by preparation method, is embedded in the oxide phase. Then, catalysts were not subjected to a reducing pre-treatment. Although, catalysts were not reduced, the two former materials are efficient as catalysts in F–T reaction to produce C2–C4 (50 wt.%) with high alkene:alkane ratio and a low selectivity of CO2 (25% molar at CO conversion of 5%); the third catalyst presents a typical distribution of hydrocarbons obtained with cobalt catalyst in F–T reaction. The possible modifications of the catalysts during the catalytic reaction are studied by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). High resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) show the surface composition under test is identical for the first two catalysts, although their initial bulk composition is different. The characterisation results, obtained by combined methods (XRD, electron-microscopy, surface analysis) provide explanations to individual catalytic behaviour of the three catalysts studied.
Keywords: Fischer–Tropsch; Light alkenes; Iron; Cobalt; Spinel; TEM; XPS; XRD;
Influence of the metal and of the support on the activity and stability of bifunctional catalysts for toluene hydrogenation by J. Chupin; N.S. Gnep; S. Lacombe; M. Guisnet (43-56).
Gas phase hydrogenation of toluene, diluted in inert n-hexane in order to minimise the thermal effects was investigated in a fixed bed reactor at 110°C over series of bifunctional catalysts in which Pt or Pd was deposited on alumina or on an acidic HFAU zeolite. Practically no deactivation was observed when the metals were deposited on alumina, even in mixture with the HFAU zeolite, whereas there was a rapid initial deactivation when Pd and especially Pt were deposited on the acidic zeolite. However, even in this latter case, the activity of the fresh catalysts can be obtained with a good accuracy thanks to the use of a multiple loop value. For given metal and support, a linear correlation was found between the hydrogenating activity and the number of accessible metal atoms. However, Pt was found to be 20–60 times more active than Pd, both metals being more active on HFAU zeolite than on alumina. This acidity effect could be explained by the hydrogenation of aromatic molecules adsorbed on acidic sites by hydrogen spilled over from the metal surface. The initial deactivation of Pt- and Pd-HFAU zeolite catalysts was due to the rapid formation of ‘coke’ molecules inside the zeolite micropores. ‘Coke’ was mainly constituted by C14 and C21 products resulting from the acid alkylation of toluene molecules by the olefinic and dienic intermediates of their hydrogenation. While the composition of ‘coke’ as well as its deactivating effect did not depend on the metal (Pt or Pd), the rate of ‘coke’ formation at isoconversion of toluene was found to be lower on Pd than on Pt zeolite catalysts, which explains their slower deactivation.
Keywords: Pt- and Pd-HFAU catalysts; Toluene hydrogenation; Activity; Deactivation; Coke composition;
Investigations on the reaction mechanism of the skeletal isomerization of n-butenes to isobutene by D. Rutenbeck; H. Papp; D. Freude; W. Schwieger (57-66).
A series of H-ZSM-5 zeolites with Si/Al ratios between 17 and 170 were tested in the skeletal isomerization of n-butenes to isobutene in the temperature range of 573–773 K. A selectivity to isobutene of ca. 20% was obtained with all zeolites at 573 K independent of the conversion of n-butenes. With increasing temperature the conversion of n-butenes increased on the zeolites with Si/Al ratios up to 70 (high number of acid sites), whereas the yield of isobutene and the selectivity to isobutene decreased. On the zeolites with higher Si/Al ratios (160 and 170) an opposite behaviour was observed; the conversion of n-butenes decreased while the yield of isobutene and the selectivity to isobutene increased with increasing temperature. A selectivity to isobutene of nearly 90% could be obtained with the latter zeolites at 773 K. These observations are interpreted in such a way that on H-ZSM-5 zeolites with a high number of acid sites, isobutene is formed via the bimolecular mechanism independent of the reaction temperature. On H-ZSM-5 zeolites with a low number of acid sites, a change from the bimolecular to the monomolecular mechanism takes place with increasing temperature.
Keywords: Skeletal isomerization; Isobutene; ZSM-5; Reaction mechanism;
Hydrocarbon reactions on Pd–Re/Al2O3 catalysts by Wojciech Juszczyk; Zbigniew Karpiński (67-78).
The reactions of n-hexane, 2,2-dimethylbutane and methylcyclopentane in excess hydrogen were studied on alumina-supported Pd–Re catalysts characterized by medium metal dispersion. Palladium is much less active than rhenium in catalyzing alkane conversions. Even very small amounts of added rhenium to palladium cause big catalytic consequences. All Re-containing samples behave similarly, i.e. exhibit comparable activation energies (much lower than in the case of Pd/Al2O3) and a radical loss of isomerization capability. Accordingly, examination of these variables cannot effectively serve in probing Pd–Re surfaces. However, other useful ‘fingerprints’ have been recognized, among which the fragmentation factor in alkane conversions and the 2MP/3MP product ratio in methylcyclopentane reaction are the most valuable. Their profound specific variations with Pd–Re composition clearly suggest that rhenium interacts with surface palladium atoms.
Keywords: Pd–Re/Al2O3; Alkane catalytic conversion; n-Hexane; 2,2-Dimethylbutane; Methylcyclopentane; Catalytic probing;
Catalytic activity for synthesis of isomerized products from benzene over platinum-supported sulfated zirconia by Kiyoyuki Shimizu; Tomohito Sunagawa; Carlos Roman Vera; Koji Ukegawa (79-86).
The catalytic activity of Pt/SO4 2−/ZrO2 in the benzene hydrogenation and isomerization reaction at 250°C is superior to that of other Pt/conventional solid acid catalysts such as Pt/HY-zeolite and Pt/H-mordenite. The catalytic activity of SO4 2−/ZrO2 for cyclohexane isomerization to methylcyclopentane at 250°C is higher than that of HY-zeolite and H-mordenite. SO4 2−/ZrO2 and HM10 have more Brönsted acid sites of the highest strength and show a higher percentage of isomerization conversion. In contrast, ZrO2, which contains almost no Brönsted acid sites, and HY5.6, which contains almost no Brönsted acid sites of the highest strength, show a lower conversion percentage. Consequently, Brönsted acid sites of the highest strength are active sites responsible for cyclohexane isomerization. However, the isomerization conversion percentage does not completely correlate with the number of highest-strength Brönsted acid sites, suggesting that not all of these sites contribute to the reaction nor do only Brönsted acid sites influence cyclohexane isomerization. Neither the total number nor the number of highest-strength Lewis acid sites correlates with the isomerization conversion rate, indicating that Lewis acid sites are not responsible for cyclohexane isomerization.
Keywords: Pt-supported sulfated zirconia; Benzene hydroisomerization; Cyclohexane isomerization; Brönsted acid site; Lewis acid site;
Improving deactivation behaviour of HZSM-5 catalysts by A de Lucas; P Cañizares; A Durán (87-93).
Different treatments were performed to HZSM-5 catalysts in order to improve their deactivation behaviour during the conversion of acetone/n-butanol mixtures (obtained from fermentation products) to hydrocarbons. Internal and external poisoning, selective external dealumination with silicon tetrachloride and addition of water to the feed were studied.The extent of poisoning (with pyridine or 4-methylquinoline) largely influences selectivity and deactivation behaviour of the catalyst, although no improvement is achieved since poison restricts the access to zeolitic channels also.Selective external dealumination with silicon tetrachloride leads to a slight increase in stability only for catalysts smoothly dealuminated and with indexes of specificity for external surface deacidification, S D, higher than 0.8. This is due to the fact that internal sites are mainly responsible for coke deposition. An increase in the internal deacidification degree is achieved if catalysts are severely dealuminated, thus causing a decrease in coke content; however, external coke is more toxic and deactivation becomes faster. Furthermore, damage of the zeolite structure may take place.Addition of water to the feed leads to stabilisation of aromatisation activity, since strong Brönsted sites responsible for coke deposition are deshydroxilated to Lewis sites, thus decreasing the rate of coke formation.
Keywords: Deactivation; Dealumination; Poisoning; Water; ZSM-5;
Catalytic transfer hydrogenation of citral on calcined layered double hydroxides by Marı́a A Aramendı́a; Victoriano Borau; César Jiménez; José M Marinas; José R Ruiz; Francisco J Urbano (95-101).
The catalytic transfer hydrogenation of citral with 2-propanol (a Meerwein–Pondorf–Verley reaction) on basic catalysts obtained by calcination of Mg/Al, Mg/Al, Ga, Mg/Ga, Mg/In and Ca/Al layered double hydroxides (LDHs) was studied. The LDHs used were characterized by X-ray diffraction (XRD) and their textural and surface chemical properties were determined. All the catalysts studied were found to provide excellent results as regards catalytic activity and selectivity in the hydrogenation process. Conversion always exceeded 95% and selectivity 90% within the first 40 h of reaction. The catalytic activity of the LDHs was found to be a function of surface basicity (the most basic catalysts were also the most active ones).
Keywords: Hydrogenation; 2-Propanol; Layered double hydroxides;
Catalytic property of vanadyl pyrophosphates for selective oxidation of n-butane at high n-butane concentrations by Yuichi Kamiya; Eiichiro Nishikawa; Toshio Okuhara; Tadashi Hattori (103-112).
Selective oxidation of n-butane to maleic anhydride was studied at high concentrations of n-butane up to 5.0 vol.% using three kinds of (VO)2P2O7 catalysts having differently shaped microcrystallites; rose-petals (catalyst A), plates (catalyst B), and blocks (catalyst C). The catalytic activity for maleic anhydride formation per unit surface area greatly depended on the kinds of catalysts at the high concentration of n-butane (5.0 vol.%); catalyst A was much more active, while there was no difference at the low concentrations. That catalyst A gave higher rates of the re-oxidation and reduction, which was established from the measurements of reduction of the catalyst, aged in the reaction mixture, with n-butane and subsequently re-oxidation with O2. In addition, catalyst A showed a larger reaction order of n-butane concentration. Therefore, the higher catalytic performance of catalyst A at the high concentration of n-butane is attributed to the higher redox ability of the catalyst, and this is probably brought about from the structural disorder of the surface.
Keywords: Vanadyl pyrophosphate; Selective oxidation of n-butane; Maleic anhydride; Redox property; High n-butane concentration;
XPS and TPR examinations of γ-alumina-supported Pd-Cu catalysts by Jurka Batista; Albin Pintar; Djordje Mandrino; Monika Jenko; Vincent Martin (113-124).
Alumina-supported palladium-copper catalysts, which promote liquid-phase nitrate reduction, have been prepared according to different impregnation sequences of γ-Al2O3 support and characterized by X-ray photoelectron spectroscopy (XPS), X-ray induced Auger electron spectroscopy (XAES) and temperature-programmed reduction (TPR). Analysis of Pd XPS/XAES spectra reveals that palladium is present on the γ-alumina support in the metallic form. Copper is reduced at lower temperatures in the presence of palladium particles compared to the CuO/γ-Al2O3 sample. Due to the low copper content in catalysts (σ Cu≈1014 atoms cm−2), the XPS/XEAS spectral features of reduced copper species are quite different from those of bulk copper. As shown by TPR and XPS/XAES data, formation of highly dispersed Pd-Cu bimetallic clusters is suggested. It was discovered by means of TPR analysis that the catalyst preparation in which the γ-alumina support is impregnated first by copper salt, results in higher formation of the Pd-Cu alloy.
Keywords: Supported Pd-Cu catalysts; γ-Kind alumina; Pd-Cu bimetallic clusters; X-ray photoelectron spectroscopy (XPS); Temperature-programmed reduction (TPR);
The preparation of highly ordered single layer ZSM-5 coating on prefabricated stainless steel microchannels by E.V. Rebrov; G.B.F. Seijger; H.P.A. Calis; M.H.J.M. de Croon; C.M. van den Bleek; J.C. Schouten (125-143).
An elegant way to prepare catalytically active microreactors is by applying a coating of zeolite crystals onto a metal microchannel structure. In this study the hydrothermal formation of ZSM-5 zeolitic coatings on AISI 316 stainless steel plates with a microchannel structure has been investigated at different synthesis mixture compositions. The procedures of coating and thermal treatment have also been optimized. Obtaining a uniform thickness of the coating within 0.5 mm wide microchannels requires a careful control of various synthesis variables. The role of these factors and the problems in the synthesis of these zeolitic coatings are discussed. In general, the synthesis is most sensitive to the H2O/Si ratio as well as to the orientation of the plates with respect to the gravity vector. Ratios of H2O/Si=130 and Si/template=13 were found to be optimal for the formation of a zeolitic film with a thickness of one crystal at a temperature of 130°C and a synthesis time of about 35 h. At such conditions, ZSM-5 crystals were formed with a typical size of 1.5 μm×1.5 μm×1.0 μm and a very narrow (within 0.2 μm) crystal size distribution. The prepared samples proved to be active in the selective catalytic reduction (SCR) of NO with ammonia. The activity tests have been carried out in a plate-type microreactor. The microreactor shows no mass transfer limitations and a larger SCR reaction rate is observed in comparison with pelletized Ce-ZSM-5 catalysts.
Keywords: Zeolite; ZSM-5; Microreactor; XRD; Preparation; DeNO x ;
Patent report (145-150).