Applied Catalysis A, General (v.238, #2)
Acid-catalysed benzene hydroconversion using various zeolites: Brönsted acidity, hydrogenation and side-reactions by O. Cairon; K. Thomas; A. Chambellan; T. Chevreau (167-183).
Several zeolites (cubic and hexagonal faujasites, steamed or not) are tested as acid catalysts. The strength and number of Brönsted acid sites are determined from FTIR studies of adsorbed probe molecules (CO, pyridine). Direct benzene hydrogenation leading to cyclohexane is observed only at low temperature (500 K) with the less acid zeolites (H 0=−8.5). Side-reactions grow progressively with the acid strength of the catalyst and, in some cases, with increasing reaction temperature (in other cases, a drastic deactivation is observed). Coke is generated by the more acid hydroxyl groups (H 0=−12). The occurrence of the various steps of the scheme describing the benzene hydroconversion process depends on the strength of Brönsted acid sites and reaction temperature.
Keywords: Benzene hydrogenation; Benzene hydroconversion; Acid zeolite; Brönsted acidity strength;
Influence of SnO2-doped W-Mn/SiO2 for oxidative conversion of methane to high hydrocarbons at elevated pressure by Lingjun Chou; Yingchun Cai; Bing Zhang; Jianzhong Niu; Shengfu Ji; Shuben Li (185-191).
The SnO2-doped 5% Na2WO4-2% Mn2O3/SiO2 catalyst for oxidative conversion of methane to high hydrocarbons has been studied in a micro-stainless-steel reactor at elevated pressure. At 1053 K, 1.0×105 h−1 GHSV and 0.6 MPa, a CH4 conversion of 33.0% with C2+ selectivities of 73.1% is obtained; here the C2, C3 and C4 hydrocarbons selectivities of 36.8, 14.2 and 22.1% are observed. On addition of SnO2, conversion of methane and selectivities of C3–C4 hydrocarbons increase obviously. The observed results show the storage-oxygen capability in Na-W-Mn/SiO2 catalyst is enhanced with adding SnO2, for Mn and Na2WO4 migrate to near-surface to result in a marked shift to higher molecular weight products. The distribution of products at the operating conditions and content of SnO2 loading has been described.
Keywords: Conversion of methane; Effect of SnO2; Na-Mn-W/SiO2 catalyst;
Polymerization of 1,3-butadiene by cobalt dichloride activated with various methylaluminoxanes by Dilip Chandra Deb Nath; Takeshi Shiono; Tomiki Ikeda (193-199).
1,3-Butadiene polymerization was conducted at 0 °C with cobalt dichloride (CoCl2) activated by different cocatalysts: MAO (methylaluminoxane), dried-MAO (substantially free of trimethylaluminum), MMAO (triisobutylaluminum-modified methylaluminoxane), dried-MMAO (substantially free of trialkylaluminum) and TMA (trimethylaluminum). MAO and MMAO were effective cocatalysts for 1,3-butadiene polymerization. CoCl2 activated with MAO showed slowly-initiated living polymerization which has been reported previously, whereas, that with MMAO showed deactivation. Neither dried-MAO nor dried-MMAO, TMA activated the catalyst, whereas dried-MAO-TMA (mixtures of dried-MAO and TMA) and dried-MMAO-TMA (mixtures of dried-MMAO and TMA) allowed the polymerization. These results indicated that trialkylaluminums were necessary with MAOs for generating the active species. Dried-MAO-TMA caused frequent chain transfer reactions, whereas dried-MMAO-TMA showed the living like polymerization not only with slow initiation but with slow propagation also, suggesting that the nature of the active species was strongly dependent on the structure of alkylaluminums and MAOs. The microstructure of the resulting polymers analyzed by 1 H and 13 C NMR was cis-1,4 (98–97%); the percentage slightly decreased in the following order: MAO>dried-MAO>MMAO>dried-MMAO, accompanied by the increase of trans-1,4 and 1,2-inserted units.
Keywords: 1,3-Butadiene; Cobalt dichloride; Methylaluminoxane; Living polymerization;
Phenol hydroxylation activity of metal phthalocyanine complexes encapsulated in zeolite-Y by S. Seelan; A.K. Sinha (201-209).
Metal phthalocyanine complexes (MPc; M=V, Co and Cu) were encapsulated in zeolite-Y by “in situ ligand synthesis” method and were characterized by chemical and thermal analyses, FT-IR, diffuse reflectance UV–VIS and EPR spectroscopic techniques. The Pc moiety undergoes distortion from square planarity on encapsulation. The studies have provided evidence for the encapsulation of MPc inside the supercages of zeolite-Y. The encapsulated complexes exhibited enhanced phenol hydroxylation activity with H2O2 compared to the “neat” complexes in homogeneous medium. A comparative study has revealed that the activity and product selectivity of the encapsulated complexes can be correlated with the redox potential of the M(n+1)/M n+ couple of the central metal atom of the encapsulated phthalocyanine.
Keywords: Metal phthalocyanine; Encapsulation; Zeolite; Phenol hydroxylation; Metal-activity correlation;
Formaldehyde synthesis from methanol over silver catalysts by Min Qian; M.A Liauw; G Emig (211-222).
The formaldehyde synthesis from methanol was investigated over a polycrystalline silver catalyst at temperatures up to 993 K. Water was added to the feed (water ballast process) like in the commercial BASF process. The conversion of methanol and the selectivity to formaldehyde appeared to increase with respect to the methanol ballast process with no added water. A long-time experiment was carried out lasting over more than 300 days time-on-stream. While the methanol conversion does not change significantly, there is a pronounced change in hydrogen and CO2 selectivity. A most noteworthy observation is that over months of operation, the width of the temperature region where formic acid is formed increases in a linear manner. Finally, interrupting the oxygen supply for a few hours led to a temporary deterioration of the product selectivity after oxygen re-admittance. All observations may well be interpreted in the framework of the commonly discussed silveroxygen chemistry with its three different oxygen species (Oα, Oβ and Oγ).
Keywords: Methanol oxidation; Oxidative dehydrogenation; Formaldehyde; Silver catalyst; Catalyst deactivation; Oxygen species;
Cracking behavior of organic sulfur compounds under realistic FCC conditions in a microriser reactor by X Dupain; L.J Rogier; E.D Gamas; M Makkee; J.A Moulijn (223-238).
A laboratory-scale once-through microriser reactor was used in a qualitative study on the distribution of aromatic sulfur in the catalytic cracking products of an extra heavy gas oil (EHGO) under a broad range of conditions overlapping with realistic fluid catalytic cracking (FCC) conditions. Fifteen to twenty percent of the feed was uncrackable, corresponding to the amount of polycyclic aromatics in the feed. Gasoline was not overcracked to gas. The selectivity to gasoline was found to be independent of process parameters, in contrast to the selectivity to light cycle oil (LCO) and gas. Higher temperature and catalyst-to-oil (CTO) ratio led to an increased overall cracking rate.Initially, the amount of gasoline sulfur increased with residence time due to the formation of aliphatic sulfur compounds. Subsequently, these aliphatic species were cracked to hydrocarbons and H2S. The gasoline sulfur concentration decreased as function of conversion due to the dilution of sulfur compounds by the additional formed sulfur-free gasoline hydrocarbons. Stable LCO sulfur species were predominantly formed by dealkylation of alkylated benzothiophenes from the heavy cycle oil (HCO) fraction. The LCO sulfur concentration was found to be temperature dependent. Aromatics without side chains, such as thiophene, benzothiophene and dibenzothiophene, were found to be uncrackable under the applied conditions. It is discussed if optimization of the conditions can contribute to significant lower sulfur levels in gasoline.
Keywords: Fluid catalytic cracking (FCC); Sulfur; Residence time; Catalyst-to-oil (CTO) ratio; Temperature;
Oxide supports for 12-tungstosilicic acid catalysts in gas phase synthesis of MTBE by Adam Bielański; Anna Lubańska; Joanna Poźniczek; Anna Micek-Ilnicka (239-250).
A series of simple and mixed oxides: SiO2, AlPO4, SiO2-Al2O3, TiO2, kaolin and γ-Al2O3 differing by their basicities as characterised by effective negative charge on oxygen calculated according to Sanderson’s theorem was used for the preparation of supported H4SiW12O40 catalysts. Using gas phase synthesis of MTBE as the catalytic test reaction it has been shown that on the supports of highest basicity, i.e. γ-Al2O3 and kaolin the heteropolyacid was decomposed resulting in the catalyst which exhibited only low activity. On the other hand, the least basic oxide SiO2 gave the most active catalysts. However, the sequence of activities differed from that of basicities by the fact that the activity of TiO2-supported catalyst was at the coverage with H4SiW12O40 Θ=0.25 nearly as high as SiO2 supported one and at Θ=1.0 TiO2-supported catalyst was the best. This indicates that the basicity of the support is only one of the factors determining the activity of supported heteropolyacid catalysts in acid–base type reactions. On the other hand good correlation was obtained between the catalytic activity and the neutralisation heat of the acid sites on the surface of catalyst which was determined using thermometric titration with n-butylamine solution in toluene.
Keywords: MTBE; Heteropolyacid; Catalyst supports;
Enantio selective hydrogenation of isopropyl-4,4,4-trifluoroacetoacetate in a continuous flow reactor by N Künzle; T Mallat; A Baiker (251-257).
The study aimed at clarifying the feasibility of the synthesis of a chiral trifluoromethyl alcohol by continuous hydrogenation over Pt/Al2O3. The transformation of isopropyl-4,4,4-trifluoroacetoacetate to the corresponding β-hydroxyester was studied in a fixed bed reactor under differential reactor conditions. The chiral modifier and trifluoroacetic acid additive were continuously fed into the reactor in tetrahydrofuran solvent. The actual chiral modifier of Pt was an O-methyl-cinchonidine–trifluoroacetic acid ion-pair. Up to around 90% enantio selectivity (ee) and a turn over frequency (TOF) value of 810 h−1 were achieved by varying the pressure, temperature, total liquid flow rate and feed composition.
Keywords: Enantio selective; Hydrogenation; Continuous flow reactor; Trifluoroacetoacetate; Pt/alumina; O-methyl-cinchonidine;
Optimized palladium catalyst systems for the selective liquid-phase hydrogenation of functionalyzed alkynes by T.A Nijhuis; G van Koten; J.A Moulijn (259-271).
Silica-supported palladium catalysts for the selective liquid-phase hydrogenation of alkynes to alkenes were prepared. As a model reaction the hydrogenation of 3-methyl-1-pentyn-3-ol was chosen. The kinetics of this reaction were investigated. Different approaches were used to obtain an optimal catalyst system. The selectivity of the palladium catalysts was successfully improved by modifying the catalyst with copper and the effect of this modification on the reaction mechanism was studied. The addition of quinoline as a reaction modifier to the system was investigated as a manner to improve selectivity. Monolith supported catalysts were prepared to obtain a more convenient reactor configuration.
Keywords: Hydrogenation (selective); Alkyne; Palladium; Copper; Bimetallic;
The determination of dispersity and metal content of supported palladium catalysts with redox titration by S Szabó; F Nagy; J Gyimesi (273-277).
A simple redox titration method has been developed for the measurement of the Pd content and dispersity of palladium catalysts. First, the sorbed hydrogen content, then the Pd content and finally, the amount of adsorbed oxygen must be measured and from these data the dispersity can be easily calculated.
Keywords: Palladium; Dispersity; Surface area; Redox titration;
Development of a polyfunctional catalyst for benzene production from pyrolysis gasoline by Rafig Alibeyli; Ali Karaduman; Hasip Yeniova; Ayten Ateş; Ali Y Bilgesü (279-287).
The concurrence of hydrodealkylation, hydrocracking, and hydrodesulfurization reactions necessitates a polyfunctional catalyst in the production of pure benzene from pyrolysis gasoline or other industrial mixtures containing various alkylaromatic and nonaromatic hydrocarbons. A chromium catalyst was developed in this study with comparable performance to the commercial catalyst Pyrotol H-9430 (Houdry, USA). The new catalyst contained 15 wt.% Cr and was doped with KF. When tested utilizing a hydrocleaned BTX fraction of pyrolysis gasoline, it preserved its benzene selectivity and hydrocracking activity for 3000 h, but lost about 10% of its hydrodealkylation activity. The deactivated catalyst completely recovered its original surface properties and hence activity when subjected to oxidative regeneration. The developed catalyst maintained its Cr and KF content in regeneration as it did in drying, calcination, and reaction. The characteristics of the catalyst were examined by BET, XRD, DTA, TGA and electron microscope.
Keywords: Cr/Al2O3 catalysts; Hydrodealkylation; Hydrocracking; Pyrolysis gasoline; Benzene;
Application of Pd/α-Si3N4 catalysts to radiant panels using methane catalytic combustion to obtain infrared emission by F.J Cadete Santos Aires; S Ramirez; G Garcı́a Cervantes; E Rogemond; J.C Bertolini (289-301).
Silicon nitride (α-Si3N4)-based radiant panels were prepared using the same process as that used industrially for present day alumina-based radiant panels. They were successfully tested under industrial conditions during the catalytic combustion of methane to obtain infrared emission. Both panels impregnated with palladium operated successfully at high power density (100 kW/m2; 950 °C) for 2500 h (15 weeks). From the first stages of emission, the silicon nitride-based panel exhibits a narrower power density operation range (75–100 kW/m2) than the alumina-based one (63–100 kW/m2). However, during ageing this difference decreases very slightly and after 2500 h of operation we observe a range of 83–100 kW/m2 for the silicon nitride-based panel and a range of 73–100 kW/m2 for the alumina-based one. The same tendency (lower activity of Pd/α-Si3N4) is observed in the laboratory tests during the reaction of total combustion of methane in a flow-reactor. The as-prepared Pd/α-Si3N4 exhibit poor morphological properties (size and distribution of metal particles) compared to those of Pd/alumina. This characteristic accounts for the lower activity of the former catalysts and efforts for further optimising this catalyst are currently in progress. Nevertheless, the silicon nitride-based radiant panels have operated under industrial conditions for 2500 h with rather encouraging performances.
Keywords: Methane oxidation (total); Radiant panels; Pd/Si3N4;
Interpreting mercury porosimetry data for catalyst supports using semi-empirical alternatives to the Washburn equation by Sean P Rigby; David Barwick; Robin S Fletcher; Sandra N Riley (303-318).
Semi-empirical alternatives to the traditional Washburn equation have been used to analyse the mercury porosimetry data for a sol–gel silica and five alumina catalyst supports. A combination of different porosimetry experiments, including the conventional primary mercury intrusion and retraction experiment conducted on both whole pellets and a fragmented sample together with a mercury re-injection curve, have demonstrated that a sol–gel silica sphere possesses a so-called “skin-effect.” This means that a thin band of narrow pore throats was located at the surface of the silica sphere guarding access to larger pores located within the interior. This particular interpretation of the raw data only became apparent when the new data analysis method was used. In addition, when an alternative expression to the Washburn equation is used to analyse the primary mercury intrusion curves for five alumina samples, the pore size distributions obtained all match a priori the corresponding distributions obtained from nitrogen desorption. This finding supports the view that both mercury intrusion and nitrogen desorption are invasion percolation processes.
Keywords: Mercury porosimetry; Nitrogen desorption; Catalyst support; Skin-effect;
Catalytic hydroxylation of phenol over CuM(II)M(III) ternary hydrotalcites, where M(II) = Ni or Co and M(III) = Al, Cr or Fe by A Dubey; S Kannan; S Velu; K Suzuki (319-326).
PATENTS ALERT (327-332).
AUTHOR INDEX (335-336).
SUBJECT INDEX (337-341).
CONTENTS CONTINUED (342).