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Applied Catalysis A, General (v.285, #1-2)

Inside front cover - Editorial Board (pp. co2).

Mechanistic investigation of the catalyzed vapor-phase formation of pyridine and quinoline bases using¹³CH₂O,¹³CH₃OH, and deuterium-labeled aldehydes by J.R. Calvin; R.D. Davis; C.H. McAteer (pp. 1-23).

Solid-acid catalyzed vapor-phase reactions forming pyridine and β-picoline, α- and γ-picoline, and 8-methylquinoline (8-MeQ) and 3,8-dimethylquinoline (3,8-DMQ) were examined using labeled feeds (¹³C,²H) combined with NMR spectroscopy. In the presence of¹³CH₂O, amorphous silica–alumina (S–A) converted CH₃CHO–CH₂O–NH₃ feed (480°C) to pyridine containing¹³C-4 (major) and¹³C-2 (minor). Co-product β-picoline contained¹³C-4 and¹³CH₃ (major) and¹³C-2 and¹³C-6 (minor). Replacing¹³CH₂O by¹³CH₃OH led to subtle changes in the levels of¹³C incorporation due to an induction period during which methanol converts to formaldehyde equivalent. Pyridine and β-picoline formation require a common propenimine intermediate that either condenses with aldehyde/imine species (major route) or undergoes Michael additions (minor route). Use of¹³CH₃OH and either ZnO/S–A or H⁺-MFI led to similar patterns of¹³C incorporation, albeit at lower levels than S–A. Reaction of acrolein–D₂O–ND₃ (S–A, 480°C) gave predominantly 3,5-dideuteriopyridine, 3-methyl-5-deuteriopyridine, and 3-deuteriomethyl-5-deuteriopyridine from imines (CH₂CDCHND, CD₃CHND, and CH₂ND) formed in situ. A slower Brønsted acid-catalyzed reaction of pyridine bases with D₂O incorporates deuterium at C-2,6 ring positions. The CH₃CHO–D₂O–NH₃ reaction (S–A, 440°C) showed acetaldehyde's carbonyl carbon locates at C-2, C-4, and C-6 positions in both α- and γ-picoline. Addition of either¹³CH₂O or¹³CH₃OH to CH₃CHOCH₂O- ortho-toluidine feed (S–A, 470°C) gave 8-MeQ containing¹³C-2 (major) and¹³C-4 (minor). Byproduct 3,8-DMQ contained¹³C-2 and 3-¹³CH₃ (major) and¹³C-4 (minor). Subtle changes in the¹³C incorporation patterns are once more due to an induction period for¹³CH₃OH dehydrogenation. The predominant reaction pathway to 8-MeQ and 3,8-DMQ involves N- o-tolyl-methanimine.

Keywords: Acetaldehyde; Acid catalysis; Deuterium; Carbon-13; Formaldehyde; Lutidine; Picoline; Pyridine; Quinoline; Zeolite

Preparation of carbon supported Pt and PtRu nanoparticles from microemulsion by Sergio Rojas; Francisco J. Garc�a-Garc�a; Sven J�ras; Mar�a V. Mart�nez-Huerta; Jos� Luis Garc�a Fierro; Magali Boutonnet (pp. 24-35).

A series of platinum and platinum ruthenium carbon supported electrocatalyst have been prepared by the microemulsion technique. The influence of parameters such as the preparation route, the metal loading and the PtRu stoichiometry on the morphology of the final nanoparticles has been studied. Irrespective the total metal loading, nanosized particles, displaying a narrow size distribution were obtained. In addition, particle size was found to be independent of the metal loading. Structural characteristics of these systems have been studied by XPS, X-ray diffraction, TEM, and TPR-TPO and their textural parameters by N₂ adsorption. The catalytic performance of the samples was evaluated in the electrochemical oxidation of methanol. The influence of the morphology on the catalytic performance of the catalysts is discussed in terms of their synthesis route.

Keywords: Microemulsion; Electrocatalyst; Pt; Ru; Methanol oxidation

Phase development and morphology during the thermal treatment of VOHPO₄�0.5H₂O by L. O’Mahony; T. Curtin; J. Henry; D. Zemlyanov; M. Mihov; B.K. Hodnett (pp. 36-42).

The thermal activation of VOHPO₄·0.5H₂O in O₂, air, N₂ or n-butane–air was studied using in situ X-ray diffraction and ex situ X-ray photoelectron spectroscopy and focussed ion beam microscopy with cross sectioning. In O₂ or air, an amorphous solid forms when VOHPO₄·0.5H₂O is heated above 270°C and a crystalline V⁵⁺ phase develops on heating above 350°C. By contrast, during activation in n-butane–air or in N₂, (VO)₂P₂O₇ is formed at 300°C without any intermediate amorphous phase. The interiors of VOHPO₄·0.5H₂O and (VO)₂P₂O₇ particles were identical, with the platelet like morphology of the precursor preserved during activation. By contrast the interiors of particles from the air or O₂ activation procedures had become dense and sintered like in appearance. Some oxidation of surface regions was observed during activation in n-butane–air. These results are discussed in terms of platelet type morphology of (VO)₂P₂O₇ generating a resistance to overoxidation during activation and catalytic work.

Keywords: Vanadium; Phosphorus; Activation; Butane; Pyrophosphate

In situ DRIFTS investigation of the steam reforming of methanol over Pt/ceria by Gary Jacobs; Burtron H. Davis (pp. 43-49).

In situ DRIFTS was used to probe the reaction mechanism of steam reforming of methanol over 1% Pt/ceria. Links were drawn between those results and the results of catalytic testing in a fixed bed reactor, including switching studies between deuterated and non-deuterated feeds. The steam reforming mechanism is suggested to proceed via adsorbed methoxy, formate, and carbonate species, and is selective at low conversion. At higher conversions, CO₂ reacts via reverse water–gas shift via surface formate intermediates to produce significant levels of undesired CO product.

Keywords: DRIFTS; Pt/ceria catalyst; Water–gas shift; Steam reforming; Methanol

Hydrogenation versus hydrogenolysis in the reaction of cis-2-butene-1,4-diol over supported platinum catalysts: Kinetic aspects by Maria Grazia Musolino; Paolo De Maio; Andrea Donato; Rosario Pietropaolo (pp. 50-58).

The liquid phase hydrogenation of cis-2-butene-1,4-diol has been studied in ethanol, using different platinum-supported catalysts, at a temperature ranging from 273 to 303K and at a partial H₂ pressure between 0.01 and 0.1MPa. Formation of only hydrogenation and hydrogenolysis products was detected and their selectivity was found to depend on the acid–base characteristics of the support. A yield of 96% to the fully hydrogenated product, butane-1,4-diol, at 303K and 0.1MPa H₂ pressure was obtained on Pt/MgO. The experimental data, in presence of platinum supported on TiO₂, was explained on the basis of a two paths mechanism: one leading to butane-1,4-diol, as usually, through a σ-alkyl species and the other, affording cis-crotyl alcohol and 3-buten-1-ol, involving the same unique intermediate, η³-allyl. Reaction rates were described on the basis of a Langmuir–Hinshelwood type model, assuming a non-competitive adsorption of organic species and hydrogen on the platinum active sites. Kinetic parameters for individual reaction steps were determined by a non-linear regression analysis. Furthermore, an adsorption of the olefinic substrate in a tilted mode was discussed in order to explain the hydrogenolysis reaction.

Keywords: Abbreviations; CISB; cis; -2-butene-1,4-diol; 1,4BUT; butane-1,4-diol; 2HT; 2-hydroxytetrahydrofuran; ALC; cis; -crotyl alcohol; 3BUT; 3-buten-1-ol; BUT; n; -butanol; η; η; ³; -allyl intermediate Cis; -2-butene-1,4-diol; Hydrogenolysis; Platinum-supported catalysts; η; ³; -allyl intermediate; Kinetic model

Homogeneous m-CPBA-oxidation of anthracene by electron-withdrawing metalloporphyrins in different reaction conditions by Nasser Safari; S. Shahab-al-din Naghavi; Hamid Reza Khavasi (pp. 59-64).

Anthracene was oxidized to anthrone, oxanthrone and anthraquinone with m-CPBA as oxidant and iron and manganese porphyrins as catalysts. The oxidation data in different conditions showed that CH₃CN aprotic solvent resulted in the production of anthraquinone formation high selectivity. In the presence of water, CH₃CN:H₂O (4:1), sum of the yields are higher than 100% that indicated an autoxidation mechanism involving dioxygen trapping of substrate radical.Anthracene was oxidized to anthrone, oxanthrone and anthraquinone with metachloroperbenzoic acid ( m-CPBA) as oxidant and iron and manganese porphyrins (FeF₂₀TPPCl, MnF₂₀TPPCl, FeCl₈TPPCl and MnCl₈TPPCl) as catalysts. The catalytic oxidation yields were dependent on the catalyst and solvent. In the presence of FeF₂₀TPPCl, in an acetonitrile solution, anthraquinone was formed in 60% yield with 100% selectivity. In the presence of water, CH₃CN:H₂O (4:1) with FeF₂₀TPPCl catalyst, anthrone, oxanthrone and anthraquinone were formed with respective yields of 8.4%, 84.4% and 37.6%, based on m-CPBA oxidant. When the CH₃CN:H₂O ratio changed from 4:1 to 49:1, the yields of anthrone and anthraquinone increased to 40.0% and 68.0%, respectively whereas the yield of oxanthrone decreased to 16.1%. Moreover, the effect of axial ligand and oxidant, as well as the effect of catalysts in the oxidation of anthracene, anthrone and oxanthrone were also investigated.

Keywords: Cytochrome P-450; Metalloporphyrin; m; -CPBA-oxidation; Polycyclic aromatic hydrocarbons; Anthracene

Development of catalyst libraries for total oxidation of methane by András Tompos; József L. Margitfalvi; Ernő Tfirst; Lajos Végvári; Mohyeddin A. Jaloull; Hamza A. Khalfalla; Mohammed M. Elgarni (pp. 65-78).

Using tools of combinatorial catalysis and high-throughput experimentation techniques new multi-component catalysts have been designed and tested for total oxidation of methane. The compositions of catalysts were optimized by means of holographic research strategy (HRS). In the first catalyst generation, the best hit resulted in 44% conversion of methane. However, after designing and testing 167 compositions in five generations, the best catalysts resulted in practically complete conversion of methane at 350°C. The supports of the best catalysts found by HRS consist of mostly Ce oxide and small amount of La. In the best catalyst, the concentration of Pt, Pd and Au is 2.3, 2.3 and 0.1%, respectively. In order to obtain the catalytic activity versus composition relationship, artificial neural networks (ANNs) have been trained using catalytic results of the HRS optimization. Upon combining HRS and ANNs, “virtual�? catalytic experiments were performed in order to (i) find “virtual�? optimum compositions and (ii) map the full experimental space in two dimensions. Results obtained in this study proved that HRS is a very powerful tool both in catalyst library design and visualization of the experimental space. The combination of HRS with ANNs appeared to be an excellent method for knowledge extraction. In this way, further new information can be obtained about the catalytic system investigated.

Keywords: Methane oxidation; Combinatorial catalysis; Catalyst library design; High-throughput experimentation; Artificial neural networks; Information mining; Multi-component catalysts

Fabrication of Nafion- and heteropoly acid-containing thin catalytic films without failure by L. Więcław-Solny; A.B. Jarzębski; J. Mrowiec-Białoń; W. Turek; Z. Ujma; A. Kudła; M. Gibas; J. Żak (pp. 79-85).

It has been shown that homogeneous thin films of silica heavily loaded with phosphotungstic acid (30wt.%) or Nafion (50wt.%) can be uniformly deposited on various substrates by a dip-coating to give effective structured catalysts with strong acidic properties. Experiments indicate that the use of well condensed silica sols, with over 75% of Qⁿ population in the form of Q³ sites, is a precondition to obtain crack-free films and that the withdrawal speed plays a second order role, especially at lower viscosities. Based on the quality maps of the films prepared under various conditions we conclude that defect-free coatings can be obtained provided that sol viscosity is above the specific threshold value and still within a linear part of the viscosity dependence upon time.

Keywords: Nafion; Heteropoly acid; Thin films

Partial oxidation of n-butane in a solid electrolyte membrane reactor: Periodic and steady-state operations by Yinmei Ye; Liisa Rihko-Struckmann; Barbara Munder; Kai Sundmacher (pp. 86-95).

An electrochemical membrane reactor using yttria-stabilized zirconia as a solid electrolyte membrane was applied to the selective partial oxidation of n-butane to maleic anhydride over a vanadium phosphorus oxide (VPO) catalyst. In this reactor, the oxygen required for anodic butane oxidation was generated by electrical oxygen pumping, i.e. by imposing an external current to the membrane reactor from anode to cathode. Periodic redox experiments, in which electrical oxygen pumping and butane oxidation were carried out sequentially, confirmed that the reduced activity of the VPO catalyst in the butane oxidation could be regenerated by electrical oxygen pumping. A series of steady-state experiments were carried out to assess the influence of operating conditions such as imposing current, reaction temperature, butane concentration and flow rate on the catalytic performance, where the electrochemical oxygen pumping and butane oxidation were performed simultaneously. The studied membrane reactor gave maleic anhydride yield of 10% with maleic anhydride selectivity up to 53% at reaction temperature of 753K.

Keywords: Solid electrolyte membrane reactor; Butane; Partial oxidation; Maleic anhydride; VPO catalyst; Electrical oxygen pumping

Rh/fibre catalyst for ethene hydroformylation: Catalytic activity and characterisation by T.A. Zeelie; A. Root; A.O.I. Krause (pp. 96-109).

A fibre-supported Rh-phosphine catalyst, Fibrecat™, was tested in hydroformylation of ethene and characterised by spectroscopic methods (NMR, DRIFT) before reaction, after pretreatments and after reaction. Fibrecat™ was an active and selective catalyst with 95% selectivity for propanal at 100°C and 0.5MPa. Higher temperatures were required to obtain similar activity with unmodified Rh/C and Rh/SiO₂ catalysts, and propanal selectivities remained less than 50%.³¹P NMR characterisations suggested that two kinds of Rh-P species were formed on Fibrecat™ during the catalyst preparation: a monophosphine species, Rh(acac)(CO)(PS-PPh₂), and a diphosphine species, Rh(CO)₂(PS-PPh₂)₂. An activation period of 5–10h at the beginning of the reaction on Fibrecat™ was required for transformation of the monophosphine and diphosphine species in contact with CO/H₂ to the active Rh-carbonyl hydrides. Evidently, Rh supported on phosphine-modified fibre forms catalytically active Rh-phosphine species with superior activity and selectivity to unmodified Rh catalysts and clearly higher activity than Rh-phosphine supported on silica.

Keywords: Ethene hydroformylation; Fibre supports; Phosphines; Rhodium; Heterogeneous hydroformylation; Deactivation; Pretreatments

Styrene epoxidation catalysed by manganese(III) salen complex supported on activated carbons by M�rio Cardoso; Ana Rosa Silva; Baltazar de Castro; Cristina Freire (pp. 110-118).

The hydroxyl functionalised manganese(III) salen complex, bearing a large π delocalisation, [Mn(4-HOsaldPh)Cl], was immobilised onto a commercial activated carbon and its air and acid oxidised forms using three different metal loadings. For all the materials the manganese contents were determined by ICP-AES and they were screened as heterogeneous catalysts in the epoxidation of styrene, using iodosylbenzene as oxygen source and acetonitrile as reaction media.All the heterogeneous catalysts were as chemoselective towards the styrene epoxide as the homogeneous counterpart, with the exception of the complex supported onto the acid oxidised activated carbon, which exhibited the lowest styrene epoxide selectivities, a consequence of its acidic oxygen surface groups; the highest styrene conversions and styrene epoxide yields were obtained for that complex immobilised onto the air oxidised activated carbon. Generally, an increase in styrene conversion and styrene epoxide selectivity with the manganese(III) complex loading onto all supports was observed. Upon reuse all the heterogeneous catalysts do not lose their styrene epoxide selectivity, but generally a slight decrease in the styrene epoxide yield is observed; catalyst aging studies done for one of the material prepared, [Mn(4-OHsaldPh)Cl]@C2_1%, revealed high stability and the same catalytic efficiency for almost 2 months.

Keywords: Styrene epoxidation; Manganese(III); salen; complex; Activated carbons

Ethane to acetic acid oxidation over supported heteropoly acids by M. Sopa; A. Wącław-Held; M. Grossy; J. Pijanka; K. Nowińska (pp. 119-125).

Molybdo(vanado)phosphoric heteropoly acids of Keggin structure supported on oxide supports (SiO₂, TiO₂, Al₂O₃) were used as catalysts for ethane to acetic acid oxidation in the range of reaction temperature from 250 to 400°C. Vanadium atoms introduced into Keggin structure enhanced oxidative activity of catalytic system, while vanadyl groups exchanged into cationic position diminished ethane conversion. Nature of support (acidic or base centres on the surface) influenced both ethane conversion and distribution of products. Ethane oxidation over silica- and titania-supported HPMoV_x was due to the presence of regular or defected Keggin structure while low catalytic performance on alumina-supported samples was attributed to mixed Mo–V–P oxides formed as a result of HPMoV_x decomposition. Presence of water vapours in the reaction mixture was indispensable both for catalysts surface modification and for acetic acid desorption.

Keywords: Ethane oxidation; Heteropoly acids; FT-IR spectroscopy; Acetic acid production

Liquid phase dehydration ofd-xylose in the presence of Keggin-type heteropolyacids by Ana S. Dias; Martyn Pillinger; Anabela A. Valente (pp. 126-131).

The heteropolyacids (HPAs) H₃PW₁₂O₄₀ (PW), H₄SiW₁₂O₄₀ (SiW) and H₃PMo₁₂O₄₀ (PMo) were tested as catalysts for the homogeneous liquid phase dehydration ofd-xylose to furfural. With dimethylsulfoxide (DMSO) as the solvent and a reaction temperature of 140°C, the tungsten-based HPAs are comparable with H₂SO₄ and p-toluenesulfonic acid catalysts in terms of furfural yield achieved after 4h (58–67%), whereas PMo yields less than half this amount of furfural. In the presence of PW, the temperature dependence of the initial reaction rate is approximated by the Arrhenius equation with the exponential term exp(−4767°K/ T). The initial rate of xylose conversion exhibits first-order dependence with respect to the initial xylose concentration and a non-linear dependence on initial HPA concentration. Catalytic results also vary according to the HPA composition and the nature of the solvent system (DMSO, water, water/toluene or water/isobutylmethylketone (IBMK)). Xylose conversions are higher in DMSO than in water-containing solvent systems. In DMSO, the turnover numbers (TON, mol/equiv. H⁺ calculated at 4h) follow the order PW>SiW>PMo, whereas in the water-containing systems the order changes to PMo>PW>SiW. In IBMK/water SiW is far more selective than PW (57 and 4% selectivity for SiW and PW, respectively, at 83–89% conversion) and yields more furfural (51% compared with <9% for PW and PMo, at 24h). In DMSO selectivity to furfural is slightly higher with PW (64–69%) than with SiW (52–64%), but much lower with PMo (<27%), above 87% conversion. For PW and SiW selectivity towards furfural production is higher for toluene/water than for DMSO for conversions up to 80%.

Keywords: Xylose; Furfural; Dehydration; Acid catalysis; Heteropolyacid; Reaction kinetics; Solvent effects

Application of¹²⁹Xe NMR to structural analysis of MoS₂ crystallites on Mo/Al₂O₃ hydrodesulfurization catalyst by Kazuhiko Hagiwara; Takeshi Ebihara; Nobuaki Urasato; Takashi Fujikawa (pp. 132-138).

We investigated an application of¹²⁹Xe NMR to Mo/Al₂O₃ hydrodesulfurization catalyst. When the molybdenum loading increased, a single peak shifted further to low magnetic field and became gradually broader. This result is caused by a growth of inhibition and irregularity in the motion of xenon. For a sulfided catalyst, the chemical shift δ of the peak varied nonlinearly against the amount of adsorbed xenon N. This result suggests that xenon electronically interacted with a coordinative unsaturated site at the stacked MoS₂ crystallite strongly. Moreover, we calculated the characteristic term δ₀ that is mainly dependent on collisions between xenon and other atoms on the surface. δ₀ became gradually larger with the molybdenum loading. This result shows that the increase in the molybdenum species on the surface of Al₂O₃ causes more collisions between xenon and molybdenum. In addition, δ₀ also became larger with the sulfurization temperature. This result suggests that δ₀ is a very sensitive parameter to the formation of the stacked MoS₂ crystallites. Hence,¹²⁹Xe NMR can be a powerful tool for structural analysis of Mo/Al₂O₃ catalysts.

Keywords: ¹²⁹; Xe NMR; Molybdenum alumina catalyst; Molybdenum sulfide crystallite; Molybdenum loading; Sulfurization temperature; Hydrodesulfurization; Structural analysis

The influence of chemical transport via vapour phase on the properties of chloride and caesium-doped V–Fe mixed oxide catalysts in the oxidation of butadiene to furan by J. Radnik; A. Wahab; M. Schneider; M.-M. Pohl; R. Schl�gl; B. Kubias (pp. 139-150).

Chloride and caesium-doped V–Fe mixed oxides prepared by different methods and calcined under vapour-phase transport-restricted conditions showed a high initial furan yield of up to 40mol% in the oxidation of butadiene. However, after only a few hours on stream a significant loss of activity and selectivity was observed. The reason for this undesirable property was investigated using different bulk and surface-sensitive characterisation methods such as X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and chemical methods. The data obtained for the structure, morphology, and composition of the fresh and used catalysts were correlated with their activity and selectivity properties. The presence of chloride ions was found to be surprisingly necessary for the origin of furan selectivity even up to 50%, which was however stable only for a short period of time. Chemical transport via chlorides or bromides was observed to be essential for the formation as well as the maintenance of the activity and selectivity properties of the system. The results obtained are interpreted with an assumption that the formation of volatile halides is necessary to form disperse VO_x species, which act as active and selective centres for the present reaction. Models for the formation and deactivation of these centres are discussed in this work. In addition, the possible roles of caesium and iron oxides in the catalytic system are also described and disputed.

Keywords: V–Fe mixed oxide catalysts; Butadiene oxidation; Furan; Deactivation; Chemical transport; Vapour phase; Catalyst constituents’ role

The structure of supported and unsupported vanadium oxide under calcination, reduction and oxidation determined with XAS by Geert Silversmit; Jeroen A. van Bokhoven; Hilde Poelman; Ad M.J. van der Eerden; Guy B. Marin; Marie-Fran�oise Reyniers; Roger De Gryse (pp. 151-162).

A vanadium oxide powder catalyst supported on titanium oxide (VO_x/TiO₂(anatase)) was investigated with in situ X-ray absorption spectroscopy (XAS). This system is applied in industry for partial oxidation processes. The structural changes of the supported vanadium oxide due to different treatments were determined: during a reduction–oxidation cycle at 623K after calcination in air and after heating in inert atmosphere. Unsupported crystalline V₂O₅ powder was used as a reference system. After calcination in air of the VO_x/TiO₂(anatase) a V₂O₅ bulk crystal structure appears, while an octahedral co-ordination with a VO vanadyl bond is present after heating in inert atmosphere. The redox cycle performed on fully oxidized supported vanadium oxide induces similar structural changes as for unsupported V₂O₅: a reduction to V⁴⁺ with a slightly distorted VO octahedron and a re-oxidation to the initial V₂O₅ structure. However, when the supported vanadium oxide is reduced after heating in inert, a valence lower than V⁴⁺ is obtained and a different structure is found: a symmetrical VO octahedron is present with VO and VV distances identical to the TiO and TiTi distances in TiO₂(anatase or rutile). After re-oxidation the V₂O₅ bulk structure is again obtained for the supported vanadium oxide.

Keywords: Supported vanadium oxide; Titanium oxide; Anatase; EXAFS; XANES; V; ₂; O; ₅; VO; _x; /TiO; ₂; Calcination; Reduction; Oxidation; In situ gas treatments

Aldehyde olefination with a ruthenium(II) salen catalyst by Wei Sun; Fritz E. K�hn (pp. 163-168).

A ruthenium salen complex of the type Ru(II)(salen)(PPh₃)₂ can be successfully applied as catalyst for the olefination of a broad variety of aldehydes. Dependent on the electron richness of the applied aldehydes, good to very good olefin yields are obtained and high E/ Z-selectivities are reached at 80�C reaction temperature with ethyl diazo acetate being the reaction partner. The reaction rate depends on the electron-donor capabilities of the aldehydes. Electron-poor aldehydes undergo faster reactions than electron-rich aldehydes, but both electron-rich and bulky aldehydes can be transformed to olefins in very good yields as well. Very good E/ Z-selectivities and quantitative olefin yields are obtained for aromatic aldehydes when the reaction is performed in the room-temperature ionic liquid (Bmim)PF₆ and toluene.

Keywords: Aldehyde olefination; Homogeneous catalysis; Ionic liquids; Ruthenium; Salen

Impact of cobalt-based catalyst characteristics on the performance of conventional gas-phase and supercritical-phase Fischer–Tropsch synthesis by N.O. Elbashir; P. Dutta; A. Manivannan; M.S. Seehra; C.B. Roberts (pp. 169-180).

This study covers the performance of three cobalt-based catalytic systems (high surface area 15% Co/SiO₂, low surface area 15% Co/SiO₂, and 15% Co/Al₂O₃) of different characteristics in Fischer–Tropsch synthesis (FTS) in both conventional gas-phase and supercritical hexane (SCH) phase. The reaction was conducted in a high-pressure FTS reactor setup at reaction temperature of 240°C, syngas (H₂/CO ratio of 2) flow rate of 50sccm/g_cat, and total pressures from 20 to 65bar. The surface characteristics of these catalysts were measured by N₂ physisorption using a TriStar 3000 gas adsorption analyzer. Room temperature X-ray diffraction (XRD), temperature and magnetic field ( H) variation of the magnetization ( M), and low-temperature (5K) electron magnetic resonance were used for determining the electronic states (Co⁰, CoO, Co₃O₄, Co²⁺) of cobalt for the calcined, reduced (before the reaction), and used samples (after the reaction). Correlations of the catalyst activity and selectivity with the catalysts surface characteristics reveal that pore radius of the catalyst has an influence on both syngas and CO conversions in gas-phase FTS. However, no such correlation was observed in the case of SCH-FTS, indicating an alleviation of that mass transfer limitations typically controlled by interparticle characteristics of the catalyst. This is attributed to the higher solubility of heavy products in the SCH medium that inhibits the condensation of those products inside the catalyst pores and enhances their in situ extraction. The XRD and magnetic characterizations of the used catalysts reveal that in situ reducibility of the Co₃O₄ to hcp-Co⁰ or fcc-Co⁰ is taking place during the FTS reaction. However, minimal in situ reduction was observed in the case of gas-phase FTS, whereby significant changes in the reduced cobalt electronic state and support (alumina, and silica) phase were detected under SCH-FTS conditions. As a result, both the activity and selectivity of the cobalt catalyst was found to be very stable and recoverable during SCH-FTS for relatively long time-on-stream (15 days).

Keywords: Fischer–Tropsch synthesis; Supercritical fluids; Alumina-supported cobalt catalyst; Silica-supported cobalt catalyst; Magnetization; X-ray diffraction

Enhanced photocatalytic activity of Ce³⁺–TiO₂ for 2-mercaptobenzothiazole degradation in aqueous suspension for odour control by F.B. Li; X.Z. Li; M.F. Hou; K.W. Cheah; W.C.H. Choy (pp. 181-189).

A series of cerium ion-doped titanium dioxide (Ce³⁺–TiO₂) catalysts with special 4 f electron configuration was prepared by a sol–gel process and characterized by Brunauer-Emmett-Teller method, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (DRS), and also photoluminescence (PL) emission spectroscopy. The photocatalytic activity of Ce³⁺–TiO₂ catalysts was evaluated in the 2-mercaptobenzothiazole (MBT) degradation in aqueous suspension under UV or visible light illumination. The experimental results demonstrated that the overall photocatalytic activity of Ce³⁺–TiO₂ catalysts in MBT degradation was signigicantly enhanced due to higher adsorption capacity and better separation of electron-hole pairs. The experimental results verified that both the adsorption equilibrium constant ( K_a) and the saturated adsorption amount ( Γ_max) increased with the increase of cerium ion content. The results of XPS analysis showed that the Ti³⁺, Ce³⁺, and Ce⁴⁺ ions reside in the Ce³⁺–TiO₂ catalysts. The results of DRS analysis indicated that the Ce³⁺–TiO₂ catalysts had significant optical absorption in the visible region between 400 and 500nm because electrons could be excited from the valence band of TiO₂ or ground state of cerium oxides to Ce 4 f level. In the meantime, the dependence of the electron-hole pair separation on cerium ion content was investigated by the PL analysis. It was found that the separation efficiency of electron-hole pairs increased with the increase of cerium ion content at first and then decreased when the cerium ion content exceeded its optimal value. It is proposed that the formation of two sub-energy levels (defect level and Ce 4 f level) in Ce³⁺–TiO₂ might be a critical reason to eliminate the recombination of electron-hole pairs and to enhance the photocatalytic activity.

Keywords: Adsorption; Cerium ion; Titanium dioxide; 2-Mercaptobenzothiazole; Visible light

Transesterification of diethyl oxalate with phenol using MoO₃/SiO₂ catalyst by A.V. Biradar; S.B. Umbarkar; M.K. Dongare (pp. 190-195).

Transesterification of diethyl oxalate (DEO) with phenol to form diphenyl oxalate (DPO) has been carried out in liquid phase using MoO₃/SiO₂ solid acid catalyst with high conversion and 100% selectivity. A series of MoO₃/SiO₂ catalysts with different Mo loadings (1–20wt%) were prepared using sol–gel technique and characterized using X-ray diffraction analysis (XRD), BET specific surface area, temperature-programmed desorption (TPD) of ammonia, and FTIR spectroscopic analysis of adsorbed pyridine. XRD analysis revealed the amorphous nature of the catalyst up to 10wt% MoO₃ loading and the formation of crystalline α-MoO₃ phase on amorphous silica support with higher MoO₃ loading. BET surface area showed high surface area for catalysts prepared by sol–gel technique with lower MoO₃ content; the surface area decreases with increasing MoO₃ loading. Ammonia TPD shows much higher acid strength compared to the catalysts prepared by impregnation technique. Among the series of catalysts prepared, MoO₃/SiO₂ containing 1wt% MoO₃ was found to be the most active catalyst for transesterification reaction, with a maximum DEO conversion of 80.9 and 100% selectivity for DPO. The effects of reaction temperature and catalyst concentration on conversion and product selectivity have been investigated.

Keywords: Transesterification; MoO; ₃; /SiO; ₂; Diphenyl oxalate; Diethyl oxalate; Sol–gel technique

Nanocluster iron oxide-silica aerogel catalysts for methanol partial oxidation by Chien-Tsung Wang; Shih-Hung Ro (pp. 196-204).

Nanostructured pure and silica-supported iron oxide materials have been prepared by the aerogel approach. Pure iron oxide powder derived from sol-gel ferric acetylacetonate formed agglomerates of 5–30nm small crystallites of hematite and maghemite according to TEM identification of crystal faces. Depositing ferric species to mesoporous silica aerogels generated 1–5nm particles in the amorphous matrix. They were evaluated for methanol oxidation in an ambient fixed-bed flow reactor from 225 to 300°C. Product selectivity and oxidation activity were dependent upon iron dispersion and reactor operation. The formation of dimethyl ether was mainly related to the bulk phase and Lewis acidity of iron oxide. Active catalysts that were selective to formaldehyde and methyl formate required appropriate iron dispersion on the silica surface, including a strong electronic interaction. Methoxy transformation to formaldehyde and formate species was found to be a function of surface temperature based on a Fourier transform infrared (FT-IR) analysis. Low to moderate reactor temperature and short catalyst contact time favored methanol conversion to formaldehyde. The formation of methyl formate was found to compete with that of formaldehyde. The dependence of response time on oxygen feed attenuation suggests that mobile lattice oxide ions participate in the surface reaction and that oxygen molecules help to maintain surface iron sites highly oxidized for Lewis chemisorption and redox electron transfer. A good correlation between microstructures and reaction characteristics is proposed.

Keywords: Aerogel; Nanoparticles; Nanoclusters; Iron oxide; Silica; Methanol oxidation

Calendar of Forthcoming Events (pp. 205-205).

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Applied Catalysis A, General (v.285, #1-2)

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Applied Catalysis A, General (v.285, #1-2)