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Applied Catalysis A, General (v.312, #1-230)

Editorial Board (pp. co2).

Synthesis of highly dispersed palladium alumina supported particles: Influence of the particle surface density on physico-chemical properties by M. Benkhaled; S. Morin; Ch. Pichon; C. Thomazeau; C. Verdon; D. Uzio (pp. 1-11).

Complexation with nitrite ions in aqueous medium was used to prepare highly dispersed Pd° particles supported on alumina. It has been possible to obtain catalysts with different Pd loading keeping the particle size lower than 1nm as shown by HRTEM, chemisorption, or extended X-ray absorption fine structure (EXAFS) characterizations, and as a consequence with different particle surface density. We observed that electronic properties measured by IR(CO) or X-ray photoelectron spectroscopy (XPS) measurements are strongly influenced by this last parameter and that the origin of these variations can be related to the different strengths of the interactions of the palladium precursor with the alumina surface sites as shown by low temperature CO adsorption followed by FTIR spectroscopy. On increasing Pd loading, saturation of unsaturated Lewis surface sites follows their acid strength: the more acidic ones are the first to react as germination sites, followed by the medium and finally the weaker sites. These different interactions may explain the variation of electronic properties of such small reduced particles which appears to be very sensitive to the chemical nature of their initial germination site on the oxide support. On the other hand, no such effects were observed on changing the type of alumina (δ or γ) support, in agreement with the principle of the synthesis method which tends to limit strong interaction with the support. Comparison with Pd° particles with the same particle size and particle surface density but prepared with the well known grafting of acetylacetonate precursor shows marked differences in terms of electronic properties followed by CO FTIR. This result illustrates the possibility to prepare highly dispersed Pd particles with different physico-chemical properties.

Keywords: Palladium; Heterogeneous catalyst preparation; Nano particles; Alumina; Particle surface density

XANES study of the susceptibility of nano-sized cobalt crystallites to oxidation during realistic Fischer–Tropsch synthesis by A.M. Saib; A. Borgna; J. van de Loosdrecht; P.J. van Berge; J.W. Niemantsverdriet (pp. 12-19).

The oxidation of cobalt during Fischer–Tropsch synthesis (FTS) has long been postulated as a major deactivation mechanism. In this study, wax coated samples of a Co/Pt/Al₂O₃ catalyst were taken from a 100-barrel/day slurry bubble column reactor operated at commercially relevant FTS conditions, i.e. 230°C, 20bar, (H₂+CO) conversion between 50 and 70%, feed gas composition of ca. 50vol.% H₂ and 25vol.% CO,PH2O/PH2=1–1.5,PH2O=4–6bar and quantitatively characterised by X-ray absorption near edge spectroscopy (XANES). The cobalt catalyst samples, carefully removed from the reactor during the course of Fischer–Tropsch synthesis, were protected from air by the FTS wax. It is clear from the XANES measurements that during realistic FTS conditions cobalt crystallites of 6nm supported on alumina were stable against oxidation to CoO/CoAl₂O₄ and a gradual reduction of residual cobalt oxide (i.e. following activation in pure hydrogen) was observed. This result is in line with recent thermodynamic analysis of the oxidation and re-reduction of nano-sized cobalt crystallites in water/hydrogen mixtures.

Keywords: Gas to liquids; Fischer–Tropsch; Cobalt; Alumina; Deactivation; Oxidation; XANES

Relation between photocatalytic activity and preparation conditions for nitrogen-doped visible light-driven TiO₂ photocatalysts by Soon-Kil Joung; Takashi Amemiya; Masayuki Murabayashi; Kiminori Itoh (pp. 20-26).

Nitrogen-doped visible light-driven TiO₂ photocatalyst powders were prepared at different temperatures and with different calcination times in a cylindrical tubular furnace under a stream of ammonia gas. Band-gap energy was from 2.92 to 3.04eV, corresponding to the visible light region. Optical absorbance and the intensities of electron spin resonance (ESR) spectra, which indicate the concentration of doped nitrogen, decreased with temperature and time of calcination in the visible light region, and were also independent of photocatalytic activity. We found that the temperature of preparation (673, 773, and 873K) and calcination time were important factors governing the photocatalytic reactivity of the N-doped TiO₂: the highest photocatalytic activities for samples prepared at 673 and 873K were observed with calcination times of 5 and 10min, while that for samples prepared at 773K was observed with a calcination time of 60min. Active species at each calcination temperature may be as follows: active species for samples prepared at 673K for 5 and 10min may mainly be nitrogen species (NO, NO₂, NO²⁻, NH₂, etc.); that for samples prepared at 773K for 60min may mainly be doped atomic nitrogen; and that for samples prepared at 873K for 5 and 10min may be doped atomic nitrogen and nitrogen species.

Keywords: TiO; 2−; _X; N; _X; Visible light; Photocatalyst; ESR; Nitrogen

Mechanism of partial oxidation of methane over a nickel-calcium hydroxyapatite catalyst by Jin Hyuk Jun; Tae Hoon Lim; Suk-Woo Nam; Seong-Ahn Hong; Ki June Yoon (pp. 27-34).

The mechanism of partial oxidation of methane to synthesis gas over a nickel-calcium hydroxyapatite catalyst was studied by employing pulse experiments for the powder catalyst and by measuring temperature profiles of the activated, washcoated monolith catalyst. The pulse study showed that after the catalyst was partially reduced, carbon deposition occurred to a great extent and CO was predominantly produced over CO₂. Temperature profiles of the monolith catalyst showed that the highest temperature difference between the furnace and the monolith became smaller as the furnace temperature increased. We propose that the reaction occurs primarily via the pyrolysis mechanism or direct dissociation of methane. Adsorbed CO (CO_s) is a common intermediate and it is rapidly desorbed to produce CO(g), especially at high temperature, or converted to CO₂(g), especially at low temperature. The observation that the fully reduced catalyst exhibited lower activity suggests that both metallic Ni and partially oxidized nickel are required in order to exhibit high activity and selectivity.

Keywords: Calcium hydroxyapatite; Mechanism; Methane partial oxidation; Nickel; Pulse experiment

Phase transformation of unpromoted and promoted Fe catalysts and the formation of carbonaceous compounds during Fischer–Tropsch synthesis reaction by Wensheng Ning; Naoto Koizumi; Hai Chang; Takehisa Mochizuki; Takashi Itoh; Muneyoshi Yamada (pp. 35-44).

Precipitated Fe catalysts with or without additives (Zn, K, Cu) were prepared, pretreated by CO, and then time-dependent behaviors of their FTS activities were investigated at 503K and 1.6MPa in a fixed bed reactor. Over the catalyst without additives, CO conversion showed a maximum at ca. 8h on stream and then decreased monotonically with increasing time on stream. When Zn, K and/or Cu were added, respectively, similar behaviors were observed. However, an increasing CO conversion was observed during on stream (29h) when Zn, K and Cu were added simultaneously. X-ray diffraction (XRD) analysis of these catalysts showed the formation of Fe carbides (Fe₅C₂ and Fe_xC) after the CO pretreatment irrespective of the catalyst composition. In the case of the catalyst without additives, these carbides were oxidized to Fe₃O₄ during on stream. The oxidation of the carbides was more significant on the catalyst charged near the outlet of the reactor. For the catalyst containing all the additives simultaneously, however, the Fe carbides were only phases detected by XRD analysis even after the long time on stream (29h). In addition, the formation of amorphous carbonaceous compounds was observed by laser Raman spectroscopy (LRS) for the catalysts after the CO pretreatment and/or the FTS reaction. So-called a graphite-like carbonaceous compound was not observed by LRS, which was considered as one of reasons for the catalyst deactivation in the previous studies. Therefore, it is suggested that the oxidation of the Fe carbides by H₂O vapor is a main reason for the deactivation of the Fe FTS catalyst. Because the Zn, K and Cu containing catalyst showed a higher CO₂ selectivity, the combination of these additives improves the water-gas shift activity, thereby suppresses the oxidation of the Fe carbides.

Keywords: Fischer–Tropsch synthesis; Fe catalysts; Deactivation; Laser Raman spectroscopy; Oxidation; Carbonaceous compound

Conversion of methylcyclohexane over Ir/H-β zeolite in the presence of hydrogen by Takeshi Sugii; Yuichi Kamiya; Toshio Okuhara (pp. 45-51).

We studied the conversion of methylcyclohexane into dimethylpentanes in the presence of hydrogen, catalyzed by Ir supported on H-β zeolites with different Si/Al ratios. Ir/H-β catalysts with a high Si/Al ratio (Si/Al=75 or 150) showed activity in promoting both ring-contraction (from six-membered to five-membered rings) on the acidic sites of H-β and ring-opening on Ir metal sites, resulting in high activity and selectivity toward dimethylpentanes. In contrast, Ir/H-β catalysts with a low Si/Al ratio were less active in ring-opening on the Ir metal sites, which resulted in the high selectivity for dimethylcyclopentanes. In the conversions of methylcyclohexane, 2-methylhexane, and 2,4-dimethylpentane, the dependence of the conversion rate on W/ F values demonstrated that, for the highly active and selective Ir/H-β catalyst with Si/Al=75, methylcyclohexane was first transformed into dimethylcyclopentanes on the acidic sites, followed by ring-opening on the Ir sites to form dimethylpentanes and methylhexanes. The skeletal isomerization of methylhexanes into dimethylpentanes over this catalyst was very slow under the reaction conditions studied.

Keywords: Methylcyclohexane; Dimethylpentane; Iridium; H-β zeolite; Ring-contraction; Hydrogenolysis

Enhancement of the activity for oxidative dehydrogenation of propane on calcium hydroxyapatite substituted with vanadate by Shigeru Sugiyama; Takeshi Osaka; Yuuki Hirata; Ken-Ichiro Sotowa (pp. 52-58).

Calcium hydroxyapatites substituted with vanadate were prepared for use as catalysts in the oxidative dehydrogenation of propane. Phosphate in the hydroxyapatite could not be fully substituted by vanadate, but partial substitution achieved an atomic ratio of V/P=0.15. The conversion for propane and the selectivity for propylene increased from 5.9 and 1.4% on calcium hydroxyapatite to 16.5 and 54.2%, respectively, for vanadate incorporation in hydroxyapatite at V/P=0.10 (atomic ratio). The latter correspond to results for Mg₂V₂O₇ under the same reaction conditions (14.0 and 50.9%, respectively), which is generally accepted as an active catalyst for oxidative dehydrogenation. Dehydrogenation in the absence of gaseous oxygen in the feedstream on vanadate-substituted hydroxyapatite and⁵¹V MAS NMR analyses of the catalysts used suggest that the abstraction and incorporation of lattice oxygen from and in vanadate, followed by redox between V⁴⁺ and V⁵⁺, directly contribute to the activation of propane. The effects of P(C₃H₈)/ P(O₂) in the feedstream and the catalyst weight on the oxidative dehydrogenation of propane over hydroxyapatite substituted with vanadate at V/P=0.10 are also described.

Keywords: Oxidative dehydrogenation; Propane; Calcium hydroxyapatite; Vanadate

Characterization and catalytic properties of nanosized cobaltate particles prepared by in situ synthesis inside mesoporous molecular sieves by E.V. Makshina; S.V. Sirotin; M.W.E. van den Berg; K.V. Klementiev; V.V. Yushchenko; G.N. Mazo; W. Grünert; B.V. Romanovsky (pp. 59-66).

Bulk lanthanum cobaltate (LaCoO₃) with perovskite-like structure and LaCoO_x supported onto the mesoporous MCM-41 molecular sieve were synthesized by the conventional citrate method. The prepared samples were characterized by XRD, nitrogen BET measurements, H₂-temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), XAFS and SEM-energy-dispersive X-ray (EDX) techniques. The turnover frequency of the supported cobaltate in methanol oxidation is two orders of magnitude larger than that of the bulk perovskite material. Based on the characterization results, it is concluded that the supported cobaltate does not form species of LaCoO₃ short-range order in MCM-41. The high activity is related to a highly disordered, oxygen-deficient Co oxide phase, which is probably stabilized by the La ions present.

Keywords: LaCoO; ₃; mixed oxide; Mesoporous molecular sieve MCM-41 type; Methanol oxidation

Supported gold catalysts for the total oxidation of alkanes and carbon monoxide by Benjamin E. Solsona; Tomas Garcia; Christopher Jones; Stuart H. Taylor; Albert F. Carley; Graham J. Hutchings (pp. 67-76).

Gold catalysts on oxide supports prepared by coprecipitation (CoO_x, MnO_x, CuO, Fe₂O₃ and CeO₂), deposition-precipitation (TiO₂) and impregnation (CoO_x and MnO_x) have been characterised and tested for the total oxidation of methane, ethane and propane, and the catalytic activity was contrasted with their performance for oxidation of CO at ambient temperature. Many of the oxides selected as supports are active alkane activation catalysts at high temperature (e.g. MnO_x and CoO_x). The addition of gold to these active materials for the alkane combustion leads to a marked increase in the catalytic activity in all cases investigated. All the supports were active for the oxidation of alkanes but the addition of gold leads to a decrease in the temperature at which oxidation is first observed. The most effective catalyst for alkane oxidation was Au/CoO_x which was found to retain constant high activity for a 48h test period, and the highest activity catalysts were prepared by coprecipitation rather than impregnation. Interestingly, no correlation between alkane oxidation and CO oxidation was apparent in these studies indicating that different mechanisms of oxygen activation and/or different active sites are involved. This is discussed in terms of recent observations concerning selective versus total oxidation with gold catalysts.

Keywords: Alkane oxidation; Gold catalyst; CO oxidation

Surfactant containing Si-MCM-41: An efficient basic catalyst for the Knoevenagel condensation by Leandro Martins; Tito J. Bonagamba; Eduardo R. de Azevedo; Pascal Bargiela; Dilson Cardoso (pp. 77-85).

Si-MCM-41 molecular sieves, which are largely used in a number of acid and redox catalyzed reactions, as reported by the literature, were used as basic catalyst for the Knoevenagel condensation. This reaction involves the condensation of carbonyl compounds with active methylene compounds to generate unsaturated products. The catalyst, which pores were occluded by the organic template, provided high activity in mild conditions, even under 10°C. The high activity is due to the presence of siloxy anions, of high basicity, located in the pore cavity of the hexagonally ordered mesopores. Ion exchange procedures evidenced the presence of these high basic sites as a consequence of the high pH increase of the solution containing tetramethylammonium chloride, or the high H⁺ consumption, added to a the medium as HCl, to keep constant pH. O 1s XPS and²⁹Si CP/MAS NMR measurements confirmed the existence of only ≡SiO⁻CTA⁺ ionic pair, which is the basic site itself.

Keywords: Si-MCM-41; Basic catalysis; Knoevenagel condensation; Molecular sieves

Baeyer–Villiger oxidation of cyclohexanone with hydrogen peroxide/benzonitrile over hydrotalcites as catalysts by César Jiménez-Sanchidrián; Julia María Hidalgo; Rafael Llamas; José Rafael Ruiz (pp. 86-94).

Various Mg/Al, Mg/Al/Sn and Mg/Al/Zr hydrotalcite-like compounds (HTs) were prepared for use as catalysts in the Baeyer–Villiger (BV) oxidation of cyclohexanone with H₂O₂/benzonitrile as oxidant and benzonitrile itself as the solvent. The reaction gave water and benzamide as byproducts, the latter can be recycled in an appropiate process. Analysis of the solids revealed that tin and zirconium are in fact incorporated into the HT structure. The solids containing Mg/Al and Mg/Al/Sn and their calcination products (viz. Mg/Al and Mg/Al/Sn mixed oxides) were found to be effective catalysts for the BV oxidation of cyclohexanone. The Sn solids exhibited a higher activity than a more conventional catalyst obtained from an HT containing Mg and Al only (17% in the best case). Also, the catalyst containing tin was active when we used H₂O₂/acetonitrile system as oxidant. The solids containing Zr were found to promote the decomposition of the hydrogen peroxide and hence to adversely influence the oxidation reaction. A mechanism accounting for the experimental results is proposed. The reaction was conducted under very mild conditions (viz. atmospheric pressure and a temperature of 70°C), and conversions obtained were higher than 80% in some cases and 100% selectivity after 6h. The most active catalyst, which was that containing the largest amount of tin, retained full activity after three reuses.

Keywords: Hydrotalcite; LDH; Baeyer–Villiger oxidation; Cyclohexanone; Tin; Zirconium

Catalytic combustion of methane in steam and carbon dioxide-diluted reaction mixtures by S. Eriksson; M. Boutonnet; S. Järås (pp. 95-101).

Supported palladium catalysts have been tested for methane combustion under lean conditions in the temperature range of 200–800°C. The effect of diluting the reaction mixture with high amounts of water and carbon dioxide was studied in order to simulate a combustion process with exhaust gas recirculation. The influence of support material, i.e. ZrO₂ or doped CeO₂, on the catalytic performance was also investigated.The catalyst support material was found to influence the light-off temperature significantly, which increased in the following order: Pd/ZrO₂22. The order of activity changed at higher temperatures resulting in Pd/La-CeO₂ being the most active catalyst above 670°C. This catalyst also shows a more stable performance with no distinct deactivation occurring at higher temperatures during cooling.Both water and CO₂ were found to have a negative influence on the catalytic activity. The inhibitory effect was, however, more pronounced for water. This inhibitory effect was present in the entire temperature range investigated. Adding CO₂ in the presence of water resulted in conversions similar to the ones observed when feeding water alone for Pd/ZrO₂ and Pd/La-CeO₂. On the contrary, the activity of Pd/Zr-CeO₂ was further decreased when co-feeding water and CO₂.

Keywords: Catalytic combustion; Palladium; TPO; AZEP; Water inhibition; CO; ₂; inhibition

Unexpected roles of toluene in the catalytic isomerization of 1,5- to 2,6-dimethylnaphthalene by Natthakorn Kraikul; Pramoch Rangsunvigit; Santi Kulprathipanja (pp. 102-107).

Catalytic isomerization of 1,5- to 2,6-dimethylnaphthalene (DMN) over H-beta zeolite was carried out in a continuous flow fixed bed system by using toluene as a solvent in this study. Feed flow rates, reaction temperatures and feed concentrations were varied to investigate their effect on the isomerization in the presence of the solvent. Interestingly, it was found that the presence of toluene leads to the modification of the reaction thermodynamics, resulting in the ease of the isomerization to be occurred at significant lower temperatures, besides its roles to facilitate the reaction for the flow system by dissolving the solid reactant (1,5-DMN) and enhance the system mass transfer. As a result, the maximum yield of 2,6-DMN as in the high temperature equilibrium of the solvent-free system could possibly be approached at even low temperatures when the system is not limited by mass transfer of the DMN species and the reaction kinetics.

Keywords: Dimethylnaphthalene; Isomerization; Solvent; Solvation; Toluene; Thermodynamics

Transesterification of cyclic carbonates with methanol at ambient conditions over tungstate-based solid catalysts by M. Sankar; C. Madhavan Nair; K.V.G.K. Murty; P. Manikandan (pp. 108-114).

Dimethyl carbonate synthesis with 80mol% yield is achieved through transesterification of ethylene carbonate with methanol at ambient conditions (RT and atmospheric pressure) using alkali and alkaline-earth tungstates as solid catalysts. The catalysts are efficient even at the sub-ambient temperatures. Reactions under CO₂ pressure indicate that CO₂ atmosphere retards the transesterification reaction completely below 100°C. Experimental conditions of 150°C and 3.4MPa CO₂ pressure are required to obtain maximum DMC yield of 71mol%. Synthesis of DMC by one-pot synthesis using epoxide, CO₂ and methanol is not as effective as that by two-step method with the present catalyst system. Raman and IR spectra of methanol-interacting tungstates indicate the formation of a methoxide ion species adsorbed at the catalyst surface as one possible reaction intermediates.

Keywords: Dimethyl carbonate; Sodium tungstate; Ethylene carbonate; Transesterification; Heterogeneous catalyst; Raman spectroscopy

Sol–gel entrapped dichlorobis(triphenylphosphine)palladium as an efficient recyclable catalyst for the cross-coupling of aryl halides with indium- and related alkylating reagents by Alaa Talhami; Liza Penn; Nimer Jaber; Khalil Hamza; Jochanan Blum (pp. 115-119).

Physically entrapped dichlorobis(triphenylphosphine)palladium(II) within a silica sol–gel matrix is an efficient catalyst for cross-coupling of aryl iodides, bromides and triflates with intramolecularly stabilized dimethyl- and diethylindium alkylating reagents. The coupling reactions take place in benzene or toluene and depend both on the electronic and steric nature of the substrate, and on the electronic structure of the encaged palladium complex. The immobilized catalyst is leach proof and can be recycled at least four times without significant loss of its activity. The catalyst promotes also the Suzuki coupling of aryl halides with phenylboronic acid and the Stille reaction with tributylphenyltin. In aromatic hydrocarbon solvents both cross-coupling and homocoupling take place as the major and minor processes, respectively. In dioxane homocoupling becomes more significant on account of the desired cross-coupling reaction.

Keywords: Catalysis; Cross-coupling reactions; Indium; Palladium; Silica sol–gel

Chemoselective oxidation of organic sulfides catalyzed by Fe(III) complexes by Claudio O. Kinen; Laura I. Rossi; Rita H. de Rossi (pp. 120-124).

Different iron(III) complexes were used as catalysts in sulfoxidation reactions giving excellent yields and a high chemoselectivity. Among the complexes, the best one was a solid β-cyclodextrin-FeBr₃ complex. Sulfoxidation takes place with high chemoselectivity in the presence of other groups such as benzaldehyde, benzylic alcohol, benzylic methylene and benzothiazole.

Keywords: Chemoselectivity; Sulfoxidation; Iron(III) complexes; Cyclodextrins; Catalysis

Characterization of highly dispersed cobalt sulfide catalysts by X-ray absorption fine structure and magnetic properties by Takeshi Kadono; Takeshi Kubota; Ichiro Hiromitsu; Yasuaki Okamoto (pp. 125-133).

Zeolite-supported cobalt sulfide catalysts, CoS/NaY and CoS/USY-H, were prepared using Co(CO)₃NO as a precursor. A SiO₂-supported cobalt sulfide catalyst was prepared by an impregnation method for comparison. The prepared catalysts were characterized by magnetic properties and XAFS. The cobalt sulfides in CoS/NaY are paramagnetic and can be characterized as intrazeolite dinuclear species with antiferromagnetic interactions between the Co atoms, in contrast to the cobalt sulfides in CoS/SiO₂, in which 95% of Co is Co₉S₈ and 5% is paramagnetic with a very small amount of ferromagnetic species. The structure of the cobalt sulfides in CoS/USY-H depends on the treatment after the sulfidation. Ultra-highly dispersed cobalt sulfide species initially formed during the sulfidation are transformed to highly dispersed Co₉S₈-like particles and eventually to ion-exchanged Co²⁺ cations as the evacuation temperature and duration are increased. The catalytic activity of the cobalt sulfide catalysts was measured for the hydrodesulfurization of thiophene. The results suggest a synergy generation between cobalt sulfides and surface hydroxyl groups.

Keywords: Cobalt sulfide catalysts; Hydrodesulfurization; Magnetic property; XAFS; XANES; Zeolite

Sol–gel synthesis of V₂O₅–SiO₂ catalyst in the oxidative dehydrogenation of n-butane by Viviana Murgia; Elsa M. Farfán Torres; Juan C. Gottifredi; Edgardo L. Sham (pp. 134-143).

The sol–gel method was used to prepare V–SiO₂ catalyst by hydrolysis of vanadium acetylacetonate and silicon alkoxide. Structural changes in the vanadium species upon heat treatment at various temperatures were studied by means of XRD, XPS; DRS UV–vis, FTIR and FTIR of absorbed pyridine. From characterization studies, it was possible to conclude that during the synthesis process, vanadium acetylacetonate, is adsorbed on the external surface of silica particles formed by tetraethoxysilane hydrolysis. A catalyst prepared by wet impregnation of commercial SiO₂, with identical V/Si surface ratio was used for comparative purposes. The catalytic behaviour of the solids was studied for the oxidative dehydrogenation of n-butane. The results indicate that vanadium silicate gel calcined at 500°C is the most active solid. It was found that this preparation procedure leads to the formation of a solid with a high surface area which allows a better dispersion of active species. A direct correlation between catalytic activity and Brönsted acidity was also observed.

Keywords: Acidity; Butenes; n; -Butane; Oxidative dehydrogenation; Silica; Sol–gel; Vanadium catalyst

Determination of the stability constants for cobalt, nickel and palladium homogeneous catalyst complexes containing triphenylphosphine ligands by T. Djekić; Z. Zivkovic; A.G.J. van der Ham; A.B. de Haan (pp. 144-152).

Homogeneous catalysts are complex compounds that are always in equilibrium with their free metal, free ligand and other forms of complexes. The ratios between different species are defined by the stability constants, which are influenced by different parameters such as the type of metal, ligand, counter ion or solvent. The main goal of this paper is the determination of the stability constants for a range of different homogeneous catalyst complexes and therefore the concentration of each species present in the solution. This information is needed for the modelling and design of reverse flow adsorption (RFA) technology, a novel concept for the recovery and recycling of homogeneous catalysts [J. Dunnewijk, H. Bosch, A.B. de Haan, Sep. Purif. Technol. 40 (3) (2004) 317–320; J. Dunnewijk, H. Bosch, A.B. de Haan, Adsorption 11 (2005) 521–526]. Cobalt, nickel and palladium halogens with triphenylphosphine as a ligand are selected as complexes since they are commonly used in homogeneous catalysis. Titration experiments with UV–vis spectroscopy as analytical technique have been carried out. The results were analyzed with a stability constant model developed for 1:2 complexation and adjusted for easy handling using Microsoft Excel. The stability constants of the selected complex systems increase in order: [PdCl₂(OPPh₃)₂]_acetonitrile≈[CoCl₂(PPh₃)₂]_butanol<[CoBr₂(PPh₃)₂]_acetonitrile<[CoCl₂(PPh₃)₂]_acetonitrile<[NiBr₂(PPh₃)₂]_acetonitrile<[PdCl₂(PPh₃)₂]_DMF<[PdCl₂(PPh₃)₂]_acetonitrile. The obtained results for the stability constants could be explained with the hard and soft acid base theory in combination with the natural order of different species theory.

Keywords: Reverse flow adsorption; Cobalt; Nickel; Palladium; Triphenylphosphine; Stability constants; 1:2 Complexation model

Structural features and photocatalytic behaviour of titania deposited within the pores of SBA-15 by Alina Maria Busuioc; Vera Meynen; Evi Beyers; Myrjam Mertens; Pegie Cool; Nicolae Bilba; Etienne F. Vansant (pp. 153-164).

The growth of titania nanoparticles within the mesopores of SBA-15 has been controlled by a post-synthesis deposition using the acid-catalyzed sol–gel method (ACSG). The crystal size, the location and the crystalline phase of the titania nanoparticles can be tuned by a careful adjustment of the preparation conditions. The influence of the initial titania amount, the pH and the temperature on the characteristics of titania-SBA-15 catalyst has been studied. The combined data from the structural and chemical analysis demonstrates that titania nanoparticles with different sizes were grafted within the SBA-15 channels. The formation mechanism of the titania nanoparticles within the mesopores is discussed. The photodecomposition of rhodamine 6G (R6G) in aqueous medium was selected as probe reaction to test the photoactivity of the titania-SBA-15 powders and to verify the potential use of these materials for wastewater treatment. It was shown that the preparation method and the structural characteristics of the mesoporous materials are of great importance for the adsorption capacity and the photocatalytic activity.

Keywords: Titanium dioxide; Nanoparticles; PHTS materials; Sol–gel process; Photocatalyst

Role of cerium in promoting the stability of CuHM catalyst against HCl to reduce NO with NH₃ by Jin Woo Choung; In-Sik Nam (pp. 165-174).

To enhance the chlorine tolerance of copper ion exchanged mordenite (CuHM) catalyst under NH₃-SCR reaction condition when HCl exists in the feed gas stream, mainly from a waste incinerator, a second metal, particularly cerium, has been additionally exchanged onto the catalyst along with Cu. It prevents Cu(II) ion from being evaporated from the catalyst surface by HCl and significantly improves the catalyst deactivation. The loss of copper from CeCuHM catalyst has been observed at a reaction temperature of 450°C, while that from CuHM catalyst without Ce begins at 350°C. Ce simply stabilizes Cu(II) ion on the catalyst surface, generally recognized as an active reaction site for the present reaction system. X-ray absorption near edge spectroscopy (XANES), extended X-ray absorption fine structure (EXAFS), synchrotron radiation X-ray diffraction (SR-XRD), and X-ray photoelectron spectroscopy (XPS) have been employed to identify the stabilization of Cu(II) ion on CuHM catalyst by Ce. As confirmed by SR-XRD, the lattice parameters of the unit cell of CeCuHM catalyst are less altered than those of CuHM catalyst without Ce during the course of the catalyst deactivation. Similarly, as identified by XPS, Cu(II) on the surface of CeCuHM catalyst is less transformed to Cu(I) ions. Ce ions and Ce–Cl compounds formed on the catalyst surface may decrease the average electronegativity of the catalyst and increase the charge of the lattice oxygen in the zeolite framework, resulting in an enhancement of the stability of the Cu–O bond in the present catalytic system.

Keywords: Selective catalytic reduction of NO; _x; Deactivation of CeCuHM by HCl; Cerium; XANES; EXAFS; XPS; SR-XRD

Formation of cyclopentanone from dimethyl hexanedioate over CeO₂ by Osamu Nagashima; Satoshi Sato; Ryoji Takahashi; Toshiaki Sodesawa; Tetsu Akashi (pp. 175-180).

Cycloketonization of dimethyl hexanedioate into cyclopentanone was investigated over pure CeO₂ at a temperature between 350 and 475°C. The conversion of the diester increased with raising the reaction temperature. The selectivity to cyclopentanone, however, decreased whenever the conversion increased. The major by-product other than methanol was 2-methylcyclopentanone. It was found that methylation of cyclopentanone with methanol into 2-methylcyclopentanone proceeded over CeO₂. The decrease in the selectivity to cyclopentanone at high conversion was mainly caused by a consecutive reaction of cyclopentanone into 2-methylcyclopentanone due to alkylation with methanol.

Keywords: CeO; ₂; Dimethyl hexanedioate; Cyclopentanone; Methanol; Alkylation

Highly selective conversion of ethene to propene over SAPO-34 as a solid acid catalyst by Hiroshi Oikawa; Yasunori Shibata; Koji Inazu; Yasuyoshi Iwase; Kazuhito Murai; Shinya Hyodo; Genta Kobayashi; Toshihide Baba (pp. 181-185).

Ethene is selectively converted to propene over SAPO-34 at 723K with a yield of 52.2% and selectivity of 73.3% at ethene conversion of 71.2%. The high and selective propene yields achieved over SAPO-34 can be attributed to a shape selectivity effect of the small-pore SAPO-34 and modest acid strength of acidic protons.

Keywords: Ethene; Propene; SAPO-34; Solid acid catalyst

A neutral templating route to mesoporous titanium phosphate molecular sieves with enhanced thermal stability by Chunliu Pan; Shi Yuan; Wenxiang Zhang (pp. 186-193).

For the first time the mesoporous titanium phosphates with high surface area and highly thermal stability were synthesized using long-chain n-alkylamine as structure-directing agents under an ethanol system containing a small quantity of water. Powder X-ray diffraction (XRD) and transmission electron micrograph (TEM) show that the disorder mesopores exist in the mesostructured materials. The mesoporous titanium phosphates calcinated at 500°C for 10h still retain the refined pore structure and the high surface area. UV–vis absorption suggests most of titanium is tetrahedrally coordinated in the framework of calcinated mesoporous titanium phosphates. The high catalytic activity in the liquid-phase partial oxidation of cyclohexene with H₂O₂ oxidant supports the tetrahedral coordination of titanium in these materials.

Keywords: Mesoporous; Titanium phosphates; Thermal stability; Cyclohexene

A comparative study on the transalkylation of diisopropylbenzene with benzene over several zeolitic materials in supercritical CO₂ and liquid phase by J.L. Sotelo; L. Calvo; A. Pérez- Velázquez; D. Capilla; F. Cavani; M. Bolognini (pp. 194-201).

This work describes the catalysts screening and the analysis of the effect of supercritical carbon dioxide on the transalkylation of diisopropylbenzene with benzene. The catalysts included three acidic commercial zeolites: beta, Y and mordenite with different aluminum contents (e.g. Si/Al molar ratio). Their performance was compared in terms of cumene yield and selectivity, taking into account the competitive isomerization, and the by-products formation. The influence of the Si/Al molar ratio on the catalytic activity was discussed in terms of total acidity and strength of acid sites. Liquid, subcritical and supercritical conditions were comparatively investigated. The results proved that transalkylation rates were not accelerated by the increase in pressure from subcritical to supercritical conditions. Comparing to conventional liquid phase conditions, the use of supercritical CO₂ did not result in superior catalytic transalkylation activity for the Y-zeolite. On the contrary, an important improvement in product yield was obtained with the beta and mordenite zeolites. Results were related to reactant mixture mass transport properties and catalysts structure.

Keywords: Beta zeolite; Y-zeolite; Mordenite zeolite; Supercritical carbon dioxide; Transalkylation; Diisopropylbenzene; Benzene; Cumene

A comprehensive study of the synthesis, characterization and activity of TiO₂ and mixed TiO₂/SiO₂ photocatalysts by José Aguado; Rafael van Grieken; María-José López-Muñoz; Javier Marugán (pp. 202-212).

The use of titania–silica materials in photocatalytic processes has been proposed as an alternative to the conventional TiO₂ catalysts, in order to facilitate the separation of the solids after the reaction. However, despite the large number of works in this field, up to date it is not totally clarified the mechanism governing the photocatalytic activity of the mixed TiO₂/SiO₂ oxides. In the present work, several titania–silica materials have been prepared through a sol–gel method controlling the main variables to obtain materials with different textural properties, degree of titanium incorporation and dispersion of such species and crystallinity of titanium dioxide. Characterization of the samples and correlation with their activity for the photocatalytic oxidation of cyanide has permitted to determine that the main factors conditioning the photoactivity of these materials are: (i) textural properties and accessibility of the titania surface, (ii) formation of anatase nanocrystals of suitable size and band gap energy and (iii) quality of the titania crystal network, improved by the use of a hydrothermal crystallization procedure.

Keywords: Photocatalysis; Titania–silica xerogels; Sol–gel; Hydrothermal crystallization; Cyanide

Properties and metathesis activity of molybdena-alumina, molybdena-silica-alumina and molybdena-silica catalysts—a comparative study by Jarosław Handzlik; Jan Ogonowski; Jerzy Stoch; Maciej Mikołajczyk; Piotr Michorczyk (pp. 213-219).

The properties of molybdena-alumina, molybdena-silica-alumina and molybdena-silica systems prepared by thermal spreading of MoO₂(acac)₂ complex were investigated with XRD and XPS. The activity of the catalysts in propene metathesis was measured for a wide range of Mo loadings. For the low Mo content, the specific activity of the molybdena-silica-alumina catalyst is much higher than for both other systems, while for the high Mo loadings, the molybdena-alumina catalyst exhibits the highest efficiency.

Keywords: Molybdenum; Alumina; Silica-alumina; Silica; Metathesis

Finely dispersed Pd-Zn catalyst supported on an organized mesoporous alumina for hydrogen production by methanol steam reforming by Maurizio Lenarda; Elisa Moretti; Loretta Storaro; Pasquale Patrono; Fulvia Pinzari; Enrique Rodríguez-Castellón; Antonio Jiménez-López; Guido Busca; Elisabetta Finocchio; Tania Montanari; Romana Frattini (pp. 220-228).

This work describes the preparation and the characterization of a catalytic system for the production of hydrogen by oxidative steam reforming of methanol (OSRM), prepared by deposition of palladium acetate on an organized mesoporous alumina, followed by pre-reduction at room temperature with a zinc borohydride solution. This procedure allows one to obtain intimately interacting Pd-Zn species that easily generate the 1:1 Pd/Zn alloy, as a result of thermal treatment in reducing conditions at 500°C. The alloy formation was clearly proven by X-ray diffraction measurements. The samples were also characterized by N₂ adsorption–desorption, atomic absorption spectroscopy (AAS), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (FT-IR). This type of material was found to be active in the oxidative steam reforming of methanol, in the temperature range between 100 and 400°C, producing a hydrogen/CO₂ mixture with low concentrations of CO.

Keywords: Hydrogen production; OSRM; Methanol oxidative steam reforming; Pd/ZnO/Al; ₂; O; ₃; catalyst; PdZn alloy

Calendar of Forthcoming Events (pp. 229-229).

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Applied Catalysis A, General (v.312, #1-230)