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Applied Catalysis A, General (v.324, #)

Editorial Board (pp. co2).

Contents (pp. iii-vi).

Mn(III) oxide pillared titanium phosphate (TiP) for catalytic deep oxidation of VOCs by D.P. Das; K.M. Parida (pp. 1-8).

Mn(III) oxide pillared titanium phosphate was prepared by varying the weight percentage of trinuclear Mn(III) acetato complex. Modified as well as neat samples were characterized by PXRD, FTIR, TG–DTA, surface oxygen, redox sites determination and BET-surface area analysis. By varying experimental conditions it was observed that 15wt% Mn(III) intercalated TiP activated at 300°C show higher activity towards deep oxidation of representative volatile organic compounds (VOCs) such as acetone, methanol, 2-propanol and diethyl ether at low temperatures forming CO₂ and H₂O.▪A series of trinuclear acetato complex of Mn(III) intercalated TiP was successfully prepared by ion-exchange process, by varying the wt% of Mn(III) and activated at various temperatures. The calcined and uncalcined samples were characterized by PXRD, FTIR, TG–DTA, BET-surface area, pore size distribution, surface oxygen, surface oxidizing and reducing sites. The PXRD and FTIR analyses support that the pillaring has been taken place in the interlayer of the layered materials. All the catalysts were found to be mesoporous in character. The number of reducing sites was found to be higher than that of oxidizing sites. With increase in the calcination temperature of 15wt% Mn(III)/TiP, surface area and surface oxygen increase up to 300°C, thereafter exhibits slow decrease up to 500°C. But the oxidizing and reducing properties go on decreasing with activation temperature. Catalytic decomposition of acetone, methanol, diethyl ether and 2-propanol was studied to find out the suitability of the material for VOCs decomposition reactions. Mn(III) pillared TiP (15wt%) with high manganese content, surface area, surface oxygen shows higher catalytic activity towards the complete decomposition of VOCs. Time-on-stream (TOS) experiments justify the stability of the catalysts at least 24h with minor change in the activity. Titanium phosphate pillared with 15wt% Mn(III) and calcined at 300°C showed complete decomposition of VOCs in the range of 180–290°C. The catalytic activity of these materials is comparable with other reported catalysts.

Keywords: Mn(III) oxide pillared TiP; VOCs; Activation temperature; Surface oxygen

Hydrogenation and ring opening of naphthalene on bulk and supported Mo₂C catalysts by Shahrzad Jooya Ardakani; Xuebin Liu; Kevin J. Smith (pp. 9-19).

A series of Mo₂C catalysts have been investigated for the hydrogenation and ring opening (ROP) of naphthalene. At 573K and 3MPa H₂, bulk Mo₂C showed no selectivity for ROP whereas ROP yield on Mo₂C/HY catalysts was dependent upon the HY zeolite SiO₂:Al₂O₃ ratio and the Mo₂C loading, as shown in figure. ▪A series of Mo₂C catalysts have been investigated for the hydrogenation and ring opening of naphthalene. At 573K and 3MPa H₂, bulk Mo₂C showed no selectivity for ring-opening products (ROP) and, although treating the bulk catalysts in oxygen increased stability and naphthalene conversion, ROP selectivity remained low. Supporting the Mo₂C on HY zeolites significantly increased the hydrogenation of naphthalene and the subsequent formation of ROP, as compared to the HY zeolites alone or the bulk materials. ROP yields were dependent upon the HY zeolite SiO₂:Al₂O₃ ratio and the Mo₂C loading, the optimum loading being dependent upon the zeolite acidity. The maximum ROP yield of 33wt.% was obtained with 7.4wt.% Mo₂C supported on HY zeolite of moderate acidity (SiO₂:Al₂O₃ ratio of 12) and the yield is comparable to yields reported for noble metal catalysts on acidic supports. The Mo₂C/HY zeolite bifunctional catalysts are most effective for ring opening of naphthalene when the acidity is adjusted to an intermediate level that limits deactivation and the Mo₂C loading provides sufficient hydrogenation capability to achieve high conversion to the primary product tetralin.

Keywords: Ring opening; Catalysts; Bifunctional catalysts; Molybdenum carbide; Zeolite

Light olefin transformation over ZSM-5 zeolites by P. Borges; R. Ramos Pinto; M.A.N.D.A. Lemos; F. Lemos; J.C. Védrine; E.G. Derouane; F. Ramôa Ribeiro (pp. 20-29).

The acid-catalysed transformation of light olefins (ethylene, propylene, and butene) was studied at various temperatures and partial pressures over ZSM-5 with varying acidic contents. A single kinetic model describing the rate of consumption of the three reactants as a function of temperature and pressure was developed. Apparent negative activation energies were observed which are related to adsorption enthalpy of the reactants, possible intermediates, and confinement effects but not catalyst deactivation. Results shown in the graph are for the conversion of propylene.▪The acid-catalysed transformation of light olefins was studied at various temperatures and partial pressures over ZSM-5 of varying acidic contents. It was observed that, as the temperature increased, the rate of consumption of ethene and propene decreased, whereas the rate of consumption of butene increased. Despite the fact that this reaction proceeds by a rather complex network mechanism, a single kinetic model describing the rate of consumption of the three reactants was developed, with the explicit inclusion of the step corresponding to the adsorption of the reactant molecules.

Keywords: Olefin oligomerisation; Acid catalysis; ZSM-5 zeolite; Kinetic model molecular modelling

Effect of support type on the magnitude of synergism and promotion in CoMo sulphide hydrodesulphurisation catalyst by L. Kaluža; D. Gulková; Z. Vít; M. Zdražil (pp. 30-35).

The Co, Mo and CoMo catalysts in different Co/Mo ratios supported on SiO₂, ZrO₂, TiO₂, Al₂O₃, active carbon and MgO were prepared. The catalysts were tested in the hydrodesulphurisation of benzothiophene. The order of activity of monometallic Mo catalysts was MoO₃/TiO₂>MoO₃/C>MoO₃/ZrO₂>MoO₃/SiO₂>MoO₃/Al₂O₃>MoO₃/MgO. The order of promotion of MoO₃/support by Co addition was CoMo/MgO>CoMo/C>CoMo/Al₂O₃>CoMo/TiO₂>CoMo/ZrO₂>CoMo/SiO₂. The synergism in activity was accompanied with a decrease of hydrogenation/hydrogenolysis selectivity. Hydrogenolysis was promoted more than hydrogenation and thus less dihydrobenzothiophene was formed on CoMo than on Co and Mo catalysts. The TPR patterns were measured, and the degree of reduction correlated with the activity of monometallic catalysts. The TPR patterns of CoMo catalysts were similar to the patterns of Mo catalysts, and no correlation with magnitude of promotion was found.The magnitude of promotion by Co in the hydrodesulphurisation activity decreased in the order CoMo/MgO>CoMo/C>CoMo/Al₂O₃>CoMo/ZrO₂>CoMo/TiO₂>CoMo/SiO₂. This order did not correlate with the reduction patterns of the catalysts in TPR. The promotion in the hydrogenolysis activity is higher than in hydrogenation and is thus accompanied by characteristic decrease of the hydrogenation/hydrogenolysis selectivity. ▪

Keywords: Hydrodesulphurisation; Synergistic effect; Promotion; Sulphide catalysts

Effects of acidification and basification of impregnating solution on the performance of Mo/HZSM-5 in methane aromatization by P.L. Tan; C.T. Au; S.Y. Lai (pp. 36-41).

Mo/HZSM-5 catalyst prepared with a basic ammonium heptamolybdate solution showed improved Mo dispersion. This catalyst exhibited good activity and stability for the methane aromatization reaction. With the addition of 5.6vol.% O₂ or 9.6vol.% CO₂ in the methane feed, steady aromatics yield of ca. 8.4% could be obtained for a period of 6h at 800°C.▪The effects of acidification and basification of ammonium heptamolybdate solution during impregnation of HZSM-5 on the catalytic performance of Mo/HZSM-5 in methane dehydro-aromatization have been investigated. At reaction temperature of 700°C and GHSV=1600mlh⁻¹g⁻¹, a 2wt.% Mo/HZSM-5 prepared with H₂SO₄-acidified solution gave a high aromatics yield of 7.2% but the catalytic activity declined drastically with time on-stream. A 2wt.% Mo/HZSM-5 prepared with NH₃-basified solution showed both high activity (7.1% aromatics yield) and good stability. With a rise in reaction temperature, the 2wt.% Mo/HZSM-5 prepared with NH₃-basified solution gave increased initial aromatics yields of 10.2 and 15.5% at 750 and 800°C, respectively. The extent of catalyst deactivation with on-stream time increased with increasing reaction temperature or reactants space velocity but was less severe compared to that over a similar catalyst prepared without pH adjustment of the impregnation solution. The catalyst stability could be further improved by adding an appropriate concentration of CO₂ or O₂ in the reactant stream. With 5.6vol.% O₂ or 9.6vol.% CO₂ in the methane feed, steady aromatics yield of ca. 8.4% at 800°C and 1600mlh⁻¹g⁻¹ was obtained for a period of 6h.

Keywords: Methane aromatization; Mo/HZSM-5; Acidification; Basification; Impregnation condition

Preparation of a multilayered composite catalyst for Fischer–Tropsch synthesis in a micro-chamber reactor by L. Guillou; D. Balloy; Ph. Supiot; V. Le Courtois (pp. 42-51).

A 20wt% Co/SiO₂ catalyst grafted on a stainless steel substrate was used for Fischer–Tropsch synthesis (FTS) in a micro-chamber reactor. The fabrication of the catalyst was a complex process involving several steps. The first one, the pre-treatment of the AISI316L substrate through a plasma assisted chemical vapour deposition process (PACVD), allowed the formation of a silicon based polymer. This thin polymeric film was thermally degraded into a silicon oxide bonding layer. The coating of this bonding layer with sol–gel precursor of the Co/SiO₂ catalysts was done with a spray coating process. The sequential combination of these steps led to a multilayered catalyst with a complex morphology.This material demonstrated high activity under FTS reaction. Activity and selectivity were higher under micro-chamber conditions than in a classical fixed-bed catalytic test. This was attributed to the increase of mass and heat transfers within the micro-device. Moreover distribution of metallic masses within the catalyst showed significant evolutions post FTS, including steel compound migrations and possible cobalt segregation.A sequential process including a catalyst spray-drying step for grafting a 20wt% Co/SiO₂ catalyst on a stainless steel substrate is proposed. The obtained materials had a multilayered internal structure and a complex porous morphology.Tested under low pressure Fischer–Tropsch synthesis conditions in a micro-chamber reactor they showed high activity and selectivity. After 720h under reaction, cobalt segregation and contamination by steel compounds were detected.The sequential combination of these steps led to a multilayered catalyst with a complex morphology.▪

Keywords: Fischer–Tropsch synthesis; Micro-reactor; Coating; Cobalt; Sol–gel catalyst

Nanotubular titanate supported palladium catalysts: The influence of structure and morphology on phenol hydrogenation activity by Lucky M. Sikhwivhilu; Neil J. Coville; Dhachapally Naresh; Komandur V.R. Chary; Venkataraman Vishwanathan (pp. 52-61).

Pd supported tubular titanates catalysed the hydrogenation of phenol to cyclohexanone (97% conversion; 99% selectivity) at 165°C. ▪Nanotubular titanates were synthesized by a simple methodology using a commercial TiO₂ (Degussa P25 containing anatase and rutile phases) and a base (KOH) solution. Prior to the removal of KOH, the samples of TiO₂ were aged for three different time intervals (0, 2, 61 days). The freshly prepared synthetic samples were characterized for their structural and morphological properties by BET, XRD, Raman, TEM, HRTEM, EDX and SEM. Both TEM and SEM analysis revealed that ageing time influenced the tubular structure and morphology of the new materials. Raman and surface analysis data also showed that ageing time affected both the structural and surface properties of TiO₂. The XRD results indicated that the crystallinity of the TiO₂ decreased with increasing ageing time. Energy dispersive X-ray spectroscopy (EDX) showed that the tubes derived from TiO₂ are comprised of potassium, titanium and oxygen. Catalysts A, B and C were prepared by the addition of 1wt% Pd (wet impregnation) to the titanate formed by ageing TiO₂ in KOH for 0, 2 and 61 days, respectively and revealed Pd particle sizes of <1nm for catalyst B. The catalysts were tested for the vapour phase hydrogenation of phenol in a fixed-bed micro-reactor within the temperature range of 165–300°C under atmospheric pressure. Of the three catalysts, catalyst B showed the best activity (conversion 97%) and total selectivity to cyclohexanone (99%). In contrast, catalyst C, which showed a moderate activity favoured selectivity to cyclohexanol. These results are attributed to differences in surface morphologies between the two catalysts B and C, associated with a change in the surface properties. Catalyst B also showed a higher resistance towards deactivation and maintained a higher total selectivity to cyclohexanone than did catalyst C.

Keywords: Nanotubular titanate; Titanium dioxide; Phenol; Cyclohexanone; Structure and morphology; Hydrogenation activity

Supported trifluoromethanesulfonic acid as catalyst in the synthesis of flavone and chromone derivatives by D.O. Bennardi; G.P. Romanelli; J.C. Autino; L.R. Pizzio (pp. 62-68).

Solid acid catalysts based on trifluoromethanesulfonic acid (triflic acid, TFMS) were synthesized using titania with different textural properties as support, obtained by increasing the calcination temperature. They were characterized by FT-IR, DTA-TGA, and BET. The acidic characteristics of the catalysts were determined by potentiometric titration with n-butylamine.The new catalysts were tested in the cyclization of 1-(2-hydroxyphenyl)-3-phenyl-1,3-propanedione. In all cases, the product (flavone) was obtained with high selectivity. The activity of the catalysts is dependent on the textural properties of the support used to obtain the catalysts and the amount of triflic acid firmly adsorbed on it.▪Solid acid catalysts based on trifluoromethanesulfonic acid (triflic acid, TFMS) were synthesized using titania with different textural properties as support, obtained by increasing the calcination temperature (Ti₁₀₀, Ti₂₀₀, Ti_300, and Ti₄₀₀). They were characterized by FT-IR, DTA-TGA, and BET. The acidic characteristics of the catalysts were determined by potentiometric titration with n-butylamine. According to this technique, the catalysts present very strong acid sites. Their acid strength decreases slightly in the order Ti₁₀₀>Ti₂₀₀>Ti₃₀₀>Ti₄₀₀, as a result of the partial dehydroxylation that takes place during the thermal treatment of the supports.The amount of trifluoromethanesulfonic acid firmly adsorbed on the support depends on the number of –OH groups available on the titania to be protonated, which decreases with the increase in the calcination temperature.The new catalysts were tested in the cyclization of 1-(2-hydroxyphenyl)-3-phenyl-1,3-propanedione. The reaction experiments were performed using toluene as the solvent at reflux. In all cases, the product (flavone) was obtained with high selectivity. The activity of the catalysts is dependent on the textural properties of the support used to obtain the catalysts and the amount of triflic acid firmly adsorbed on it. The same reaction conditions were applied to the preparation of eight substituted flavones and chromones. Conversions up to 88% were obtained using the Ti₁₀₀ supported TFMS catalyst.

Keywords: Supported trifluoromethanesulfonic acid; Supported triflic acid; Flavones; Chromones; Titania

Synthesis and characterization of Fe- and Cu-doped molybdovanadophosphoric acids and their application in catalytic oxidation by P. Villabrille; G. Romanelli; L. Gassa; P. Vázquez; C. Cáceres (pp. 69-76).

Keggin heteropolycompounds based on H₄PMo₁₁VO₄₀, were synthesized and doped with Cu²⁺ or Fe³⁺. They were characterized by Fourier transform infrared spectroscopy,³¹P nuclear magnetic resonance, diffuse reflectance spectroscopy, X-ray diffraction, thermal analysis, potentiometric titration, and cyclic voltammetry. The catalytic performance testing showed that the prepared materials have high catalytic activity for the room temperature conversion of 2,6-dimethylphenol to 2,6-dimethyl-1,4-benzoquinone using aqueous hydrogen peroxide as oxidizing agent.▪Heteropolycompounds, where one molybdenum atom of molybdophosphoric acid (M12P) was substituted by one vanadium atom, H₄PMo₁₁VO₄₀, were synthesized and doped with Cu²⁺ or Fe³⁺. The prepared molybdovanadophosphates were characterized by Fourier transform infrared spectroscopy,³¹P nuclear magnetic resonance, diffuse reflectance spectroscopy, X-ray diffraction, thermal analysis, potentiometric titration, and cyclic voltammetry. The catalytic performance testing showed that the prepared materials have high catalytic activity for the room temperature conversion of 2,6-dimethylphenol to 2,6-dimethyl-1,4-benzoquinone using aqueous hydrogen peroxide as oxidizing agent.

Keywords: Iron-(copper)-doped Keggin molybdovanadophosphate; Catalytic oxidation; 2,6-Dimethylphenol; 2,6-Dimethyl-1,4-benzoquinone

Visible-light photocatalytic properties and electronic structure of Zr-based oxynitride, Zr₂ON₂, derived from nitridation of ZrO₂ by Takahiro Mishima; Motohide Matsuda; Michihiro Miyake (pp. 77-82).

A new photocatalyst responsive to visible light was found in Zr-based oxynitrides derived from nitridation of ZrO₂ in flowing NH₃. Zr₂ON₂ with the bandgap of 2.6eV functioned with irradiation of visible light, yielding H₂ and O₂ by water reduction and oxidation in the presence of sacrificial reagents, respectively. The Zr₂ON₂ was stable during the photocatalytic reaction. Calculation of electronic structure for the Zr₂ON₂, based on plane-wave-based density functional theory (DFT), gave information that the main components of valence and conduction bands were the O 2p, N 2p and Zr 4d atomic orbitals, and no isolated band existed within the bandgap. In this paper, the visible-light photocatalytic properties of Zr₂ON₂ are discussed in terms of the electronic band structure calculated.A novel Zr₂ON₂ was successfully prepared by nitridation of ZrO₂ in flowing NH₃. The absorption band was significantly shifted toward the visible region compared with that of ZrO₂, as predicted by DFT calculations. Zr₂ON₂ was discovered to exhibit stable photocatalytic activity for water oxidation and reduction in the presence of sacrificial reagents under visible-light irradiation. ▪

Keywords: Photocatalyst; Zr; ₂; ON; ₂; Visible-light irradiation

Electrocatalytic reductive dehalogenation of polyhalogenated phenols in aqueous solution on Ag electrodes by Yinghua Xu; Yinghong Zhu; Fengming Zhao; Chun-an Ma (pp. 83-86).

The electrocatalytic properties of Ag towards the dehalogenation of a variety of polychloro- and polybromo-phenols in basic aqueous solution have been evaluated. Experimental evidence is presented that Ag exhibited powerful electrocatalytic activity for dehalogenation of polyhalogenated phenols to less, or non-halogenated phenols.Ag appears to be an excellent electrocatalytic material for direct electrodehalogenation of phenolic halides in basic aqueous solution. Complete debromination of polybrominated phenols with excellent current efficiency can be successfully achieved without resorting to the use of organic solvents. The more resistant polychlorinated phenols can also be dehalogenated partially in the catalytic system.▪

Keywords: Reductive dehalogenation; Polyhalogenated phenol; Ag electrode; Aqueous solution

Comment on the issues of statistical modelling with particular reference to the use of artificial neural networks by W. Sha (pp. 87-89).

Predictive performance of “highly complex” artificial neural networks by András Tompos; József L. Margitfalvi; Ernő Tfirst; Károly Héberger (pp. 90-93).

The effectiveness and the “indeterminacy” of artificial neural networks (ANNs) are discussed. In the way of determination of parameters of different models a clear distinction should be made between two approaches: (i) parameter estimation ( classical approach) and (ii) ANN approach with the aim of prediction (mainly interpolation). In the classical approach different regression procedures are used, while in latter one the so-called “training” using back propagation algorithm is applied. The latter approach is widely employed in combinatorial materials science for “information mining” purposes. Parameters obtained in classical approach should have a definite physical meaning. It also means that in the absence of a presumed hypothetical model the classical regression procedures cannot be applied. The advantage of the usage of ANNs is that it does not require a casual model for the system investigated. However, parameters obtained by ANN have no physical meaning. Generally, in ANNs the number of parameters to be determined is significantly higher than the number of data in the training set. It has to be emphasized that in ANN approach the good predictive ability has superior importance to physical meaning of parameters.

Keywords: Catalyst library design; Combinatorial catalysis; Holographic research strategy; Genetic algorithm; Visualization; Chemometrics; Artificial neural networks; Overfit

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Applied Catalysis A, General (v.324, #)