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Applied Catalysis A, General (v.305, #1)

Editorial Board (pp. co2).

Preparation and characterization of 20wt.% V₂O₅–TiO₂ catalyst oxidation of cyclohexane by A. Bellifa; D. Lahcene; Y.N. Tchenar; A. Choukchou-Braham; R. Bachir; S. Bedrane; C. Kappenstein (pp. 1-6).

The 20wt.% V₂O₅–TiO₂ catalyst was prepared by the sol–gel route and calcined at 300°C. XRD, TEM, EDX and FT-IR analysis showed that the material presents a crystalline structure with the presence of both TiO₂ rutile and anatase varieties. BET analysis showed a low oxide surface area (27m²/g).Cyclohexane oxidation with hydrogen peroxide in presence of the catalyst showed a low conversion. The use of acetic acid as solvent and acetone as initiator presented an approximate 8% conversion into cyclohexanol, with 76% selectivity.

Keywords: Sol–gel; Mixed oxide; V; ₂; O; ₅; –TiO; ₂; Cyclohexane oxidation; Hydrogen peroxide

SCR of NO by NH₃ over V₂O₅ supported sulfated Ti-pillared clay: Reactivity and reducibility of catalysts by L. Khalfallah Boudali; A. Ghorbel; P. Grange (pp. 7-14).

Vanadia supported on sulfated Ti-pillared clays with different vanadia loading have been prepared and characterized. The catalytic activity of the synthesized materials in the selective catalytic reduction (SCR) of NO by NH₃ in presence of oxygen have been evaluated. The results showed that the increase of vanadia content influences the reduction behavior of sulfate. It was found that the presence of small amount of sulfate (1%) with high vanadia content on the sulfated titanium pillared clay may affect a variety of catalyst properties, including the acidity and reducibility of catalyst, and the overall amount of sulfate species. The performance of vanadia supported sulfated Ti-pillared clay in the SCR reaction was compared to a physical mixture of pure V₂O₅ with sulfated Ti-pillared clay. From the results obtained, it appears that the presence of a Bronsted acid site in close proximity with the vanadia site on sulfated Ti-pillared clay results in a promoting effect on SCR-NO activity.

Keywords: Sulfated Ti-pillared clay; Vanadia; Acid and redox sites; SCR-NO

Ultra-deep oxidative desulfurization of diesel fuel with H₂O₂ catalyzed under mild conditions by polymolybdates supported on Al₂O₃ by José Luis García-Gutiérrez; Gustavo A. Fuentes; Maria Eugenia Hernández-Terán; Florentino Murrieta; Juan Navarrete; Federico Jiménez-Cruz (pp. 15-20).

The evaluation of the catalytic oxidative desulfurization (OD) activity of alumina-supported polymolybdates (Mo/Al₂O₃) was carried out using organosulfur model compounds and diesel fuel. Hydrogen peroxide was the oxidizing reagent. Ultra-deep desulfurization, 97.8% removal of sulfur in diesel fuel, was achieved by reaction under mild conditions followed by solvent extraction. The catalyst was prepared by equilibrium adsorption and characterized by infrared, Raman, X-ray photoelectron,³¹P and²⁷Al MAS NMR spectroscopies. Our results indicate that the phosphomolybdate used during synthesis of the catalysts decomposes and forms hydrated hepta- and octamolybdates as well as phosphate ions on the surface of alumina.

Keywords: Desulfurization; Molybdenum; Polymolybdates; Oxidation; Sulfur; 4,6-Dimethyldibenzothiophene; Hydrogen peroxide; Catalysis; Diesel fuel

Catalytic transformation of C₇–C₉ methyl benzenes over USY-based FCC zeolite catalyst by S. Al-Khattaf; N.M. Tukur; A. Al-Amer; U.A. Al-Mubaiyedh (pp. 21-31).

Catalytic transformation of three methyl benzenes (toluene, m-xylene, and 1,2,4-trimethylbenzene) has been investigated over USY-based FCC zeolite catalyst in a novel Riser Simulator at different operating conditions. The effect of reaction conditions on the variation of isomerization to disproportionation products ratio (I/D), distribution of trimethylbenzene (TMB) isomers (1,3,5-to-1,2,3-) and values of p-xylene/ o-xylene (P/O) ratios are reported. The sequence of reactivity of the three alkyl benzenes was found to decrease as the number of methyl group per benzene ring decreases, as follows: 1,2,4-trimethylbenzene> m-xylene>toluene . This is true at all temperatures investigated over the USY zeolite. Toluene was found unreactive in our reaction condition. Effectiveness factor ( η_ss) of both 1,2,4-TMB and m-xylene have been estimated. While m-xylene's η_ss was close to unity at all condition, 1,2,4-TMB's η_ss was less than that of m-xylene. The effectiveness factor was estimated from the quasi-steady state approximation modeling of the experimental data involving a decay function based on “Time on Stream�? (TOS). Based on the present study, it was found that the number of methyl groups has the most important role on the reactivity of 1,2,4-TMB, m-xylene and toluene over Y-based catalyst.

Keywords: FCC zeolite catalyst; USY; Toluene; m; -Xylene; Disproportionation; Isomerization

Liquid phase bromination of phenol by D.P. Das; K.M. Parida (pp. 32-38).

Heteropoly acid (HPA)-impregnated zirconium phosphate (ZrP) was prepared by an incipient wetness impregnation method by varying the wt.% of HPAs like phosphotungstic acid (PWA), phosphomolybdic acid (PMoA), silicotungstic acid (SiWA) and silicomolybdic acid (SiMoA). All the samples were characterized by X-ray diffraction studies, FTIR, determination of acid sites and TG–DTA. The catalytic activities of all the samples were evaluated by carrying out the liquid phase bromination of phenol using KBr and hydrogen peroxide. The reaction products were analysed by GC through a capillary column. From the product analysis it was found that PWA/ZrP shows the highest conversion. Even so SiWA/ZrP heated at 110°C shows the highest para-selectivity (in the range of 32–41%), higher than any other HPA/ZrP. The selectivity increases with an increase in the activation temperature up to 400°C and thereafter it remains constant. The reaction proceeds through the formation of Br⁺ (bromonium ion) which attacks the phenol ring, forming different brominated products.

Keywords: Heteropoly acid-impregnated zirconium phosphate; Bromination; Potassium bromide; Hydrogen peroxide; Para; -selectivity

Catalytic decomposition of sulfur trioxide on the binary metal oxide catalysts of Fe/Al and Fe/Ti by Tae-Ho Kim; Gyeong-Taek Gong; Byung Gwon Lee; Kwan-Young Lee; Hee-Young Jeon; Chae-Ho Shin; Honggon Kim; Kwang-Deog Jung (pp. 39-45).

The iodine–sulfur (IS) cycle has been focused for hydrogen production by water splitting using a very high temperature nuclear reactor (VHTR) which is a high temperature heat source. The nuclear energy was absorbed at the temperature ranges of 750–900°C by SO₃ decomposition reaction to SO₂ and O₂ in IS cycle. In this work, the activity of Fe/Al and Fe/Ti catalysts prepared by a co-precipitation was studied in an attempt to find some suitable catalysts for the decomposition of sulfur trioxide as the oxygen-generating reaction in the thermo-chemical water splitting process. The SO₃ decomposition was performed in the temperature range of 750–950°C at a space velocity of 72,000cm³/gcat.h in a fixed bed reactor. The catalytic activity of Fe/Al and Fe/Ti catalysts increased with an increase in Fe loadings, indicating that the Fe component should be active. The mechanism for the SO₃ decomposition on metal oxides can be described as follows: the metal sulfate formation (MO+SO₃→MSO₄) and the decomposition of metal sulfate (MSO₄→MO₂+SO₂ and MO₂→MO+1/2O₂).

Keywords: IS cycle; SO; ₃; decomposition; Metal sulfate decomposition; Hydrogen production

IR spectroscopy and phase behavior studies of the catalytic synthesis of propylene carbonate: Expanded liquid versus supercritical fluid by Michael Ramin; Jan-Dierk Grunwaldt; Alfons Baiker (pp. 46-53).

A covalently immobilized zinc pyridine bromide complex was investigated in the solvent-less synthesis of propylene carbonate (PC) by fixation of carbon dioxide (CO₂) in propylene oxide (PO). The reaction was optimized using phase behavior studies based on video monitoring, transmission and attenuated total reflection (ATR) infrared measurements. At first the immobilization process was monitored by DRIFTS which confirmed the successful fixation of the ZnBr₂(Py)₂-complex on the silica matrix. Phase behavior studies of the reaction mixture showed three different regions that influenced strongly the reaction rate: (i) At low overall density a biphasic region with small liquid phase (high molar ratio of PC) was observed. The catalytic activity of this system was poor. (ii) A decreasing CO₂ content at the same density resulted in an expanded liquid phase, which was up to a certain PO/PC ratio beneficial for the catalytic activity. However, at too low content of CO₂ (ratio CO₂/(PO+PC)<4) the rate decreased again, because CO₂ is not only solvent but also reactant in the synthesis of PC. (iii) Finally, experiments at higher pressure led to a single-phase system (“supercritical conditions�?). Despite of optimal mass transfer properties the lowest conversion was achieved under these reaction conditions. These observations provided important insight into the reaction system. In situ ATR-IR studies of the catalyst surface during reaction revealed drastic changes in the phase behavior in the first minutes and gave important insight into the solid/fluid interface under reaction conditions.

Keywords: Phase behavior; Carbon dioxide; Propylene oxide; Propylene carbonate; Infrared spectroscopy; Expanded liquid; Supercritical fluid

Preparation of TiO₂/ITO and TiO₂/Ti photoelectrodes by magnetron sputtering for photocatalytic application by C. He; X.Z. Li; N. Graham; Y. Wang (pp. 54-63).

Two types of immobilized TiO₂ films with nanostructure, TiO₂/ITO conductive glass and TiO₂/Ti mesh, were prepared by a radio frequency magnetron sputtering technique, in which a titanium (Ti) target was sputtered in a gaseous mixture of argon and oxygen. The TiO₂ films were characterized by X-ray diffraction, AFM microscopy, SEM microscopy and photoelectrochemical measurements. Their photocatalytic (PC) activity, photoelectrocatalytic (PEC) activity and electrochemical (EC) activity were evaluated in the degradation of 2,4,6-trichlorophenol (TCP) in aqueous solution. The experiments confirmed that the TiO₂ films sputtered at 2.0Pa had relatively high PC activity due to more active sites formed on the surface of TiO₂ films. The experiments demonstrated that the PEC activity of the TiO₂/Ti mesh was better than that of TiO₂/ITO, resulting from less impedance between the TiO₂ film and Ti mesh. Furthermore, the experiments also demonstrated that at a higher anodic potential, the TiO₂/Ti mesh exhibited not only a PEC reaction but also an EC oxidation reaction at the backed Ti mesh in the degradation of TCP. This study concludes that the sputtered TiO₂/Ti mesh is an effective photoelectrode for achieving an enhanced TCP degradation in such a PEC reaction system.

Keywords: Photoelectrocatalysis; Photoelectrochemistry; Photocatalysis; TiO; ₂; 2,4,6-Trichlorophenol

Periodic density functional and tight-binding quantum chemical molecular dynamics study of catalytic properties on γ-Al₂O₃ supported Pt catalysts by Ryota Ishimoto; Changho Jung; Hideyuki Tsuboi; Michihisa Koyama; Akira Endou; Momoji Kubo; Carlos A. Del Carpio; Akira Miyamoto (pp. 64-69).

We investigated the interactions of platinum metal clusters on the γ-alumina using a periodic density functional theory method. Results showed that electron transfer occurs between platinum metal clusters and γ-Al₂O₃. We also investigated NO adsorption properties (NO–Pt₄/γ-Al₂O₃) in order to clarify the support effect on NO activation in terms of the elongation of N–O bond length and NO molecular charge. In our results, the support increases NO activation for three-fold sites but decreases it for on-top and bridge sites. Moreover, the support changes the site preference of NO adsorption. In addition, in order to clarify the support effect at finite temperature, we studied the dynamic behaviors of supported precious metal catalysts by using a tight-binding quantum chemical molecular dynamics program named ‘Colors’.

Keywords: Supported precious metal catalyst; Quantum chemical molecular dynamics; Density functional theory

Catalytic evaluation of small-pore molecular sieves with different framework topologies for the synthesis of methylamines by Hee-Young Jeon; Chae-Ho Shin; Hye Ja Jung; Suk Bong Hong (pp. 70-78).

The catalytic properties of the proton form of seven different small-pore aluminosilicate zeolites (levyne, MCM-35, sigma-1, UZM-5, SSZ-13, SSZ-16, and rho), together with the silicoaluminophosphate analogs (SAPO-35, SAPO-34, and SAPO-56) of some of these zeolites, are compared in the synthesis of methylamines. Among the molecular sieves studied here, H-SSZ-16 was found to exhibit selectivities to monomethylamine and dimethylamine comparable to those of H-rho, the most widely studied catalyst for this reaction, at about 90% methanol conversion (NH₃/MeOH=1.0). However, no good stability is observed over even these two small-pore zeolites, while the absence of strong acids sites in silicoaluminophosphate materials appears to be an inherent drawback in terms of their application as amination catalysts. The overall results of this study lead us to conclude that the pore dimensionality, eight-ring cage volume, number and strength of acid sites, and thermal stability of small-pore materials, as well as their eight-ring pore dimension, are of considerable importance in achieving high amination activity and selectivity.

Keywords: Methylamine synthesis; Small-pore molecular sieves; Pore structure and acidity; MMA and DMA selectivities

Kinetic, mechanistic and spectral investigations of ruthenium(III)/osmium(VIII)-catalysed oxidation of paracetamol by alkaline diperiodatoargentate(III) (stopped flow technique) by Kiran T. Sirsalmath; Chanabasayya V. Hiremath; Sharanappa T. Nandibewoor (pp. 79-89).

The kinetics of the oxidation of ruthenium(III)- and osmium(VIII)-catalysed oxidation of paracetamol by diperiodatoargentate(III) (DPA) in aqueous alkaline medium at a constant ionic strength of 0.10moldm⁻³ was studied spectrophotometrically. The reaction between DPA and paracetamol in alkaline medium exhibits 2:1 stoichiometry in both catalysed reactions (DPA:PAM). The main products were identified by spot test, IR, NMR and GC–MS. Probable mechanisms are proposed and discussed. The activation parameters with respect to the slow step of the mechanism are computed and discussed and thermodynamic quantities are also calculated. It has been observed that the catalytic efficiency for the present reaction is in the order of Os(VIII)>Ru(III). The active species of catalyst and oxidant have been identified.

Keywords: Kinetics; Diperiodatoargentate(III); Oxidation; Paracetamol; Ruthenium(III) catalysis; Os(VIII) catalysis

Transformation of thiophenic compounds over acidic zeolites by T. Boita; M. Moreau; F. Richard; G. Pérot (pp. 90-101).

The transformation of thiophenic compounds (2-methylthiophene; 3-methylthiophene; 2,3-dimethylthiophene; 2,5-dimethylthiophene; 2-methylbenzothiophene; 3-methylbenzothiophene) was carried out over HY zeolite at 350°C under atmospheric pressure in a fixed bed reactor. The transformation of some of them was also carried out over Hβ, HZSM5 and H-mordenite (HMOR). In the presence of HY, all the reactants underwent both isomerization and disproportionation in various proportions depending on their structure. HZSM5 catalyzed isomerization only and disproportionation was also very limited compared to isomerization with Hβ and with HMOR. HMOR deactivated so rapidly that it was not possible to measure its activity accurately. Isomerization occurred essentially through an acid-catalyzed step by step intramolecular mechanism. The disproportionation product distribution was explained on the basis of the relative stabilities of the intermediates involved in the reaction. As expected, disproportionation was more sensitive to catalyst deactivation than isomerization.

Keywords: Zeolites HY; Hβ; HZSM5; HMOR; Methylthiophenes; Methylbenzothiophenes; Dimethylthiophenes; Isomerization; Disproportionation

Interfacial properties of ZrO₂ supported precious metal catalysts: A density functional study by Changho Jung; Ryota Ishimoto; Hideyuki Tsuboi; Michihisa Koyama; Akira Endou; Momoji Kubo; Carlos A. Del Carpio; Akira Miyamoto (pp. 102-109).

In this study, we performed periodic DFT calculations to clarify the interfacial properties of zirconia-supported precious metal catalyst systems. Atomic precious metals (Pt, Pd and Rh) and four-metal-atom clusters (Pt₄, Pd₄ and Rh₄) were deposited on the ZrO₂(111) surface. The Pt and Rh show much stronger interaction with the ZrO₂(111) surface than the Pd, indicating that the Pt–ZrO₂ and Rh–ZrO₂ interfaces are energetically more stable than the corresponding Pd–ZrO₂ interface. The effect of support relaxation on the adsorption energies reveals that a larger support relaxation effect can be observed on the Pt–ZrO₂ interface compared to the Pd–ZrO₂ interface. The Pt adsorption was associated with the largest support rearrangement with strong Pt–Zr interaction. The precious metal atoms on the ZrO₂(111) surface were positively charged. The electron transferred from the precious metal to the ZrO₂(111) surface was localized on the Zr atom. Moreover, electron exchanges on the Pt–ZrO₂ and Rh–ZrO₂ interfaces were more significant than that on the Pd–ZrO₂ interface. Additionally, the oxidization effects on the interaction between the precious metals and the ZrO₂ support were also investigated. The oxidization weakened the metal–metal interaction of the M₄ cluster, while the metal–ZrO₂ interaction was increased by the oxidization.

Keywords: ZrO; ₂; Precious metal; Density functional theory; Automotive catalyst

Studies on the SbOx species of SbOx/SiO₂ catalysts for methane-selective oxidation to formaldehyde by Haidong Zhang; Keqiang Sun; Zhaochi Feng; Pinliang Ying; Can Li (pp. 110-119).

Sb₂O₃/SiO₂ and Sb₂O₅/SiO₂ catalysts were prepared and characterized by N₂-adsorption, XRD, XPS, UV–vis DRS, UV Raman and H₂-TPR and investigated in methane-selective oxidation. No crystalline antimony oxide can be detected on catalysts even when antimony oxides loading reaches 20wt.%. On Sb₂O₃/SiO₂ catalysts, the oxidation of highly dispersed Sb³⁺ oxidic entities is more difficult than that of aggregated Sb³⁺ oxidic entities. The concentration of Sb⁵⁺ oxidic entities increases with Sb₂O₃ loading and about half the amount of Sb³⁺ oxidic entities can be oxidized to Sb⁵⁺ oxidic entities on 20wt.% Sb₂O₃/SiO₂ catalyst. On Sb₂O₅/SiO₂ catalysts, SbOx species are all Sb⁵⁺ oxidic entities and aggregated SbOx species emerge as Sb₂O₅ loading reaches 5wt.%. In methane-selective oxidation, highly dispersed SbOx species are more active than aggregated SbOx species and the depression of deep oxidation towards CO₂ is more favorable on aggregated SbOx species than on highly dispersed SbOx species regardless of the oxidation state of Sb. Furthermore, highly dispersed Sb³⁺ oxidic entities are more active than highly dispersed Sb⁵⁺ oxidic entities. Such tendency is in line with that, for both Sb₂O₃/SiO₂ and Sb₂O₅/SiO₂ catalysts, the redox performance of aggregated SbOx species are poor compared to that of highly dispersed SbOx species. This results in their decreasing activity but increasing selectivity to CO and formaldehyde with increasing loading of antimony oxides in methane-selective oxidation.

Keywords: Antimony oxide; Species evolution; Methane; Selective oxidation; Formaldehyde

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Applied Catalysis A, General (v.305, #1)