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Applied Catalysis A, General (v.374, #1-2)

Editorial Board (pp. co2).

Contents (pp. iii-x).

Atmospheric hydrodesulfurization of diesel fuel using Pt/Al₂O₃ catalysts prepared by supercritical deposition for fuel cell applications by Shaker Haji; Ying Zhang; Can Erkey (pp. 1-10).

Hydrodesulfurization (HDS) of low-sulfur model and commercial diesel fuel (500ppmw S) using Pt/Al₂O₃ catalysts prepared by supercritical carbon dioxide (scCO₂) deposition method is investigated at atmospheric pressure and in temperature range of 290–350°C and is found to be feasible. The HDS of dibenzothiophenes is found to proceed only via the direct desulfurization route (CS bond scission) under the studied conditions.Hydrodesulfurization (HDS) of low-sulfur model and commercial diesel fuel (500ppmw S) using Pt/Al₂O₃ catalysts prepared by supercritical carbon dioxide (scCO₂) deposition method is investigated at atmospheric pressure and in temperature range of 290–350°C. The reactivity of the investigated organosulfur compounds followed the known trend, that is: BT>2-MDBT>DBT≫4-MDBT>4,6-DMDBT, despite the nonconventional operating conditions and catalyst. The HDS of dibenzothiophenes was found to proceed only via the direct desulfurization route (CS bond scission) under the studied conditions whereas HDS at high H₂ pressure proceeds via both direct desulfurization and hydrogenation routes. This limitation had several consequences. Under atmospheric pressure, the HDS reaction exhibited low reactivity particularly towards the stericly hindered substituted dibenzothiophenes. HDS of commercial diesel at atmospheric pressure using catalyst prepared by supercritical fluid deposition technique was found to be feasible, however, the catalyst had to have high metal loading and the reactor had to be operated under high H₂/fuel ratio with low hourly space velocity.

Keywords: Atmospheric hydrodesulfurization; Diesel fuel; Supercritical deposition; Fuel cell; Platinum/alumina catalyst

Cerium-incorporated cage-type mesoporous KIT-6 materials: Synthesis, characterization and catalytic applications by Azhagapillai Prabhu; Loganathan Kumaresan; Muthaiahpillai Palanichamy; Velayutham Murugesan (pp. 11-17).

The large pore cubic Ia3d mesoporous Ce-KIT-6 was successfully synthesized by a hydrothermal method with triblock copolymer Pluronic P123 as the structure-directing agent. The synthesized materials were well characterized. Liquid phase oxidation of cyclohexane to cyclohexanol and cyclohexanone was carried out over Ce-KIT-6 catalyst with different Si/Ce ratios. Ce-KIT-6 (5) is suggested to be a better catalyst than the others.Ce-KIT-6 with Si/Ce=5, 10, 20, 50, 100 and 150 mesoporous molecular sieves were successfully synthesized by a hydrothermal method. The synthesized materials were characterized extensively to understand the physico-chemical properties of the materials. The low-angle powder XRD patterns of calcined Ce-KIT-6 material showed a phase that can be indexed to cubic Ia3d. The UV–vis spectra of Ce-KIT-6 samples exhibited two distinct bands with maxima at 265 and 300nm due to charge transfer to Ce³⁺ and Ce⁴⁺ respectively. Their intensity increased with increase in the Ce content of the samples. The BET surface area was found to be in the range of 668.4–836.9m²/g. HR-TEM images revealed well-ordered cubic 3-D mesoporous channels. The catalytic activity was tested in the liquid phase oxidation of cyclohexane with hydrogen peroxide. Cyclohexanol was found to be the major product. Ce-KIT-6 (5) gave 74% cyclohexane conversion, which is higher than other catalysts. Ce⁴⁺ is suggested to activate hydrogen peroxide by coordination to oxidise cyclohexane.

Keywords: Cage-type materials; Ce-KIT-6; Oxidation; Cyclohexane; Cyclohexanol; Cyclohexanone; Hydrogen peroxide

Novel aluminophosphate (AlPO) bound ZSM-5 extrudates with improved catalytic properties for methanol to propylene (MTP) reaction by Yun-Jo Lee; Ye-Won Kim; Nagabhatla Viswanadham; Ki-Won Jun; Jong Wook Bae (pp. 18-25).

The interaction of phosphorus with pseudo-boehmite facilitates the formation of high-density aluminophosphate (AlPO) phases of alpha-cristobalite and tridymite to exhibit significant decreases in mesoporosity and extra-ordinary improvements.Novel aluminophosphate (AlPO) binders consisting of dense phases of alpha-cristobalite and tridymite were prepared by the treatment of pseudo-boehmite (AlO(OH)) with phosphoric acid. The ZSM-5 extrudates prepared by using AlPO binders have been characterized by XRD, N₂ sorption, NH₃-TPD,²⁷Al and³¹P NMR techniques to elucidate the changes that occurred in the textural properties of the catalyst and their implications on the catalytic activity of the resultant ZSM-5-based extrudates towards methanol to propylene (MTP) reaction. XRD indicated the chemical interaction of P with the alumina binder to form a highly dense crystalline phase of aluminophosphate, alpha-cristobalite. N₂ adsorption, while NH₃-TPD studies revealed the changes in pore morphology of AlO(OH) binder and acidity of ZSM-5 in phosphorus containing extrudates. The drastic decrease in mesoporosity of the AlO(OH) observed after phosphorus addition indeed envisions the disappearance of inter-crystalline voids in the AlO(OH), probably due to a change in its morphology from the crystalline phase to amorphous AlPO phase.²⁷Al and³¹P NMR studies further confirmed the formation of AlPO in these samples. The resultant ZSM-5-based extrudates exhibited enhanced properties of hydrothermal stability, mechanical strength, propylene yield and coke resistance in methanol to propylene (MTP) reaction. The positive aspect of P addition was continuously increased with P amount; at optimum P/Al (binder) ratio of ∼0.8, the catalyst exhibited about 80% yield to C₂–C₄ olefins with the major component being propylene (∼50%) at near 100% methanol conversion. The catalyst also exhibited the stable performance in the studied period of 150h.

Keywords: Aluminophosphate; ZSM-5; Acidity control; Mechanical strength; MTP

Nickel oligomerization catalysts heterogenized on zeolites obtained using ionic liquids as templates by Marcelo L. Mignoni; Michèle O. de Souza; Sibele B.C. Pergher; Roberto F. de Souza; Katia Bernardo-Gusmão (pp. 26-30).

Synthesis of zeolites using 1-butyl-3-methylimidazolium chloride (BMI.Cl) as a template yields highly crystalline materials after a few days reaction time. Depending on the Si/Al ratio the system crystallizes differently, giving selectively ZSM-5 or β-zeolite structures. The β-zeolite was used as support for a nickel-β-diimine complex and the system used in ethylene catalytic oligomerization reactions.Synthesis of zeolites using 1-butyl-3-methylimidazolium chloride (BMI.Cl) as a template yields highly crystalline materials after a 3-day reaction time. SEM micrographs of material obtained with a Si/Al molar ratio of 50 showed formation of very regular microspherical agglomerates with approximate diameters of 30μm composed of ZSM-5 crystallites with 3–5μm long edges. The regular format of these crystallites has been attributed to the formation of micellar aggregates due to the ionic liquid. Decreasing the Si/Al molar ratio to 20 reduces the diameter of the microspheres to less than 1μm. The ZSM-5 zeolites show a specific area of 384m²g⁻¹ and a microporous volume of 0.10cm³g⁻¹, and the β-zeolite, obtained after 7 days of crystallization, shows a specific area of 418m²g⁻¹ and a microporous volume of 0.11cm³g⁻¹. The β-zeolite was used as support for a nickel β-diimine complex and the system used in ethylene catalytic oligomerization reactions.

Keywords: Zeolite ZSM-5; β-Zeolite; Ionic liquid; Oligomerization

Hydroisomerization of n-decane over Ni–Pt–W supported on amorphous silica–alumina catalysts by Yacine Rezgui; Miloud Guemini (pp. 31-40).

A series of (NiPt)_AC catalysts containing nickel, tungsten and platinum were prepared via a hybrid method, characterized by several techniques and tested in the hydroisomerization of n-decane. The collected data showed that after 100min TOS, the catalyst with 12% of nickel and 0.2% platinum ((Ni₁₂Pt_0.2)_AC showed the best results (47.1% of conversion and 55.6% selectivity) at 250°C.A series of NiPtW/silica–alumina catalysts (wt.%: Ni, 12–17; W: 10, Pt: 0.1–1) were prepared via a hybrid method: sol–gel and incipient wetness impregnation and characterized by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), BET, temperature-programmed desorption of ammonia (NH₃-TPD), pyridine adsorption followed by FTIR and TPO techniques. On these catalysts, n-decane hydroisomerization was carried out under the following conditions: fixed bed reactor, atmospheric pressure, temperature ranging from 150 to 300°C, weight hourly space velocity of 4h⁻¹ and molar hydrogen/hydrocarbon ratio of 5. Pt was found to promote activity and stability, the effect being optimal for 0.2wt.% Pt. Isomers and cracking products yields were a function of both metal (Ni and Pt) content and conversion. Whatever n-decane conversion, monobranched isomers were found to be predominant. Besides, up to 10% conversion, the cracked products were not produced in significant amounts. For a time on stream of 100min, the best results (47% conversion and 56% isomerization selectivity) were obtained at 250°C over the catalyst containing 12% Ni, 10% W and 0.2% Pt).

Keywords: Platinum; Nickel; Isomerization; Cracking; n; -Decane; Stability

Conversion of 1-hexanol to di-n-hexyl ether on acidic catalysts by Eduardo Medina; Roger Bringué; Javier Tejero; Montserrat Iborra; Carles Fité (pp. 41-47).

The reaction of dehydration of hexanol to di-n-hexyl ether (DNHE) has been studied on Amberlyst 70 (a thermally stable ion-exchange resin), NR50 (a Nafion catalyst) and the zeolite H-BEA-25 at 150–190°C. The resin Amberlyst 70 gives the highest conversion and yield, but NR50 was a little more selective. Besides DNHE, hexanes, and branched ethers were detected as by-products. The attached graph shows hexanol conversion ( X_Hexanol) and selectivity to DNHE ( S_DNHE), branched ethers ( S_ethers) and C₆ olefins ( S_alkenes) at 190°C over 1g Amberlyst 70. As seen a selectivity of about 88% is obtained, quite attractive to a potential industrial process of obtaining the ether.Conversion, selectivity and yield of 1-hexanol liquid phase dehydration to di-n-hexyl ether (DNHE) were determined at 150–190°C on three acidic catalysts, the thermally stable resin Amberlyst 70, the perfluoroalkanesulfonic Nafion NR50 and the zeolite H-BEA-25, in a batch reactor. The highest conversion and yield were achieved on Amberlyst 70 at 190°C, but the most selective catalyst was Nafion NR50. Good results were obtained at 190°C on the zeolite. Apparent activation energies for the three catalysts were in the range 108–140kJ/mol. Unlike H-BEA-25, the reaction of DNHE synthesis on Amberlyst 70 and NR50 was a bit more active but less selective than the analogous 1-pentanol dehydration to di-n-pentyl ether (DNPE).

Keywords: Di-n-hexyl ether; 1-Hexanol; Amberlyst 70; Nafion NR50; H-BEA-25; Dehydration reaction

Fine tuning the surface acid/base properties of single step flame-made Pt/alumina by Bjoern Schimmoeller; Fatos Hoxha; Tamas Mallat; Frank Krumeich; Sotiris E. Pratsinis; Alfons Baiker (pp. 48-57).

The surface acid/base properties of Pt/Al₂O₃ were modified by doping the support with SiO₂ or Cs₂O, and the remarkable effect on the electronic properties of the Pt–H system was proven in the chemoselective hydrogenation of acetophenone.The acid/base properties of Pt/Al₂O₃ were modified by doping the support with SiO₂ or Cs₂O and the catalysts were prepared by flame spray pyrolysis in a rapid, single step process with excellent reproducibility. The catalysts contained 4.7wt.% Pt and the support composition varied in the range 0–100wt.% SiO₂ or 0–10wt.% Cs₂O. Up to 50wt.% SiO₂ the BET surface areas could be kept in a narrow range (141±15m²g⁻¹), while higher SiO₂ content increased the surface area and diminished the crystallinity of the support. CO chemisorption and XRD showed a positive correlation between the SiO₂ content and the size of the dominantly spherical Pt particles. The catalysts containing 22–30wt.% SiO₂ were the most acidic as evidenced by TPD of NH₃. In the hydrogenation of acetophenone the SiO₂-doped catalysts were highly active and the selectivity to the hydrogenolysis byproducts increased with increasing SiO₂ content by more than 20-fold. This is a confirmation of the effect of support acidity on the properties of the Pt–H system. On the other hand, addition of Cs₂O barely affected the Pt particle size and TPD of CO₂ confirmed the increase of surface basicity with increasing Cs₂O content. Cs₂O was probably enriched at the Al₂O₃ surface and strongly influenced the acid/base properties and thus the catalytic performance already at very low concentrations. Only 0.25wt.% Cs₂O blocked the hydrogenolysis of 1-phenylethanol to ethylbenzene.

Keywords: Flame spray pyrolysis; Metal-support interaction; Acid/base properties; Hydrogenolysis; Hydrogenation; Acetophenone

The selective hydrogenation of acetylene over a Ni/SiO₂ catalyst in the presence and absence of carbon monoxide by David L. Trimm; Irene O.Y. Liu; Noel W. Cant (pp. 58-64).

Carbon monoxide is shown to have several effects on the selective hydrogenation of acetylene over a Ni/SiO₂ catalyst. It inhibits conversion, decreases the yield of C₂ products in total and retards hydrogenation of ethylene to ethane. The changes are consistent with literature information concerning the relative strengths of adsorption of the species present in the system.The effect of carbon monoxide on the selective hydrogenation of acetylene over a 2% Ni/SiO₂ catalyst at temperatures below 100°C has been investigated. The product distribution is constant over a wide range of conversions. In the absence of carbon monoxide approximately two-third of the acetylene which reacts is converted to C₂ products with an ethane to ethylene ratio of 1:2. The addition of carbon monoxide lowers activity, with a kinetic order of −0.2, decreases the selectivity to C₂ products and decreases the extent of ethane formation. These trends are consistent with a parallel reaction scheme in which CO lowers the availability of hydrogen on the nickel surface. Further hydrogenation of product ethylene to ethane, which is intrinsically much faster than that of acetylene, is minimal for acetylene conversions below 99%. However, it does occur with feeds containing excess ethylene. The catalyst shows slow, continuous deactivation during repeated reactions. The deactivation is not due to migration of nickel, as would be expected if Ni(CO)₄ was formed. It is associated with the build-up of carbonaceous matter in amounts greatly exceeding the number of surface nickel atoms but less than that known to cause loss of activity through blockage of pores.

Keywords: Acetylene hydrogenation; Selective hydrogenation; Carbon monoxide inhibition; Ni/SiO; ₂; catalyst; Product distribution; Kinetics

Preparation of MgCl₂-supported Ziegler–Natta catalyst systems with new electron donors by Maria de Fátima V. Marques; Renata da Silva Cardoso; Micheli Galvão da Silva (pp. 65-70).

Catalyst systems employing various internal and external donors were evaluated in propylene polymerization. The newly prepared catalysts did not achieve the same polymer yields compared with the reference catalyst. On the other hand, the catalysts with the new internal donors produced polymers with isotactic index up to 98% under the polymerization conditions employed.In the present work, the effect of new internal and external electron donors for Ziegler–Natta systems of the type MgCl₂/DI/TiCl₄/DE/AlR₃ was compared with the conventional use of n-butyl phthalate and dimethoxy-diphenylsilane as electron donors. Catalyst systems employing various internal and external donors were evaluated in propylene polymerization. The polymers were characterized by infrared absorption spectroscopy, differential scanning calorimetry and heptane extraction. The prepared catalysts with the new internal donors produced polypropylene with isotactic index up to 98% under the polymerization conditions employed.

Keywords: Ziegler catalysts; Electron donors; Polypropylene; Isotacticity

Stability, activity and selectivity study of a zinc aluminate heterogeneous catalyst for the transesterification of vegetable oil in batch reactor by Véronique Pugnet; Sylvie Maury; Vincent Coupard; A. Dandeu; Anne-Agathe Quoineaud; Jean-Louis Bonneau; Didier Tichit (pp. 71-78).

The transesterification reaction of rapeseed oil by methanol was thoroughly studied using a zinc aluminate catalyst. Extra-attention was paid to the catalyst stability as it is a key property in the development of an industrial process. Zinc leaching was very low amounting to no more than 4ppm by weight in the ester phase after 6h of contact time.The transesterification reaction of rapeseed oil by methanol was studied using a zinc aluminate catalyst in order to develop an alternative to the currently used homogeneous processes. At first, the reaction parameters such as catalyst particle size, stirring rate and amount of catalyst required to perform the transesterification reaction under a kinetically controlled-regime were determined. Thorough study of the catalyst stability was performed, in particular leaching of active species. A peculiar activity of the reactor walls was observed and XPS analysis allowed to determine that it stemmed from adsorption on the reactor walls of zinc species coming from catalysts prone to leaching. A method was therefore proposed to free oneself from this phenomenon. The zinc aluminate catalyst was found to be particularly stable as compared to ZnO catalyst.Optimization of the reaction parameters for achieving high yields and obtaining high quality products was performed. Indeed the influence on the activity, stability and selectivity of the temperature, the reactants ratio, and the presence of water in the reactants, was studied.Finally a pseudo-homogeneous kinetic model was validated and used to determine the kinetic parameters of the reaction.

Keywords: Biodiesel; Transesterification; Catalyst; Leaching; Zinc aluminate

Synthesis of CNT-supported cobalt nanoparticle catalysts using a microemulsion technique: Role of nanoparticle size on reducibility, activity and selectivity in Fischer–Tropsch reactions by Mariane Trépanier; Ajay K. Dalai; Nicolas Abatzoglou (pp. 79-86).

The Co/CNT catalysts were produced by two techniques: microemulsion and incipient wetness impregnation. FTS selectivity and activity was dependant on cobalt particle size. The confinement of the cobalt particles inside has changed the expected catalyst's structure-sensitive results. CNT-supported Cobalt catalysts synthesized by the microemulsion technique increased the CO conversion by 15% compared to those prepared by incipient wetness impregnation.The influence of cobalt particle size on catalyst performance in Fischer–Tropsch synthesis (FTS) has been investigated using inert carbon nanotube (CNT)-supported catalysts. The catalysts were produced by the core reverse micelle reactions with cobalt particles of various sizes (3–10nm). It has been shown that particle size is proportional to the water-to-surfactant ratio (3–10) used for the catalyst preparation. Very narrow particle size distributions have been produced by the microemulsion technique and at relatively high loading (Co 10wt%). Selectivity and activity were found to be dependant on cobalt particle size. The FTS rate increases from 0.36 to 0.44gHC/g_cat./h and the C₅₊ selectivity increases from 89 to 92.5wt% with increasing the average cobalt particle size from 2–3 to 9–10nm, respectively. According to TEM analysis, small Co particles (2–6nm) are mostly confined inside the CNTs where influence of its electron deficiency in the inside surface has changed the commonly expected catalyst's structure-sensitive results. Finally, the CNT-supported cobalt nanoparticles synthesized by the proposed microemulsion technique increased the CO conversion by 15% compared to those prepared by incipient wetness impregnation.

Keywords: Microemulsion; Cobalt catalysts; Carbon nanotubes; Fischer–Tropsch synthesis; Nanoparticles

Heteropoly acid catalysts in the valorization of the essential oils: Acetoxylation of β-caryophyllene by Kelly A. da Silva Rocha; Nathália V.S. Rodrigues; Ivan V. Kozhevnikov; Elena V. Gusevskaya (pp. 87-94).

H₃PW₁₂O₄₀ (PW), the strongest heteropoly acid in the Keggin series, is an active and environmentally friendly catalyst for the liquid-phase conversion of one of the most abundant sesquiterpenes, i.e., β-caryophyllene (1), to β-caryolanyl acetate (2), which is a potentially valuable fragrance compound, in up to 100% GC yield.H₃PW₁₂O₄₀ (PW), the strongest heteropoly acid in the Keggin series, is an active and environmentally friendly catalyst for the liquid-phase conversion of β-caryophyllene (1) to β-caryolanyl acetate (2) in homogeneous and heterogeneous systems. An efficient and clean method for the synthesis of2, providing a mixture containing two stereoisomeric β-caryolanyl acetates2a and2b,2a/2b=80/20mol/mol, with 100% GC yield, has been developed using PW as a homogeneous catalyst under mild reaction conditions. The reaction occurs at 25°C with a catalyst turnover number of 2000. The catalyst can be recovered without neutralization and reused without loss of activity and selectivity.

Keywords: Acetoxylation; β; -Caryophyllene; Acid catalysis; Heteropoly acid

CO desorption kinetics at concentrations and temperatures relevant to PEM fuel cells operating with reformate gas and PtRu/C anodes by A. Pitois; A. Pilenga; G. Tsotridis (pp. 95-102).

The kinetics of the CO desorption process have been determined using isotopic exchange experiments at concentrations and temperatures relevant to PEM fuel cells operating with reformate gas and PtRu/C anodes. The proposed desorption rate values at the lower 10–100ppm CO concentration range and at relevant temperatures are believed to be of added value for the modelling of PEM fuel cells operating with reformate gas.The kinetics of the CO desorption process have been determined using isotopic exchange experiments at concentrations and temperatures relevant to PEM fuel cells operating with reformate gas and commercial carbon supported platinum–ruthenium alloy anodes. The CO desorption kinetics have been studied as a function of CO concentration, temperature and flow rate. Desorption rate constants have been determined experimentally for a wide range of concentrations (100–500ppm) and temperatures (25–150°C) and have been extrapolated to one order of magnitude lower CO concentration range between 10 and 100ppm, which is directly relevant to PEM fuel cells operating with reformate gas. The desorption rates measured for the 100–500ppm CO concentration range appear to be significantly larger than previously published CO oxidation data, suggesting that the CO desorption process plays a more significant role in determining the equilibrium CO coverage at the fuel cell anode than the electrochemical CO oxidation process. The proposed desorption rate values at the lower 10–100ppm CO concentration range and at relevant temperatures are believed to be of added value for the modelling of PEM fuel cells operating with reformate gas and PtRu/C anodes, since significantly different empirical values have been used up to now for the modelling of the CO desorption process. The variation of the apparent Arrhenius parameters as a function of CO concentration provides also some insight into the CO poisoning effect and the underlying adsorption/desorption processes.

Keywords: CO tolerance; Catalysis; Platinum; Ruthenium; Desorption; Isotope exchange; Temperature dependence; Concentration dependence; Proton exchange membrane fuel cell; Modelling; Reformate gas

Vanadia–titania thin films for photocatalytic degradation of formaldehyde in sunlight by Rokhsareh Akbarzadeh; Shubhangi B. Umbarkar; Ravindra S. Sonawane; Srikant Takle; Mohan K. Dongare (pp. 103-109).

Thin films of vanadia–titania with good adhesion to the substrates have been deposited on various substrates by simple sol–gel dip coating using peroxide gel. The V₂O₅/TiO₂ thin films showed very high photocatalytic activity in sunlight for degradation of methylene blue as model dye and degradation of formaldehyde from aqueous solution as an industrial pollutant.Thin films of vanadia–titania with good adhesion to the substrates have been deposited on various substrates such as glass slides, glass helix and silica raschig rings by simple sol–gel dip coating process using vanadium and titanium peroxide gel. The optimum concentration of vanadia in titania for obtaining good uniform viscous gel was found to be 0.5–4wt% beyond which the vanadia particles disturb the gel network, resulting in the formation of a gelatinous precipitate. The films of vanadia–titania as well as the dried powder of the bulk gel were characterized by different characterization techniques. Optical characterization by UV–vis spectrophotometer showed a shift in optical absorption wavelength to the visible region that may be due to the incorporation of vanadia into titania structure. The XRD revealed the formation of anatase phase in pure titania as well as titania with up to 2% vanadia loading, whereas formation of rutile as minor phase along with anatase as major phase was observed at higher vanadia loading. The XRD did not show any peaks of vanadia phase up to 5% vanadia loading indicating either incorporation of vanadia into titania structure or high dispersion of amorphous vanadia on titania support. The pure and vanadia doped TiO₂ thin films were evaluated for their photocatalytic activity for degradation of methylene blue as a model pollutant under sunlight. Doping of V₂O₅ in TiO₂ showed an increase in the photo-degradation rate of methylene blue by a factor of 3–6.6 times compared to pure TiO₂. The highest rate has been obtained for 4% V₂O₅-doped TiO₂ films. Vanadia doped TiO₂ thin films were also found to be very active for photocatalytic degradation of formaldehyde from aqueous solution in sunlight.

Keywords: Photocatalysis; Sunlight; V; ₂; O; ₅; /TiO; ₂; Thin films; Methylene blue; Formaldehyde

Preyssler catalyst: An efficient catalyst for esterification of cinnamic acids with phenols and imidoalcohols by Diego M. Ruiz; Gustavo P. Romanelli; Patricia G. Vázquez; Juan C. Autino (pp. 110-119).

A series of eco-friendly Preyssler solid acids and their salts have been used as catalysts for the direct esterification of cinnamic acids with phenols or 2-(N-phthalimidoethanol). The catalysts were characterized by several techniques (DRS, FTIR, SEM, XRD, among others) and the effects of the reaction conditions were studied, including temperature, reaction time, and type and amount of catalyst.In the present work a series of eco-friendly Preyssler solid acids and their salts H₁₄[NaP₅W₂₉MoO₁₁₀] (PW), H₁₄[NaP₅W₃₀O₁₁₀] (PWMo), K_12.5Na_1.5[NaP₅W₃₀O₁₁₀]·15H₂O (PWK), K_12.5Na_1.5[NaP₅W₂₉MoO₁₁₀]·15H₂O (PWMoK) and 10% silica-supported H₁₄[NaP₅W₂₉MoO₁₁₀] (PWSiO₂), and H₁₄[NaP₅W₃₀O₁₁₀] (PWMoSiO₂) have been used as catalysts for the direct esterification of cinnamic acids with phenols or 2-(N-phthalimidoethanol). Effects of the reaction conditions were studied, including temperature, reaction time, and type and amount of catalyst. These solids were characterized by several techniques, such as diffuse reflectance spectroscopy, Fourier transformed infrared spectroscopy, optical and scanning electron microcopies, and X-ray diffraction, among others.The most adequate catalyst for performing the title reaction was H₁₄[NaP₅W₃₀O₁₁₀] (PWMo). The catalyst was applied for the synthesis of various substituted cinnamates, giving very good yields.

Keywords: Acid catalysis; Cinnamates; Esterification; Heteropolyacid; Preyssler heteropolyacids

Further support for the two-mechanisms hypothesis of Fischer–Tropsch synthesis by J. Gaube; H.-F. Klein (pp. 120-125).

The hypothesis of two incompatible mechanisms of chain growth finds strong support by detailed interpretation of CH₂N₂ co-feeding experiments and the selectivity of branched hydrocarbons. Deviations of the carbon number distribution from the strict superposition of two ASF distributions are interpreted by the subsequent chain growth of readsorbed 1-alkenes via the mechanism characterized by CH₂-insertion.The recently proposed hypothesis of two incompatible mechanisms of chain growth based on CH₂- and CO-insertion is furthermore supported by a detailed interpretation of the¹³CH₂N₂ co-feeding experiments of Maitlis and co-workers and of the selectivity of branched hydrocarbons.The carbon number distribution is discussed considering in particular the role of readsorption and incorporation of 1-alkenes and its subsequent chain growth.

Keywords: Fischer–Tropsch synthesis; Mechanisms

Magnetic resonance imaging as an emerging tool for studying the preparation of supported catalysts by Anna A. Lysova; Jaap A. Bergwerff; Leticia Espinosa-Alonso; Bert M. Weckhuysen; Igor V. Koptyug (pp. 126-136).

Several magnetic resonance imaging (MRI) approaches are presented that can be used to study transport processes of various components of an impregnation solution when supported catalysts are prepared by impregnation. Multinuclear MRI is also used to map the solid phase distribution of the active component precursors and additives within the impregnated support bodies after their drying.Several magnetic resonance imaging (MRI) approaches are presented that can be used to study transport processes when supported catalysts are prepared by impregnating mm-sized porous support bodies. Both diamagnetic and paramagnetic components of an impregnation solution such as the solvent, the metal-containing precursors of an active component, and various organic and inorganic additives can be visualized with MRI. Their spatial distributions within a catalyst support body and the evolution of these distributions in time can be characterized not only qualitatively but also quantitatively, if calibration procedures are used to convert the images into corresponding concentration profiles. In particular, the physicochemical interactions between γ-Al₂O₃ support bodies and the aqueous solutions containing Cu, Co, Mo, citrate and phosphate ions are investigated upon pore volume impregnation as a function of concentration and solution pH. Furthermore, it is shown that multinuclear and solid state MRI can be used to map the solid phase distribution of the active component precursors and additives within the impregnated support bodies after their drying. Based on the case studies discussed, it can be concluded that MRI is an emerging versatile tool for studying the transport processes in support bodies upon their impregnation and the distribution of the key components after drying of the impregnated bodies.

Keywords: Magnetic resonance imaging; Supported catalyst preparation; Pore volume impregnation; Transport of active component

Influence of W loading on the environment of Si in WO₃/ZrO₂–SiO₂ catalysts by Sebastien Lecarpentier; Jacob van Gestel; Karine Thomas; Jean-Pierre Gilson; Marwan Houalla (pp. 137-141).

The location of Si species (surface or bulk) added to stabilize the surface area of tungstated zirconia and their degree of aggregation, were studied as a function of W addition. NMR and infrared results indicated that W addition brings about a progressive evolution of the Si environment towards that of silica-like species.Tungstated zirconias consist typically of WO_x species deposited on zirconia support. Additives like Si can be added to stabilize the catalyst surface area. The aim of this work is to identify the location of the Si (surface or bulk) as a function of W addition. Zirconia doped with 1.2wt% Si remained purely tetragonal and exhibited a high specific surface area (150m²/g) following calcination at 1023K. Infrared quantification of the silanol band at 3745cm⁻¹ indicated that Si is essentially present at the surface. The²⁹Si NMR chemical shift of the zirconia is characteristic of isolated silicium. This result is corroborated with infrared by the absence of the structural band ascribed to Si–O–Si vibrations. NMR and infrared results indicated that W addition brings about a progressive evolution of the Si environment towards that of silica-like species. These results can be tentatively explained by a ligand enhanced dissolution of the support on W deposition. Si leached from the surface will then aggregate, forming small SiO₂-like domains on the zirconia.

Keywords: Zirconia; ²⁹; Si NMR-MAS; Infrared; CO adsorption

Investigation of catalytic activity of CrSBA-1 materials obtained by direct method in the dehydrogenation of propane with CO₂ by Piotr Michorczyk; Jan Ogonowski; Marta Niemczyk (pp. 142-149).

Cr-containing SBA-1 cubic mesoporous catalysts with various Cr/Si atomic ratios have been prepared by direct method, characterized by different physicochemical techniques and investigated in the dehydrogenation of propane to propene with CO₂. In the case of the most active, 0.04CrSBA-1 catalyst, the effect of various reaction parameters such as, reaction temperature, reaction time and feed gas composition on the conversion of propane, yield and selectivity to propene as well as on molar ratio of CO/H₂ has been evaluated.A series of the Cr-containing SBA-1 ( xCrSBA1) cubic mesoporous catalysts with various Cr/Si molar ratios have been prepared by direct method using cetyltriethylammonium bromide, ammonium dichromate, tetraethyl orthosilicate and hydrochloric acid. The obtained materials have been characterized by different physicochemical techniques including ICP, XRD, UV–vis DRS, H₂-TPR and N₂-adsorption. XRD and N₂-adsorption results have revealed that xCrSBA1 materials possess well organized three-dimensional pore structure. However, incorporation of Cr into the SBA-1 framework leads to small perturbation of the structural order. ICP results have shown that the amount of Cr incorporation in SBA-1 can be controlled by adjustment of the molar ratio of (NH₄)₂Cr₂O₇ to Si(C₂H₅O)₄ in the gel. Finally, the catalytic activity of pure SBA-1 and Cr-containing SBA-1 materials were investigated in the dehydrogenation of propane with CO₂. In the case of the most active, 0.04CrSBA1 catalyst, the effect of various reaction parameters such as, reaction temperature, reaction time and feed gas composition on the conversion of propane, yield and selectivity to propene as well as on molar ratio of CO/H₂ has been evaluated. Moreover, stability of the catalyst during the dehydrogenation/regeneration conditions was studied as well. It has been found that during the fourth consecutive cycle the catalyst undergoes two types of deactivation processes – reversible and irreversible. The former is caused mainly by the coke deposition, which can easily overcome by air treatment of the catalyst at 550°C. The latter one, insignificant, is due to partial collapse of mesoporous structure of the catalysts.

Keywords: Dehydrogenation with CO; ₂; Propene; Chromium catalysts; SBA-1

Active site distribution analysis of hydrodenitrogenation catalyst using Fredholm integral equation by Akira Miyata; Hiroyuki Tominaga; Masatoshi Nagai (pp. 150-157).

Fredholm integral equation of the first kind gives the activity distribution of active sites:r(t)=∫h(t,k)f(k)dk,h(t,k)⁡=⁡exp(−tk)and11+kt.A non-parametric analysis using the Fredholm integral equation of the first kind exploits the distribution of the catalytic active sites during the hydrodenitrogenation (HDN) of carbazole on nitrided and reduced 12.5% Mo/Al₂O₃ catalysts. The approach was combined with the reactivity data and the surface property measurements. The equation describes two kinds of active sites (Site 1 with a small rate coefficient and Site 2 with a high rate coefficient) on the catalysts. The 1173K-nitrided catalyst had a high activity and large Site 1 population along with a very low population and the highest value of Site 2, while the treatment at 773K with NH₃ or H₂ produced less Site 1 than Site 2. The 973K-nitrided catalyst had the highest k₂· x₂ value of the four catalysts, showing that it was superior to the other catalysts for Site 2. Based on the reaction product selectivity, Site 1 of the nitrided catalyst was responsible for the hydrogenation of carbazole, while Site 2 was responsible for the C–N hydrogenolysis of perhydrocarbazole. The turnover frequency (carbazole disappearance rate divided by the CO adsorption) was correlated to the k₁ x₁ value, but not to the k₂ x₂ value, showing that Site 1 facilitated the HDN reaction controlled by the carbazole hydrogenation. The two sites and mechanism for the carbazole HDN are discussed.

Keywords: Carbazole; Fredholm integral equation; Hydrodenitrogenation; Mo nitride; Site distribution

Catalytic hydroconversion of tricaprylin and caprylic acid as model reaction for biofuel production from triglycerides by László Boda; György Onyestyák; Hanna Solt; Ferenc Lónyi; József Valyon; Artrur Thernesz (pp. 158-169).

Palladium/activated carbon and promoted molybdena–alumina catalysts were used. The hydroconversion was found to proceed in consecutive steps of triglyceride hydrogenolysis to carboxylic acid and propane, and hydrodeoxygenation of the acid intermediate. Two hydrodeoxygenation routes were distinguished: (i) over Pd/C the prevailing reaction route was the decarbonylation, whereas (ii) over molybdena–alumina catalysts the main reaction was the reduction of oxygen to get water.There is strong interest in the production of fuels from triglycerides of biological origin. In this work tricaprylin (TC) and caprylic acid (CA) were used as model compounds to study the catalytic hydroconversion process of triglycerides to acyclic aliphatic hydrocarbons. Supported metal and metal oxide catalysts, such as palladium on activated carbon (Pd/C), and promoted molybdena–alumina (Ni,Mo/γ-Al₂O₃) were used. The reaction was found to proceed in consecutive steps: hydrogenolysis (HYS) of TC to CA and propane, followed by hydrodeoxygenation (HDO) of the CA intermediate. The overall reaction rate was governed by the rate of the HDO reaction. Two distinct HDO routes were distinguished: (i) hydrodecabonylation and (ii) reduction of oxygen. Over Pd/C the prevailing reaction route of CA hydroconversion was the decarbonylation giving mainly C₇ alkane and CO, whereas the HDO over the Ni,Mo/γ-Al₂O₃ catalysts proceeded in consecutive H₂ addition and dehydration steps giving predominantly C₈⁼ alkenes, C₈ alkanes and water. In reaction route (ii) alcohol and traces of aldehyde were detected as acid-to-alkane intermediates. Results suggest that reaction route (i) passes through formic acid intermediate that, in the presence of H₂, rapidly decomposes to CO and H₂O.

Keywords: Tricaprylin hydroconversion; Caprylic acid hydroconversion; Ni,Mo/γ-alumina; Pd/carbon

Catalytic degradation of low and high density polyethylenes using ethylene polymerization catalysts: Kinetic studies using simultaneous TG/DSC analysis by A. Coelho; I.M. Fonseca; I. Matos; M.M. Marques; Ana M. Botelho do Rego; M.A.N.D.A. Lemos; F. Lemos (pp. 170-179).

The catalytic degradation of polyethylene, using catalysts based on transition metals supported on zeolite Y, is analysed using simultaneous TG/DSC. These catalysts were active for ethylene polymerization, the reverse reaction of the one we are interested in. They were also able to promote the degradation process of polyethylene. A kinetic model was used to provide insight into the processes involved.In this work, the catalytic degradation of high and low density polyethylenes, using catalysts based on transition metals supported on zeolite Y, is analysed using simultaneous thermogravimetry (TG) and differential scanning calorimetry (DSC). The results obtained in the catalytic degradation are compared with those that were obtained in the purely thermal degradation. The transition metals used, vanadium, zirconium and nickel, supported on NaY or HY were studied since they were found to be active, although with different degrees of efficiency, for ethylene polymerization, which is, in a way, the reverse reaction of the one we are interested in. It was found that they are also able to promote the degradation process of polyethylene, also with varying efficiencies. A kinetic model capable to describe the performance of the catalytic degradation, and which has already been used to analyse its thermal degradation, has been applied. Fitting this model to the experimental results obtained by TG and DSC made it possible to estimate several kinetic parameters and to gain some insight into the processes involved.

Keywords: Polyethylene; Thermal degradation; Supported catalysts; Kinetic modelling; Differential scanning calorimetry (DSC); Thermogravimetry (TG)

Pd–In₂O₃ interaction due to reduction in hydrogen: Consequences for methanol steam reforming by Harald Lorenz; Stuart Turner; Oleg I. Lebedev; Gustaaf Van Tendeloo; Bernhard Klötzer; Christoph Rameshan; Kristian Pfaller; Simon Penner (pp. 180-188).

Despite the striking similarities of Pd supported on ZnO, Ga₂O₃ and In₂O₃ regarding bimetallic formation and catalytic selectivity in methanol steam reforming, In₂O₃ shows pronounced additional strong metal–support interaction effects at very low temperatures seriously affecting the catalytic properties of Pd/In₂O₃ catalysts.Two different Pd/In₂O₃ samples including a thin film model catalyst with well-defined Pd particles grown on NaCl(001) supports and a powder catalyst prepared by an impregnation technique are examined by electron microscopy, X-ray diffraction and catalytic measurements in methanol steam reforming in order to correlate the formation of different oxide-supported bimetallic Pd–In phases with catalytic activity and selectivity.A PdIn shell around the Pd particles is observed on the thin film catalyst after embedding the Pd particles in In₂O₃ at 300K, likely because alloying to PdIn and oxidation to In₂O₃ are competing processes. Increased PdIn bimetallic formation is observed up to 573K reduction temperature until at 623K the film stability limit in hydrogen is reached. Oxidative treatments at 573K lead to decomposition of PdIn and to the formation of an In₂O₃ shell covering the Pd particles, which irreversibly changes the activity and selectivity pattern to clean In₂O₃.PdIn and Pd₂In₃ phases are obtained on the powder catalyst after reduction at 573K and 673K, respectively. Only CO₂-selective methanol steam reforming is observed in the reduction temperature range between 473K and 573K. After reduction at 673K encapsulation of the bimetallic particles by crystalline In₂O₃ suppresses CO₂ formation and only activity and selectivity of clean In₂O₃ are measured.

Keywords: Electron microscopy; Pd–In intermetallics; PdIn; Pd; ₂; In; ₃; Methanol steam reforming

Efficient synthesis of chalcone derivatives catalyzed by re-usable hydroxyapatite by A. Solhy; R. Tahir; S. Sebti; R. Skouta; M. Bousmina; M. Zahouily; M. Larzek (pp. 189-193).

Hydroxyapatite was found to be a very efficient heterogeneous catalyst for the preparation of chalcone derivatives via Claisen–Shmidt condensation using microwave irradiation. The impact of water on the catalyst reactivity was studied and demonstrated to act as co-catalyst when combined with hydroxyapatite, making the process highly efficient. The catalyst was easily recovered and efficiently re-used.Hydroxyapatite was found to be a very efficient heterogeneous catalyst for the preparation of chalcone derivatives via Claisen–Schmidt condensation using microwave irradiation. The impact of water on the catalyst reactivity was studied and was thought to act as co-catalyst due to the high activation observed in its presence. To investigate the origin of this activation, different organic solvents of similar or higher microwave absorbance as/to water were also tested, and it was confirmed that water is acting as co-catalyst when combined with hydroxyapatite, making the process highly efficient. The catalyst was easily recovered and efficiently re-used.

Keywords: Hydroxyapatite; Water; Claisen–Schmidt condensation

The influence of perhydroazepine and piperidine as further ancillary ligands on Ru-PPh₃-based catalysts for ROMP of norbornene and norbornadiene by José L. Silva Sá; Laís H. Vieira; Eduardo S.P. Nascimento; Benedito S. Lima-Neto (pp. 194-200).

Complexes of type [RuCl₂(PPh₃)₂(amine)], amine=piperidine or perhydroazepine, are efficient catalyst precursors for ring opening metathesis polymerization (ROMP) of norbornadiene and norbornene. The effects of the solvent volume, reaction time and atmosphere (argon or air) on the polymer yields were investigated.Polynorbornadiene and polynorbornene were synthesized via ring opening metathesis polymerization (ROMP) with [RuCl₂(PPh₃)₂(amine)] as catalyst precursors, amine=piperidine (1) or perhydroazepine (2) in the presence of 5μL of ethyl diazoacetate (EDA) ([monomer]/[Ru]=5000; 40°C with1; 25°C with2). The effects of the solvent volume (2–8mL of CHCl₃), reaction time (5–120min) and atmosphere type (argon and air) on the yields were investigated to observe the behavior of the two different precursors. Quantitative yields were obtained for 60 or 120min regardless of the starting volumes, either in argon or air, with both Ru species. However, low yields were obtained for short times (5–30min) when the reactions are performed with large volumes (6–8mL). In argon, the yields were larger with2, associated to a faster propagation reaction controlled by the Ru active species. In air, the yields were larger with1, associated to a higher resistance to O₂ of the starting and propagating Ru species. The different activities between1 and2 are discussed considering the steric hindrance and electronic characteristics of the amines such as ancillary ligands and their arrangements with PPh₃ and Cl⁻ ions in the metal centers.

Keywords: ROMP; Ancillary ligand; Ruthenium; Piperidine; Perhydroazepine

One-pot synthesis of alcohols from olefins catalyzed by rhodium and ruthenium complexes by Joseph Zakzeski; Hae Ryun Lee; Yi Ling Leung; Alexis T. Bell (pp. 201-212).

The one-pot synthesis of butanol and heptanol from propene and 1-hexene, respectively, was performed using Ru(PPh₃)Cl₂ and Rh(CO)₂(acac) in the presence of triphenylphosphene. Two methods for performing the one-pot synthesis were developed and are discussed.The one-pot synthesis of butanol and heptanol from propene and 1-hexene, respectively, was performed using Ru₃(PPh₃)Cl₂ and Rh(CO)₂(acac) in the presence of triphenylphosphene. The effects of various reaction parameters, including catalyst concentration, gas partial pressures, and temperature, were investigated. Two methods for performing the one-pot synthesis were developed and are discussed. In the first method, stoichiometric quantities of CO and propene or 1-hexene were fed to the autoclave. It was found that residual carbon monoxide necessary for the hydroformylation poisoned the Ru catalyst used for the hydrogenation. Venting the hydroformylation gases was therefore necessary for hydrogenation of the aldehyde to proceed. In the second method, sub-stoichiometric quantities of CO relative to olefin were fed to the autoclave, and CO conversion was driven to nearly 100%. In this case, the low residual CO concentration allowed the hydrogenation to proceed readily. The optimal temperatures and gas pressures for the hydroformylation were not the optimal temperatures and pressures for the hydrogenation. A strategy is described for maximizing the performance of both steps. Under optimal conditions, 100% conversion of propene to butanol could be achieved with 97% selectivity, and 99% conversion of 1-hexene to hepatanol could be achieved with 98% selectivity. The only byproduct observed in the latter case was a small amount of 2-hexene, which did not undergo hydroformylation. A possible reaction mechanism is proposed for both the hydroformylation of the olefin and the hydrogenation of aldehyde based on spectroscopic evidence.

Keywords: Olefin; Alcohol; Aldehyde hydrogenation; Hydroformylation; One-pot synthesis

Effect of reaction temperature in the selective synthesis of single wall carbon nanotubes (SWNT) on a bimetallic CoCr-MCM-41 catalyst by Codruta Zoican Loebick; Darlington Abanulo; Magda Majewska; Gary L. Haller; Lisa D. Pfefferle (pp. 213-220).

A bimetallic CoCr-MCM-41 catalyst was used for production of SWNT by CO disproportionation. The effect of reaction temperature over the size-controllability of the catalyst particles and the morphology of the resultant SWNT was studied. Decrease in reaction temperature favored the selective synthesis of very small diameter nanotubes. Lower reaction temperature was favorable for the selective synthesis of certain tube identities.Synthesis of single wall carbon nanotubes (SWNT) on a CoCr-MCM-41 bimetallic catalyst by CO disproportionation has been carried out at five different temperatures between 500 and 900°C. A series of methods have been employed for a comprehensive assessment effect of temperature on the size-controllability of the catalyst particles and the morphology of the resultant SWNT. By extended fine structure X-ray absorption, thermogravimetric analysis, resonance Raman spectroscopy, photoluminescence excitation (PLE) mapping and transmission electron microscopy we found an optimal synthesis temperature window between 600 and 800°C. In this window, modifying the reaction temperature leads to significant changes in the SWNT yield, diameter and chirality distribution. Decrease in reaction temperature favored the selective synthesis of very small diameter carbon nanotubes (as low as 0.6nm). Chirality dependence of SWNT on temperature has been measured by PLE. A progressive suppression of larger diameter SWNT identities in the measured SWNT population was noted when reaction temperature decreased. In the measured PL maps, two near armchair structures (6,5) and (7,3) were dominant at 600 and 700°C.

Keywords: Carbon nanotubes; Diameter; Selectivity; Bimetallic; Catalyst; Cobalt; Chromium; Temperature

Effect of the metal precursor on the properties of Ru/ZnO catalysts by E.V. Ramos-Fernández; J. Silvestre-Albero; A. Sepúlveda-Escribano; F. Rodríguez-Reinoso (pp. 221-227).

The effect of the ruthenium precursor, Cl-containing or Cl-free, on the characteristics of Ru/ZnO catalysts and on their behaviour in the vapour-phase hydrogenation of crotonaldehyde is studied.The effect of the ruthenium precursor (chlorinated or chlorine-free) on the properties and the catalytic behaviour of Ru/ZnO catalysts in the vapour phase hydrogenation of crotonaldehyde (2-butenal) has been studied. Two catalysts were prepared, using ruthenium (III) chloride (Ru(Cl)/ZnO) and ruthenium (III) acetylacetonate (Ru(A)/ZnO) as the metal precursors. The catalysts have been characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), H₂ temperature-programmed desorption (H₂-TPD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM), and their catalytic behaviour has been evaluated in the title reaction after reduction at low (473K) and high (623K) temperatures. Ru(Cl)/ZnO showed better catalytic behaviour after both reduction treatments, what has been explained on the basis of a well controlled metal-support interaction. For Ru(A)/ZnO this interaction is too high, resulting in a dramatic lost of active sites that yields worse catalytic behaviour. It is important to remark that both catalysts were very active and selective to the desired product, the unsaturated alcohol (crotyl alcohol, 2-buten-1-ol).

Keywords: Ru/ZnO catalysts; Chlorine effects; XPS; TEM; Crotonaldehyde hydrogenation

Effect of citric acid addition on the hydrodesulfurization activity of MoO₃/Al₂O₃ catalysts by Nino Rinaldi; Takeshi Kubota; Yasuaki Okamoto (pp. 228-236).

Effects of citric acid addition were studied on the HDS activity of MoO₃/Al₂O₃ catalysts prepared by simultaneous impregnation and post-treatment methods. The post-treatment of MoO₃/Al₂O₃ with citric acid greatly increased the HDS activity at a high Mo content (>20wt% Mo) as well as the edge dispersion of MoS₂ particles. The addition of citric acid also improved the sulfidation degree of Mo at a high Mo content.A series of MoO₃/Al₂O₃ catalysts was prepared using citric acid (CA) as a chelating agent by a simultaneous impregnation method or by a post-treatment method. The catalyst was tested for the HDS of thiophene. The catalysts were characterized by means of LRS, XRD, Mo K-edge EXAFS and XANES, NO adsorption capacity, and surface area measurements. The catalysts were also subjected to a chemical vapor deposition (CVD) technique using Co(CO)₃NO as a precursor of Co to prepare CVD-Co/MoS₂ catalysts. The addition of citric acid to 8.7wt% Mo/Al₂O₃ increased neither the HDS activity nor the edge dispersion of MoS₂ particles. On the other hand, the addition of citric acid by the post-treatment to MoO₃/Al₂O₃ catalysts having a higher Mo content (>20wt% Mo) significantly enhanced the edge dispersion of MoS₂ particles and thus the catalytic activity of MoS₂/Al₂O₃ and CVD-Co/MoS₂/Al₂O₃. The addition of citric acid by the post-treatment resulted in the formation of well-dispersed Mo species on the catalyst surface at the expense of crystalline MoO₃. The Mo K-edge XAFS and XANES showed that the sulfidation degree of Mo is greatly improved by the addition of citric acid at a high Mo content regardless of the addition procedure.

Keywords: Catalyst preparation; Citric acid; Hydrodesulfurization; MoO; ₃; /Al; ₂; O; ₃; catalyst; Mo K-edge XAFS; Thiophene; Post-treatment

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Applied Catalysis A, General (v.374, #1-2)