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Applied Catalysis A, General (v.310, #1-208)

Editorial Board (pp. co2).

Review of absorption and adsorption in the hydrogen–palladium system by Linda L. Jewell; Burtron H. Davis (pp. 1-15).

The hydrogen–palladium system has been the subject of much study, both experimentally and computationally. In this review article the authors have set out to draw a comparison between the experimentally determined thermodynamic data for this system and the calculated energies, in order to attempt to bridge the gap between computational chemistry and experimental work and so gain insight into the absorption and adsorption of hydrogen on palladium.Rigorous thermodynamic analysis of the data for the absorption of hydrogen into palladium metal shows that although constant volume measurements have been made, the analysis that has been applied in the literature in several instances is valid only for a constant pressure system. Re-analysis of the data has lead to a heat of formation for β-palladium hydride which is not a function of composition and a weak function of temperature. Values for the internal energy of absorption of −36.7, −35.2 and −34.4kJ/mol of H₂ were obtained at 0°C and in the temperature ranges from 200 to 313°C and from 366 to 477°C, respectively. There is a good agreement between these values and the calculated values.The implicit assumptions that underpin the integrated form of the Clausius–Clapeyron equation are that an isobaric system is being analyzed, and that the enthalpy is not a function of composition or temperature. Since heat of adsorption is known to be a function of surface coverage and is generally measured in a constant volume system, the application of the integrated Clausius–Clapeyron equation to determine the enthalpy of adsorption as a function of surface coverage has been questioned and an alternative thermodynamic analysis has been proposed that enables one to calculate the differential change in internal energy of adsorption with surface coverage. It has been found that the internal energy of adsorption varies with increasing surface coverage in a similar manner to the way in which internal energy varies as two atoms approach each other. It is noted that the variation in internal energy with surface coverage (0.1< θ<0.94) calculated in this work is of the order of 100J/mol, while the heat of adsorption in the literature is of the order of −87,000J/mol. Thus, except at very high coverages, the change in internal energy or enthalpy of adsorption with changes in surface coverage is very small compared to the overall heat of adsorption.The computationally determined energies of adsorption do not reflect this trend and appear to under estimate the electrostatic repulsion (or over estimate the attraction) between gas phase molecules and atoms that are already adsorbed on the surface for this system.

Keywords: Surface coverage; Experimental and computational determination of heat of adsorption; Heat of absorption; Palladium hydride; Hydrogen adsorbed on palladium

Surface-appropriate lipophobicity—Application in isobutene oligomerization over Teflon-modified silica-supported 12-silicotungstic acid by Guifang Chen; Jing Li; Xiangguang Yang; Yue Wu (pp. 16-23).

A series of silica-supported 12-silicotungstic acid catalysts (H₄SiW₁₂O₄₀, abbreviated as HSiW), modified with various loadings of Teflon (HSiW/SiO₂-Teflon), were prepared by an impregnation method. The surface properties of the catalysts were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), BET, infrared (IR) spectroscopy, NH₃-TPD and the Drop Shape Analysis (DSA). SEM results combined with energy-dispersive X-ray (EDX) measurements of HSiW/SiO₂-Teflon revealed that F-compound (Teflon) is effectively coated on the catalyst surface. The contact angles for water and oil of 50wt% HSiW/SiO₂ and HSiW/SiO₂-Teflon indicate that HSiW/SiO₂-Teflon catalyst enhances not only the surface hydrophobicity but also the surface lipophobicity by means of the addition of Teflon. Silica-supported 12-silicotungstic acid modified with Teflon exhibits higherC8= selectivity and longer lifetime than that of silica-supported 12-silicotungstic acid in isobutene oligomerization. Thus, surface-appropriate lipophobicity of catalysts may be effective for decreasing the interaction between coke precursors and the catalyst surface and for removing deposited coke more easily.

Keywords: Lipophobicity; Teflon; Silica-supported 12-silicotungstic acid; Isobutene oligomerization

Studies on precipitated iron catalysts for Fischer–Tropsch synthesis by Hiroshi Hayakawa; Hisanori Tanaka; Kaoru Fujimoto (pp. 24-30).

The silica-containing precipitated iron catalysts had higher STY (C5+ hydrocarbon productivity), but were more difficult to be reduced with syngas (mixtures of hydrogen and carbon monoxide) than the silica-free precipitated iron catalyst. The results suggested that the added silicate suppresses the crystal growth of hematite from the structure of catalyst precursor. X-ray diffraction (XRD) studies of catalysts after activation under various conditions revealed that the presence of iron carbide (CFe_2.5) was related to the active sites in the FT reaction, and that the relative quantity of iron carbide (CFe_2.5) to magnetite (Fe₃O₄) was closely related to the number of active sites available for FT synthesis. The effects of copper on the silica-containing precipitated iron catalyst were to enhance the activity and the rate of reduction, as judged from the XRD and TPR studies.

Keywords: Fischer–Tropsch synthesis; Iron catalyst; Reduction behavior; Iron carbide

Synthesis, characterization and catalytic properties of vanadium aluminophosphate molecular sieves VAPO-31 and VAPSO-Amr from non-aqueous media by N. Venkatathri (pp. 31-39).

Vanadium samples containing aluminophosphate molecular sieve (VAPO-31) and amorphous vanadium silicoaluminophosphate (VAPSO-Amr) have been synthesized using hexamethyleneimine template from non-aqueous media for the first time. XRD and SEM analyses confirm the phase purity of the synthesized samples. FT-IR analysis suggests the incorporation of V⁴⁺ in the aluminophosphate framework. ESR, UV–vis spectroscopic, and XPS techniques and cyclicvoltametric studies confirm the incorporation of vanadium and reveal its presence in tetrahedral and square pyramidal environments in the as-synthesized samples. Cyclic voltammetry reveals the presence of two redox couples in VAPO-31. This catalyst is found to be a good oxidation catalyst. Although most of the properties of VAPO-31NA and VAPSO-Amr are similar, the latter can access more vanadium and V⁴⁺ ions. Compared to aqueous media samples, it can incorporate more vanadium especially V⁵⁺ ions and has been found to be better oxidation catalyst. The physicochemical properties also change with media.

Keywords: VAPO-31; Non-aqueous; XRD; SEM; TG/DTA; FT-IR; ESR; UV–vis; XPS; Cyclic voltammetry; MAS NMR

Investigation of the physico-chemical implications of the hydrogen presence during H₂-assisted catalytic combustion of methane using Pd(10wt.%)/γ-Al₂O₃ catalyst by Olivier Demoulin; Isabelle Seunier; Michaël Navez; Claude Poleunis; Patrick Bertrand; Patricio Ruiz (pp. 40-47).

The influence of the presence of H₂ on the physico-chemical properties of a Pd(10wt.%)/γ-Al₂O₃ catalyst was investigated. Catalysts were treated under methane combustion conditions with various amounts of H₂ in the feed. Samples obtained were characterized by BET, CO-chemisorption, XRD, XPS and/or ToF-SIMS techniques. The effect of H₂ is essentially to sinter the palladium phase and to help remove surface chlorine coming from the palladium precursor. In presence of low amounts of H₂, O migration phenomena are suggested to occur to maintain the surface of the palladium particles in an oxidized state while, as the H₂ concentration increases, metallic palladium progressively forms in the bulk. Above a threshold value, the H₂ concentration becomes too high, metallic palladium is formed on the surface.

Keywords: Palladium; Methane oxidation; Hydrogen; Assisted-combustion

Esterification of oleic acid in supercritical carbon dioxide catalyzed by functionalized mesoporous silica and an immobilized lipase by Michael A. Jackson; Isa K. Mbaraka; Brent H. Shanks (pp. 48-53).

Organosulfonic acid-functionalized mesoporous silicas were tested for catalytic performance in the esterification of oleic acid with methanol in flowing supercritical carbon dioxide. The energy of activation of the sulfonic acid catalysts was found to be about 42kJ/mol and was shown to be independent of pore size. The catalytic activity of the functionalized silicas was compared to a standard acidic resin, Amberlyst 15, and to an immobilized lipase, Novozym 435. The most active catalyst was Novozym 435.

Keywords: Solid acid catalysts; Novozym 435; Methyl oleate; Supercritical carbon dioxide

Catalytic partial oxidation of methane over Pt/ceria-doped catalysts: Effect of ionic conductivity by Maria Salazar; David A. Berry; Todd H. Gardner; Dushyant Shekhawat; Donald Floyd (pp. 54-60).

Catalyst deactivation due to carbon deposition during the production of hydrogen rich synthesis gas has proven to be a major impediment in hydrocarbon fuel reforming. Several Pt-deposited catalysts were prepared and tested to study the role of ionic conductivity of the support material upon which they were deposited. Ceria-based supports used in this work were synthesized by a hydrothermal method and the catalysts were prepared by Pt addition (1wt.%). Characterization of ceria-based supports included composition, surface area, crystal phases, reducibility and ionic conductivity. In order to study the influence of ionic conductivity on carbon deposition, Pt/(Ce_0.56Zr_0.44)O2−_x, Pt/(Ce_0.91Gd_0.09)O2−_x, Pt/(Ce_0.71Gd_0.29)O2−_x and Pt/CeO₂ were utilized as catalysts in the conversion of methane to syn-gas at varying oxygen-to-carbon ratios. Carbon content on the catalysts measured post-test revealed that the gadolinium-doped catalysts generated less carbon deposition between the catalysts tested. Stability tests of Pt/ceria-based catalysts showed stable performance during a 24h reaction period. In order to compare carbon formation by oxygen ion conducting and non-oxygen ion conducting catalysts, the partial oxidation of methane was carried out over Pt/γ-Al₂O₃ and Pt/(Ce_0.71Gd_0.29)O2−_x. Interestingly, the CH₄ conversion for both materials was comparable. However, the amount of carbon deposited on Pt/(Ce_0.71Gd_0.29)O2−_x was observed to be much less than on the alumina-supported Pt catalyst.

Keywords: Ceria; Platinum; Ionic conductivity; Alumina; Partial oxidation of methane

New Pd/hierarchical macro-mesoporous ZrO₂, TiO₂ and ZrO₂-TiO₂ catalysts for VOCs total oxidation by H.L. Tidahy; S. Siffert; J.-F. Lamonier; E.A. Zhilinskaya; A. Aboukaïs; Z.-Y. Yuan; A. Vantomme; B.-L. Su; X. Canet; G. De Weireld; M. Frère; T.B. N’Guyen; J.-M. Giraudon; G. Leclercq (pp. 61-69).

Macro-mesoporous ZrO₂, TiO₂ and ZrO₂-TiO₂ have been synthesized and used as catalytic supports for volatile organic compounds (VOCs) oxidation. These supports present high surface areas. Stability of the porous structure is observed after calcination at 400°C for ZrO₂-TiO₂ and TiO₂ but partial breakdown of the structure occurs for ZrO₂ by the crystallization into tetragonal phase. All these Pd impregnated catalysts are found to be powerful catalysts for total oxidation of toluene and chlorobenzene. Pd/TiO₂ presents the highest catalytic potential. The lowest toluene adsorption enthalpy, the low coke content observed after the catalytic test, PdO particles easily reducible should explain the interesting catalytic behaviour of Pd/TiO₂. However, production of polychlorinated compounds PhCl_x (with x=2–6) occurs at low temperature during the chlorobenzene oxidation and this amount is lower over Pd/TiO₂-ZrO₂ compared to Pd/TiO₂. But chlorobenzene is readily converted into HCl, CO₂ and H₂O at a temperature of 530°C.

Keywords: Nanostructured mesoporous zirconia and titania; Total oxidation of VOC; Palladium; Toluene and chlorobenzene adsorptions

Methanol steam reforming over ex-hydrotalcite Cu–Zn–Al catalysts by G. Busca; U. Costantino; F. Marmottini; T. Montanari; P. Patrono; F. Pinzari; G. Ramis (pp. 70-78).

Cu–ZnO–Al₂O₃ catalysts have been prepared via hydrotalcite-like hydroxycarbonate precursors and tested in the oxidative steam reforming of methanol (MOSR) to produce hydrogen with poor CO content. The surface chemistry of the catalysts has been investigated by IR spectroscopy of low temperature CO adsorption. The aim was to gain indications on the optimal catalyst composition for MOSR and on the role of the CO into CO₂ conversion step. The conclusions are that the catalytic activity is almost independent on the copper content in the range 5–12% (atomic metal content). The direct oxidation of CO to CO₂ by Cu²⁺ ions is likely a key step both for MOSR and water gas shift over these catalysts.

Keywords: Hydrogen production; Methanol steam reforming; Hydrotalcite precursors; CO adsorbed; IR spectroscopy; Cu–Zn–Al catalysts

Organosilanesulfonic acid-functionalized Zr-TMS catalysts: Synthesis, characterization and catalytic applications in condensation reactions by M. Chidambaram; C. Venkatesan; A.P. Singh (pp. 79-90).

Organosilanesulfonic acid (–Si–R₃S–R₄SO₃H, OSA)-functionalized mesoporous Zr-TMS (Zr-TMS–Si–R₃S–R₄SO₃H, Zr-TMS–OSA) was synthesized either by post-synthetic modification of Zr-TMS (zirconia-based transition metal oxide mesoporous molecular sieves) with 3-mercaptopropyltrimethoxysilane (3-MPTS) and further with 1,4-butanesultone (1,4-BS) or by in situ one-pot synthesis procedure. A number of physico-chemical characterization techniques have been used to show that the organosilanesulfonic acid groups were anchored on to the walls of Zr-TMS. MCM-41–Si–R₃S–R₄SO₃H-20 (MCM-41–OSA-20) was also prepared by post-synthesis procedure for comparison. Physico-chemical properties of in situ made A-Zr–OSA-20, Zr-TMS–SO₃H-20 and MCM-41–OSA-20 were compared with Zr-TMS–OSA catalysts. The catalytic activity of the materials was tested in liquid phase condensation of aniline with p-formaldehyde to 4,4′-diaminodiphenylmethane (4,4′-DADPM). Results showed that Zr-TMS–OSA catalysts were more active than Zr-TMS–SO₃H-20, MCM-41–OSA-20 and A-Zr–OSA-20 and more selective than Zr-TMS–SO₃H-20 and A-Zr–OSA-20 catalysts.

Keywords: Acid catalyst; Mesoporous ZrO; ₂; Organosilanesulfonic acid; Organic functionalization; Condensation of aniline

Unusual CH₄ dry reforming performance over Ni-based catalyst separated from nickel metal hydride battery waste by Tomohiro Kanamori; Motohide Matsuda; Michihiro Miyake (pp. 91-96).

The Ni-based compound (s-NiO) has been successfully separated from nickel metal hydride battery waste by a series of acid and base treatments. The catalytic activity of s-NiO reduced to Ni metal was investigated for the CH₄ dry reforming at 780°C. It was found that the CH₄ conversion over s-NiO was superior to that over regent NiO (r-NiO) and exhibited an unusual behavior. The differences of catalytic activities between s-NiO and r-NiO were examined in terms of carbon deposition and the sinterability of the samples. Carbon deposited by side reactions prevented Ni particles from sintering, and Ni fine particles were highly dispersed on the deposited carbon in the sample obtained from s-NiO.

Keywords: CH; ₄; dry reforming; Nickel metal hydride battery; Resource recovery

Promoting effect of Rh, Pd and Pt noble metals to the Ni/Mg(Al)O catalysts for the DSS-like operation in CH₄ steam reforming by Takeshi Miyata; Dalin Li; Masato Shiraga; Tetsuya Shishido; Yasunori Oumi; Tsuneji Sano; Katsuomi Takehira (pp. 97-104).

Effects of the additions of noble metal, i.e. Rh, Pd and Pt, on Ni/Mg(Al)O catalyst have been investigated for the daily start-up and shut-down (DSS) operation under steam purging in the steam reforming of CH₄. Mg_2.5(Ni_0.5)-Al hydrotalcite was prepared by coprecipitation and calcined to form Mg_2.5(Al,Ni_0.5)O periclase. When the powders of the periclase were dipped in an aqueous solution of the nitrate of Rh(III), Pd(II) or Pt(II), the hydrotaclite was reconstituted on the surface of Mg_2.5(Al,Ni_0.5)O particles due to a “memory effect,�? resulting in the formation of highly dispersed noble metal-Ni supported catalysts after the calcination followed by the reduction. The addition of noble metal on Ni resulted in a decrease in the reduction temperature of Ni²⁺ in Mg_2.5(Al,Ni_0.5)O periclase and an increase in the amount of H₂ uptake on the Ni⁰ over the Ni/Mg_2.5(Al)O catalyst. When Rh-, Pd- and Pt-Ni_0.5/Mg_2.5(Al)O catalysts were tested for the DSS-like operation under steam purging, the deactivation due to the Ni metal oxidation by steam was effectively suppressed by hydrogen spillover from noble metal to Ni. Especially, only 0.05wt% of noble metal loading was enough to suppress effectively the deactivation during the DSS-like operation in the case of using both Rh and Pt.

Keywords: CH; ₄; steam reforming; H; ₂; production; DSS operation; Ni/Mg(Al)O catalyst; Rh, Pd and Pt addition; Memory effect; Hydrotalcite

Formation of high surface area Li/MgO—Efficient catalyst for the oxidative dehydrogenation/cracking of propane by C. Trionfetti; I.V. Babich; K. Seshan; L. Lefferts (pp. 105-113).

In this study nanoscale clusters of Li/MgO oxide with varying lithium contents are prepared via the sol–gel method. The preparation routine consists of co-gelation of LiNO₃ and Mg(OCH₃)₂ in methanol/water solution followed by drying at 50°C under vacuum and calcination at 500°C in air. The structural and textural transformations that take place during oxide formation are studied with TGA–DSC–MS and FTIR spectroscopy. The obtained materials are characterized by TEM, N₂ physisorption and XRD. Presence of increasing amounts of lithium precursor causes extensive hydrolysis of the alkoxide sol. Appreciable amounts of lithium ions can be incorporated in the magnesia gel even under the mild conditions during sol–gel transformation. Non-incorporated lithium ions form a separate carbonate phase, which has a detrimental effect on the surface area due to enhanced sintering. The Li/MgO oxide materials thus prepared possess high surface area (50–190m²/g) depending on Li content. Small amounts of lithium ions, when present as a dispersed phase, do not seem to influence the structural and textural characteristics of the magnesia gel and, in these cases, nanoscale Li/MgO oxide clusters with high surface areas similar to pure MgO can be prepared. Sol–gel derived Li/MgO provides significantly higher olefin yields in ODH of propane in comparison with conventional Li/MgO catalysts, especially at lower temperatures.

Keywords: Sol–gel Li/MgO; Nanoscale oxide; Oxidative dehydrogenation

Effect of Ti(IV) loading on CO oxidation activity of gold on TiO₂ doped amorphous silica by A.M. Venezia; F.L. Liotta; G. Pantaleo; A. Beck; A. Horváth; O. Geszti; A. Kocsonya; L. Guczi (pp. 114-121).

Amorphous SiO₂, doped with various amount of TiO₂, was used as support for gold nanoparticles. Gold was deposited through the controlled sol formation technique. The effect of the TiO₂ loading on the structural and surface properties was investigated by transmission electron microscopy, X-ray diffraction, Raman and X-ray photoelectron spectroscopy. The catalytic behavior was tested in the oxidation of CO. A significant enhancement in the activity was observed for the gold supported on mixed oxide with low TiO₂ loading. On the basis of characterization data, the positive effect is assigned to the electronic modification of the Ti(IV) of the newly formed TiOSi bonds.

Keywords: Gold nanoparticles; TiO; ₂; /SiO; ₂; supports; CO oxidation

Strong inhibition effect of sulfur impurities in alumina supports on the catalytic activity of Rh in the CH₄–CO₂ reforming reaction by Shigeru Yokota; Kazu Okumura; Miki Niwa (pp. 122-126).

The influence of the sulfur impurity on the CH₄–CO₂ reforming reaction over Rh catalyst was studied. The activity of Rh/Al₂O₃ varied remarkably depending on the kinds of Al₂O₃ support. Based on the EXAFS and TPR measurements, the variations were ascribed to the changes in the reducibility of Rh as a result of the interaction with SO₄²⁻ present as impurity in the alumina support. In agreement with the assumption, the activity of Rh improved significantly as SO₄²⁻ was removed from the Al₂O₃ support. Based on the EXAFS analysis, the role of SO₄²⁻ anion was ascribed to the inhibition of the reduction of RhCl₃ to give metal Rh.

Keywords: Dry reforming reaction; Rhodium; Sulfur; Alumina; EXAFS

Effect of metal oxide additives on the activity and stability of Cu/ZnO/ZrO₂ catalysts in the synthesis of methanol from CO₂ and H₂ by J. Słoczyński; R. Grabowski; P. Olszewski; A. Kozłowska; J. Stoch; M. Lachowska; J. Skrzypek (pp. 127-137).

The Cu/ZnO/ZrO₂ catalyst has been modified by adding small amounts of B, Ga, In, Gd, Y, Mn and Mg oxides. Two series of catalysts were obtained: series A: by the co-precipitation of basic carbonates and series B: by complexing with citric acid. The oxide additives were found to influence the catalytic activity in the reaction of methanol synthesis from CO₂, dispersion of Cu, surface composition of the catalyst, and the stability of catalysts during their operation. In both series of catalysts, the Ga₂O₃ additive was especially useful. The mechanism of copper sintering and the performance of the oxide additives are discussed.

Keywords: CO; ₂; hydrogenation; Methanol synthesis; Effect of oxide additions; Sintering of Cu

Hydrogen production from methanol using a SiC fiber-containing paper composite impregnated with Cu/ZnO catalyst by Shuji Fukahori; Hirotaka Koga; Takuya Kitaoka; Akihiko Tomoda; Ryo Suzuki; Hiroyuki Wariishi (pp. 138-144).

Copper-zinc oxide catalyst powders were successfully impregnated into paper-based composites (catalyst paper) of ceramic and silicon carbide (SiC) fibers, prepared using an established wet papermaking process. The catalyst powders were homogeneously scattered over the fiber-mix networks tailored within the catalyst paper. Samples of catalyst paper were subjected to the methanol steam reforming (MSR) process below 300°C to produce hydrogen gas for fuel cell applications. During this process, the catalyst paper samples exhibited a higher methanol conversion efficiency and lower carbon monoxide concentration than those produced either by a commercial pellet-type Cu/ZnO catalyst or the original powdered Cu/ZnO catalyst. The high heat conductivity of the SiC fibers enhanced the catalytic performance, especially contributing to the suppression of the reverse water gas shift reaction. The heat transfer and the heat distribution inside the catalyst paper were improved by the SiC fibers. The MSR efficiency per catalyst weight was greatly influenced by the addition of pulp fibers, which made the catalyst paper porous. Results indicated that these in-paper void structures are suitable for the MSR reaction. Flexible catalyst paper is a promising, easy-to-handle material for practical MSR applications, due to the controllable heat and pore characteristics involved in the MSR performance.

Keywords: Methanol steam reforming; Catalyst paper; Porous structure; Silicon carbide; Fiber; Heat transfer

Rate parameters from low-pressure steady-state protolytic cracking and dehydrogenation of isobutane over zeolite catalysts by Cam Le Minh; Trevor C. Brown (pp. 145-154).

An improved low-pressure steady-state technique has been used to accurately determine kinetic parameters for isobutane protolytic cracking and dehydrogenation over HZSM-5 (SiO₂/Al₂O₃=33.0), HZSM-5 (94.2), ferrierite (55.2) and mordenite (20.0). Apparent activation energies for cracking are 104±5kJmol⁻¹ over HZSM-5 (33.0) and 101±10kJmol⁻¹ over mordenite. For isobutane dehydrogenation, energy barriers are 136±6kJmol⁻¹ over HZSM-5 (33.0), HZSM-5 (94.2) and ferrierite, while over mordenite the dehydrogenation energy barrier is 95±5kJmol⁻¹. Differences in rate-determining steps, in desorption and in intrinsic reaction are proposed to explain the similarities and differences in these apparent energies. The magnitudes of these energies agree with most literature values and so validate the technique. Associated intrinsic preexponential factors are not as sensitive to the zeolite structure or the reaction pathway, but magnitudes agree with the assumption that rate-determining steps are first order. An exponent m for the coverage is required in the kinetic analyses because, under low-pressure conditions, a temperature-dependent or non-steady-state effect such as diffusion causes apparent non-linear Arrhenius plots.

Keywords: Kinetics; Cracking; Dehydrogenation; Molecular flow; Isobutane; HZSM-5; Mordenite; Ferrierite

Tungstophosphoric acid supported on MCM-41 mesoporous silicate: An efficient catalyst for the di- tert-butylation of cresols with tert-butanol in supercritical carbon dioxide by Gunda Kamalakar; Kenichi Komura; Yoshihiro Sugi (pp. 155-163).

Tungstophosphoric acid (HPW) supported on MCM-41 mesoporous silicate was an excellent catalyst for the tert-butylation of cresols in supercritical CO₂. The tert-butylation of p-cresol gave 2,6-di- tert-butyl-4-methylphenol (2,6-DTBPC) in high yield (the best yield: 58%) in supercritical CO₂; however, zeolites, H-Y and H-beta, gave only 2- tert-butyl-4-methylphenol (2-TBPC) because of their limitation in pore size. The yield of 2,6-DTBPC over HPW(30)/MCM-41 was maximum at 110°C, and further increase in temperature decreased the yield. There was the optimal CO₂ pressure on the yield of 2,6-DTBPC at 10MPa, and further increase of the pressure resulted in rapid decrease in the yield.Thermogravimetric analysis of used catalysts showed that the deactivation is minimized in supercritical CO₂ compared to the other reaction media such as hexane as solvent and without solvent under N₂ atmosphere. HPW(30)/MCM-41 was recyclable without significant loss of catalytic activity, and retained mesoporous structure even after three recycles.The tert-butylation of o- and m-cresols over HPW(30)/MCM-41 gave the 2,4-di- tert-butyl-6-methylphenol, 2,4-di- tert-butyl-5-methylphenol, respectively, in good to moderate yields.

Keywords: Tungstophosphoric acid; MCM-41; Supercritical CO; ₂; tert; -Butylation; p; -Cresol; 2,6-Di-; tert; -butyl-4-methylphenol

Catalytic combustion of methane over Ce1−_xLa_xO2− x_/2/Al₂O₃/FeCrAl catalysts by Fengxiang Yin; Shengfu Ji; Biaohua Chen; Zhongliang Zhou; Hui Liu; Chengyue Li (pp. 164-173).

A series of the Ce1−_xLa_xO2− x_/2/Al₂O₃/FeCrAl monolithic catalysts ( x=0–1) were prepared. The structure of the catalysts was characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM) and temperature-programmed reduction (TPR). The catalytic activity of the catalysts for the methane combustion was evaluated with a fixed bed reactor. The results showed that in the Ce1−_xLa_xO2− x_/2/Al₂O₃/FeCrAl catalysts the phase structure was the Ce1−_xLa_xO2− x_/2 solid solutions, α-Al₂O₃ and γ-Al₂O₃. The molar ratio of Ce to La in the Ce1−_xLa_xO2− x_/2 solid solutions significantly influenced the surface particle shape and size of the catalysts. The catalytic activity for the methane combustion strongly depended on the La component of the Ce1−_xLa_xO2− x_/2/Al₂O₃/FeCrAl catalysts, and the order of the catalytic activity in terms of x was 0.7>0.9>0.5>0.3>0>1. TPR analyses of the catalysts revealed the existence of a strong interaction among the Ce1−_xLa_xO2− x_/2 solid solutions, the Al₂O₃ washcoats and the FeCrAl support. This interaction remarkably enhanced the redox properties of the catalysts resulting in the higher catalytic activity.

Keywords: Monolithic catalysts; Ce; 1−; _x; La; _x; O; 2−; x; _/2; Methane catalytic combustion; XRD; SEM; TPR

Ni:CeO₂ nanocomposite catalysts prepared by polymeric precursor method by Antoninho Valentini; Neftali L.V. Carreño; Luiz F.D. Probst; A. Barison; A.G. Ferreira; Edson R. Leite; Elson Longo (pp. 174-182).

The biopolymer Chitosan was used as polymeric precursor for the synthesis of Ni:CeO₂ nanocomposite catalysts. Evidences for the formation of a hybrid polymer, of the Ce-citrate complex and the chitosan by polyesterification reaction, was provided by¹³C NMR and Raman spectroscopy. After the heat-treatment of the hybrid polymer at several temperatures, the materials were characterized by N₂ physisorption, H₂ and CO₂ chemisorption, XRD, EDX, TEM and Raman analyses. The results show that the presence of residual carbon has a positive influence on the samples properties. It was found that residual carbon contributes to a high surface area and to direct formation of Ni metal during the pyrolysis in N₂ atmosphere. In addition, due to the presence of residual carbon, the catalytic performance in CO₂ reforming of CH₄ indicated an enhanced stability and coking resistance of the catalysts.

Keywords: Nanocomposite; Ni-ceria catalyst; Polymeric route

Effect of microemulsion composition on textural and photocatalytic activity of titania nanomaterial by P. Mohapatra; T. Mishra; K.M. Parida (pp. 183-189).

Nanosized titania powders were synthesized by the reverse microemulsion (water/CTAB-butanol/cyclohexane) process varying the water content in the range of 5–30wt.%. Materials were characterized by TEM, XRD, FT-IR, DRS, BET surface area measurement. Average crystallite size, particle size and anatase to rutile ratio was correlated with the photocatalytic decomposition of 4-nitropheol and hexavalent chromium reduction. Photocatalytic activity was evaluated by varying the pH, time of reaction, catalyst amount, etc. in aqueous phase. Highest hexavalent chromium reduction and decomposition of 4-nitrophenol was observed with the titania derived from the microemulsion having 15wt.% of water. Prepared catalysts were found to be active in presence of sunlight.

Keywords: Microemulsion; Particle size; 4-Nitrophenol; Photodecomposition; Photoreduction; Hexavalent chromium

A solid acid of tungsta-niobia more active than aluminosilicates for decompositions of cumene, ethylbenzene, and toluene by Makoto Hino; Mitsuhiko Kurashige; Hiromi Matsuhashi; Kazushi Arata (pp. 190-193).

A solid acid of tungsten-niobium oxide was obtained by evaporating the water from a mixed solution of ammonium metatungstate and niobium ammonium oxalate in water in the ratio 7:1 of W to Nb, followed by calcining in air at 400°C. The catalytic activity of the solid acid for decompositions of toluene, ethylbenzene, and cumene was higher than those of tungstated zirconia, mordenite, and silica-alumina. The chief ingredient of Nb in the mixture was less effective. The acid strength was estimated by the heat of Ar adsorption to be 18.1kJmol⁻¹, the value being coincident with that of H-mordenite (18.3kJmol⁻¹).

Keywords: Solid acid; WO; ₃; -Nb; ₂; O; ₅; Cracking; Cumene; Ethylbenzene; Toluene; Ethanol; Ar; Adsorption

Low temperature hydrogenation of tetralin over supported rhodium catalysts in supercritical carbon dioxide solvent by Norihito Hiyoshi; Eiichi Mine; Chandrashekhar V. Rode; Osamu Sato; Masayuki Shirai (pp. 194-198).

Hydrogenation of tetralin was studied over supported rhodium catalysts in supercritical carbon dioxide solvent at 333K. The results were compared with those in an organic solvent and under neat conditions. Higher cis-decalin yield was obtained in supercritical carbon dioxide solvent than under non-supercritical conditions. It was observed that higher hydrogen concentration at the surface in supercritical carbon dioxide solvent led to fast direct hydrogenation of tetralin to cis-decalin; the flipping of the intermediate, octalin, to give trans-decalin could be prevented.

Keywords: Supercritical carbon dioxide; Hydrogenation; Tetralin; Supported rhodium catalysts; cis; -Decalin; Hydrogen storage

Dehydrogenation of ethylbenzene to styrene catalyzed by Co, Mo and CoMo catalysts supported on natural and aluminum-pillared clays by Alexander Moronta; María E. Troconis; Eduardo González; Cesar Morán; Jorge Sánchez; Angel González; Jackeline Quiñónez (pp. 199-204).

In this work Co, Mo and CoMo catalysts supported on a montmorillonite clay (STx-1, Texas, USA) in its natural and Al-pillared forms were prepared. These catalysts in their unreduced and reduced forms were tested over the dehydrogenation of ethylbenzene to study the effect of the metal reduction. The catalysts were prepared by impregnation with aqueous solutions of CoCl₂·6H₂O and (NH₄)₆Mo₇O₂₄·4H₂O and characterized by N₂ adsorption, X-ray diffraction, temperature programmed reduction and CO chemisorption. The total metal content of cobalt and/or molybdenum was 4wt.% in the monometallic and bimetallic catalysts, varying the Co–Mo mass ratio in 1:3, 2:2 and 3:1 (Co:Mo atomic ratios of 0.54, 1.63 and 4.84) in the latter. The surface areas of the natural and Al-pillared clays were 72 and 123m²/g, while the areas of the Co, Mo and CoMo catalysts supported on ST and Al-ST were 48–69 and 77–89m²/g. The reduction profiles revealed the presence of different Co and Mo species and the existence of metal-support interactions. The use of cobalt chloride formed particles of large sizes and Cl⁻ blocks the active sites. The reduced catalysts showed greater activity than the unreduced catalysts at 400°C. The most active catalysts were the one that contained 4wt.% of Mo (in the monometallic) and that with the higher Mo content (in the bimetallic).

Keywords: Clays; CoMo catalysts; Ethylbenzene dehydrogenation; Pillared clays

Erratum to “Non-oxidative propane dehydrogenation over Pt–Zn-containing zeolites�? [Appl. Catal. A: Gen. 306 (2006) 85–97] by Patrizia Laura De Cola; Roger Gläser; Jens Weitkamp (pp. 205-206).

Calendar of Forthcoming Events (pp. 207-208).

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Applied Catalysis A, General (v.310, #1-208)