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Applied Catalysis A, General (v.354, #1-2)

Editorial Board (pp. co2).

Contents (pp. iii-viii).

Effect of hydrogen sulfide on the direct internal reforming of methane in solid oxide fuel cells by Tyler R. Smith; Anthony Wood; Viola I. Birss (pp. 1-7).

The direct internal reforming (DIR) ability of Ni–YSZ (yttria stabilized zirconia) anodes creates fuel flexibility in solid oxide fuel cells (SOFCs), as DIR allows Ni–YSZ anodes to use hydrocarbons directly as a fuel source. Electrochemical full cell evaluation of a Versa Power Systems TSC-2 SOFC was conducted in 1ppmv hydrogen sulfide (H₂S) at 750°C with 25%, 35% and 50% levels of DIR of methane. The addition of H₂S significantly degrades both the cell voltage as well as the DIR activity of the cell. With the removal of H₂S, the cell voltage partially recovers to pre-H₂S exposure levels, while the DIR activity fully recovers. Secondary time-of-flight mass spectroscopy analysis post-testing indicates that some sulfur remains present on the Ni surface after steady-state recovery.Electrochemical full cell evaluation of a Versa Power Systems TSC-2 solid oxide fuel cell was conducted in 1ppmv hydrogen sulfide (H₂S) at 750°C with 25%, 35% and 50% levels of direct internal reforming (DIR) of methane. It is shown that the addition of H₂S significantly degrades both the cell voltage as well as the DIR activity of the cell, as evidenced by gas chromatographic analysis of the cell exhaust gas. With the removal of H₂S, the cell voltage recovers, but not to pre-H₂S exposure levels. The onset of degradation of electrochemical activity commences before the onset of DIR activity degradation, indicating that H₂S penetrates to the Ni-containing anode functional layer before saturation coverage of Ni with sulfur in the support layer. Secondary ion mass spectrometric post-analysis indicated that, while adsorbed sulfur remains on the surface of Ni after recovery for ∼200h in H₂S-free gas, there remains sufficient active Ni surface area in the anode substrate to continue to catalyze the DIR reactions.

Keywords: Solid oxide fuel cells; Sulfur poisoning; Direct internal reforming; Methane; Hydrogen sulfide; Performance degradation; Secondary ion mass spectrometry

Photoelectrocatalytic activity of mesoporous TiO₂ thin film electrodes by Wee Yong Gan; Huijun Zhao; Rose Amal (pp. 8-16).

A serial thin-layer photoelectrocatalysis system was developed to study the relationships between the photoelectrocatalytic activity and the structural characteristics of the mesoporous TiO₂ film electrodes prepared by an evaporation-induced self-assembly method. The structural characteristics of the mesoporous film electrodes were altered by using Pluronic F127 as the structural directing agent and by controlling relative humidity and temperature during the coating and thermal treatment processes.A serial thin-layer photoelectrocatalysis system was developed to study the relationships between the photoelectrocatalytic activity and the structural characteristics of the mesoporous TiO₂ film electrodes prepared by an evaporation-induced self-assembly method. The structural characteristics of the mesoporous film electrodes were altered by using Pluronic F127 as the structural directing agent and by controlling the relative humidity and the temperature during coating and thermal treatment processes. Key structural characteristics of the resultant mesoporous TiO₂ thin film electrodes were measured. For the mesoporous TiO₂ film, the crystallinity can be introduced at a low thermal treatment temperature of 350°C while at lest 450°C thermal treatment temperature will be required to introduce the same degree of crystallinity to a TiO₂ film prepared via a conventional sol–gel process. The effect of key structural parameters on the photoelectrocatalytic activity was investigated using glucose and succinic acid as the model organic compounds to represent weak and strong adsorbents, respectively. The reported key structural properties, such as porosity, surface area and crystallinity, that affect the photocatalytic activity were found to also critically affect the photoelectrocatalytic activity but in a different manner. This is because, for a photocatalysis application, the performance of a catalyst is mainly determined by the characteristics of individual catalyst particles, while for a photoelectrocatalysis application the performance of a catalyst also depends on the photoelectron transport process within the photocatalyst layer this in turn relies strongly on attributes such as photocatalyst particles’ interconnectivity and the contact to the conducting substrate.

Keywords: Titanium dioxide; Mesoporous; Photoelectrocatalytic activity

Oxidative kinetic resolution of alcohols using chiral Mn–salen complex immobilized onto ionic liquid modified silica by Suman Sahoo; Pradeep Kumar; F. Lefebvre; S.B. Halligudi (pp. 17-25).

A supported ionic liquid strategy has been applied for the immobilization of chiral Mn(III) salen complex. This catalyst system was utilized in the oxidative kinetic resolution of a range of alcohols. This catalyst can be recovered and recycled for four times without any loss of activity and enantioselectivity.The supported ionic liquid strategy has been applied for the immobilization of chiral Mn(III) salen complex onto ionic liquid modified silica. Chiral Mn(III) salen complex was immobilized over silica through a thin film of covalently anchored imidazolium ionic liquid. These catalysts were characterized by N₂ sorption, XRD, FTIR, DRUV–vis, and elemental analysis. The results showed that the chiral Mn(III) salen complex could be successfully immobilized onto the modified mesoporous materials and that the long-range mesoporous ordering of parent supports was maintained after the immobilization. The immobilized catalyst provided good enantioselectivity and activity in the heterogeneous catalysis of the oxidative kinetic resolution of secondary alcohol and can be recovered and recycled for four times without obvious loss of enantioselectivity and activity. Oxidative kinetic resolutions of meso-diols, hydroxyl ester and primary alcohol were also studied using this catalyst system.

Keywords: Oxidative kinetic resolution; Secondary alcohol; Mn(III) salen; Mesoporous silica; Supported ionic liquid

Study of reaction intermediates of methanol decomposition and catalytic partial oxidation on Pt/Al₂O₃ by Chundi Cao; Keith L. Hohn (pp. 26-32).

Methanol decomposition and catalytic partial oxidation on Pt/Al₂O₃ catalysts were studied using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Methanol adsorption was conducted on different catalyst states and CPO was studied at different temperatures methanol to oxygen ratios. It is suggested that formate was one of the important intermediates in the reaction pathway. Indirect formate decomposition is dominant for CO₂ production in the reactions at higher temperatures.Methanol is considered a promising liquid fuel for hydrogen fuel cell systems. Catalytic partial oxidation (CPO) of methanol offers the potential of producing hydrogen for these systems, and is capable of high hydrogen production rates with no heat addition. However, the mechanism of methanol CPO is not completely understood due to its complexity. In this work, methanol CPO on Pt/Al₂O₃ catalysts was studied using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and mass spectrometry.Methanol adsorption experiments were conducted on different catalyst states. Methoxy species, CH₃O_s, were formed during dissociative adsorption of methanol. As temperature was increased, formate adspecies, likely formed by reaction of methoxy species with surface hydroxyls, were increasingly formed. Ignition of CPO was also studied, and it was found to occur at room temperature on both reduced and oxidized powder catalysts. Formate disappeared during this process, while CO species and CO₂ were detected in the products.CPO was studied at different temperatures from 723K to 973K, and for methanol to oxygen mole ratios from 2 to 4. It was found that CO₂ productivity increased at lower temperatures and H₂ and CO had a higher selectivity at higher temperatures. Fuel lean conditions favored H₂ and HCOOH production. CO₂ increased when O₂ concentration increased in the reaction mixture.These results suggest that formate was one of the important intermediates in the methanol partial oxidation reaction pathway. Indirect formate decomposition is dominant for CO₂ production in the reactions at higher temperatures.

Keywords: In situ DRIFTS; Catalytic partial oxidation; Methanol; Pt/Al; ₂; O; ₃

Modulating the acid strength of zeolite H-ZSM-5 to increase the selectivity in the racemization of 1-phenylethanol by Luís Costa; Anabela Coelho; Francisco Lemos; Fernando Ramôa Ribeiro; Joaquim M.S. Cabral (pp. 33-37).

Racemization of 1-phenylethanol, a model substrate for dynamic kinetic resolution processes, was catalyzed by zeolite H-ZSM-5 in organic medium. The only significant by-product detected, corresponding to the dehydration of the alcohol, was styrene. Reaction selectivity, defined as the ratio of the kinetic rate constants of racemization and dehydration, was enhanced by selective poisoning of the zeolite with ammonia.The racemization of 1-phenylethanol, a chiral alcohol of industrial value, was catalyzed by zeolite H-ZSM-5 in organic medium. In its fully active form, this zeolite was capable of racemizing the substrate at high rates and with limited formation of secondary products. The only significant by-product detected, corresponding to the dehydration of the alcohol, was styrene. To further limit this side reaction, the zeolite acid strength was reduced by ammonia poisoning. After saturation of the acid sites with ammonia, the poison was desorbed at increasingly higher temperatures to produce a series of progressively more acid catalysts. The poisoned zeolites were characterized by temperature-programmed desorption of ammonia, which was also used to determine the acid site strength distributions.The poisoned zeolite series was tested in the racemization reaction and the selectivity, defined as the ratio of the kinetic rate constants of the racemization and dehydration, could be enhanced when compared to the original catalyst, while keeping a high racemization activity.

Keywords: Racemization; Zeolite ZSM-5; Selective poisoning; 1-Phenylethanol; Kinetic modeling

Catalytic transfer hydrogenolysis of α-methylbenzyl alcohol using palladium catalysts and formic acid by Jian Feng; Chaofen Yang; Dinglin Zhang; Jinbo Wang; Haiyan Fu; Hua Chen; Xianjun Li (pp. 38-43).

The catalytic transfer hydrogenolysis (CTH) of α-methylbenzyl alcohol (MBA) was studied using palladium catalysts and formic acid, with the intent of developing a new approach for the production of propylene oxide (PO). The effects of support, hydrogen donor, molar ratio of HCOOH to MBA, water content, reaction temperature and catalyst recycling were evaluated. Using formic acid as hydrogen donor and Pd/C as catalyst, one can convert MBA to ethylbenzene (EB) with very high selectivity (98.8%) and high conversion (98.8%) at 80°C for 40min. H⁺ ion plays an important role, for it promotes the formation of active hydrogen species in the reaction process. A reaction mechanism was proposed to account for the results obtained in the study.The catalytic transfer hydrogenolysis of α-methylbenzyl alcohol was studied using palladium catalysts and formic acid, with the intent of developing a new approach for the production of propylene oxide by a recycling process.

Keywords: Catalytic transfer hydrogenolysis; α-Methylbenzyl alcohol; Palladium catalysts; Formic acid; Propylene oxide; Reaction mechanism

Natural zeolite catalyzed cracking-assisted light hydrocarbon extraction of bitumen from Athabasca oilsands by A.S.M. Junaid; H. Yin; A. Koenig; P. Swenson; J. Chowdhury; G. Burland; W.C. McCaffrey; S.M. Kuznicki (pp. 44-49).

Bitumen in the Canadian oilsands is predominantly recovered by water-intensive hot water extraction. In this alternative waterless process, light n-alkanes (n-pentane and n-hexane) extract natural zeolite-cracked bitumen fractions from the oilsands matrix. Catalytic cracking of oilsands bitumen facilitates increased extraction of liquid petroleum fractions with pentane (right), when compared to raw (left) and thermally cracked (centre) samples.The bitumen in the Canadian oilsands reserves, one of the largest petroleum resources in the world, has higher viscosity and higher concentrations of contaminant heteroatoms and heavy metals than those found in typical crude oil. Current extraction processes, predominantly hot water extraction methods, are extremely water-intensive and generate high volumes of waste that is challenging to treat prior to reuse or release. Natural minerals such as chabazite and clinoptilolite, when acidified, have the ability to catalyze the cracking of bitumen, lowering the viscosity while adsorbing a large fraction of the undesirable compounds. In this study, light hydrocarbons (pentane and hexane) are employed instead of water to extract natural zeolite-cracked bitumen fractions from the oilsand matrix. Boiling point analysis of the light hydrocarbon-extracted bitumen fractions demonstrates that catalytic cracking by clinoptilolite reduces the vacuum residual fraction generated from pentane- and hexane-extracted bitumen by 50% (from 25% to as low as 12%). The products are almost entirely extractable using light hydrocarbons, indicating that the asphaltene fraction has been cracked. Based on these results, one can envision a waterless self-extraction process in which natural zeolites break down bitumen into lighter, less viscous components, remove contaminants, and produce light hydrocarbons in situ.

Keywords: Zeolite; Chabazite; Clinoptilolite; Oilsands upgrading; Waterless extraction

Stability and phase transitions of potassium-promoted iron oxide in various gas phase environments by Zheng Li; Brent H. Shanks (pp. 50-56).

To better understand the deactivation mechanism of potassium-promoted iron oxide dehydrogenation catalysts, stabilities of iron oxide phases including α-Fe₂O₃, KFeO₂, K₂Fe₁₀O₁₆/K₂Fe₂₂O₃₄, and K-Fe₂O₃ in various gas phases (H₂, CO₂, ethylbenzene and steam) were investigated by thermogravimetric analysis (TGA) and X-ray powder diffraction. A model was also established to illustrate the intrinsic phase transitions of these materials.Potassium-promoted iron oxide dehydrogenation catalysts are the primary catalysts used for producing styrene. In this process, a large amount of steam is used and for economic reasons it is desirable to be able to operate at lower steam/ethylbenzene molar ratios without creating severe short-term deactivation. To address this issue, it is essential to understand how the catalyst deactivates. In this study, the stabilities of α-Fe₂O₃, K-Fe₂O₃ (10wt% K⁺), KFeO₂ (30wt% K⁺), and a potassium polyferrite mixed phase (K₂Fe₁₀O₁₆/K₂Fe₂₂O₃₄) were investigated in different gas phases including H₂, CO₂, and ethylbenzene. The effect of simultaneous steam addition was also considered. Thermogravimetric analysis and X-ray powder diffraction were used to monitor sample weight variation and phase change, respectively. α-Fe₂O₃ and K₂Fe₁₀O₁₆/K₂Fe₂₂O₃₄ were stable in CO₂ but not stable in H₂. KFeO₂ was resistant to H₂ but easily decomposed by CO₂. K-Fe₂O₃ was adversely impacted by both H₂ and CO₂. The results suggest that the reduction of the iron oxide in this system was mainly caused by surface deposited carbon instead of H₂. A transformation diagram is proposed for the phase changes of potassium-promoted iron oxide materials in the reaction-relevant gas phase conditions.

Keywords: Potassium-promoted iron oxide; Ethylbenzene dehydrogenation; Potassium ferrite; Styrene

Study of the activity and backscattered electron image of Pt/CNTs prepared by the polyol process for flue gas purification by Chi-Yuan Lu; Ming-Chi Wei; Shin-Hsien Chang; Ming-Yen Wey (pp. 57-62).

Pt catalyst is supported on the carbon nanotubes (CNTs) by the polyol process. To evaluate the activity of Pt/CNTs, we performed catalytic redox reactions with various reaction constituents, such as CO, toluene, CO and NO, and toluene and NO in the presence of 6% O₂. These investigations indicated that the efficient removal of pollutants is attributed to the high dispersion of 2–3nm Pt particles on the CNTs. Based on the backscattered electron image, platinum dispersion on carbon supports can be observed clearly. In the presence of toluene and NO, the Pt/CNTs catalyst shows a good redox reaction for NO removal, and toluene is a better reductant than CO.This study investigated the employment of the CNTs as catalyst supports, where the catalyst is prepared by the polyol process. Based on the backscattered electron image, platinum (2–3nm) dispersion on carbon supports can be observed clearly.

Keywords: Backscattered electron image; Polyol process; Catalytic redox reaction; Flue gas purification

Power-bench demonstration of the Pt-catalysed C₃H₆-SCR of NOx in a diesel exhaust by G. Garrigós-Pastor; S. Parres-Esclapez; A. Bueno-López; M.J. Illán-Gómez; C. Salinas-Martínez de Lecea (pp. 63-71).

The SCR of NOx by C₃H₆ has been performed under real diesel gas streams in a power bench using a 0.1wt.% Pt/Al₂O₃ catalyst. 96% NOx conversion has been reached under optimum conditions. The effect of a ceria promoter, reaction temperature, total hydrocarbon concentration and GHSV is discussed.The SCR of NOx by C₃H₆ using a 0.1wt.% Pt/Al₂O₃ catalyst has been successfully performed under real diesel gas streams in a power bench. The influence of some experimental variables affecting NOx, CO, and THC conversions, such as hydrocarbon concentration, reaction temperature and space velocity effect, are discussed. 96% NOx conversion has been reached under optimum conditions. The highest NOx conversion level is maintained in the range 250–325°C but slightly higher temperature (350°C) is desired to ensure a stable temperature and complete CO and THC removal. An optimum THC concentration is found (1500ppm THC), higher THC concentration having a negative effect in the NOx conversion. From experiments performed at different GHSV, the reactor volume required for total NOx removal in a real exhaust stream has been estimated to be 6.5L. Additionally, the effect of CeO₂ on platinum behaviour has been studied, concluding that it enhances N₂ formation as NOx reduction product with respect to N₂O, but lowers the platinum activity for NOx reduction and CO and THC oxidation.

Keywords: Pt catalyst; SCR; DeNOx; Diesel; Power-bench; CeO; ₂

Binary Cr–Mo oxide catalysts supported on MgO-coated polyhedral three-dimensional mesoporous SBA-16 for the oxidative dehydrogenation of iso-butane by Lei Zhang; Jiguang Deng; Hongxing Dai; Chak Tong Au (pp. 72-81).

Cr–Mo oxides (Cr( x)Mo( y), x/ y=nominal Cr/Mo molar ratio) supported on MgO-coated mesoporous SBA-16 were prepared. The Cr3Mo1 catalyst performs the best in iso-butane oxidative dehydrogenation, giving 75.0% iso-butene selectivity and 7.5% iso-butene yield at 540°C.Binary Cr–Mo oxide catalysts (denoted as Cr( x)Mo( y), x/ y=nominal Cr/Mo molar ratio) supported on MgO-coated polyhedral three-dimensional (3D) mesoporous SBA-16 (MS) were fabricated for the oxidative dehydrogenation of iso-butane. The materials were characterized by a number of techniques for the establishment of the relationships between physicochemical properties and catalytic performance. The use of high-surface-area 3D MS as support for Cr–Mo oxide catalysts leads to increases of catalytic activity and of selectivity to iso-butene. The Cr( x)Mo( y) catalysts show higher iso-butene yield than the Cr/MS or Mo/MS catalyst. Under the conditions of iso-butane/O₂ molar ratio=1/2, space velocity=30,000mL/(gh), and reaction temperature=540°C, maximal iso-butene yield of 7.5% ( iso-butane conversion=10.0% and iso-butene selectivity=75.0%) can be achieved over the Cr3Mo1 catalyst. Based on the results of characterization and activity evaluation, we conclude that the excellent catalytic performance can be attributed to the moderate basicity, good dispersion of CrO_x and MoO_x, high Cr⁶⁺ content, and high initial H₂ consumption rate of Cr3Mo1.

Keywords: iso; -Butane oxidative dehydrogenation; MgO-coated mesoporous silica; Supported binary Cr–Mo oxide catalyst; Three-dimensional polyhedral SBA-16

Influence of solid acids as co-catalysts on glycerol hydrogenolysis to propylene glycol over Ru/C catalysts by M. Balaraju; V. Rekha; P.S. Sai Prasad; B.L.A. Prabhavathi Devi; R.B.N. Prasad; N. Lingaiah (pp. 82-87).

Selective glycerol hydrogenolysis to 1,2-propanediol and ethylene glycol has been achieved over Ru/C in combination with solid acid as co-catalyst. The glycerol conversion and selectivity are related to the acidity of the catalysts, because there exists a linear relation between acidity and glycerol conversion.Glycerol hydrogenolysis to propane diols was carried out over Ru/C catalysts using different solid acids as co-catalysts. Solid acids such as niobia, 12-tungstophosphoric acid (TPA) supported on zirconia, cesium salt of TPA and cesium salt of TPA supported on zirconia were used. The acidities of the solid acid catalysts were measured by temperature programmed desorption of ammonia. The conversion of glycerol depends on the total acidity of the catalysts and there exists a linear correlation between conversion and acidity. The selectivity towards 1,2-propanediol and the glycerol conversion varied with the change in the concentrations of both Ru/C and solid acid catalysts, suggesting a synergetic effect of the reaction. This reaction requires minimum amount of both acid and metal sites to obtain reasonable activity. Different reaction parameters were studied and optimized reaction conditions were established.

Keywords: Glycerol; Niobia; Ruthenium; Hydrogenolysis; Propanediol; Ethylene glycol

Immobilization of metallocene within silica–titania by a non-hydrolytic sol–gel method by Adriano G. Fisch; Nilo S.M. Cardozo; Argimiro R. Secchi; Fernanda C. Stedile; Paolo R. Livotto; Denise S. de Sá; Zênis N. da Rocha; João H.Z. dos Santos (pp. 88-101).

[Cp₂ZrCl₂] was immobilized within SiO₂–TiO₂ via a non-hydrolytic sol–gel route. Different coordinatively unsaturated Ti specimens were identified within the oxide structure depending on the TiO₂ content, which interact with the encapsulated metallocene complex affecting its catalyst performance in the ethylene polymerization. Higher activities were found for the catalyst synthesized with the support exhibiting Ti–O–Ti structure. Theoretical calculations showed the interaction formed between the metallocene and the Ti–O–Ti structure.Bis(cyclopentadienyl)zirconium dichloride was immobilized within binary oxides of SiO₂–TiO₂ via a non-hydrolytic sol–gel route. Different coordinatively unsaturated Ti species were identified within the oxide structure depending on the TiO₂ content, which can interact with the encapsulated metallocene complex and affect its catalystic performance in ethylene polymerization. The catalysts were shown to be active in the polymerization using MAO as the cocatalyst in a low Al/Zr ratio. High molecular weight polymer was obtained, probably due to the suppression of chain termination reactions that occur by β-elimination. Furthermore, oxide network structures are suggested from analysis of the catalysts (via Rutherford backscattering spectrometry, infrared spectroscopy, UV–vis diffuse reflectance spectroscopy, diffuse pulse voltammetry), molecular simulation and polymerization performance.

Keywords: Metallocene; Sol–gel; Polymerization; Polyethylene

Carbon deposition as a deactivation mechanism of cobalt-based Fischer–Tropsch synthesis catalysts under realistic conditions by D.J. Moodley; J. van de Loosdrecht; A.M. Saib; M.J. Overett; A.K. Datye; J.W. Niemantsverdriet (pp. 102-110).

In this study, the formation of carbon deposits on samples of a Co/Pt/Al₂O₃ catalyst, taken from a 100-barrel/day slurry bubble column reactor operated over 6 months at commercially relevant FTS conditions is reported. There is a slow accumulation of polymeric carbon on the metal and support. The polymeric carbon on the metal may play a role in catalyst deactivation.Deactivation of cobalt-based Fischer–Tropsch synthesis (FTS) catalysts by carbonaceous species has been previously postulated. This mechanism, however, is difficult to prove due to the presence of long chain hydrocarbon wax product and the potential accumulation of inactive carbon on the catalyst support. Furthermore, due to the slow build-up of low quantities of inactive carbon with time on stream, the investigation of carbon deposition necessitates the use of data from extended FTS runs. In this study, the formation of carbon deposits on samples of a Co/Pt/Al₂O₃ catalyst, taken from a 100-barrel/day slurry bubble column reactor operated over a period of 6 months at commercially relevant FTS conditions is reported. The spent catalysts were wax extracted in an inert environment and the amount, nature and location of carbon deposits were then studied using temperature programmed hydrogenation and oxidation (TPH/TPO), energy filtered transmission electron microscopy (EFTEM), high sensitivity low energy ion scattering (HS-LEIS) and hydrogen chemisorption. TPH/TPO showed that there is an increase in polymeric carbon with time on stream which may account for a part of the observed long-term catalyst deactivation. Carbon maps from EFTEM as well HS-LEIS data show that the polymeric carbon is located both on the alumina support and cobalt. Although there is clearly an interplay of various deactivation mechanisms which may also include sintering, poisoning and cobalt reconstruction, the evidence presented shows that the polymeric carbon on the metal may be linked with a part of the longer term catalyst deactivation.

Keywords: Cobalt; Fischer–Tropsch; Carbon; Deactivation; EFTEM; Gas-to-liquid

Transient analysis of reactions between NO and H₂ with Pt-Al₂O₃ thin film catalyst by Kohei Okumura; Tomoyoshi Motohiro; Yoshiyuki Sakamoto; Tomoyuki Kayama; Yoshimi Kizaki; Hirofumi Shinjoh (pp. 111-118).

Transient pulse techniques using time-of-flight mass spectrometry were used to investigate the reduction of NO by H₂ over Pt/Al₂O₃ thin film. A typical result measured at 400°C shows different behaviors of N₂, NH₃ and N₂O. Changing the temperature with corresponding numerical simulations, we elucidated that N₂O was produced via a consecutive process of NO reduction with NH₃ molecules.A specially designed apparatus employing (1) pulse valves for injection of reactant molecules onto catalysts and (2) a time-of-flight mass spectrometer was used to investigate processes of NO+H₂ reaction using Pt-Al₂O₃ thin film on Si substrate. First, the planar layer of the catalyst was located in a vacuum chamber and the reactants were supplied onto the surface by pulse valves. This process is considered to involve few consecutive reactions. There, the transient production of N₂ and NH₃ was observed simultaneously. Second, the reactants were supplied into the micro reactor filled with square pieces of planar catalysts spaced with SiC balls. Here, N₂O was observed as well as NH₃ and N₂. The experiments and the numerical simulation of the NO and H₂ reaction rates clearly elucidated some aspects of NO reduction passes, i.e., while N₂ and NH₃ were directly produced from N and H adatoms dissociated from NO and H₂ admolecules, N₂O was produced via consecutive process of NO reduction with NH₃ molecules which were produced in transient reactions.

Keywords: Time-of-flight mass spectrometry; Millisecond time resolution; NO reduction; Pt-Al; ₂; O; ₃; NH; ₃; formation; N; ₂; O formation

Polyoxometalate–zirconia (POM/ZrO₂) nanocomposite prepared by sol–gel process: A green and recyclable photocatalyst for efficient and selective aerobic oxidation of alcohols into aldehydes and ketones by Saeid Farhadi; Masoumeh Zaidi (pp. 119-126).

A polyoxometalate–zirconia (POM/ZrO₂) nanocomposite was prepared via the sol–gel process and used as a recyclable heterogeneous photocatalyst for selective aerobic oxidation of a variety of activated alcohols into the corresponding carbonyl compounds in high yields.A polyoxometalate–zirconia (POM/ZrO₂) nanocomposite was prepared through entrapment of H₃PW₁₂O₄₀ polyoxometalate into zirconia matrix by sol–gel technique involving the hydrolysis of zirconium (IV) n-butoxide, Zr( n-OBu)₄, as the ZrO₂ source. The catalyst was characterized by using XRD, FT-IR, SEM, TEM and surface area measurement and used as an efficient heterogeneous photocatalyst for aerobic oxidation of alcohols. Various primary and secondary benzylic alcohols were oxidized into the corresponding aldehydes and ketones in high yields under O₂ atmosphere in the presence of photoexcited POM/ZrO₂ nanocomposite. Also, nonactivated aliphatic alcohols were oxidized in good yields albeit after longer reaction times in comparison with benzylic alcohols, so that the selective oxidation of a benzylic OH group in the presence of a non-benzylic OH group could be achieved by the appropriate choice of the reaction time. The photocatalyst has been reused several times, without observable loss of activity and selectivity. Indeed, the photocatalytic activity of the POM/ZrO₂ was higher than that of pure POM.

Keywords: Alcohols; Polyoxometalate; Zirconia; Photocatalyst; Aerobic oxidation; Nanocomposite

Novel methane steam-reforming catalyst of Ni-Bi₂O₃/GDC to reduce CO for hydrogen production by Ta-Jen Huang; Meng-Chin Huang; Ming-Siang Huang (pp. 127-131).

Novel catalysts of Ni-Bi/gadolinia-doped ceria (GDC) were employed to perform steam reforming of methane at 700–850°C. The presence of Bi₂O₃ enhanced CO₂ formation and reduced CO selectivity. The quantity of Ni-Bi interface is an important factor for enhanced CO₂ formation to reduce CO concentration in the product. At 700–800°C, the CO selectivity over co-impregnated Ni-Bi/GDC was at most 1%.Novel catalysts of Ni-Bi/gadolinia-doped ceria (GDC) were employed to perform steam reforming of methane at 700–850°C. The Bi species under the operating condition of this work was mostly Bi₂O₃. The presence of Bi₂O₃ enhanced CO₂ formation and reduced CO selectivity. Over co-impregnated Ni-Bi/GDC, the formation rate of CO₂ plus CO increased with increasing Bi content. The two-step impregnated catalyst had higher reforming activity but also higher CO selectivity than the co-impregnated one. The quantity of Ni-Bi interface is an important factor for enhanced CO₂ formation to reduce CO concentration in the product. At 700–800°C, the CO selectivity over co-impregnated Ni-Bi/GDC was at most 1%.

Keywords: Nickel; Bismuth; Gadolinia-doped ceria; Steam reforming of methane; Hydrogen production; CO selectivity

Characteristics of lanthanum loaded TiO₂-ZSM-5 photocatalysts: Decolorization and degradation processes of methyl orange by A. Neren Ökte; Özge Yılmaz (pp. 132-142).

Novel photocatalytic materials are prepared by incorporation of lanthanum ions on TiO₂ supported ZSM-5. The presence of lanthanum ions concentrates MO molecules on the supported catalyst surface, increases the lifetime of the photogenerated charge carriers, and thereby possesses improved photocatalytic activities.Novel photocatalytic materials were prepared by incorporation of lanthanum ions on TiO₂ supported ZSM-5. These materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV–vis diffuse reflectance spectra (UV–vis DRS), atomic force microscopy (AFM), scanning electron microscopy SEM with energy dispersive X-ray analysis (EDX) and surface area (BET) measurements. XRD and FTIR results showed adsorption of TiO₂ and La₂O₃ nanoparticles on the surface of ZSM-5 support. AFM and SEM images revealed obvious variations in the surface morphology of raw ZSM-5 after TiO₂ and La₂O₃ loading. Photocatalytic activities of the supported catalysts were examined for decolorization and degradation processes of methyl orange (MO) solution under UV irradiation. Incorporation of lanthanum ions improved the photocatalytic activities of TiO₂ supported ZSM-5 catalysts. Effects of TiO₂ content, lanthanum ion content and calcination temperature were investigated. Quantum efficiencies, relative photonic efficiencies as well as reuse performances of the supported catalysts were also demonstrated. A rough model was postulated for TiO₂ and La₂O₃ loading on the surface of ZSM-5.

Keywords: Lanthanum ion; TiO; ₂; ZSM-5; Supported catalyst; Methyl orange

A comparative kinetic study on the oxidative coupling of methane over LSCF perovskite-type catalyst by Z. Taheri; N. Seyed-Matin; A.A. Safekordi; K. Nazari; S. Zarrin Pashne (pp. 143-152).

The kinetic models of the OCM reaction were investigated over La_0.6Sr_0.4Co_0.8Fe_0.2O3−_δ perovskite catalyst. Two mechanisms of Eley–Rideal type were chosen for fitting the experimental data with calculated result for methane conversion, C₂H₆ and CO_X formation rates. The kinetic parameters were estimated and compared for chosen models.A gas-phase heterogeneous kinetics is described over perovskite with formula La_0.6Sr_0.4Co_0.8Fe_0.2O3−_δ (LSCF) for the oxidative coupling of methane under differential conversion conditions in a microcatalytic fixed-bed reactor. The ethane (C₂H₆) and carbon oxides (CO_X) formation and methane conversion rates were obtained as a function of methane and oxygen partial pressure under experimental conditions of:0.20F-test statistical analysis were indicated mechanism “a” involving the formation of CH₃O₂ (methylperoxy) intermediate species can be suggested as the favorable (main) model for the analysis of kinetic parameters of OCM reaction over LSCF perovskite catalyst. Furthermore, the kinetic rate constants and activation energies were estimated for the selected models. Eventually the best model was introduced in course of conceptual and statistical analysis.

Keywords: Abbreviations; OCM; oxidative coupling of methane; EDTNAD; ethylene diamine N,N,N′,N′-tetra N-acetyl diamine; GC; gas chromatographyPerovskite catalyst; Kinetic model; Mechanism; OCM; Reaction rate

Selective nitration of phenol over nanosized tungsten oxide supported on sulfated SnO₂ as a solid acid catalyst by A.S. Khder; A.I. Ahmed (pp. 153-160).

WO₃ loaded on nano-crystalline sulfated tin oxide solid acid catalyst has been synthesized and studied for selective nitration of phenol. The catalysts were characterized by various analytical and spectroscopic techniques including thermal analysis, powder X-ray diffraction (XRD), N₂ adsorption and FTIR spectra. The surface acidity was measured by no aqueous potentiometric titration and FTIR spectra of chemically adsorbed pyridine.The acidity measurements showed that the samples contain both Lewis and Brønsted acid sites; moreover, the total acidity increases with the rise of WO₃ content up to 30wt.% (monolayer coverage) and decreases thereafter. The results also showed the possibilities of interaction of WO₃ with sulfate and/or SnO₂ surface that led to some changes in the surface structure of the catalyst. The catalytic activity well correlates with Brønsted acid sites of these catalysts. The effect of the reaction parameters, i.e. reactants molar ratio, reaction temperature and time was also investigated. The catalyst was reused for five times with excellent percentage conversion and high selectivity towards ortho isomer. The possible reaction mechanism for the formation of ortho and para isomers was also discussed.WO₃ loaded on nano-crystalline sulfated tin oxide solid acid catalyst has been synthesized and studied for selective nitration of phenol. The catalysts were characterized by various analytical and spectroscopic techniques including thermal analysis, powder X-ray diffraction (XRD), N₂ adsorption and FTIR spectra. The surface acidity was measured by no aqueous potentiometric titration and FTIR spectra of chemically adsorbed pyridine.The acidity measurements showed that the samples contain both Lewis and Brønsted acid sites; moreover, the total acidity increases with the rise of WO₃ content up to 30wt.% (monolayer coverage) and decreases thereafter. The results also showed the possibilities of interaction of WO₃ with sulfate and/or SnO₂ surface that led to some changes in the surface structure of the catalyst. The catalytic activity well correlates with Brønsted acid sites of these catalysts. The effect of the reaction parameters, i.e. reactants molar ratio, reaction temperature and time was also investigated. The catalyst was reused for five times with excellent percentage conversion and high selectivity towards ortho isomer. The possible reaction mechanism for the formation of ortho and para isomers was also discussed.

Keywords: Sulfated tin oxide; WO; ₃; Surface acidity; Nitration reaction; ortho; and; para; Nitrophenol; Reaction mechanism

Influence of additives on the Pt metal activity of naphtha reforming catalysts by Vanina A. Mazzieri; Javier M. Grau; Juan C. Yori; Carlos R. Vera; Carlos L. Pieck (pp. 161-168).

Alumina supported bimetallic Pt–Re, Pt–Sn and Pt–Ge naphtha reforming catalysts were studied. The Pt concentration was kept constant at 0.3 % (weight basis) while the concentration of the second metal was varied in order to assess its influence. The experimental results showed that the addition of a second metal (Re, Sn, Ge) to the Pt catalyst produced a modification of the metal and acid functions. Sn and Ge produce similar modifications of the metal function: a marked decrease of the dehydrogenation and hydrogenolytic capacity of Pt. The addition of Re modifies the dehydrogenation capacity to a lower extent than the addition of Sn or Ge. The hydrogenolytic capacity is increased upon Re addition. The changes on the acid function are different depending on which metal is added. Re and Ge modify the acid strength distribution; they favor the formation of sites of lower acid strength but they keep the total concentration of acid sites almost constant. Conversely Sn addition not only produces a change in the acid strength distribution but also a decrease of the total acidity of the catalyst.Alumina supported bimetallic Pt–Re, Pt–Sn and Pt–Ge naphtha reforming catalysts were studied. The Pt concentration was kept constant at 0.3% (weight basis) while the concentration of the second metal was varied in order to assess its influence. The experimental results showed that the addition of a second metal (Re, Sn, Ge) to the Pt catalyst produces a modification of the metal and acid functions. Sn and Ge produce similar modifications of the metal function: a marked decrease of the dehydrogenation and hydrogenolytic capacity of Pt. The addition of Re modifies the dehydrogenation capacity to a lower extent than the addition of Sn or Ge. The hydrogenolytic capacity is increased upon Re addition. The changes on the acid function are different depending on which metal is added. Re and Ge modify the acid strength distribution; they favor the formation of sites of lower acid strength but they keep the total concentration of acid sites almost constant. Conversely Sn addition not only produces a change in the acid strength distribution but also a decrease of the total acidity of the catalyst.

Keywords: Naphtha reforming; Bimetallic catalysts

Particle size effect and its influence on the adsorbed complex stability by Jiří Švrček; David Karhánek; Petr Kačer; Eliška Leitmannová; Jana Šplíchalová; Libor Červený (pp. 169-175).

The work had focused on the research area of structural effects, primarily the effect of the particle size of the active metal on the stability of an adsorbed complex, i.e. the key structure produced during a reactant transformation to a product on the surface of heterogeneous catalysts. The obtained results show that significant changes occur in the stability of adsorbed complexes of unsaturated alcohols according to changes in the particle size of the active metal of platinum catalysts.The work had engaged in the research area of structural effects and its influences on the course of heterogeneously catalyzed hydrogenation of alkenic substances in the liquid phase on platinum catalysts. The combination of experimental (kinetic method and physical–chemical characterization) and theoretical methods (calculations based on molecular modeling) was utilized in order to efficiently study these effects having impact both on the side of model substrates (alkenic alcohols differing in the location of CC bond and OH group) and the catalyst active site. This approach allowed comparing the stability of an absorbed complex of all selected model substrates, i.e. the key structure produced during the reactant transformation to a product on the surface of heterogeneous catalysts. The main attention was dedicated to the effect of the particle size of the catalyst active metal that took a significant part in the stability change of the adsorbed complexes of the model substrates as well as the utilization of findings acquired from appositely selected theoretical models to explain this change. The acquired results inferred that it is possible to use the frontier orbitals model to describe the interaction between the active site represented by particles with D>5–6nm and CC bond of the alkenic alcohols. The formed adsorbed complex demonstrated larger stability with hept-1-en-4-ol (β-position of the OH group to the CC bond) substrate in comparison to pent-1-en-3-ol (α-position of the OH group to the CC bond). The model of a planar metal complex with the substrate as its ligand appeared to be promising in the case of hydrogenation proceeding on small particles ( D<5–6nm). The stability of the complexes with α- and β-hydroxyalkenes demonstrated the opposite order of values in comparison with catalysts with larger particles ( D>5–6nm) – particle size effect.

Keywords: Structure effects; Adsorbed complex; Particle size effect; Molecular modeling

Selective hydroxyalkylation of phenol to bisphenol F over dodecatungstophosphoric acid (DTP) impregnated on fumed silica by A.C. Garade; V.S. Kshirsagar; C.V. Rode (pp. 176-182).

A well-dispersed 20% DTP/SiO₂ catalyst gave the highest product yield (34.2%) and bisphenol F selectivity (90.1%) in hydroxyalkylation of phenol due to an appropriate combination of both strong and weak acid sites. For 40% DTP/SiO₂ catalyst, an increase in strong acid sites caused further reaction of bisphenol F to give a trimer with a decrease in selectivity (75%) to bisphenol F.The catalyst activity of various solid acids, such as fumed silica (SiO₂), dodecatungstophosphoric acid (DTP), DTP impregnated on SiO₂, amberlyst-15 and montmorillonite KSF/0, was studied for the hydroxyalkylation of phenol to bisphenol F. A well-dispersed DTP on SiO₂ catalyst was prepared by the wet impregnation method. The effect of DTP loading on SiO₂ was also compared with bulk DTP and other solid acid catalysts. 20% DTP/SiO₂ catalyst gave the highest products yield of 34.2% and selectivity of 90.1% to bisphenol F, at 353K and with a phenol-to-formaldehyde mole ratio of 5:1. Ammonia TPD studies of various catalysts showed that an appropriate combination of both strong and weak acid sites of DTP/SiO₂ was mainly responsible, rather than only the stronger acidity of bulk DTP, for its highest catalytic activity and selectivity. The effect of various reaction parameters like mole ratio, catalyst concentration, temperature and reaction time on product yield and bisphenol F selectivity was also investigated. The catalyst recycle was established by catalyst activity testing.

Keywords: Hydroxyalkylation; Bisphenol F; Solid acid catalysts; NH; ₃; -TPD; Reaction pathways

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Applied Catalysis A, General (v.354, #1-2)