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Applied Catalysis A, General (v.303, #2)
Iridium/H-ZSM-5 zeolite catalyst promoted via hydrochlorination or hydrofluorination for the hydroconversion of cyclohexene by Ahmed K. Aboul-Gheit; Noha A.K. Aboul-Gheit (pp. 141-151).
The hydroconversion of cyclohexene (CHE) was carried out in a flow reactor at atmospheric pressure and temperatures of 50–400°C using: Ir/H-ZSM-5, Ir/H-ZSM-5(HCl), and Ir/H-ZSM-5(HF) catalysts. The acid site strength distribution, Ir dispersion, XRD, SEM photography for these catalysts were evaluated. The hydroconversion reaction steps of CHE were found to proceed as follows: CHE→cyclohexane; CHE→methylcyclopentenes (MCPEs)→methylcyclopentane (MCPA); CHE→cyclohexadienes (CHDEs)→benzene; benzene→alkylbenzenes; CHE and others→hydrocracked products.The doping of Ir/H-ZSM-5 catalyst with HCl enhanced its acid sites number and strength but reduced the Ir metal dispersion, whereas doping with HF enhanced acid sites number and strength as well as Ir metal dispersion. The hydrogenation step of CHE to CHA was significantly inhibited via HCl doping of Ir/H-ZSM-5 because of agglomeration of Ir crystallites, but significantly enhanced via HF doping due to improving Ir dispersion and increasing acid sites number and strength of the catalyst. Also, MCPEs hydrogenation and CHE dehydrogenation were highest on the untreated Ir/H-ZSM-5 catalyst because it doesn’t suffer diffusion limitation caused by deposited halo-aluminium debris. CHE isomerisation does not critically depend on acid site parameters or on Ir dispersion in the catalysts. Hydrocracking reactions were more active on the HCl treated catalyst.
Keywords: Cyclohexene; Hydrogenation; Isomerisation; Ir; Cyclohexadienes; Benzene; Methylcyclopentenes; Alkylbenzenes
Photocatalytic properties of zeolite-based materials for the photoreduction of methyl orange by Nidhi Dubey; Sadhana S. Rayalu; Nitin. K. Labhsetwar; Rashmi R. Naidu; Ravikrishna V. Chatti; Sukumar Devotta (pp. 152-157).
Novel photocatalytic materials have been prepared by incorporation of TiO2, a transition metal and, heteropolyacid (HPA) in the zeolite structure. These materials have been characterized using XRD, UV–vis diffuse reflectance spectroscopy and elemental analysis. The photocatalytic activity of the materials in visible light has been evaluated for photoreduction of methyl orange solution in the presence of a sacrificial electron donor 1:40 ethanol–water mixture. The material Zeo-Y/TiO2/Co2+/HPA photoreduces methyl orange effectively to the extent of about 4.11mg/g TiO2 and shows better photocatalytic activity as compared to Zeo-Y/TiO2/HPA, indicating the role of transition metal ions. The improved photocatalytic properties in the visible region could be due to the combined effect of transition metal ions and HPA, while these constituents along with the zeolite framework are also likely to contribute towards delay in charge recombination.
Keywords: Photocatalysis; Zeolite; Photoreduction; TiO; 2; Transition metals; Heteropolyacid
Selective thermomorphic biphasic hydroformylation of higher olefins catalyzed by HRhCO(PPh3)3/P(OPh)3 by Jimoh Tijani; Bassam El Ali (pp. 158-165).
A thermomorphic approach to rhodium-catalyzed biphasic hydroformylation of higher olefins (C>6) has been developed based on HRhCO(PPh3)3/P(OPh)3/propylene carbonate/ n-heptane catalytic system. The catalyst system showed excellent selectivity toward the desired linear aldehyde ( n/ i ratio>8) and high catalytic activity demonstrated by the efficient recycling without significant loss of the catalyst activity. The effects of the temperature, the total pressure, the ratio of CO/H2, the reaction time and the type of ligand have been thoroughly studied.
Keywords: Hydroformylation; Thermomorphic; Biphasic; Aldehydes; Rhodium; 1-Octene; Phosphine; Phosphite; Syngas
Modeling the high-temperature catalytic partial oxidation of methane over platinum gauze: Detailed gas-phase and surface chemistries coupled with 3D flow field simulations by Raúl Quiceno; Javier Pérez-Ramírez; Jürgen Warnatz; Olaf Deutschmann (pp. 166-176).
The high-temperature catalytic partial oxidation (CPO) of methane over a platinum gauze reactor was modeled by three-dimensional numerical simulations of the flow field coupled with heat transport as well as detailed gas-phase and surface reaction mechanisms. Model results agree well with data of CPO experiments over Pt-gauzes in the literature, confirming the presence of strong mass and heat-transport limitations. The conversions of CH4 and O2 increase with an increased contact time and were practically constant in the temperature range of 1000–1200K. The selectivity to CO linearly increases with temperature. H2 was only observed above 1200K, below this temperature H2O was the only hydrogen-containing product. The contribution of heterogeneous steps in the overall process is prominent, but in the later stages of the reactor, gas-phase reactions become significant at certain conditions of temperature, pressure, and residence time. For example, simulations predicted some gas-phase production of ethane and ethylene via methane oxidative coupling at elevated pressure and residence time. The study shows that today's CFD tools allow the implementation of detailed homogeneous and heterogeneous reaction schemes even for complex catalyst geometries.
Keywords: Methane partial oxidation; Pt metal gauze; CFD; Modeling; Reaction mechanisms
Kinetic modeling to estimate fundamental yield bounds for selective propylene oxidation over bifunctional catalysts by Hsi-Wu Wong; Mark C. Cesa; Joseph T. Golab; James F. Brazdil; William H. Green (pp. 177-191).
The selective oxidation of propylene via heterogeneous catalysts is one of the most successful commercial processes to produce acrylic acid (CH2CHCOOH). For this catalytic oxidation process where multiple products are possible, it is desirable to understand how a catalyst can control the reactivity of the system toward desired products. In this work, an elementary-step kinetic mechanism for the catalytic oxidation of propylene was constructed based on information in the literature and analogous surface and gas-phase reactions. This model was used in several distinct ways: to fit experimental data, to see if there are fundamental limits on the achievable yield, and to explore how the catalyst parameters would have to change to allow better yields. Such information can provide guidance to experimentalists designing new real-world catalysts with improved yields and selectivities, a process which is often expensive and time-consuming. From our modeling results, some byproducts are inevitable, but it appears that there is no fundamental reason that high (∼99%) yields of acrylic acid could not be obtained with the right catalyst, in either the one-step or the two-step process through acrolein. Some properties of any high-yield catalyst for acrylic acid production are outlined.
Keywords: Selective oxidation; Propylene; Acrylic acid; Optimization; Kinetic modeling
Structure characterization of Pt-Re/TiO2 (rutile) and Pt-Re/ZrO2 catalysts for water gas shift reaction at low-temperature by Hajime Iida; Akira Igarashi (pp. 192-198).
Pt-Re/TiO2 (R: rutile) and Pt-Re/ZrO2 catalysts, which have superior catalytic activity for the water gas shift reaction at low temperature (LT-WGS), were characterized by TEM and XPS measurements in order to examine the role of Re in enhancing catalytic activity. For the TiO2 (R)-supported catalysts, TEM micrographs showed that Pt dispersion increased by Re addition to Pt/TiO2 (R). XPS spectra indicated that the electronic interaction between Pt and Re on the TiO2-supported catalysts is stronger than that on the ZrO2-supported catalysts, and that the state of Re was stable on Pt-Re/TiO2 (R) under the LT-WGS conditions. These results indicate that one of reasons for the superior catalytic activity of Pt-Re/TiO2 (R) catalyst is an increase in Pt dispersion. The stable Re acts as anchors for Pt particles, resulting in high Pt dispersion. On the other hand, for the ZrO2-supported catalysts, TEM micrographs showed that the Pt dispersion decreased by Re addition to Pt/ZrO2. XPS spectra indicated that the interaction between Re and support on Pt-Re/ZrO2 catalysts is stronger than that on Pt-Re/TiO2 (R), and that the redox reaction between Re4+ and Re7+ was repeated on Pt-Re/ZrO2 in the course of the LT-WGS reaction. These results suggested that the Re redox reaction significantly contributes to the high catalytic activity of the Pt-Re/ZrO2 catalyst, although Pt-Re/ZrO2 had lower Pt dispersion than Pt/ZrO2. Therefore, it was determined that the additive effect of Re on Pt dispersion and catalytic activity was largely affected by the state of Re.
Keywords: Water gas shift reaction at low-temperature (LT-WGS); Pt-Re/TiO; 2; (R: rutile); Pt-Re/ZrO; 2; Pt dispersion; Re redox reaction
Photochemical and photocatalytic degradation of salicylic acid with hydrogen peroxide over TiO2/SiO2 fibres by Cristina Adán; Juan M. Coronado; Ricardo Bellod; Javier Soria; Hiroyuki Yamaoka (pp. 199-206).
The effect of hydrogen peroxide on the photo-oxidation of salicylic acid (SA) in aqueous solutions under UV-irradiation was investigated in both purely homogeneous and photocatalytic conditions. Results obtained show that in absence of photocatalyst and under UV-irradiation, the SA degradation rate increases with increasing the amount of hydrogen peroxide added, although for high concentrations of H2O2 the enhancement of the activity is progressively attenuated. In the case of the photocatalytic degradation, nanocrystallites of anatase immobilised over SiO2 fibres were used as catalyst. In the present of TiO2/SiO2, the addition of hydrogen peroxide results in almost a three-fold increment of the photoactivity at low concentration (29.1mM). In contrast, when the amount of H2O2 added exceeds certain limit, the rate of SA removal becomes slightly lower than those measured in absence of photocatalyst. A simple kinetic model which considers the summation of both photochemical and photocatalytic contributions is used to account for the dependence of the rate on the H2O2 concentration. The efficiency of the SA mineralization was also evaluated by monitoring the evolution of total organic carbon (TOC) with irradiation time. In this respect, remarkable differences are found when comparing pure photochemical degradation, which only reduce the TOC concentration in about a 3% after 300min of irradiation, with the photocatalytic treatment, which achieve a 38% of SA mineralization in the same period.
Keywords: Advanced oxidation processes; Photocatalysis; H; 2; O; 2; TiO; 2; /SiO; 2; fibres; Kinetic; Salicylic acid
The effect of MCM-41 structure on the chemical properties of grafted vanadium oxide species by R. Dimitrova; M. Spassova; N. Kostova; T. Tsoncheva; L. Ivanova; Chr. Minchev (pp. 207-212).
A solid state ion exchange method is described that introduces vanadium into zeolite MCM-41. Two types of vanadium species (VO2+ complex in a silanol nest and vanadium ions in cationic position) are identified when the amount of V2O5 is equivalent to sample acidity. The vanadium MCM-41 samples are characterized by the methods of FTIR, UV–vis spectroscopies and temperature programmed reduction/oxidation cycles (TPR/TPO). The effect of the grafted vanadium ions and the efficiency of vanadium centres have been investigated in liquid phase benzene hydroxylation and complete ethylacetate oxidation.
Keywords: Vanadium MCM-41; Reductive solid state ion exchange; Ethylacetate oxidation; Benzene hydroxylation
Rh(I) or Rh(III) supported on MCM-41-catalyzed selective hydroformylation–acetalization of aryl alkenes: Effect of the additives by Bassam El Ali; Jimoh Tijani; Mohammed Fettouhi (pp. 213-220).
Rh(I) and Rh(III) impregnated on mesoporous supports such as MCM-41 have demonstrated a very high catalytic activity in the production of acetals under the hydroformylation conditions of alkenes. The one pot process that combines hydroformylation and acetalization processes leading to acetals as major products was carefully studied. R(I) supported catalysts combined with the heteropolyacid H3PW12O40 showed high catalytic activity towards the formation of acetals. However, Rh(III) supported catalysts were much more active in the absence of any additive. The addition of P(OPh)3 increased significantly the selectivity of the reaction towards the branched acetals. The effects of the addition of different types of phosphine and phosphite ligands were studied.
Keywords: Hydroformylation; Acetalization; Aldehydes; Acetals; Rhodium; Styrene; Phosphine; Phosphite; Syngas
Mn(Br8TPP)Cl supported on polystyrene-bound imidazole: An efficient and reusable catalyst for biomimetic alkene epoxidation and alkane hydroxylation with sodium periodate under various reaction conditions by Valiollah Mirkhani; Majid Moghadam; Shahram Tangestaninejad; Hadi Kargar (pp. 221-229).
In the present work, an account of biomimetic oxidation, Mn(Br8TPP)Cl has been successfully bonded to imidazole modified polystyrene. Polystyrene-bound imidazole (PSI) is not only a heterogeneous axial base but also is a support for immobilization of Mn(Br8TPP)Cl. Mn(Br8TPP)Cl-PSI catalyzes alkene epoxidation with sodium periodate under agitation with magnetic stirring. Alkylaromatics and cycloalkanes were oxidized efficiently to their corresponding alcohols and ketones in the presence of this catalyst. Ultrasonic irradiation enhanced the catalytic activity of this catalyst in alkene epoxidation and alkane hydroxylation and this led to shorter reaction times and higher product yields. This new heterogenized catalyst is of high stability and reusability in the oxidation reactions.
Keywords: Alkene; Epoxidation; Alkane; Hydroxylation; Ultrasonic irradiation; Sodium periodate
Catalytic activity of CpTiCl2(OC6H4Cl-p) supported on the carbonaceous materials modified by nitrogen for the polymerisation of styrene by L. Wachowski; W. Skupiński; M. Hofman (pp. 230-233).
The catalytic polymerisation of styrene with CpTiCl2(OC6H4Cl-p) catalyst supported on carbonaceous materials characterised by different degree of coalification are reported. The effect of the modification of the support materials by nitrogen on the efficiency of the catalytic system in polymerisation of styrene is analysed. The catalytic activity of the modified carbonaceous materials has been found lower than that of the unmodified material, which can be explained by the nature of the surfaces of the support materials.
Keywords: Carbonaceous materials enriched in nitrogen; Titanium metallocene; Polymerisation of styrene
Effect of composition and thermal pretreatment on properties of Ni–Mg–Al catalysts for CO2 reforming of methane by Oscar W. Perez-Lopez; Andressa Senger; Nilson R. Marcilio; Marla A. Lansarin (pp. 234-244).
Ni–Mg–Al catalysts prepared by continuous coprecipitation were evaluated for carbon dioxide reforming of methane carried out between 500 and 700°C. The mixed oxides obtained after calcination exhibit higher surface area values and lower crystallinity. The activity results obtained with different samples demonstrated that the catalytic properties of Ni–Mg–Al catalysts are more affected by the MII/MIII ratio than the Ni/Mg ratio. For samples with constant MII/MIII ratio the best results were obtained for 5≥Ni/Mg>1 ratios. Among the thermal pretreatment effects, the reduction temperature was revealed as a strong influence on the activity and selectivity for the CO2 reforming of methane. In contrast, the catalytic properties can be considered practically independent from the calcination temperature, and the influence of this parameter is restricted to the decrease of the surface area values with the increase of the calcination temperature.
Keywords: Ni–Mg–Al catalysts; Mixed oxides; Hydrotalcite-like compounds; Thermal pretreatment; CO; 2; reforming of methane
Modelling coke formation and deactivation in a FCCU by M. García-Dopico; A. García; A. Santos García (pp. 245-250).
In this paper we describe a new model of catalyst deactivation due to riser reactions in a FCCU. For this purpose, we analyse different coke types and model the formation of each type based on oil feed properties rather than considering all cokes as being equal like other authors do. Thereafter, we examine different deactivation kinetic equations and propose an alternative that describes catalyst deactivation against coke as opposed to against time as in conventional approaches. Although it is easier to model deactivation against time, our model is more flexible and intuitive since it can simulate special situations, such when the catalyst is partially regenerated.
Keywords: Coke; Catalyst deactivation; Deactivation by coke; Riser; FCCU
Effects of solvent on Fischer–Tropsch synthesis by Xiaohao Liu; Wensheng Linghu; Xiaohong Li; Kenji Asami; Kaoru Fujimoto (pp. 251-257).
The influence of solvent on the selectivity of α-olefin in the product hydrocarbon as a function of carbon number over a 20wt.% Co on SiO2 catalyst under the typical reaction conditions of 513K, 4.5MPa and H2/CO=2 has been investigated. Hydrocarbons with different carbon numbers and molecular structures, including n-hexane, n-octane, n-decane, n-dodecane, n-hexadecane, iso-octane and decahydronaphthalene, were used as solvents. Although the selected solvents did not obviously affect the catalytic activity or chain growth probability ( α-value), they exhibited remarkable influences on the α-olefin selectivity. In the case of n-hexane solvent, the α-olefin content in the product decreased markedly with increasing carbon number of the product. The n-decane solvent gave the highest olefin content. It was independent of carbon number on the C6+ product at the level of about 40%. This could be attributed to quicker desorption, diffusion and more suppressed re-adsorption of primary FTS product (α-olefin).
Keywords: Fischer–Tropsch reaction; Solvent; α-Olefin synthesis; Co/SiO; 2; catalyst
Mathematical modelling of oscillatory behaviour during methane oxidation over Ni catalysts by M.M. Slinko; V.N. Korchak; N.V. Peskov (pp. 258-267).
There are many experimental demonstrations of oscillatory behaviour during methane oxidation over Ni catalysts however the origin of the nonlinear behaviour in this system is not clearly understood yet. The new kinetic scheme for methane oxidation over Ni catalysts and mathematical model of the nonlinear reaction dynamics are developed. The model is derived in the mean field approximation and describes qualitatively the main properties of oscillatory behaviour observed experimentally during the reaction of methane oxidation over Ni catalysts. It was demonstrated that thermokinetic oscillations in this system originate due to periodic oxidation–reduction of the catalyst surface, the variation of the selectivity of the process and the competition of reactants for the free active sites.
Keywords: Oscillations; Mathematical modelling; Methane oxidation; Ni catalysts
A study of alumina–zirconia mixed oxides prepared by the modified Pechini method as Co catalyst supports in CO hydrogenation by Soipatta Soisuwan; Joongjai Panpranot; David L. Trimm; Piyasan Praserthdam (pp. 268-272).
In this study, the modified Pechini method has been used to prepare alumina–zirconia mixed oxides with 0.5, 1, 25, 40, and 75mol% of alumina in zirconia. At low Al contents (<25%), tetragonal phase zirconia was observed, while at higher Al contents, the mixed oxide exhibited only amorphous phase. When they were employed as supports for Co catalyst for CO hydrogenation, it was found that the catalytic activities of low Al-modified zirconia supported Co catalysts increased by ca. 30% compared to the ones supported on pure zirconia or pure alumina, suggesting that the modification of zirconia by alumina has resulted in higher Co dispersion. However, when supports with high alumina contents (40–75mol% Al) were used, low Co dispersion and poor catalytic performance were obtained despite their higher surface areas. It is likely that cobalt formed metal support compounds with the amorphous phases of these mixed oxides.
Keywords: Nano-crystalline zirconia; Alumina–zirconia mixed oxides; CO hydrogenation; Cobalt catalysts
Formation of stable Cu2O from reduction of CuO nanoparticles by Jenna Pike; Siu-Wai Chan; Feng Zhang; Xianqin Wang; Jonathan Hanson (pp. 273-277).
In situ time-resolved X-ray diffraction (TR-XRD) using synchrotron radiation has been used to capture the dynamics of the reduction of nanocrystalline CuO using a normal supply of CO gas. Copper(II) oxide nanoparticles 4–16nm in width, as measured by XRD peak broadening, are synthesized using an aqueous organic-nitrate method and reduced in isothermal and temperature ramping reduction experiments. Temperature-programmed reduction of CuO nanoparticles using a ramping heating profile was observed to result in the sequential reduction process CuO→Cu2O→Cu, with CuO reducing completely to the intermediate Cu2O phase before further reduction to metallic copper. Isothermal reduction experiments at 250°C show that CuO nanoparticles completely reduce to Cu2O, and this phase remains stable without further reduction with continued exposure to CO. In contrast to what is typically observed in bulk CuO in both isothermal and ramping reduction conditions, nanocrystalline CuO reduces to a stable Cu2O phase rather than forming metallic copper directly. The behavior of the CuO nanoparticles in temperature ramping reducing conditions is controlled by the particle size, with the smaller CuO nanoparticles exhibiting a greater stability and withstanding a higher temperature before their reduction to Cu2O and then to metallic copper nanoparticles.
Keywords: Copper oxide; Nanoparticles; Reduction of oxides; X-ray diffraction