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Applied Catalysis A, General (v.332, #1)
Influence of reducing agent (CO, H2, and C2H4) and of H2O on NO x reduction on a Pt-Ba/γ-Al2O3 catalyst by C.M.L. Scholz; B.H.W. Maes; M.H.J.M. de Croon; J.C. Schouten (pp. 1-7).
NO x reduction/regeneration of Pt-Ba/γ-Al2O3 catalyst is studied, using H2, CO, and C2H4 as reductant in the absence and presence of H2O in the rich phase. Without H2O, H2 and C2H4 are capable of reducing all stored NO x. Pt sites are poisoned by C2H4 and CO through carbon decomposition, and, for CO, also through formation of isocyanates. H2O in the rich phase prevents poisoning, and all three reductants show comparable efficiencies. ▪In this paper, a comparative study on the NO x reduction/regeneration capabilities at 300°C of a Pt-Ba/γ-Al2O3 catalyst is presented. Different reductants (H2, CO, and C2H4) are used in the absence and presence of H2O in the rich phase. Lean/rich cycling experiments show that in the absence of H2O both H2 and C2H4 are capable of reducing all the stored NO x, although C2H4 poisons the Pt sites by carbon decomposition. CO not only poisons the catalyst through carbon decomposition but also through formation of strongly bound isocyanates on barium sites. These isocyanates are removed by O2 in the lean phase. The type of reducing agent also affects the NO x storage route in the lean phase. H2O in the rich phase prevents poisoning of the catalyst by CO and C2H4, and all three reducing agents show comparable reduction efficiencies.
Keywords: NO; x; reduction; Lean-burn; H; 2; CO; C; 2; H; 4; Pt-Ba/γ-Al; 2; O; 3; catalyst
Mathematical modeling and simulation of hydrotreating reactors: Cocurrent versus countercurrent operations by Fabián S. Mederos; Jorge Ancheyta (pp. 8-21).
This paper describes a model to predict the behavior of trickle-bed reactors used for catalytic hydrotreating of oil fractions with cocurrent and countercurrent operation modes. A dynamic plug-flow heterogeneous one-dimensional model, which has been previously validated with experimental data obtained in an isothermal pilot plant reactor with cocurrent operation, was employed to compare both modes of operation. The reactor model considers the main reactions present in the hydrotreating process: hydrodesulfurization, hydrodenitrogenation, and hydrodearomatization. Simulations were performed for both pilot and commercial trickle-bed reactors, and the results are discussed in terms of variations with time and axial position of partial pressure, temperature and concentrations in liquid phase. A superior performance of countercurrent operation mode was found over cocurrent mode. It was recognized that countercurrent mode can have great potential to be used for deep hydrodesulfurization of oil fractions since it minimizes the inhibiting effect of some products (e.g. H2S) in reactor zones where these species tend to concentrate in cocurrent operation, i.e. at the bottom of the catalytic bed. ▪This paper describes a model to predict the behavior of trickle-bed reactors used for catalytic hydrotreating of oil fractions with cocurrent and countercurrent operation modes. A dynamic plug-flow heterogeneous one-dimensional model, which has been previously validated with experimental data obtained in an isothermal pilot plant reactor with cocurrent operation, was employed to compare both modes of operation. The reactor model considers the main reactions present in the hydrotreating process: hydrodesulfurization, hydrodenitrogenation, and hydrodearomatization. Simulations were performed for both pilot and commercial trickle-bed reactors, and the results are discussed in terms of variations with time and axial position of partial pressure, temperature and concentrations in liquid phase. A superior performance of countercurrent operation mode was found over cocurrent mode. It was recognized that countercurrent mode can have great potential to be used for deep hydrodesulfurization of oil fractions since it minimizes the inhibiting effect of some products (e.g. H2S) in reactor zones where these species tend to concentrate in cocurrent operation, i.e. at the bottom of the catalytic bed.
Keywords: Modeling; Hydrotreating; Cocurrent; Countercurrent
DFT calculations of the alkylation reaction mechanisms of isobutane and 2-butene catalyzed by Brönsted acids by Peng Wang; Daxi Wang; Chunming Xu; Jinsen Gao (pp. 22-26).
Isobutane alkylation with 2-butene catalyzed by proton acids is simulated by DFT using Gaussian 03W programme. Carbonium ion mechanism is confirmed and two transition states of the hydride transfer reaction between isobutane and sec-butyl carbonium ion coming from 2-butene and the addition reaction between tert-butyl carbonium ion and 2-butene are displayed in the picture. Some kinetical parameters are calculated too. ▪Density functional theory method was employed to determine the alkylation reaction course of 2-butene and isobutane. A carbonium ion mechanism is supported through this theoretical simulation. The first step is the formation of sec-C4H9+ from the protonation of 2-butene. The carbonium ion reacts with isobutane to form tert-butyl carbonium ion via hydride transfer. This carbonium ion reacts with 2-butene quickly to produce trimethylpentane carbonium ion (TMP+), which is finally converted to TMP at a high reaction rate via hydride transfer from isobutane. Their transition states are obtained by QST2 method and the transition states are verified by frequency analysis. The calculation results indicate that the energy barrier of each reaction is below zero, suggesting that each reaction step is fast because of the characteristics of carbonium ions. However, the additive reaction is considered to be the rate-limiting step.
Keywords: Alkylation; Addition reaction; Hydride transfer; Molecular simulation
Characterization and catalytic properties of Rh–Sn/Al2O3 catalyst prepared by organometallic grafting by Mounir Chamam; Károly Lázár; Laurence Pirault-Roy; Irina Boghian; Zoltán Paál; Attila Wootsch (pp. 27-36).
Three different phases were found on bimetallic Rh–Sn/Al2O3 catalysts: SnO2, Rh2Sn and RhSn4 alloys. Neither RhSn4 nor Rh2Sn was active in MCP ring-opening (RO). Their position affected the performance of Sn-free Rh: on the surface of low-Miller-index micro-facets if Rh/Sn=0.2 – selective RO, random surface deposition when Sn/Rh=0.34, and in bulk position when Sn/Rh=0.6 – unselective RO. Sn/Rh=0.75 was inactive. ▪Sn was added to a 1% Rh/Al2O3 catalyst ( D=75%) by controlled surface reaction of Sn( n-C4H9)4 in amounts corresponding nominally to 1/4, 1/2, 1 and 2 monolayers. The Sn/Rh ratios obtained were 0.19, 0.34, 0.60 and 0.75, respectively. The Sn–Rh catalysts were characterized by H2 chemisorption, TEM, CO-FTIR,119Sn-Mössbauer spectroscopy and in the test reaction of methylcyclopentane (MCP). Three different Sn phases were found after reduction: SnO2, Sn-poor (most probably Rh2Sn alloy) and Sn-rich phase (most probably RhSn4 alloy). Tin transformed entirely to SnO2 upon oxidation. The effect of oxidation (373K) and reduction (at 473K) appeared to be reversible. Neither RhSn4 nor Rh2Sn was active catalytically in MCP ring-opening, but their position on the surface affected the performance of Rh not interacting with Sn. On the catalyst with Sn/Rh=0.19, the strongly bonded adsorption of intermediates was hindered by the selective deposition of Sn on low-Miller-index micro-facets (as indicated also by CO-FTIR), causing increased activity in selective ring-opening reaction of MCP and decreasing the production of fragments. With Sn/Rh=0.34, sites active in ring-opening reactions (low-coordination facets) were also partly blocked by tin addition. On catalysts with even higher Sn loading, tin also penetrated into the particles forming possibly alloy-like phases. On Sn/Rh=0.6 some surface Rh still remained Sn-free, and was active in non-selective ring-opening of MCP. The catalyst with Sn/Rh=0.75 was inactive in MCP ring-opening reaction. The latter two samples represent “bulk-bimetallic” catalysts, as opposed to “surface-bimetallic” with lower amounts of tin. The present results indicate the co-existence of electronic and geometric effects, inasmuch as chemically interacting Rh–Sn patches located on certain surface sites influence the catalytic behavior.
Keywords: Rh; Sn–Rh catalysts; Rhodium; Methylcyclopentane ring-opening; Organometallic grafting
Influence of the pretreatment method on the properties of trimetallic Pt–Ir–Ge/Al2O3 prepared by catalytic reduction by Petrisor Samoila; Marieme Boutzeloit; Viviana Benitez; Silvana A. D’Ippolito; Catherine Especel; Florence Epron; Carlos R. Vera; Patrice Marécot; Carlos L. Pieck (pp. 37-45).
Pt–Ir/Al2O3 catalysts were modified by addition of germanium, in order to suppress the strong hydrogenolytic activity of this type of naphtha reforming catalyst. The trimetallic systems were prepared by a surface redox reaction. The objective of the study is to examine the influence of the Ge addition step and of the activation step of these systems on their catalytic properties.Selectivity to methane obtained in the reaction of isomerization of n-C5 at 240min of time-on-stream for the Pt–Ir–Ge/Al2O3 catalysts activated by direct reduction (R) or by calcination–reduction (C-R).▪Pt–Ir/Al2O3 catalysts were modified by addition of an inactive metal, germanium, in order to suppress the strong hydrogenolytic activity of this type of naphtha reforming catalyst. The trimetallic systems were prepared by a surface redox reaction called catalytic reduction method. The objective of the study is to examine the influence of the Ge addition step and of the activation step (calcination–reduction or only reduction) of these systems on their catalytic properties. The Pt–Ir metallic function deposited on alumina does not suffer a significant sintering of the particles neither during the catalytic reduction procedure (i.e. an immersion in acidic medium under hydrogen flow) nor during the final activation step. On the other hand, an inhibition of the acidic function of the bimetallic parent catalysts is observed after the catalytic reduction treatment. Ge affects both the metal and the acidic functions of the Pt–Ir–Ge trimetallic catalysts, the effects depending on the deposited Ge content and on the activation treatment. The best catalytic properties are obtained for the Pt–Ir–Ge/Al2O3 catalyst with the lowest Ge content (0.1wt%) and directly reduced.
Keywords: Trimetallic reforming catalysts; Pt–Ir–Ge/Al; 2; O; 3; Catalytic reduction method
Characterization and hydroisomerization performance of SAPO-11 molecular sieves synthesized in different media by Shengzhen Zhang; Sheng-Li Chen; Peng Dong; Guimei Yuan; Keqi Xu (pp. 46-55).
SAPO-11 molecular sieves were synthesized in conventional aqueous medium, two-liquid phase medium and HF medium. The physicochemical properties of the SAPO-11, especially the morphologies and the acidity, were strongly influenced by the synthesis medium. The n-hexadecane hydroisomerization performance of Pt/SAPO-11 prepared in different synthesis medium had been evaluated and the relationship between the performance of hydroisomerization and the acidity was analyzed.▪Silicoaluminophosphates SAPO-11 molecular sieves were synthesized from a conventional aqueous medium, a two-liquid phase medium and a HF medium, respectively, and were characterized by various methods such as XRD, SEM, pyridine-FT-IR, NH3-TPD,29Si MAS-NMR. The morphologies of the SAPO-11 molecular sieves obtained from the conventional aqueous medium and the two liquid-phase media exhibit pseudo-spherical aggregates ranging from 7 to 10μm assembled from cubic plate microcrystallites, whereas the SAPO-11 molecular sieves synthesized from the HF medium exhibit hexagonal prismatic aggregates of about 1–3μm length. The synthesis media used highly influenced the number and the strength of SAPO-11 acid sites. Compared to SAPO-11 obtained from conventional aqueous medium, SAPO-11 prepared from two-liquid phase media possessed a similar number of BrØnsted acid sites but a much larger number of Lewis acid sites, whereas the SAPO-11 synthesized from HF medium had a similar number of Lewis acid sites but a much lower number of BrØnsted acid sites. The29Si MAS-NMR spectra showed that the HF could change the manner of Si incorporation into the SAPO-11 framework. The hydroisomerization of n-hexadecane on Pt/SAPO-11 samples showed that Pt/SAPO-11 obtained from the two-liquid phase media had the largest yield of isomers. The conversion activity of n-hexadecane was dependent on the amount of BrØnsted acid of SAPO-11 molecular sieves, while its hydrocracking activity was related to the strong acid sites of SAPO-11.
Keywords: SAPO-11; Hydroisomerization; Hydrocracking; n-; Hexadecane
Hydrodeoxygenation of aldehydes catalyzed by supported palladium catalysts by Dana Procházková; Petr Zámostný; Martina Bejblová; Libor Červený; Jiří Čejka (pp. 56-64).
Hydrogenation and hydrodeoxygenation of aldehydes, especially benzaldehyde, proceed on supported palladium catalysts with zeolites and active carbon as supports. Zeolites beta were the most suitable supports for this reaction.▪This contribution focuses on the hydrogenation and hydrodeoxygenation of aldehydes (benzaldehyde, 2-phenylpropionaldehyde, 3-phenylpropionaldehyde, cinnamaldehyde, 4-isopropylbenzaldehyde, heptanal) on supported palladium catalysts, namely zeolites and active carbon. The effects of the substrate structure, solvent, type of support and its acidity, reaction temperature and pressure on activity and selectivity of Pd catalysts were investigated in detail. Catalytic hydrodeoxygenation of aldehydes was carried out in a liquid phase in an autoclave in the temperature range from 30 to 130°C and at pressure ranging from 1 to 6MPa. Hydrogenation reactions performed in non-polar hexane proceeded with a significantly higher rate than in a polar methanol. The presence of isopropyl substituent in 4-isopropylbenzaldehyde increased both the reaction rate as well as the selectivity to hydrodeoxygenation. Hydrodeoxygenation of 2-phenylpropionaldehyde, 3-phenylpropionaldehyde, cinnamaldehyde, and heptanal did not proceed, the main products were dialkylethers, which evidences the importance of the direct attachment of CO group to the benzene ring. The presence of hydrogenation—hydrogenolytic mechanism as well as the direct hydrogenolysis of CO bond in the transformation of benzaldehyde was verified.
Keywords: Hydrogenation; Hydrodeoxygenation; Benzaldehyde; Cinnamaldehyde; Phenylpropionaldehyde; Pd supported catalysts; Zeolites; Pd carbon catalyst
Polymer-supported methylselenite for the oxidative carbonylation of aniline by Eun Hee Jeon; Mai Dao Nguyen; Cheong Il Chung; Yong Jin Kim; Hoon Sik Kim; Minserk Cheong; Je Seung Lee (pp. 65-69).
Polymer-supported methylselenites were synthesized from the direct polymerization of monomeric analogues, and these polymer-supported heterogeneous catalysts exhibited reasonably high activity for the oxidative carbonylation of aniline under experimental conditions. The catalyst recycle test showed that the supported catalyst can be reused at least up to five times with a moderate loss of activity.▪Polymer-supported methylselenites including poly(1-methyl-3-vinylimidazolium methylselenite) and poly(1-ethyl-3-vinylimidazolium methylselenite) were synthesized from the direct polymerization of 1-methyl-3-vinylimidazolium methylselenite and 1-ethyl-3-vinylimidazolium methylselenite. The results of Fourier Transform Infrared (FT-IR) spectra and thermogravimetric analysis (TGA) clearly showed that methylselenite is tightly immobilized on the imidazolium-based polymer. These polymer-supported heterogeneous catalysts exhibited reasonably high activity for the oxidative carbonylation of aniline under experimental conditions. The catalyst recycle test showed that the supported catalyst can be reused at least up to five times with a moderate loss of activity.
Keywords: Oxidative carbonylation; Methylselenite; Ionic liquid; Polymer-supported; Urea; Carbamate
Decomposition and/or hydrogenation of hydrogen peroxide over Pd/Al2O3 catalyst in aqueous medium: Factors affecting the rate of H2O2 destruction in presence of hydrogen by Vasant R. Choudhary; Chanchal Samanta; Prabhas Jana (pp. 70-78).
The destruction of H2O2 by its decomposition and/or hydrogenation over Pd/Al2O3 catalyst is strongly influenced by the presence of H2, nature of halide anions (F−, Cl−, Br− or I−) in the reaction medium or in the catalyst, concentration of halide anions and protons (acid) in the medium and oxidation state of Pd in the catalyst.▪Hydrogen peroxide destruction by its decomposition and/or hydrogenation to water in the presence of H2 over Pd(5wt.%)/Al2O3 catalyst in an aqueous reaction medium, similar to that used in the H2-to-H2O2 oxidation, has been thoroughly investigated at different reaction conditions. The H2O2 destruction is strongly influenced by the oxidation state of Pd in the catalyst and also by the presence of different halide anions (viz. F−, Cl−, Br− and I−) in the acidic aqueous medium or in the catalyst, depending upon the concentration of halide anions. The cations associated with halide anions have, however, a little or no influence on the H2O2 destruction. The iodide anions strongly poisoned the catalyst, even at their very low concentration. The fluoride anions have only a small effect on the H2O2 destruction. The chloride or bromide anions drastically inhibit the rapid H2O2 decomposition, but promote the slower H2O2 hydrogenation. The H2O2 destruction reactions are strongly influenced by the halide anion and acid concentrations. The presence of acid (protons) plays a very important role in drastically reducing the H2O2 destruction, particularly in the presence of chloride anions. Both in the presence and absence of Cl− or Br− anions, the H2O2 destruction activity of the catalyst is markedly reduced because of the oxidation of Pd but it is drastically increased due to the presence of H2. A plausible reaction mechanism for the rapid H2O2 decomposition and slower H2O2 hydrogenation reactions, prevailing under the different reaction conditions, has also been discussed.
Keywords: Hydrogen peroxide; Decomposition of H; 2; O; 2; Hydrogenation of H; 2; O; 2; Pd/Al; 2; O; 3; Halide anions as catalyst promoter or indicator
RuB/Sn-SBA-15 catalysts: Preparation, characterization, and catalytic performance in ethyl lactate hydrogenation by Ge Luo; Shirun Yan; Minghua Qiao; Kangnian Fan (pp. 79-88).
A series of Sn-containing mesoporous SBA-15 molecular sieves were synthesized and used as supports for the preparation of RuB/Sn-SBA-15 catalysts. Effects of Sn doping on the structure of the SBA-15 and on properties and catalytic performance of the catalyst in ethyl lactate hydrogenation were studied.▪A series of Sn-containing mesoporous SBA-15 molecular sieves were synthesized and used as supports for RuB catalysts. Effects of Sn doping on the structure of the SBA-15 and on properties and catalytic performance of the RuB/Sn-SBA-15 catalyst in ethyl lactate hydrogenation were studied. The samples were characterized by inductively coupled plasma–atomic emission spectroscopy (ICP–AES), N2 physisorption, powder X-ray diffraction (XRD), diffuse reflectance UV–vis spectroscopy (DRUVS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and catalytic tests. The results showed that Sn-containing SBA-15 supports prepared by direct hydrothermal synthesis method maintained the characteristic structure of SBA-15 with Sn species highly dispersed in the support when Si/Sn nominal ratio was above 30. The RuB catalysts supported on the Sn-containing SBA-15 prepared by the direct hydrothermal synthesis method showed higher dispersion and better catalytic performance than corresponding one prepared by the impregnation method. The best catalytic performance was achieved over catalyst with Si/Sn nominal ratio of 30.
Keywords: SBA-15; Tin modification; RuB; Ethyl lactate; Hydrogenation
Effects of catalytic walls on hydrogen/air combustion inside a micro-tube by Guan-Bang Chen; Chih-Peng Chen; Chih-Yung Wu; Yei-Chin Chao (pp. 89-97).
Numerical simulation with detailed heterogeneous and homogeneous chemistries of hydrogen/air mixture reaction inside a catalytic micro-tube is performed. The characteristics of heterogeneous and homogeneous interaction are delineated in terms of flow velocity, tube diameter and wall thermal conductivity. The existence of heterogeneous reaction has two competing effects on homogeneous combustion. Three characteristic reaction types can be schematically depicted in terms of tube diameter and flow velocity in Fig. 1. Moreover, since the homogeneous combustion is ignited and sustained by the heat from heterogeneous reaction, the effect of wall thermal conductivity is not as obvious as that in the micro-tube without catalyst walls.▪Numerical simulations with detailed heterogeneous and homogeneous chemistries of hydrogen/air mixture reactions inside a catalytic micro-tube were performed. The characteristics of heterogeneous and homogeneous interaction are delineated in terms of flow velocity, tube diameter and wall thermal conductivity. With the catalytic wall, the homogeneous combustion is obviously weakened. The heterogeneous reactions will consume part of the fuel near the entrance and will make the homogeneous combustion region shift downstream. The micro-tube can be divided into two regions. The upstream region is dominated by the heterogeneous reaction and the downstream region is dominated by the homogeneous combustion. With increasing inlet velocity, the region dominated by heterogeneous reactions expanded downstream and finally occupied the whole tube. Decreasing the tube diameter enhanced the heterogeneous reactions. However, the increased heat released at the wall will be beneficial for homogeneous combustion. The maximum allowed inlet velocity for homogeneous combustion first increased and then decreased to almost zero at 0.2mm tube. This means that homogeneous combustion can not be sustained inside such a small catalytic micro-tube. Finally, three different wall materials are simulated. Higher wall temperature gradient for lower wall thermal conductivity will promote the homogeneous combustion shift upstream and will have a wider temperature distribution. Since the homogeneous combustion is ignited and sustained by the heat from the heterogeneous reaction, the effect of wall thermal conductivity is not as obvious as it is in the micro-tube without catalyst walls.
Keywords: Numerical simulation; Hydrogen; Catalyst; Micro-tube
Self-activation and self-regenerative activity of trace Rh-doped Ni/Mg(Al)O catalysts in steam reforming of methane by Dalin Li; Tetsuya Shishido; Yasunori Oumi; Tsuneji Sano; Katsuomi Takehira (pp. 98-109).
Trace Rh-doped Ni0.5/Mg2.5(Al)O catalyst prepared by adopting “memory effect” of hydrotalcite showed self-activation as well as regenerative activity in the steam reforming of methane not only in stationary but also in daily star-up and shut-down operation. ▪Ni/Mg(Al)O catalyst doped with trace amounts of Rh was tested in steam reforming of methane and the catalytic behavior was compared with the Ru-doped catalyst. Rh-doped Ni/Mg(Al)O catalyst showed a self-activation without any reduction treatment due to the ability for hydrogen production by CH bond cleavage. Such production led to the reduction of lattice Ni2+ in Mg(Al,Ni)O periclase to metallic Ni by hydrogen-spillover. The Rh-doped Ni/Mg(Al)O catalyst showed also a self-regenerative activity during a daily start-up and shut-down (DSS) operation of steam reforming of methane. NiRh alloy was formed in the surface layer of metallic Ni particles and Rh was located more profoundly in the particles than Ru in NiRu alloy on the Ru-doped catalyst. The Rh-doping exhibited a prominent performance, whilst the Ru-doping resulted in neither self-activation nor stable activity in the DSS operation. Although the catalyst deactivation took place by the Ni0 oxidation into the lattice Ni2+ in Mg(Al,Ni)O periclase, trace Rh assisted the regeneration of the active metallic Ni from the lattice Ni2+ by hydrogen-spillover. Even metallic Ni particles that had been strongly sintered on the Rh-Ni/Mg(Al)O catalyst by steaming at 900°C were re-dispersed during the DSS operation, resulting in high and stable activity. The self-regeneration of the Rh-doped Ni/Mg(Al)O catalyst has been achieved by continuous rebirth of active Ni metal particles due to reversible reduction–oxidation between the metallic Ni on the surface and the lattice Ni2+ in Mg(Ni,Al)O periclase, i.e., oxidative incorporation of surface Ni0 into the lattice Ni2+ of Mg(Al,Ni)O and reductive migration of the lattice Ni2+ to the surface Ni0 by hydrogen-spillover.
Keywords: CH; 4; reforming; Self-activation; Daily start-up and shut-down operation; Self-regeneration; Ni/Mg(Al)O catalyst; Rh-doping; Memory effect
Ethylene polymerization using tris(pyrazolyl)borate titanium(IV) catalyst supported in situ on MAO-modified silica by Marcelo P. Gil; Osvaldo L. Casagrande Jr. (pp. 110-114).
The in situ immobilization of TpMs*TiCl3 (1) on MAO-modified SiO2 is able to produce high-density polyethylenes with different properties. The viscosity-average molecular weight of the polyethylenes can be controlled by varying the [Al]/[Ti] molar ratio and temperature of polymerization. The use of TMA at low Al concentration ([Al]/[Ti]=100) showed comparable activity to that found using MAO.▪The immobilization “in situ” of soluble catalyst TpMs*TiCl3 (1) on MAO-modified silica (4.0wt.% Al/SiO2) yields active supported catalyst for ethylene polymerization. This supported catalyst showed activities between 132 and 461kg of PE/mol[Ti]hatm which varies according to the nature of cocatalyst (MAO>TMA>TiBA>IPRA). Upon activation with MAO, no significant impact on the activity has been observed at 30 and 60°C; however at higher temperature (90°C) the activity decreases substantially as result of a partial catalyst deactivation. Studies related to the influence of the [Al]/[Ti] molar ratio using TMA as cocatalyst have shown that this supported catalyst presented higher activities using Al concentrations as low as 25:1. The viscosity-average molecular weights (M¯v) of the PE's produced with1/SMAO-4 are strongly influenced by the Al concentration varying from 0.41 to 13.6×105g/mol. Resulting polyethylenes can replicate the support morphology. The scanning electron microscopy (SEM) studies revealed that the spherical morphology of the supported catalyst is replicated in the polyethylene particles.
Keywords: Titanium; Tris(pyrazolyl)borate ligand; In situ polymerization; Silica; Polyethylene
Cr-containing magnetites Fe3− xCr xO4: The role of Cr3+ and Fe2+ on the stability and reactivity towards H2O2 reactions by F. Magalhães; M.C. Pereira; S.E.C. Botrel; J.D. Fabris; W.A. Macedo; R. Mendonça; R.M. Lago; L.C.A. Oliveira (pp. 115-123).
The results showed that the presence of Cr caused a significant increase on the activity for the oxidation of the dyes with complete discoloration and high degree of mineralization. The higher activity of Fe2.93Cr0.07O4 was discussed in terms of a coupling of the redox pairs Fe3+/Fe2+ and Cr2+/Cr3+ producing a more efficient regeneration of the Fenton active specie Fe2+.▪A series of Cr-containing magnetites, Fe3− xCr xO4 ( x=0.00, 0.07, 0.26, 0.42 and 0.51) has been prepared using conventional co-precipitation method. Mössbauer and powder X-ray diffraction measurements suggested the formation of the spinel crystalline phase with initial substitution ofFeoct3+ by Cr3+ and for higher Cr contents, chromium also replacesFeoct2+andFetet3+ in the crystalline structure. N2 adsorption/desorption revealed that the presence of Cr has a remarkable effect on the texturial properties of the material decreasing the pore diameter from meso- to micropore with a significant increase on the BET surface area. Thermal analyses (TG and DTA) coupled with XRD and Mössbauer showed that thermal treatment up to 270°C with O2 leads to the oxidation ofFeoct2+ producing Cr-substituted maghemite but at 600°C the cubic maghemite is converted to the hexagonal hematite and Cr is expelled from the iron oxide structure. The reactivity of Fe3− xCr xO4 was investigated using two H2O2 reactions, i.e. the decomposition to O2 and the oxidation of the dye methylene blue used as model contaminant. The obtained results showed that the presence of Cr directly promoted the H2O2 decomposition. On the other hand, the presence of small concentration of Cr, i.e. Cr0.07 and Cr0.21, caused a significant increase on the activity for the oxidation of the dyes with complete discoloration and high degree of mineralization. The higher activity of Fe2.93Cr0.07O4 was discussed in terms of a coupling of the redox pairs Fe3+/Fe2+ and Cr2+/Cr3+ producing a more efficient regeneration of the Fenton active specie Fe2+.
Keywords: Magnetite; Chromium; Fenton reaction
The effect of metal and support particle size on NiO/CeO2 and NiO/ZrO2 catalyst activity in complete methane oxidation by Malgosia M. Pakulska; Catherine M. Grgicak; Javier B. Giorgi (pp. 124-129).
The particle size of single components in NiO/CeO2 and NiO/ZrO2 was varied independently to investigate the effect of metal and support particle size on activity for complete methane oxidation. Ceria particle size significantly affects the Arrhenius parameters, suggesting ceria forms part of the active site for the more active NiO catalyst. In contrast, zirconia remains an inert support.▪The catalytic oxidation of methane was examined over 5% (w/w) NiO- on CeO2 or ZrO2. The particle size of single components was varied independently to investigate the effect of metal and support particle size on activity for complete methane oxidation. Catalyst activity is most affected by NiO particle size, however the support particle size also plays an active role. Results show that the particle size of ceria has a greater effect on activity than that of zirconia. This is attributed to ceria's greater oxygen transport capacity and contribution to the reaction mechanism. Changes in ceria particle size significantly affected the Arrhenius parameters, suggesting ceria forms part of the active site on a ceria-supported NiO catalyst. In contrast, zirconia particle size did not result in changes in activation energy, but affected only the number of catalytic sites as seen by changes in the pre-exponential factor. Ceria was also found to reduce deactivation of the catalyst due to increased oxygen transport to the active sites during reaction.
Keywords: Methane oxidation; NiO; Ceria; Zirconia
Copper-modified alumina as a support for iron Fischer–Tropsch synthesis catalysts by Kamonchanok Pansanga; Nattaporn Lohitharn; Andrew C.Y. Chien; Edgar Lotero; Joongjai Panpranot; Piyasan Praserthdam; James G. Goodwin Jr. (pp. 130-137).
It was found that the use of Cu-modified Al2O3 supports increased significantly the overall activity of the Fe/Al2O3 catalysts. There were no changes in FT product selectivity, chain growth probability ( α), or olefin selectivity due to any effect of the Cu-modified Al2O3 or Cu-promotion. However, the more calcination steps used during preparation, the higher the catalyst activity obtained.▪In the present study, the effect of Cu-modified Al2O3 on the properties of Al2O3-supported Fe catalysts in the Fischer–Tropsch synthesis was investigated. Ten weight percent Cu was first impregnated into γ-alumina to produce Cu-modified Al2O3 supports; then 20wt.% of Fe and (in some cases) 1wt.% Cu were added to the supports by the sequential impregnation method. Two different pretreatment methods (drying or drying and calcining) were employed after each metal impregnation. It was found that the use of Cu-modified Al2O3 supports increased significantly the overall activity of the Fe/Al2O3 catalysts. Addition of 1% Cu as a reduction promoter to the Cu-modified supported Fe catalysts was not necessary since it did not further enhance the activity of the catalysts. There were no changes in FT product selectivity, chain growth probability ( α), or olefin selectivity due to any effect of the Cu-modified Al2O3 or Cu-promotion. However, the more calcination steps used during preparation, the higher the catalyst activity obtained. Cu-modification of the alumina most probably diminished the interaction/reaction of the Fe with the support, thereby improving its chemisorption and catalytic properties.
Keywords: Iron catalysts; Alumina-supported catalysts; Copper modification; Fischer–Tropsch synthesis
Highly efficient tungsten trioxide containing mesocellular silica foam catalyst in the O-heterocyclization of cycloocta-1,5-diene with aqueous H2O2 by Ruihua Gao; Wei-Lin Dai; Xinli Yang; Hexing Li; Kangnian Fan (pp. 138-145).
WO3-containing mesocellular silica foam (MCF) catalysts have been synthesized via an in situ method by using tetraethyl orthosilicate (TEOS) and sodium tungstate as the precursors and via a traditional impregnation method. All catalysts are highly efficient in the O-heterocyclization of cycloocta-1,5-diene (COD) (see Scheme 1 in Section 3.2) to 2,6-dihydroxy-9-oxabicyclo[3.3.1]nonane (1) and 2-hydroxy-9-oxabicyclo[3.3.1]nonane-6-one (2) with a COD conversion up to 100% and (1+2) selectivity up to 98%. The WO x species are well dispersed in the W-containing catalysts via the in situ method with the WO3 loading up to 20wt.%, as proved by XRD, TEM, Raman, and UV–vis DRS. TPR and XRD results show that the WO3–MCF catalysts derived from the in situ method show much stronger interactions between active tungsten oxide species and the MCF support than the WO3/MCF obtained by the traditional impregnation method. The in situ method-derived catalyst also shows far better stability than the impregnation one according to the results from the recycling experiment.WO3-containing mesocellular silica foam (MCF) catalysts have been synthesized via in situ synthesized method and traditional impregnated method. All catalysts are active in the O-heterocyclization of cycloocta-1,5-diene (COD) to 9-oxabicyclo[3.3.1]nonane-2,6-dioles and 2-hydroxy-9-oxabicyclo[3.3.1]nonane-6-one. It is demonstrated from the recycle experiment that the WO3–MCF catalysts show far better stability than the impregnated one.▪
Keywords: WO; 3; -containing mesocellular silica foam (MCF) catalyst; Cycloocta-1,5-diene (COD); O; -Heterocyclization; Hydrogen peroxide
An Ir/WO3 catalyst for selective reduction of NO with CO in the presence of O2 and/or SO2 by Hironori Inomata; Masahide Shimokawabe; Masahiko Arai (pp. 146-152).
An Ir/WO3 catalyst is effective for the selective reduction of NO with CO in the presence of O2 and/or SO2. It is thus a promising catalyst for the practical use under lean-burn conditions. FTIR measurements were made to examine the surface species formed during the reactions under various conditions and possible reaction mechanisms are discussed. ▪The catalytic performance of Ir/WO3 catalyst has been studied in the reduction of NO with CO in the presence of O2 and/or SO2. The catalyst was active for the selective reduction of NO to N2 without foreign gases. The conversion of NO to N2 was further enhanced by the addition of a small amount of O2 while that to N2O was reduced. The N2 conversion went through a maximum, which depended on the composition of the reacting gaseous mixture (NO and CO). The catalyst was still active at higher O2 concentrations up to 5%, so this Ir/WO3 catalyst can be used effectively under lean-burn conditions. The presence of SO2 (100ppm) caused a significant deactivation but this negative effect was completely removed by co-existing O2. The reaction mechanisms and the effects of co-existing O2 and SO2 gases are discussed on the bases of those reaction results, those of the reduction of NO2 instead of NO, and FTIR measurements of the catalysts after the reactions under various conditions. Possible reaction pathways are proposed, which depend on the concentration of O2 added in the reaction mixture.
Keywords: Selective catalytic reduction; Nitrogen monoxide; Iridium catalyst; Tungsten oxide support; Lean-burn condition
Nickel-based tri-reforming catalyst for the production of synthesis gas by Jung Shik Kang; Dae Hyun Kim; Sang Deuk Lee; Suk In Hong; Dong Ju Moon (pp. 153-158).
Tri-reforming reaction, the combination of partial oxidation, steam and dry reforming of methane, was carried out over NiO–YSZ–CeO2 catalyst. It was found that the tri-reforming was a desirable process for the effective production of syngas with desired H2/CO ratio without CO2 pre-separation. Also, the NiO–YSZ–CeO2 catalyst showed higher catalytic activity and stability than commercial steam reforming catalysts.▪The tri-reforming reaction was carried out over NiO–YSZ–CeO2 catalyst to produce a synthesis gas from greenhouse gases like CH4 and CO2 contributing to the greenhouse effect. The NiO–YSZ–CeO2 catalysts were characterized by N2 physisorption, X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM) techniques. It was found that the tri-reforming reaction was more favorable than the dry reforming reaction for the production of synthesis gas. It was also observed that NiO–YSZ–CeO2 catalyst showed higher catalytic activity and stability than commercial Holder Topsoe (HT) and Imperial Chemical Industries (ICI) catalysts in the tri-reforming of CH4. The results suggest that the tri-reforming process can be applied to the production of high-valued chemicals and the fuel processor of solid oxide fuel cell (SOFC) and molten carbonate fuel cell (MCFC) systems.
Keywords: Nickel-based catalyst; Tri-reforming; Dry reforming; CO; 2; reforming; Synthesis gas; CO; 2; reduction
Direct and efficient transformation of gaseous alkanes into carboxylic acids catalyzed by vanadium containing heteropolyacids by Marina V. Kirillova; José A.L. da Silva; João J.R. Fraústo da Silva; Armando J.L. Pombeiro (pp. 159-165).
The vanadium containing heteropolyacids H4[PMo11VO40]×34H2O (HPA-1), H5[PMo10V2O40]×32H2O (HPA-2) and H6[PMo9V3O40]×34H2O (HPA-3) act as highly active catalysts for the direct transformation of light C1–C3 alkanes into the corresponding carboxylic acids in the presence of CO and in the K2S2O8/CF3COOH system. ▪The vanadium containing heteropolyacids H4[PMo11VO40]×34H2O (HPA-1), H5[PMo10V2O40]×32H2O (HPA-2) and H6[PMo9V3O40]×34H2O (HPA-3) act as highly active catalysts for the direct transformation of light C1–C3 alkanes into the corresponding carboxylic acids in the presence of CO and in the K2S2O8/CF3COOH system. Propionic acid (ca. 70% yield), iso- and n-butyric acids (ca. 65% overall yield), and acetic acid (ca. 20%) are the major products obtained from the carboxylation of ethane, propane and methane, respectively, with vanadium playing a main catalytic role. The effects of the catalyst amount have been studied and overall turnover numbers (TONs) up to ca. 12×103 (for the ethane and propane conversions) or up to 3×103 (for the methane carboxylation to acetic acid) have been achieved for very high alkane-to-catalyst molar ratios which also promote the selectivity towards acetic acid.
Keywords: Alkanes; C–H activation; Heteropolyacids; Vanadium; Carboxylation; Carboxylic acids; Homogeneous catalysis
2,2′-Bipyridine and related N-chelants as very effective promoters for Cu catalysts in the decarboxylation by A.S. Lisitsyn (pp. 166-170).
Bipyridine-like chelating ligands accelerate decarboxylation of aromatic acids with copper catalysts much greater than the traditional monodentate promoters, and the reaction rapidly goes to completion when alternative catalysts show poor performance under the same conditions. ▪Effect of 2,2′-bipyridine (bipy) and analogous ligands on decarboxylation of 2,4-dimethylbenzoic (DMBA) and 4-hydroxybenzoic acids with Cu catalysts has been compared with that of quinoline. The chelating ligands were shown to exceed the traditional promoter in efficiency by two to three orders of magnitude per a mol basis. In combination with bipy-like promoters, Cu catalysts ensured complete conversion of even the low reactive DMBA for 15–30min and gave expected product in >95% yield (S/C 40–100, Ph2O as solvent, 250°C). In the decarboxylation of individual aromatic acids, the (Cu+bipy) system greatly surpassed carbon and Pd/C catalysts as well, but lost activity in solutions of natural acidic mixtures. The later was assigned to reduction of Cu ions by H-donor constituents of such mixtures.
Keywords: Decarboxylation; Aromatic acids; Cu catalysts; Promoting; N; -chelants; 2,2′-Bipyridine