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Applied Catalysis A, General (v.340, #1)
1-Pentene isomerization over SAPO-11, BEA and AlMCM-41 molecular sieves by Carmen M. López; Leyda Ramírez; Virginia Sazo; Vanessa Escobar (pp. 1-6).
The skeletal isomerization of 1-pentene at atmospheric pressure and 89mm Hg 1-pentene partial pressure was investigated over SAPO-11, BEA and AlMCM-41 molecular sieves. The effect of the reaction temperature between 250 and 400°C was studied. Acidity of the catalysts seems to play a more important role than the pore size in the reaction conditions used.The skeletal isomerization of 1-pentene at atmospheric pressure and 89mm Hg 1-pentene partial pressure was investigated over SAPO-11, BEA and AlMCM-41 molecular sieves. The effect of the reaction temperature between 250 and 400°C was studied. Acidity of the catalysts seems to play a more important role than the pore size in the reaction conditions used.▪
Keywords: Skeletal isomerization; 1-Pentene; Molecular sieves; Zeolites
The effect of sulfur addition during the preparation of Co/Zn/TiO2 Fischer–Tropsch catalysts by Nobuntu N. Madikizela-Mnqanqeni; Neil J. Coville (pp. 7-15).
The effect of changing the order of impregnating cobalt, zinc and a sulfur precursor (ammonium sulfide) on Co(10%)/Zn( xwt%)/TiO2 ( x=0, 10) catalysts was investigated by TPR, XPS and Fischer–Tropsch reactor studies. A model is proposed that explains the reactions of sulfur with Zn, Co and TiO2 and is consistent with the characterisation and activity results.▪The effect of sulfur on Co(10%)/Zn( xwt%)/TiO2 ( x=0 and 10) catalysts was investigated by TPR, XPS and Fischer–Tropsch (FT) reactor studies. The catalysts were prepared by impregnating different amounts of sulfur on Co(10%)/Zn( xwt%)/TiO2( x=0 and 10) catalysts, using ammonium sulfide (20% in water) as a sulfur precursor. The effect of changing the order of impregnating cobalt, zinc and the sulfur precursor was also investigated. Based on the XPS results, impregnation of different amounts of sulfur on Co/Zn( xwt%)/TiO2( x=0 and 10) catalysts indicated that sulfur preferentially reacts with cobalt and zinc instead of titania and blocked the active sites for FT reactions. These catalysts were inactive towards FT synthesis. Impregnating sulfur onto TiO2 prior to Co and Zn addition gave a Co/Zn/S/TiO2 catalyst that showed lower FT activity when compared to the unsulfided Co/Zn/TiO2 catalyst. XPS data revealed that sulfur reacted with titania and zinc as well as cobalt species prior to FT synthesis. A drastic increase in the C1–C11 selectivity and a decrease in the C12+ selectivities were observed for the sulfided catalysts (Co/Zn/S/TiO2 and Co/S/Zn/TiO2). The FT results correlated with the XPS and TPR results. The unsulfided catalysts with or without zinc produced higher molecular weight products (C12+) and less methane when compared to the sulfided catalysts. A model is proposed that explains the reactions of sulfur with Zn, Co and TiO2 and is consistent with the characterisation and activity results.
Keywords: Fischer–Tropsch catalysis; Cobalt; Zinc; Sulfur; Titania; XPS
Copper (II) phthalocyanines immobilized on alumina and encapsulated inside zeolite-X and their applications in photocatalytic degradation of cyanide: A comparative study by R.M. Mohamed; Mohamed Mokhtar Mohamed (pp. 16-24).
The oxidation of CN− that follows first order rate kinetics exhibited remarkable activity on CuPc/ZX (0.1min−1) compared with other catalysts emphasizing the dependence of the electronic transition on zeolite structure.▪Copper phthalocyanine (CuPc) complexes either deposited on alumina (CuPc/Al); synthesized by sol–gel, or encapsulated inside zeolite-X (CuPc/ZX) while in situ synthesis were characterized by X-ray diffraction (XRD), DSC, FT-IR, diffuse reflectance UV–vis, dynamic light scattering and N2 adsorption techniques. These materials were tested for photocatalytic oxidation of cyanide in comparison with ZX and CuPc free complex. Unlike the case on Al, CuPc was accommodated inside ZX, as confirmed from lattice parameter increment (from 25.101 of ZX to 25.250Å of CuPc/ZX) and decreasing both SBET and pore volume (705m2/g, 0.550cm3/g) as compared to the neat zeolite (837m2/g, 0.684cm3/g). Bending modes vibrations of δC–H showed bands at 1041 and 970cm−1 for CuPc/Al where CuPc/ZX did not, suggesting that these bonds are formed while CuPc vibrating on the former. Contrarily, they are restricted in the latter proposing accommodation of the complex inside zeolite cages as emphasized from Δ S values that showed marked decrease in disorderness (−29J/molK) compared with CuPc (−13J/molK). In accordance, Q band revealed a red shift from 614 to 632nm. A very strong photo-oxidation capability of oxidizing CN− was exhibited for the encapsulated complex (CuPc/ZX; 100% removal in 1h; rate constant=0.1min−1) comprehending the importance of electron transfer reactions within ZX to external surfaces, and the zeolite framework that seems participating efficiently in the electron transfer process.
Keywords: CuPc/ZX; CuPc/Al; Characterization; Photocatalysis; Cyanide removal
l-Proline anchored hydrotalcite clays: An efficient catalyst for asymmetric Michael addition by S. Vijaikumar; A. Dhakshinamoorthy; K. Pitchumani (pp. 25-32).
l-Proline-anchored hydrotalcite catalyst was tested for the asymmetric Michael additions between nitroalkene and acetone and between α,β-unsaturated ketones and nitroalkanes. This chiral amino catalyst acts as a better catalyst for both enamine types as well as for iminium-type Michael additions. Suitable mechanisms are proposed. ▪l-Proline has been immobilized onto the inter layers of hydrotalcite clay. Thisl-proline-anchored hydrotalcite (HTLP) has good catalytic activity in the asymmetric Michael addition reaction between β-nitrostyrene and acetone. An inversion in the asymmetric induction is observed when compared to the reaction using purel-proline catalysis. The same Michael adduct has been prepared by two methods: first, by addition of acetone to β-nitrostyrene (an enamine-type addition) and secondly, by addition of nitromethane to benzylideneacetone (an iminium-type addition). This chiral amino catalyst (HTLP) acts as a better catalyst for both enamine-type and iminium-type additions, indicating clearly that hydrotalcite is a better support forl-proline. It also acts as a cocatalyst in the title reaction. Suitable mechanisms are proposed for both enamine- and iminium-type additions.
Keywords: Hydrotalcite; l; -Proline; Immobilization; Michael addition; Asymmetric synthesis
Effect of phosphoric acid on catalytic combustion of trichloroethylene over Pt/P-MCM-41 by Dao Li; Yi Zheng; Xingyi Wang (pp. 33-41).
Pt-loaded MCM-41 catalysts modified with phosphorus acids at various Si/P ratios were prepared. Phosphoric acid molecules may react with surface Si–OH groups, which prevented the direct attack of H2PtCl4 on mesostructure and improved the structural stability of Pt-loaded catalysts. Ammonia temperature-programmed desorption (NH3-TPD) indicated that P-MCM-41 samples possessed weak Brønsted acidities, and the Brønsted acidities on P-MCM-41 decreased with the incorporation of Pt, depending on the phosphoric acid loading. The interaction of Pt with phosphoric species resulted in the change of Pt oxidation state and the Brønsted acidity strength. The results of catalytic combustion of trichloroethylene over these catalysts showed that the modification with phosphoric acid endowed the catalysts with good catalytic performance of high trichloroethylene conversion and absence of tetrachloroethylene. The combination of Brønsted acidities and oxidation state Pt would propose a novel catalytic material suitable for the combustion of chlorinated volatile organic compounds. Carbon deposit over acid sites resulted in the deactivation of Pt/P-MCM-41 catalysts, and the deactivated catalysts were recovered at 500°C in air.Pt-loaded MCM-41 catalysts modified with phosphorus acids at various Si/P ratios were prepared. High activity for catalytic combustion of TCE on these catalysts was observed without the formation of tetrachloroethylene. The combination of Brønsted acidities and oxidation state Pt would propose a novel catalytic material suitable for the combustion of CVOC.▪
Keywords: Trichloroethylene; Phosphoric acid; MCM-41; Catalytic combustion; Platinum catalyst
A facile and efficient pinacol–pinacolone rearrangement of vicinal diols using ZnCl2 supported on silica as a recyclable catalyst by Dharita J. Upadhyaya; Shriniwas D. Samant (pp. 42-51).
An efficient pinacol rearrangement of various primary, secondary and tertiary diols has been investigated using ZnCl2/SiO2 (silzic) as solid acid catalyst. ZnCl2 co-ordiantes with surface hydroxyl groups of silica to form –O–Zn–Cl as Lewis acid sites on silica surface. The interesting facet of this communication is the highly efficient synthesis of cyclic spiroketones using silzic as reusable catalyst hitherto unknown. ▪An efficient pinacol rearrangement of variety of primary, secondary and tertiary, symmetrical as well as asymmetrical diols has been investigated using ZnCl2/SiO2 (silzic) as solid acid catalyst. The catalyst is prepared by co-grinding silica gel with anhydrous ZnCl2 followed by thermal activation. The nature of interaction has been investigated using powder XRD, TG-DTA and DSC analyses, FT-IR spectroscopy and by testing the catalytic properties in pinacol–pinacolone rearrangement. FT-IR spectra of catalyst using pyridine as probe molecule shows presence of predominant Lewis acid sites. The results of FT-IR, TG-DTA, DSC analyses and XRD indicated that dispersed ZnCl2 co-ordinates with surface hydroxyl groups leading to formation of a new zinc ion species of –O–Zn–Cl as Lewis acid sites. Various highly substituted aldehydes and ketones were obtained in high isolated yield with excellent selectivity. The catalyst was found to be highly efficient and reusable without any loss of activity. The fact that ZnCl2 did not leach in presence of 1,2-dichloroethane as solvent makes silzic an alternative heterogeneous acid catalyst for pinacol rearrangement to the conventional homogeneous acids. The other interesting facet of this communication is highly efficient synthesis of cyclic spiroketones using silzic as reusable solid acid catalyst hitherto unknown.
Keywords: Pinacol–pinacolone Rearrangement; Zinc chloride supported on silica; Silzic; Spiroketones
Oxidation of 2,3,6-trimethylphenol with potassium peroxymonosulfate catalyzed by iron and cobalt phthalocyanine tetrasulfonates in a methanol–water mixture by Yasemin Çimen; Hayrettin Türk (pp. 52-58).
Oxidation of 2,3,6-trimethylphenol (TMP) with potassium peroxymonosulfate (KHSO5) was efficiently catalyzed by iron phthalocyanine tetrasulfonate ([FePcTS]) in a 8-to-1 methanol–water mixture. When cobalt phthalocyanine tetrasulfonate ([CoPcTS]) was used as catalyst instead of [FePcTS], slower reaction rate for the oxidation was observed. ▪Oxidation of 2,3,6-trimethylphenol (TMP) with potassium peroxymonosulfate (KHSO5) catalyzed by iron phthalocyanine tetrasulfonate ([FePcTS]) in an 8-to-1 methanol–water mixture resulted in 43.2–100.0% conversion of TMP and 60.5–100.0% selectivity of trimethyl-1,4-benzoquinone (TMQ) after 5min at ambient temperature when the oxidant/substrate molar ratio was changed from 1 to 4 at a constant substrate/catalyst molar ratio of 300. Higher conversion of TMP and selectivity of TMQ were obtained when the reaction time was extended to 30min. A minor product, 2,2′,3,3′,5,5′-hexamethyl-4,4′-biphenol (BP), was formed in reactions carried out with an oxidant/substrate molar ratio of 3 or lower. When cobalt phthalocyanine tetrasulfonate ([CoPcTS]) was employed as a catalyst instead of [FePcTS], a slower reaction rate for the oxidation of TMP was observed and the product composition was about the same as that observed in the [FePcTS] catalysis. Oxone, which is a solid consisting of a 2:1:1 mixture of KHSO5, KHSO4, and K2SO4, was used to introduce KHSO5 into the reaction mixture.
Keywords: 2,3,6-Trimethylphenol; Trimethyl-1,4-benzoquinone; Phthalocyanine tetrasulfonate; Peroxymonosulfate; Oxidation
Electrocatalytic properties of ruthenium modified with Te metal for the oxygen reduction reaction by Yoshinori Hara; Noriko Minami; Hiroaki Itagaki (pp. 59-66).
Chalcogenide (S, Se, and Te)-modified ruthenium catalysts demonstrated the electrocatalytic activities in the order of Ru–Te>Ru–Se>Ru–S for the oxygen reduction reaction (ORR) in acidic media. The catalyst obtained at a Te/Ru=2 produced the maximum value current density, the reaction was confirmed to form a RuTe2 intermetallic compound. RuTe2/C showed a comparable activity with regard to the cathodic current to that of the conventional Pt/C catalyst at the same metal loading. ▪Chalcogenide (S, Se, and Te)-modified ruthenium catalysts prepared by a wet impregnation method demonstrated the electrocatalytic activities in the order of Ru–Te>Ru–Se>Ru–S for the oxygen reduction reaction (ORR) in acidic media. The ORR activity of Ru–Te supported on carbon black (Ru–Te/C) significantly depends on the initial Te/Ru atomic ratio. The catalyst obtained at a Te/Ru=2 produced the maximum value current density, the reaction was confirmed to form a RuTe2 intermetallic compound, based on the XRD. The TEM image of RuTe2/C shows that the loaded RuTe2 particles consist of well-crystallized plate-like particles with diameters of about 10nm. Rotating ring disk electrode (RRDE) measurements indicated that RuTe2/C generates about 4% H2O2 during the ORR, preferentially proceeding via the four-electron charge transfer pathway to form H2O. RuTe2/C showed a comparable activity with regard to the cathodic current to that of the conventional Pt/C catalyst at the same metal loading. Unfortunately, the onset electrode potential for oxygen reduction by RuTe2/C was more negative than that catalyzed by the commercial Pt/C by about 0.2V.
Keywords: Ruthenium chalcogenide; Oxygen reduction reaction; Ruthenium ditelluride; Four-electron reduction; PEFC
Oxidation of cyclohexane over iron and copper salen complexes simultaneously encapsulated in zeolite Y by Binbin Fan; Hongyu Li; Weibin Fan; Chun Jin; Ruifeng Li (pp. 67-75).
Fe(salen) and Cu(salen) complexes simultaneously encapsulated in zeolite Y by the flexible ligand method showed much higher activity than the neat Cu(salen) and Fe(salen) or the Cu(salen)/Y and Fe(salen)/Y or their physical mixtures in the oxidation of cyclohexane with aqueous H2O2 solution as a result of the existence of a synergetic effect.▪Iron and copper salen complexes have been simultaneously encapsulated in zeolite Y by using the flexible ligand method, as substantiated by infrared spectroscopy, diffuse reflectance UV–vis spectroscopy, thermo-gravimetric and differential-thermal analyses and N2 adsorption/desorption experiments at −196°C. The prepared material showed much higher activity than the neat Cu(salen) and Fe(salen) or the Cu(salen)/Y and Fe(salen)/Y or their physical mixtures in the oxidation of cyclohexane with H2O2. The existence of a synergetic effect is the cause of this high activity. This synergetic effect may originate from the formation of dinuclear salen complexes and/or the interaction of adjacent partially coordinated Cu(salen) and Fe(salen) complex molecules through the lattice oxygen of the zeolitic host. This assumption is supported by extensive investigations of the catalytic performance of different types of catalysts as well as cyclic voltammetry and diffuse reflectance UV–vis spectroscopy. The optimum molar ratio of Cu2+ to Fe3+ in the prepared material is 1.93:1. The reaction time and temperature strongly influenced the catalytic performance. Although this catalyst was not highly stable because of degradation of metal salen complexes in the presence of H2O2 aqueous solution, this work provides a new route for designing and preparing highly active “ship-in-a-bottle” materials.
Keywords: Cyclohexane oxidation; Salen; Ship-in-a-bottle material; Synergetic effect; Zeolite-encapsulated complex
Measurements of number and strength distribution of Brønsted and Lewis acid sites on sulfated zirconia by ammonia IRMS–TPD method by Naonobu Katada; Takuya Tsubaki; Miki Niwa (pp. 76-86).
Number and strength distributions of Brønsted and Lewis acid sites were completely analyzed by the ammonia IRMS–TPD method. The detected presence of strong Brønsted acid sites on samples prepared by impregnation of H2SO4 on low temperature-calcined zirconia was in agreement with the high catalytic activity.▪The ammonia IRMS–TPD (infrared-mass spectroscopy/temperature-programmed desorption) method was applied to sulfated zirconia in order to measure the acidic properties [number, strength and type (Brønsted or Lewis) of acid site]. Because the TPD profile was broad, the acid strength distribution was calculated by means of a simulation method on the basis of theoretical equations. The Brønsted acid strength distribution changed according to the calcination temperature of zirconia support. The presence of strong Brønsted acid site on samples prepared by an equilibrium adsorption of H2SO4 was in agreement with the high catalytic activity of these samples for reaction (mainly cracking) of heptane.
Keywords: Sulfated zirconia catalyst; Acidic property; Ammonia IRMS–TPD; Alkane cracking
Co-decorated carbon nanotubes as a promoter of Co–Mo–K oxide catalyst for synthesis of higher alcohols from syngas by Xiao-Man Wu; Yan-Yan Guo; Jin-Mei Zhou; Guo-Dong Lin; Xin Dong; Hong-Bin Zhang (pp. 87-97).
A Co-decorated multi-walled carbon nanotube (MWCNT)-promoted Co–Mo–K oxide catalyst was developed that displayed excellent performance for the selective formation of C2–9-alcohols from syngas. The space–time-yield of C2–9-alcohols over the Co1Mo1K0.05–12%(4.2% Co/MWCNT) catalyst was significantly higher than that of both the MWCNT-free host catalyst and the simple MWCNT-promoted counterpart. The mechanism of the improved performance for the higher alcohol synthesis (HAS) with the addition of 4.2% Co/MWCNT to the Co1Mo1K0.05 host was investigated and discussed. ▪A metal cobalt-decorated multi-walled carbon nanotube (MWCNT)-promoted Co–Mo–K oxide-based catalyst was developed, with excellent performance for the selective formation of C2–9-alcohols from syngas. Under reaction condition of 5.0MPa and 593K, the space–time-yield of C2–9-alcohols reached 628mg/(gh) over the Co1Mo1K0.05–12%(4.2% Co/MWCNT) catalyst. The addition of a minor amount of the Co-decorated MWCNTs into the Co1Mo1K0.05 host catalyst caused little change in the apparent activation energy for the higher alcohol synthesis (HAS), but led to an increase of surface concentration of the two kinds of catalytically active species, CoO(OH)/Co3O4 and Mo4+, both closely associated with the alcohol generation. Addition of 5% CO2 in the feed gas at properly elevated reaction temperature (593K) could further enhance the surface concentration of those active Mo and Co species. An excellent adsorption performance of the Co-decorated MWCNTs as promoter for H2 would be conducive to generating a surface micro-environment with a high concentration of H-adspecies on the functioning catalyst, thus increasing the rate of surface hydrogenation reactions in the HAS. In addition, high concentration of H-adspecies on the catalyst would, through synergistic action with the CO2 in the feed gas, greatly inhibit the water–gas-shift side-reaction. All these factors contribute to an increase in the yield of alcohols.
Keywords: Co-decorated carbon nanotubes; Co–Mo–K catalyst; Higher alcohol synthesis
Effective photocatalytic decomposition of VOC under visible-light irradiation on N-doped TiO2 modified by vanadium species by Shinya Higashimoto; Wataru Tanihata; Yoshinori Nakagawa; Masashi Azuma; Hiroyoshi Ohue; Yoshihisa Sakata (pp. 98-104).
The added vanadium species having oxidation states between +IV and +V that interact with surface N-TiO2 play a significant role as redox mediators in the enhancement of photocatalytic decompositions of volatile organic compounds (VOC) under visible light irradiation.▪Photocatalytic activity of nitrogen-doped TiO2 (N-TiO2) will greatly increase by adding vanadium species for the decomposition of various volatile organic compounds (VOC) under both visible light and UV-light irradiation. The added vanadium species having oxidation states between +IV and +V that interact with surface N-TiO2 play significant roles as redox mediators in the enhancement of photocatalytic activity.
Keywords: N-doped TiO; 2; Photocatalyst; Visible light; Vanadium; VOC; Decomposition; ESR; Photocharged potential; Redox mediator
Molecular modelling and experimental studies on steam gasification of low-rank coals catalysed by iron species by George Domazetis; Monthida Raoarun; Bruce D. James; John Liesegang (pp. 105-118).
Catalytic steam gasification of brown coal containing iron species at 900°C gave an apparent turn-over of 12–22mole C/mole Fe, and high H2 yield. The molecular mechanism was H2O sticking on [Fe–C] to form the coordination bond [Fe←OH2], hydrogen abstraction and iron hydride to yield H2, and oxygen insertion into [Fe–C], followed by decomposition of [Fe–O–C] into [Fe–C] and CO. ▪Pyrolysis and catalytic steam gasification of brown coal containing iron hydroxyl complexes have been investigated experimentally and with semi-empirical and density functional theory molecular modelling. Pyrolysis yielded mainly CO2, CO, and reduced iron species. Catalytic steam gasification at 900°C after 15min, consumed 20wt.% additional char and a higher than expected yield of H2 due to post-gasification reactions; inorganic and organic oxygen in char increased compared to pyrolysis. Apparent turnover numbers for catalytic gasification were 12–22mole of carbon per mole of iron. The distribution of iron species in brown coal indicated small iron clusters are likely to form on heating; pyrolysis was thus modelled using molecules of char with [Fe3], [Fe5] and [Fe3O], and the active site for gasification was shown to be [Fe–C]. The mechanism of catalytic gasification involved H2O chemi-adsorbed on [Fe–C], formation of the [Fe←OH2] coordination bond, with H2 produced via iron hydride complexes. Formation of CO was via oxygen insertion into [Fe–C] to form [Fe–O–C] that decomposed into CO and another [Fe–C] site. Lower activation barriers were obtained for concerted chemistry involving iron-hydrides. Active sites in char were accessible to H2O as pores had developed around iron species; large sized iron species were not catalytically active but caused large pores to form in char.
Keywords: Steam gasification; Brown coal; Iron catalyst; Molecular models
Kinetic model for the dimerisation of 1-hexene over a solid phosphoric acid catalyst by Renier Schwarzer; Elizabeth du Toit; Willie Nicol (pp. 119-124).
A sequential reaction pathway is proposed for this reaction. The three reaction steps included in the model are firstly linear isomerisation of 1-hexene followed by skeletal isomerisation and finally dimerisation and cracking (see figure). The model is tested by using a skeletal hexene isomer – 2,3-dimethyl-2-butene (DMB) – as reactant.▪Batch kinetic experiments at 150°C, 200°C and 250°C showed that the reaction can be modeled with a three step sequential reaction scheme. This involves firstly linear isomerisation of 1-hexene followed by skeletal isomerisation and finally dimerisation and cracking. The first and last steps in the sequence are modeled as reversible reactions. When first order reaction kinetics is assumed for each of the reactions, the model gave a very good representation of the experimental data. In order to test the validity of the series pathway hypothesis, the reaction was repeated with a skeletal hexene isomer – 2,3-dimethyl-2-butene (DMB) – as reactant. Although the rate and equilibrium constants for the third reaction step as obtained from the 1-hexene conversion data gave a good prediction of the DMB conversion at 200°C and 250°C, it failed to predict the reaction rate at 150°C. This suggests that a different reaction pathway – where linear hexene isomers are directly converted to dimer product – becomes more significant at lower temperatures. The relatively high activation energy of the linear to skeletal hexene reaction may be to blame for this observation. However, this needs to be confirmed be further experimental work. The same equilibrium conversions of both 1-hexene and DMB were observed at all three temperatures investigated—suggesting that the equilibrium conversion is independent of the type of hexene isomer in the reaction mixture.
Keywords: Solid phosphoric acid; Hexene; Dimerisation; Isomerisation; Kinetic modeling
Aluminium foams as structured supports for volatile organic compounds (VOCs) oxidation by Oihane Sanz; F. Javier Echave; Maialen Sánchez; Antonio Monzón; Mario Montes (pp. 125-132).
In this work aluminium foams were studied as structured supports for the elimination of volatile organic compounds (VOCs, toluene). Foams of different pore density, 10, 20 and 40pores per inch (ppi), were used in an anodisation process to produce a very thin layer of alumina. This alumina layer was impregnated with the active phase, platinum, by wet impregnation. Anodisation process variables (temperature, time and current density) and their effect on the alumina layer were studied. Finally, their catalytic activity was tested in the toluene complete oxidation reactions. Catalytic activity increases both with the increasing platinum content and with the pore density of the foam showing the importance of the mass-transfer phenomena (contact between the gas phase and the solid catalyst).Aluminium foams were studied as structured supports for the elimination of volatile organic compounds (toluene). Foams were used in an anodisation process to produce a very thin layer of alumina and impregnated with platinum. The effect of the anodisation variables on the alumina layer was studied and their catalytic activity was tested in the toluene oxidation. ▪
Keywords: Aluminium foams; Catalytic structured supports; VOC catalytic oxidation; Aluminium anodisation
Preparing Au/ZnO by precipitation–deposition technique by Kátia R. Souza; Adriana F.F. de Lima; Fernanda F. de Sousa; Lucia Gorenstin Appel (pp. 133-139).
This report presents results related to the preparation of Au/ZnO using the deposition–precipitation technique. Many samples were synthesized taking into account different pH values, gold concentration, procedures and contact times between the gold precursor and support. The exposure of gold compounds to radiation in the visible range was also examined during the preparation. These syntheses show that precipitation–deposition is, in this case, an ionic exchange. It could be observed that exposure to light and competition among anions change the gold content of the catalyst. Therefore, these are important parameters in the preparation of gold catalyst by ionic exchange. The results also show that by using this technique it is possible to prepare active catalysts for the preferential oxidation of carbon monoxide (PROX) reaction.This report presents results related to the Au/ZnO preparation by precipitation–deposition, which is in this case an ionic exchange. As exposure to light and competition among anions change the gold content they are important parameters in Au/ZnO synthesis. These results show that using this technique it is possible to prepare active catalysts for preferential oxidation of carbon monoxide (PROX) reaction.▪
Keywords: Gold; Zinc; Precipitation–deposition; Ionic exchange
SO2 poisoning of LaFe0.8Cu0.2O3 perovskite prepared by reactive grinding during NO reduction by C3H6 by Runduo Zhang; Houshang Alamdari; Serge Kaliaguine (pp. 140-151).
SO2 poisoning of nanoscale LaFe0.8Cu0.2O3 during NO+C3H6+O2 reaction was investigated. A reversible poisoning at SO2 ≤20ppm was found. SO2 (80ppm) leads to a destruction of the perovskite structure and an irreversible activity loss. Partial regeneration of this spent sample was realized by treating in 5% H2/He at 500°C.▪Nanoscale LaFe0.8Cu0.2O3 was prepared by reactive grinding, characterized by XRD, SEM, H2-TPR, O2-, NO+O2-, and C3H6-TPD (with and without SO2), FTIR, tested for catalytic reduction of NO by C3H6 and aged in presence of SO2 to investigate the effect of sulfurous species on its catalytic behavior. Two distinct poisoning mechanisms depending on SO2 feed concentration were thus proposed. At low concentration SO2 (≤20ppm) can cause a reversible poisoning due to the competitive adsorption of SO2 and reactants as well as the coverage of active sites by surface sulfite and sulfate species. By contrast, 80ppm SO2 leads to a severe sulfatation with destruction of the perovskite structure and the generation of La2(SO4)3 and Fe2O3 phases resulting in an irreversible loss of activity in NO reduction by C3H6. Partial regeneration of this spent sample can be realized by releasing sulfur from the perovskite under a 5% H2/He atmosphere followed by reconstructing the perovskite structure under an oxygen containing atmosphere.
Keywords: Perovskite; Reactive grinding; NO reduction; Propene; SO; 2; poisoning; TPD; FTIR