Applied Catalysis B, Environmental (v.60, #3-4)
Contents continued (IV).
FULL TITLE (i).
CONTENTS OF VOLUME (I-II).
Cu-ZSM-5 zeolite highly active in reduction of NO with decane by L. Čapek; J. Dědeček; B. Wichterlová; L. Cider; E. Jobson; V. Tokarová (147-153).
The effect of framework aluminum content and local density on the NO x reduction with decane under lean burn conditions, i.e. in high excess of oxygen and water vapor (12%) over Cu-ZSM-5 zeolites with various Cu/Al and Si/Al ratios was investigated. The concentration of “Al pairs” located in one ring and balanced by divalent cations was estimated using divalent cobalt ions as probes. The portion of Cu ions located in vicinity of “Al pairs” or adjacent to a single framework AlO2 − entity was monitored by vis–NIR spectra of Cu2+ ions. The most active and stable Cu ions in C10H22-SCR-NO x under lean burn conditions appeared to be those located in vicinity of two Al atoms in one ring coordinated the cation.
Keywords: Cu-ZSM-5; NO reduction; SCR-NO x ; Lean burn conditions; Decane; Al pairs; UV–vis spectroscopy;
Photocatalytic degradation of acetone by Ni-doped titania thin films prepared by dc reactive sputtering by C.M. Visinescu; R. Sanjines; F. Lévy; V.I. Pârvulescu (155-162).
Two series of titania-based photocatalysts were prepared by the sputtering method, in Ar/H2O atmosphere, utilizing a Ti target modified with 1–6 Ni inserts. The first catalysts series (samples 1–5) was deposited under the total pressure of 6 × 10−3 mbar (16% water vapor), while for the second series (catalysts 6–9) the total pressure was 3 × 10−3 mbar (33% H2O). XRD data showed that Ni could accommodate to the titania matrix only within certain concentration limits. Ni presence in the catalysts composition does not influence significantly the morphology or the electric properties of the films, but exhibits a strong influence over the photocatalytic properties. The highest conversion in the photocatalytic decomposition of acetone was obtained in the first catalysts series for sample 2 (0.41 Ni at.%, conversion rate 47%), while in the second series, the most active catalyst was sample 7 (0.13 Ni at.%, conversion rate 25%). Reusing sample 3 for several runs leaded to an improvement in its catalytic behavior. The photocatalytic activity was found to be strongly influenced by the amount of Ni and the deposition conditions.
Keywords: Titania photocatalyst; Acetone photodecomposition; Nickel ions doping; XRD; AFM; DR-UV–vis;
Catalytic destruction of chlorinated POPs—Catalytic oxidation of chlorobenzene over PtHFAU catalysts by M. Taralunga; J. Mijoin; P. Magnoux (163-171).
Catalytic oxidation of monochlorobenzene (667 ppm) in wet air was investigated over PtHFAU(5) catalysts, differing by their Pt content (from 0 to 1.1 wt.%), their Pt dispersion (for identical Pt content) and the electronic state of Pt. PtHFAU(5) catalysts show a higher activity compared to more conventional PtAl2O3 and PtSiO2 samples.For a given temperature, chlorobenzene oxidation over PtHFAU(5) is independent of the platinum particles size. On the other hand, a plateau in activity is reached from 0.4 to 0.6% Pt.Amount of polychlorinated benzenes (PhCl2+) were produced in the order PtAl2O3 > PtSiO2 > PtHFAU(5). The formation of these compounds, especially PhCl2, over PtHFAU(5) was function on the Pt content (PhCl2 isomers appear only from 0.6% PtHFAU), and of the electronic state of Pt. Thus PhCl2, were mainly found over reduced Pt0 particles certainly through a chlorination of platinum (formation of PtCl x species). A reaction scheme for the PhCl2 formation was proposed.
Keywords: Catalytic combustion; Persistent organic pollutants; Chlorobenzene; Platinum; HFAU zeolites;
TiO2-SiO2 and V2O5/TiO2-SiO2 catalyst: Physico-chemical characteristics and catalytic behavior in selective catalytic reduction of NO by NH3 by Motonobu Kobayashi; Ryoji Kuma; Sinyuki Masaki; Noboru Sugishima (173-179).
TiO2-SiO2 with various compositions prepared by the coprecipitation method and vanadia loaded on TiO2-SiO2 were investigated with respect to their physico-chemical characteristics and catalytic behavior in SCR of NO by NH3 and in the undesired oxidation of SO2 to SO3, using BET, XRD, XPS, NH3-TPD, acidity measurement by the titration method and activity test. TiO2-SiO2, compared with pure TiO2, exhibits a remarkably stronger acidity, a higher BET surface area, a lower crystallinity of anatase titania and results in allowing a good thermal stability and a higher vanadia dispersion on the support up to high loadings of 15 wt% V2O5. The SCR activity and N2 selectivity are found to be more excellent over vanadia loaded on TiO2-SiO2 with 10–20 mol% of SiO2 than over that on pure TiO2, and this is considered to be associated with highly dispersed vanadia on the supports and large amounts of NH3 adsorbed on the catalysts. With increasing SiO2 content, the remarkable activity decrease in the oxidation of SO2 to SO3, favorable for industrial SCR catalysts, was also observed, strongly depending on the existence of vanadium species of the oxidation state close to V4+ on TiO2-SiO2, while V5+ exists on TiO2, according to XPS. It is concluded that vanadia loaded on Ti-rich TiO2-SiO2 with low SiO2 content is suitable as SCR catalysts for sulfur-containing exhaust gases due to showing not only the excellent de-NO x activity but also the low SO2 oxidation performance.
Keywords: TiO2-SiO2; V2O5/TiO2-SiO2 catalyst; SCR; SO2 oxidation; Acidity;
Heterogeneous photo-Fenton degradation of phenolic aqueous solutions over iron-containing SBA-15 catalyst by F. Martínez; G. Calleja; J.A. Melero; R. Molina (181-190).
A novel iron-containing mesostructured material has been successfully tested for the heterogeneous photo-Fenton degradation of phenolic aqueous solutions using near UV–vis irradiation (higher than 313 nm) at room temperature and close to neutral pH. This catalyst is a composite material that contains crystalline hematite particles embedded into the mesostructured SBA-15 matrix in a wide distribution of size (30–300 nm) and well dispersed ionic iron species within the siliceous framework. The outstanding physico-chemical properties make this material a promising photocatalyst leading to better activity than other unsupported iron oxides. An experimental design model has been applied to assign the weight of catalyst and hydrogen peroxide concentrations in the photo-Fenton processes over this particular material. The catalytic performance has been monitored in terms of aromatics and total organic carbon (TOC) conversions, whereas the catalyst stability was evaluated according to the metal leached into the aqueous solution. Hydrogen peroxide concentration plays an important role in the stability of the iron species, preventing their leaching out into the solution, in contrast to the effect shown in typical dark-Fenton reaction. The homogeneous leached iron species result in very little contribution to the overall photocatalytic process. Catalyst loadings of 0.5 g/L and concentration of hydrogen peroxide close to the stoichiometric amount have yielded a total abatement of phenol and a remarkable organic mineralization.
Keywords: Photo-Fenton; Heterogeneous catalysts; SBA-15; Experimental design and phenol;
Bimetallic Pt/Pd diesel oxidation catalysts by A. Morlang; U. Neuhausen; K.V. Klementiev; F.-W. Schütze; G. Miehe; H. Fuess; E.S. Lox (191-199).
Extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD) studies on supported bimetallic Pt/Pd diesel oxidation catalyst (Pt:Pd weight ratio 2:1) after various treatments were compared with those of monometallic Pd and Pt catalysts prepared under similar conditions. After calcination and thermal ageing, the coexistence of alloyed bimetallic Pt/Pd particles and of tetragonal PdO has been found in the bimetallic Pt/Pd catalyst. PdO is present in form of crystals at the surface of the Pt/Pd particles or as isolated PdO crystals on the support oxide. Bimetallic Pt/Pd nanoparticles were already formed in the Pt/Pd catalyst after calcination. Hydrogen treatment causes the formation of randomly alloyed Pt/Pd nanoparticles. In the thermally aged catalyst, a strong indication for an enrichment of Pt in the interior of the particle and of Pd at its outer shell was found. In the monometallic catalyst, the Pd is found to be completely oxidised already after calcination and to consist of metallic Pd in zero-valent state exclusively after reductive treatment. Ageing under hydrothermal oxidative atmosphere leads to complete oxidation of the Pd species. After calcinations, the catalytic activity of the Pt/Pd catalyst studied is comparable to those of monometallic Pt catalysts. In contrast to monometallic Pt catalysts, the alloyed system show significant stabilisation against sintering and a much higher activity after the thermal ageing step. This stabilisation of dispersion and the presence of Pt atoms on the surface of the Pt/Pd particles are considered to cause the higher catalytic activity of metallic particles for the oxidation of carbon monoxide and propene after ageing.
Keywords: Platinum; Palladium; Bimetallic; Alumina; Oxidation catalyst; EXAFS; XRD;
Cu-ZSM-5 zeolite highly active in reduction of NO with decane under water vapor presence by L. Čapek; K. Novoveská; Z. Sobalík; B. Wichterlová; L. Cider; E. Jobson (201-210).
Selective catalytic reduction of NO x (SCR-NO x ) with decane, and for comparison with propane and propene over Cu-ZSM-5 zeolite (Cu/Al 0.49, Si/Al 13.2) was investigated under presence and absence of water vapor. Decane behaves in SCR-NO x like propene, i.e. the Cu-zeolite activity increased under increasing concentration of water vapor, as demonstrated by a shift of the NO x –N2 conversion to lower temperatures, in contrast to propane, where the NO x –N2 conversion is highly suppressed. In situ FTIR spectra of sorbed intermediates revealed similar spectral features for C10H22– and C3H6–SCR-NO x , where –CH x , R–NO2, –NO3 −, Cu+–CO, –CN, –NCO and –NH species were found. On contrary, with propane –CH x , R–NO2, NO3 −, Cu+–CO represented prevailing species. A comparison of the in situ FTIR spectra (T–O–T and intermediate vibrations) recorded at pulses of propene and propane, moreover, under presence and absence of water vapor in the reaction mixture, revealed that the Cu2+–Cu+ redox cycle operates with the C3H6–SCR-NO x reactions in both presence/absence of water vapor, while with C3H8–SCR-NO x , the redox cycle is suppressed by water vapor. It is concluded that decane cracks to low-chain olefins and paraffins, the former ones, more reactive, preferably take part in SCR-NO x . It is concluded that formation of olefinic compounds at C10H22–SCR-NO x is decisive for the high activity in the presence of water vapor, while water molecules block propane activation. The increase in NO x –N2 conversion due to water vapor in C10H22–SCR-NO x should be connected with the increased reactivity of intermediates. These are suggested to pass from R–NO x → –CN → –NCO → NH3; the latter reacts with another activated NO x molecule to molecular nitrogen. The positive effect of water vapor on the NO x –N2 conversion is attributed to increased hydrolysis of –NCO intermediates.
Keywords: Cu-ZSM-5; NO reduction; HC–SCR; Lean-burn; FTIR;
Fabrication and characterization of Ag–TiO2 multiphase nanocomposite thin films with enhanced photocatalytic activity by Jiaguo Yu; Jianfeng Xiong; Bei Cheng; Shengwei Liu (211-221).
Ag–TiO2 multiphase nanocomposite thin films were prepared on quartz substrates by the liquid phase deposition (LPD) method from a mixed aqueous solution of ammonium hexafluouotitanate, silver nitrate and boric acid under ambient temperature and atmosphere followed by calcination at 500 °C for 1 h. The grain growth of anatase was depressed upon Ag+ doping. However, silver ions not only promoted (or catalyzed) the formation of brookite phase but also reduced the phase transformation temperature of anatase to rutile. With increasing AgNO3 concentration, the transmittance and band gap of the composite thin films decreased; however, the intensity of surface plasmon absorption (SPA) peaks increased and their peak position shifted to a longer wavelength range. When AgNO3 concentration was higher than 0.03 M, the prepared samples consisted of anatase, brookite, rutile and metal silver nanocrystal particles, and their grain size ranges were 5–30 nm. The photocatalytic activity of the Ag–TiO2 multiphase nanocrystal composite thin films prepared by this method exceeded that of pure TiO2 thin films by a factor of more than 6.3 when AgNO3 concentration was kept in the range of 0.03–0.05. This was attributed to the fact that there were many hetero-junctions, such as anatase/rutile, anatase/brookite, Ag/anatase, Ag/rutile and so on, existed in the Ag–TiO2 multiphase nanocomposite films.
Keywords: Ag; TiO2; Multiphase; Nanocomposite; Thin film; Liquid phase deposition; Photocatalytic activity;
Effects of zeolite structure and aluminum content on thiophene adsorption, desorption, and surface reactions by Antonio Chica; Karl G. Strohmaier; Enrique Iglesia (223-232).
The adsorption and desorption of thiophene and the reactions of thiophene-derived adsorbed species in He, H2, and O2 were examined on H-ZSM5, H-Beta, and H-Y with varying Si/Al ratios. Thiophene adsorption uptakes (per Al) were independent of Al content, but were above unity and influenced by zeolite structure (1.7, 2.2, and 2.9 on H-ZSM5, H-Beta, and H-Y). These data indicate that thiophene oligomers form during adsorption and that their size depends on spatial constraints within zeolite channels. Adsorption and oligomerization occur on Brønsted acid sites at 363 K. Thiophene/toluene adsorption from their mixtures show significant thiophene selectivity ratios (10.3, 7.9, and 6.4, for H-ZSM5, H-Beta, and H-Y zeolites), which exceed those expected from van der Waals interactions and reflect specific interactions with Brønsted acid sites and formation of toluene–thiophene reaction products. Treatment of thiophene-derived adsorbed species above 363 K in He or H2 led to depolymerization of thiophene oligomers and to the formation of unsaturated adsorbed species with a 1:1 thiophene/Al stoichiometry on all zeolites and at all Si/Al ratios. These unsaturated species desorb as stable molecules, such as H2S, hydrocarbons, and larger organosulfur compounds, formed via ring opening and hydrogen transfer from H2 or co-adsorbed species, and also form stranded unsaturated organic deposits. Smaller channels and higher Al contents preferentially formed H2S, benzotiophenes, and arene products during treatment in He or H2, as a result of diffusion-enhanced of secondary reactions of desorbed thiophene molecules with adsorbed thiophene-derived species. Only oxidative regeneration treatments led to full recovery of thiophene uptake capacities. A preceding treatment in H2, however, led to the partial recovery of thiophene-derived carbon atoms as useful hydrocarbons and decreased the amount of CO2 and SO2 formed during subsequent oxidative treatments required for regeneration.
Keywords: Thiophene; Zeolites; Adsorption; Desorption; Oligomerization; Regeneration;
In situ visible microscopic study of molten Cs2SO4·V2O5–soot system: Physical interaction, oxidation rate, and data evaluation by Agus Setiabudi; Niels K. Allaart; Michiel Makkee; Jacob A. Moulijn (233-243).
In situ visible microscopy has been used to characterise the physical interaction between soot and Cs2SO4·V2O5, a potentially attractive catalyst, under oxidation conditions. Upon heating to its melting point, Cs2SO4·V2O5 shows both mobility and attachment to the soot particle. This creates a liquid catalyst–soot–gas interface that is favourable for the oxidation reaction. Microscope image data can be used to estimate the oxidation rate, which is in good agreement with data obtained from TGA and fixed bed experiments.
Keywords: Cs2SO4·V2O5; Liquid catalyst; Diesel soot oxidation; Contact soot catalyst;
The photocatalytic destruction of the cyanotoxin, nodularin using TiO2 by Iain Liu; Linda A. Lawton; Detlef. W. Bahnemann; Peter K.J. Robertson (245-252).
Titanium dioxide (TiO2) photocatalysis has been used to initiate the destruction of nodularin, a natural hepatotoxin produced by cyanobacteria. The destruction process was monitored using liquid chromatography–mass spectrometry analysis which has also enabled the identification of a number of the photocatalytic decomposition products. The reduction in toxicity following photocatalytic treatment was evaluated using protein phosphatase inhibition assay, which demonstrated that the destruction of nodularin was paralleled by an elimination of toxicity.
Keywords: TiO2; Photocatalysis; Nodularin; Cyanotoxin;
Deactivation of V2O5-WO3-TiO2 SCR catalyst at a biomass-fired combined heat and power plant by Yuanjing Zheng; Anker Degn Jensen; Jan Erik Johnsson (253-264).
The deactivation of a commercial type V2O5-WO3-TiO2 monolith catalyst under biomass combustion was studied at a full-scale grate-fired power plant burning straw/wood using a slip stream pilot scale reactor. The aerosols in the flue gas consisted of a mixture of potassium chloride and sulphate. Three catalyst elements were exposed at 350 °C, and one element was exposed at 250 °C for comparison. The catalyst activity was measured in the reactor at the exposure temperature by addition of NH3 and extra NO. The activity, in terms of a first-order rate constant, dropped by 52% after about 1140 h indicating a very fast deactivation compared to coal firing. It was also found that the reactor temperature was not of importance for the deactivation rate. SEM-EDX analysis showed that particle deposition and pore blocking contributed to the deactivation by decreasing the diffusion rate of NO and NH3 into the catalyst. However, potassium also penetrated into the catalyst wall and the resulting average K/V ratio in the catalyst structure was high enough (about 0.3–0.5) for a significant chemical deactivation. Chemisorption studies carried out in situ showed that the amount of chemisorbed NH3 on the catalyst decreased as a function of exposure time, which reveals that Brøndsted acid sites had reacted with potassium compounds and thereby rendered inactive. When washed by 0.5 M H2SO4 the regenerated catalyst regains a higher activity than that of the fresh catalyst at temperatures higher than 300 °C, but even though reactivation is possible, the deactivation rate appears too high for practical use of the SCR process in straw combustion.
Keywords: Selective catalytic reduction; NO x ; V2O5-WO3-TiO2; Potassium; Aerosol; Deactivation; Regeneration; Biomass combustion;
Pt-Ba/alumina NO x storage-reduction catalysts: Influence of Ba loading on NO x storage behavior by M. Piacentini; M. Maciejewski; A. Baiker (265-275).
The NO x storage behavior of a series of Pt-Ba/Al2O3 catalysts, prepared by wet impregnation of Pt/Al2O3 with Ba(Ac)2, has been investigated. The catalysts with Ba loadings in the range 4.5–28 wt.% were calcined at 500 °C in air and subsequently exposed to NO pulses in 5 vol.% O2/He atmosphere. Catalysts were characterized by means of thermogravimetry (TG) combined with mass spectroscopy (MS) and XRD before and after exposure to NO pulses. Characterization of the calcined catalysts corroborated the existence of three Ba-containing phases which are discernible based on their different thermal stability: BaO, LT-BaCO3 and HT-BaCO3. Characterization after NO x exposure showed that the different Ba-containing phases present in the catalysts possess different reactivity for barium nitrate formation, depending on their interfacial contact. The different Ba(NO3)2 species produced upon NO x exposure could be distinguished based on their thermal stability. The study revealed that during the NO x storage process a new thermally instable BaCO3 phase formed by reaction of evolved CO2 with active BaO. The fraction of Ba-containing species that were active in NO x storage depended on the Ba loading, showing a maximum at a Ba loading of about 17 wt.%. Lower and higher Ba loading resulted in a significant loss of the overall efficiency of the Ba-containing species in the storage process. The loss in efficiency observed at higher loading is attributed to the lower reactivity of the HT-BaCO3, which becomes dominant at higher loading, and the increased mass transfer resistance.
Keywords: NO x storage efficiency; NO x storage mechanism; Pt-Ba/Al2O3; Effect of Ba loading; Stability of Ba-containing phases; Thermogravimetry combined with mass spectrometry; Pulse thermal analysis; Temperature programmed reaction–desorption; Barium oxide; Barium carbonate; Barium nitrate;
Ir-based additives for NO reduction and CO oxidation in the FCC regenerator: Evaluation, characterization and mechanistic studies by E.F. Iliopoulou; E.A. Efthimiadis; L. Nalbandian; I.A. Vasalos; J.-O. Barth; J.A. Lercher (277-288).
Ir-based additives, developed to reduce NO and CO emitted during the regeneration of spent fluid catalytic cracking (FCC) catalysts were characterized to correlate physicochemical properties with catalytic performance. Support, metal loading and the state of the metal significantly affected the catalytic performance. Increasing the Ir loading or using a Ce-promoted γ-alumina (CPBase) support results in the formation of larger Ir particles. Local reduction of iridium oxide surface in such particles leads to coexisting Ir and Ir2O phases being very beneficial for the catalytic activity.NO reduction and CO oxidation take place thermally at 700 °C. Increasing the O2 concentration in the feed favors CO oxidation at the expense of NO reduction. With 500ppmIr/CPBase and 1000ppmIr/CPBase additives, complete NO reduction and CO oxidation is achieved in the presence of 40% excess oxygen. Higher oxygen excess, however, reduces or eliminates the NOx reduction activity of these materials. IR studies suggest that NO reduction by CO proceeds on Ir/alumina additives via the dissociative adsorption of NO, the formation of NCO species on Ir and their migration to the alumina support, where N2 and CO2 are formed. IR spectroscopy indicates that Ce modifies the Ir surface enhancing the CO oxidation and enabling NO reduction via the NO2 formation.
Keywords: Ir; Ce; NO; Reduction; Regenerator; FCC;
Catalytic decomposition of nitrous oxide over catalysts prepared from Co/Mg-Mn/Al hydrotalcite-like compounds by L. Obalová; K. Jirátová; F. Kovanda; K. Pacultová; Z. Lacný; Z. Mikulová (289-297).
Co/Mg-Mn/Al hydrotalcite-like compounds with Co:Mg:Mn:Al molar ratios of 4:0:2:0, 2:2:2:0, 2:2:1:1, 4:0:1:1, 4:0:0:2 and 2:2:0:2 were prepared by coprecipitation method. The mixed oxides obtained by calcination at 500 °C were characterized using various techniques (XRD, IR, BET surface area measurements, TPD and TPR). The activities of calcined hydrotalcites were tested for N2O decomposition in an inert gas, and in the presence of oxygen and water vapor as well. Among the catalysts screened, the catalyst prepared from Co hydrotalcite containing Al and Mn as the trivalent cation showed the highest activity, which was retained in the presence of oxygen but was inhibited by water vapor. Redox properties of the catalysts play an important role in the reaction and optimum extent of reduction is necessary for achievement of the highest catalytic activity.
Keywords: Nitrous oxide; Catalytic decomposition; Layered double hydroxides; Mixed oxide catalysts;
Resistance to sulfur poisoning of hot gas cleaning catalysts for the removal of tar from the pyrolysis of cedar wood by Keiichi Tomishige; Tomohisa Miyazawa; Takeo Kimura; Kimio Kunimori; Naoto Koizumi; Muneyoshi Yamada (299-307).
In the partial oxidation of tar derived from the pyrolysis of cedar wood, the effect of H2S addition was investigated over non-catalyst, steam reforming Ni catalyst, and Rh/CeO2/SiO2 using a fluidized bed reactor. In the non-catalytic gasification, the product distribution was not influenced by the presence of H2S. Steam reforming Ni catalyst was effective for the tar removal without H2S addition, however, the addition of H2S deactivated drastically. In contrast, Rh/CeO2/SiO2 exhibited higher and more stable activity than the Ni catalyst even under the presence of high concentration of H2S (280 ppm). On the Ni catalyst, the adsorption of sulfur was observed by XPS and Ni species was oxidized during the partial oxidation of tar. In the case of Rh/CeO2/SiO2, the adsorption of sulfur was below the detection limit of XPS. This can be related to the self-cleaning of catalyst surface during the circulation in the fluidized bed reactor for the partial oxidation of tar derived from cedar pyrolysis.
Keywords: Biomass; Tar; Partial oxidation; Sulfur resistance; Hot gas cleaning;