Applied Catalysis B, Environmental (v.35, #3)
The influence of NO x on soot oxidation rate: molten salt versus platinum by Agus Setiabudi; Barry A.A.L van Setten; Michiel Makkee; Jacob A Moulijn (159-166).
A systematic study was carried out to assess the influence of simulated diesel exhaust on the activity of molten salt, Cs2SO4·V2O5, supported on ceramic foam and Pt/γ-alumina catalysts in the oxidation of diesel soot. Gas compositions containing O2, NO x , CO, C3H6, and SO2 were used. The activity of molten salt catalyst, an active catalyst for the oxidation of soot with O2, is slightly affected by the gas component due to NO2 already present in NO x . In contrast, the presence of NO x , significantly increases the soot oxidation rate with platinum catalyst. These changes were due to the catalytic oxidation of NO to NO2 with platinum, followed by soot oxidation with NO2. Three configurations are compared, viz. a fixed bed containing a physical mixture of Pt catalyst and soot, Pt catalyst upstream of a fixed bed containing soot, and Pt catalyst upstream of soot loaded on ceramic foam supported molten salt. The reaction cycle of oxidation of NO, followed by soot oxidation with the NO2 produced, was observed only in a physical mixture of platinum catalyst and soot.
Keywords: Molten salt; Platinum; Soot oxidation; No x ; Reaction cycle;
Pyrylium salt-photosensitized degradation of phenolic contaminants present in olive oil wastewater with solar light by Miguel A. Miranda; Marı́a L. Marı́n; Ana M. Amat; Antonio Arques; Sergio Seguı́ (167-174).
Photodegradation of tyrosol and p-hydroxyphenylacetic acid, present in olive oil wastewater, can be achieved using 2,4,6-triphenylpyrylium salt as solar photocatalyst. Fluorescence quenching measurements support the involvement of electron transfer as the key step in this process, with formation of substrate-derived radical cations. Important degradation yields are achieved. Other advanced oxidation methods (ozone and/or UV-radiation) have been tested as well; as expected, tyrosol and p-hydroxyphenylacetic acid abatement is faster, but ozone and UV are dangerous and expensive for industrial uses. However, ozone and UV do not show an important synergistic effect in tyrosol and p-hydroxyphenylacetic acid oxidation. p-Hydroxymandelic acid and p-hydroxybenzaldehyde have been detected and identified by HPLC as intermediates; on the basis of these data, a reaction mechanism involving oxidation at the benzylic position is proposed.
Keywords: 2,4,6-Triphenylpyrylium; Tyrosol; p-Hydroxyphenylacetic acid; Photodegradation; Solar light; Oxidation; Ozone; Wastewater;
Catalytic properties of La0.8A0.2MnO3 (A = Sr, Ba, K, Cs) and LaMn0.8B0.2O3 (B = Ni, Zn, Cu) perovskites by Florina-Corina Buciuman; Florin Patcas; Jean-Christophe Menezo; Jacques Barbier; Thomas Hahn; Hans-Günther Lintz (175-183).
The perovskites La0.8A0.2MnO3 (A=Sr, Ba, K, Cs) and LaMn0.8B0.2O3 (B=Ni, Zn, Cu) were studied as catalysts for the oxidation of lean mixtures of hydrogen or propene in the temperature range of 200–450°C (hydrogen) and 150–550°C (propene), respectively. The catalytic features were correlated with the redox behavior of the oxides as revealed by temperature-programmed reduction (TPR) experiments. The highest activity for hydrogen oxidation was found over strontium, barium and copper substituted manganites, whereas in the case of propene oxidation the copper substituted perovskite showed substantially lower activity, which was assigned to the stronger bonding of the produced carbon dioxide to the copper centers. The results are discussed with regard to the concepts of suprafacial and intrafacial catalysis. Apart from the temperature control, the occurrence of one or another of the two mechanisms is imposed by the nature of the substituted cation.
Keywords: Perovskite; Lanthanum manganite; Hydrogen; Propene; Oxidation; Catalyst;
Preparation, characterization and activity of novel silica-pillared layered titanoniobate supported copper catalysts for the direct decomposition of NO by Xueguang Wang; Wenhua Hou; Xiaoshu Wang; Qijie Yan (185-193).
A series of silica-pillared layered titanoniobate supported copper catalysts (Cu/Si-TiNbO5) were prepared for the direct decomposition of NO. It was found that Cu/Si-TiNbO5 catalysts were highly active for the reaction of NO (0.1 vol.% in He) decomposition in the space velocity range of 3000–30,000 cm3 g−1 h−1. The 3.5 wt.% Cu/Si-TiNbO5 catalyst showed the highest conversion into N2 for NO decomposition. While 2.0 wt.% Cu/Si-TiNbO5 had the highest specific activity at low temperature (≤550°C) and 1.0 wt.% Cu/Si-TiNbO5 showed the highest specific activity at high temperature (>550°C). XRD and temperature-programmed reduction (TPR) results indicated that there existed well-dispersed copper oxide species and large copper oxide particles in the catalysts. Well-dispersed copper oxide species were reduced more easily than large copper oxide particles by H2. X-ray photoelectron spectra (XPS) and Auger electron spectra (AES) results revealed that Cu+ species existed in Cu/Si-TiNbO5 catalysts and that the copper oxide species in Cu/Si-TiNbO5 catalysts after used for NO decomposition were different from those before the reaction. Well-dispersed copper oxide species were active for NO decomposition and the most active sites might be the dimeric copper oxide species over the support.
Keywords: NO decomposition; Copper oxide; Layered titanoniobate; Pillaring; Silica;
Catalytic activity of Co-Mg-Al, Cu-Mg-Al and Cu-Co-Mg-Al mixed oxides derived from hydrotalcites in SCR of NO with ammonia by Lucjan Chmielarz; Piotr Kuśtrowski; Alicja Rafalska-Łasocha; Dorota Majda; Roman Dziembaj (195-210).
M-Mg-Al hydrotalcites (where M=Cu2+, Co2+ and Cu2++Co2+) with M ranging from 5 to 20% (as atomic ratio) were prepared by co-precipitation method. Obtained samples were characterised by XRD and TGA techniques. The influence of transition metal content on thermal decomposition of hydrotalcites was observed. Calcination of the hydrotalcites at 600°C resulted in the formation of mixed oxides with surface areas in the range 71–154 m2/g. Calcined hydrotalcites were tested as catalysts in the selective reduction of NO with ammonia (NO-SCR). The catalytic activity depends on the kind of transition metal, as well as its content. For the NO-SCR the following reactivity order was found: Cu-Mg-Al>Cu-Co-Mg-Al>Co-Mg-Al. Temperature-programmed methods (TPD, TPSR, stop flow-TPD), as well as FT-IR spectroscopy have been applied to determine interaction of NO and NH3 molecules with the catalyst surface.
Keywords: Hydrotalcites; Cobalt; Copper; Mixed oxides; DeNO x ; NH3; TPD; TPSR;
Hydrodechlorination of 1,2-dichloroethane catalyzed by Pt–Cu/C: effect of catalyst pretreatment by David R. Luebke; Lalith S. Vadlamannati; Vladimir I. Kovalchuk; Julie L. d’Itri (211-217).
The catalytic performance of Pt–Cu/C with Pt/Cu atomic ratios of 1:1 and 1:3 in the reaction of 1,2-dichloroethane dechlorination at 200°C and atmospheric pressure was investigated to understand the molecular phenomena governing the change in ethylene selectivity with time on stream (TOS). When the Pt1–Cu3/C catalyst is prereduced in H2 at 220°C, ethane is the major product at early TOS, while ethylene is the major product at longer TOS. Pretreatment in flowing He at 220°C eliminates the transient behavior and significantly increases steady state selectivity toward ethylene for both Pt–Cu catalysts. The transient behavior is also eliminated after reduction at 220°C followed by treatment with HCl at the same temperature. Quite different behavior is observed with a Pt/C catalyst in that ethane is the major product regardless of the type of pretreatment. The results are interpreted via a molecular scheme including the formation of mixed PtCuCl x species during the non-reductive pretreatment. These PtCuCl x particles are converted into the corresponding alloy during subsequent reduction by H2 or reaction mixture. The enrichment of the catalysts’ surface with Cu results from the pretreatment with HCl.
Keywords: Hydrogen-assisted dechlorination; 1,2-Dichloethane; Ethylene; Carbon; Platinum; Copper; Alloying;
UV Raman studies of adsorbed oxygen and NO x species on Pt/γ-alumina catalysts by Dairene Uy; Ann E. O’Neill; Willes H. Weber (219-225).
Raman spectra at 244 nm are obtained in situ from several Pt/γ-Al2O3 catalysts under gas flows containing O2, CO, NO2, and H2 at temperatures from 20 to 600°C. With O2 or NO2, a broad peak at 571 cm−1 is observed which we attribute to the Pt–O stretch mode of atomic oxygen. This marks the first direct spectroscopic observation of this fundamental species on a real catalyst. The peak can be easily removed with CO or H2, even at room temperature, and the process is completely reversible. With NO2 exposure, several peaks associated with surface NO x species also appear, the most prominent of which is a nitrate line at 1048 cm−1. Under reaction conditions, at 350°C with a stoichiometric CO/O2/N2 gas stream, the steady-state O coverage on the Pt particles is about half of the maximum coverage achieved with only an O2 flow. This observation paves the way for future in situ studies of catalytic mechanisms addressing the role of atomic O as an intermediate.
Keywords: Raman (UV) spectroscopy; Platinum; Oxygen; Atomic oxygen adsorption; Nitrogen oxides; Alumina;
Highly active SO2-resistant ex-framework FeMFI catalysts for direct N2O decomposition by J Pérez-Ramı́rez; F Kapteijn; G Mul; J.A Moulijn (227-234).
Ex-framework FeMFI catalysts, prepared by isomorphous substitution of iron in the aluminosilicate or gallosilicate MFI-type framework and activation by calcination at 823 K and steaming (300 mbar H2O in N2) at 873 K, show high activity and stability in N2O decomposition in the presence of O2, CO2, H2O, and SO2. The N2O conversion of the ex-framework catalysts in simulated tail-gas mixtures was >80% at 800 K and 75,000 h−1. The specific activity per mole of Fe (turnover frequency, TOF) of the ex-framework catalysts in N2O–He is four to nine times higher than observed for catalysts prepared by conventional solid and liquid-ion exchange, and sublimation methods. The stability of ex-framework catalysts for the direct N2O decomposition, in the absence of any reductant, is remarkable, showing no significant deactivation (at N2O conversion levels ranging from 20 to 65%) after 600 h on stream. Sublimed and especially ion-exchanged FeZSM-5 catalysts show a strong irreversible deactivation in feed mixtures containing H2O and SO2. The effect of SO2 on the catalytic performance of FeMFI catalysts is discussed, as well as the applicability of the ex-framework FeMFI catalysts in fluid-bed combustion facilities.
Keywords: N2O decomposition; FeZSM-5; Ex-framework; Tail-gas; SO2; H2O;