Applied Catalysis B, Environmental (v.33, #3)
La, Ca and Fe oxide perovskites: preparation, characterization and catalytic properties for methane combustion by P Ciambelli; S Cimino; L Lisi; M Faticanti; G Minelli; I Pettiti; P Porta (193-203).
La1−x Ca x FeO3 (x=0.1, 0.2, 0.3, 0.4, 0.5) perovskites prepared by citrate method and calcined at 1073 K have been investigated as catalysts for methane combustion. The formation of the perovskite structure has been shown by X-ray diffraction (XRD) for all samples. The surface area (SA) values are in the range 3–6 m2 g−1 for the samples up to x=0.4, whereas SA is 0.7 m2 g−1 for the specimen with x=0.5. The atomic susceptibility increases with increasing in Ca content. The Fe4+/Fetotal ratio has been determined by both redox titration and TPR analysis. The amount of Fe4+ enhances with Ca substitution but the Fe4+/Ca2+ ratio is quite constant giving rise to an increasing formation of oxygen vacancies to preserve charge neutrality. All perovskites show a similar intrinsic activity in CH4 combustion with activation energy, E a, of about 23 kcal mol−1. A slightly lower value of E a is shown by LaFeO3 which, in contrast with Ca substituted samples, exhibits a small cationic defectivity. Methane reaction order lower than one was found for all catalysts.
Keywords: Catalytic methane combustion; Perovskite solid solutions; La, Ca orthoferrite catalysts;
Characterization of phosphorus-poisoned automotive exhaust catalysts by M.J Rokosz; A.E Chen; C.K Lowe-Ma; A.V Kucherov; D Benson; M.C Paputa Peck; R.W McCabe (205-215).
Oil-derived contaminants on light-off catalysts from high mileage taxis were characterized by a variety of physical and chemical methods. The contaminants (mostly phosphates) deposit in a strong axial gradient from the front to the back of the monolithic catalyst channels. Two major forms of phosphorus contamination were observed: (1) an overlayer of Zn, Ca, and Mg phosphates, and (2) aluminum phosphate within the washcoat. The data also suggest the formation of cerium(III) phosphate. Laboratory catalytic reaction measurements on core samples from the taxi catalysts confirm a strong deactivating effect due to the phosphorus contamination. The activity improves dramatically after removing phosphorus via an oxalic acid wash.
Keywords: Phosphorus; Poisoning; TWC;
Supported gold catalysts used for ozone decomposition and simultaneous elimination of ozone and carbon monoxide at ambient temperature by Zhengping Hao; Daiyun Cheng; Yun Guo; Yihong Liang (217-222).
Investigations of catalytic ozone decomposition and CO oxidation show that Au/Fe2O3 catalyst was a good catalytic material for ozone decomposition and simultaneous elimination of ozone and carbon monoxide at ambient temperature, and also suitable for use in relatively severe conditions, without the stoichiometric limitations. The structure of Au/Fe2O3 catalyst was studied by BET, XRD, XPS, XAFS and O2-TPD characterization techniques. This new type of Au catalytic material shows great potential as an environmental catalyst, particularly for indoor environmental pollution control.
Keywords: Supported gold catalyst; Simultaneous elimination of ozone and carbon monoxide; Ozone decomposition;
NO decomposition over physical mixtures of Cu-ZSM-5 with zeolites or oxides by V.I Pârvulescu; P Grange; B Delmon (223-237).
The paper deals with the investigation of the activity of bicomponent Cu-M-ZSM-5 zeolites (M=Ce, Sn, Tl) and of the physical mixtures of Cu-ZSM-5 with M-ZSM-5 or with the corresponding oxides of these metals in NO decomposition. Physical mixtures of M-ZSM-5 with those corresponding oxides were investigated as well. Copper exchange degree in the zeolites varied between 21.2 and 128% while the M content varied in inverse order, between 27.2 and 18.8%. The catalysts were characterized by NO-DRIFT, O2-TPD and XPS. Catalytic tests were performed in a microreactor in the temperature range 673–873 K. It was found that the presence of a second component may indeed lead to a better positioning of Cu, resulting in an improvement of its catalytic properties. This effect is conditioned by the introduction of M together with Cu in the exchange solution. Physical mixtures of Cu-ZSM-5 with M-ZSM-5 or with M oxides are not effective, confirming the importance of the co-exchange. The chemical nature of M is a key factor in this process.
Keywords: Cu-M-ZSM-5; NO decomposition; NO-FTIR; O2-TPD; XPS;
Degradation of dibutyl phthalate by homogeneous photocatalysis with Fe(III) in aqueous solution by Oliver Bajt; Gilles Mailhot; Michèle Bolte (239-248).
The degradation of dibutyl phthalate (DBP) photoinduced by Fe(III) in aqueous solution has been investigated under monochromatic irradiation and sunlight. Hydroxyl radicals •OH, responsible of the degradation, are formed via an intramolecular photoredox process in excited Fe(III) aquacomplexes. The concentration in Fe(OH)2+ in the starting Fe(III) solution appears to be a controlling parameter of the degradation rate, as already stated in our previous works. The first step of the decomposition of DBP involves the hydrogen abstraction on the butyl chain mainly on the carbon in α-position to aromatic ring. The major primary photoproducts are hydroxy, dihydroxy and carboxylic derivatives. For prolonged irradiations, DBP and its photoproducts are completely mineralized due to the regeneration of the absorbing species and the continuous formation of •OH radicals that confers a catalytic aspect to the process. Consequently, the degradation photoinduced by Fe(III) could be an efficient method of DBP removal from water.
Keywords: Dibutyl phthalate (DBP); Fe(III); Hydroxyl radicals; •OH; Photodegradation;
Regeneration of spent RFCC catalyst irreversibly deactivated by Ni, Fe, and V contained in heavy oil by Se In Cho; Kwang Seop Jung; Seong Ihl Woo (249-261).
Three different regeneration methods to recover the catalytic activity of spent resid fluid catalytic cracking (RFCC) catalyst were investigated. Carbochlorination method was the most effective to remove contaminant metals from spent equilibrium catalyst (E-cat). However, catalytic activity was not restored due to severe chlorination condition. The attempt to remove Fe, Ni, and V as a volatile corresponding metal carbonyl compound from E-cat was not effective due to low reactivity between contaminant metals and CO. The most effective method to rejuvenate spent E-cat was washing with weak acid after converting metals to a water-soluble form by calcination. Electron probe micro analysis (EPMA) for the cross-sectional profile of Ni, Fe, and V of the regenerated catalyst particle showed that three regeneration methods removed Ni, Fe, and V uniformly throughout the catalyst particle.
Keywords: RFCC catalyst; Regeneration; Metal contamination; Demetallization;
Surface species during catalytic reduction of NO by propene studied by in situ IR-spectroscopy over Pt supported on mesoporous Al2O3 with MCM-41 type structure by Walter Schießer; Hannelore Vinek; Andreas Jentys (263-274).
The selective catalytic reduction of NO by propene (HC-SCR) in the presence of excess oxygen over Pt/MCM-41 (Al2O3) and MCM-41 (Al2O3) catalysts has been studied by simultaneous in situ IR-spectroscopy and catalytic activity measurements. IR-spectra of Pt/MCM-41 (Al2O3) and MCM-41 (Al2O3) were compared during the adsorption of the single reactants (NO and C3H6) and during the NO reduction with C3H6 in presence of excess O2 (NO+C3H6+O2 reaction). The adsorption of NO resulted in the formation of surface nitrate species on the Al2O3 support and surface NO species on Pt. Adsorption of propene led to the formation of carboxylate species on Al2O3. Under reaction conditions nitrates, carboxylates, acetates, hydrocarbon fragments, isocyanate, cyanide species and CO were present on the catalyst surface. The surface concentration of the isocyanate species was found to be strongly correlated to the activity of the Pt/MCM-41 catalyst. Besides the formation of isocyanate, cyanide species were also observed on the surface. Both species increased in concentration with increasing oxygen concentration in the feed. The isocyanate species were found to be a reaction intermediate during the NO reduction, whereas the cyanide species were stable against further reaction. For the cyanide formation, a reaction pathway via isocyanate by abstraction of an oxygen atom by propene was observed.
Keywords: DeNO x ; Mechanism; In situ IR-spectroscopy; Pt/MCM-41;