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Applied Catalysis B, Environmental (v.62, #3-4)
Synergistic effect between Pt and K in the catalytic reduction of NO and N2O by Filomena Gonçalves; José L. Figueiredo (pp. 181-192).
The simultaneous reduction of NO+N2O was studied with carbon supported K/Pt catalysts. High conversion levels of both gases were achieved at relatively low temperatures (350°C), and the catalyst stability was confirmed in long duration experiments. A synergistic effect between the two metals was observed under different reaction conditions, and for different metal load combinations, similarly to the effect previously reported for Ni and K. This synergy was analysed and explained in terms of different properties of the system, as well as by the simultaneous participation of K and Pt in the reaction mechanism.
Keywords: Nitrous oxide; NO; x; Selective catalytic reduction; Carbon supported catalysts; Bimetallic catalysts; Synergistic effect
Photoelectrochemical treatment of the dye reactive red 198 using DSA® electrodes by Marciana Catanho; Geoffroy R.P. Malpass; Artur J. Motheo (pp. 193-200).
The study of the oxidation of the dye reactive red 198 on Ti/Ru0.3Ti0.7O2 electrode is presented. Three different techniques were employed: photocatalytic (interaction of UV radiation and electrode surface), electrochemical (application of a constant current) and photoelectrochemical (simultaneous application of a constant current and UV radiation). The effect of temperature (20–45°C) and current density (5–89mAcm−2) were investigated. No significant temperature effect was observed for the three techniques used. It was observed that at low current densities (5–30mAcm−2) the photoelectrochemical (PhEC) rate of colour and TOC removal is simply the sum of the photocatalytic (PC) and electrochemical (EC) rates. However, as the current density increases, the rate of PhEC removal is much greater. This phenomenon is interpreted as being due to the increased production of O2, which goes on to interact with the UV radiation and cause the oxidation of the dye.
Keywords: Photoelectrochemical oxidation; DSA; ®; Remazol Red 198; Degradation of pollutants
Photonic efficiency for methanol photooxidation and hydroxyl radical generation on silica-supported TiO2 photocatalysts by Javier Marugán; Dirk Hufschmidt; María-José López-Muñoz; Volker Selzer; Detlef Bahnemann (pp. 201-207).
Hydroxyl radical species are considered to be responsible for many oxidation pathways of chemical compounds initiated by advanced oxidation technologies and particularly in heterogeneous photocatalytic processes. However, not many attempts have been made to quantify the generation rate of these species for newly developed photocatalysts, especially for the large number of supported photocatalysts synthesized during the last years. This work focuses on the evaluation of the photonic efficiency for the hydroxyl radical generation on several silica-supported TiO2 photocatalysts recently developed. The study has been carried out by using methanol as hydroxyl radical scavenger. The influence of the mesoporous structure of the support and of its titania loading on the photonic efficiency of the materials has been analyzed. The importance of diffusional restrictions within the porous structure of the support has also been investigated by using a larger hydroxyl radical scavenger molecule, namely n-butanol.
Keywords: Photonic efficiency; Methanol; n; -Butanol; Hydroxyl radicals; Supported TiO; 2
Photocatalytic decomposition and reduction reactions of nitric oxide over Degussa P25 by Neil Bowering; Gavin S. Walker; Philip G. Harrison (pp. 208-216).
Photocatalytic nitric oxide (NO) decomposition and reduction reactions, using carbon monoxide (CO) as a reducing gas, have been investigated over Degussa P25 titanium dioxide photocatalysts, using a continuous flow reactor. The effects of thermal pretreatment temperature and reaction gas composition on the activity and selectivity of the decomposition and reduction reactions have been evaluated. Prepared materials were characterised by X-ray diffraction (XRD), N2 physisorption, transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) and findings from these techniques were used to explain the observed photocatalytic properties. XRD and TEM results indicated that for the pretreatment temperatures used (70, 120, 200, 450 and 600°C) there was no appreciable change in the phase composition and the original composition of ca. 77vol.% anatase and 23vol.% rutile was maintained even after treatment at 600°C. It was found that the photocatalytic activity for both the decomposition and reduction reactions decreased with increasing pretreatment temperature. This was attributed to the removal of surface hydroxyl species that act as active sites for reaction. For the decomposition reactions the only products observed were nitrogen and nitrous oxide and the selectivity for nitrogen formation remained constant (ca. 23%) regardless of the pretreatment temperature. The presence of CO in the reaction gas had a dramatic effect on the selectivity of the reactions with nitrogen selectivities as high as 65% being observed. It was found that as the CO/NO ratio increased the selectivity for nitrogen formation increased.
Keywords: Titanium dioxide; Nitric oxide; Photocatalysis; Decomposition; Reduction; Thermal processing; Selectivity
Thermal and catalytic decomposition of HNF and HAN liquid ionic as propellants by Laurence Courthéoux; Dan Amariei; Sylvie Rossignol; Charles Kappenstein (pp. 217-225).
Binary aqueous hydroxylammonium nitrate (HAN: [NH3OH]+[NO3]−) and hydrazinium nitroformate (HNF: [N2H5]+[C(NO2)3]−) have been prepared, then thermally and catalytically decomposed. The HAN solutions were prepared with different concentrations (20, 40, 79wt.%), whereas HNF solution contains is 40wt.% due to its lower solubility limit (about 50wt.%). The catalyst was prepared by impregnation of modified support (Si-modified alumina) with monometallic active phase precursor (platinum) and characterized by transmission electron microscopy, X-ray diffraction and chemisorption. The reactions were followed by thermal analysis and by using a constant volume batch reactor. This work shows the essential effect of the monopropellant concentration to determine the best formulation for an industrial application. Moreover, HAN laboratory made solutions are more efficient for catalytic decomposition due to the absence of stabilizer to inhibit the catalyst. The Pt(10%)/Al2O3Si+HAN79% lab association shows lower decomposition temperatures (down to room temperature), larger reaction rates and leads to higher amount of gaseous products, giving the most efficient system. With the same catalyst, HNF solution gave lower performances than HAN solutions, suggesting that the catalyst needs to be improved for this oxidizer.
Keywords: Monopropellant; HAN; HNF; Catalytic decomposition; Propulsion
Aqueous-phase reforming of ethylene glycol over supported Pt and Pd bimetallic catalysts by George W. Huber; John W. Shabaker; Steven T. Evans; James A. Dumesic (pp. 226-235).
More than 130 Pt and Pd bimetallic catalysts were screened for hydrogen production by aqueous-phase reforming (APR) of ethylene glycol solutions using a high-throughput reactor. Promising catalysts were characterized by CO chemisorption and tested further in a fixed bed reactor. Bimetallic PtNi, PtCo, PtFe and PdFe catalysts were significantly more active per gram of catalyst and had higher turnover frequencies for hydrogen production (TOFH2) than monometallic Pt and Pd catalysts. The PtNi/Al2O3 and PtCo/Al2O3 catalysts, with Pt to Co or Ni atomic ratios ranging from 1:1 to 1:9, hadTOFH2 values (based on CO chemisorption uptake) equal to 2.8–5.2min−1 at 483K for APR of ethylene glycol solutions, compared to 1.9min−1 for Pt/Al2O3 under similar reaction conditions. A Pt1Fe9/Al2O3 catalyst showedTOFH2 values of 0.3–4.3min−1 at 453–483K, about three times higher than Pt/Al2O3 under identical reaction conditions. A Pd1Fe9/Al2O3 catalyst had values ofTOFH2 equal to 1.4 and 4.3min−1 at temperatures of 453 and 483K, respectively, and these values are 39–46 times higher than Pd/Al2O3 at the same reaction conditions. Catalysts consisting of Pd supported on high surface area Fe2O3 (Nanocat) showed the highest turnover frequencies for H2 production among those catalysts tested, with values ofTOFH2 equal to 14.6, 39.1 and 60.1min−1 at temperatures of 453, 483 and 498K, respectively. These results suggest that the activity of Pt-based catalysts for APR can be increased by alloying Pt with a metal (Ni or Co) that decreases the strengths with which CO and hydrogen interact with the surface (because these species inhibit the reaction), thereby increasing the fraction of catalytic sites available for reaction with ethylene glycol. The activity of Pd-based catalysts for APR can be increased by adding a water-gas shift promoter (e.g. Fe2O3).
Keywords: Aqueous phase reforming; Hydrogen production; Renewable energy; Fuel cells; Bimetallic catalysts; High throughput
Effect of yttrium on the performances of zirconia based catalysts for the decomposition of N2O at high temperature by P. Granger; P. Esteves; S. Kieger; L. Navascues; G. Leclercq (pp. 236-243).
Abatement processes for the reduction of N2O emissions from acid nitric plants can be implemented in different positions. Among the different possibilities, a catalytic process set up between the ammonia converter and the absorber could be a practicable solution. In those running conditions, at high temperature, in the presence of NO, O2 and water, the catalytic decomposition of N2O (in the absence of a reducing agent) can take place. However, catalysts usually suffer from a strong deactivation owing to the occurrence of thermal sintering which significantly lowers their specific surface area. Catalytic testing performed at laboratory scale showed that zirconia based catalysts stabilised by yttrium incorporation could be of potential interest. However, the mode of yttrium incorporation seems to be a key factor. According to the preparation procedure, surface yttrium enrichment may occur and then strongly inhibit the catalytic decomposition of N2O. Co-precipitation methods can be profitably used for the preparation of modified-ZrO2 catalysts in order to obtain yttrium homogeneously distributed in the bulk material. According to this preparation method, a synergy effect on the catalytic activity and also on the stability has been observed on ZrO2 containing low amount of yttrium whereas an inhibiting effect prevails on highly loaded yttrium based catalysts irrespective of the mode of yttrium incorporation.
Keywords: Green house gas; Nitrous oxide; N; 2; O catalytic decomposition; Zirconia based catalysts; Nitric acid plant
Evidence of the vital role of the pore network on various catalytic conversions of N2O over Fe-silicalite and Fe-SBA-15 with the same iron constitution by M. Santhosh Kumar; J. Pérez-Ramírez; M.N. Debbagh; B. Smarsly; U. Bentrup; A. Brückner (pp. 244-254).
Fe-silicalite and Fe-SBA-15 with similar iron content have been characterized by N2 adsorption, small angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), scanning electron microscopy (SEM), high-resolution transmission electron micrographs (HRTEM), UV–vis–DRS and EPR, and tested in direct N2O decomposition, N2O reduction by CO and N2O-mediated propane oxidative dehydrogenation. Both catalysts contain almost exclusively isolated Fe3+ sites of similar concentration and structure, which are, however, stabilized in markedly different pore geometries (intersecting channels of ca. 0.55nm diameter in Fe-silicalite versus parallel linear pores of ca. 7.5nm diameter in Fe-SBA-15). This aspect is of vital importance in order to exclusively ascribe different catalytic performances to the environment where the iron species are stabilized. Fe-silicalite revealed to be much more active than Fe-SBA-15 in all reactions studied. This clearly illustrates that the confinement of the iron species in pores of suitable geometry (structure and size) is essential to originate their remarkable catalytic properties. The large pores in ordered mesoporous materials apparently do not generate the required intimate contact between potentially active Fe sites and reactant molecules.
Keywords: N; 2; O decomposition; N; 2; O reduction; Propane oxidative dehydrogenation; Fe-silicalite; Fe-SBA-15; Pore geometry; Iron species; EPR; UV–vis; SAXS
TiO2 photocatalytic films on stainless steel: The role of Degussa P-25 in modified sol–gel methods by Yongjun Chen; Dionysios D. Dionysiou (pp. 255-264).
The role of Degussa P-25 loading (0–100g/L) in the alkoxide sol was investigated for the synthesis of immobilized TiO2 photocatalytic films on 304 stainless steel using the P-25 powder-modified sol–gel method (PPMSGM). The structural properties of the films (PPMSGFs) obtained after gel drying and calcination at 600°C were examined using different materials characterization techniques including X-day diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of films with good adherence to the stainless steel support were evaluated using 4-chlorobenzoic acid (4-CBA) as a model organic contaminant and UV-A radiation. The P-25 loading did not have a significant effect on the size of the crystallites in the films. However, increasing the P-25 loading in the sol resulted in an increase in (i) the amount of crystalline material retained on the support (i.e., for both anatase (101) and rutile (110) crystal phases); (ii) the number of grains (aggregates of P-25 particles and crystallites formed from the alkoxide sol); (iii) the number of pores in the film (in the range of 0–50g/L); and (iv) the number of microcracks on the surface of PPMSGFs. On the other hand, increasing the P-25 loading in the sol resulted in a decrease in the size of grains on the surface of PPMSGFs. XPS analysis revealed the presence of Cr3+, Mn3+ and Fe3+ on the surface of PPMSGFs as a result of diffusion of these species from the stainless steel support during film calcination at 600°C. The concentration of these foreign species on the film surface decreased with an increase in the P-25 loading in the sol. Increasing P-25 loading in the sol yielded films with higher photocatalytic activity but a concentration of 50g/L P-25 in the sol was found as the maximum for obtaining films with good adherence on the stainless steel support. Increase in the photocatalytic activity of the films with increasing P-25 loading in the sol was mainly attributed to the enhancement of the number of P-25 active sites exposed to the solution due to film morphology and surface characteristics and to the reduction in Cr3+ and Fe3+ concentrations on the surface of the films.
Keywords: Photocatalytic; Photocatalysis; TiO; 2; Degussa P-25; Activity; Active sites; Structural property; Powder; Modified; Sol–gel; Coatings; Films; Immobilized; Water treatment; Water purification
MnO x–CeO2 mixed oxide catalysts for complete oxidation of formaldehyde: Effect of preparation method and calcination temperature by Xingfu Tang; Yonggang Li; Xiumin Huang; Yide Xu; Huaqing Zhu; Jianguo Wang; Wenjie Shen (pp. 265-273).
MnO x–CeO2 mixed oxides prepared by sol–gel method, coprecipitation method and modified coprecipitation method were investigated for the complete oxidation of formaldehyde. Structure analysis by H2-TPR and XPS revealed that there were more Mn4+ species and richer lattice oxygen on the surface of the catalyst prepared by the modified coprecipitation method than those of the catalysts prepared by sol–gel and coprecipitation methods, resulting in much higher catalytic activity toward complete oxidation of formaldehyde. The effect of calcination temperature on the structural features and catalytic behavior of the MnO x–CeO2 mixed oxides prepared by the modified coprecipitation was further examined, and the catalyst calcined at 773K showed 100% formaldehyde conversion at a temperature as low as 373K. For the samples calcined below 773K, no any diffraction peak corresponding to manganese oxides could be detected by XRD measurement due to the formation of MnO x–CeO2 solid solution. While the diffraction peaks corresponding to MnO2 phase in the samples calcined above 773K were clearly observed, indicating the occurrence of phase segregation between MnO2 and CeO2. Accordingly, it was supposed that the strong interaction between MnO x and CeO2, which depends on the preparation route and the calcination temperature, played a crucial role in determining the catalytic activity toward the complete oxidation of formaldehyde.
Keywords: MnO; x; –CeO; 2; mixed oxide; Solid solution; Molecule oxygen activation; Formaldehyde complete oxidation
Photocatalytic degradation of imidazolinone fungicide in TiO2-coated optical fiber reactor by Anne Danion; Jean Disdier; Chantal Guillard; Olivier Païssé; Nicole Jaffrezic-Renault (pp. 274-281).
The photocatalytic degradation of the fungicide fenamidone is studied in a TiO2-coated optical fiber photoreactor. Fenamidone is slowly transformed with a kinetic order of 1 and a degradation rate of 0.02h−1. Intermediate products were isolated and identified by means of solid phase extraction (SPE) coupled to liquid chromatography-mass spectrometry techniques (LC-MS). A proposed degradation pathway of fenamidone is presented, involving mainly hydroxylation and oxidation reactions. Carboxylic acids and sulfate ions resulting from the same reaction in a powder reactor were also identified.
Keywords: Optical fiber reactor; Titanium dioxide; Photocatalysis; Fenamidone
Effects of Sn dopant on the photoinduced charge property and photocatalytic activity of TiO2 nanoparticles by Jing Liqiang; Fu Honggang; Wang Baiqi; Wang Dejun; Xin Baifu; Li Shudan; Sun Jiazhong (pp. 282-291).
In this paper, Sn-doped TiO2 nanoparticles were prepared by a sol–gel method, and also were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), infrared spectrum (IR), ultraviolet–visible diffuse reflection spectrum (UV–vis DRS), photoluminescence spectrum (PL), surface photovoltage spectroscopy (SPS) and electrical field induced surface photovoltage spectroscopy (EFISPS). The sample activity was evaluated by photocatalytic oxidation reactions of phenol solution. The effects of thermal treatment temperature and Sn amount on photoinduced charge property, mainly involving charge separation and bound excitons resulting from surface states, and photocatalytic activity of TiO2 nanoparticles were principally investigated. The results show that an appropriate calcination temperature and Sn dopant amount can greatly enhance the SPS responses of TiO2 nanoparticles related not only to the band–band transitions but also to the bound excitons, and obviously weaken the PL signal, while the photocatalytic activity remarkably raises. These demonstrate that the separation rate of photoinduced charges of TiO2 nanoparticles can be effectively improved by doping Sn, which is responsible for the obvious increase in the photocatalytic activity. Moreover, the existence of bound excitons related to surface states also favor the photocatalytic activity. In addition, it can be found that the SPS responses related to the bound excitons could easily exhibit in the TiO2 sample consisting of much of anatase and little of rutile, which is possibly ascribed to the heterojunction between the anatase and rutile phase.
Keywords: TiO; 2; Sn dopant; Photoinduced charge; Surface photovoltage; Photocatalysis
On the catalytic nature of Mn/sulfated zirconia for selective reduction of NO with methane by Ning Li; Aiqin Wang; Zhimin Liu; Xiaodong Wang; Mingyuan Zheng; Yanqiang Huang; Tao Zhang (pp. 292-298).
In this work, the catalytic nature of Mn loaded sulfated zirconia (SZ) catalysts for the selective catalytic reduction (SCR) of NO with methane was investigated by a combination of reactions and characterizations such as FT-IR spectroscopy, H2-TPR, UV–vis diffuse reflectance spectroscopy (DRS) and NO-TPD. It was found from the results of reactions and FT-IR spectra that the strong Brønsted and Lewis acid sites in the Mn/SZ catalysts were essential for the SCR of NO with methane. The loading of Mn increased the number of strong Lewis acid sites on the surface of SZ catalyst, which is one reason for its promoting effect. On the other hand, FT-IR spectra, H2-TPR and UV–vis DRS of the catalysts demonstrated that the presence of the SO42− species occupied the terminal OH sites on the surface of ZrO2 support and thereby restrained the formation of more oxidative and nonstoichiometrically dispersed MnO x (1.5< x<2) phase. Such an effect of SO42− suppressed the combustion reaction of CH4 by O2 and increased the selectivity towards NO reduction. The NO-TPD showed that the loading of Mn increased the adsorption of NO over SZ catalyst, which is another reason for the promoting effect of Mn.
Keywords: NO reduction; Methane; Mn; Sulfated zirconia
Adsorption of tetrahydrothiophene on faujasite type zeolites: Breakthrough curves and FTIR spectroscopy study by Igor Bezverkhyy; Kamel Bouguessa; Christophe Geantet; Michel Vrinat (pp. 299-305).
Adsorption of tetrahydrothiophene (THT) on NaX, CaX, AgX, and H-USY was studied by dynamic adsorption method and FTIR spectroscopy. The stoichiometric adsorption capacities are not very different for all materials, which is indicative of a complete micropore filling. In contrast, the overall rate constant of adsorption, determined from fitting the breakthrough curves with Bohart–Adams equation, is two times greater for H-USY than for type X zeolites. For NaX, CaX and H-USY, heating under N2 flow at 300°C allows to restore completely their initial adsorption capacities. In the case of AgX the same treatment results in a twofold lose of capacity accompanied by a collapse of the zeolite structure as evidenced by XRD. The nature of interaction between THT molecules and zeolites was characterized by FTIR spectroscopy. Only a weak interaction through hydrogen bonding was observed for THT on H-USY leading to an almost complete desorption at 100°C. For NaX and CaX adsorbed molecules are gradually eliminated when heated to 300°C while completely different pattern was observed for THT adsorbed on AgX on which the amount of the adsorbate remains nearly constant between 25 and 200°C, but rapidly decreases on further heating. Such a behavior is indicative of much stronger interaction between THT molecules and Ag+ cations in agreement with the data on the regeneration of the adsorbents.
Keywords: Tetrahydrothiophene; Adsorption; Zeolite; Breakthrough curves
Electrochemical hydrogenation of dinitrogen to ammonia on a polyaniline electrode by Fatih Köleli; Thorsten Röpke (pp. 306-310).
The fixation of molecular nitrogen (dinitrogen) to ammonia was investigated depending on applied potential, pressure and temperature on a Pt-plate coated with polyaniline (PAn) film in methanol/LiClO4/H+ solution. The reaction product was only ammonia with a maximum concentration of ca. 57μmolL−1 after 5h electrolysis time. Maximum current efficiency for ammonia formation was ca. 16%. The optimum film thickness was found to be 1.5μm, N2-pressure 50bar and an optimum electrolysis potential was only −0.12V (NHE).
Keywords: Polyaniline; N; 2; -fixation; Ammonia; H; ad; formation; Electrochemistry
Selective reduction of NO by NH3 over manganese–cerium mixed oxides: Relation between adsorption, redox and catalytic behavior by F. Eigenmann; M. Maciejewski; A. Baiker (pp. 311-318).
Manganese–cerium mixed oxide catalysts with different molar ratio Mn/(Mn+Ce) (0, 0.25, 0.50, 0.75, 1) were prepared by citric acid method and investigated concerning their adsorption behavior, redox properties and behavior in the selective catalytic reduction of NO x by NH3. The studies based on pulse thermal analysis combined with mass spectroscopy and FT-IR spectroscopy uncovered a clear correlation between the dependence of these properties and the mixed oxide composition. Highest activity to nitrogen formation was found for catalysts with a molar ratio Mn/(Mn+Ce) of 0.25, whereas the activity was much lower for the pure constituent oxides. Measurements of adsorption uptake of reactants, NO x (NO, NO2) and NH3, and reducibility showed similar dependence on the mixed oxide composition indicating a clear correlation of these properties with catalytic activity. The adsorption studies indicated that NO x and NH3 are adsorbed on separate sites. Consecutive adsorption measurements of the reactants showed similar uptakes as separate measurements indicating that there was no interference between adsorbed reactants. Mechanistic investigations by changing the sequence of admittance of reactants (NO x, NH3) indicated that at 100–150°C nitrogen formation follows an Eley–Rideal type mechanism, where adsorbed ammonia reacts with NO x in the gas phase, whereas adsorbed NO x showed no significant reactivity under conditions used.
Keywords: Manganese–cerium mixed oxides; NO; NO; 2; and NH; 3; adsorption; Redox behavior; Selective catalytic reduction of NO; x; by NH; 3; Pulse thermal analysis combined with mass spectroscopy and Fourier transform infrared spectroscopy
The reduction phase in NO x storage catalysis: Effect of type of precious metal and reducing agent by Hussam Abdulhamid; Erik Fridell; Magnus Skoglundh (pp. 319-328).
The effect of different reducing agents (H2, CO, C3H6 and C3H8) on the reduction of stored NO x over PM/BaO/Al2O3 catalysts (PM=Pt, Pd or Rh) at 350, 250 and 150°C was studied by the use of both NO2-TPD and transient reactor experiments. With the aim of comparing the different reducing agents and precious metals, constant molar reduction capacity was used during the reduction period for samples with the same molar amount of precious metal. The results reveal that H2 and CO have a relatively high NO x reduction efficiency compared to C3H6 and especially C3H8 that does not show any NO x reduction ability except at 350°C over Pd/BaO/Al2O3. The type of precious metals affects the NO x storage-reduction properties, where the Pd/BaO/Al2O3 catalyst shows both a high storage and a high reduction ability. The Rh/BaO/Al2O3 catalyst shows a high reduction ability but a relatively low NO x storage capacity.
Keywords: NO; x; reduction; Lean-burn; Precious metal; Reducing agents; H; 2; , CO, C; 3; H; 6; , C; 3; H; 8
Hydrothermal doping method for preparation of Cr3+-TiO2 photocatalysts with concentration gradient distribution of Cr3+ by Jiefang Zhu; Zhigang Deng; Feng Chen; Jinlong Zhang; Haijun Chen; Masakazu Anpo; Jiazhen Huang; Lizhong Zhang (pp. 329-335).
Cr3+-doped anatase titanium dioxide photocatalysts were prepared by the combination of sol–gel process with hydrothermal treatment. The samples were characterized by UV–vis diffuse reflectance spectroscopy, X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) specific surface area ( SBET), transmission electron microscopy (TEM), atomic absorption flame emission spectroscopy (AAS), electron paramagnetic resonance (EPR) spectroscopy and X-ray photoelectron spectroscopy (XPS). It was confirmed that Cr substitutes Ti4+ in TiO2 lattice in trivalent ionic state, and the concentrations of dopants Cr3+ decrease from the exterior to the interior of doped TiO2. The photocatalytic activity of Cr-TiO2 was investigated for the photocatalytic degradation of XRG aqueous solution both under UV and visible light irradiation. Due to the excitation of 3d electron of Cr3+ to the conduction band of TiO2, Cr-TiO2 shows a good ability for absorbing the visible light to degrade XRG. Doping of chromium ions effectively improves the photocatalytic activity under both UV light irradiation and visible light irradiation with an optimal doping concentration of 0.15% and 0.2%, respectively. The special distribution of dopants Cr3+ seems having a good effect on enhancing the photocatalytic activity of Cr-TiO2.
Keywords: Titanium dioxide; Photocatalyst; Sol–gel; Hydrothermal treatment; Doping; Cr; 3+
Catalytic activity of dispersed CuO phases towards nitrogen oxides (N2O, NO, and NO2) by Simona Bennici; Antonella Gervasini (pp. 336-344).
A systematic reactivity study of N2O, NO, and NO2 on highly dispersed CuO phases over modified silica supports (SiO2–Al2O3, SiO2–TiO2, and SiO2–ZrO2) has been performed. Different reaction paths for the nitrogen oxide species abatement were studied: from direct decomposition (N2O) to selective reductions by hydrocarbons (N2O, NO, and NO2) and oxidation (NO to NO2). The oxygen concentration, temperature, and contact time, were varied within suitable ranges in order to investigate the activity and in particular the selectivity in the different reactions studied. The support deeply influenced the catalytic properties of the active copper phase. The most acidic supports, SiO2–Al2O3 and SiO2–ZrO2, led to a better activity and selectivity of CuO for the reactions of N2O, NO, and NO2 reductions and N2O decomposition than SiO2–TiO2. The catalytic results are discussed in terms of actual turnover frequencies starting from the knowledge of the copper dispersion values.
Keywords: Copper catalysts; De-NO; x; catalytic activity; Turnover frequencies
Catalytic ozonation of natural organic matter on alumina by B. Kasprzyk-Hordern; U. Raczyk-Stanisławiak; J. Świetlik; J. Nawrocki (pp. 345-358).
The paper aims to show the potential of catalytic ozonation in the presence of alumina for the removal of natural organic mater from drinking water. An investigation into the efficiency of catalytic ozonation, ozonation by-products formation and their biodegradability was the main goal of the paper. Characterisation of fresh and worn alumina was also conducted. The results clearly indicated the high activity of alumina over a long period of time, which is crucial in water treatment technology. The application of alumina to the ozonation system doubled the efficiency of NOM removal from water when compared to ozonation alone. Furthermore, catalytic ozonation resulted in lower by-products and biodegradable organic carbon formation.
Keywords: Ozone; Water treatment; Catalytic ozonation; Alumina; NOM
Model bimetallic Pd-Ni automotive exhaust catalysts: Influence of thermal aging and hydrocarbon self-poisoning by A.B. Hungría; J.J. Calvino; J.A. Anderson; A. Martínez-Arias (pp. 359-368).
Bimetallic Pd-Ni catalysts supported on Al2O3 and (Ce,Zr)O x/Al2O3 were examined with respect to their catalytic performance for the elimination of CO, NO and C3H6 under stoichiometric conditions. The effects of a thermal aging treatment at 1273K, reactant competition in the presence of the hydrocarbon and the influence of the presence of nickel in the catalyst have been analysed by XRD, HREM, catalytic activity measurements and in situ DRIFTS spectroscopy. Self-poisoning effects, induced by the presence of the hydrocarbon in the reactant mixture, were identified as the main factor affecting the light-off activity. While a Ni-induced preferential interaction between Pd and the Ce-Zr mixed oxide component appears, in general terms, to be beneficial for the catalytic performance of the fresh (Ce,Zr)O x/Al2O3-supported bimetallic catalyst, it is shown to be detrimental for the aged system as a consequence of a facilitated degradation of the (Ce,Zr)O x component and encapsulation of the active palladium particles.
Keywords: Pd-Ni bimetallic catalysts; TWC; CeO; 2; -ZrO; 2; Al; 2; O; 3; CO oxidation; NO reduction; Propene oxidation; XRD; In situ DRIFTS; HREM
Catalytic performance of various mesoporous silicas modified with copper or iron oxides introduced by different ways in the selective reduction of NO by ammonia by L. Chmielarz; P. Kuśtrowski; R. Dziembaj; P. Cool; E.F. Vansant (pp. 369-380).
Mesoporous silicas (MCM-48, SBA-15, MCF), reflecting various porous structures, were modified with copper and iron oxides by two different methods. For a first series of the samples the molecular designed dispersion (MDD) method using acetylacetonate complexes of copper and iron was applied for the deposition of transition metal oxides on the silica supports. A second series of the catalysts was obtained by the incipient impregnation technique using aqueous solutions of the suitable metal nitrates. The modified materials were characterized with respect to the texture (BET), composition (electron microprobe analysis), coordination of the transition metals (UV–vis–DRS) and surface acidity (NH3-TPD, FTIR). The mesoporous silica supports modified with transition metal oxides were tested as catalysts of the selective reduction of NO with ammonia. The catalytic performance of the studied samples depended on the method used for the deposition of transition metal oxide as well as the kind of mesoporous silica used as a catalytic support. In general, the Cu-containing mesoporous samples effectively operated at lower temperatures than silicas modified with iron. The samples obtained by the MDD method have been found to be more active and selective compared to the analogous samples prepared by the impregnation technique. An introduction of water vapor into the reaction mixture only slightly decreased the NO conversion and selectivity towards N2 over the MCF mesoporous silica modified with copper or iron oxide.
Keywords: Mesoporous silicas; Copper; Iron; DeNO; x; NH; 3