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Applied Catalysis B, Environmental (v.78, #1-2)
Photocatalytic oxidation of toluene and trichloroethylene in the gas-phase by metallised (Pt, Ag) titanium dioxide by Cissillia Young; Tuti Mariana Lim; Ken Chiang; Jason Scott; Rose Amal (pp. 1-10).
The photodegradation of single component and binary mixtures of toluene and trichloroethylene (TCE), on TiO2, Pt/TiO2 and Ag/TiO2 was investigated. Intermediates formed during toluene photodegradation resulted in photocatalyst deactivation. Pt deposits improved the photocatalyst lifetime, delaying toluene breakthrough by up to 2.5 times and improving mineralisation by a factor of 3.5. Ag deposits had a negligible effect on photocatalyst performance. Deactivation was not evident during TCE photodegradation by neat or metallised TiO2. Pt deposits deterred TCE photodegradation with this effect ascribed to poisoning of the metallic Pt sites by photogenerated chloride radicals. In contrast, low Ag loadings were beneficial for TCE photodegradation with this effect ascribed to the temporary interaction between metallic Ag sites and chloride radicals to form AgCl. AgCl possesses semiconductor characteristics which may assist with TCE photodegradation. Photodegradation of the binary toluene/TCE mixture was observed to merge the positive and negative interactions between the metal deposits, organics and intermediates.
Keywords: Photocatalysis; Titanium dioxide; Toluene; Trichloroethylene
Multivariate analysis of phenol mineralisation by combined hydrodynamic cavitation and heterogeneous advanced Fenton processing by Anand G. Chakinala; David H. Bremner; Parag R. Gogate; Kyu-Cheol Namkung; Arthur E. Burgess (pp. 11-18).
Phenolic compounds in wastewaters are difficult to treat using the conventional biological techniques such as activated sludge processes because of their bio-toxic and recalcitrant properties and the high volumes released from various chemical, pharmaceutical and other industries. In the current work, a modified heterogeneous advanced Fenton process (AFP) is presented as a novel methodology for the treatment of phenolic wastewater. The modified AFP, which is a combination of hydrodynamic cavitation generated using a liquid whistle reactor and the AFP is a promising technology for wastewaters containing high organic content. The presence of hydrodynamic cavitation in the treatment scheme intensifies the Fenton process by generation of additional free radicals. Also, the turbulence produced during the hydrodynamic cavitation process increases the mass transfer rates as well as providing better contact between the pseudo-catalyst surfaces and the reactants.A multivariate design of experiments has been used to ascertain the influence of hydrogen peroxide dosage and iron catalyst loadings on the oxidation performance of the modified AFP. Higher TOC removal rates were achieved with increased concentrations of hydrogen peroxide. In contrast, the effect of catalyst loadings was less important on the TOC removal rate under conditions used in this work although there is an optimum value of this parameter. The concentration of iron species in the reaction solution was measured at 105min and its relationship with the catalyst loadings and hydrogen peroxide level is presented.
Keywords: Hydrodynamic cavitation; Advanced Fenton process (AFP); Phenol; Multivariate analysis; Wastewater treatment
Effect of suspended TiO2 physicochemical characteristics on benzene derivatives photocatalytic degradation by D. Gumy; S.A. Giraldo; J. Rengifo; C. Pulgarin (pp. 19-29).
Seven different TiO2 samples suitable for water detoxification were systematically characterized according to their physicochemical properties. Except for one mixed catalyst anatase–rutile from Degussa P25, all photocatalysts had a pure anatase crystalline phase. The particle size of the TiO2 samples varied from about 5 to 700nm and was inversely correlated with the BET specific surface area ( ABET). Surface properties of colloidal suspensions measured by electroacoustic methods were evaluated at different pH values. The aggregate size appeared to be dependent on the pH value of the solution. The isoelectric point (IEP) of the TiO2 samples ranged from very acidic (IEP<3) to neutral values.Four benzene derivatives were chosen as model pollutants to assess the TiO2 samples efficiency on water detoxification.The organic degradation kinetics were influenced in a different way by the TiO2 characteristics. The surface charge of TiO2 samples was found to affect significantly the organic degradation kinetics. Indeed, the compounds degradation was greatly enhanced by acidic TiO2. Moreover, the compounds primary degradation and the total mineralization were affected differently by the ABET. The primary degradation kinetics of strongly adsorbed pollutants, i.e. those containing a carboxyl group, benzoic acid (BA) and 4-hydroxybenzoic acid (HBA), is enhanced by large ABET, whereas phenol and 4-nitrophenol (NP) degradation was not. On the other hand, a small ABET was not advantageous, and there is an optimum value for an efficient total organic carbon (TOC) removal. In addition, the mixed crystalline structure, Degussa P25, showed a higher photoactivity than pure anatase TiO2, as generally accepted and reported in previous studies.
Keywords: Water detoxification; TiO; 2; photoactivity; Benzoic acid; 4-Hydrobenzoic acid; Phenol; 4-Nitrophenol
Catalytic wet air oxidation of phenol with pelletized ruthenium catalysts by Jianbing Wang; Wanpeng Zhu; Shaoxia Yang; Wei Wang; Yunrui Zhou (pp. 30-37).
The pelletized ruthenium catalysts were prepared by impregnation of different pelletized supports: CeO2 and ZrO2-CeO2. Their mechanical strength, specific surface area, pore size distribution and adsorption capacity for phenol were studied. Catalytic wet air oxidation of phenol with pelletized catalyst of Ru/ZrO2-CeO2 was performed in a continuous packed-bubble column reactor. The fresh and used Ru/ZrO2-CeO2 catalysts were compared. It shows that introduction of ZrO2 into Ru/CeO2 increased the mechanical strength, specific surface area and adsorption capacity of pelletized catalyst. In the experiment of wet air oxidation of phenol with Ru/ZrO2-CeO2 for 100h, phenol and TOC removal stabilized around 100 and 96%, respectively. The concentrations of intermediates were low. The leaching concentrations of active species during the reaction were also low. After reaction, the textures, morphologies, microcosmic crystal pattern of catalyst and oxidation state of catalytic active phase of zirconium, cerium, ruthenium and oxygen did not change much, but the carbonaceous deposits on the surface of used catalyst were observed, and they would be fully oxidized at about 300°C. The pelletized catalyst of Ru/ZrO2-CeO2 possesses the possibility of practical use.
Keywords: Catalytic wet air oxidation; Pelletized ruthenium catalyst; Ru/ZrO; 2; -CeO; 2
A comparative study of Pt/Ba/Al2O3 and Pt/Fe-Ba/Al2O3 NSR catalysts: New insights into the interaction of Pt–Ba and the function of Fe by Jin-Yong Luo; Ming Meng; Yu-Qing Zha; Ya-Ning Xie; Tian-Dou Hu; Jing Zhang; Tao Liu (pp. 38-52).
The influence of the introduction of Pt and/or Fe on the structures, NO x storage property and sulfur removal performance of Ba/Al2O3 catalyst was studied. The techniques of TG/DTA, XRD, FT-IR, H2-TPR, EXAFS and DRIFTS were employed for the careful characterization of the catalysts. Two types of Ba species are identified, namely a well-spread monolayer of Ba species and a bulk BaAl2O4 phase. The addition of Fe inhibits the Ba dispersion by enhancing the bulk BaAl2O4 formation, thus slightly decreasing the SO x absorption and greatly suppressing the growth of the bulk BaSO4, and its addition also promotes the NO x storage by increasing the mobility of the stored NO x, contributing to the formation of bulk Ba(NO3)2. The introduction of Pt always re-disperses the bulk BaAl2O4 phase via a hydration process, and enhances both the NO x and SO x absorption capacity of the catalyst. Whereas the co-existence of Pt and Fe was detrimental for the NO x storage and sulfur removal as compared with Pt/Ba/Al2O3 catalyst, although it favors the reduction of BaSO4 phase. Based upon the EXAFS, in situ DRIFTS and repeated H2-TPR results, it is found that the interaction between Pt and Ba species is of great importance for NO x storage and sulfur removal. This Pt–Ba interaction not only accelerates the NO x spillover which is a key step during storage, but also facilitates the selective reduction of BaSO4 into H2S, favorable to sulfur removal and catalyst regeneration. The introduction of Fe to the Pt/Ba/Al2O3 catalyst decreases this Pt–Ba interaction by encapsulation of Pt in the matrix of Fe/FeO x lattice after repeated redox cycles, leading to the decrease of NO x storage capacity (NSC) of the catalyst, and making sulfur removal more difficult since Fe selectively catalyzes the reduction of BaSO4 into BaS.
Keywords: Pt; Fe; NO; x; storage; Sulfur removal; Pt–Ba interaction
Catalytic hydrodechlorination of chlorinated ethenes by nanoscale zero-valent iron by Hocheol Song; Elizabeth R. Carraway (pp. 53-60).
The reduction of six chlorinated ethenes by nanoscale iron (<100nm diameter) synthesized by borohydride reduction was studied in order to determine reaction rates and product distributions and to gain insight into reaction pathways. The transformation of chlorinated ethenes by nanoscale iron proceeded to fully dechlorinated products (ethene and ethane), with no production of chlorinated intermediates, and the reaction rate constants for disappearance of chlorinated ethenes increased with decreasing chlorination (vinyl chloride (VC)>dichloroethenes (DCEs)>trichloroethene (TCE)>tetrachloroethene (PCE)). This trend suggests the reduction of chlorinated ethenes by nanoscale iron did not occur under thermodynamic control (e.g. reduction potential), rather, it proceeded via a catalytic pathway involving reactive hydrogen species. The reduction of TCE under five different conditions of initial dissolved hydrogen concentrations which varied from about 0.02 to 1.2mM confirmed the importance of hydrogen in the reaction pathway and revealed an excellent linear correlation between rate constant and hydrogen concentration. Reduction of a chlorinated ethane (1,1,1,2-tetrachloroethane) which produced 1,1-DCE as an intermediate, showed no dependence on hydrogen concentrations but the disappearance of the ethene intermediate did. TCE reduction by commercial grade micro-sized iron samples, in contrast, showed insignificant dependence on hydrogen concentration, suggesting the nanoscale iron synthesized by borohydride reduction of iron salts is particularly suited for hydrogen utilization through a catalytic reduction of chlorinated ethenes.
Keywords: Nanoscale iron; Boron; Hydrogen; Catalytic hydrogenation; Reductive dechlorination; Chlorinated compounds
Simultaneous removal of NO x and diesel soot over nanometer Ln-Na-Cu-O perovskite-like complex oxide catalysts by Jian Liu; Zhen Zhao; Chun-ming Xu; Ai-jun Duan (pp. 61-72).
The nanometric Ln-Na-Cu-O (Ln=La, Pr, Nd, Sm, Gd) perovskite-like complex oxide catalysts were prepared by sol–gel auto-combustion method using citric acid as a ligand and an adjusting agent of particle-size and morphology. Their structures and physico-chemical properties were examined by chemical analysis, XRD, SEM, FT-IR, H2-TPR and MS-NO-TPD. The catalytic performances of these perovskite-like oxides for the simultaneous removal of soot and NO x were investigated by a technique of the temperature-programmed reaction (TPR). In the Ln-Na-Cu-O catalysts, the partial substitution of Na for La at A-site led to the formation of Cu3+ and/or oxygen vacancy, thus the catalytic activity was remarkably enhanced. The optimal substitution amount of Na ( x) is equal to 0.3 for the reduction of NO x, and x is equal to 0.7 for soot combustion. Moreover, attributing to the effects of very small surface particle sizes of the catalysts and the strong oxidizing ability of NO2 which was produced from NO and O2 in the reactant gases on these catalysts, the nanometric Ln-Na-Cu-O perovskite-like oxides exhibit very high catalytic activities for soot combustion even under loose contact conditions between soot and the catalyst.
Keywords: Nanometer; Ln-Na-Cu-O perovskite-like complex oxides; Soot; NO; x; Simultaneous removal
Catalytic combustion of ethanol on pure and alumina supported K-Mn oxides: An IR and flow reactor study by Miguel A. Peluso; Estela Pronsato; Jorge E. Sambeth; Horacio J. Thomas; Guido Busca (pp. 73-79).
Mn-based catalysts prepared by oxidation of Mn(II) by KMnO4, pure and supported on alumina, calcined at 350 and 500°C have been characterized and tested in the total oxidation of ethanol. IR experiments allowed us to have an indication on some aspects of the reaction mechanisms. The unsupported catalysts calcined at 350°C, mostly constituted by a cryptomelane phase were the most active, allowing the total conversion of ethanol at 180°C, with excellent stability for at least 80h. The reaction is initiated by the fast conversion of ethanol to acetate species via acetaldehyde. Later, the conversion of acetates to CO2 appears to be a slow step. On alumina-supported catalysts, which are (in spite of the much higher surface area) active only above 240°C, part of acetate species are adsorbed on the support and act as inactive spectators.
Keywords: Cryptomelane; Manganese oxide; VOCs; FTIR; Ethanol oxidation
Non-aqueous sol–gel synthesis, characterization and catalytic properties of metal fluoride supported palladium nanoparticles by Pratap T. Patil; Anton Dimitrov; Holm Kirmse; Wolfgang Neumann; Erhard Kemnitz (pp. 80-91).
High surface area (HS) metal fluoride supported palladium catalysts (Pd0/MF x) (MF x=AlF3, MgF2, CaF2 and KMgF3) together with the respective Pd-free HS-MF x catalysts have been prepared via a novel sol–gel synthesis. In a first step, the reaction of anhydrous hydrogen fluoride (aHF) with the respective solutions of the metal alkoxides containing up to 10% Pd(acac)2 yielded the catalyst precursors as HS-gels. In a second step, gas phase fluorination followed by H2-treatment was employed to obtain the final Pd0/MF x catalysts. X-ray diffraction (XRD) indicated the formation of mainly amorphous AlF3 and Pd0/AlF3, whereas bulk MgF2, CaF2 and KMgF3 and the respective Pd-loaded phases were partially crystalline. The XRD patterns of Pd0/MF x revealed besides the occurrence of broad MF x-reflections only very weak reflections for Pd0 supporting a uniform dispersion of Pd nanoparticles inside the highly distorted MF x structures as it was independently reconfirmed by TEM-investigations. FTIR photo-acoustic spectroscopy with pyridine chemisorption (FTIR-PAS) and dismutation activities showed that AlF3 and MgF2 bulk as well as the supported Pd samples possess strong to moderate Lewis acidities. CaF2 and KMgF3 bulk as well as the respective Pd samples were found to be neutral. BET specific surface areas of MF x and Pd0/MF x are very high, up to ten times higher than known from literature. TEM showed homogeneously dispersed Pd nanoparticles on MF x matrices with a mean particle size of ∼5 to 8nm. Catalytic activities of the samples were tested for the conversion of CHClF2 into valuable compounds by gas phase dismutation, hydrodehalogenation and pyrolysis, in presence as well as absence of hydrogen. Based on the obtained results and D/H-isotope exchange measurements, a carbene mechanism involving competitive dismutation coupled with consecutive reactions is proposed for the hydrodehalogenation process.
Keywords: Metal fluorides; Supported palladium nanoparticles; Sol–gel synthesis; CHClF; 2; conversion; Hydrodehalogenation; CH; 2; F; 2
Preparation and photocatalytic activity of boron-modified TiO2 under UV and visible light by Adriana Zaleska; Janusz W. Sobczak; Ewelina Grabowska; Jan Hupka (pp. 92-100).
Synthesis of new boron-containing TiO2 powders (B-TiO2) and their activity under UV and visible light are reported. The catalysts were prepared by the sol–gel method and by grinding anatase powder with a dopant. Boric acid triethyl ester and boric acid were used as boron sources in both catalysts preparation procedures. The photocatalytic activity of obtained powders in UV and visible light was estimated by measuring the decomposition rate of phenol (0.21mmol/dm3) in an aqueous solution. Carbon and boron presence in all prepared photocatalysts was confirmed by the XPS technique. The oxidation state of B atoms incorporated in TiO2 particles was mainly B3+, as determined from the X-ray photoelectron spectra (XPS). It was confirmed that boron-doped TiO2 was activated by visible light and used as effective catalyst in photooxidation reactions.
Keywords: Titanium dioxide; Boron-doped TiO; 2; Visible light
Phase change of catalysts derived from a LDH-deoxycholate intercalated compound and its impacts on NO reduction from stationary source emissions by Thakul Wongkerd; Apanee Luengnaruemitchai; Sirirat Jitkarnka (pp. 101-111).
Deoxycholate and keggin-type polyoxometalate (PW12O40 and SiW12O40) pillared-hydrotalcite-type clay catalysts were prepared, and the effects of calcination temperature were studied on selective catalytic reduction of NO by NH3 over excess oxygen in the reaction temperature range 150–450°C. The results showed that over 99% N2/N2O selectivity was achieved at all testing temperatures for all pillared-clay catalysts. The activity of all pillared-clay catalysts increased significantly with temperature beyond 300°C. It was found that all pillared clays had different thermal transition behaviors at various stages of calcinations temperature, which affected the SCR activity. The dehydroxylated intermediates and amorphous mixed oxide forms, whose Brønsted acid sites were still preserved after calcinations, appeared to yield high NO conversion with high N2/N2O selectivity. Generally, the PW12-clay-derived catalysts seem to have the highest activity. Five percent Fe loading by impregnation method significantly increased activity of pillared-clay catalysts while high N2/N2O selectivity was maintained. Fe-loaded catalysts also showed obviously higher N2/N2O selectivity than the commercial catalyst; 4.4% V2O5–8.2% WO3/TiO2.
Keywords: SCR; Keggins; Polyoxometalates; Pillared clay; Hydrotalcite
The effect of N-doping and halide-doping on the activity of CuCoO4 for the oxidation of elemental mercury by Zhijian Mei; Zhemin Shen; Zhiyuan Mei; Yejian Zhang; Fei Xiang; Jinping Chen; Wenhua Wang (pp. 112-119).
The investigations for vapor-phase Hg0 oxidation ability of Al2O3 (AL) loaded with CuCoO4 (AL-C), CuCoO4+NH4Cl (AL-CCl), and CuCoO4+NH4Br (AL-CBr) are carried out in an attempt to produce more economical and effective sorbents for the control of Hg0 emission from combustion processes. According to the X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) and mass balance analysis on mercury, we find that N-doped AL-C has bigger SBET than AL-C and the nitrogen doping greatly improves AL-C's Hg0 oxidation ability, especially at low temperatures. It is considered that nitrogen atoms in doped AL-C's polycrystalline are responsible for the significant enhancement in Hg0 oxidation ability of AL-CCl and AL-CBr. The Hg0 oxidation abilities of AL-CCl and AL-CBr under various adulteration values and adsorption temperatures were studied. When adulteration value is equal to 30%, AL-CCl and AL-CBr perform the best and their Hg0 oxidation abilities are remarkably higher than AL-C over wide range temperatures. AL-CCl and AL-CBr's breakthrough times increases from AL-C's 26h to 158h and 208h, respectively. The effects of 0.31% SO2 on AL-C, AL-CCl and AL-CBr's Hg0 oxidation abilities are insignificant, which indicates that N-doping has no adverse effect on both Co3+ and Cu2+-octahedral cations structure.
Keywords: Mercury; N-dope; Gas-phase; CuCoO; 4
Preparation, characterization and catalytic behavior of nanostructured mesoporous CuO/Ce0.8Zr0.2O2 catalysts for low-temperature CO oxidation by Jian-Liang Cao; Yan Wang; Tong-Ying Zhang; Shi-Hua Wu; Zhong-Yong Yuan (pp. 120-128).
High-surface area mesoporous CuO/Ce0.8Zr0.2O2 catalysts were prepared by a surfactant-assisted method of nanocrystalline particle assembly, and characterized by XRD, N2 adsorption, TEM, H2-TPR, TG-DTA and XPS techniques. The catalytic properties of the CuO/Ce0.8Zr0.2O2 nanocatalysts were evaluated by low-temperature carbon monoxide oxidation using a microreactor-GC system. XRD and TEM analysis indicated that the catalyst particles were nanoscaled with cubic, fluorite structure. N2 adsorption–desorption isotherms revealed a mesoporous nanocatalyst system with high-surface area and uniform pore-size distribution. The results of catalytic activity measurements showed that these mesoporous nanostructured CuO/Ce0.8Zr0.2O2 catalysts were very active for low-temperature CO oxidation. The catalytic behavior depended on the CuO loading amount, the calcination temperature, the surface area and the particle size of the catalyst. The catalyst with 25mol% CuO loading and calcined at 400°C exhibited the highest catalytic activity.
Keywords: CuO/Ce; 0.8; Zr; 0.2; O; 2; catalysts; Mesoporous; Nanostructured; Low-temperature CO oxidation; Catalytic activity
In-situ catalytic abatement of NO x during fluidized bed combustion—A literature study by Khanh-Quang Tran; Pia Kilpinen; Narendra Kumar (pp. 129-138).
In this study, opportunities, challenges, and possibilities to develop a bed material for in-situ catalytic reduction of NO x during fluidized bed combustion have been identified. Various catalytic materials and processes for abatement of NO x at high temperatures are reviewed, which include De-NO x catalysis, catalytic decomposition, and selective catalytic oxidation of NO x precursors in combustion processes. Possibilities to utilize fly ash from combustion itself for the development are discussed.
Keywords: In-situ NO; x; abatement; High temperature catalyst; FBC; Fly ash; Waste utilization
Photoassisted mineralization of aromatic and aliphatic N-heterocycles in aqueous titanium dioxide suspensions and the fate of the nitrogen heteroatoms by Hisao Hidaka; Elisa García-López; Leonardo Palmisano; Nick Serpone (pp. 139-150).
The photoassisted degradation of aromatic heterocycles (pyrrole, imidazole, pyrazole, isoxazole, oxazole and thiazole) and N-containing alicycles (aliphatic heterocycles: pyrrolidine, 4-butanelactam and 5-pentanelactam) was examined in liquid–solid dispersions. Complete mineralization (TOC) of the aromatic heterocycles was attained within ca. 1h of UV irradiation of the TiO2/heterocycle system in acidic (pH 3), near-neutral (pH 6.0–7.6) and alkaline (pH 11) media. Mineralization kinetics were, in general, not appreciably influenced by the presence of acid but tended to be somewhat slower in alkaline media. N-alicycles were photomineralized more slowly than were the aromatics. The former could be mineralized in acidic and near-neutral media in less than 2h, but not in alkaline media in which pyrrolidine, 4-butanelactam and 5-pentanelactam (and for comparison 4-butanelactone) were not mineralized even after 3h of UV irradiation. Final products were, in all cases, CO2, NH4+ and NO3− ions and SO42− ions in the case of thiazole. Nitrogen (N2) gas was detected only during the photooxidation of pyrazole (contains two adjacent N heteroatoms) but not imidazole in which the N atom are separated by a C atom. The molar ratio NH4+/NO3− depended closely on the chemical structure of the substrates at the longer irradiation times. The site and mode of adsorption of these heterocycles onto the TiO2 particle surface were inferred from point charge calculations and the point of zero charge of the TiO2 (pHpzc ∼6.7); the position of elecrophilic attack by the photogeneratedOH radicals was deduced from calculated frontier electron densities.
Keywords: Photomineralization; Titanium dioxide; Photodegradation; N-bearing compounds; Aliphatic heterocycles; Aromatic heterocycles; Alicycles
Microwave-enhanced catalytic degradation of 4-chlorophenol over nickel oxides by Teh-Long Lai; Chia-Chan Lee; Gim-Lin Huang; Youn-Yuen Shu; Chen-Bin Wang (pp. 151-157).
A mix-valenced nickel oxide was obtained from nickel nitrate aqueous solution through a precipitation with sodium hydroxide and an oxidation by sodium hypochlorite. Furthermore, the oxide was heated under microwave-assisted to fabricate a high-active mix-valenced nickel oxide (assigned as NiO x). Pure nickel oxide was obtained from the NiO x by calcination at 300, 400 and 500°C (labeled as C300, C400 and C500, respectively). They were characterized by thermogravimetry (TG), X-ray diffraction (XRD), infrared spectroscopy (IR), temperature-programmed reduction (TPR), nitrogen adsorption at 196°C and scanning electron microscopy (SEM). Their catalytic activities towards the degradation of 4-chlorophenol were further studied under continuous bubbling of air through the liquid phase. Also, the effects of pH, temperature and kinds of nickel oxide on the efficiency of the microwave-enhanced catalytic degradation (MECD) of 4-chlorophenol have been investigated. The results showed that the 4-chlorophenol had degraded completely into harmless products (CO2·H2O and mineral acids) within 5min of investigation, under pH 7 and T=70°C over the fabricated NiO x.
Keywords: Nickel oxide; Microwave; Degradation of 4-chlorophenol
Catalytic abatement of acetaldehyde over oxide-supported precious metal catalysts by Tomohiro Mitsui; Kazuki Tsutsui; Toshiaki Matsui; Ryuji Kikuchi; Koichi Eguchi (pp. 158-165).
Catalytic combustion of acetaldehyde was investigated on various oxide-supported metal catalysts prepared by impregnation method. Among the as-calcined catalysts tested, SnO2-supported precious metal catalysts showed the highest activity at low temperatures despite low BET surface area, whereas the catalytic activity of the SnO2-supported samples was significantly degraded by reduction treatment in H2 atmosphere. The catalytic activity of ZrO2- and CeO2-supported metal catalysts was improved by reduction treatment, as compared with the as-calcined catalysts. Among the reduced catalysts, ZrO2-supported metal catalysts exhibited the highest activity for acetaldehyde combustion. To reveal these phenomena, all the catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), and BET surface area. The catalytic activity was strongly related to the surface species easily reducible at low temperatures. Over the as-calcined SnO2-supported catalysts, Pt particles were highly dispersed and the existence of platinum species reducible at room temperature was inferred from XPS and TPR, which disappeared by the H2 reduction treatment, leading to deterioration of the activity. On the other hand, over the ZrO2- and CeO2-supported samples, precious metal species were reduced to metallic state by the H2 reduction treatment and stabilized to maintain the enhanced catalytic activity under oxidative atmosphere during acetaldehyde combustion.
Keywords: Volatile organic compounds; Catalytic combustion; Supported metal catalysts; Acetaldehyde
Washcoating of Pt-ZSM5 onto aluminium foams by Oihane Sanz; Luciano C. Almeida; Juan M. Zamaro; María A. Ulla; Eduardo E. Miró; Mario Montes (pp. 166-175).
The anodisation conditions of aluminium foam monoliths are studied in order to produce alumina with controlled properties. When anodisation conditions are extreme, an important cracking of the surface appears with width and depth cracks that depend on the anodisation parameters, i.e., electrolyte temperature, anodisation time and applied current density. Different surface treatments for aluminium foams (rough anodisation, smooth anodisation, and no anodisation) were used to observe the mechanical stability of Pt/ZSM5 coatings. Roughness of the surface improved adhesion of Pt/ZSM5 coatings because the size of the cracks was high enough to occlude the zeolite particles promoting a mechanical anchorage of the coating. The washcoated aluminium foam monoliths were tested in total oxidation of toluene showing very high activity.
Keywords: Aluminium foams; Anodisation; Zeolite washcoating; Catalyst coating adhesion
Influence of amine template on the photoactivity of TiO2 nanoparticles obtained by hydrothermal treatment by G. Colón; M.C. Hidalgo; J.A. Navío; E. Pulido Melián; O. González Díaz; J.M. Doña (pp. 176-182).
TiO2 nanoparticles have been prepared by amine template-assisted sol–gel precipitation and further hydrothermal treatment. We have investigated the effect of different amines (hydrazine and triethylamine) in the final surface and structural properties. It has been stated that the different amounts of amine could act as an interesting template upon hydrothermal treatment. Further thermal treatment also leads to a significant improvement in the photocatalytic properties of the studied systems. Surface and morphological features notably differ from TiO2 prepared using different synthetic routes. Wide surface and structural characterization of the samples have been carried out, and correlations with precipitation pH are pointed out from this characterization. In all cases, amine template TiO2 obtained exhibit high conversion values for phenol photo-oxidation reaction. Further calcination treatment of all the studied systems clearly leads to photocatalytic conversions higher than that exhibited by TiO2 Degussa P25.
Keywords: TiO; 2; Hydrazine; Triethylamine; Alkoxide; Sol–gel; Hydrothermal; Photocatalysis
NO and N2O decomposition and their reduction by hydrocarbons over Fe–Zn manganite spinels by Giuseppe Fierro; Roberto Dragone; Giovanni Ferraris (pp. 183-191).
In this work the catalytic behaviour of zinc manganite-based catalysts doped with iron in small amounts is reported for the reduction of NO by propane and propene. All catalysts are monophasic and are characterized by a spinel structure. On the most representative catalysts the NO and N2O decomposition and the reduction of N2O by propane and propene were also investigated. The NO reduction by hydrocarbons is enhanced by the presence of iron and the catalytic activity increases on increasing the iron loading. On the other hand, the catalytic activity of N2O reduction appears to be less sensitive to either the presence of iron and the type of hydrocarbon. Moreover, it is almost comparable to that of N2O decomposition which, in turn, occurs much easier than the NO decomposition. In all reactions the selectivity to N2 and CO2 is almost 1 at the maximum temperature explored of 873K. Along the NO and N2O reduction by hydrocarbons iron preserves in some extent the catalyst from reduction which tends to occur in propene at higher temperatures disaggregating the spinel phase into a mixture of ZnO and MnO oxides.
Keywords: Iron–zinc manganites; NO and N; 2; O reduction by propane; NO and N; 2; O reduction by propene; NO and N; 2; O decomposition