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Applied Catalysis B, Environmental (v.60, #1-2)
UV-induced photocatalytic degradation of azo dyes by organic-capped ZnO nanocrystals immobilized onto substrates by R. Comparelli; E. Fanizza; M.L. Curri; P.D. Cozzoli; G. Mascolo; A. Agostiano (pp. 1-11).
ZnO nanocrystals (mean particle size: 6nm) with different surface organic coating and commercial ZnO powder (mean particle size: 200nm) have been immobilized onto transparent substrates and comparatively examined as photocatalysts for the UV-induced degradation of two azo dyes, Methyl Red and Methyl Orange, in water. The effects of the pH, of the catalyst surface status, and of the dye chemical structure on the course of the photocatalysis are discussed. Reasonable degradation pathways for both target molecules are proposed on the basis of the structural identification of several by-products. The results demonstrate that surfactant-capped ZnO nanocrystals exhibit more versatile performances than those of conventional ZnO-based photocatalysts, because the surface organic coating makes the oxide resistant to photocorrosion and to pH changes. Surface-protected ZnO nanocrystals can be regarded as a valuable alternative to standard TiO2 photocatalysts.
Keywords: Nanocrystals; ZnO; Organic capping; Azo dyes; UV-induced photocatalysis
Ultra-active Fe/ZSM-5 catalyst for selective catalytic reduction of nitric oxide with ammonia by Gongshin Qi; Ralph T. Yang (pp. 13-22).
We report a Fe/ZSM-5 catalyst that has higher catalytic activities for the selective catalytic reduction (SCR) of NO by ammonia as compared to other known catalysts. This Fe/ZSM-5 catalyst was prepared by a simple impregnation method using NH4-ZSM-5 and FeCl2. The preparation process is in fact a combination of the conventional impregnation and solid-state ion exchange but the gas atmosphere for calcination is not an inert gas. Another process in which the Fe/ZSM-5 sample was first calcined in an inert gas (He) instead of air and then calcined in air was also investigated, and the activities of the catalysts prepared by these two processes were not different by much, which indicated that even in air the exchange between NH4+ and Fe2+ took place as evidenced by the ESR results and that the exchange was incomplete. Such incomplete exchange led to the formation of Brönsted type acid in the catalysts after the decomposition of NH4-ZSM-5, which is considered as the active site for ammonia adsorption. XRD and TEM clearly showed that there existed fine iron oxide particles located on the external zeolite surfaces. XPS results show that, unlike the Fe-ZSM-5 catalyst prepared by aqueous ion exchange, large amount of Fe2+ species were found in the Fe/ZSM-5 catalyst prepared by this method. Compared to the activities of different Fe/ZSM-5 catalysts, the existence of the Fe2+ species and the highly dispersed FeO x species may have contributed to the high activity of this Fe/ZSM-5 catalyst, especially in the low temperature ranges. Characterization of the catalyst and the reaction mechanism were also investigated by FTIR.
Keywords: Selective catalytic reduction (SCR); SCR of NO; NH; 3; –SCR; Fe/ZSM-5; TEM; TPR; XRD; FTIR
The catalytic activity of FeO x/ZrO2 and FeO x/sulphated-ZrO2 for the NO abatement with C3H6 in the presence of excess O2 by Valerio Indovina; Maria Cristina Campa; Franco Pepe; Daniela Pietrogiacomi; Simonetta Tuti (pp. 23-31).
Iron containing catalysts were prepared by (i) impregnation of ZrO2 with aqueous solutions of Fe(NO3)3, Fe/Zi, or aqueous solutions of NH4Fe(SO4)2, FeS/Z; (ii) chemical vapour deposition (CVD) of FeCl3 on ZrO2, Fe/ZCVD; and (iii) impregnation of sulphated-ZrO2 with toluene solutions of Fe(acetylacetonate)3, Fe/SZ. After calcining at 823K, samples were characterised by temperature-programmed reduction with H2 and Fourier transformed IR spectroscopy. NO reduction with C3H6 in the presence of excess O2 was studied in a flow apparatus fed by a reactant mixture of NO:C3H6:O2=2000ppm:2000ppm (or 2700ppm):20,000ppm in He.FTIR characterisation by CO adsorption showed that various carbonyl-like species formed on Fe n+ sites (0≤ n<3). Their relative amounts depended not on the iron content, but on the catalyst preparation method.The reducibility of FeIII to FeII in H2 increased in the order FeS/ZCVDi. In the C3H6+O2 reaction, the catalytic activity for C3H6 oxidation increased in parallel with the reducibility. In the NO+C3H6+O2 reaction, the selectivity to CO2 (rather than to CO) increased in parallel with the reducibility. By contrast, the selectivity of C3H6 towards NO rather than O2 increased in the reverse order. These results suggest that the catalytic activity and selectivity of the various samples depend on the chemical behaviour of the FeIII/FeII redox couple.
Keywords: NO abatement; Sulphated-ZrO; 2; Supported iron oxide
Supported perovskites for total oxidation of toluene by M. Alifanti; M. Florea; S. Somacescu; V.I. Parvulescu (pp. 33-39).
Supported LaCoO3 perovskites with 10 and 20wt.% loading were obtained by incipient wetness impregnation of different Ce1− xZr xO2 ( x=0–0.3) supports with a “citrate� solution, prepared from La and Co nitrates, and citric acid. Ce1− xZr xO2 were also prepared using the “citrate method�. All materials were calcined at 700°C for 6h and investigated by N2 adsorption at −196°C, XRD and XPS. XRD patterns evidenced the formation of a pure perovskite phase. These materials were tested in toluene total oxidation in the temperature range 100–500°C. All catalysts showed a lower T50 than the corresponding Ce1− xZr xO2 supports or pure LaCoO3 perovskite. The activity of the catalysts was found to increase with the perovskite loading, irrespective of the support composition. For the same loading, the support composition influences drastically the oxidative abilities of LaCoO3.
Keywords: Catalytic combustion; Toluene oxidation; Supported perovskite; CeO; 2; –ZrO; 2; supports
Zn-promoted Rh/SiO2 catalyst for the selective reduction of NO with H2 in the presence of O2 and SO2 by Yoshitake Hasegawa; Masaaki Haneda; Yoshiaki Kintaichi; Hideaki Hamada (pp. 41-47).
The effect of metal additives on the catalytic performance of Rh/SiO2 for the selective reduction of NO with H2 in the presence of O2 and SO2 was investigated. The addition of Zn was effective to enhance the catalytic activity of Rh/SiO2 for NO reduction at low temperatures and high O2 concentrations. The structural characterizations of Zn/Rh/SiO2 samples and in situ FT-IR measurements revealed that Zn additive plays two important roles in enhancing the catalytic activity of Rh/SiO2: (i) prevention of catalyst deactivation as an oxidation–retardant for the active Rh metal species supported on SiO2 and (ii) promotion of a reaction step, which generates NH x species as a key reaction intermediate for NO reduction by H2 in the presence of O2 and SO2.
Keywords: Nitrogen monoxide; Selective reduction; Hydrogen; Rh/SiO; 2; Zn/Rh/SiO; 2; FT-IR
Oxidation behavior of cyclohexane on alumina-supported manganese oxides with ozone by Hisahiro Einaga; Shigeru Futamura (pp. 49-55).
Catalytic oxidation of cyclohexane with ozone was carried out over alumina-supported manganese oxides at 295K. The catalytic activities decreased steeply with time on stream, and then reached a steady state. At the steady state, the mole fractions of CO2 and CO were 90 and 10%, respectively, with the carbon balance of around 50%. The decomposition ratio was estimated to be 8–10, independent of Mn loadings and support materials. Partially oxidized compounds including alcohols, ketones, acid anhydrides and carboxylic acids were formed on the catalyst surface. These compounds were decomposed by ozone feed. On the other hand, highly resistant species containing CO, COO– and CH groups remained on the catalyst surface, which caused the gradual deactivation of the catalyst. The CO groups were decomposed at relatively lower temperatures (<473K), while higher temperature (>473K) was necessary to decompose the COO– and CH groups.
Keywords: Catalytic ozonation; Decomposition; Manganese oxides; Cyclohexane
The amplification of ammonia by reaction with NO and CO over dual function platinum and palladium catalyst systems with isocyanic acid as an intermediate by Noel W. Cant; Dean C. Chambers; Irene O.Y. Liu (pp. 57-63).
The hypothesis that ammonia concentrations can be amplified by reaction with NO in excess CO to form isocyanic acid (HNCO) which is then hydrolysed back to NH3 has been tested. With 1000ppm NO and 400ppm NH3 in 3400ppm CO, the HNCO produced in a dry feed over Pd/SiO2 and Pt/SiO2 is sufficient to allow potential multiplications of 1.9 and 2.2, respectively. With Pt/SiO2 a greater multiplication is possible if water is present since additional HNCO is formed using surface hydrogen generated by the water–gas shift reaction. Isocyanic acid is completely hydrolysed to NH3 if oxides more active than silica are located downstream, or used to support the platinum group metal, provided excess water is present. An actual amplification of six has been demonstrated starting from 150ppm NH3 with CeO2/SiO2 downstream of Pt/SiO2. With Pt/Al2O3, 300ppm NH3 can be multiplied by 3.6 in the temperature range 300–450°C.
Keywords: Ammonia amplification; Isocyanic acid synthesis; Isocyanic acid hydrolysis; NO reduction by CO; Pt/SiO; 2; Pd/SiO; 2; Pt/Al; 2; O; 3; CeO; 2; –SiO; 2
An investigation on the mechanism of NO decomposition over Rh/SiO2 catalysts in presence of pulse injected H2 by H. Papp; D.P. Sabde (pp. 65-71).
Rh/SiO2 catalysts were prepared by sol–gel, micro-emulsion and grafting methods. They were characterized by BET, EDXRF and TEM. Their catalytic activity was studied for NO decomposition under steady state transient conditions with pulse injected H2. The reactions were carried out in the temperature range of 100–400°C. NO, N2O, NO2, O2, H2, NH3, N2 and H2O were monitored and analyzed by mass spectroscopy. Rh/SiO2 catalysts were highly active and selective for NO reduction to N2. H2 pulse experiments revealed that pulse injected H2 removed the adsorbed atomic oxygen and nitrogen species from the catalyst surface to form water and NH3, respectively. Based on the pulse experiments, the mechanism for the formation of N2, H2O, NH3 and N2O has been proposed.
Keywords: NO decomposition; NO; +; H; 2; Rh/SiO; 2; MS analysis
Pd supported on tetragonal zirconia: Electrosynthesis, characterization and catalytic activity toward CO oxidation and CH4 combustion by Marco Faticanti; Nicola Cioffi; Sergio De Rossi; Nicoletta Ditaranto; Piero Porta; Luigia Sabbatini; Teresa Bleve-Zacheo (pp. 73-82).
Catalysts made of Pd supported on ZrO2 were prepared via a sacrificial anode electrosynthesis route. Tetragonal zirconia was added to an electrolytic cell assembled for the preparation of colloidal Pd nanoparticles. Several samples were prepared varying the electrolysis time and thus the Pd loading in the nanocomposite. XRD analysis showed the presence of the tetragonal ZrO2 mainly and some small reflections due to monoclinic ZrO2. BET surface areas were in the range 70–80 m2g−1. The morphology and surface chemical composition of the nano-materials were, respectively, assessed by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analyses. From TEM evidence, the Pd-ZrO2 powders revealed to be composed of spherical Pd nanoparticles (average core diameter: 6.9±1.8nm) evenly dispersed on the surface of ZrO2 nano-grains (average grain size: 150±70nm, average size of crystallites composing each grain: 40±10nm). XPS allowed to quantify the surface elemental composition of the nanomaterials and to study the different chemical states of the nano-dispersed palladium. Catalysts were tested for CH4 total combustion and for CO oxidation. The conversion increased with Pd content in the CH4 combustion experiments whereas decreased with Pd content in the CO oxidation experiments. The apparent activation energies were about 25 and 9kcalmol−1 for CH4 combustion and CO oxidation, respectively. Hypothesis was made that different reaction mechanisms and different active sites were probably involved in the two reactions.
Keywords: Electrosynthesis; Pd nanoparticle; Nanocomposite; XPS; Catalytic CO oxidation; CH; 4; combustion
In situ sulphated CuO x/ZrO2 and CuO x/sulphated-ZrO2 as catalysts for the reduction of NO x with NH3 in the presence of excess O2 by Daniela Pietrogiacomi; Alessandro Magliano; Diana Sannino; Maria Cristina Campa; Paolo Ciambelli; Valerio Indovina (pp. 83-92).
Sulphated catalysts containing the same amount of sulphates (2.6 SO4nm−2) and a different amount of copper (0.3–3.9 Cu atomsnm−2), Cu/SZ, were prepared by impregnation of sulphated-ZrO2 with toluene solutions of Cu(acetylacetonate)2. Sulphated catalysts containing the same amount of copper (0.3 or 2.5 atomsnm−2) and a different amount of sulphates (up to 4.9 SO2nm−2), Cu/ZSg, were prepared by sulphation of CuO x/ZrO2 (Cu/Z) via the gas-phase. Samples were characterised by Fourier transformed IR spectroscopy. The selective catalytic reduction of NO with NH3 in the presence of excess O2 (SCR reaction), the NH3+O2 and the NO+O2 reactions were studied in a flow apparatus.Activity and selectivity did not depend on the sulphation method used for catalyst preparation but depended on the amount of copper and sulphate, particularly on the sulphate/copper ratio.As on Cu/Z, on Cu/SZ CuII was active for both SCR and NH3+O2 reactions. The presence of covalent sulphates caused lower reducibility of CuII to CuI and higher Lewis acid strength of CuI in Cu/SZ than in Cu/Z.For (i) SCR, (ii) NH3+O2 and (iii) NO+O2, Cu/ZSg were less active than the parent Cu/Z. As the sulphate content in Cu/ZSg increased, the NO yield in the NH3+O2 reaction markedly decreased, thus accounting for the increased selectivity in the SCR reaction. In CuO x/sulphated-ZrO2 copper ions were less prone reversibly to undergo the redox process CuII/CuI.These findings provide new information on the role of copper and sulphate in determining the activity and selectivity for the SCR with NH3.
Keywords: NO abatement; SCR; Sulphated-ZrO; 2; Supported copper oxide
Titanium dioxide mediated heterogeneous photocatalytic degradation of gaseous dimethyl sulfide: Parameter study and reaction pathways by Kristof Demeestere; Jo Dewulf; Bavo De Witte; Herman Van Langenhove (pp. 93-106).
This paper deals with the photocatalytic degradation of gaseous dimethyl sulfide (DMS) in a wide range of inlet concentrations (3ppmv<[DMS]in<545ppmv), gas residence times (5s< τ<55s) and relative humidities (3%2 Degussa P25 as a photocatalyst in a flat-plate photoreactor. DMS removal efficiencies increased with lower [DMS]in and higher τ, while the optimum RH was 22%. Although DMS removal efficiencies higher than 90% (peaks over 97%) could be obtained for at least 180min at τ=55s, RH<53% and [DMS]in<10ppmv, prolonged irradiation and/or increased [DMS]in resulted into catalyst deactivation due to accumulation of reaction products on the TiO2 surface. During photocatalytic DMS degradation at [DMS]in≥100ppmv, dimethyl disulfide, carbon dioxide and sulfur dioxide were detected as gas-phase reaction products, while solid–liquid extraction revealed dimethyl sulfoxide, dimethyl sulfon, methane sulfonic acid and sulfate as reaction products adsorbed on the exposed catalyst. Consequently, detailed photocatalytic DMS degradation pathways were proposed, starting with TiO2(h+) orOH mediated DMS oxidation and followed by CS bond cleavage, S-oxidation and C-oxidation. Carbon and sulfur mass balances were closed for 90–105% and 98–110%, respectively. [DMS]in did not have an important effect on product distribution, but interesting trends in DMS degradation products were observed as a function of RH.
Keywords: Photocatalysis; Titanium dioxide; Degussa P25; Volatile organic sulfur compounds; Dimethyl sulfide; Gas-phase; Relative humidity; Inlet concentration; Deactivation; Reaction pathways
Catalytic dry reforming of methane over high surface area ceria by N. Laosiripojana; S. Assabumrungrat (pp. 107-116).
High surface area ceria (CeO2 (HSA)), synthesized by a surfactant-assisted approach, was found to have useful dry reforming activity for H2 and CO production under solid oxide fuel cells (SOFCs) conditions. The catalyst provides significantly higher reforming reactivity and excellent resistance toward carbon deposition compared to Ni/Al2O3 and conventional low surface area ceria (CeO2 (LSA)) under dry reforming conditions. These enhancements are due to the high redox property of CeO2 (HSA). During the dry reforming process, the redox reactions between the gaseous components in the system and the lattice oxygen (O x) take place on ceria surface. Among these reactions, the rapid redox reactions of carbon compounds such as CH4, and CO with lattice oxygen (CH4+O x→CO+H2+O x−1 and CO+O x=CO2+O x−1) can prevent the formation of carbon species from the methane decomposition and Boudard reactions even at low inlet carbon dioxide concentration.In particular, the dry reforming rate over CeO2 (HSA) is proportional to the methane partial pressure and the operating temperature. Carbon dioxide presents weak positive impact on the methane conversion, whereas both carbon monoxide and hydrogen inhibit the reforming rate. The activation energies and reforming rates under the same methane concentration for CeO2 toward the dry reforming are almost equal to the steam reforming as previously reported [1–4]. This result suggests the similar reaction mechanisms for both the steam reforming and the dry reforming over CeO2; i.e., the dry reforming rate is governed by the slow reaction of adsorbed methane, or surface hydrocarbon species, with oxygen in CeO2, and a rapid gas–solid reaction between CO2 and CeO2 to replenish the oxygen.
Keywords: Ceria; Dry reforming; High surface area; Hydrogen; SOFC
Influence of oxychlorination treatments on the redox and oxygen storage and release properties of thermally aged Pd-Rh/Ce xZr1− xO2/Al2O3 model three-way catalysts by R.A. Daley; S.Y. Christou; A.M. Efstathiou; J.A. Anderson (pp. 117-127).
Model Pd-Rh/Al2O3 three-way catalysts with and without Ce xZr1− xO2 as oxygen storage component have been compared in their fresh, thermally aged and oxychlorinated treated surface states to determine the potential regenerating effects of the latter thermo-chemical treatments. Special attention has been made on the characterisation of the metal dispersion, redox properties and the oxygen storage and release properties of the catalyst following each of the treatment stages. It was found that thermal aging under the conditions employed leads to a loss of metal dispersion, but with negligible sintering of the ceria–zirconia mixed metal oxide. Loss of oxygen storage capacity is a consequence of the loss in metal area that results in a loss of interfacial contact with the storage component. Oxychlorination of the aged samples leads to even greater than 100% recovery of metal dispersion and a significant recovery of the oxygen storage capacity. As a consequence of these effects, catalytic activity for the CO/O2 and NO/H2/O2 reactions was shown to improve significantly. The role of residual chloride following regenerating treatment is discussed in terms of ceria reducibility.
Keywords: Three-way catalysts; Aging; Regeneration; OSC; Oxychlorination; PdRh; Ceria–zirconia
Complete hydrodechlorination of chlorobenzene and its derivatives over supported nickel catalysts under liquid phase conditions by Wenhei Wu; Jie Xu; Ryuichiro Ohnishi (pp. 129-137).
Liquid phase hydrodechlorination of chlorobenzene was studied over Ni/active carbon (Ni/AC), Ni/γ-Al2O3, Ni/SiO2 and Raney Ni. The complete hydrodechlorination of chlorobenzene was realized at 333–343K on Ni/AC under hydrogen atmosphere of 1.0MPa in the presence of alkaline hydroxide. Aryl halides, three chlorotoluenes ( o-, m- and p-), three chloroanilines, three chlorobenzotrifluorides, three dichlorobenzenes and two trichlorobenzenes (1,2,3- and 1,2,4-) were also completely hydrodechlorinated under the similar conditions. Chlorobenzene derivatives having either an electron-donating group or an electron-withdrawing group decreased their reactivities with respect to the unsubstituted chlorobenzene. The reactivities of polychlorinated benzenes slightly decreased with the increasing chlorine atom number in a molecule. The steric effect of trichlorobenzene gave a large influence on the product distribution.The reaction rate did not depend on chlorobenzene concentration and increased with increasing hydrogen pressure. The reaction did not proceed in the absence of alkaline hydroxide. The active catalysts were characterized by hydrogen chemisorption and transmission electron microscopy techniques. The apparent activity strongly depends on the active surface area of nickel on catalyst surface. Based on the above results, the reaction route was discussed.The deactivation of Ni catalyst was observed in the dechlorinating process. An accumulation of NaCl on the catalyst surface is probably one of the reasons for the deactivation. The deactivated catalysts can be partially recovered by washing with distillated water and reactivating.
Keywords: Hydrodechlorination; Substituted chlorobenzenes; Polychlorinated benzenes; Nickel carbon; Substituent effect
The selective oxidation of ammonia over alumina supported catalysts–experiments and modelling by J.M. Jones; M. Pourkashanian; A. Williams; R.I. Backreedy; L.I. Darvell; P. Simell; K. Heiskanen; P. Kilpinen (pp. 139-146).
Hot gas-clean up will improve the efficiency of emerging gasification technologies. Selective catalytic oxidation (SCO) of ammonia is a promising approach for dealing with the main fixed nitrogen species. The work presented here comprises both laboratory scale experimental measurements of potential SCO catalysts, as well as the development of a simple four-step reaction model to describe the behaviour of one of the more promising catalysts. A range of transition metal oxides supported on γ-alumina were studied for their activity in the SCO of ammonia in a simulated gasification gas mixture containing CO, H2O, H2, CO2, CH4, H2S and toluene as model tar species. Both copper and chromium based catalysts demonstrated a window of operating temperature over which they were resistant to poisoning by H2S; Cu/Al2O3 was in fact promoted by this gas for the SCO reaction. The ammonia conversion over 7% Cu/Al2O3 was studied in more detail, and this data was further used to develop a kinetic model for the reactions taking place over the temperature range 723–906K. Excellent conversion and selectivity to N2 was found in the temperature window 973–1173K and 2.6vol% O2. However, it also catalyses a rapid H2O2 reaction. This reaction consumes all remaining available oxygen so that no other oxidation reactions take place (e.g. of methane or ‘tar’). The four-step reaction model was developed using the PLUG application of Chemkin and Surface Chemkin software coupled with the gas-phase mechanism Kilpinen 97. Rates for the heterogeneous oxidation of ammonia and hydrogen are included as well as forward and reverse reactions of the water gas shift. Over the temperature range in question, the surface reaction rates are much faster than the gas-phase reactions. The model is applicable for the 723–906K temperature range using a gas mixture containing 0.4vol% ammonia and 0.01vol% H2S in the presence of O2 (0–2.6 vol%).
Keywords: Ammonia (selective catalytic oxidation); Gasification (biomass); Modelling (kinetics; ammonia oxidation)