Abstract: A series of Fe exchanged zeolites (MOR, USY, BEA and ZSM-5) were prepared by wet ion exchange and tested for N2O catalytic reduction by NH3. Fe-MOR exhibits the highest activity and this is attributed to its highest content of isolated Fe3+ ions and little Fe(III)(x)O-y clusters, since isolated Fe3+ ions are the active species for N2O reduction while Fe(III)(x)O-y clusters inhibit N2O dissociation due to strong NH3 adsorption. Moreover. Fe-MOR not only achieved N2O and NO simultaneously reduction at a very low temperature (700 K) but also showed good durability under simulated conditions at a typical nitric acid plant. (C) 2011 Elsevier B.V. All rights reserved.
Abstract: In this study, monometallic Co-mordenite (MOR) and bimetallic CoFe-MOR catalysts were prepared via simple wet ion exchange and tested for N2O decomposition. Strong promotion effect of Fe on the activity and stability of Co ions in the zeolites was observed. To investigate the origin of this promotion effect, X-ray diffraction, H-2-temperature programmed reduction, UV-Vis spectroscopy, extended X-ray absorption fine structure analysis, and N2O temperature-programmed desorption were used to characterize the bimetallic and monometallic catalysts. The characteristic results indicated that higher contents of Co ions located at beta sites after Fe addition provided cooperation on N2O splitting by two neighboring Co ions. Consequently, a greater amount of surface NOx species were formed in situ and were more strongly bonded to the catalyst, facilitating the removal of O and increasing the activity. Moreover, extended X-ray absorption fine structure analysis indicated that beta-type Co ions exhibited stronger coordination to framework oxygen after Fe addition, and higher exchange level was obtained in the bimetallistic CoFe-MOR. Both of them contribute to prevent the relocation of Co2+ ions to form cobalt oxides, thus, high activity was maintained. Consequently, the CoFe-MOR catalyst demonstrates a superior catalytic activity and a high durability in N2O decomposition, showing great potential as a cost-effective catalyst for N2O elimination in future applications.
Abstract: Catalysts of Co1.5Mg1.5/Al0.9Ti0.1O and Co1.5Mg1.5/AlO were successfully prepared by calcinations of corresponding hydrotalcite-like compounds at 800 degrees C for 4 hr. The derived oxides were of spinel phase and a small quantity of Ti substitution did not change the crystal purity. Their catalytic performance for the NO storage/decomposition was investigated. Ti incorporation enhanced the NO decomposition activity while has an opposite effect on the storage capacity of catalyst. In situ FT-IR spectra of the catalysts showed that the final adsorption species on the catalysts was coordinated nitrates/nitrites. In addition, NO storage/decomposition mechanism has been discussed on the basis of these observations.
Abstract: We systematically investigated the reaction mechanism and effect of O-2 on N2O reduction by NH3 over an Fe Mordenite (MOR) catalyst. O-2 has no inhibitory effect on N2O reduction, and NH3 selective catalytic reduction (SCR) of N2O is superior to NH3 oxidation by O-2. We found that the mechanism of NH3 SCR of N2O involves the redox cycle of Fe(III) OH sites, with Fe(III) OH reduction by NH3 as the first and rate-determining step. Then N2O is activated at the reduced Fe(II)-OH sites into NO/N or N-2/O, receddizing the Fe(II)-OH into-Fe(III) OH sites. Next, the NO formed in situ reacts with adsorbed NH2 to form NH2NO, which further decomposes to N-2 and water. In addition, some NO may join with O to form NC2, which reacts with NH4+ to produce NH4NO2 and further decomposes to N-2 and water. It is possible that under the steady 'state, N-NO breaking accounts for two-thirds of N2O splitting. The formation of NO intermediates plays a crucial role in this reaction. The structural arrangement of MOR zeolites and the high content of Fe ions provides two proximal Fe ions, that is, Fe(III)center dot center dot center dot Fe(III) pairs, as the active sites for this N-NO breaking, resulting in the high activity of Fe-MOR.
Abstract: A series of Co exchanged zeolites with ZSM-5, BEA, MOR and USY structures were prepared and investigated for N2O catalytic decomposition under identical reaction conditions. It is found that Co-zeolites with different structures show dramatically different catalytic activities, which could be attributed to various Co species formed in them. Co-ZSM-5, Co-BEA and Co-MOR exhibit much higher activities than Co-USY catalysts, which is attributed to the predominant formation of active isolated Co2+ ions in the ion exchange positions; while in Co-USY Co mainly exists as less active Co oxides. Moreover, it is observed that the activities of Co2+ ions in ZSM-5, BEA and MOR zeolites are quite different and are related to the specific Co ion sites presented in each zeolite structure. In Co-ZSM-5, the most active sites are the alpha-type Co ions, which are weakly coordinated to framework oxygens in the straight channel. On the other hand, in Co-BEA and Co-MOR, the most active sites are beta-type Co ions, which are coordinated to the framework oxygens of the elongated six-membered ring of BEA and the interconnected small channel of MOR, respectively. The main factors affecting the activities of these individual Co ions are indicated to be their location in the zeolite structure, their chemical coordination and the distances between the Co ions. The highest activity of the alpha-type Co ions in ZSM-5 could be attributed to their favorite location in the zeolite and weak coordination to framework oxygens, which make them easily accessible and coordinated to reactants. The large number of beta-sites and their structural arrangement in MOR allow the formation of two unique adjacent beta-Co ions in Co-Co pairs, which cooperate in N2O splitting, consequently yielding the high activity of beta-Co ions in MOR.
Abstract: A series of novel Pd/CO3AlO catalysts derived from hydrotalcite-like compounds (HTlcs) have been prepared and investigated for total oxidation of toluene. The HTlcs phase Co-Al precursors were prepared by coprecipitation method and Pd active species were introduced by different approaches, i.e., impregnation (IMP), wet ion exchange (WIE) or directly at coprecipitation stage (COP). It is found that all hydrotalcitederived Pd/CO3AlO catalysts are much more active than the Pd/CO3AlO catalyst prepared via traditional thermal combustion method (TCB) in toluene elimination. The activities of all synthesized catalysts obey the following sequence: Pd/CO3AlO (COP) > Pd/CO3AlO (WIE) >= Pd/CO3AlO (IMP) > Pd/CO3AlO (TCB). Excellent catalytic activities of the novel hydrotalicite-derived Pd/CO3AlO catalysts could be contributed to their high surface area, small mean crystallized size of support and highly dispersed PdO particles. Besides, they are well positively associated with catalyst reducibilities and the amounts of oxygen vacancies. According to the XPS. TEM and TPR results, it was found that the strong synergistic effect between Co3O4 and PdO, but not the amount of the surface palladium species which are generally believed to be the active sites, is the main factors determining the catalytic activity in this work. The stability tests indicate that all Pd/CO3AlO catalysts have no obvious deactivation, and some catalysts even show improved activities during the reaction process due to the emergence of metal Pd. (C) 2010 Elsevier B.V. All rights reserved.
Abstract: Co contained MOR zeolite catalysts with high Co loadings were successfully synthesized by buffered ion exchange at pH 8, and were tested for N(2)O catalytic decomposition. The high exchange level of synthesized CoMOR(x)-BIE catalysts probably benefits from the maximizing hydroxycomplexes Co(OH)(+) ion in the buffered solution, which is more preferred for the ion exchange with the zeolites. It has been found that the novel CoMOR(x)-BIE catalysts exhibit excellent catalytic activities, which is attributed to the large population of isolated Co(2+) ions on ion exchange positions. The most active CoMOR(130)-BIE catalyst shows high resistance to the inhibition of oxygen, NO and water vapor. Furthermore, stability tests indicate that the CoMOR(130)-BIE catalyst has no obvious deactivation under simulated emission conditions after reaction for more than 100 h. This extraordinary durability could be related to its high Co(2+) content and low Brönsted acidity sites in the catalyst, which facilitate the stability of active isolated Co(2+) on ion exchange positions. Thus, the CoMOR(130)-BIE catalyst shows a great potential as a cost-effective catalyst for N(2)O elimination in future applications.
Abstract: Co(1.5)M(1.5)/Al(1-x)Ti(x) hydrotalcite-like compounds (where M = Co, Ca and x = 0, 0.1) were synthesized by a constant-pH coprecipitation. The derived oxides from hydrotalcites upon calcination at 800 degrees C for 4 h were all of spinel phase without crystalline TiO(2) phase being detected. Substitution of partial Al for Ti significantly enhanced NO direct decomposition activity of these catalysts. In particular, catalyst Co(3.0)/Al(0.9)Ti(0.1)O (CATO) showed the highest NO direct decomposition percentage, up to 86% at 300 degrees C with GHSV of 30 000 h(-1) (800 ppm of NO and 8% O(2) in N(2) stream). CATO also showed the highest resistance to SO(2) poisoning to NO direct decomposition, with the activity being only reduced by 16% in the presence of 64 ppm of SO(2) in the mixed gas stream at 300 degrees C. The in-situ FT-IR spectra indicate different adsorption species over the catalysts, revealing NO surface storage/decomposition involves different adsorption reactions that determine the NO decomposition activity and resistance to SO(2) poisoning.
Abstract: Co contained MOR zeolite catalysts with high Co loadings were successfully synthesized by buffered ion exchange at pH 8, and were tested for N(2)O catalytic decomposition. The high exchange level of synthesized CoMOR(x)-BIE catalysts probably benefits from the maximizing hydroxycomplexes Co(OH)(+) ion in the buffered solution, which is more preferred for the ion exchange with the zeolites. It has been found that the novel CoMORx-BIE catalysts exhibit excellent catalytic activities, which is attributed to the large population of isolated Co(2+) ions on ion exchange positions. The most active CoMOR(130)-BIE catalyst shows high resistance to the inhibition of oxygen, NO and water vapor. Furthermore, stability tests indicate that the CoMOR(130)-BIE catalyst has no obvious deactivation under simulated emission conditions after reaction for more than 100 h. This extraordinary durability could be related to its high Co(2+) content and low Bronsted acidity sites in the catalyst, which facilitate the stability of active isolated Co(2+) on ion exchange positions. Thus, the CoMOR(130)-BIE catalyst shows a great potential as a cost-effective catalyst for N(2)O elimination in future applications. (C) 2011 Elsevier B.V. All rights reserved.
Abstract: ZSM-5/MCM-48 composite materials with various acidities have been successfully assembled on zeolite seeds via a two-step crystallization process. The characterization results reveal that the ZSM-5 seeds are present in the framework of the resulting composite materials with its content gradually increasing with the Si/Al molar ratio, and Al atoms prefer the tetrahedral coordination in composite products. The amount of strong acid sites increases as the Si/Al molar ratio decreases, while that of weak acid sites is almost unchanged. The activity tests demonstrate that the catalytic activity of Pd-loaded ZSM-5/MCM-48 composite catalysts is much higher than that of Pd/ZSM-5 and Pd/MCM-48, and all these catalysts are active and stable in the total oxidation of benzene. Both Pd(0) and Pd(2+) are responsible for the oxidation reaction, and the catalytic activity is closely related to the support acidity, the CO(2) desorption capability and the Pd dispersion. This research thus indicates that the novel composite materials have promised as active Pd-supported catalysts in the elimination of volatile organic compound (VOCs). (C) 2010 Elsevier B.V. All rights reserved.
Abstract: The deposition of binary M-ZrO(2) (M = Al(2)O(3), SiO(2) or TiO(2)) as secondary support on cordierite substrate by dip-coating was investigated and the as-prepared M-ZrO(2)/cordierite was characterized by means of XRD and SEM techniques. After two successive dip-coating processes, the highest washcoat loading of 25.1% was achieved in Al(2)O(3)-ZrO(2)/cordierite, followed by 18.7% in TiO(2)-ZrO(2)/cordierite and then 17.4% in SiO(2)-ZrO(2)/cordierite. The optimal parameters to prepare Al(2)O(3)-ZrO(2) washcoat on cordierite were investigated in detail. After introduction of noble metal active components (Rh and Pd) to the secondary support, the obtained Rh/M-ZrO(2)/cordierite and Pd/M-ZrO(2)/cordierite were further tested as monolithic catalysts for the decomposition of nitrous oxide and the deep oxidation of benzene, respectively. (C) 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Abstract: Reaction behaviors and kinetics of catalytic oxidation of benzene, toluene, and ethyl acetate with feed concentrations in the range of 700-5,000 ppm over Pd/ZSM-5 catalyst were investigated. Results for single components show that ethyl acetate (T (50) = 190-200A degrees C) is more easily oxidized than benzene (T (50) = 215-225A degrees C) and toluene (T (50) = 225-235A degrees C). The conversion of ethyl acetate was increased with the increase of its feeding concentration, while the opposite behaviors were observed for benzene and toluene as their conversion rates were decreased with the increase of the inlet concentration. Different behaviors were observed in catalytic oxidation of volatile organic compound (VOC) multi-components, the presence of benzene or toluene inhibits the conversion of ethyl acetate, and the aromatic hydrocarbons inhibit each other in all cases. Ethyl acetate possesses obvious inhibitory effect on benzene oxidation, while it is interesting to note that ethyl acetate has a promotion effect on toluene conversion. The kinetic data were fitted by the Power-law and Mars-van Krevelen kinetic models. The fitting result shows that the Power-law model is more suitable for predicting the conversion of benzene than the other VOCs, and the Mars-van Krevelen model can accurately express the reaction rate of all investigated VOCs.
Abstract: In this paper, we report a convenient and effective approach to synthesizing mesoporous SBA-15 materials with increased surface area (up to 836.7 cm(3)/g) and expanded microporosity (up to 0.22 cm(3)/g), where the textural properties of the synthesized materials can be systematically controlled. These micro/mesoporous composite materials exhibit excellent performance in catalysis, adsorption and separation. Moreover, the synthesized materials that supported Pd catalysts obtained through impregnation and grafting approaches were tested to explore their flexibility in toluene elimination. Grafting is an effective method to obtain highly dispersed Pd nanoparticles compared with traditional impregnation approach. The catalyst prepared via the grafting procedure possesses higher activity and CO(2) selectivity than that was prepared by impregnation method. Moreover, the catalytic performance of synthesized catalysts can be well sustained during the stability tests. Therefore, these novel Pd-supported catalysts are promising materials for effective removal of some types of volatile organic compounds (VOCs) such as toluene. (C) 2010 Elsevier B.V. All rights reserved.
Abstract: Low-temperature catalysts of mesoporous Co3O4 and AU/Co3O4 with high catalytic activities for the trace ethylene oxidation at 0 degrees C are reported in this paper. The catalysts were prepared by using the nanocasting method, and the mesostructure was replicated from three-dimensional (3D) cubic KIT-6 silicas. High resolution transmission electron microscopy (HRTEM) studies revealed that {110} facets were the exposed active surfaces in the mesoporous Co3O4, whereas the Co3O4 nanosheets prepared by the precipitation method exhibited the most exposed {112} facets. We found that the mesoporous Co3O4 was significantly more active for ethylene oxidation than the Co3O4 nanosheets. The results indicated that the crystal facet {110} of Co3O4 played an essential role in determining its catalytic oxidation performance. The synthesized Au/Co3O4 materials, in which the gold nanoparticles were assembled into the pore walls of the Co3O4 mesoporous support, exhibited stable, highly dispersed, and exposed gold sites. Gold nanoparticles present on Co3O4 readily produced surface-active oxygen species and promoted ethylene oxidation to achieve a 76% conversion at 0 degrees C, which is the highest conversion reported yet.
Abstract: The oxidation of NO to NO2 was studied on Pt/TiO2 catalysts prepared by wet impregnation and photo-deposition method. Pt/TiO2 prepared by photo-deposition exhibited quite higher activity for NO oxidation to NO2 than that prepared by wet impregnation and over 90% NO conversion could be achieved at below 250 degrees C at a high GHSV of 180,000 h(-1). The effects of catalysts pretreatment conditions and feed gas composition, i.e. SO2 and H2O in the stream, on No oxidation were investigated in details. The different Pt/TiO2 samples were characterized by means of X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) techniques. The Pt-TiO2 electron-interaction was studied based on the characterization results and the role of Pt-TiO2 electron-interaction on the catalytic performance of Pt/TiO2 was further discussed. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.
Abstract: Co(x)Mg(3-x)/Al composite oxides (xCoMAO-800) were prepared by calcination of Co(x)Mg(3-x)/Al hydrotalcites (x = 0.0, 0.5,1.0,1.5,2.0,2.5,3.0, respectively) at 800 degrees C. The materials were characterized using XRD, TG-DSC, N(2) adsorption-desorption and TPR. The methane catalytic combustion over the xCoMAO-800 was assessed in a fixed bed micro-reactor. The results revealed that cobalt can be homogenously dispersed into the matrices of the hydrotalcites and determines the structure, specific surface areas and porosity of the derived xCoMAO-800 oxide catalysts. The thermal stability and homogeneity of the hydrotalcites markedly depends on the cobalt concentration in the hydrotalcites. The Co-based hydrotalcite-derived oxides exhibit good activity in the catalytic combustion of methane. The catalytic activity over the xCoMAO-800 oxides enhances with increasing x up to 1.5, but subsequently decreases dramatically as cobalt loadings are further increased. The 1.5CoMAO-800 catalyst shows the best methane combustion activity, igniting methane at 450 degrees C and completing methane combustion around 600 degrees C. The catalytic combustion activity over the xCoMAO-800 oxides are closely related to the strong Co-Mg/Al interaction within the mixed oxides according to the TG-DSC, TPR and activity characteristics. (C) 2009 Elsevier B.V. All rights reserved.
Abstract: ZSM-5/MCM-48 composite materials with different acidities and enhanced thermal stability have been synthesized via a simple and reliable in situ overgrowth method. The as-prepared biporous materials and the Pd-impregnated catalysts were systematically investigated by various techniques, including XRD, ICP-OES, N(2) adsorption/desorption, H(2) chemisorption, SEM, TEM/HRTEM, FT-IR, (27)Al MAS NMR, NH(3)-TPD, H(2)-TPR and XPS. The characterization results reveal that all composite catalysts exhibit high surface area, large pore volume and long pore diameter. The quantity of acid sites increases as the ZSM-5 additive amount increases, and Al atoms are in the tetrahedral coordination positions in composite materials. The activity tests demonstrate that all the Pd-loaded catalysts are active in the total elimination of benzene, while the catalytic activity values of Pd-loaded ZSM-5/MCM-48 composite catalysts are much higher than those of Pd/ZSM-5 or Pd/MCM-48 alone. Both Pd(0) and Pd(2+) are responsible for the oxidation reaction, and the catalytic activities are primarily related to the support acidity and the Pd dispersion. In addition, the stability of the composite catalysts also improves with an appropriate amount of ZSM-5 additives in MCM-48. This research shows that the novel Pd-loaded composite catalysts are promising materials in the elimination of VOCs. (c) 2010 Elsevier B.V. All rights reserved.
Abstract: In this study, mesoporous SBA-15 supported Pd catalysts were synthesized through impregnation and grafting approaches. Moreover, the influences of different solvents (ethanol, H(2)O, tetrahydrofuran, dimethyl sulphoxide and N,N-dimethylformamide) on the dispersion of supported Pd nanoparticles were also systematically investigated. The prepared materials were comprehensively explored by various techniques. including XRD, EDS, ICP-OES, H(2) chemisorption, N(2) adsorption/desorption, TG-DSC, FT-IR, TEM and STEM. It is found that the traditional impregnation method has some disadvantages in obtaining highly dispersed Pd active phase. Whereas, the grafting method could highly disperse Pd nanoparticles within the mesoporous channels of support material, and the grafting procedure should be promising in designing highly dispersed Pd particles on the silica-based mesoporous materials. The catalyst prepared via the grafting procedure possesses much higher activity and selectivity than that prepared by impregnation method for deep catalytic oxidation of toluene. (C) 2010 Elsevier B.V. All rights reserved.
Abstract: Au/HMS catalysts are prepared by impregnation method and direct synthesized method and evaluated for the selective oxidation of benzyl alcohol. Among all the catalysts studied, Au/HMS catalyst prepared by impregnation method exhibits the best activity, the benzyl alcohol conversion of 42.9% and benzaldehyde selectivity of 95% can be achieved at 80 degrees C, 1 atm O(2) and existence of Na(2)CO(3) aqueous solution. The Au/HMS catalysts are characterized by low-angle X-ray diffraction (XRD), wide-angle XRD, N2 adsorption/ desorption and transmission electron microscopy (TEM) techniques. The effects of prepared method, gold particle size and HMS structure are investigated in detail. The active phase of gold catalysts for selective oxidation of benzyl alcohol is explored based on the catalytic performance and characterization results. Moreover, the possible activation mechanism for selective oxidation of benzyl alcohol on Au/HMS catalysts is studied by means of CO and O(2) adsorption in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS). (C) 2010 Elsevier B.V. All rights reserved.
Abstract: The surface species formed during NO oxidation in the absence/presence of SO(2) over Pt/TiO(2) catalyst prepared by photo-deposition are investigated by in situ FTIR spectroscopy. During the adsorption of NO-O(2), predominant various nitrates are formed on the surface of TiO(2). The addition of SO(2) to NO-O(2) greatly suppresses the formation of surface nitrates and also changes the types of nitrates formed. The decomposition of surface nitrates on Pt/TiO(2) is observed at elevated temperature of ca. 250 degrees C and the decomposition temperature is retarded to ca. 350 degrees C with the addition of SO(2) during NO-O(2) adsorption. The direct oxidation of gaseous NO to NO(2) is proposed as the main pathway for NO(2) formation and the decomposition of surface nitrates at elevated temperatures plays a negative role on NO oxidation. (C) 2010 Elsevier B. V. All rights reserved.
Abstract: Low-temperature catalysts of mesoporous Co(3)O(4) and Au/Co(3)O(4) with high catalytic activities for the trace ethylene oxidation at 0 degrees C are reported in this paper. The catalysts were prepared by using the nanocasting method, and the mesostructure was replicated from three-dimensional (3D) cubic KIT-6 silicas. High resolution transmission electron microscopy (HRTEM) studies revealed that {110} facets were the exposed active surfaces in the mesoporous Co(3)O(4), whereas the Co(3)O(4) nanosheets prepared by the precipitation method exhibited the most exposed {112} facets. We found that the mesoporous Co(3)O(4) was significantly more active for ethylene oxidation than the Co(3)O(4) nanosheets. The results indicated that the crystal facet {110} of Co(3)O(4) played an essential role in determining its catalytic oxidation performance. The synthesized Au/Co(3)O(4) materials, in which the gold nanoparticles were assembled into the pore walls of the Co(3)O(4) mesoporous support, exhibited stable, highly dispersed, and exposed gold sites. Gold nanoparticles present on Co(3)O(4) readily produced surface-active oxygen species and promoted ethylene oxidation to achieve a 76% conversion at 0 degrees C, which is the highest conversion reported yet.
Abstract: The feasibility of Pd/Ti-SBA-15 catalysts in the elimination of benzene was explored comprehensively. The effects of the titanium incorporation on catalyst physicochemical property and activity were investigated by X-ray diffraction, N(2) adsorption/desorption, Fourier transform infrared spectroscopy, DRUV-vis, NH(3)-TPD, scanning electron microscope, and transmission electron microscope techniques. Only a certain quantity of titanium can be incorporated into the support, and titanium has a positive influence on active phase dispersion. Titanium-modified catalysts possess larger pore diameter than the pure Pd/SBA-15 and titanium can introduce the acid sites to the support. The evaluation result shows that the titanium incorporation can noticeably improve the catalytic activity, and all evaluated catalysts possess excellent stability, without obviously activity loss during 60 h test. (C) 2010 American Institute of Chemical Engineers Environ Prog, 29: 435-442, 2010
Abstract: Large-molecule polyhydroxy organic acids such as tartaric acid and citric acid were found to significantly promote the cooperative formation of mesoporous silica SBA-15 with homogeneous well-defined hexagonal mesostructure under much weaker acidities without addition of volatile inorganic acids; therefore a novel environmental benign route for SBA-15 synthesis was developed, It is suggested that the polar groups of polyhydroxy acid molecules can greatly strengthen the assembly interactions between the silica species and the triblock copolymer by providing hydrogen bonding. More interestingly, by controlling the strength of hydrogen-bonding interaction that is dependent on the concentration of carboxylic acids, the particle size of the product can be tailored. The silica with small particle size synthesized with a small amount of polyhydroxy acids was favorable support of palladium catalyst for the complete oxidation of volatile organic compounds in atmosphere, probably due to the facilitated diffusion of reactant molecules.
Abstract: La2Zr2O7 and La2TM0.3Zr1.7O7-delta (TM = Fe, Mn, and Co) pyrochlores were investigated as catalysts for methane combustion at moderate-high temperatures. They were prepared by the coprecipitation method and characterized by XRD, DSC, H-2-TPR, IR, and N-2 adsorption/desorption techniques. The introduction of transition metals strongly influences the Zr-O bond strength, the temperature of pyrochlore phase formation, the redox properties, and crystallite size of pyrochlores. Among the catalysts tested, La2Fe0.3Zr1.7O7-delta gives the highest catalytic activity. The catalytic activities of La2TM0.3Zr1.7O7-delta pyrochlore oxides for methane combustion were mainly dependent on the textural properties (BET area, crystallite size). Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.
Abstract: The feasibility and mechanism of five molecular sieves-supported palladium catalysts in elimination of benzene, toluene, and ethyl acetate were investigated. The experimental results indicate that Pd particles are well dispersed on these porous supports with size of 2-10 nm, while mesoporous supports with a larger specific surface area and pore diameter lead to a better dispersion. The activity of freshly made catalysts obeys the following order: Pd/Beta > Pd/ZSM-5 > Pd/SBA-15 > Pd/MCM-48 > Pd/MCM-41. Although Pd/Beta has the highest activity for removal of these VOCs in the beginning, its activity quickly decreases. However, Pd/ZSM-5 and Pd/SBA-15 show a good stability, without activity loss in a 72 h test. Our research reveals that higher acidity can facilitate catalytic reaction and gives rise to higher activity, but it also enhances coke formation and decreases the catalyst stability. In addition, the porosity of supports has a certain impact on catalytic oxidation of VOCs.
Abstract: A series of TiO(2) supported catalysts were prepared by impregnation method in a rotary evaporator and evaluated for the oxidation of NO to NO(2). Among all catalysts studied, Ru/TiO(2) catalyst exhibited the best activity and a maximal NO conversion of c.a. 94% could be achieved at c.a. 275 degrees C at a high GHSV of 180,000 h(-1). For ruthenium catalysts, the effects of supports, ruthenium loadings, pretreatment conditions and experiment conditions (feed gas composition, GHSV) on NO oxidation to NO(2) were investigated in detail. The ruthenium catalysts were characterized by means of X-ray diffraction (XRD), CO pulse chemisorption, transmission electron microscopy (TEM) and temperature-programmed reduction (TPR) techniques. The active ruthenium species for NO oxidation were discussed based on the catalytic and characterization results. Moreover, the reaction mechanism for NO oxidation over Ru/TiO(2) catalyst was studied by means of in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS). (C) 2008 Elsevier B.V. All rights reserved.
Abstract: Effective control and removal of nitrogen oxides (NOx) emission from vehicles exhausts under leanburn condition is one of the most important targets in scientific research of environmental protection. A comprehensive introduction of NOx storage and reduction (NSR), the most promising lean-NOx control technology, is given including the SUM-Lip of NSR materials, catalytic activity and related reaction mechanisms. Emphasis is put on the novel multifunctional NSR catalysts, derived from hydrotalcite-like compounds, with characteristic of simultaneous NOx strorage-decomposition-reduction. Finally, future research directions in the area of lean-NOx control based on mixed oxide catalysts derived from hydrotalcite-like materials is also proposed. (C) 2009 Elsevier Inc. All rights reserved.
Abstract: With initial aging at low temperature for enough time, silicas with large mesoporosity were synthesized using triblock copolymer as template agent under weak acidities. SBA-15 with periodic mesostructure and short mesochannels could be synthesized at pH 2.5-3.0 within weak acidity range, and the surface areas, pore diameters and pore volumes reached up to ca. 1000 m(2)/g, 8.8 nm and 2.0 cm(3)/g, respectively, which were significantly higher than those of the conventional SBA-15 synthesized under strong acidities. Mesoporous silica with wormhole structure and abundant textural porosity was formed at pH similar to 3.5. The increased hydrophobic volume of the copolymer micelles at elevated pH values was responsible for the enlargement of mesoporosity in the products. The materials synthesized under weak acidities showed lower hexagonal ordering in comparison to the general SBA-15 synthesized under strong acidities because the decreased hydronium ion concentration induced relatively weaker assembly forces during the synthesis. Nonetheless, the short mesochannels and large pore diameter in the products might be beneficial to some applications in which fast diffusion of molecules is required. (C) 2009 Elsevier Inc. All rights reserved.
Abstract: In this paper, we report the synthesis of Au/SBA-15 and Au-Pd/SBA-15 materials by impregnation and grafting methods. It was found that the Au-Pd/SBA-15 sample prepared by the grafting method could highly disperse metal nanoparticles in mesoporous channels of SBA-15 and exhibit excellent catalytic performances for the selective oxidation of benzyl alcohol to benzaldehyde at mild reaction conditions (air atmosphere, 80 degrees C). The prevention of agglomeration and leaching of gold nanoparticles by restricting them inside the mesopores of SBA-15 leads to a high stability of Au-Pd/SBA-15. In both approaches. the addition of Pd to Au/SBA-15 catalysts can decrease the size of gold nanoparticles, which attributes to higher activity for the selective aerobic oxidation of benzyl alcohol. (C) 2009 Elsevier B.V. All rights reserved.
Abstract: Effective control and removal of nitrogen oxides (NO(x)) emission from vehicles exhausts under lean-burn condition is one of the most important targets in scientific research of environmental protection. A comprehensive introduction of NO(x) storage and reduction (NSR), the most promising lean-NO(x) control technology, is given including the sum-up of NSR materials, catalytic activity and related reaction mechanisms. Emphasis is put on the novel multifunctional NSR catalysts, derived from hydrotalcite-like compounds, with characteristic of simultaneous NO(x) strorage-decomposition-reduction. Finally, future research directions in the area of lean-NO(x) control based on mixed oxide catalysts derived from hydrotalcite-like materials is also proposed.
Abstract: With initial aging at low temperature for enough time, silicas with large mesoporosity were synthesized using triblock copolymer as template agent under weak acidities. SBA-15 with periodic mesostructure and short mesochannels could be synthesized at pH 2.5-3.0 within weak acidity range, and the surface areas, pore diameters and pore volumes reached up to ca. 1000m(2)/g, 8.8nm and 2.0cm(3)/g, respectively, which were significantly higher than those of the conventional SBA-15 synthesized under strong acidities. Mesoporous silica with wormhole structure and abundant textural porosity was formed at pH approximately 3.5. The increased hydrophobic volume of the copolymer micelles at elevated pH values was responsible for the enlargement of mesoporosity in the products. The materials synthesized under weak acidities showed lower hexagonal ordering in comparison to the general SBA-15 synthesized under strong acidities because the decreased hydronium ion concentration induced relatively weaker assembly forces during the synthesis. Nonetheless, the short mesochannels and large pore diameter in the products might be beneficial to some applications in which fast diffusion of molecules is required.
Abstract: A series of Pd-containing hydrotalcite precursors (M3Al-HT) with different M2+ (M=Mg, Co, Ni, Cu, Zn) ions were synthesized by a co-precipitation method. Pd/M3AlO catalysts were derived from these hydrotalcite-like compounds by calcination. X-ray Diffraction (XRD), thermogravimetry-differential thermal gravimetry (TG-DTG), N-2 adsorption and desorption, temperature programmed reduction (H-2-TPR), and temperature programmed desorption (O-2-TPD) techniques were used to study the influence of different M2+ ions on the composition and structures of the Pd/M3AlO catalysts and their performance during the catalytic oxidation of chlorobenzene. XRD and TG-DTG data showed that hydrotalcite precursors could be successfully prepared with different M2+ ions except Cu2+ ion. And Pd was well dispersed in different hydrotalcite precursors. The M2+ ions greatly influence the activities of the serial catalysts. Among the investigated catalysts, the activity of the Pd supported Co-containing oxide was found to be much higher than the other catalysts. The light-off and complete oxidation temperatures were 1.82 and 283 degrees C, respectively. H-2-TPR and O-2-TPD results show that higher reduction abilities and higher intensities of the surface oxygen active species as well as the synergetic effect between Pd and Co contribute to excellent Pd/Co3AlO catalytic activity.
Abstract: Various XnY3-n-Al-hydrotalcite-like compounds (HTIcs) were synthesized by the constant pH coprecipitation method with the (X2+ + Y2+)/AI(3+) molar ratio fixed at 3.0. Well-mixed oxides XnY3-n AlO were derived from corresponding HTIcs precursors upon calcination. Physicochemical characterization with X-ray diffraction analysis, Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA), and the Brunauer-Emmett-Teller equation indicates that the derived oxides are of either periclase or spinel phase, with an interparticle pore diameter of 9.6-15.4 nm. These oxides generally show a high CO2 adsorption capability at 350 C. For example, CaCoAlO captures 1.39 mmol/g of CO2 (i.e., 6.12 wt %) from a gas mixture (8% CO2 in N-2) at 350 degrees C and 1 atm in a fixed-bed reactor within 20 min. All other mixed oxides adsorb 0.87-1.28 mmol/g (3.83-5.63 wt %) of CO2. Therefore, these mixed oxides are potential cost-effective CO2 sorbents for environmental remediation. In addition, the CO2 adsorption behavior is well-described with the deactivation model. The species of CO2 formed on the sorbents are various carbonates, as revealed by in situ IR spectra as well as TGA.
Abstract: A series of La2CoxSn2-xO7-delta oxides with pyrochlore structure have been synthesized by the co-precipitation method as high-temperature catalysts for methane combustion. The dopant strongly influences the thermal stability and redox properties of these pyrochlores. IR measurements show that the Sn-O bond strength was weakened with increasing amount of Co doped in the La2Sn2O7, thus promoting the formation of oxygen vacancy. The reduction rates and the amount of oxygen vacancy would significantly affect catalytic activities of La2CoxSn2-xO7-delta in CH4 oxidation. Among the doped pyrochlores, La2Co0.3Sn1.7O7-delta and La2Co0.5Sn1.5O7-delta possessed optimum activities for methane combustion at low and high temperature, respectively. (c) 2007 Elsevier B.V. All rights reserved.
Abstract: Various XnY(3-n)Al-hydrotalcite-like compounds (HTlcs) were synthesized by the constant pH coprecipitation method with the (X2+ + Y2+)/Al3+ molar ratio fixed at 3.0. Well-mixed oxides Xn,Y(3-n)AlO were derived from corresponding HTlcs precursors upon calcination. Physicochemical characterization with X-ray diffraction analysis, Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA), and the Brunauer-Emmett-Teller equation indicates that the derived oxides are of either periclase or spinel phase, with an interparticle pore diameter of 9.6-15.4 nm. These oxides generally show a high CO2 adsorption capability at 350 degrees C. For example, CaCoAlO captures 1.39 mmol/g of CO2 (i.e., 6.12 wt %) from a gas mixture (8% CO2 in N2) at 350 degrees C and 1 atm in a fixed-bed reactor within 20 min. All other mixed oxides adsorb 0.87-1.28 mmol/g (3.83-5.63 wt %) of CO2. Therefore, these mixed oxides are potential cost-effective CO2 sorbents for environmental remediation. In addition, the CO2 adsorption behavior is well-described with the deactivation model. The species of CO2 formed on the sorbents are various carbonates, as revealed by in situ IR spectra as well as TGA.
Abstract: Reactions of carbonyl sulfide (OCS) oil atmospheric particles were investigated in a flowing system using Fourier transform infrared (F-FIR) at 293 K. Results show that OCS Could he Slowly oxidized and hydrolyzed on atmospheric particles. As a simplified model. alumina (Al2O3) was used to further compare the two reactions and the results indicate that hydrolysis reaction of OCS has an advantage over oxidation reaction to take place at given time and that heterogeneous reactions of OCS on particles at atmospheric conditions may include oxidation and hydrolysis reactions. To explore the effect of metals oil hydrolysis reaction, zinc (Zn), iron (Fe), calcium (Ca), and magnesium (Mg) Supported oil Al2O3 were prepared by incipient wetness method, and the results suggest that all metal oxides significantly enhance the initial intrinsic activity of OCS when compared with unmodified Al2O3. The Zn-modified Al2O3 gives a significant increase of CO2 produced throughout the time-scale of these experiments and the possible reaction processes are proposed. (C) 2008 Curtin University of Technology and John Wiley & Sons, Ltd.
Abstract: Novel Cu(1)Co(2)/X(0.2)Al(0.8) well-mixed oxides (where X = Fe, Mn, Ce, La) were synthesized by calcinations of corresponding hydrotalcite-like compounds at 800 degrees C for 4 h. Their catalytic performance for the methane combustion was investigated. The oxides and their precursors were characterized by X-ray diffraction (XRD), thermogravimetry-differential scanning calorimetry (TG-DSC), temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), and N(2) adsorption/desorption techniques. The derived oxides are mainly of spinel and tenorite phase, with surface area of 10-30 m(2)/g, where new phase CeO(2) and LaCoO(3) are segregated in Ce- and La-containing oxides, respectively. The catalytic activities of the catalysts are related to the redox properties of the metal cations and the species in the surface. Incorporation of the Mn and Fe element is helpful to the reduction of the oxide catalysts, which may lead to the enhancement of the catalytic activity. Among the catalysts investigated, Cu(1)Co(2)/Mn(0.2)Al(0.8) gives the highest catalytic activity. Light-off and complete oxidation temperature was centered at about 374 and 496 T, respectively. The less active was Cu(1)Co(2)/Fe(0.2)Al(0.8). The intensities of surface oxygen species over Mn- and Fe-containing oxides are much higher than other catalysts, implying the higher activity of surface oxygen for the methane combustion.
