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1.
Formation of H2O2 from H2 and O2 and decomposition/hydrogenation of H2O2 have been studied in aqueous acidic medium over Pd/SiO2 catalyst in presence of different halide ions (viz. F−, Cl− and Br−). The halide ions were introduced in the catalytic system via incorporating them in the catalyst or by adding into the reaction medium. The nature of the halide ions present in the catalytic system showed profound influence on the H2O2 formation selectivity in the H2 to H2O2 oxidation over the catalyst. The H2O2 destruction via catalytic decomposition and by hydrogenation (in presence of hydrogen) was also found to be strongly dependent upon the nature of the halide ions present in the catalytic system. Among the different halides, Br− was found to selectivity promote the conversion of H2 to H2O2 by significantly reducing the H2O2 decomposition and hydrogenation over the catalyst. The other halides, on the other hand, showed a negative influence on the H2O2 formation by promoting the H2 combustion to water and/or by increasing the rate of decomposition/hydrogenation of H2O2 over the catalyst. An optimum concentration of Br− ions in the reaction medium or in the catalyst was found to be crucial for obtaining the higher H2O2 yield in the direct synthesis. 相似文献
2.
Oxidation of bulk samples of 〈Al〉 by water and H2O/CO2 mixture at sub- and supercritical conditions for uniform temperature increase and at the injection of H2O (665 K, 23.1 MPa) and H2O/CO2 (723 K, 38.0 MPa) fluids into the reactor has been studied. Transition of 〈Al〉 into AlOOH and Al2O3 nanoparticles has been found out. Aluminum samples oxidized by H2O and H2O/CO2 fluids at the injection mostly consist of large particles (300-500 nm) of α-Al2O3. Those oxidized for uniform temperature increase contain smaller particles (20-70 nm) of γ-Al2O3 as well. Mechanism of this phenomenon is explained by orientation of oxygen in H2O polar molecules to the metal in the electric field of contact voltage at Al/AlOOH and Al/Al2O3 boundary. Addition of CO2 to water resulted in CO, CH4, CH3OH and condensed carbon, increase in size of Al2O3 nanoparticles and significant decrease in time delay. In pure CO2 〈Al〉 oxidation resulted in oxide film. Using temperature and time dependences of gaseous reactant pressure and Redlich-Kwong state equation, kinetics of H2 formation has been described and oxidation regularities determined. At aluminum oxidation by H2O and H2O/CO2 fluids, self-heating of the samples followed by oxidation rate increase has been registered. The samples of oxidized aluminum have been studied with a transmission electronic microscope, a thermal analyzer and a device for specific surface measurement. The effect of oxidation conditions on the characteristics of synthesized nanoparticles has been found out. 相似文献
3.
Jianrong Ma Zhenyu Liu Qingya Liu Shijie Guo Zhanggen Huang Yong Xiao 《Fuel Processing Technology》2008
Supporting V2O5 onto an activated coke (AC) has been reported to significantly increase the AC's activity in simultaneous SO2 and NO removal from flue gas. To understand the role of V2O5 on SO2 removal, V2O5/AC is studied through SO2 removal reaction, surface analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) techniques. It is found that the main role of V2O5 in SO2 removal over V2O5/AC is to catalyze SO2 oxidation through a VOSO4-like intermediate species, which reacts with O2 to form SO3 and V2O5. The SO3 formed transfers from the V sites to AC sites and then reacts with H2O to form H2SO4. At low V2O5 loadings, a V atom is able to catalyze as many as 8 SO2 molecules to SO3. At high V2O5 loadings, however, the number of SO2 molecules catalyzed by a V atom is much less, due possibly to excessive amounts of V2O5 sites in comparison to the pores available for SO3 and H2SO4 storage. 相似文献
4.
在小型紫外光-鼓泡床反应器中,对UV/H2O2氧化联合Ca(OH)2吸收同时脱除燃煤烟气中NO与SO2的主要影响因素[H2O2浓度、紫外光辐射强度、Ca(OH)2浓度、NO浓度、溶液温度、烟气流量以及SO2浓度]进行了考察。采用烟气分析仪和离子色谱仪分别对尾气中的NO2和液相阴离子作了检测分析。结果显示:在本文所有实验条件下,SO2均能实现完全脱除。随着H2O2浓度、紫外光辐射强度和Ca(OH)2浓度的增加,NO的脱除效率均呈现先大幅度增加后轻微变化的趋势。NO脱除效率随烟气流量和NO浓度的增加均有大幅度下降。随着溶液温度和SO2浓度的增加,NO脱除效率仅有微小的下降。离子色谱分析表明,反应产物主要是SO42-和NO3-,同时有少量的NO2-产生。尾气中未能检测到有害气体NO2。 相似文献
5.
6.
Mercury emission from coal combustion is an increasing environmental concern due to its high volatility and toxicity, and activated carbon (AC) adsorption has been proven an effective mercury-control method, with high-cost limit. The renewable bioresource of bamboo constitutes an important precursor for activated carbon, and the bamboo charcoal (BC) may act as low-cost sorbent used in the mercury-control. The adsorptive potential of BC and modified BC using H2O2 for elemental mercury was investigated for the first time through a parametric study conducted with a bench-scale bed. The effects of pore structure and surface chemistry were investigated based on BET, XPS. Which suggest that BC materials have excellent adsorption potential for elemental mercury, especially after modified by H2O2. The modification using H2O2 altered the physical and chemical properties of BC materials, making the sorbents more effective in mercury adsorption even at a relative higher temperature, and the enhancing-effect was more obvious with increasing H2O2. 相似文献
7.
UV/H2O2氧化联合CaO吸收脱除NO的传质-反应动力学 总被引:3,自引:0,他引:3
在实验室规模的光化学反应器中,基于实验研究﹑动力学理论以及双膜理论,研究了UV/H2O2氧化联合CaO吸收(UV/H2O2-CaO工艺)脱除燃煤烟气中NO的传质-反应动力学。分析了NO吸收的传质-反应过程,明确了NO吸收过程的主要控制步骤和强化措施,测定了关键的动力学参数,推导了NO吸收过程的理论模型。结果表明:在实验范围内,NO吸收速率随着NO浓度的增加几乎呈线性增加。随着H2O2浓度和CaO浓度的增加,NO的吸收速率均呈现先增加后变缓的趋势。UV/H2O2-CaO工艺脱除NO是一个拟一级快速反应过程,强化气相主体扰动﹑增加气液接触面积和提高NO分压可有效提高NO的吸收速率。NO吸收速率方程的计算值和实验值具有较好的一致性。 相似文献
8.
Kyoung-Soo Kang Chang-Hee Kim Ki-Kwang Bae Won-Chul Cho Seong-Uk Jeong Yun-Je Lee Chu-Sik Park 《Chemical Engineering Research and Design》2014
Fe2O3 is a promising oxygen carrier for hydrogen production in the chemical-looping process. A set of kinetic studies on reduction with CH4, CO and H2 respectively, oxidation with water and oxygen containing Ar for chemical-looping hydrogen production was conducted. Fe2O3 (20 wt.%)/ZrO2 was prepared by a co-precipitation method. The main variables in the TGA (thermogravimetric analyzer) experiment were temperatures and gas concentrations. The reaction kinetics parameters were estimated based on the experimental data. In the reduction by CH4, CO and H2, the reaction rate changed near FeO. Changes in the reaction rate due to phase transformation were observed at low temperature and low gas concentration during the reduction by CH4, but the phenomenon was not remarkable for the reduction by CO and H2. The reduction rate achieved using CO and H2 was relatively faster than achieved using CH4. The Hancock and Sharp method of comparing the kinetics of isothermal solid-state reactions was applied. A phase boundary controlled model (contacting sphere) was applied to the reduction of Fe2O3 to FeO by CH4, and a different phase boundary controlled model (contacting infinite slab) was fit well to the reduction of FeO to Fe by CH4. The reduction of Fe2O3 to Fe by CO and H2 can be described by the former phase boundary controlled model (contacting sphere). This phase boundary controlled model (contacting sphere) also fit well for the oxidation of Fe to Fe3O4 by water and FeO to Fe2O3 by oxygen containing Ar. These kinetics data could be used to design chemical-looping hydrogen production systems. 相似文献
9.
This laboratory study was designed to investigate the degradation of 4-chloronitrobenzene ([CNB] = 2.4 × 10?6 mol L?1; pH = 7.5) by H2O2/UV and by O3/UV oxidation processes which involve the generation of very reactive and oxidizing hydroxyl free radicals. The effects of the oxidant doses (H2O2 or aqueous O3), liquid flow rate (or the contact time), and bicarbonate ions acting as OH· radical scavengers on the CNB removal rates were studied. For a constant oxidant dose, the results show that the O3/UV system appears to be more efficient than the H2O2/UV system to remove CNB because of the greatest rate of OH· generation by ozone photodecomposition compared to H2O2 photolysis. However, for a given amount of oxidant decomposed, the H2O2/UV oxidant system was found to be more efficient than O3/UV. Moreover, high levels of bicarbonate ions in solution (4 × 10?3 mol L?1) significantly decrease the efficiency of CNB removal by H2O2/UV and by O3/UV oxidation processes. 相似文献
10.
The wastewater from textile industries containing non-biodegradable and toxic dye compounds is one important sources of environmental contamination. This study aims at investigating the decomposition of azo dye by UV/H2O2 process with varying H2O2 concentrations, dye concentrations, initial pHs, and UV irradiation powers. The results show that the initial rate increases with increase in initial H2O2 concentration, initial dye concentration to a certain point and then decreases with further increase in the above factors; the initial rate remains almost constant at lower pH and then decreases with increase in pH; the initial rate linearly increases with increase in UV irradiation power. A comprehensive kinetic model, based on reaction network analysis, was developed to predict the effects of H2O2 concentration, dye concentration, solution pH, and UV irradiation power on the initial dye reaction rate. The experimental data and the predicted results are in good agreement. 相似文献
11.
P. Kirszensztejn B. Czajka Tai-Cheng Sheng T. N. Bell I. D. Gay 《Catalysis Letters》1995,32(3-4):305-312
The surface acidic properties of two series of samples,-Al2O3 and-Al2O3-SnO2 after reaction with CCl2F2/H2 (CFC12/H2), have been investigated by solid state high resolution CP/MAS 31-PNMR, using trimethylphosphine (TMP) as a probe molecule. It was found after reaction, that Brønsted acid sites were formed on the-Al2O3 surface. The longer the reaction time, the more rigidly TMP bonded to the acid sites. For the-Al2O3-SnO2 system, Brønsted acid sites were also found on both the Al2O3 and SnO2 surfaces after reaction of the-Al2O3-SnO2 system with CFC12/H2. The signal intensity relevant to these sites, indicates that the SnO2 component is attached to, and therefore covers Brønsted sites of-Al2O3. Two types of Lewis acid site initially present on SnO2 were not observed after reaction with CFC12/H2. 相似文献
12.
This paper deals with the kinetics of the NO + H2 + O2 reactions on Pd/γ-Al2O3. Steady state rate measurements have been discussed in the light of previous mechanism proposals involving a dissociation
step of molecular NO adsorbed species on Pd. In the absence of oxygen, the dissociation of NOads species is assisted by chemisorbed H atoms. However, different kinetic features have been observed in the presence of oxygen.
Practically, the light-off curve of NO shifts towards higher temperature in the presence of O2. In addition the H2 + O2 reaction extensively occurs in the temperature range of this study. Such tendencies have been explained by changes in the
adsorptive properties of noble metals and also in the nature of elementary steps for the dissociation of NO. In the presence
of a large extent of O2, hydrogen coverage would sharply drop and would not further assist the dissociation of NO as in the absence of O2. 相似文献
13.
Dal-Ryung Park Bum-Jong Ahn Hyung-Sang Park Hiromi Yamashita Masakazu Anpo 《Korean Journal of Chemical Engineering》2001,18(6):930-934
The complete photocatalytic oxidation of C2H4 with O2 into CO2 and H2O has been achieved on ultrafine powdered TiO2 photocatalysts and the addition of H2O was found to enhance the reaction. The photocatalytic reaction has been studied by IR, ESR, and analysis of the reaction
products. UV irradiation of the photocatalysts at 275 K led to the photocatalytic oxidation of C2H4 with O2 into CO2, CO, and H2O. The large surface area of the photocatalyst is one of the most important factors in achieving a high efficiency in the
photocatalytic oxidation of C2H4. The photoformed OH species as well as O
2
−
and O
3
−
anion radicals play a significant role as a key active species in the complete photocatalytic oxidation of C2H4 with O2 into CO2 and H2O. Interestingly, small amount of Pt addition to the TiO2 photocatalyst increased the amount of selective formation of CO2 which was the oxidation product of C2H4 and O2. 相似文献
14.
Yunfang Huang Jihuai Wu Taohai Li Shancun Hao Jianming Lin 《Journal of Porous Materials》2006,13(1):55-59
H2La2Ti3O10/ TiO2 intercalated nanomaterial was fabricated by successive intercalation reactions of H2La2Ti3O10 with n-C6H13NH2/C2H5OH mixed solution and acid TiO2 sol, followed by irradiating with a high-pressure mercury lamp. The intercalated materials possess a gallery height of 0.46
nm and a specific surface area of 31.58 m2·g−1, which indicate the formation of a porous material. H2La2Ti3O10/TiO2 shows photocatalytic activity for the decomposition of organic dye under irradiation with visible light and the activity
of TiO2 intercalated material was superior to the unsupported one. 相似文献
15.
Both the conversion and H2O2 selectivity (or yield) in direct oxidation of H2-to-H2O2 (using 1.7 mol% H2 in O2 as a feed) and also the H2O2 decomposition over zeolite (viz. H-ZSM-5, H-GaAlMFI and H-
) supported palladium catalysts (at 22 °C and atmospheric pressure) are strongly influenced by the zeolite support and its fluorination, the reaction medium (viz. pure water, 0.016 M or 1.0 M NaCl solution or 0.016 M H2SO4, HCl, HNO3, H3PO4 and HClO4), and also by the form of palladium (Pd0 or PdO). The oxidized (PdO-containing) catalysts are active for the H2-to-H2O2 conversion and show very poor activity for the H2O2 decomposition. However, the reduced (Pd0-containing) catalysts show higher H2 conversion activity but with no selectivity for H2O2, and also show much higher H2O2 decomposition activity. No direct correlation is observed between the H2-to-H2O2 conversion activity (or H2O2 selectivity) and the Pd dispersion or surface acidity of the catalysts. Higher H2O2 yield and lower H2O2 decomposition activity are, however, obtained when the non-acidic reaction medium (water with or without NaCl) is replaced by the acidic one. 相似文献
16.
A model for H2O2 formation, transport, and reaction in PEMFCs is established for the first time. Profiles of oxygen and H2O2 concentration inside the fuel cell are simulated using the agglomerate model for the electrode. The predicted concentration of H2O2 shows the same trend as experimental data under different conditions, but the level was only of the same magnitude. Low humidity, high temperature, and high oxygen/hydrogen partial pressures were found to increase the concentration of H2O2. An increase in membrane thickness or metal ion contaminant level reduces the concentration of H2O2 in the membrane. Lowering the oxygen permeability in the ionomer is the most important and effective method to reduce the formation of H2O2. The simulation results also show little change in H2O2 concentration while operating the fuel cell above 0.6 V. Anodes designed with considerable thickness, high catalyst loadings and active areas can also help to suppress H2O2 formation. Finally, recommendations are made to mitigate the effects of H2O2 and prolong membrane lifetimes. 相似文献
17.
Hyun-Seog Roh Yong Wang David L. King Alexandru Platon Ya-Huei Chin 《Catalysis Letters》2006,108(1-2):15-19
Supported Rh catalysts have been developed for selective H2 production at low temperatures. Ethanol dehydration is favorable over either acidic or basic supports such as γ-Al2O3 and MgAl2O4, while ethanol dehydrogenation is more favorable over neutral supports. CeO2–ZrO2-supported Rh catalysts were found to be especially effective for hydrogen production. We focused on a support prepared by
a co-precipitation method having composition Ce0.8Zr0.2O2. A 2%Rh/Ce0.8Zr0.2O2 catalyst, prepared via impregnation without pre-calcination of support, exhibited the highest H2 yield at 450 °C among various supported Rh catalysts evaluated in this study. This may be due to both the strong interaction
between Rh and Ce0.8Zr0.2O2 and the high oxygen transfer rate favoring reforming of acetaldehyde instead of methane production. 相似文献
18.
P. Granger F. Dhainaut S. Pietrzik P. Malfoy A. S. Mamede L. Leclercq G. Leclercq 《Topics in Catalysis》2006,39(1-2):65-76
This paper reports a comparative kinetic investigation of the overall reduction of NO in the presence of CO or H2 over supported Pt-, Rh- and Pd-based catalysts. Different activity sequences have been established for the NO+H2 reaction Pt/Al2O3>Pd/Al2O3>Rh/Al2O3 and for the NO+CO reaction Rh/Al2O3>Pd/Al2O3> Pt/Al2O3. It was found that both reactions differ from the rate determining step usually ascribed to the dissociation of chemisorbed
NO molecules. The rate enhancement observed for the NO+H2 reaction has been mainly related to the involvement of a dissociation step of chemisorbed NO molecules assisted by adjacent
chemisorbed H atoms. The calculation of the kinetic and thermodynamic constants from steady-state rate measurements and subsequent
comparisons show that Pd and Rh are predominantly covered by chemisorbed NO molecules in our operating conditions which could
explain either changes in activity or in selectivity with the lack of ammonia formation on Rh/Al2O3 during the NO+H2 reaction. Interestingly, Pd and Rh exhibit similar selectivity behaviour towards the production of nitrous oxide (N2O) irrespective of the nature of the reducing agent (CO or H2). A weak partial pressure dependency of the selectivity is observed which can be related to the predominant formation of
N2 via a reaction between chemisorbed NO molecules and N atoms, while over Pt-based catalysts the associative desorption of
two adjacent N atoms would occur simultaneously. Such tendencies are still observed under lean conditions in the presence
of an excess of oxygen. However, a detrimental effect is observed on the selectivity with an enhancement of the competitive
H2+O2 reaction, and on the activity behaviour with a strong oxygen inhibiting effect on the rate of NO conversion, particularly
on Rh. 相似文献
19.
A series of Mo/Al2O3 and Mo/TiO2-Al2O3 catalysts were investigated by temperature programmed sulfiding (TPS) and laser Raman spectroscopy (LRS). The effect of TiO2 on the sulfidability of molybdena was studied in detail. It is found that Mo/Al2O3 catalysts can be partially sulfided by O-S exchange at low temperature, forming molybdenum oxysulfide. The Mo-S bond subsequently ruptures in the presence of H2 to produce H2S. At 530–550 K deep sulfiding of molybdenum oxysulfide occurs forming crystalline MoS2. When the surface of Al2O3 was covered by a monolayer of TiO2, the sulfiding rate of molybdena at low temperature was not only greatly increased, but H2S produced in the reduction of Mo-S species caused deep sulfiding of the catalyst which resulted in a decrease of the TPS peak temperature by 80–100 K. The results indicate that this promotion of the sulfiding of molybdena is enhanced with TiO2 loading. The function of TiO2 is explained by the weakened interaction between MoO3 and Al2O3 due to the coverage of the Al2O3 surface by TiO2. 相似文献
20.
Metal-assisted etching of silicon in HF/H2O2/H2O solutions with Ag nanoparticles as catalyst agents was investigated. SEM observations and etch rate measurements were carried out as a function of the etching solution composition. Depending on the relative amount of HF and H2O2, different regimes of dissolution take place and a strong similarity with the etching in HF-HNO3 solution is evidenced, for the first time. Formation of meso- and macroporous Si, etched craters and polished Si are observed as the HF/H2O2 ratio decreases. The dissolution mechanisms are discussed on the basis of a localized hole injection from the Ag nanoparticles into Si and in terms of the well known chemistry of Si dissolution in HF-based chemical and electrochemical systems. At high HF/H2O2 ratio, there is no formation of oxide at the surface. Hole injection and Si dissolution occur at the level of the Ag nanoparticle only, resulting in the formation of meso and macropores depending on the Ag nanoparticle size. At low HF/H2O2 ratio, the Si surface is oxidized, the injected holes are homogeneously distributed and thus polishing occurs. There is an intermediate range of composition in which injected holes diffuse away from the Ag nanoparticles and cone-shaped macropores, several tens of nm in diameter are formed. 相似文献