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1.
The emissions of CO 2, NO x and SO 2 from the combustion of a high-volatile coal with N 2- and CO 2-based, high O 2 concentration (20, 50, 80, 100%) inlet gases were investigated in an electrically heated up-flow-tube furnace at elevated gas temperatures (1123–1573 K). The fuel equivalence ratio, φ, was varied in the range of 0.4–1.6. Results showed that CO 2 concentrations in flue gas were higher than 95% for the processes with O 2 and CO 2-based inlet gases. NO x emissions increased with φ under fuel-lean conditions, then declined dramatically after φ=0.8, and the peak values increased from about 1000 ppm for the air combustion process and 500 ppm for the O 2(20%)+CO 2(80%) inlet gas process to about 4500 ppm for the oxygen combustion process. When φ>1.4 the emissions decreased to the same level for different O 2 concentration inlet gas processes. On the other hand, NO x emission indexes decreased monotonically with φ under both fuel-lean and fuel-rich combustion. SO 2 emissions increased with φ under fuel-lean conditions, then declined slightly after φ>1.2. Temperature has a large effect on the NO x emission. Peak values of the NO x emission increased by 50–70% for the N 2-based inlet gas processes and by 30–50% for the CO 2-based inlet gas process from 1123 to 1573 K. However, there was only a small effect of temperature on the SO 2 emission. 相似文献
2.
A series of 1 wt.%Pt/ xBa/Support (Support = Al 2O 3, SiO 2, Al 2O 3-5.5 wt.%SiO 2 and Ce 0.7Zr 0.3O 2, x = 5–30 wt.% BaO) catalysts was investigated regarding the influence of the support oxide on Ba properties for the rapid NO x trapping (100 s). Catalysts were treated at 700 °C under wet oxidizing atmosphere. The nature of the support oxide and the Ba loading influenced the Pt–Ba proximity, the Ba dispersion and then the surface basicity of the catalysts estimated by CO 2-TPD. At high temperature (400 °C) in the absence of CO 2 and H 2O, the NO x storage capacity increased with the catalyst basicity: Pt/20Ba/Si < Pt/20Ba/Al5.5Si < Pt/10Ba/Al < Pt/5Ba/CeZr < Pt/30Ba/Al5.5Si < Pt/20Ba/Al < Pt/10BaCeZr. Addition of CO 2 decreased catalyst performances. The inhibiting effect of CO 2 on the NO x uptake increased generally with both the catalyst basicity and the storage temperature. Water negatively affected the NO x storage capacity, this effect being higher on alumina containing catalysts than on ceria–zirconia samples. When both CO 2 and H 2O were present in the inlet gas, a cumulative effect was observed at low temperatures (200 °C and 300 °C) whereas mainly CO 2 was responsible for the loss of NO x storage capacity at 400 °C. Finally, under realistic conditions (H 2O and CO 2) the Pt/20Ba/Al5.5Si catalyst showed the best performances for the rapid NO x uptake in the 200–400 °C temperature range. It resulted mainly from: (i) enhanced dispersions of platinum and barium on the alumina–silica support, (ii) a high Pt–Ba proximity and (iii) a low basicity of the catalyst which limits the CO 2 competition for the storage sites. 相似文献
3.
Ni catalysts supported on γ-Al 2O 3, CeO 2 and CeO 2–Al 2O 3 systems were tested for catalytic CO 2 reforming of methane into synthesis gas. Ni/CeO 2–Al 2O 3 catalysts showed much better catalytic performance than either CeO 2- or γ-Al 2O 3-supported Ni catalysts. CeO 2 as a support for Ni catalysts produced a strong metal–support interaction (SMSI), which reduced the catalytic activity and carbon deposition. However, CeO 2 had positive effect on catalytic activity, stability, and carbon suppression when used as a promoter in Ni/γ-Al 2O 3 catalysts for this reaction. A weight loading of 1–5 wt% CeO 2 was found to be the optimum. Ni catalysts with CeO 2 promoters reduced the chemical interaction between nickel and support, resulting in an increase in reducibility and stronger dispersion of nickel. The stability and less coking on CeO 2-promoted catalysts are attributed to the oxidative properties of CeO 2. 相似文献
4.
Phenol was oxidized in supercritical water at 380–450°C and 219–300 atm, using CuO/Al 2O 3 as a catalyst in a packed-bed flow reactor. The CuO catalyst has the desired effects of accelerating the phenol disappearance and CO 2 formation rates relative to non-catalytic supercritical water oxidation (SCWO). It also simultaneously reduced the yield of undesired phenol dimers at a given phenol conversion. The rates of phenol disappearance and CO 2 formation are sensitive to the phenol and O 2 concentrations, but insensitive to the water density. A dual-site Langmuir–Hinshelwood–Hougen–Watson rate law used previously for catalytic SCWO of phenol over other transition metal oxides and the Mars–van Krevelen rate law can correlate the catalytic kinetics for phenol disappearance over CuO. The supported CuO catalyst exhibited a higher activity, on a mass of catalyst basis, for phenol disappearance and CO 2 formation than did bulk MnO 2 or bulk TiO 2. The CuO catalyst had the lowest activity, however, when expressed on the basis of fresh catalyst surface area. The CuO catalyst exhibited some initial deactivation, but otherwise maintained its activity throughout 100 h of continuous use. Both Cu and Al were detected in the reactor effluent, however, which indicates the dissolution or erosion of the catalyst at reaction conditions. 相似文献
5.
A method to quantify DRIFT spectral features associated with the in situ adsorption of gases on a NO x adsorber catalyst, Pt/K/Al 2O 3, is described. To implement this method, the multicomponent catalyst is analysed with DRIFT and chemisorption to determine that under operating conditions the surface comprised a Pt phase, a pure γ-Al 2O 3 phase with associated hydroxyl groups at the surface, and an alkalized-Al 2O 3 phase where the surface –OH groups are replaced by –OK groups. Both DRIFTS and chemisorption experiments show that 93–97% of the potassium exists in this form. The phases have a fractional surface area of 1.1% for the 1.7 nm-sized Pt, 34% for pure Al 2O 3 and 65% for the alkalized-Al 2O 3. NO 2 and CO 2 chemisorption at 250 °C is implemented to determine the saturation uptake value, which is observed with DRIFTS at 250 °C. Pt/Al 2O 3 adsorbs 0.087 μmol CO 2/m 2and 2.0 μmol NO 2/m 2, and Pt/K/Al 2O 3 adsorbs 2.0 μmol CO 2/m 2and 6.4 μmol NO 2/m 2. This method can be implemented to quantitatively monitor the formation of carboxylates and nitrates on Pt/K/Al 2O 3 during both lean and rich periods of the NO x adsorber catalyst cycle. 相似文献
6.
A novel process concept called tri-reforming of methane has been proposed in our laboratory using CO 2 in the flue gases from fossil fuel-based power plants without CO 2 separation [C. Song, Chemical Innovation 31 (2001) 21–26]. The proposed tri-reforming process is a synergetic combination of CO 2 reforming, steam reforming, and partial oxidation of methane in a single reactor for effective production of industrially useful synthesis gas (syngas). Both experimental testing and computational analysis show that tri-reforming can not only produce synthesis gas (CO + H 2) with desired H 2/CO ratios (1.5–2.0), but also could eliminate carbon formation which is usually a serious problem in the CO 2 reforming of methane. These two advantages have been demonstrated by tri-reforming of CH 4 in a fixed-bed flow reactor at 850 °C with supported nickel catalysts. Over 95% CH 4 conversion and about 80% CO 2 conversion can be achieved in tri-reforming over Ni catalysts supported on an oxide substrate. The type and nature of catalysts have a significant impact on CO 2 conversion in the presence of H 2O and O 2 in tri-reforming in the temperature range of 700–850 °C. Among all the catalysts tested for tri-reforming, their ability to enhance the conversion of CO 2 follows the order of Ni/MgO > Ni/MgO/CeZrO > Ni/CeO 2 ≈ Ni/ZrO 2 ≈ Ni/Al 2O 3 > Ni/CeZrO. The higher CO 2 conversion over Ni/MgO and Ni/MgO/CeZrO in tri-reforming may be related to the interaction of CO 2 with MgO and more interface between Ni and MgO resulting from the formation of NiO/MgO solid solution. Results of catalytic performance tests over Ni/MgO/CeZrO catalysts at 850 °C and 1 atm with different feed compositions confirm the predicted equilibrium conversions based on the thermodynamic analysis for tri-reforming of methane. Kinetics of tri-reforming were also examined. The reaction orders with respect to partial pressures of CO 2 and H 2O are different over Ni/MgO, Ni/MgO/CeZrO, and Ni/Al 2O 3 catalysts for tri-reforming. 相似文献
7.
A multi-component NO x-trap catalyst consisting of Pt and K supported on γ-Al 2O 3 was studied at 250 °C to determine the roles of the individual catalyst components, to identify the adsorbing species during the lean capture cycle, and to assess the effects of H 2O and CO 2 on NO x storage. The Al 2O 3 support was shown to have NO x trapping capability with and without Pt present (at 250 °C Pt/Al 2O 3 adsorbs 2.3 μmols NO x/m 2). NO x is primarily trapped on Al 2O 3 in the form of nitrates with monodentate, chelating and bridged forms apparent in Diffuse Reflectance mid-Infrared Fourier Transform Spectroscopy (DRIFTS) analysis. The addition of K to the catalyst increases the adsorption capacity to 6.2 μmols NO x/m 2, and the primary storage form on K is a free nitrate ion. Quantitative DRIFTS analysis shows that 12% of the nitrates on a Pt/K/Al 2O 3 catalyst are coordinated on the Al 2O 3 support at saturation. When 5% CO2 was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by 45% after 1 h on stream due to the competition of adsorbed free nitrates with carboxylates for adsorption sites. When 5% H2O was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by only 16% after 1 h, but the Al2O3-based nitrates decreased by 92%. Interestingly, with both 5% CO2 and 5% H2O in the feed, the total storage only decreased by 11%, as the hydroxyl groups generated on Al2O3 destabilized the K–CO2 bond; specifically, H2O mitigates the NOx storage capacity losses associated with carboxylate competition. 相似文献
8.
The reforming of CH 4 with CO 2 over activated carbon- or silica-supported cobalt catalysts with and without added MgO as promoter has been studied over a range of temperatures (500–700°C). A significant effect of the MgO on catalyst efficiency was observed. The presence of MgO markedly reduces the carbon deposition on the surface of the catalyst and therefore, contributes to the stability of the catalyst. Based on temperature-programmed surface reaction experiments of chemisorbed CO 2, the role of MgO may be ascribed to the formation of strongly adsorbed CO 2 species over its surface. These CO 2 species can easily react with the surface carbon deposits under CO 2-reforming reaction conditions, preventing in this way catalyst deactivation. 相似文献
9.
Direct nitric oxide decomposition over perovskites is fairly slow and complex, its mechanism changing dramatically with temperature. Previous kinetic study for three representative compositions (La 0.87Sr 0.13Mn 0.2Ni 0.8O 3−δ, La 0.66Sr 0.34Ni 0.3Co 0.7O 3−δ and La 0.8Sr 0.2Cu 0.15Fe 0.85O 3−δ) has shown that depending on the temperature range, the inhibition effect of oxygen either increases or decreases with temperature. This paper deals with the effect of CO 2, H 2O and CH 4 on the nitric oxide decomposition over the same perovskites studied at a steady-state in a plug-flow reactor with 1 g catalyst and total flowrates of 50 or 100 ml/min of 2 or 5% NO. The effect of carbon dioxide (0.5–10%) was evaluated between 873 and 923 K, whereas that of H 2O vapor (1.6 or 2.5%) from 723 to 923 K. Both CO 2 and H 2O inhibit the NO decomposition, but inhibition by CO 2 is considerably stronger. For all three catalysts, these effects increase with temperature. Kinetic parameters for the inhibiting effects of CO 2 and H 2O over the three perovskites were determined. Addition of methane to the feed (NO/CH 4=4) increases conversion of NO to N 2 about two to four times, depending on the initial NO concentration and on temperature. This, however, is still much too low for practical applications. Furthermore, the rates of methane oxidation by nitric oxide over perovskites are substantially slower than those of methane oxidation by oxygen. Thus, perovskites do not seem to be suitable for catalytic selective NO reduction with methane. 相似文献
10.
The application of compressed carbon dioxide as an alternative reaction medium was investigated for the heterogeneously catalysed partial oxidation of propane. The catalytic tests were performed in a stirred batch as well as in a continuous flow reactor at 553–623 K, 2.6–11.3 MPa and a CO 2:synthetic air:propane molar ratio of 94–124:4–7:1 using precipitated CoO x/SiO 2 (2.4–3.7 wt.% Co) catalysts. In addition, the critical temperature and pressure of the reaction mixture were determined by the opalescence method in a high-pressure optical cell. The catalytic experiments revealed a significantly higher cumulative oxygenate selectivity (i.e. acetic acid, methanol, acrolein, acetone) with increasing pressure. It is supposed that the formed oxygenates were removed more easily from the catalyst surface without being totally oxidised due to the higher solvent power of the dense CO 2 in the supercritical phase. 相似文献
11.
Kinetic study of CO oxidation in combination with experiments of temperature-programmed oxidation (TPO) and reduction (TPR) have been performed on various unsupported crystalline manganese oxides (MnO x); while the reactivity shows an order of MnO ≤ MnO 2 < Mn 2O 3 in a mixture of unit ratio of O 2/CO at/below 523 K. We propose that under the current conditions the interaction of adsorbed CO and O is mainly responsible for CO 2 formation on Mn 2O 3 and MnO 2 catalysts, following either the Langmuir–Hinshelwood mechanism or Eley–Rideal mechanism. Meanwhile, direct evidence from transient CO oxidation suggests that the Mars-van-Krevelen mechanism may occur for all catalysts simultaneously, especially, it is predominant for the MnO catalyst. The evidence of structural modifications during reaction was confirmed by Raman spectra obtained from used MnO. 相似文献
12.
In this study chabazite zeolites were prepared and exchanged with alkali cations – Li, Na, K and alkaline-earth cations – Mg, Ca, Ba and were studied to assess their potential for CO 2 capture from flue gas by vacuum swing adsorption for temperatures below 120 °C. Isotherm measurements (CO 2 and N 2) were made for all samples at 273 K, 303 K and 333 K using a volumetric apparatus and represented with the Dual-site Langmuir model for CO 2 and N 2. Henry’s constants and isosteric heats of adsorption were calculated and qualitative analyses performed for all samples. Adiabatic separation factor (ASF) and capture figure of merit (CFM) were proposed and used as indices for assessing adsorbent performance and compared with a commercial NaX-zeolite sample. It was found that NaCHA and CaCHA hold comparative advantages for high temperature CO 2 separation whilst NaX shows superior performance at relatively low temperatures. 相似文献
13.
The kinetics of CO and H 2 oxidation over a CuO-CeO 2 catalyst were simultaneously investigated under reaction conditions of preferential CO oxidation (PROX) in hydrogen-rich mixtures with CO 2 and H 2O. An integral packed-bed tubular reactor was used to produce kinetic data for power-law kinetics for both CO and H 2 oxidations. The experimental results showed that the CO oxidation rate was essentially independent of H 2 and O 2 concentrations, while the H 2 oxidation rate was practically independent of CO and O 2 concentrations. In the CO oxidation, the reaction orders were 0.91, −0.37 and −0.62 with respect to the partial pressure of CO, CO 2 and H 2O, respectively. In the H 2 oxidation, the orders were 1.0, −0.48 and −0.69 with respect to the partial pressure of H 2, CO 2 and H 2O, respectively. The activation energies of the CO oxidation and the H 2 oxidation were 94.4 and 142 kJ/mol, respectively. The rate expressions of both oxidations were able to predict the performance of the PROX reactor with accuracy. The independence between the CO and the H 2 oxidation suggested different sites for CO and H 2 adsorption on the CuO-CeO 2 catalyst. Based on the results, we proposed a new reaction model for the preferential CO oxidation. The model assumes that CO adsorbs selectively on the Cu + sites; H 2 dissociates and adsorbs on the Cu 0 sites; the adsorbed species migrates to the interface between the copper components and the ceria support, and reacts there with the oxygen supplied by the ceria support; and the oxygen deficiency on the support is replenished by the oxygen in the reaction mixture. 相似文献
14.
The decomposition of CO 2 was investigated as a process of both industrial and environmental importance. Copper ferrite was obtained by the thermal decomposition of acetate precursors. CuFe 2O 4 were isothermally reduced in H 2 flow at 400–600 °C, the isothermal reduction profiles obtained in this study show that a topochemical mode of reduction is done by which the reduction process proceeds. The nano-wires metallic phase of iron (106 nm) and copper (56 nm), produced from the complete reduction of CuFe 2O 4, were subjected to the direct reoxidation in CO 2 flow at 400–600 °C. The reoxidation process was found to be controlled by both the reduction and reoxidation temperatures. CO 2 decomposes to carbon nano-tubes during the reoxidation of the freshly reduced CuFe 2O 4. The prepared, completely reduced and reoxidized CuFe 2O 4 compacts, were characterized by XRD, SEM, TEM and reflected light microscope. For the reoxidation process, it is found that at the initial stages the reaction is controlled by the interfacial chemical reaction mechanism with some contribution to the gaseous diffusion mechanism. On the other hand at the intermediate and final stages the mechanism by which the reoxidation process proceeds was found to be the solid-state diffusion. 相似文献
15.
Silicoaluminophosphate (SAPO) membranes with Si/Al gel ratios from 0.05 to 0.3 were synthesized by in situ crystallization onto porous, tubular stainless steel support. Pure SAPO-34 membranes were obtained when the Si/Al ratio was 0.15 or higher. The adsorbate polarizability correlated with the adsorption capacity on SAPO-34, and the amounts of gases adsorbed were in the order: CO 2 > CH 4 > N 2 > H 2. The Si/Al ratio did not affect the pore volume significantly, but it changed the CO 2 and CH 4 adsorption equilibrium constants. The SAPO-34 membranes effectively separated CO 2 from CH 4 for feed pressures up to 7 MPa. At 295 K, for a pressure drop of 138 kPa and a 50/50 feed, the CO 2/CH 4 selectivity was 170 for a membrane with a Si/Al gel ratio of 0.15. At 7 MPa, the CO 2/CH 4 selectivity was 100 and the CO 2 permeance was 4 × 10 −8 mol/(m 2 · s · Pa) at 295 K. This membrane was also separated CO 2/N 2 (selectivity = 21) and H 2/CH 4 (selectivity = 32) mixtures at 295 K and a pressure drop of 138 kPa. Competitive adsorption and difference in diffusivities are responsible for CO 2/CH 4 and CO 2/N 2 separations, whereas the H 2/CH 4 separation was due to diffusivity differences. For a membrane with Si/Al gel ratio of 0.1, a mixture of SAPO-34 and SAPO-5 formed, and the CO 2/CH 4 selectivity was lower. 相似文献
16.
Coupled semiconductor (CS) Cu/CdS–TiO 2/SiO 2 photocatalyst was prepared using a mutli-step impregnation method. Its optical property was characterized by UV–vis spectra. BET, XRD, Raman and IR were used to study the structure of the photocatalyst. Fine CdS was found dispersed over the surface of anatase TiO 2/SiO 2 substrate. Chemisorption and IR analysis showed methane absorbed in the molecular state interacted weakly with the surface of catalyst, and the interaction of CO 2 with CS produced various forms of absorbed CO 2 species that were primarily present in the form of formate, bidentate and linear absorption species. Photocatalytic direct conversion of CH 4 and CO 2 was performed under the operation conditions: 373 K, 1:1 of CO 2/CH 4, 1 atm, space velocity of 200 h −1 and UV intensity of 20.0 mW/cm 2. The conversion was 1.47% for CH 4 and 0.74% for CO 2 with a selectivity of acetone up to 92.3%. The reaction mechanisms were proposed based on the experimental observations. 相似文献
17.
The partial oxidation of ethanol was investigated over Ru and Pd catalysts supported onto yttria over a wide range of temperatures (473–1073 K). The product distributions obtained over these catalytic systems were correlated with diffuse reflectance infrared spectroscopy analyses (DRIFTS). Results showed that reaction route depended strongly on the type of metal. The decomposition of ethoxy species to CH 4 and CO or oxidation to CO 2 was promoted by Pd, and the acetaldehyde desorption was predominant over Ru in the low temperature region. Furthermore, the acetate and carbonate formation prevailed over Pd, which explained the lower acetaldehyde selectivity. The presence of CH 4 and CO 2 at high temperature is assigned to the decomposition of acetate species via carbonates over Pd-based catalysts. Ru was more suitable system for H 2 production than Pd by achieving a selectivity of about 59%. 相似文献
18.
In this paper, the effect of CO 2 and H 2O on NO x storage and reduction over a Pt–Ba/γ-Al 2O 3 (1 wt.% Pt and 30 wt.% Ba) catalyst is shown. The experimental results reveal that in the presence of CO 2 and H 2O, NO x is stored on BaCO 3 sites only. Moreover, H 2O inhibits the NO oxidation capability of the catalyst and no NO 2 formation is observed. Only 16% of the total barium is utilized in NO storage. The rich phase shows 95% selectivity towards N 2 as well as complete regeneration of stored NO. In the presence of CO 2, NO is oxidized into NO 2 and more NO x is stored as in the presence of H 2O, resulting in 30% barium utilization. Bulk barium sites are inactive in NO x trapping in the presence of CO 2·NH 3 formation is seen in the rich phase and the selectivity towards N 2 is 83%. Ba(NO 3) 2 is always completely regenerated during the subsequent rich phase. In the absence of CO 2 and H 2O, both surface and bulk barium sites are active in NO x storage. As lean/rich cycling proceeds, the selectivity towards N 2 in the rich phase decreases from 82% to 47% and the N balance for successive lean/rich cycles shows incomplete regeneration of the catalyst. This incomplete regeneration along with a 40% decrease in the Pt dispersion and BET surface area, explains the observed decrease in NO x storage. 相似文献
19.
The kinetics of the reaction of NO, N 2O and CO 2 with activated carbon without catalyst and impregnated with a precursor salt of vanadium (ammonium monovanadate) was investigated. The conversion of NO, N 2O and CO 2 was studied (450–900°C) using a TGA apparatus and a fixed bed reactor. The reactor effluents were analysed using a GC/MS on line. The addition of vanadium increased carbon reactivity and adsorption at lower temperatures. For NO and N 2O conversion the main products obtained were N 2, N 2O, CO and CO 2 but for CO 2 conversion only CO was detected. In situ XRD was a useful tool for interpreting catalyst behaviour and identifying phases present during reaction conditions. The catalytic effect of vanadium can be explained by the occurrence of redox processes in which the catalyst is reduced to lower oxidation states such as V 2O 5/V 6O 13. 相似文献
20.
The activity of mixed steam and CO 2 reforming of CH 4 to produce synthesis gas was investigated and compared with those of steam reforming alone and CO 2 reforming alone at 600–900°C under atmosphere pressure on MgO-supported noble metals. Mixed reforming shows a far lower CH 4 conversion than the value for thermodynamic equilibrium. The activity decreases following the order Ru,Rh> Ir> Pt,Pd. Little deactivation was observed for Ru, Rh and Ir catalysts. An isotope labelled 13CO 2 experiment was carried out in situ for mixed reforming on Rh/MgO and the results suggest that CO 2 dissociates as CO-M and O-M. The results of the temperature program reaction (TPR) of mixed reforming shows that CH 4 adsorbs and dissociates before reaction starts and that CO 2 reforming and steam reforming start simultaneously. A possible reaction mechanism is discussed. 相似文献
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