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1.
A vanadium pentoxide supported activated coke (V 2O 5/AC) catalyst-sorbent has been reported to be very active for simultaneous removal of SO 2 and NO under dry conditions at temperatures of 200 °C and below. Regeneration of the SO 2-captured catalyst-sorbent is a key step in operation of such a process, which influences the catalyst-sorbent's SO 2 and NO removal activities, lifetime, as well as recovery of sulfur. Due to limited information in this regard, this paper studies thermal regeneration of a V 2O 5/AC catalyst-sorbent with emphases on the effect of atmosphere. The optimum regeneration temperature is found to be 380 °C in an Ar stream and 300 °C in a 5% NH 3/Ar stream. Compared to the fresh V 2O 5/AC, the V 2O 5/ACs regenerated in Ar show lower SO 2 adsorption capacities and higher NO removal activities, while the regenerated V 2O 5/ACs by 5% NH 3/Ar show higher and stable SO 2 adsorption capacities and higher NO removal activities. Two types of reactions occur during the regeneration: reduction of the adsorbed sulfur species by carbon to SO 2 and CO 2, and oxidation of carbon by oxygen in the V 2O 5/AC to CO 2. The carbon consumption of the latter is much more than that of the former in an Ar atmosphere, but fully suppressed by the presence of 5% NH 3. Detailed analysis and characterization of the V 2O 5/AC subjected to the regenerations are presented. 相似文献
2.
In this study, the behaviour of different activated carbons and some inorganic solids (alumina, silica, titania, magnesia and silicon carbide) as dispersants for Ca(OH) 2-derived CaO under two cycles of SO 2 retention at 300 °C, is analysed. Before performing the second SO 2 adsorption, a regeneration treatment in N 2 at 880 °C is carried out. During the first retention of SO 2, no influence of the dispersant was appreciated, being CaO the only phase responsible of SO 2 capture. However, during the second SO 2 adsorption the nature of the dispersants is important. Thus, comparing the behaviour of the inorganic solids with that exhibited by the activated carbons, it is observed that the activity loss, after the regeneration treatment, was significantly reduced when the activated carbons were used, especially at high dispersant content. The most effective dispersants were found to be those with meso and macroporosity which prevent the CaO (particle size of about 5 nm) sinterisation–agglomeration. This feature was exhibited by the activated carbons chosen. 相似文献
3.
Activated carbon impregnated with precursor salts of Ba, Co, Cu, Fe, Mg, Mn, Ni, Pb and V and their binary mixtures was used for adsorption of SO 2 at 20 °C. The most promising materials for SO 2 removal are carbons doped with V, Cu and mainly their binary mixtures, which show a synergetic effect. Kinetic curves and isotherms of SO 2 adsorption were obtained at 20 °C. These isotherms are reasonably well fitted by the Langmuir model and the respective parameters were determined. TPD experiments show that adsorption of SO 2 increases the oxygenated groups on the carbon surface. The sample doped with V, after SO 2 adsorption at 20 °C, presents an increase of basic oxygenated groups, which may be responsible for the observed extra adsorption of SO 2. 相似文献
4.
Supported Au catalysts Au-Au +-Cl x/Fe(OH) y ( x < 4, y ≤ 3) and Au-Cl x/Fe 2O 3 prepared with co-precipitation without any washing to remove Cl − and without calcining or calcined at 400 °C were studied. It was found that the presence of Cl − had little impact on the activity over the unwashed and uncalcined catalysts; however, the activity for CO oxidation would be greatly reduced only after Au-Au +-Cl x/Fe(OH) y was further calcined at elevated temperatures, such as 400 °C. XPS investigation showed that Au in catalyst without calcining was composed of Au and Au +, while after calcined at 400 °C it reduced to Au 0 completely. It also showed that catalysts precipitated at 70 °C could form more Au + species than that precipitated at room temperatures. Results of XRD and TEM characterizations indicated that without calcining not only the Au nano-particles but also the supports were highly dispersed, while calcined at 400 °C, the Au nano-particles aggregated and the supports changed to lump sinter. Results of UV–vis observation showed that the Fe(NO 3) 3 and HAuCl 4 hydrolyzed partially to form Fe(OH) 3 and [AuCl x(OH) 4−x] − ( x = 1–3), respectively, at 70 °C, and such pre-partially hydrolyzed iron and gold species and the possible interaction between them during the hydrolysis may be favorable for the formation of more active precursor and to avoid the formation of Au–Cl bonds. Results of computer simulation showed that the reaction molecular of CO or O 2 were more easily adsorbed on Au + and Au 0, but was very difficultly absorbed on Au −. It also indicated that when Cl − was adsorbed on Au 0, the Au atom would mostly take a negative electric charge, which would restrain the adsorption of the reaction molecular severely and restrain the subsequent reactions while when Cl − was adsorbed on Au + there only a little of the Au atom take negative electric charge, which resulting a little impact on the activity. 相似文献
5.
Potassium-based sorbents were prepared by impregnation with potassium carbonate on supports such as activated carbon (AC), TiO 2, Al 2O 3, MgO, SiO 2 and various zeolites. The CO 2 capture capacity and regeneration property were measured in the presence of H 2O in a fixed-bed reactor, during multiple cycles at various temperature conditions (CO 2 capture at 60 °C and regeneration at 130–400 °C). Sorbents such as K 2CO 3/AC, K 2CO 3/TiO 2, K 2CO 3/MgO, and K 2CO 3/Al 2O 3, which showed excellent CO 2 capture capacity, could be completely regenerated above 130, 130, 350, and 400 °C, respectively. The decrease in the CO 2 capture capacity of K 2CO 3/Al 2O 3 and K 2CO 3/MgO, after regeneration at temperatures of less than 200 °C, could be explained through the formation of KAl(CO 3) 2(OH) 2, K 2Mg(CO 3) 2, and K 2Mg(CO 3) 2·4(H 2O), which did not completely converted to the original K 2CO 3 phase. In the case of K 2CO 3/AC and K 2CO 3/TiO 2, a KHCO 3 crystal structure was formed during CO 2 absorption, unlike K 2CO 3/Al 2O 3 and K 2CO 3/MgO. This phase could be easily converted into the original phase during regeneration, even at a low temperature (130 °C). Therefore, the formation of the KHCO 3 crystal structure after CO 2 absorption is an important factor for regeneration, even at the low temperature. The nature of support plays an important role for CO 2 absorption and regeneration capacities. In particular, the K 2CO 3/TiO 2 sorbent showed excellent characteristics in CO 2 absorption and regeneration in that it satisfies the requirements of a large amount of CO 2 absorption (mg CO 2/g sorbent) and fast and complete regeneration at a low temperature condition (1 atm, 150 °C). 相似文献
6.
This work investigates performances of supported transition-metal oxide catalysts for the catalytic reduction of SO 2 with C 2H 4 as a reducing agent. Experimental results indicate that the active species, the support, the feed ratio of C 2H 4/SO 2, and pretreatment are all important factors affecting catalyst activity. Fe 2O 3/γ-Al 2O 3 was found to be the most active catalyst among six γ-Al 2O 3-supported metal oxide catalysts tested. With Fe 2O 3 as the active species, of the supports tested, CeO 2 is the most suitable one. Using this Fe 2O 3/CeO 2 catalyst, we found that the optimal Fe content is 10 wt.%, the optimal feed ratio of C 2H 4/SO 2 is 1:1, and the catalyst presulfidized by H 2+H 2S exhibits a higher performance than those pretreated with H 2 or He. Although the feed concentrations of C 2H 4:SO 2 being 3000:3000 ppm provide a higher conversion of SO 2, the sulfur yield decreases drastically at temperatures above 300 °C. With higher feed concentrations, maximum yield appears at higher temperatures. The C 2H 4 temperature-programmed desorption (C 2H 4-TPD) and SO 2-TPD desorption patterns illustrate that Fe 2O 3/CeO 2 can adsorb and desorb C 2H 4 and SO 2 more easily than can Fe 2O 3/γ-Al 2O 3. Moreover, the SO 2-TPD patterns further show that Fe 2O 3/γ-Al 2O 3 is more seriously inhibited by SO 2. These findings may properly explain why Fe 2O 3/CeO 2 has a higher activity for the reduction of SO 2. 相似文献
7.
An environmentally friendly solid acid catalyst, Ce(SO 4) 2/TiO 2 was prepared simply by modifying TiO 2 with Ce(SO 4) 2 for acid catalysis of volatile organic chemicals, 2-propanol and cumene. The characterization of prepared catalysts was performed using FTIR, XRD and DSC. The surface area of 7-Ce(SO 4) 2/TiO 2 calcined at 300 °C was very high (206.0 m 2/g) compared to that of unmodified TiO 2 (115.2 m 2/g) due to the interaction between Ce(SO 4) 2 and TiO 2. 7-Ce(SO 4) 2/TiO 2 containing 7 wt% Ce(SO 4) 2 and calcined at 300 °C exhibited maximum catalytic activities for both reactions, 2-propanol dehydration and cumene dealkylation. The catalytic activities for both reactions were correlated with the acid amounts of catalysts measured by an ammonia chemisorption method. The role of Ce results in an increase in the thermal stability of the surface sulfate species and consequently the acid amount of Ce(SO 4) 2/TiO 2 is increased. The asymmetric stretching frequency of the SO bonds for Ce(SO 4) 2/TiO 2 catalysts was related to the acidic properties and to the catalytic activity for acid catalysis to remove volatile organic chemicals, 2-propanol and cumene. 相似文献
8.
The influence of the thermal treatments of Pt/SO 42−-Zr(OH) 4 catalysts on the activity for the metal-catalyzed reaction of cyclohexane dehydrogenation and the acid-catalyzed reaction of n-butane isomerization, were studied in this work. A mutual antagonism between the conditions for optimal activity of the acid and metal functions was found and was seemingly related to the crystallization of the support. In order to be able to isomerize n-butane, SO 42−-Zr(OH) 4 had first to be calcined in air at Tcalc>400 °C. The onset of activity and strong acid properties coincided with the appearance of the tetragonal crystal phase. SO 42−-Zr(OH) 4 supported Pt, prepared from chloroplatinic acid, was tried to be converted to the metal state (Pt 0) in order to have full catalytic capacity. When Pt/SO 42−-Zr(OH) 4 was first calcined in air at Tcalc>400 °C, Pt remained in a seemingly oxidized state, with no de/hydrogenation properties even after reduction in H 2 at 300 °C. Under certain conditions, Pt metal properties were improved: (i) calcining Pt/SO 42−-Zr(OH) 4 in air at Tcalc<400 °C; (ii) calcining Zr(OH) 4 at Tcalc>400 °C before sulfating the support; and (iii) calcining Pt/SO 42−-Zr(OH) 4 in N 2 instead of air. In these cases, though Pt dehydrogenation activity increased, the activity of the acid function decreased (iii) or was practically null ((i) and (ii)). The support was amorphous in case (i) and mainly monoclinic in case (ii). Sulfate loss and conversion into the monoclinic phase occurred in case (iii). As compared to sulfate-free Pt/ZrO 2, sulfur poisoning always decreased the metal activity of sulfated catalysts but the decrease was higher for mainly tetragonal sulfate-doped catalysts. The final conclusion is that the optimum activation conditions for the metal and acid functions in Pt/SO 42−-Zr(OH) 4 are mutually excluding. The deleterious effect of SO 42−-ZrO 2 (SZ) on Pt metal activity is closely related to the growth and/or the presence of the tetragonal phase and cannot be prevented if a high activity of the acid function is demanded by the reacting system. 相似文献
9.
The gas-phase oxidative dehydrogenation of ethylbenzene to styrene was carried out by using as catalyst a series of metal phosphates (Al, Fe, Ni, Ca and Mn) and stoichiometric (Al/Fe = Al/Ca = 1) mixed systems: FeAl(PO 4) 2 and Ca 3Al 3(PO 4) 5, that were prepared by an ammonia gelation method. Their amorphous character was determined through several physical methods: nitrogen adsorption, DRIFT and XRD patterns. These results were compared to those obtained with 24 commercial inorganic solids (several metal oxides, sulfates and phosphates). Reactions were also carried out without oxygen, under non-oxidative conditions, where the catalytic activity was always appreciably lower than under oxidative conditions. Experimental results indicated that the oxidative gas-phase dehydrogenation of ethylbenzene to styrene could be related to the total number of acid and basic sites of catalysts, so that this reaction probably needs selected acid–basic pairs for coke formation, where the oxidative dehydrogenation process is developed. The main practical conclusion of the catalyst screening was that the best results were obtained with the synthesized amorphous AlPO4, where 43% ethylbenzene conversion and 99.7% styrene selectivity were achieved. A very reduced number of commercial inorganic solids like Al2(SO4)3, Cr2(SO4)3, Fe2(SO4)3, NiSO4, Al2O3 and Fe2O3 were also able to obtain an acceptable catalytic behavior, with conversions ranging between 18 and 23% and selectivity in the 95–100% range. Among the other synthesized solids, Ni3(PO4)2-A-450 was the only metal phosphate exhibiting results in such a range. All the other catalysts studied were rather inactive and/or selective. Additional experiments carried out at longer times on stream (3.5 h) and longer contact times (W/F 0.254 and 0.654) confirmed the superior catalytic behavior of amorphous AlPO4. Consequently, this solid could be a good candidate for application as a catalyst in the industrial oxydehydrogenation of ethylbenzene to styrene. 相似文献
10.
Activity for hydrolysis of CCl 2F 2 (CFC12) on various metal sulfate was investigated. Zr(SO 4) 2 was found to be the most active while FeSO 4, Cr 2(SO 4) 3, Al 2(SO 4) 3, La 2(SO 4) 3 and Ce 2(SO 4) 3 had intermediate activity. MnSO 4, CoSO 4, and MgSO 4 showed low activity and SrSO 4, CaSO 4, and BaSO 4 had even less activity. The major carbon containing product was CO 2 and small amount of CClF 3 and CO were formed over several sulfates. The crystal structure of the sulfates was stable during decomposition of CCl 2F 2, and the conversion reached a steady state after initial decrease at 275 °C over Zr(SO 4) 2 catalyst. The concentration of surface hydroxyl was larger than that over AlPO 4-based catalysts and a reaction mechanism similar to that over AlPO 4-based catalysts was proposed. 相似文献
11.
Mechanochemical synthesis has been applied for many novel material preparations and gained more and more attention due to green and high-efficiency recently. In order to explore the influences of iron precursors on structure and performance of iron molybdate catalyst prepared by mechanochemical route, three typical and cheap iron precursors have been used in preparation of iron molybdate catalyst. Many characterization methods have been employed to obtain the physical and chemical properties of iron molybdate catalyst. Results indicate that iron precursors have the significant impact on the phase composition, crystal morphology and catalytic performance in the conversion of methanol to formaldehyde. It is hard to regulate the phase composition by changing Mo/Fe mole ratios for Fe_2(SO_4)_3 as iron precursor. In addition, as for Fe_2(SO_4)_3, the formaldehyde yield is lower than that from iron molybdate catalyst prepared with Fe(NO_3)_3·9H_2O due to the reduction in Fe_2(MoO_4)_3 phase as active phase. Based on mechanochemical and coprecipitation method, the solvent water could be a key factor for the formation of MoO_3 and Fe_2(MoO_4) for FeCl_3·6H_2O and Fe_2(SO_4)_3 as precursors. Iron molybdate catalyst prepared with Fe(NO_3)_3·9H_2O by mechanochemical route, shows the best methanol conversion and formaldehyde yield in this reaction. 相似文献
12.
The sulphur tolerance and thermal stability of a 2 wt% Ag/γ-Al 2O 3 catalyst was investigated for the H 2-promoted SCR of NO x with octane and toluene. The aged catalyst was characterised by XRD and EXAFS analysis. It was found that the effect of ageing was a function of the gas mix and temperature of ageing. At high temperatures (800 °C) the catalyst deactivated regardless of the reaction mix. EXAFS analysis showed that this was associated with the Ag particles on the surface of the catalyst becoming more ordered. At 600 and 700 °C, the deactivating effect of ageing was much less pronounced for the catalyst in the H 2-promoted octane-SCR reaction and ageing at 600 °C resulted in an enhancement in activity for the reaction in the absence of H 2. For the toluene + H 2-SCR reaction the catalyst deactivated at each ageing temperature. The effect of addition of low levels of sulphur (1 ppm SO 2) to the feed was very much dependent on the reaction temperature. There was little deactivation of the catalyst at low temperatures (≤235 °C), severe deactivation at intermediate temperatures (305 and 400 °C) and activation of the catalyst at high temperatures (>500 °C). The results can be explained by the activity of the catalyst for the oxidation of SO 2 to SO 3 and the relative stability of silver and aluminium sulphates. The catalyst could be almost fully regenerated by a combination of heating and the presence of hydrogen in the regeneration mix. The catalyst could not be regenerated in the absence of hydrogen. 相似文献
13.
The delaminated Fe 20 3-pillared clay shows high activities for selective catalytic reduction (SCR) of NO by NH 2. Temperature program desorption (TPD) studies show that large amounts of NO., are adsorbed on the pillared clay catalyst at the SCR reaction temperatures (i.e. near 400°C). This result indicates that a Langmuir-Hinshelwood type mechanism (for reaction between chemisorbed NO, and NH, on the surface to form N 2) is operative for the pillared clay catalyst, which is in contrast to the SCR reaction on the commercial vanadia-based catalysts. The SCR activities for the delaminated Fe 20 3-pillared clay catalyst are higher than that of a commercial-type V 2O 5 + WO 3/TiO 2 catalyst under SO 2 + H 20 free conditions, but became lower in the presence of SO 2 +l H 20. However, when promoted by doping 1-3% Cr 20 3, the pillared clay catalyst exhibits higher SCR activities than the commercial-type catalyst in the presence of S0 2 + H 2O at all practical SCR reaction temperatures 相似文献
14.
In this work, we investigated the activity and stability of Ag–alumina catalysts for the SCR of NO with methane in gas streams with a high concentration of SO 2, typical of coal-fired power plant flue gases. Ag–alumina catalysts were prepared by coprecipitation–gelation, and dilute nitric-acid solutions were used to remove weakly bound silver species from the surface of the as prepared catalysts after calcination. SO 2 has a severe inhibitory effect, essentially quenching the CH 4-SCR reaction on this type catalysts at temperatures <600 °C. SO 2 adsorbs strongly on the surface forming aluminum and silver sulfates that are not active for CH 4-SCR of NO x. Above 600 °C, however, the reaction takes place without catalyst deactivation even in the presence of 1000 ppm SO 2. The reaction light-off coincides with the onset of silver sulfate decomposition, indicating the critical role of silver in the reaction mechanism. SO 2 is reversibly adsorbed on silver above 600 °C. While alumina sites remain sulfated, this does not hinder the reaction. Sulfation of alumina only decreases the extent of adsoption of NO x, but adsorption of NO x is not the limiting step. Methane activation is the limiting step, hence the presence of sulfur-free Ag–O–Al species is a requirement for the reaction. Strong adsorption of SO 2 on Ag–alumina decreases the rates of the reaction, and increases the activation energies of both the reduction of NO to N 2 and the oxidation of CH 4, the latter more than the former. Our results indicate partial contribution of gas phase reactions to the formation of N 2 above 600 °C. H 2O does not inhibit the reaction at 625 °C, and the effect of co-addition of H 2O and SO 2 is totally reversible. 相似文献
15.
蛋白土具有良好的应用前景,但是其自然白度较低制约了其开发应用。蛋白土硫酸铵煅烧法可去除其中的显色金属氧化物,提高蛋白土的白度,同时提取其中Al 2O 3。本文采用热重-差示扫描量热(TG-DSC)、同步热分析与红外质谱(TG-FTIR-MS)联用系统,结合X射线衍射对煅烧过程的固相及气相产物进行了表征分析,明析了其化学过程。结果表明,蛋白土中的Al 2O 3和Fe 2O 3在200~350℃时反应生成(NH 4) 3(Al,Fe)(SO 4) 3,同时逸出NH 3和H 2O;350~450℃时,进一步反应转化为NH 4(Al,Fe)(SO 4) 2,同时逸出NH 3、H 2O、SO 2和O 2;450~550℃时,NH 4(Al,Fe)(SO 4) 2分解生成(Al,Fe) 2(SO 4) 3,同时逸出NH 3、H 2O、SO 2和O 2;550~750℃时(Al,Fe) 2(SO 4) 3分解生成Al 2O 3和Fe 2O 3,同时逸出SO 2和O 2。采用Kissinger微分法与Ozawa积分法分别计算出4个阶段表观活化能后取二者平均值,分别为101.74kJ/mol、104.52kJ/mol、201.40kJ/mol、232.51kJ/mol,并获得对应4个热化学反应阶段的频率因子、反应级数和动力学方程。 相似文献
16.
Combined effect of H 2O and SO 2 on V 2O 5/AC the activity of catalyst for selective catalytic reduction (SCR) of NO with NH 3 at lower temperatures was studied. In the absence of SO 2, H 2O inhibits the catalytic activity, which may be attributed to competitive adsorption of H 2O and reactants (NO and/or NH 3). Although SO 2 promotes the SCR activity of the V 2O 5/AC catalyst in the absence of H 2O, it speeds the deactivation of the catalyst in the presence of H 2O. The dual effect of SO 2 is attributed to the SO 42− formed on the catalyst surface, which stays as ammonium-sulfate salts on the catalyst surface. In the absence of H 2O, a small amount of ammonium-sulfate salts deposits on the surface of the catalyst, which promote the SCR activity; in the presence of H 2O, however, the deposition rate of ammonium-sulfate salts is much greater, which results in blocking of the catalyst pores and deactivates the catalyst. Decreasing V 2O 5 loading decreases the deactivation rate of the catalyst. The catalyst can be used stably at a space velocity of 9000 h −1 and temperature of 250 °C. 相似文献
17.
The formation of the active phases during the activation process of monolithic catalysts based on V 2O 5–K 2SO 4 supported on diatomaceous earth for SO 2 to SO 3 oxidation in flue gases, has been shown to be a crucial factor to achieve satisfactory catalytic performance. As the temperature is increased from room temperature to 470°C, SO 2 and SO 3 are taken up by the green catalyst and the precursors are transformed into the active species. The role of each component of the catalyst during the activation was analyzed by studying the behavior towards SO 2 adsorption of four materials, which contained: diatomaceous earth, diatomaceous earth + V, diatomaceous earth + K, and diatomaceous earth + V + K. The influence of the potassium sulfate accessibility in the green catalyst was studied by using two different preparation methods, which gave rise to differences in the catalysts SO 2 adsorption properties and catalytic performance. Furthermore, the influence of the activation atmosphere was studied using nitrogen, oxygen or a flue gas composition. It was shown that pyrosulfate species should be formed at temperatures below 400°C, to keep the vanadium in the active 5+ oxidation state. 相似文献
18.
The porosity and hydrogen storage properties of the dehydrated Prussian blue type solids Ga[Co(CN) 6], Fe 4[Fe(CN) 6] 3, M 2[Fe(CN) 6] (M = Mn, Co, Ni, Cu), and Co 3[Co(CN) 5] 2 are reported and compared to those of M 3[Co(CN) 6] 2 (M = Mn, Fe, Co, Ni, Cu, Zn). Nitrogen sorption measurements suggest partial framework collapse for M 2[Fe(CN) 6] (M = Co, Ni) and Co 3[Co(CN) 5] 2, and complete collapse for Mn 2[Fe(CN) 6]. Hydrogen sorption isotherms measured at 77 K reveal a correlation between uptake capacity and the concentration of framework vacancies, with Langmuir–Freundlich fits predicting saturation values of 1.4 wt.% for Ga[Co(CN) 6], 1.6 wt.% for Fe 4[Fe(CN) 6] 3, 2.1 wt.% for Cu 3[Co(CN) 6] 2, and 2.3 wt.% for Cu 2[Fe(CN) 6]. Enthalpies of H 2 adsorption were calculated from isotherms measured at 77 and 87 K. Importantly, the values obtained for compounds with framework vacancies are not significantly greater than for the fully-occupied framework of Ga[Co(CN) 6] (6.3–6.9 kJ/mol). This suggests that the exposed metal coordination sites in these materials do not dominate the hydrogen binding interaction. 相似文献
19.
Zirconium sulfate supported on γ-Al 2O 3 catalysts were prepared by impregnation of powdered γ-Al 2O 3 with zirconium sulfate aqueous solution followed by calcining in air at high temperature. For Zr(SO 4) 2/γ-Al 2O 3 samples, no diffraction line of zirconium sulfate was observed up to 50 wt.%, indicating good dispersion of Zr(SO 4) 2 on the surface of γ-Al 2O 3. The acidity of catalysts increased in proportion to the zirconium sulfate content up to 40 wt.% of Zr(SO 4) 2. 40-Zr(SO 4) 2/γ-Al 2O 3 calcined at 400 °C exhibited maximum catalytic activities for 2-propanol dehydration and cumene dealkylation. The catalytic activities for both reactions, 2-propanol dehydration and cumene dealkylation were correlated with the acidity of catalysts measured by ammonia chemisorption method. 相似文献
20.
Since the electromechanical devices move towards enhanced power density, high mechanical quality factor ( Qm) and electromechanical coupling factor ( kp) are commonly needed for the high powered piezoelectric transformer with Qm≥2000 and kp=0.60. Although Pb(Mn 1/3Nb 2/3)O 3–PbZrO 3–PbTiO 3 (PMnN–PZ–PT) ceramic system has potential for piezoelectric transformer application, further improvements of Qm and kp are needed. Addition of 2CaO–Fe 2O 3 has been proved to have many beneficial effects on Pb(Zr,Ti)O 3 ceramics. Therefore, 2CaO–Fe 2O 3 is used as additive in order to improve the piezoelectric properties in this study. The piezoelectric properties, density and microstructures of 0.07Pb(Mn 1/3Nb 2/3)O 3–0.468PbZrO 3–0.462PbTiO 3 (PMnN–PZ–PT) piezoelectric ceramics with 2CaO–Fe 2O 3 additive sintered at 1100 and 1250 °C have been studied. When sintering temperature is 1250 °C, Qm has the maximum 2150 with 0.3 wt.% 2CaO–Fe 2O 3 addition. The kp more than 0.6 is observed for samples sintered at 1100 °C. The addition of 2CaO–Fe 2O 3 can significantly enhance the densification of PMnN–PZ–PT ceramics when the sintering temperature is 1250 °C. The grain growth occurred with the amount of 2CaO–Fe 2O 3 at both sintering temperatures. 相似文献
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