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1.
Redox properties of the supported Li 2O/MgO, K 2O/Al 2O 3 and PbO/Al 2O 3 catalysts are studied. New mechanism of the catalyst re-oxidation is suggested. Re-oxidation of the catalyst in the course of steady-state reaction can proceed as an oxidative dehydrogenation of surface OH groups. 相似文献
2.
The effects of the addition of MgO and TiO 2 to fly ash on the nucleation and crystal growth mechanisms of the derived glass are investigated with the aid of differential thermal analysis, dilatometry, X-ray diffraction and scanning electron microscopy (SEM). Phase separation occurs on heating the investigated glass. The glass-ceramic materials obtained contain anorthite (CaOAl 2O 32SiO 2) and cordierite (2MgO2Al 2O 35SiO 2) as the main crystalline phases. The morphology of the glass-ceramic material was investigated by SEM and it was consistent with the double-framework structure of the phase-separated glass and it was constituted by a low viscosity phase almost completely crystallised and high viscosity phase scarcely or not crystallised, depending on the heat-treatment. 相似文献
3.
以分析纯试剂CaCO 3、Al 2O 3和Na 2CO 3为原料,在1350℃烧结1 h合成了Na 2O掺杂铝酸钙熟料,并采用XRD、SEM和EDS等方法研究了Na 2O掺杂CaO-Al 2O 3体系铝酸钙化合物的物相演变规律及熟料浸出性能。结果表明:当CaO和Al 2O 3的摩尔比为1.0时,CaO-Al 2O 3体系铝酸钙由CaO·Al 2O 3和12CaO·7Al 2O 3组成,而Na 2O掺杂铝酸钙熟料由CaO·Al 2O 3、12CaO·7Al 2O 3、Na 2O·Al 2O 3和Na 4Ca 3(AlO 2) 10组成。除形成含Na 2O化合物外,熟料中掺杂的Na 2O固溶于12CaO·7Al 2O 3中,而CaO·Al 2O 3中几乎不含Na 2O。随着熟料中Na 2O掺杂量的升高,12CaO·7Al 2O 3和Na 4Ca 3(AlO 2) 10的含量逐渐增加,CaO·Al 2O 3的含量逐渐降低;12CaO·7Al 2O 3和Na 4Ca 3(AlO 2) 10的结晶度逐渐降低,CaO·Al 2O 3的结晶度逐渐升高。Na 2O的掺杂提高了熟料在碳酸钠溶液中的浸出性能,并且使浸出渣中CaCO 3的空间群由R-3CH、P63/MMC两种转变为只含有R-3CH一种。 相似文献
4.
本文用传统高温熔融法熔制Li 2O-Al 2O 3-SiO 2系高铝玻璃,改变碱金属氧化物 n(Li 2O)/ n(Na 2O)的摩尔比,运用阿基米德排水法、热膨胀仪、DSC、傅里叶变换红外光谱和拉曼光谱等测试手段和仪器,探究了混合碱金属效应对Li 2O-Al 2O 3-SiO 2系玻璃结构和热膨胀性能的影响。结果显示:随着 n(Li 2O)/ n(Na 2O)比例增大,混合碱金属效应对Li 2O-Al 2O 3-SiO 2系玻璃的密度和热膨胀系数的影响一致,表现为先增大后减小,当 R=0.25( R= n(Li 2O)/[ n(Li 2O)+ n(Na 2O)],摩尔比)时,出现极值,此时密度达到最大2.447 4 g/cm 3,热膨胀系数达到最大7.811 7×10 -6/℃;对玻璃特征温度的影响随着温度的升高而逐渐减弱至消失;对玻璃的析晶能力有一定的提升作用;对玻璃三维骨架结构中的硅氧四面体Q n的影响也各不相同。 相似文献
5.
A glass of composition: SiO 2 = 59·84%; Al 2O 3 = 11·45%; MgO = 15·34%; TiO 2 = 4·23%; K 2O = 3·80%; Na 2O = 2·48%; CaO = 1·08%; Fe 2O 3 = 1·78%; was prepared from porphyric sands by addition of MgO and TiO 2. The quenched glass is demixed on a very fine scale. The non-isothermal devitrification has been studied. Three-dimensional crystal growth has been observed. The experimental data suggest a mechanism controlled by the crystal-glass interface reaction. The crystal growth activation energy E c = 467 ± 20 kJ/mole has been evaluated. The temperature of most efficient nucleation is approximately T N = 720°C. 相似文献
6.
对锂辉石-氧化钙烧结过程进行热力学分析,绘制了各反应Gibbs自由能与温度的关系图。结果表明,Al 2O 3会优先和Na 2O、Li 2O、K 2O反应,然后与CaO反应生成CaO·Al 2O 3,而且烧结温度需高于1060℃以保证LiAlSi 2O 6能够完成晶形转变。并探讨了锂辉石-氧化钙烧结法提锂的反应机理。考察了不同烧结条件对锂浸出率的影响并对熟料进行X射线衍射(XRD)分析表征。实验结果表明,在配料比为1∶1.25、烧结温度1150℃、烧结时间60min时,锂的浸出率达到92.14%,熟料中的主要物相为Ca 2SiO 4与LiAlO 2。利用XRD和扫描电镜-能谱联用仪(SEM-EDS)对熟料与浸出渣的物相、显微形貌及元素分布情况进行了分析表征。为了确定烧结反应的控制性步骤,在最优烧结条件的基础上对烧结过程进行动力学分析,结果表明,锂辉石-氧化钙烧结体系属于球形颗粒三维界面化学反应控制,烧结过程的动力学拟合方程为 。 相似文献
7.
分别以自制固体碱K 2O/Al 2O 3和Na 3PO 4/MgO为催化剂,1,2-丙二醇为反应溶剂,催化松香与蔗糖合成松香酸蔗糖酯。以酯化率为指标,考察了反应温度、催化剂的负载量、反应时间、松香与蔗糖质量比对松香酸蔗糖酯合成的影响。通过SEM和BET等手段对催化剂进行表征,并对松香酸蔗糖酯的乳化、发泡、表面张力等性能进行测试。结果表明:K 2O/Al 2O 3与Na 3PO 4/MgO比表面积分别为142.52和19.38m 2/g;在松香酸蔗糖酯的合成反应中,催化剂K 2O/Al 2O 3的活性高于Na 3PO 4/MgO。K 2O/Al 2O 3为催化剂时,最优合成工艺条件为反应时间2.5h,反应温度125℃,K 2O/Al 2O 3催化剂用量3%,催化剂中K 2O负载量30%,松香和蔗糖质量比1:2,该条件下酯化率达到98%。合成的松香酸蔗糖酯与市场广泛使用的脂肪酸蔗糖酯相比,具有更好的表面活性。 相似文献
8.
The crystallization characteristics, phase assemblages and solid solution developed from thermally treated glasses based on LiFeSi 2O 6-CaMgSiO 6 system have been investigated. Varieties of pyroxene solid solutions of diopside, hedenbergite and augite nature are mostly detected by the X-ray analysis of the crystallization products of high CaO, Mg-containing glasses. However, lithium iron pyroxene, lithium ferrite (LiFe5O8), lithium ferrate (LiFeO2) and iron oxides were crystallized in the high Li2O, Fe2O3-containing varieties. In most cases small amounts of lithium disilicate and -quartz were also encountered. The conditions at which these phases are formed are discussed. 相似文献
9.
Catalytic activities of various metal oxides for decomposition of nitrous oxide were compared in the presence and absence of methane and oxygen, and the general rule in the effects of the coexisting gases was discussed. The reaction rates of nitrous oxide were well correlated to the heat of formation of metal oxide, i.e., a V-shaped relationship with a minimum at −Δ Hf0 around 450 kJ (O mol) −1 was observed in N 2O decomposition in an inert gas. In the case of metal oxides having the heat of formation lower than 450 kJ (O mol) −1, CuO, Co 3O 4, NiO, Fe 2O 3, SnO 2, In 2O 3, Cr 2O 3, the activities were strongly affected by the presence of methane and oxygen. On the other hand, the activities of TiO 2, Al 2O 3, La 2O 3, MgO and CaO were almost independent. The reaction rate of nitrous oxide was significantly enhanced by methane. The promotion effect of methane was attributed to the reduction of nitrous oxide with methane: 4N 2O+CH 4→2N 2+CO 2+2H 2O. The activity was suppressed in the presence of oxygen on the metal oxides having lower heat of formation. On the basis of Langmuir–Hinshelwood mechanism, the effect of oxygen on nitrous oxide decomposition was rationalized with the strength of metal–oxygen bond. 相似文献
10.
通过固定床反应器,对4种金属氧化物(Al 2O 3、MgO、CaO、Fe 2O 3)对油页岩热解所得油、气产率及成分的影响进行了研究。结果显示,碱性CaO对油、水、气、焦产率分布影响较为突出,可提高页岩油与半焦产率,并降低热解气产率;而酸性较强的Al 2O 3可同时提高页岩油、热解气和热解水的产率,有利于促进挥发分的析出;比较而言,MgO和Fe 2O 3的作用相对较弱。4种金属氧化物均可提高热解气中H 2、CH 4和C 2的产率;CaO作用下CO 2含量降低,而其他金属氧化物对CO 2的产生有不同程度的促进作用;Fe 2O 3可促进H 2产生;Al 2O 3作用下CH 4含量有所增加。4种金属氧化物均可促进页岩油中芳香烃的产生,并且CaO和MgO两种碱土金属氧化物作用下,短链(C 6~C 12)烷烃和烯烃含量均增加,而掺混Al 2O 3时页岩油中仅短链(C 6~C 12)烷烃含量增加。对此机理进行推测认为,碱性CaO和MgO首先与以脂肪酸形式存在的有机质进行酸碱反应,得到脱羧活性更高的羧酸盐,后者脱羧所得中间产物具有生成烷烃或烯烃两条可能路径,同时得到碳酸盐;而在具有Lewis酸特征的Al 2O 3作用下,脱羧产物为CO 2,并同时得到饱和烃产物。 相似文献
11.
The effect of deposition and order of potassium introduction on the texture and activity of Mo/γ-Al 2O 3 catalysts in water gas shift (WGS) reaction was investigated. The samples were synthesised by incipient wetness impregnation of the carrier with aqueous solutions of the corresponding salts followed by drying and calcination after each deposition step. The prepared catalyst precursors were sulphided at 400°C for 2 h with 6% H 2S in H 2 before testing in WGS reaction in a glass flow apparatus at 400°C under atmospheric pressure. The results show that potassium deposition alone on the bare γ-Al2O3 (sample K/Al2O3) decreases the specific surface after calcination by blocking the constrictions between the pores in the primary porous texture. In the WGS reaction conditions part of the pores are deblocked and a redistribution in the pore volumes occurs. The deposition of the Mo (sample Mo/Al2O3) also results in a decrease in both specific surface and total pore volume with respect to the bare support. However after catalytic activity test no substantial changes in its texture were observed. The addition of K to the Mo (sample KMo/Al2O3) leads to nonuniformity in distribution of molybdenum–oxygen entities due to partial migration of the MoOx species to the external surface. The specific surface is not changed during the reaction test. The deposition of Mo on K/Al2O3 contributes to the uniform distribution of oxomolybdenum species in the porous texture of the support. This uniformity is preserved to a high extent in the catalytic reaction as well. The activity in the synthesised samples in the WGS reaction decreases in the order MoK/Al2O3 > Mo/Al2O3 > KMo/Al2O3. 相似文献
12.
Subsolidus phase relationships in the region bounded by Si 3N 4, SiO 2, CaSiO 3, 2CaO.Al 2O 3.SiO 2, CaO.Al 2O 3, Al 2O 3 and β'-Si 2Al 4O 4N 4(β 60) have been studied. A new quinary phase with composition near to CaO. 1·33Al 2O 3.0·67Si 2N 2O (designated as S-phase) and a complete series of solid solution between S-phase and CaO.2Al 2O 3 were found. Fourteen compatible tetrahedra, of which five contain S-phase, occur in the region explored. They are as follows: X 1-SiO 2-anorthite-mullite; X 1-anorthite-mullite-Al 2O 3; X 1-anorthite-Al 2O 3-β 60; X 1-anorthite-β 60-Si 3N 4; X 1-anorthite-Si 3N 4-Si 2N 2O; X 1-anorthite-Si 2N 2O-SiO 2; anorthite-Si 2N 2O-SiO 2-CaSiO 3; anorthite-Si 2N 2O-CaSiO 3-gehlenite; anorthite-Si 2N 2O-gehlenite-Si 3N 4; S-anorthite-Al 2O 3-β 60; S-Al 2O 3-CaO.2Al 2O 3-gehlenite; S-Al 2O 3-gehlenite-anorthite; S-gehlenite-anorthite-Si 3N 4; S-anorthite-Si 3N 4-β 60. 相似文献
13.
The correlation between the catalytic activity towards N 2O decomposition and fuel type was studied for the bed materials sampled from the bottom bed of two industrial CFB boilers, a 12 MW th and a 550 MW th, burning biomass fuels and wastes, alone or as a mixture. It was found that the elemental composition of the surface of the bed material particles changed according to the composition of the ash from the parent fuel. The measured catalytic activity of the bed material samples increased with the amount of the catalytically active oxides (CaO, MgO, Fe 2O 3, Al 2O 3). In the case of limestone addition, the activity of the bed material was influenced by both the elemental composition of the fuel, and the ratio between lime and sulfated lime. 相似文献
14.
叙述了复合生料釉的研制过程,讨论了MgO、CaO、ZnO、Al 2O 3、SiO 2等氧化物及Al 2O 3/SiO 2比、烧成制度和其他因素对无光釉的影响。 相似文献
15.
The formation of ettringite (3CaO · Al 2O 3 · 3CaSO 4 · 32H 2O) and monosulfate (3CaO · Al 2O 3 · CaSO 4 · 12H 2O) from tricalcium aluminate (3CaO · Al 2O 3) and gypsum (CaSO 4 · 2H 2O) in sodium hydroxide (NaOH) solutions was investigated by isothermal calorimetry and X-ray diffraction analyses. Tricalcium aluminate/gypsum mixtures with a molar aluminate-to-sulfate ratio of 1:3 were hydrated at constant temperatures from 40 to 80°C in deionized water and 200 and 500 mM of NaOH solutions. Ettringite was the only crystalline phase ultimately formed between 40 and 80°C, regardless of whether hydration was carried out in deionized water or sodium hydroxide solutions. The rates of ettringite formation were retarded in sodium hydroxide solutions at all temperatures when compared to hydration in deionized water. The apparent activation energy for the conversion of the tricalcium aluminate/gypsum mixture to ettringite was observed to depend on the concentration of sodium hydroxide. 相似文献
16.
利用分析纯试剂制备了酸碱比为0.82,但Na 2O、CaO、MgO和Fe 2O 3含量不同的合成灰,并在815℃下在马弗炉中进行灼烧后,对其熔融温度进行测定。同时利用扫描电子显微镜-能谱仪(SEM-EDS)和X射线衍射仪(XRD)对样品微观形貌和矿物组成进行表征。结果表明:随着Na 2O质量分数从4%升高到12%,合成灰变形温度(DT)、软化温度(ST)、半球温度(HT)和流动温度(FT)分别从1225℃、1233℃、1255℃和1297℃下降为1162℃、1174℃、1181℃和1189℃,意味着Na 2O对合成灰具有较强的助熔效果;随着CaO和MgO含量在合成灰中分别增加,DT、ST和HT均单调上升,而FT则呈先下降后上升趋势,说明二者含量变化与合成灰熔融温度呈非线性关系;随着Fe 2O 3质量分数由5%增加至30%,FT由1215℃上升至1308℃,而其他3个熔融特征温度并无显著变化。通过SEM-EDS和XRD表征发现,合成灰中耐熔矿物(SiO 2和CaAl 2Si 2O 8等)和助熔矿物(CaMgSi 2O 6和NaAlSiO 4等)的比例变化和含钠矿物、含钙矿物之间低温共熔反应程度是影响其熔融温度的主要原因。综合对比所有合成煤灰熔融特征温度和化学组成发现,对于具有相同酸碱比的煤灰,DT主要与样品中Na 2O含量和碱土金属总量(CaO+MgO)密切相关影响,而FT主要受Na 2O和Fe 2O 3含量影响。 相似文献
17.
Catalytic reduction of NO by propene in the presence of oxygen was studied over SnO 2-doped Ga 2O 3–Al 2O 3 prepared by sol–gel method. Although SnO 2-doped Ga 2O 3–Al 2O 3 gave lower NO conversion than Ga 2O 3–Al 2O 3 in the absence of H 2O, the activity was enhanced considerably by the presence of H 2O and much higher than that of Ga 2O 3–Al 2O 3. The presence of SnO 2 and Ga 2O 3–Al 2O 3 species having intimate Ga–O–Al bondings was found to be essential for the promotional effect of H 2O. The promotional effect of H 2O was interpreted by the following two reasons. The first one is the removal of carbonaceous materials deposited on the catalyst surface by H 2O. The other is the selective inhibition by H 2O of the reaction steps resulting in propene oxidation to CO x without reducing NO. 相似文献
18.
Li 2O-Al 2O 3-SiO 2(LAS)系微晶玻璃是一种高性能的实用微晶玻璃体系,以Li 2O、Al 2O 3和SiO 2作为主要原料,采用整体析晶法制备了以透锂长石(LiAlSi 4O 10)为主晶相的微晶玻璃,并采用低温离子交换单元盐浴的方法,对其进行化学强化。利用X射线衍射仪、扫描电子显微镜等设备研究了LAS系微晶玻璃化学强化后的表面形貌和机械性能。结果表明,化学强化后此体系微晶玻璃表面出现去结晶相,维氏硬度显著降低,但抗弯强度显著提高,强化10 h时,表面出现约740 nm的非晶相层,抗弯强度达到最大值472 MPa。 相似文献
19.
Effect of additives, In 2O 3, SnO 2, CoO, CuO and Ag, on the catalytic performance of Ga 2O 3–Al 2O 3 prepared by sol–gel method for the selective reduction of NO with propene in the presence of oxygen was studied. As for the reaction in the absence of H 2O, CoO, CuO and Ag showed good additive effect. When H 2O was added to the reaction gas, the activity of CoO-, CuO- and Ag-doped Ga 2O 3–Al 2O 3 was depressed considerably, while an intensifying effect of H 2O was observed for In 2O 3- and SnO 2-doped Ga 2O 3–Al 2O 3. Of several metal oxide additives, In 2O 3-doped Ga 2O 3–Al 2O 3 showed the highest activity for NO reduction by propene in the presence of H 2O. Kinetic studies on NO reduction over In 2O 3–Ga 2O 3–Al 2O 3 revealed that the rate-determining step in the absence of H 2O is the reaction of NO 2 formed on Ga 2O 3–Al 2O 3 with C 3H 6-derived species, whereas that in the presence of H 2O is the formation of C 3H 6-derived species. We presumed the reason for the promotional effect of H 2O as follows: the rate for the formation of C 3H 6-derived species in the presence of H 2O is sufficiently fast compared with that for the reaction of NO 2 with C 3H 6-derived species in the absence of H 2O. Although the retarding effect of SO 2 on the activity was observed for all of the catalysts, SnO 2–Ga 2O 3–Al 2O 3 showed still relatively high activity in the lower temperature region. 相似文献
20.
采用分步浸渍法制备了碱/碱土金属修饰Ni基催化剂Ni-M/Al 2O 3 (M=K 2CO 3, Na 2CO 3, MgO, CaO)。探究了碱/碱土金属的添加对改性Ni基催化剂CO 2吸附和甲烷化性能的影响。研究发现,碱/碱土金属的添加提高了Ni/Al 2O 3催化剂表面的碱性活性位点密度,强化了其CO 2吸附性能。碱/碱土金属类型影响Ni-M/Al 2O 3催化剂碱性活性位点的分布、NiO物相的转化及Ni的分散度,进而影响其甲烷化性能。MgO添加使NiO物相转化为与载体呈强相互作用的β型和γ型NiO,降低了催化剂表面的强碱性活性位点比例,有利于CO 2吸附活化。Ni-MgO/Al 2O 3的CO 2吸附容量最高为0.68mmolCO 2/g,其CO 2转化率和CH 4选择性分别高达58.4%和95.4%,其在烟气CO 2捕集与原位甲烷化中极具应用前景。 相似文献
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