MgO改性CuZnAl催化剂上甲醇裂解制氢

为了提高甲醇裂解制氢的气体收率,减少液相副产物的生成量,采用共沉淀法制备MgO改性CuZnAl催化剂,通过BET、XRD、SEM、H_2-TPR、CO2-TPD对催化剂结构和物化性能进行表征分析,固定床中考察MgO改性CuZnAl催化剂对甲醇裂解制氢催化性能。结果表明,引入适量的MgO可提高催化剂比表面积和CuO的分散度,改善催化剂氧化还原性,提高催化剂活性和选择性。得到优化的催化剂CuZnAlMg_2,其组分质量比为m(CuO)∶m(ZnO)∶m(Al_2O_3)∶m(MgO)=16∶13∶3∶2。在反应温度280℃、反应压力1.0MPa和空速0.6h-1条件下,CuZnAlMg_2催化剂上甲醇裂解转化率为99.1%,气体收率为97.0%。对液相产物进行分析表明,加入适量MgO提高催化剂碱性,能有效抑制液相副产物生成,提高气体收率。     

MgO助剂对CH4/CO2重整反应Ni/BaTiO3催化剂性能的影响

采用分步浸渍法制备了MgO改性的Mg-Ni/BaTiO3催化剂,考察了MgO助剂对催化剂性能的影响,运用H2-TPR、XRD、BET等测试技术对催化剂进行表征,并与催化剂Ni/BaTiO3、Ni/γ-Al2O3比较。发现MgO的添加有利于提高催化剂的催化活性和抗积炭性能;适量的MgO助剂可以改善催化剂的性能,但过量的MgO却会对催化剂的性能产生不良影响,随着MgO含量的增加,反应活性基本呈下降趋势。同时研究了不同的制备方法对催化剂催化活性的影响,用溶胶-凝胶法制备的催化剂具有更高的催化活性。     

用于低温液相合成甲醇的Cu/MgO/ZnO催化剂

采用并流共沉淀法制备了不同Cu:(Mg+Zn)及Mg:Zn摩尔比的铜基催化剂Cu/MgO/ZnO,用于低温液相甲醇的合成,并对比了Cu/ZnO及Cu/MgO催化剂,分析了催化剂中载体MgO的作用. 结果表明,MgO的引入有利于催化剂中Cu+的生成并均匀分散在载体中,可提高催化剂的催化活性. 以合成气CO+H2为原料,在443 K和5.0 MPa条件下,采用液体石蜡作溶剂,考察了催化剂的催化性能. 结果表明,Cu/MgO/ZnO催化剂的活性优于Cu/ZnO和Cu/MgO催化剂,且当Cu:Mg:Zn=2:1:1时催化性能最好,此时合成气中CO的转化率为63.56%,甲醇的选择性为99.09%,时空收率为5.413 mol/(kg×h). 分析了Cu/MgO催化剂在高温反应条件下的失活现象,认为铜烧结是其失活的主要原因.     

不同方法制备的MgO负载金属Ni催化水蒸汽重整乙酸制氢

应用浸渍法,在两种不同MgO载体上浸渍N(iNO3)2,经焙烧后得到NiO/MgO固溶体,再经H2还原得到Ni/NixMg1-xO催化剂。对比研究了两种方法所制备催化剂,催化水蒸汽重整乙酸制氢反应的活性和稳定性。结果表明,介孔MgO作载体所得催化剂催化水蒸汽重整乙酸制氢反应中,乙酸的转化率可达97.5%、H2的产率为2.1mol·mol-1,并且反应20h后无明显失活现象,明显高于普通方法制备的MgO作载体所得催化剂的稳定性和活性。结合N2吸附表征可知,介孔MgO具有较高的比表面积和较大的孔径,故其有利于活性组分Ni分散,以及有利于反应物和产物在催化剂孔道中的扩散。因此,介孔MgO作载体所得Ni/NixMg1-xO催化剂,具有更高的催化活性和稳定性。     

MgO对Ni/Al_2O_3催化剂CO甲烷化性能的影响

采用浸渍法制备了添加MgO助剂的Ni/Al2O3催化剂,并用固定床微反装置考察了催化剂在CO甲烷化反应中的催化性能。利用N2物理吸附、X射线衍射、H2程序升温还原、H2脉冲化学吸附和热重等手段对催化剂的结构进行了表征。通过分析样品的还原特性发现,活性组分Ni与Al2O3间的强相互作用会导致催化剂上Ni物种较难还原。MgO的引入可以明显削弱Ni与载体间的强相互作用,提高催化剂的还原度,增加催化剂活性位的数目,同时MgO的存在还能促进Ni颗粒的分散,提高催化剂的抗积碳性能,进而提高催化剂的甲烷化活性。     

煤焦油裂解催化剂制备及催化裂解特性

煤快速热解/循环流化床燃烧/催化反应器耦合分级转化工艺易于操作维护，经济效益显著，是实现煤炭资源清洁、高效利用的有效途径之一。但由于煤快速热解工艺产生的焦油油质偏重、污染元素含量较高，造成催化剂频繁失活及再生，因此制备了一种廉价高效的非再生性催化剂。在固定床催化反应装置上，以低温煤焦油为原料，以天然白云石为研究对象，考察催化剂煅烧温度及改性方式对煤焦油催化裂解特性的影响。在催化剂最佳制备条件下制备了1%Ni/2%Fe-白云石催化剂，考察了反应温度对煤焦油催化裂解的影响。结果表明，随煅烧温度升高，促进白云石主要组分CaCO₃和MgCO₃转化为CaO和MgO活性物质，天然白云石催化剂活性逐渐升高后趋于稳定，最佳煅烧温度为750℃;单独引入Fe后并未促进焦油裂解，同时引入Ni和Fe,明显改善了天然白云石催化剂的催化活性，最佳改性方式为1%Ni/2%Fe-白云石；助剂Fe的引入保护了活性组分Ni的硫中毒失活，同时引入Ni和Fe缓解了催化剂的烧结现象，且Fe作为助剂可减缓催化过程中积碳的产生，Ni改性后白云石催化剂促进了脂肪族化合物及含硫化合物的裂解，...     

MgO/NaY催化甲醇与碳酸乙烯酯酯交换合成碳酸二甲酯

以硝酸镁为前体,通过等体积浸渍法制备不同负载量的MgO/NaY催化剂,用CO2-TPD和TEM对催化剂进行了表征,考察MgO负载量、反应温度、反应时间等条件对甲醇与碳酸乙烯酯（EC）酯交换反应合成对碳酸二甲酯（DMC）的影响。实验结果表明：MgO的负载量对催化剂表面的碱量和MgO分散程度有着重要影响。高分散的MgO物种越多,其催化剂碱量越高。采用12%MgO/NaY为催化剂、反应温度70 ℃、n(甲醇)∶n(EC)= 8∶1、反应时间3 h时,EC的转化率和DMC的选择性最佳,DMC收率高达89%。     

MgO复合载体负载Ni催化乙醇水蒸气重整制氢

将稀土化合物CeO_2和La_2O_2CO_3分别与MgO载体复合负载Ni,制备Ni/MgO-La_2O_2CO_3(NML)和Ni/MgO-CeO_2(NMC)催化剂,用于催化乙醇水蒸气重整制氢。通过XRD研究负载催化的晶相,程序升温还原(TPR)对催化剂的综合性能进行分析。结果表明:稀土化合物复合的NMC,NML能明显提高Ni/MgO(NM)的低温乙醇转化率,350℃时,NM的乙醇转化率为78.3%,而此时NML,NMC的乙醇转化率却已接近100%,400—500℃范围内,NMC和NML明显提高了NM的H_2选择性,CO_2选择性也有所提高,同时降低了NM的CO,CH_4选择性,其中NMC的H_2选择性高于NML,而CO_2,CO,CH_4选择性却均低于NML,综合考虑乙醇转化率,NMC和NML能明显提高NM的综合催化性能,其中MgO-CeO_2复合载体负载Ni(NMC)对乙醇重整制氢的催化效果最好。     

NiO/MgO/Al2O3固体碱负载磺化酞菁钴催化剂的制备及表征

采用浸渍法制备了NiO/MgO/Al2O3负载磺化酞菁钴(CoPcS)催化剂,研究了其催化硫醇常温氧化反应性能,并用X射线衍射、BET法和CO2-程序升温脱附等技术进行表征.与MgO/Al2O3-CoPcS催化剂相比,NiO/MgO/Al2O3-CoPcS催化剂具有较高的初活性和良好的稳定性.     

Mn/MgO催化剂上乙腈和甲醇选择性合成丙烯腈的研究

采用浸渍法制备了Mn/MgO催化剂,考察了催化剂的活性组分含量及反应温度等因素对乙腈和甲醇选择性合成丙烯腈的影响,并对催化剂进行了XRD和CO2-TPD表征。结果表明,随着Mn的加入,催化剂的性能有很大提高,当m(Mn)∶m(MgO)=5∶100时,乙腈转化率达到最高;420℃反应时,催化剂具有较好的反应性能,乙腈转化率为40 5%,丙烯腈选择性达86 3%。CO2-TPD研究发现,Mn/MgO催化剂表面强碱中心数目越多,越有利于乙腈和甲醇选择性合成丙烯腈反应。     

甲烷催化裂解制备氢气和碳纳米管

采用浸渍法制备出3种MgO负载型过渡金属催化剂Fe/MgO、Co/MgO和N i/MgO,系统研究了甲烷在3种催化剂上于650,700和750℃下的裂解产物。结果表明,该3种催化剂均对甲烷裂解产氢并协同生长碳纳米管表现出较高活性。     

Comparison of Co/MgO and Ni/MgO catalysts for the steam reforming of naphthalene as a model compound of tar derived from biomass gasification

The catalytic performances of 12 wt.% Co/MgO catalyst pre-calcined at 873 K and of Ni catalysts for the steam reforming of naphthalene were investigated. The results of characterizations (TPR, XRD, and CO adsorption) for Ni catalysts showed that Ni metal particles were formed over the catalysts pre-calcined at 873 K with high Ni loading via reduction of NiO–MgO phases. A few Ni metal particles were obtained over the catalysts pre-calcined at 1173 K with all Ni loading values.The catalytic performance data showed that Co/MgO catalyst had higher activity (conv., 23%, 3 h) than any kinds of Ni/MgO catalysts tested in this study, under lower steam/carbon mole ratio (0.6) and higher concentration of fed naphthalene (3.5 mol%) than those used in the other works. The steam reforming of naphthalene proceeded when there was a stoichiometric ratio between the carbon atoms of naphthalene and H₂O over Co catalyst; however, the activation of excess H₂O happened over the Ni catalyst and this phenomenon can lead to having lower activity than Co catalyst. We concluded that these observations should be attributed to different catalytic performances between Co/MgO and Ni/MgO catalysts.     

Production of hydrogen for MC fuel cell by steam reforming of ethanol over MgO supported Ni and Co catalysts

Steam reforming of ethanol, in simulated MCFC operative conditions was investigated over MgO supported Ni and Co catalysts. Ni/MgO catalysts exhibit higher activity and selectivity to H₂ than Co/MgO catalysts because of the lower tendency of Ni to oxidize during reaction and to promote carbon monoxide methanation and ethanol decomposition reactions. Coke formation was strongly depressed due to the benefits gained through the use of basic carrier (MgO). Endurance tests carried out at low gas hourly space velocity (10,000 h⁻¹) for 630 h showed that Ni/MgO catalyst possesses adequate characteristics to be proposed as an efficient catalytic system for the production of hydrogen for MCFC.     

Kinetic study of carbon nanotube synthesis over Mo/Co/MgO catalysts

The kinetics of carbon nanotube (CNT) synthesis by decomposition of CH₄ over Mo/Co/MgO and Co/MgO catalysts was studied to clarify the role of catalyst component. In the absence of the Mo component, Co/MgO catalysts are active in the synthesis of thick CNT (outer diameter of 7-27 nm) at lower reaction temperatures, 823-923 K, but no CNTs of thin outer diameter are produced. Co/MgO catalysts are significantly deactivated by carbon deposition at temperatures above 923 K. For Mo-including catalysts (Mo/Co/MgO), thin CNT (2-5 walls) formation starts at above 1000 K without deactivation. The significant effects of the addition of Mo are ascribed to the reduction in catalytic activity for dissociation of CH₄, as well as to the formation of Mo₂C during CNT synthesis at high temperatures. On both Co/MgO and Mo/Co/MgO catalysts, the rate of CNT synthesis is proportional to the CH₄ pressure, indicating that the dissociation of CH₄ is the rate-determining step for a catalyst working without deactivation. The deactivation of catalysts by carbon deposition takes place kinetically when the formation rate of the graphene network is smaller than the carbon deposition rate by decomposition of CH₄.     

金属／MgO上的乙醇水蒸气重整制氢

研究了氧化镁负载镍、铁、钴、锰、钼、铜和锡等金属催化剂在乙醇水蒸气重整反应的性能,结果表明在650℃,101．3kpa条件下,所有催化剂的活性都较高,乙醇接近完全转化,而对氢的选择性顺序为：Ni〉Co〉Sn〉Cu〉Fe〉Mo〉Mn。除镍的选择性是随温度上升之外,其他催化剂的选择性都随温度变化有个最佳值。镍催化剂的TPR和XRD表征表明,催化剂中存在3种形态的镍。     

Partial oxidation of methane to syngas over Ni/MgO, Ni/CaO and Ni/CeO2

Partial oxidation of methane to syngas at atmospheric pressure and 750°C was examined over Ni/MgO, Ni/CaO and Ni/CeO₂ catalysts with nickel loading of 13 wt%. All catalysts had similar high conversion of methane and high selectivity to syngas, which nearly approached the values predicted by thermodynamic equilibrium. However, only Ni/MgO showed high resistance to carbon deposition under thermodynamically severe conditions (CH₄/O₂ = 2.5, a higher CH₄ to O₂ ratio than the stoichiometric ratio). Its catalytic activity remained stable during 100 h of reaction, with no detectable carbon deposition. The oxidation of carbon deposited from pure CH₄ decomposition and from pure CO disproportionation was investigated by in situ TPO-MS study which showed that both were effectively inhibited over Ni/MgO. In addition, the catalysts were characterized by TPR, XRD and XPS. It was revealed that the excellent performance of Ni/MgO resulted from the formation of an ideal solid solution between NiO and MgO. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study of Methane Decomposition on Fe/MgO-Based Catalyst Modified by Ni,Co, and Mn Additives

Catalytic decomposition of methane (CDM) generates clean hydrogen and carbon nanomaterials. In this study, methane decomposition to hydrogen and carbon was investigated over Ni-, Co-, or Mn-doped Fe/MgO catalysts. The doping effect of different metals, varying from 3 to 10?wt%, was investigated. The catalytic performance of the obtained materials (noted 15%Fe+x%metal/MgO) revealed that the doping effect of Ni, Co, and Mn significantly improved the activity of Fe/MgO. Among the Ni-doped catalyst series, the 15%Fe+3%Ni/MgO catalyst performed better than the rest of the Ni catalysts. The 6%Co-containing catalyst remained the best in terms of activity in the Co-doped catalyst series and the 15%Fe+6%Mn/MgO solid showed better methane conversion for the Mn-doped series. Overall, 3%Ni-containing catalyst displayed the best catalytic performance among all Ni-, Co-, and Mn-doped catalysts. XRD, N₂ sorption, and H₂ temperature-programmed reduction (TPR), Laser–Raman spectroscopy, thermogravimetric analysis (TGA) under air, and temperature-programmed oxidation (TPO) were used for catalyst characterization. The results revealed that all the doped catalysts exhibited better metallic active site distribution than 15%Fe/MgO and proved that metal doping played a crucial role in catalytic performance.     

High growth of SWNTs and MWNTs from C2H2 decomposition over Co-Mo/MgO catalysts

A series of MgO supported catalysts having Co and Mo metals 5-40 wt.% in a ratio of 1:1 was prepared by impregnation method. Carbon nanotubes (CNTs) were grown over the catalysts by decomposition of C₂H₂ at 800 °C for 30 min. It was found that 5 and 10 wt.% Co-Mo/MgO catalysts produced single-wall nanotubes (SWNTs), whereas 20, 30 and 40 wt.% Co-Mo/MgO catalysts produced multi-wall nanotubes (MWNTs). The catalyst Mo/MgO was inactive in growing CNTs. In Co-Mo/MgO catalysts, however Mo generated a favorable environment to grow SWNTs. The growth of SWNTs was strongly dependent on the formation of small clusters of cobalt, which may generate from the decomposition of CoMoO₄ species during the nanotube growth. MWNTs were produced over comparatively larger cobalt clusters generated from Co₃O₄ phase during the nanotube growth stage. The yields of SWNTs were about 6% and 27% over 5 and 10 wt.% Co-Mo/MgO catalysts, respectively. MWNTs yield (576%) was observed over 40 wt.% Co-Mo/MgO catalyst. Carbon yield (%) highly varied with acetylene concentration.     

Decomposition of metal carbides as an elementary step of carbon nanotube synthesis

The role of catalyst components in catalysts containing molybdenum, Mo/M/MgO (MNi, Co, and Fe), as well as Mo-free catalysts, M/MgO (MNi, Co, and Fe), for carbon nanotube (CNT) synthesis have been investigated by TEM, XRD, and Raman spectroscopy. CNT synthesis by the catalytic decomposition of CH₄ over M/MgO catalysts can proceed at reaction temperatures higher than the decomposition temperature of the metal carbides (Ni₃C, Co₂C, and Fe₃C), which indicates that carbon in the CNT originates from the graphitic carbon formed on the catalyst surface by the decomposition of metal carbides. For all catalysts containing Mo, thin CNT formation starts at an identical temperature of 923 K, corresponding to the decomposition temperature of MoC_1−x into Mo₂C. The significant effect of the addition of Mo is concerned with the formation of Mo₂C in a catalyst particle during CNT synthesis at high reaction temperatures. The presence of a stable Mo₂C phase leads to the formation of thin CNT with better crystallinity at high reaction temperatures. The role of Ni, Co, and Fe in the Mo/M/MgO catalysts is ascribed to the dissociation of CH₄.     

Effect of the catalyst structure on the formation of carbon nanotubes over Ni/MgO catalyst

Ni/MgO solid solution catalyst was prepared by decomposition of nickel and magnesium nitrate using dielectric barrier discharge (DBD) plasma operated at atmospheric pressure and less than 175 °C. Well-defined lattice fringes of the Ni (111) plane are clearly observed in the plasma prepared Ni/MgO catalyst. The plasma prepared catalyst possesses fewer defects, compared to the catalyst prepared by thermal decomposition at elevated temperature. It results in a better balance between the carbon formation and the carbon nanotube (CNT) growth. The crystallinity of the Ni particle from thermal decomposition is more complex. It is difficult to distinguish the Ni planes with the thermal decomposed catalyst. CNTs from CO decomposition over the plasma made catalyst show a narrow diameter distribution with a high aspect ratio. The DBD plasma decomposition is a facile, simple and effective way for the preparation of Ni catalysts to fabricate high quality CNTs.