Zr改性Ni/γ-Al2O3催化剂用于浆态相合成气的低温甲烷化

采用浆态床反应器,在低温(300~330 ℃)下进行合成气的甲烷化反应.实验中通过共浸渍法(包括含浸-旋蒸法)制备了锆(Zr)修饰的Ni/γ-Al₂O₃催化剂,并考察其与单一NiO、未掺杂Zr 的Ni/γ-Al₂O₃催化剂的催化性能差异.研究表明,载体γ-Al₂O₃的引入能够明显地提高CO的转化率和甲烷的选择性,而Zr的掺杂会进一步提升催化剂的催化活性.在325 ℃,空速为4 200 mL·g^-1·h^-1时,CO的转化率可以达到86.41%,甲烷选择性为90.53%.催化剂的表征结果表明,Zr的添加促进了Ni在催化剂表面的分散、减弱了活性Ni与载体的相互作用,抑制了低甲烷化活性的NiAl₂O₄的生成,使得催化剂的反应性能得到较大提高.     

TiO2对Ni/Al2O3催化剂CO甲烷化性能的影响

采用溶胶凝胶法制备了一系列不同TiO₂含量的TiO₂-Al₂O₃复合载体,并通过浸渍法制备了NiO/TiO₂-Al₂O₃催化剂。分别考察了不同TiO₂含量的NiO/TiO₂-Al₂O₃催化剂及反应温度对CO甲烷化催化性能的影响。实验结果表明,当复合载体中TiO₂质量分数为30%,反应温度为350～450 ℃时,催化剂催化活性较高。利用N₂吸附-脱附(BET)、X射线衍射(XRD)及H₂程序升温还原(H₂-TPR)等手段对催化剂物化性能进行了表征。结果表明,加入适量的TiO₂能抑制镍铝尖晶石NiAl₂O₄物种的生成,改善NiO的表面分散性能,避免大晶粒NiO的形成,也改善了催化剂的还原性能,从而提高催化剂的CO甲烷化活性。     

XPS study of carbonation of Mn/Y2O3 catalysts

XPS spectra in the Ols range of binding energy demonstrate a steady decline of concentration of surface carbonate groups as Mn loading in Mn/Y2O3 oxide catalysts increases from 0 to 50 at.%.     

ZrO2和Al2O3载体对Mo基催化剂上甲烷化反应性能的影响

通过共沉淀法制备了ZrO₂和Al₂O₃载体,采用等体积浸渍法制备了MoO₃质量分数为5%的Mo/ZrO₂和Mo/Al₂O₃催化剂,并用于甲烷化反应。在三种反应气氛下对两种预硫化的Mo基催化剂进行评价,发现ZrO₂载体均可显著促进甲烷化反应,同时能够促进水汽变换（WGS）反应。通过XRD、H₂-TPR、XPS和TEM等表征发现,两种载体上Mo物种的硫化程度以及暴露的活性位数量不同,从而导致两种催化剂上催化性能差异显著。与Mo/Al₂O₃相比,Mo/ZrO₂催化剂上的MoO₃更易被还原,硫化程度也更高,并且Mo⁴⁺的含量更高,Mo⁶⁺的含量更低。虽然ZrO₂载体上MoS₂尺寸较大,边位置的Mo比例有所降低,但是由于MoS₂沿ZrO₂颗粒表面弯曲生长,使得MoS₂基面成为反应的活性位;因此,Mo/ZrO₂催化剂在甲烷化与WGS反应中表现出更优异的催化性能。     

Methanation of syngas over coral reef-like Ni/Al_2O_3 catalysts

Coral reef-like Ni/Al2O3 catalysts were prepared by co-precipitation of nickel acetate and aluminium nitrate with sodium carbonate aqueous solution in the medium of ethylene glycolye.Methanation of syngas was carried out over coral reef-like Ni/Al2O3 catalysts in a continuous flow type fixed-bed reactor.The structure and properties of the fresh and used catalysts were studied by SEM,N2 adsorption-desorption,XRD,H2-TPR,O2-TPO,TG and ICP-AES techniques.The results showed that the coral reef-like Ni/Al2O3 catalysts exhibited better activity than the conventional Ni/Al2O3-H2O catalysts.The activities of coral reef-like catalysts were in the order of Ni/Al2O3-673>Ni/Al2O3-573>Ni/Al2O3- 473>Ni/Al2O3-773.Ni/Al2O3-673-EG catalyst showed not only good activity and improved stability but also superior resistance to carbon deposition,sintering,and Ni loss.Under the reaction conditions of CO/H2(molar ratio)=1:3,593 K,atmospheric pressure and a GHSV of 2500 h-1,CH4 selectivity was 84.7%,and the CO conversion reached 98.2%.     

Effect of promoters on the catalytic performance of Ni/Al2O3 catalyst for partial oxidation of methane to syngas

The effect of promoters such as Ce, La and Ca on catalytic performance of Ni catalyst was measured in a continuous fixed bed reactor. The effect of promoters on Ni/a-Al₂O₃ catalyst is more significant than on Ni/g-Al₂O₃ catalyst. Ce was proved to be the best promoter among the three promoters tested and the optimum loading of Ce was 1%. The catalyst was characterized by TG, XPS, TPR and XRD techniques. TPR results showed that Ce can improve the reducibility of the Ni/Al₂O₃ catalyst. XRD results indicated that Ce was highly dispersed when its loading was low, but at higher loading it was crystallized into bulk CeO₂, thus, decreased the catalytic activity. This revised version was published online in June 2006 with corrections to the Cover Date.     

The effect of Li and La on NiO/Al2O3 catalyst for CH4/O2 to syngas reaction

The thermal stability and an 80 h life test over nickel-based catalysts for CH₄/O₂ to syngas reaction were investigated by flow-reactor, XPS, XRD and AAS analysis. The results indicate that the introduction of Li and La not only stabilized the support γ-Al₂O₃ phase, but also suppressed the sintering and loss of nickel, and in addition, enhanced the ability to suppress the carbon-deposition over NiO/Al₂O₃ during the high-temperature reaction.     

Effect of CeO2 addition on Ni/Al2O3 catalysts for methanation of carbon dioxide with hydrogen

The Ni-CeO2/Al2O3 catalysts with a nickel content of 15 wt% prepared via impregnating boehmite were found to be highly active and stable for methanation of carbon dioxide with hydrogen at a H2/CO2 molar ratio of 4.The effects of CeO2 content and reaction temperature on the performance of the Ni-CeO2/Al2O3 catalysts were studied in detail.The results showed that the catalytic performance was strongly dependent on the CeO2 content in Ni-CeO2/Al2O3 catalysts and that the catalysts with 2 wt%CeO2 had the highest catalytic activity among the tested ones at 350℃.The XRD and H2-TPR characterizations revealed that the addition of CeO2 decreased the reduction temperature by altering the interaction between Ni and Al2O3,and improved the reducibility of the catalyst.Preliminary stability test of 120 h on stream over the Ni-2CeO2/Al2O3 catalyst at 350℃ revealed that the catalyst was much better than the unpromoted one.     

Methane steam reforming over rhodium promoted Ni/Al2O3 catalysts

The effect of Rh addition upon catalyst characteristics and performance in methane steam reforming was investigated using Rh-promoted Ni/Al₂O₃ catalysts. The number of reduced metal atoms exposed on the surface increased for the Rh-promoted catalysts. Rh-promoted catalysts showed an increase in CH₄ reforming activity; however, constant turnover frequencies for promoted and unpromoted catalysts suggest that the increase in the number of metal surface atoms caused the activity enhancement. Rh also facilitated reduction of Ni/Al₂O₃.     

Hydrodechlorination of dichlorodifluoromethane (CFC-12) over Pd/Al2O3 and Pd-Au/Al2O3 catalysts

During an initial stage of the reaction of CCl₂F₂ with hydrogen on alumina-supported Pd and Pd-Au catalysts, an extensive defluorination occurs. However, at steady state, this undesired defluorination is greatly reduced; CH₄ and CH₂F₂ constitute the only major reaction products. A temperature programmed hydrogen treatment study shows retention of fluorine (and carbon) in used catalysts. This revised version was published online in June 2006 with corrections to the Cover Date.     

制备条件对Ni/ZrO2-SiO2催化剂煤气甲烷化的影响

采用浸渍法制备了ZrO₂-SiO₂复合载体和Ni质量分数为6%的Ni/ZrO₂-SiO₂催化剂,考察了载体制备时浸渍溶液pH值、焙烧温度和催化剂制备时的焙烧温度对Ni/ZrO₂-SiO₂催化剂煤气甲烷化反应性能的影响。采用X射线衍射、程序升温还原和扫描电子显微镜等方法对催化剂进行了表征。结果表明,载体浸渍溶液pH值为8.0～9.0, 载体焙烧温度为550 ℃,催化剂焙烧温度为450 ℃时,Ni/ZrO₂-SiO₂催化剂在煤气甲烷化反应中显示了最优的催化性能,CO转化率100%,CO₂转化率1.8%,CH₄生成速率16.6 mmol/(h·g)。进一步表征发现,制备ZrO₂-SiO₂复合载体时,增大浸渍溶液的pH值有利于形成粒径较小的亚稳态四方晶相ZrO₂,可见四方晶相ZrO₂更有利于甲烷化反应;载体焙烧温度会影响到NiO粒径的大小和其在催化剂表面的分散,温度过高和过低都会导致NiO粒径大小的不适宜以及分散性的降低;催化剂焙烧温度过高则会导致NiO与载体间的相互作用减弱,NiO分散性降低。     

Investigation of the acidity of Ni/Al2O3 and Ni/SiO2?Al2O3 catalysts

Acidity of Ni-modified alumina and silica-alumina catalysts was determined using n-butylamine titration and pyridine adsorption methods. Strong influence of Ni²⁺ ions on the Brönsted acidity of silicaalumina was observed. Improved Brönsted acidity of such system was confirmed by the results of the test reaction.     

柠檬酸对MoO3/CeO2-Al2O3催化剂耐硫甲烷化性能的影响

将柠檬酸（CA）作为络合剂添加至CeO₂-Al₂O₃复合载体中,并考察了CA对MoO₃/CeO₂-Al₂O₃催化剂耐硫甲烷化性能的影响。活性评价结果显示,催化剂活性随柠檬酸添加量的增大而增大,当n（CA）/n（Ce）为3时,CO转化率可达60%。催化剂BET、XRD、H₂-TPR及XPS等表征结果表明,在CeO₂-Al₂O₃复合载体中加入CA,可以增大载体及催化剂的比表面积,使Mo物种分散性提高。同时,CA对Ce物种起络合作用,致使催化剂表面Ce元素含量明显增加,进而减弱了活性组分Mo物种与载体间相互作用力,并最终导致了催化剂活性的提升。     

Ce含量对Ni-Ce/Al_2O_3催化剂结构及浆态床CO甲烷化性能的影响

以γ-Al2O3为载体,采用等体积浸渍法制备了不同Ce含量的Ni-Ce/Al2O3催化剂,并考察了其浆态床CO甲烷化反应性能。借助XRD、BET、H2-TPR及CO-TPD等对催化剂进行了表征分析,研究了催化剂的微观结构与甲烷化性能之间的关系。结果表明,助剂Ce的引入能够加强Ni物种与载体之间的相互作用、增强活性组分Ni对CO的吸附能力。随着Ce含量的升高,Ni物种在载体表面的分散度提高、Ni晶粒粒径减小,催化剂的比表面积及与载体相互作用较强的β-NiO相对含量先升后降。催化剂的浆态床甲烷化活性随Ce含量的升高呈现规律性的变化,CO转化率和CH4时空收率先增加后略有下降,当Ce含量为4%(质量分数)时,催化剂甲烷化活性最佳。     

Effects of CeO2 and CaO composite promoters on the properties of eggshell Ni/MgO-Al2O3 catalysts for partial oxidation of methane to syngas

The effects of CeO₂ and CaO composite promoters on the properties of eggshell Ni/MgO-Al₂O₃ catalysts of 1.5 mm diameter for the partial oxidation of methane to syngas were investigated. The addition of 1wt.% promoters could enhance the catalytic performance of the Ni/MgO-Al₂O₃ catalyst, while further increasing the promoter content to 4wt.% results in the decrease of reactivity. The catalytic property is related to the oxidizability of surface nickel species.     

临CO_2气氛下钼基催化剂耐硫甲烷化性能研究

在反应温度550℃、空速5 000 h~(-1)和1.2%H_2S浓度下,考察了反应气中添加CO_2对负载型Mo基催化剂甲烷化活性的影响。结果表明,添加CO_2会促进逆水煤气变换反应,从而降低Mo O_3/Al2O_3催化剂的耐硫甲烷化活性。与Mo O_3/Al2O_3催化剂相比,添加CO_2对铈铝复合载体负载的Co-Mo双组分催化剂的影响较小。通过表征发现,添加CO_2引起催化剂活性下降的主要原因是由于其增强了逆水煤气变换反应过程,使甲烷化过程可用氢气量减小。另外,逆水煤气变换反应生成的水会影响催化剂表面结构和组成。在连续加入10%CO_220 h后停止加入CO_2,催化剂的耐硫甲烷化活性可以得到恢复,因此,认为CO_2加入量低于10%时,对催化剂及甲烷化反应的影响是可逆的;但CO_2加入量大于10%后由于生成的水量增大会破坏催化剂的结构并减少活性位,从而造成催化剂的不可逆失活。     

Influence of MgO in the CO2 – steam reforming of methane to syngas by NiO/MgO/ α-Al2O3 catalyst

Simultaneous steam and CO₂ reforming of methane to syngas (H₂and CO) over NiO/MgO/a-Al₂O₃ catalyst have been investigated at different MgO wt.%. The catalyst has been characterized by temperature-programmed reduction and XRD techniques. Addition of MgO reduced the carbon deposition and energy consumption. The stability and less coking on MgO-promoted catalysts are attributed to the lewis basicity of MgO.     

NiO@SiO_2核壳催化剂在浆态床中低温甲烷化研究

采用改进的Stber方法,可控制备出具有不同形貌的NiO@SiO_2核壳结构催化剂,并在浆态床反应器(320℃)上,对其合成气低温甲烷化性能进行评价;同时借助XRD、TEM、XPS和N_2物理吸附等方法对反应前后催化剂的物化性质进行了表征。研究表明,实验制备的催化剂形貌规整、粒径均匀,且具有较好的热稳定性。在相同的制备条件下,核颗粒粒径增大,其SiO_2壳层的厚度随之增加。在反应过程中,部分催化剂的核壳结构遭到破坏并出现SiO_2空壳,是CO与壳层内的Ni作用生成易迁移的Ni羰基化物种(Ni(CO)_x)所致。催化剂的甲烷化活性随着核颗粒粒径的增加呈现下降趋势;在不同的反应阶段,催化剂的失活速率存在明显差异,在反应的前20 h内,催化剂出现快速失活,20 h后失活缓慢,但是催化剂的甲烷选择性都保持在80%左右。催化剂的失活,一方面,是因为反应过程中,Ni核颗粒发生了长大;另一方面,是由于壳层中3-5 nm的介孔的减少以及催化剂比表面积、孔容的下降。     

Comparative study of fluidized-bed and fixed-bed reactor for syngas methanation over Ni-W/TiO2-SiO2 catalyst

In this work, syngas methanation over Ni-W/TiO₂-SiO₂ catalyst was studied in a fluidized-bed reactor (FBR) and its performance was compared with a fixed-bed reactor (FIXBR). The effects of main operating variables including feedstock gases space velocity, coke content, bed temperature and sulfur-tolerant stability of 100 h life were investigated. The structure of the catalysts was characterized by XRD, N₂ adsorption-desorption and TEM. It is found that under same space velocity from 5000 h^?1 to 25000 h^?1 FBR gave a higher CH₄ yield, lower coke content, and lower bed temperature than those obtained in FIXBR. Ni-W/TiO₂-SiO₂ catalyst possessed excellent sulfur-tolerant stability on the feedstock gases less than 500 ppm H₂S in FBR. The carbon deposits formed on the spent catalyst were in the form of carbon fibers in FBR, while in the form of dense accumulation distribution appearance in FIXBR.     

助剂对甲烷部分氧化制合成气镍基催化剂性能的影响

考察了添加助剂铈、镧和钙对镍基催化剂反应性能的影响，发现助剂对以α-Al2O3为载体的镍基催化剂的调变作用比以γ-Al2O3为载体的镍基催化剂好，且助剂铈对催化剂的性能改善最好。在此基础上，研究了不同载量的铈对催化剂性能的影响。结果表明，铈的质量分数为1%时对催化剂的性能改善最好。同时采用XRD、XPS、TG等技术，研究了助剂铈对10％Ni/γ-Al2O3催化剂的改性作用。XRD分析表明，铈负载量较低时，催化剂中的CeO2高度分散在催化剂表面，铈负载量较高时，CeO2形成微晶颗粒，降低了催化活性。