阶跃升温分解法对非负载型镍催化甲烷分解活性的影响

 以乙醇为洗涤溶剂采用沉淀法制备了非负载型 Ni 催化剂, 考察了预处理过程对催化剂上 CH4 分解活性的影响. X 射线衍射及 CH4 程序升温表面反应结果表明, 降低还原温度可减小 Ni 粒子尺寸, 从而提高催化剂活性. 同时, 采用 CH4 多温度逐步分解 (多点阶跃升温分解) 法可形成较稳定的 Ni 粒子, 有效提高催化剂的活性及稳定性, 500 oC 下 CH4 初始转化率可达 8.40%, 反应 120 min 时升至 11.20%; 而在 350 和 500 oC 两点阶跃升温分解的 CH4 最高转化率只有 1.61%.     

Ni/SiO2催化剂上甲烷催化裂解制氢

研究了固定床反应器上甲烷在Ni/SiO2催化剂上的裂解反应，并分别用O2、H2O进行催化剂失活/活化循环实验，并对催化剂用XRD进行分析。结果表明,Ni/SiO2催化剂具有良好的催化性能,甲烷转化率～40%，并能在150 min的时间内保持其活性，无论是用空气氧化还是水蒸气汽化，都能有效地活化已失活的催化剂。XRD实验显示，多次裂解－再生循环过程，对催化剂结构没有明显破坏。     

Methane Decomposition over Ni/α-Al2O3 Promoted by La2O3 and CeO2

The decomposition of methane on Ni/a-Al2O3 modified by La2O3 and CeO2 with differ-ent contents has been investigated and the ralationship between methane decomposition and removal of carbon by CO2 over these catalyst has also been studied by pulse-chromatography. The catalysts were characterized by TPR and XRD. It was shown that Ni/a-Al2O3 could be promoted by adding La2O3, and the carbon species produced over this catalyst was activated and eliminated by CO2. But CeO2 would suppress the decomposition of methane over Ni crystallite. Both La2O3 and CeO2 can inhibit aggregation of the Ni particles. Decomposition of methane over the Ni-based catalysts is structure sensitive to a certain extent.     

Methane Decomposition over Ni/α-Al_2O_3 Promoted by La_2O_3 and CeO_2

The decomposition of methane on Ni/a-Al2O3 modified by La2O3 and CeO2 with different contents has been investigated and the ralationship between methane decomposition and removal of carbon by CO2 over these catalyst has also been studied by pulse-chromatography. The catalysts were characterized by TPR and XRD. It was shown that Ni/a-Al2O3 could be promoted by adding La2O3, and the carbon species produced over this catalyst was activated and eliminated by CO2. But CeO2 would suppress the decomposition of methane over Ni crystallite. Both La2O3 and CeO2 can inhibit aggregation of the Ni particles. Decomposition of methane over the Ni-based catalysts is structure sensitive to a certain extent.     

Enhanced methane decomposition over transition metal-based tri-metallic catalysts for the production of COx free hydrogen

In this study, COx-free hydrogen production via methane decomposition was studied over Cu–Zn-promoted tri-metallic Ni–Co–Al catalysts. The catalysts have been prepared by the constant pH co-precipitation method, and the nominal Ni metal loading was fixed at 50 wt % along with other metals at 10 wt% each. The catalyst activity for methane decomposition reaction was examined in a reactor between 400 °C and 700 °C and at atmospheric pressure. Different techniques such as N₂-physisorption, X-ray diffraction, H₂-TPR SEM, TEM, ICP-MS, TGA, and Raman spectroscopy were applied to characterize the catalysts. The relation between the catalyst composition and their catalytic activity has been investigated. The controlled synthesis has resulted in a series of catalysts with a high surface area. Ni–Co–Cu–Zn–Al was the most active and productive catalyst. Various characterizations indicate that the promotional effects of Cu–Zn interaction were the critical factor in catalysts' activity and stability. Ni–Co–Cu–Zn catalyst gave the highest methane conversion of 85% at 700 °C. Zn addition improves the stability of the catalyst by retaining the active metal size during the decomposition reaction. The catalyst was active for 80 h of stability study. The rapid deactivation of the Ni–Co catalyst was due to the sintering of the catalyst at 650 °C. Moreover, carbon species accumulated during the methane decomposition reaction depend on the catalysts' composition. Zn promotes the growth of reasonably long and thin carbon nanotubes, whereas the diameter of carbon nanotubes on unpromoted catalysts was large.     

流化床中甲烷裂解制氢与催化剂再生过程研究

对流化床中甲烷裂解制氢与催化剂再生过程进行了研究。选用25Ni/CuAl2O3和75Ni/CuAl2O3两种催化剂，分别在500℃和650℃进行甲烷裂解制氢与催化剂再生，反应与再生过程的温度与时间保持相同，催化剂再生时采用空气进行再生，气体流量均为370mL/min（STP）。实验结果表明,镍质量分数较低时催化剂表现出较好的稳定性，温度增加催化剂的稳定性降低。甲烷转化率随操作周期呈下降趋势，在500℃制氢与再生操作达到第五周期时，甲烷转化率趋于稳定。对切换时间的影响研究表明，切换时间存在一个最佳值，即切换5min时甲烷裂解制氢效率最高。对生成碳产品进行了XRD和TEM表征，并对实验结果进行了讨论。     

Production of Hydrogen from Methane by a CO2 Emission-Suppressed Process: Methane Decomposition and Gasification of Carbon Nanofibers

Catalytic methane decomposition into hydrogen and carbon nanofibers and the oxidations of carbon nanofibers with CO₂, H₂O and O₂ were overviewed. Supported Ni catalysts (Ni/SiO₂, Ni/TiO₂ and Ni/carbon nanofiber) were effective for the methane decomposition. The activity and life of the supported Ni catalysts for methane decomposition strongly depended on the particle size of Ni metal on the catalysts. The modification of the catalysts with Pd enhanced the catalytic activity and life for methane decomposition. In particular, the supported Ni catalysts modified with Pd showed high turnover number of hydrogen formation at temperatures higher than 973 K with a high one-pass methane conversion (>70%). However, sooner or later, every catalyst completely lost their catalytic activities due to the carbon layer formation on active metal surfaces. In order to utilize a large quantity of the carbon nanofibers formed during methane decomposition as a chemical feedstock or a powdered fuel for heat generation, they were oxidized with CO₂, H₂O and O₂ into CO, synthesis gas and CO₂, respectively. In every case, the conversion of carbon was greater than 95%. These oxidations of carbon nanofibers recovered or enhanced the initial activities of the supported Ni catalysts for methane decomposition.     

Catalytic decomposition of CH4 over Ni-Al2O3-SiO2 catalysts: Influence of pretreatment conditions for the production of H2

This article reports the production of COx free hydrogen and carbon nanofibers by the catalytic decomposition of methane over Ni-Al2O3-SiO2 catalysts. The influence of reaction temperature, pretreatment temperature, and effect of reductive pretreatment on the decomposition of methane activity is investigated. The physico-chemical characteristics of fresh and deactivated samples were characterized using BET-SA, XRD, TPR, SEM/TEM, CHNS analyses and correlated with the methane decomposition results obtained. The Ni-Al-Si （4 ： 0.5 ： 1.5） catalyst reduced with hydrazine hydrate produced better H2 yields of ca. 1815 mol H2/mol Ni than the catalyst reduced with 5% H2/N2.     

表面性质对甲烷芳构化Mo基催化剂反应性能的影响

研究了不同载体对Mo基催化剂反应性能的影响，发现对于在无氧条件下的甲烷芳构化反应，分子筛酸性，结构和金属氧化物的存在这3个因素是至关重要的，考察了作为第2组分的Zn,W,Cu,Cr,Ni5种元素对Mo/HZSM-5反应性能的影响，发现第2组分的添加均在不同程度上提高了催化剂的甲烷芳构化活性和选择性，异丙醇分解反应的结果表明，Zn,W,Cu的加入，增加了催化剂的脱氢中心强度，Cr,Ni的加入，增加了催化剂的酸中心强度，酸中心和脱氢中心的加强有利于甲烷芳构化反应。     

甲烷芳构化反应催化剂的研究——Mo-M/HZSM-5在无氧条件下的催化性能和表面性质

苯;甲烷芳构化反应催化剂的研究——Mo-M/HZSM-5在无氧条件下的催化性能和表面性质     

甲烷部分氧化制合成气Ni/MgO和Ni-MgO/MgO催化剂的研究

甲烷氧化偶联制乙烷、乙烯以及甲烷选择氧化制甲醇、甲醛等反应 ,因其转化率和收率低 ,故短期内无法实现工业化 .目前 ,工业上应用甲烷蒸汽转化制合成气 ,进而合成氨等化工产品 .甲烷蒸汽转化制的合成气 ,其 H2 /CO≥ 3,不适用于甲醇合成和 F- T合成 .而甲烷部分氧化制的合成气 ,其H2 /CO≤ 2 ,因而最适合用于甲醇合成和 F- T合成 ,故近 1 0年来倍受科学家的关注[1 ,2 ] .在 CH4部分氧化制合成气中 ,钌、铑、钯、铂等贵金属催化剂的活性高、选择性好、稳定性好[1 ] ,但价格昂贵 (负载量以 1 2 %～ 4 0 %为佳 ) ,因而难以实现商品化 .N…     

Ni/Al2O3催化甲烷裂解

分别通过浸渍法和共沉淀法制备了不同Ni负载量的Ni/Al2O3催化剂。考察了Ni负载量、制备方法以及反应温度对Ni/Al2O3催化甲烷裂解性能的影响。结果表明,在550℃,浸渍法制备的Ni/Al2O3催化剂,当Ni负载量为20%(质量分数)、Ni金属平均粒径为11.25 nm时,具有最佳的甲烷催化裂解效果,其每摩尔Ni的氢气产量和每克Ni碳产量分别为164 mol和15.30 g。催化剂制备方法对Ni/Al2O3甲烷催化裂解反应有显著影响,相同Ni负载量共沉淀法制备的Ni/Al2O3甲烷催化裂解总体效果要好于浸渍法制备的Ni/Al2O3,而且反应过程中生成的碳纤维较长,管径也较均一。550℃时,共沉淀法制备的Ni负载量为41.2%(质量分数)的Ni/Al2O3催化剂在反应至350 min时,仍保持着30%以上的转化率。     

Effect of decomposition of catalyst precursor on Ni/CeO2 activity for CO methanation

CO methanation on Ni/CeO₂ has recently received increasing attention. However, the low-temperature activity and carbon resistance of Ni/CeO₂ still need to be improved. In this study, plasma decomposition of nickel nitrate was performed at ca. 150°C and atmospheric pressure. This was followed by hydrogen reduction at 500 °C in the absence of plasma, and a highly dispersed Ni/CeO₂ catalyst was obtained with improved CO adsorption and enhanced metal-support interaction. The plasma-decomposed catalyst showed significantly improved low-temperature activity with high methane selectivity (up to 100%) and enhanced carbon resistance for CO methanation. For example, at 250°C, the plasma-decomposed catalyst showed a CO conversion of 96.8% with high methane selectivity (almost 100%), whereas the CO conversion was only 14.7% for a thermally decomposed catalyst.     

Rh doping effect on coking resistance of Ni/SBA-15 catalysts in dry reforming of methane

A series of SBA-15 supported bimetallic Rh–Ni catalysts with different weight ratio of Rh/Ni in the range of 0–0.04 were prepared for carbon dioxide reforming of methane. The doping effect of Rh on catalytic activity as well as carbon accumulation and removal over the catalysts was studied. The characterization results indicated that the addition of a small amount of Rh promoted the reducibility of Ni particles and decreased the Ni particle size. During the dry reforming reaction, the carbon deposition was originated from CH4 decomposition and CO disproportionation. The Rh–Ni catalyst with small metallic particle size inhibited the carbon formation and exhibited high efficiency in the removal of coke. In comparison with bare Ni-based catalyst, the Rh–Ni bimetallic catalysts showed high activity and stability in the dry reforming of methane.     

高稳定度CH4/CO2重整Ni/MgO催化剂的研究

用TPR,TPD,TPO,TPMC(程序升温CH₄解离积炭)和活性评价等手段研究了普通浸渍法与载体盐助分散浸渍法制得的CH₄/CO₂重整制合成气Ni基催化剂的性能.结果表明,用载体盐助分散浸渍制备的催化剂Ni-O-Mg间作用较强,吸附CO₂能力较大,CH₄解离积炭量少,因此其稳定性及寿命较好.     

Effect of pressure on the efficiency of nickel and nickel-copper catalysts in decomposition of methane

Methane decomposition into hydrogen and nanofibrous carbon in the presence of high-percentage catalysts (70–90)% Ni–(0–20)% Cu–10% Al at a temperature of 948 K and pressures of 1 to 5 atm was studied in order to develop a technology for enrichment of natural gas with hydrogen. It was found that, With an increasing copper content in the catalyst and and with increasing pressure, the average, methane decomposition rate decreases by 10–20% and the catalyst lifetime and the specific yield of hydrogen (mol/mol_Ni+Cu) become (3.8–12) times higher over the catalyst deactivation period. The mechanisms by which the pressure and the copper content of the catalyst affect these process characteristics are discussed.     

抗积炭CH_4/CO_2重整用Ni/Al_2O_3催化剂

甲烷转化制备的合成气是合成液体燃料和含氧有机化合物的原料 .甲烷转化制合成气的方法有甲烷蒸汽重整、甲烷部分氧化和甲烷、二氧化碳重整 3种 [1～ 3] .对于 CH4/CO2 重整反应 ,调节进料比可制备出 H2 /CO≤ 1、富含 CO的合成气 ,它适于羰基合成和 F- T合成 .这种方法一方面充分利用碳资源 ,缓解能源危机 ;一方面可减少温室气体的排放 ,改善人类的居住环境 .目前倍受关注 .CH4/CO2 重整制合成气 ,Rh、Ru、Pd、Ir等贵金属有很高的活性和稳定性 [4] .但其价格昂贵 ,高温易流失 ,商业化困难 .Ni基催化剂的活性与贵金属相当 ,但它易积…     

甲烷在Ni/TiO2催化剂表面的活化

考察了Ni/TiO2催化剂甲烷部分氧化和二氧化碳重整制合成气的反应活性,实验表明,以TiO2为载体的镍系催化剂对于甲烷部分氧化制合成气反应具有较好的活性,尤其对H2的选择性较高,对二氧化碳重整制合成气反应具有较好的低温反应活性.采用脉冲-质谱在线分析等技术,在无气相氧条件下向Ni/TiO2催化剂脉冲CH4,发现甲烷在催化剂表面的活化（转化）及其氧化产物的选择性与金属催化剂表面氧的浓度密切相关.CH4与Ni/TiO2催化剂作用过程中存在明显的氢溢流和氧溢流现象,可能是这种溢流效应使得Ni/TiO2催化剂具有良好的反应活性和抗积碳性能.     

甲烷在Ni/TiO_2催化剂表面的活化

考察了Ｎｉ／ＴｉＯ２催化剂甲烷部分氧化和二氧化碳重整制合成气的反应活性,实验表明,以ＴｉＯ２为载体的镍系催化剂对于甲烷部分氧化制合成气反应具有较好的活性,尤其对Ｈ２的选择性较高,对二氧化碳重整制合成气反应具有较好的低温反应活性．采用脉冲－质谱在线分析等技术,在无气相氧条件下向Ｎｉ／ＴｉＯ２催化剂脉冲ＣＨ４,发现甲烷在催化剂表面的活化（转化）及其氧化产物的选择性与金属催化剂表面氧的浓度密切相关．ＣＨ４与Ｎｉ／ＴｉＯ２催化剂作用过程中存在明显的氢溢流和氧溢流现象,可能是这种溢流效应使得Ｎ／ＴｉＯ２催化剂具有良好的反应活性和抗积碳性能．     

Ni-Cu/CeO2催化剂上乙醇水蒸气重整反应

 研究了Ni-Cu/CeO2催化剂在乙醇水蒸气重整反应中的催化性能. 以具有高比表面积的CeO2为载体,用沉积沉淀法制备了一系列不同担载量的Ni, Cu双组分催化剂,采用X射线衍射、程序升温还原和透射电子显微镜对催化剂的晶相组成、还原性能和形貌进行了表征. 结果表明, CuO, NiO和CeO2的相互作用明显改善了NiO的分散. 适量CuO的加入使NiO分散度增大,颗粒明显变小,从而使催化剂具有更好的催化性能,但过多CuO的加入反而降低了催化剂的活性. Ni和Cu的催化性能差异较大, Ni具有优异的断裂C-C键性能,在低温下即可实现乙醇的完全转化,而在高温区则具有很好的甲烷重整性能,可获得很高的氢气产率; Cu在低温区倾向于使乙醇脱氢生成乙醛以及进一步脱羰基生成丙酮,在高温区也具有一定的乙醇裂解性能.