Ni/SiO2催化甲烷裂解制氢和纤维炭

甲烷催化裂解制氢具有过程简单、产物易分离、无COx产生等优点,是一种潜在的制氢工艺.本工作采用浸渍法制备Ni/SiO2介孔催化剂,通过N2吸附-脱附、X射线衍射、程序升温还原、扫描电子显微镜和透射电子显微镜对反应前后的催化剂结构及生成炭的形貌进行表征,研究了焙烧温度、金属负载量和反应温度对其甲烷催化裂解性能的影响.结果...     

甲烷在活性炭上裂解制氢研究

在连续流动石英固定床反应器上研究了甲烷在活性炭上裂解制氢的反应,并对反应前后活性炭的比表面积以及孔径分布等的变化进行了测定。结果表明,甲烷在五种活性炭上的裂解行为基本相同,反应初期转化率最高,随着反应进行转化率逐渐降低直至一个平稳的状态;降低甲烷分压和增加甲烷与活性炭的接触时间可提高甲烷转化率;温度的升高有利于初始转化率的提高,但不利于活性炭的稳定性;反应后活性炭比表面积、孔容及微孔孔容都明显降低,平均孔径增大,孔径分布向中孔方向迁移,说明甲烷的裂解导致了活性炭孔特别是微孔内的炭沉积以及进一步的孔堵塞。     

Ni-Mg复合催化剂催化裂解CH_4制氢动力学研究

基于定温热重实验,建立了甲烷催化裂解反应动力学模型和催化剂表面积炭失活动力学模型。其中,甲烷催化裂解动力学模型将初始产氢速率视为催化剂未积炭条件下的动力学基础数据;催化剂表面积炭失活动力学则基于甲烷催化裂解速率的降低。实验使用Ni-Mg复合催化剂,分别在535、585、635℃,甲烷分压10~4、2×10~4、3×10~4Pa条件下展开甲烷催化裂解动力学特性研究。结果表明,甲烷催化裂解的反应级数为0.5,活化能为82 k J/mol;Ni-Mg复合催化剂反应失活级数为0.5,催化剂失活活化能为118 k J/mol。实验条件下均制得了多壁碳纳米管。     

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。     

处理方法对活性炭在流化床反应器内甲烷催化裂解制氢活性的影响

在流化床反应器内,初步研究了处理方法对活性炭在甲烷裂解制氢过程中催化活性的影响。结果表明,浓硝酸处理后,活性炭表面会生成大量的含氧基团,未处理的活性炭上,850℃和900℃时甲烷的初始转化率在8%和11%左右,浓硝酸处理后,850℃和900℃时初始转化率分别上升到12%和16%,稳定性也明显改善。离子交换法负载微量金属的活性炭比采用浸渍法负载的有更好的活性和稳定性。     

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。     

液态金属催化裂解甲烷制氢动力学研究

液态金属催化甲烷热解是一种高效生产氢气且无二氧化碳排放的新兴技术.本文开发了一个液态金属裂解反应器催化甲烷热解的数值模型,在实验室自主搭建的液态金属制氢平台上得到的实验数据与模型预测结果吻合良好.该模型是基于甲烷在气液界面发生的催化热解、气泡内部发生的非催化热解过程和气泡上升过程中的流动行为,耦合了催化和非催化反应动力学和流体力学所建立的.使用气体体积流速、压力、气体成分、温度和液态金属性质(密度、黏度和表面张力)预测气泡尺寸和熔体中的气含率.该模型较好地预测了液态铜铋合金(Cu_0.45Bi_0.55)催化甲烷热解实验中不同温度、不同甲烷进气流量和液态金属高度下的甲烷转化率,得到了催化甲烷热解过程中的气含率、表观气体速率和压力沿液态金属高度的分布.实验数据与模型预测结果的高度吻合证明了模型的可靠性,该模型未来将有助于反应器优化和氢产率提高.     

碳质与金属催化剂热催化裂解甲烷产氢研究进展

甲烷裂解制氢方法具有产氢纯度高和清洁无污染的特点,被认为是当前最有前景的制氢方法之一.现阶段甲烷裂解制氢的研究工作主要集中于制备活性与稳定性兼备的催化剂.我们综述了近年来甲烷裂解制氢反应中碳质催化剂和金属催化剂两大系列催化剂的研究进展,从载体、活性组分、助剂3个方法对目前催化剂裂解甲烷产氢性能的影响进行了系统分析,总结了反应机理和催化剂的失活与再生情况,在以上基础上对催化剂未来的发展趋势进行了展望.     

催化裂解CH4制备不同形貌的碳纳米管

通过甲烷于较低温度(500～700℃)下在镍催化剂上催化裂解制备了各种形貌的碳纳米管.透射电镜测试结果表明,碳纳米管的外径和内径明显地受催化剂的大小和形貌的影响.本文考察了催化剂前驱体的种类、反应温度和原料气流速对镍催化剂和碳纳米管形貌的影响.     

IM-5分子筛在Ni-Cu催化剂甲烷热裂解制氢反应中的作用研究

甲烷热裂解制氢并生成高附加值的纳米碳材料,被认为是极具发展前景的氢气生产途径,但高性能催化剂的研发仍存在诸多挑战.我们选择多种载体(TS-1、 IM-5、 Y、介孔SiO₂、 γ-Al₂O₃、 CNTs),采用浸渍法制备Ni-Cu负载催化剂,通过低温N2吸附-脱附、 XRD、 SEM和H₂-TPR等系列表征方法对样品进行分析,考察不同载体对催化剂甲烷裂解制氢和纳米碳材料的影响.实验结果发现,分子筛载体独特的孔道结构有利于金属颗粒的分散,能有效避免反应中界面效应导致的催化剂失活,可提高催化剂反应活性并延长反应寿命,也显著提高了其碳产率.其中以IM-5分子筛为载体的催化剂表现最佳,在反应温度为700℃时, NiCu/IM-5催化剂甲烷转化率高达80%,氢气选择性达100%,反应400 min后活性未见明显降低. NiCu/IM-5催化剂碳产率高达1 446 g_C/g_cat,是NiCu/SiO₂催化剂的5.7倍, NiCu/γ-Al     

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。     

旋转滑动弧氩等离子体裂解甲烷制氢

采用切向气流和磁场协同驱动的旋转滑动弧氩等离子体,先通过光谱分析法计算了其电子温度和电子密度,了解其物理特性,将其应用于甲烷裂解制氢,研究了进气流量和CH_4/Ar比对反应效果的影响。结果表明,该滑动弧系统电子温度为1.0-2.0 e V,电子密度高达1015cm~(-3),是介于热与低温等离子体之间的一种等离子体形式,具有独特的物理特性,可以在达到较高反应效率的同时,保持较大的处理量;在CH_4裂解制氢实验中,CH_4转化率可达22.1%-70.2%,并随进气流量和CH_4/Ar比的增大均逐渐降低;H_2选择性为21.2%-61.2%,并随进气流量的增大先基本不变后有所增大,随CH_4/Ar比的增大逐渐降低;与应用于甲烷裂解的不同形式的低温等离子体对比(如微波、射频、介质阻挡放电等)可以发现,旋转滑动弧在获得较高甲烷转化率、较高H_2选择性和较低制氢能耗的同时,还可以保持较大的处理量,即进气流量可达6-20 L/min。     

Influences of reaction conditions on methane decomposition over non-supported Ni catalyst

Effects of reaction temperature and methane gas hourly space velocity (GHSV) on methane decomposition over non-supported Ni catalyst have been investigated in this work.Methane molecules activation,Ni particles growth and nano-carbon diffusion were the main factors influencing methane decomposition stability of non-supported Ni.The results of methane decomposition activity test on the non-supported Ni catalyst showed that the prepared non-supported Ni could exhibit a good methane decomposition performance with 273 gC/gNi and 2667 molH2/molNi at 500 -C and 45000 mL/(gcat h).Scanning electron microscope (SEM),X-ray powder diffraction (XRD) and temperature-programmed oxi- dation (TPO) have been carried out to characterize the used catalysts.The deposited carbon was carbon nanofibers,among which graphitic carbon formation increased with the reaction time of methane decomposition.Ni particle size was not the decisive factor during the carbon growing stage.     

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.     

Catalytic decomposition of hydrogen peroxide by Cu/M heterobimetallic complexes (M = Mn, Zn) with Schiff bases in the presence of electrolytes

A study was carried out on the effect of electrolytes KCl, CaCl₂, MnCl₂, ZnCl₂, CuCl₂, KNO₃, Ca(NO₃)₂, Mn(NO₃)₂, Zn(NO₃)₂, and Cu(NO₃)₂ on the kinetics of the decomposition of H₂O₂ catalyzed by [Cu(L¹/L²)][MCl₄] complexes (M = Zn, Mn; L¹ is 4,6,6-trimethyl-1,9-diamino-3,7-diaza-3-nonene, L² is 1,15-dihydroxy-7,9,9-trimethyl-3,6,10,13-tetraaza-6-pentadecene). The chloride ions were found to reversibly inhibit the catalyst. The major kinetic characteristics of this reaction were obtained using a mathematical model taking account of the reversible and irreversible inhibition of the catalyst. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 4, pp. 240–247, July–August, 2008.     

Catalytic decomposition of CFCs

Catalytic decomposition of CCI₂F₂ was studied over a number of single and complex metal oxides using a fixed-bed reactor. The ZrO₂–Cr₂O₂ catalyst exhibited the highest activity and CO₂ and CCIF₃ were formed at 350–450°C. Selective decomposition of CCI₂F₂ required the presence of both oxygen and water vapor over the catalyst. Catalytic activity gradually declined with time on stream because of the fluorination of ZrO₂. Treatment of the catalyst with both oxygen and water vapor promoted the removal of fluoride ions in sub-surface layers of the catalyst, which is effective for the recovery of the activity. CCI₂F₂ was decomposed at 300–450°C over AIPO₄. No fluorination of the AIPO₄ catalyst took place after the reaction for 1000 h. CH₂FCF₃, an alternative CFC, was completely decomposed over the mixed catalyst of Ce promoted AIPO₄ and Cr₂O₃ at 400–500°C. Catalytic decomposition is a rational method for destruction of used CFCs.