【作者】 赵安民；

【导师】 房鼎业； 应卫勇；

【作者基本信息】 华东理工大学 ， 化学工艺， 2012， 博士

【摘要】 天然气的主要成分为甲烷,是一种低碳、清洁和高效的能源。以煤为原料经合成气制备天然气是弥补我国气源不足的有效途径之一。在煤制天然气的工艺中,合成气甲烷化催化剂是核心,但目前国内尚无成熟催化剂。针对合成气甲烷化制备合成天然气的工艺特点,分别开发了适用于中低温反应的合成气甲烷化催化剂和适用于高温条件的合成气甲烷化催化剂。以Al203为载体制备了负载型Ni基催化剂,考察了Ni含量,助剂Mn添加量对合成气甲烷化反应的催化活性的影响,考察了温度、压力和空速对CO、CO2转化率和CH4生成速率的影响,并对催化剂进行了N2低温吸附、XRD、H2-TPR、SEM和TEM表征。结果显示,Ni含量为12、18和24 wt%的催化剂中,含Ni 24 wt%的24Ni催化剂的催化活性最好。加入助剂Mn可以促进Ni物种在催化剂表面分散,防止Ni物种在焙烧和还原过程中烧结。在Ni含量为24 wt%的条件下,含1wt%Mn的催化剂24Ni-1Mn催化剂具有最好的高温稳定性,而含3wt%Mn的24Ni-1Mn催化剂具有最好的低温催化活性。在相同反应条件下,加入助剂Mn对产物选择性影响很小,温度是影响产物分布的重要因素。增大反应压力,CO和C02转化率均升高,Cl和C2的选择性略有降低,C3-C6的选择性略有升高。因此,合成气甲烷化反应在温度为280-450℃,压力为0.1-2.0 MPa和空速为30000～45000ml·g-1·h-1的条件下操作比较合适。以活性A1203为载体制备了一组负载型Ni催化剂,考察了La和Mn的加入对催化剂催化活性的影响,并对催化剂进行了N2低温吸附、XRD、H2-TPR和TEM表征。结果显示,加入助剂不仅能够降低Ni晶粒的尺寸,而且能防止Ni物种在焙烧和还原过程中的烧结。24Ni-2La、24Ni-2Mn和24Ni-2La-2Mn催化剂具有相似的粒径(12.8-13.2nm),由此可知,加入不同种类的助剂主要是电子效应的不同。活性评价结果显示,24Ni-2La催化剂在相同条件下活性最高,体现出最好的协同效应。以α-Al203为载体,制备了负载型Ni催化剂,在Ni含量10 wt%的条件下考察了La助剂加入量对催化剂低温合成气甲烷化反应的催化活性高温稳定性,并进行了N2低温吸附、XRD、H2-TPR、SEM和TEM表征。结果表明,在10Ni催化剂中加入适量助剂La可以显著促进Ni物种的分散,经过焙烧和还原,有利于形成较小的Ni晶粒；在10Ni催化剂中加入过量助剂La后,催化剂上的Ni物种变的难以还原,导致低温活性低。加入2wt%的La的催化剂具有最好的低温活性和高温稳定性。利用燃烧法制备了Ni基甲烷化催化剂,考察了Ni含量(10～50 wt%),焙烧温度(700-1000℃),不同制备介质(水、乙醇和乙二醇)和添加不同助剂(2～8%Ce,4 wt% La、Zr、Mn和Mg)对合成气甲烷化反应活性和高温稳定性的影响,并进行了N2低温吸附、XRD、H2-TPR、SEM和TEM表征。燃烧法制备的催化剂Ni物种分散均匀,Ni物种周围被A1203空间隔离,有效防止了Ni的聚集和烧结,因而具有较好的低温催化活性和高温稳定性。在Ni含量10-50 wt%的范围内,30Ni-A1催化剂具有最好的低温催化活性和高温稳定性。Ni含量超过20 wt%的催化剂获得了良好的高温稳定性。Ni基催化剂上合成气甲烷化是一个结构敏感型反应,存在一个最优的Ni粒子直径。甲烷生成速率随着Ni晶粒的增大呈现先增大后减小的趋势,并在30Ni-A1催化剂(Ni粒子直径为41.8nm)上达到最大。在焙烧温度700-1000℃的范围内,随着焙烧温度的增加,Ni物种与载体的相互作用逐渐增强,生成NiA1204尖晶石物种越来越多,消耗大量Ni物种,导致催化剂活性降低。焙烧温度为700℃的30Ni-700催化剂获得了最好的低温催化活性。制备介质的影响考察表明,在以乙二醇为介质制备的催化剂上,Ni物种分散更加均匀,还原后具有最小的Ni粒子直径。在以水为介质制备的次之,以乙醇为介质制备的效果最差。加入助剂的影响考察表明,加入2、4、6和8 wt% Ce作为助剂降低了催化剂的低温催化活性；加入4 wt%的Zr,Mn,La和Mg作为助剂也降低了催化剂的低温催化活性。更多还原

【Abstract】 Natural gas is widely used as a low carbon, high efficiency and environment friendly fuel all over the world. The large expected demand for gas, the shortage of natural gas, and the high price of gas by other alternatives have made the manufacture of SNG (Synthetic Natural Gas) from coal attractive. Syngas methanation catalyst has been recognized as the most important part in the process of coal to SNG. We developed low temperature methanation catalysts and high temperature methanation catalysts according to the process of coal to SNG.Ni-based catalysts were supported on Al2O3 using impregnation method. The effect of Ni and Mn loading on catalytic activity were investigated by syngas methanation. The effect of temperature, pressure and space velocity on carbon oxides (CO and CO2) conversion and CH4 formation rate were also investigated. The as-prepared catalysts were characterized using N2 adsorption-desorption, X-ray diffraction (XRD), H2 temperature programmed reduction (H2-TPR), scanning electron microscope (SEM) and transmission electron microscope (TEM).24Ni catalysts with 24 wt% Ni-loading show the best catalytic activity among 12Ni,18Ni and 24Ni catalyst. The addition of Mn to Ni-based catalysts can increase the catalyst surface area, pore volume and decrease NiO crystallite size which lead to higher activity and stability.24Ni-3Mn catalyst shows the best low temperature catalytic activity (250～300℃) while 24Ni-1Mn catalyst shows the best high temperature stability (450℃). Though the addition of Mn can increase the conversion of CO and CO2 under the same condition, it has little effect on product distribution (C1, C2 and C3～C6). Temperature plays an important role on CO, CO2 conversion and product distribution. With the increase of reaction pressure, CO and CO2 conversion increase, selectivity of C1 and C2 decrease slightly, selectivity of C3-C6 increase slightly. Space velocity plays an important role on the conversion of CO and CO2. Syngas methanation operating at 280～450℃,30000～45000 mL·g-1·h-1 and 0.1～2.0 MPa would be appropriate.24Ni-2La,24Ni-2Mn and 24Ni-2La-2Mn catalysts supported on another Al2O3 were prepared by co-impregnation method for syngas methanation, and characterized by N2 adsorption-desorption, XRD, H2-TPR and TEM. The addition of La and/or Mn as promoters can decrease the crystal size of Ni particles, and prevent the growth of Ni particles during calcination and reduction.24Ni-2La,24Ni-2Mn and 24Ni-2La-2Mn have similar average Ni particle size, which is in the range of 12.8～13.2 nm. For syngas methanation,24Ni-2La presents better synergism effect.The 10Ni catalysts supported onα-Al2O3 with different amounts of La as promoter from 0 to 4 wt% were prepared, characterized and their catalytic activity was investigated in syngas methanation reaction. Effects of reaction temperature and lanthanum loading on carbon oxides conversion and methane selectivity were also studied. Adding certain amount of lanthanum to lONi catalysts can decrease the average NiO crystallite diameter which leads to higher activity and stability while excessive addition would cause deactivation quickly. Stability on stream towards deactivation was observed up to 800 min at 500℃, 0.1 MPa and 600000 mL·g-1·h-1.Ni-Al2O3 catalysts with various Ni content (10～50 wt%), calcinations temperature (700～1000℃), preparation medium (water, ethanol and glycol), Ce content (2～8%) and promoter (4 wt% La, Zr, Mn and Mg) were prepared by solution combustion method for syngas methanation. The as-prepared catalysts were characterized by N2 adsorption-desorption, XRD, H2-TPR, SEM and TEM. Ni-based catalyst prepared by combustion method has better low temperature and high temperature stability than that prepared by impregnation method. The results show that the Ni-Al2O3 catalysts exhibit good low temperature activity and an optimum catalytic activity for syngas methanation can be achieved on on 30Ni-Al catalyst. Moreover, catalysts with Ni content over 20 wt% show good high temperature stability, which is due to Ni nanoparticles scattered and spatially isolated by Al2O3. Catalytic activity for syngas methanation over the Ni-Al2O3 catalysts is sensitive to Ni particle size and a maximum production rate of methane per unit mass of nickel can be achieved on Ni crystals around 41.8 nm (30Ni-Al). The production rate of methane per unit mass of nickel showed volcano-shaped trend with respect to nickel content and average Ni diameter. The interaction between Ni species and Al2O3 increased with the increase of calcinations temperature from 700℃to 1000℃. The catalystic activity as well as surface area and pore volume decreased with the increase of calcinations temperature. 30Ni-Al catalyst prepared in glycol (30Ni-G) possesses the best low temperature activity and high temperature stability, prepared in water take the second place, and then prepared in ethanol. The addition of Ce as a promoter was investigated. The results show that the addition of Ce decreased the low temperature activity. The addition of 4 wt% La, Zr, Mn and Mg was investigated. The addition of promoter decreased the low temperature activity.更多还原