TPR-IR，TPSR-IR法研究Ni/Al2O3和Ni/MgO催化剂的担体效应

用程序升温反应原位红外跟踪法(TPR-IR),程序升温表面反应法(TPSR)和程序升温表面反应原位红外跟踪法(TPSR-IR)研究了Ni/Al_2O_3,Ni/MgO催化剂的甲烷化反应。发现Ni/Al_2O_3催化剂的活性高于Ni/MgO催化剂,而后者的CO_2选择性远高于前者。通过观察程序升温反应过程中CO吸附态的动态行为,考察了催化剂活性中心的种类和性质,从表面键的角度分析了表面碳物种与活性中心的关系,认为担体对催化剂活性的影响在于改变了催化剂活性中心的种类和性质,担体改变CO_2产物的选择性可能是担体影响了金属中心上的两个竞争反应,其微观机制可能与CO_2由镍中心向MgO担体上的迁移有关。     

甲烷二氧化碳转化制备富含一氧化碳合成气

研究了甲烷二氧化碳转化反应的热力学特性,计算了反应平衡常数及平衡组成,分析和确定了抑制积碳的生成条件,采用固定床流动和脉冲反应装置研究了Ni/Al_2O_3催化剂对甲烷二氧化碳转化的催化性能。     

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.     

Ni/γ-Al2O3催化剂上CH4-CO2重整体系中积碳-消碳的研究

用动态热重技术和色谱技术联用以及XRD和TEM等表征手段,研究了Ni/γ-Al2O3催化剂上甲烷－二氧化碳重整体系的积碳和消碳及其与一氧化碳产率之间的关系。结果表明,二氧化碳与甲烷有不同的活性中心,二氧化碳的存在不改变甲烷活化积碳的本质,但可通过及时将表面含碳物种转化为一氧化碳而降低积碳速率,二氧化碳能消去活泼的须状碳,但不易消去惰性的石墨碳。等摩尔条件下二氧化碳消碳能力弱于甲烷活化积碳,二氧化碳适度过量可有效抑制积碳,n(CO2)/n(CH4)≈1.3为进料比最佳值,此时积碳－消碳达到动态平衡,可获得最高的一氧化碳产率和较低的积碳速率,且该值不受温度影响。Ni/γ-Al2O3催化剂有很强的再生能力,但反复积碳－消碳会使催化剂镍晶粒度增大,分散度下降,从而导致不可逆失活。     

Ni/Ce-Zr-Al-O催化剂的表面碱性和CO2＋CH4重整性能

用水热法制备了不同NiO含量的Ni/Ce-Zr-Al-O催化剂.用H2-TPD (程序升温脱附),DRIFTS(漫反射红外傅立叶变换光谱),CO2-TPD等方法考察了NiO的含量对催化剂表面碱性的影响,并和反应稳定性以及抗积碳性能相关联.H2-TPD结果表明,随NiO含量的增加,催化剂表面的Ni含量增加.DRIFT和CO2-TPD结果表明CO2的化学吸附主要是碳酸盐和碳酸氢盐形式.添加少量Ni能够使表面碱性位数量显著增加,碱强度减弱.Ni可能优先占据在催化剂表面较强的碱性位上,再增加Ni的含量则会使碱强度减弱,碱性位有所减少,降低CO2的吸附性能,从而减弱从CO2获得活动氧以消碳的能力.这种作用使NiO含量为7.0％(w)的样品活性随反应进行而减低,积碳量是NiO含量为4.0％(w)的样品的3.7倍.     

Ni基六铝酸镧LaNiAl11O19催化剂表面甲烷CO2的重整积炭速率

甲烷二氧化碳重整制合成气反应过程中,催化剂表面积炭是制约催化反应顺利进行的关键因素。研究催化剂表面积炭物种及积炭速率,找出影响催化剂表面积炭的动力学因素,对建立合理的催化重整反应体系,完善催化剂表面积炭的动力学理论具有重要的理论和实际意义。目前有关催化剂表面积炭速率的研究报道较少[1,2]。Ｎｉ基六铝酸盐催化剂对甲烷二氧化碳重整制合成气具有很好的催化活性和稳定性[3,4]。本文利用Ｘ 射线光电子能谱(ＸＰＳ)和热重分析(ＴＧＡ)技术,在还原态Ｎｉ基六铝酸镧ＬａＮｉＡｌ11Ｏ19催化剂表面研究了甲烷裂解积炭和甲烷二氧…     

碱性助剂的添加对Ni/CaO-Al2O3催化剂性能的影响

在CH4、 CO2和O2制合成气的反应中, 通过在Ni/CaO-Al2O3催化剂中添加碱性助剂K2O、 MgO和La2O3, 使催化剂的性能得到了改善. 实验结果表明, MgO和La2O3助剂的添加, 有利于提高催化剂的活性;添加K2O, 却相反. 测得催化剂上积炭量的顺序为: Ni-La2O3/CaO-Al2O3相似文献   

低Ni含量和低比表面积六铝酸盐LaNiAl_(11)O_(19-δ)催化剂上CH_4-CO_2重整反应的积炭

利用X射线粉末衍射、氢程序升温还原、X射线光电子能谱和透射电镜技术研究了在低Ni含量和低比表面积六铝酸盐催化剂LaNiAl_(11)O_(19-δ)上CH_4-CO_2重整反应的积炭行为,考察了该催化剂表面积炭的形貌、来源、积炭物种及其反应性能.结果表明,LaNiAl_(11)O_(19-δ)催化剂表面积炭主要由甲烷裂解产生,并以Ni的碳化物形式存在于活性中心Ni的周围.根据积炭物种活化程度的难易可分为C_α,C_β和C_γ三种类型,其中C_α为容易被CO_2消除的化合碳,而C_β和C_γ则是不易被CO_2消除的石墨碳.透射电镜结果表明,C_α以碳纳米管形式分布于催化剂颗粒周围,但金属Ni活性中心仍能暴露于气相中,因而不影响催化剂的活性.     

氧化锆担载镍甲烷干重整催化剂的载体形貌效应（英文）

煤层气是储量十分丰富的煤炭伴生资源,也是煤炭开采中最大的安全隐患之一,同时还是重要的温室气体.研究煤层气的高效、清洁资源化利用具有资源和环境双重意义.因此,世界主要产煤国均十分重视煤层气的开发和利用.煤层气的主要成分是甲烷,目前主要通过两种方式实现其资源化利用:(1)直接转化,主要通过氧化偶联、催化氧化官能团化或脱氢芳构化等途径将其转化为高碳烃、含氧化合物及芳烃等;(2)间接转化,甲烷首先经催化重整反应制取合成气,而后再经Fischer-Tropsch合成、甲醇化和氢甲酰化等过程来合成饱和烃、烯烃、甲醇及其他含氧化物.对于前者,由于热力学限制,反应收率很低,应用前景较差,而经由合成气这一平台产物的间接转化路线被认为是一条甲烷资源化利用颇具工业前景的转化路线.因此,甲烷催化重整制合成气备受关注.研究表明,贵金属具有较好的甲烷重整催化性能,但其储量有限、价格昂贵的内在缺陷不利于甲烷大规模转化和资源化利用.Ni基催化剂具有与贵金属可比的催化活性和选择性,且其储量丰富,价格低廉,因此在甲烷重整反应中备受青睐.但是,相对于贵金属,Ni基催化剂易于积碳和烧结失活,这已成为制约其大规模工业化应用的瓶颈.迄今,大量文献报道关注如何提高Ni基催化剂的催化稳定性.而载体形貌调控是调节负载型催化剂的有效途径.本文开展了用作载Ni催化剂的氧化锆载体的形貌调控研究,以期可以有效调节载Ni催化剂的物化性质,进而调控载Ni催化剂的甲烷重整催化性能.采用水热法成功制备了松球状和鹅卵石状的单斜相氧化锆载体,进一步负载镍,制备了载镍催化剂,用于甲烷重整制合成气反应.具有分级结构的松球状氧化锆载Ni催化剂(Ni/ZrO_2-ipch)展示出比鹅卵石状氧化锆和常规氧化锆纳米粒子载Ni催化剂显著好的催化活性和稳定性.采用XRD、N_2吸附、TEM、H_2-TPR、CO化学吸附、CO_2-TPD、XPS和TGA等手段研究了松球状氧化锆载Ni催化剂高催化活性和稳定性的原因和机制.发现,其较高的催化活性主要归因于高的Ni分散度、改善的可还原性、促进的氧流动性以及较多的碱性位和较强的碱性,这些物化性质依赖于氧化锆载体的独特形貌.分级结构的松球状氧化锆载Ni催化剂高的甲烷重整催化稳定性主要源于催化剂的高抗烧结、抗积碳性能.加强的金属载体效应和介孔限域效应可以阻止金属Ni的高温烧结,而优良的抗积碳稳定性主要源于催化剂良好的氧流动性、较多的碱性位、较强的碱性以及小的Ni粒子尺寸.鉴于分级结构松球状氧化锆载Ni催化剂高的催化活性和优良的抗积碳、抗烧结稳定性,该催化剂用于甲烷重整制合成气具有广阔前景.而所制备的分级结构松球状氧化锆由于具有独特的结构和优良的热稳定性,可以作为性能优良的载体用于其他反应,尤其对于高温转化过程可望表现出明显优势.     

MgO助剂对甲烷部分氧化Ni/Al2O3催化剂结构和性能的影响

采用分步浸渍法制备了MgO改性的Ni/Al2O3催化剂，采用BET、XRD、H2 TPR、TEM和活性评价等研究方法，考察了MgO助剂对Ni/Al2O3催化剂物化性质和甲烷部分氧化制合成气反应性能的影响。实验结果表明，MgO助剂提高了催化剂镍物种的均一性，抑制了NiAl2O4尖晶石的形成，并且增强了镍物种与载体的相互作用，这与MgO、NiO形成固溶体及与Al2O3形成MgAl2O4有关。同时，适量的MgO助剂可以提高Ni物种在催化剂中分散度，并提高其有效利用率，改性后的催化剂在甲烷部分氧化反应中显示出较好的反应性能。过量的MgO助剂对催化剂的反应性能产生负面影响，MgO的碱性可以促进逆水煤气变换反应，从而导致H2选择性降低和CO选择性提高。     

制备方法对Ni/MgO/Al2O3催化剂在甲烷与二氧化碳重整反应活性的影响

采用浸渍－还原法制备的Ｎｉ／ＭｇＯ／Ａｌ２Ｏ３在ＣＨ４与ＣＯ２重整制合成气反应中显示出良好的催化性能和一定的抗积炭能力;在１０２３Ｋ下流动反应气氛中连续运转１００ｈ,未见活性下降,ＣＨ４及Ｃ弦均为９０％左右,ＣＯ收率高于９０％,实验还发现,ＣＨ４转化率随着原料气中ＣＯ２浓度的增加而升高,当Ｖ（ＣＯ２）／Ｖ（ＣＨ４）＝２时ＣＨ４转化率可达１００％,通过ＢＥＴ比表面积测定及ＸＲＤ,ＴＥＭ等分析手段,比     

载体对担载Ni催化剂甲烷与二氧化碳重整反应活性的影响

制备了 Zr O2 、Mg O改性的 Al2 O3、Ti O2 复合载体 ,并应用 X-射线粉末衍射 (XRD)、比表面积测定、扫描电镜 (SEM)等手段进行了表征 .结果表明 ,这些氧化物在 Al2 O3上的晶粒尺寸小、比表面积大 ,分散较好 ,而在Ti O2 上的分散性较差 .对经 10 73K焙烧的 Mg O/ Ti O2 ,还发现部分 Ti O2 载体由锐钛矿变为金红石 ,同时生成Mg Ti O3 新相 .考察了载体对 Ni催化剂的 CH4与 CO2 重整反应活性的影响 ,其次序为 :Mg O/ Al2 O3>Zr O2 /Al2 O3>Al2 O3>Mg O >Zr O2 >Ti O2 >Mg O/ Ti O2 . Ti O2 及 Mg O/ Ti O2 担载 Ni催化剂的低活性可能与 Ti O2 本身的还原性有关     

CH4-CO2 reforming to syngas over Pt-CeO2-ZrO2/MgO catalysts: Modification of support using ion exchange resin method

Pt-CeO2-ZrO2/MgO (Pt-CZ/MgO) catalysts with 0.8 wt% Pt, 3.0 wt% CeO2 and 3.0 wt% ZrO2 were prepared by wet impregnation method. Support MgO was obtained using ion exchange resin method or using commercial MgO. XRD, BET, SEM, TEM, DTA-TG and CO2-TPD were used to characterize the catalysts. CH4-CO2 reforming to synthesis gas (syngas) was performed to test the catalytic behavior of the catalysts. The catalyst Pt-CZ/MgO-IE(D) prepared using ion exchange resin exhibits more regular structure, smaller and more unique particle sizes, and stronger basicity than the catalyst Pt-CZ/MgO prepared from commercial MgO. At 1073 K and atmospheric pressure, Pt-CZ/MgO-IE(D) catalyst has a higher activity and greater stability than Pt-CZ/MgO catalyst for CH4-CO2 reforming reaction at high gas hourly space velocity of 36000 mL/(g·h) with a stoichiometric feed of CH4 and CO2. Activity measurement and characterization results demonstrate that modification of the support using ion exchange resin method can promote the surface structural property and stability, therefore enhancing the activity and stability for CH4-CO2 reforming reaction.     

钡改性的Ni/γ- Al2O3催化剂用于甲烷部分氧化的研究

800 ℃、80 000 h－1、CH4/O2/N2=14/7/79下比较了质量分数20%的Ni/γ- Al2O3和Ba改性的Ni/γ- Al2O3催化剂，用于甲烷部分氧化反应的活性和选择性。结果表明，Ba的添加提高了镍基催化剂的活性和稳定性。BET和XRD表明，Ba的加入有利于高温焙烧下抑制大颗粒的Ni Al2O4的形成，保持了高比例的活性镍组分，提高了催化剂催化活性。常压下，xCH4接近100%，sCO、sH2达到92.2%和98.1%，催化剂15 h内活性稍微下降。Ba的加入使Al2O3的晶型转化温度由800 ℃提高到900 ℃，提高了载体的稳定性。     

CH4/CO2重整Ni基催化剂制备与催化性能的关系

用四种浸渍程序制备Ｎｉ－Ｍｇ／γ－Ａｌ２Ｏ３催化剂,其ＣＨ４／ＣＯ２重整制合成气的活性和积炭量的测试表明真空浸渍法最好,其次是二次不等量浸渍。现场ＣＯ歧化和ＣＨ４解离积炭实验表明,Ｎｉ基催化剂的积炭主要从反应生成物ＣＯ的歧化而来     

Effect of MgO promoter on Ni-based SBA-15 catalysts for combined steam and carbon dioxide reforming of methane

A series of Ni/SBA-15 catalysts with Ni contents ranging from 5 wt% to 15 wt%, as well as another series of 10%Ni/MgO/SBA-15 catalysts, in which the range of the MgO content was from 1 wt% to 7 wt%, were prepared, and their catalytic performances for the reaction of combined steam and carbon dioxide reforming of methane were investigated in a continuous flow microreactor. The structures of the catalysts were characterized using the XRD, H2-TPR and CO2-TPD techniques. The results indicated that the CO selectivity for this reaction was very close to 100%, and the H2/CO ratio of the product gas could be controlled by changing the H2O/CO2 molar ratio of the feed gas. The simultaneous and plentiful existing of steam and CO2 had a significant influence on the catalytic performance of the 10%Ni/SBA-15 catalyst without modification. After reacting at 850 °C for 120 h over this catalyst, the CH4 conversion dropped from 98% to 85%, and the CO2 conversion decreased from 86% to 53%. However, the 10%Ni/3%MgO/SBA-15 catalyst exhibited a much better catalytic performance, and after reacting for 620 h, the CO2 conversion over this catalyst dropped from 92% to around 77%, while the CH4 conversion was not decreased. Oxidation of the Ni0 species as well as carbon deposition during the reaction were the main reasons for the deactivation of the catalyst without modification. On the other hand, modification by the MgO promoter improved the dispersion of the Ni0 species, and enhanced the CO2 adsorption affinity which in turn depressed the occurring of carbon deposition, and thus retarded the deactivation process.     

Ni/Al2O3 catalysts for syngas methanation: Effect of Mn promoter

Ni/Al2O3 catalysts with different amounts of manganese ranging from 1 to 3 wt% as promoter were prepared by co-impregnation method. The catalysts were characterized by N2 physisorption, XRD, TPR, SEM and TEM. Their catalytic activity towards syngas methanation reaction was also investigated using a fixed-bed integral reactor. It was demonstrated that the addition of manganese to Ni/Al2O3 catalysts can increase the catalyst surface area and average pore volume, but decrease NiO crystallite size, leading to higher activity and stability. The effects of reaction temperature, pressure and weight hourly space velocity (WHSV) on carbon oxides conversion and CH4 formation rate were also studied. High carbon oxides conversion, CH4 selectivity and formation rate were achieved at the reaction temperature range of 280 300℃.     

Energetic mapping of Ni catalysts by detailed kinetic modeling

Temperature-programmed desorption (TPD) of CO has been performed on supported and unsupported nickel catalysts. The unsupported Ni catalyst consists of a Ni(14 13 13) single crystal which has been studied under ultrahigh vacuum conditions. The desorption energy for CO at low CO surface coverage was found to be 119 kJ/mol, and the binding energy of C to the Ni(111) surface of the crystal was 703 kJ/mol. The supported catalysts consist of nickel supported on hydrotalcite-like compounds with three different Mg2+/Al3+ ratios. The experimental results show that for the supported Ni catalysts TPD of CO leads to desorption of both CO and CO2, with the latter being dominant. Dissociation of CO takes place, and considerable amounts of residue C are left on the surface. The residue C is removed by temperature-programmed oxidation (TPO). The results show that a low Mg2+/Al3+ ratio in the hydrotalcite precursor seems to result in more steplike sites, kinks, and defects for carbon monoxide dissociation. A detailed kinetic modeling of the TPO results based on elementary reaction steps has been conducted to give an energetic map of supported Ni catalysts. Experimental results from the ideal Ni surface fit nicely with literature values, providing useful information for identifying active sites on supported Ni catalysts.