自放热条件下甲烷部分氧化制合成气

天然气组成的９０％以上是甲烷．目前由天然气制合成气的主要方法是水蒸汽重整法,这种方法投资大、设备复杂、能耗高、生产的合成气不适于直接用来合成甲醇和烃类等．甲烷部分氧化可直接制得Ｈ２与ＣＯ摩尔比为２的合成气,这是一个温和的放热过程、具有大空速和低温等优...     

COMBINED PARTIAL OXIDATION AND CARBONDIOXIDE REFORMING OF METHANE PROCESS TO SYNTHESIS GAS

IntroductionIthasbccndcmonstratcdthatmcthancrcformingt"ithcarbondioxidcpr0ducessynthcsisgasrichincarbonmonoxidc-x"hichisuscfulforthcs}nthcsisofaccticacid'dimcthylcthcrando.o-alcoholsll'2].Carbondioxidcref0rmingismorccndothcrmicthanstcamrcformingfCH4 CO2,'2CO 2H2Ai/'2,,=2473kJ..ol-1(l)Accordingl\"thisrcact1onnccdshighcrtcmpcraturcandlimitsspaccvclocityoffccdgas,Wehavcprct'ious1\studicdmcthancrcformingt"lthC02inthcmonotubcproccssl3J.Inordertoconvcrtmcthancinfccdgascomplctcl}',thcspaccvcloci…     

Ni整体型催化剂大空速甲烷自热氧化制合成气

随着石油资源的逐渐减少,天然气将是未来基本化学品的主要碳源.因此,天然气的开发利用已日益受到世界范围的广泛重视.当前,天然气的化工利用主要是用于生产合成气,再由合成气制取大量化学品,如合成氨、甲醇和烃类等.目前,工业上生产合成气主要采用水蒸气催化重整工艺.     

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。     

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.     

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。     

Syngas production by combined carbon dioxide reforming and partial oxidation of methane over Ni/α-Al2O3 catalysts

Ni/α-Al2O3 catalysts were found to be active in the temperature range 600~900 ℃ for both CO2 reforming and partial oxidation of methane. The effects of Ni loading, reaction temperature and feed gas ratio for the combination of CO2 reforming and partial oxidation of CH4 over Ni/α-Al2O3 were investigated. Catalysts of xwt%Ni/α-Al2O3 (x = 2.5, 5, 8 and 12) were prepared by wet impregnating the calcined support with a solution of nickel nitrate. XRD patterns and activity tests have verified that the 5wt%Ni/α-Al2O3 was the most active catalyst, as compared with the other prepared catalyst samples. An increase of the Ni loading to more than 5 wt% led to a reduction in the Ni dispersion. In addition, by combining the endothermic carbon dioxide reforming reaction with the exothermic partial oxidation reaction, the loss of catalyst activity with time on stream was reduced with the amount of oxygen added to the feed.     

甲烷催化部分氧化制合成气的反应机理

借助脉冲反应、质谱-程序升温表面反应（MS-TPSR）等技术研究了Ni／α-Al2O3催化剂上甲烷催化部分氧化制合成气（POM）的反应机理．结果表明,NiO上CH4不能解离产生H2只有当NiO被CH4还原为Ni0后,CH4才能解高产生H2,Ni0是CH4活化和POM反应的活性相;POM反应机理遵循直接氧化机理,CH4和O2均在Ni0上活化,活化过程形成的Ni…C和Niδ…Oδ物种是反应历程中的关键物种,Niδ …Oδ物种高选择性地与CH4解离产生的碳物种Ni…C反应生成CO．     

Ni/ZrO2催化剂上甲烷水蒸气重整反应的研究

研究了Ni/ZrO2催化剂对甲烷水蒸气重整制合成气的反应性能。考察了催化剂的还原温度、载体焙烧温度以及反应温度、原料配比和空速等对催化剂性能的影响。利用XRD、TEM、XPS等手段对催化剂的织构形貌进行了表征。研究表明，Ni/ZrO2催化剂用于甲烷水蒸气重整制合成气不仅具有较高的活性，也具有较好的稳定性。水蒸气比增加，CH4转化率增大、CO选择性下降。CH4转化率及CO选择性均随空速增大而下降。使用10%Ni/ZrO2催化剂，在650 ℃、空速1.984×104 h－1、原料气配比H2O∶CH4∶N2=2∶1∶2.67的条件下，获得CH4转化率85%、CO选择性70%的结果。     

流化床甲烷部分氧化制合成气Ni催化剂及助剂La的作用

在流化床中,考察了不同Ni担载量的Ni/γ-Al2O3催化剂对POM反应的催化性能,以8％Ni最佳,TPR结果表明。催化剂表面主要有两种化学状态的NiO。当镍担载量≤2％时,催化剂表面 仅存在一种高温下才能被还原的NiO,在Ni催化剂中添加La,可削弱NiO与载体间的相互作用,并且可减缓在CH4＋O2气氛下升温过程中NiO与载体发生强相互作用 生成NiAl2O4,因此添加La的Ni催化剂在750℃就能引发甲烷部分氧化（POM）反应,且反应引发后可获得与经700℃H2还原后的Ni^0催化剂相同的反应性能。     

膜反应器中Ni-Cu催化剂上CO加氢合成乙烯的研究

 将硅藻土－TiO2－聚乙烯（或聚丙烯）疏水复合膜反应器应用于\r\nCO加氢合成乙烯的反应过程，以Ni－Cu／TiSiO和Ni－Cu／MgSiO为催化\r\n剂，考察了反应温度、空速和进料组成等因素对CO转化率和乙烯选择性\r\n的影响．结果表明：膜催化反应的产物与常规催化反应相同，催化反应\r\n机理没有区别，在适宜条件下，膜催化反应的CO转化率和乙烯选择性较\r\n之常规催化反应提高了10％左右，二氧化碳和甲烷的选择性降低，而乙\r\n烷的选择性略有增加．     

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.     

La2O3/MgO催化剂上的甲烷氧化偶联

研究了甲烷在La_2O_3/MgO催化剂上的氧化偶联。发现制备过等对催化剂的行为有显著影响。比较了催化剂的反应性能和体相结构,表明在MgO上存在着三种La_2O_3的状态:高分散La_2O_3是最活泼的;La(OH)_3不太活泼;而呈六方晶相的La_2O_3晶粒活性最低。在催化剂中加入Na_2CO_3和K_2CO_3可以改进催化剂的活性和选择性。还考察了反应条件如温度和空速的影响。     

甲烷部分氧化制合成气反应Pt/Al_2O_3和Pt/CeO2/Al_2O_3催化剂的研究(英文)

研究了Ｐｔ／Ａｌ２Ｏ３和Ｐｔ／ＣｅＯ２／Ａｌ２Ｏ３催化剂对甲烷部分氧化制合成气反应的催化活性，发现Ｐｔ／ＣｅＯ２／Ａｌ２Ｏ３显示了比Ｐｔ／Ａｌ２Ｏ３更高的甲烷转化率和合成气选择性。用Ｈ２ＴＰＲ，Ｈ２ＴＰＤ，ＳＥＭ和ＸＲＤ等手段和技术对催化剂进行了表征。ＣｅＯ２与Ｐｔ之间存在较强的相互作用（ＳＭＳＩ），这种作用促进了Ｐｔ在催化剂表面的分散，抑制了Ｐｔ在催化剂表面的迁移，大大降低了催化剂在反应中的完全燃烧活性，提高了催化剂的部分氧化活性和选择性，避免了因催化剂床层局部温度过高而导致催化剂活性下降或失活，提高了催化剂的稳定性。同时，在反应过程中，ＣｅＯ２通过促进水蒸气变换反应（ＷＧＳＲ）的进行使反应体系迅速达到平衡，提高了催化剂对Ｈ２的选择性。     

制备方法对La改性的Ni/γAl2O3催化甲烷部分氧化的研究

采用共沉淀法和浸渍法制备La改性的Ni/γAl2O3催化剂，并用于催化甲烷部分氧化反应。共沉淀法制备的催化剂表现出较高的活性和稳定性。空速为80000h－1、800℃时甲烷的转化率接近100％，H2的选择性达99.8％，且在稳定性实验中保持15h活性变化不大。实验采用BET、TPR和XRD说明共沉淀法制备的镍基氧化铝催化剂中，La的加入提高了催化剂的比表面积，有效的抑制了大颗粒NiAl2O4的形成，降低了催化剂活性组分的还原温度，对POM显示出很高的催化活性。     

Ni/TiO2 Catalyst for Partial Oxidation of Methane to Syngas

Ni/TiO₂ catalyst was firstly used for the partial oxidation of methane to produce synthesis gas. The reaction was carried out in a fixed-bed continuous flow quartz reactor at atmospheric pressure. The flow rate was regulated by a mass controller with a space velocity of 1.5×10⁵ h^-1 and a CH₄/O₂ molar ratio of 2/1. Prior to the introduction of feed gas, the Ni/TiO₂ catalyst was activated in flowing H₂ at 700℃ for 30 min. TiO₂ is known to be a poor support for partial oxidation because which can easily result in complete oxidation. But at 700℃, Ni/TiO₂ catalyst exhibited a better performance than Ni/SiO₂ and Ni/ZrO₂. The conversion of methane was 81.5, and the selectivity of hydrogen and carbon monoxide were 93.4 and 89.4 respectively. After 6h of continuous reaction, the conversion of methane descended a little and then remained a steady yield on the whole,but the selectivity of H₂ and CO gradually declined, as far as to a constant. The selectivity of H₂ was always higher than that of CO and the ratio of H₂/CO wouldn't change with the increasing of reaction time.     

在甲烷部分氧化制合成气中Pt-Ni/Al_2O_3催化剂中的Pt-Ni协同作用机理(英文)

甲烷部分氧化制合成气的研究是在Ｎｉ／Ａｌ２Ｏ３催化剂上进行的。结果表明,添加少量的Ｐｔ可显著提高甲烷转化率和ＣＯ选择性并增加Ｎｉ／Ａｌ２Ｏ３催化剂的稳定性。通过ＸＲＤ、ＸＰＳ、ＴＰＲ和ＴＰＤ等表征手段发现,Ｐｔ－Ｎｉ／Ａｌ２Ｏ３催化剂中形成了Ｐｔ－Ｎｉ合金,Ｐｔ在催化剂表面富集。分析ＴＰＲ和ＴＰＤ数据可知,Ｐｔ－Ｎｉ双金属的相互作用阻止了催化剂的烧结和Ｎｉ的流失,提高了催化剂的活性。另外,Ｐｔ－Ｎｉ的协同作用也抑制了催化剂表面积炭的产生。     

Ni-Cu-Al2O3催化剂的活性相及作用机理

对新鲜和７００℃反应过的Ｎｉ－Ａｌ和Ｎｉ－Ｃｕ－Ａｌ催化剂的ＸＲＤ、ＸＰＳ表征结果表明，新鲜ＮｉＯ－Ａｌ２Ｏ３催化剂体相中的ＮｉＯ，ＮｉＡｌ２Ｏ４经７００℃反应后转变成金属Ｎｉ，同时表面的镍物种由单一的ＮｉＡｌ２Ｏ４变为ＮｉＡｌ２Ｏ４，ＮｉＯ和金属Ｎｉ的混合物，经反应后ＮｉＯ－ＣｕＯ－Ａｌ２Ｏ３催化剂体相和表相中的ＮｉＡｌ２Ｏ４，ＣｕＡｌ２Ｏ４均转变成为Ｎｉ－Ｃｕ合金，这是此催化剂对甲烷部分氧化反     

Modulating the reactivity of Ni-containing Pt(111)-skin catalysts by density functional theory calculations

We present here a first principles density functional theory investigation of the reactivity of Pt(111)-skin catalysts, which are varied from surface alloys with Ni to bulk PtxNi 1-x (x=0.25,0.50,0.75) alloys. Molecule (CO, O, and H) adsorption and oxidation of CO+O and H+O reactions were studied and analyzed in detail. Independent of the adsorbates, the interaction between adsorbates and substrates becomes weakened with increase in Ni, due to the downshift of d-band center of surface Pt atoms. Moreover, activation barriers of CO and H oxidation toward atomic oxygen gradually decrease. In term of CO preferential oxidation (PROX) in excess of hydrogen, it turns out that the overall reactivity and selectivity rely on the optimum of various elementary steps involved such as competitive molecular (dissociative) adsorption and oxidation reaction. The present calculations show that Pt3Ni(111) with Pt overlayer is an optimum catalyst for CO PROX in excess of hydrogen.