Influence of alkali metal doping on surface properties and catalytic activity/selectivity of CaO catalysts in oxidative coupling of methane

Surface properties （viz. surface area, basicity/base strength distribution, and crystal phases） of alkali metal doped CaO （alkali metal/Ca= 0.1 and 0.4） catalysts and their catalytic activity/selectivity in oxidative coupling of methane （OCM） to higher hydrocarbons at different reaction conditions （viz. temperature, 700 and 750 ℃; CH4/O2 ratio, 4.0 and 8.0 and space velocity, 5140-20550 cm^3 ·g^-1·h^-1） have been investigated. The influence of catalyst calcination temperature on the activity/selectivity has also been investigated. The surface properties （viz. surface area, basicity/base strength distribution） and catalytic activity/selectivity of the alkali metal doped CaO catalysts are strongly influenced by the alkali metal promoter and its concentration in the alkali metal doped CaO catalysts. An addition of alkali metal promoter to CaO results in a large decrease in the surface area but a large increase in the surface basicity （strong basic sites） and the C2＋ selectivity and yield of the catalysts in the OCM process. The activity and selectivity are strongly influenced by the catalyst calcination temperature. No direct relationship between surface basicity and catalytic activity/selectivity has been observed. Among the alkali metal doped CaO catalysts, Na-CaO （Na/Ca = 0.1, before calcination） catalyst （calcined at 750 ℃）, showed best performance （C2＋ selectivity of 68.8% with 24.7% methane conversion）, whereas the poorest performance was shown by the Rb-CaO catalyst in the OCM process.     

甲烷氧化偶联反应催化剂碱性与反应性能的相关性

在催化剂甲烷氧化偶联反应性能研究的基础上，利用ＣＯ２－ＴＰＤ技术考察了不同的碱金属化合物－Ｌａ２Ｏ３／ＢａＣｏ３催化剂的表面碱性。结果表明，ＢａＣＯ３的协同作用，碱金属化合物的添加都增大了催化剂表面碱性的强度，也增加了碱性位的数量。     

氧化镧催化剂上甲烷氧化偶联—不同制备方法的比较

本文研究了５种不同制法的Ｌａ＿２Ｏ＿３对甲烷氧化偶联的催化性能，其Ｃ＿２选择性和Ｃ＿２收率的相对顺序为：Ｌａ＿２Ｏ＿３（１）＞Ｌａ＿２Ｏ＿３（２）＞Ｌａ＿２Ｏ＿３（４）＞Ｌａ＿２Ｏ＿３（５）＞Ｌａ＿２Ｏ＿３（３）。并运用ＸＲＵ、ＸＰＳ、ＣＯ＿２－ＴＰＤ、ＮＨ＿３－ＴＰＤ和ＩＰＡ转化反应等技术分别对催化剂的体相结构和表面性质，表面酸碱性进行了测定。结果表明，由于制备方法的不同，导致了Ｌａ＿２Ｏ＿３晶体表面结构的差异，这是影响催化性能的主要原因。同时还发现，催化剂的活性和Ｃ＿２选择性与表面酸碱性存在着相依性，Ｌａ＿２Ｏ＿３表面的总碱位数与总酸位数的比值，与其催化性能有较好的直接对应关系。     

Synthesis and catalytic performance on methanol conversion of NiAPSO-34 crystals (II): catalytic performance under various reaction conditions

This work has been focused on the catalytic performance for methanol conversion of NiAPSO-34 catalysts which had been synthesized by various preparation methods. The deposited coke during the hydrocarbon transformation was analyzed by temperature-programmed oxidation (TPO) method. For a catalyst with small acid sites and sharp particle size distribution, the catalytic activity and selectivity to ethylene increased compared with other catalysts. It could be confirmed that the catalysts having different acidic densities on external surface and internal surface represented different catalytic activities. Furthermore, it was elucidated that amount of coke formation was strongly related to acidic density on the external crystal surface. On the other hand, catalytic performances under various reaction conditions were exhibited variously and the deposited coke amount was also various. In particular, a surprising result was that the catalytic performance was not changed on the revived catalyst by thermal treatment at 600°C for 3 h.     

Oxidation of propane to acrylic acid and acetic acid over alkaline earth-doped Mo-V-Sb-Ox catalysts

Alkaline earth metal (Mg, Ca, Sr and Ba)-doped Mo-V-Sb-Ox catalysts, prepared by a dry-up method, have been investigated for their catalytic performance in the oxidation of propane under different reaction conditions. The catalysts have been characterized by N2 adsorption-desorption, temperature-programmed desorption (TPD) of NH3, SEM and XRD. Influence of water vapor on the catalytic performance, particularly on the selectivities to acetic acid and acrylic acid, has also been studied. The selectivity to acrylic acid was improved significantly by the doping of alkaline earth metals to Mo-V-Sb-Ox catalysts. The surface acidic sites of the catalyst decreased with the doping of the catalyst with alkaline earth metals, which ultimately was found to be beneficial for obtaining high selectivity to acrylic acid. The catalytic activity and product selectivities were found to be influenced by the reaction temperature, C3H8/O2 ratio and space velocity. A significant improvement in the selectivity to acrylic acid has also been observed by the addition of water vapor in the feed of propane and oxygen in the oxidation of propane.     

负载铯催化剂上苯酚与甲醇醚化制苯甲醚

研究了不同酸碱中心、载体、前躯体和负载量对负载铯催化剂上苯酚与甲醇醚化制苯甲醚反应行为的影响。结果表明,碱性中心比酸性中心具有更高的苯甲醚选择性,碱性中心的阳离子影响催化剂的苯甲醚选择性。载体影响铯离子的电子结合能,从而影响催化剂的醚化活性;铯离子的电子结合能越低,催化剂醚化活性越低;载体影响催化剂强碱性位数量,从而影响苯甲醚选择性;强碱性位数量越多,副反应越容易发生,苯甲醚选择性越低。不同前躯体制备的Cs/Si O2由于表面相对铯原子数量不同而活性不同;Cs/Si O2的单层负载量为1.0 mmol/g,超过单层负载量后催化剂的平均活性显著下降。     

Oxidation of propane to acrylic acid and acetic acid over alkaline earth-doped Mo-V-Sb-O_x catalysts

Alkaline earth metal (Mg,Ca,Sr and Ba)-doped Mo-V-Sb-O x catalysts,prepared by a dry-up method,have been investigated for their catalytic performance in the oxidation of propane under different reaction conditions.The catalysts have been characterized by N2 adsorption-desorption,temperature-programmed desorption (TPD) of NH3,SEM and XRD.Influence of water vapor on the catalytic performance,particularly on the selectivities to acetic acid and acrylic acid,has also been studied.The selectivity to acrylic acid was improved significantly by the doping of alkaline earth metals to Mo-V-Sb-O x catalysts.The surface acidic sites of the catalyst decreased with the doping of the catalyst with alkaline earth metals,which ultimately was found to be beneficial for obtaining high selectivity to acrylic acid.The catalytic activity and product selectivities were found to be influenced by the reaction temperature,C3H8/O2 ratio and space velocity.A significant improvement in the selectivity to acrylic acid has also been observed by the addition of water vapor in the feed of propane and oxygen in the oxidation of propane.     

过渡金属（Cu，Fe，Mn，Co）改性高分散V2O5/TiO2作为高效NH3-SCR脱硝催化剂

选择性催化还原(SCR)是目前固定源及移动源中控制NOx排放最为有效的技术手段之一.工业上应用最广泛的商业SCR催化剂是钒基催化剂.钒基催化剂经钨(钼)改性后具有较好的活性、稳定性和抗水抗硫性能,但在应用过程中仍存在N2选择性较低、活性温度窗口(300–400 oC)较窄及高温下V2O5极易流失等不足,且钨(钼)的价格十分昂贵.因此,用廉价组分提高钒基催化剂的催化性能在实际工业应用中仍具有重要意义.研究发现,很多非贵金属(如Cu, Fe, Mn, Co, Ce, Zr, Nb, Sn, La等)都可以代替钨(钼)用来提高钒基催化剂的选择性、活性温度窗口和(热)稳定性能等.引入的金属通常以氧化物或钒酸盐形式存在,并与活性组分钒物种有很强的相互作用,从而提高钒物种的氧化还原性能及分散度,同时增大表面酸性位数量,抑制锐钛矿向金红石相转变.近年来很多研究发现,经金属改性的钒基催化剂以钒酸盐形式存在时可有效提高催化剂活性和 N2选择性,尤其可显著提高催化剂的(热)稳定性.本文采用浸渍法以廉价易得、储量丰富的过渡金属改性钒基催化剂,得到高度分散的M-V/TiO2(M = Cu, Fe, Mn, Co)脱硝催化剂.结果发现, Cu-V/TiO2和Fe-V/TiO2催化剂表现出较好的催化活性和N2选择性以及优异的稳定性和抗H2O/SO2性能,其中Cu-V/TiO2的工作温度窗口扩展到225–375oC. X射线衍射、拉曼光谱和EDX-mapping表征结果证明,钒物种及引入的金属高度分散在TiO2载体表面,并生成了钒酸盐.氢气程序升温还原结果表明,钒酸盐的形成导致钒物种的还原峰向低温区移动,有利于催化剂氧化还原性能的提升. X射线光电子能谱结果表明, Cu-V/TiO2催化剂表面具有更多的活性氧物种(Oα),且具有较强的电子间相互作用,是SCR活性提高的关键原因之一. NH3程序升温脱附和原位红外光谱实验结果表明,金属的引入可以提高酸量和酸强度; Cu-V/TiO2催化剂表面主要为Lewis酸性位,而Fe-V/TiO2催化剂表面主要为Br?nsted酸性位,两者可能导致不同的SCR反应机理,但均可以提高催化剂在高温下的N2选择性.综上所述,过渡金属改性的钒基催化剂中Cu-V/TiO2具有最好的活性和N2选择性以及较强的稳定性和抗H2O/SO2性能,可能得益于其表面更多的活性氧物种和更多更强的酸性位.     

双金属金属有机骨架材料的制备及性能研究进展

金属有机骨架材料(MOFs)具有拓扑结构的多样性和丰富的比表面积,使其在催化和吸附领域具有潜在的应用价值。 双金属MOFs具有两种金属中心,较之单金属MOFs具有更加多元的催化活性位点和吸附位点,因此吸附选择性、选择催化性以及结构稳定性等均得到了提升。 本文就如何制备性能优异的双金属MOFs材料,以及这种材料的结构特点、性能提升和应用前景展开了概述。     

Impact of temperature ramping rate during calcination on characteristics of nano-ZrO2 and its catalytic activity for isosynthesis

This paper studied the effect of temperature ramping rate during calcination on characteristics of nanoscale zirconia and its catalytic performance for isosynthesis. The physical properties, i.e. BET surface area, cumulative pore volume, cumulative pore diameter and the phase composition in zirconia, acid-base properties and surface properties such as Zr³⁺ quantity, were characterized. Increase in the temperature ramping rate of calcination resulted in a higher composition of the tetragonal phase, but it showed insignificant influence on the other physical properties. Considering the catalytic activity, the acid sites did not affect the activity, but the basic sites depended on the fraction of the tetragonal phase in zirconia which was related to the selectivity to isobutene. The intensity of Zr³⁺ on the surface varied with the change in the heating rate of calcination. Both the tetragonal phase composition in zirconia and the quantity of Zr³⁺ were the key factors affecting the selectivity to isobutene in hydrocarbons. Moreover, the maximum value of the product selectivity to isobutene on the ZrO₂ (5.0) catalyst was attained at the highest concentration of Zr³⁺.     

HZSM-5沸石在邻氯甲苯异构化反应中的择形催化作用

 以HZSM-5沸石为催化剂,考察了常压、临氢条件下对邻氯甲苯异构化反应选择性的影响因素; 以4-甲基喹啉、喹啉、乙二胺为毒物分子探针,探讨了沸石催化剂内、外表面酸中心对邻氯甲苯异构化反应的贡献. 实验结果表明, HZSM-5沸石催化剂对产物分子具有形状选择作用,催化剂的内表面酸中心在反应中起主导作用.     

Directing Reaction Pathways through Controlled Reactant Binding at Pd–TiO2 Interfaces

Recent efforts to design selective catalysts for multi-step reactions, such as hydrodeoxygenation (HDO), have emphasized the preparation of active sites at the interface between two materials having different properties. However, achieving precise control over interfacial properties, and thus reaction selectivity, has remained a challenge. Here, we encapsulated Pd nanoparticles (NPs) with TiO₂ films of regulated porosity to gain a new level of control over catalyst performance, resulting in essentially 100 % HDO selectivity for two biomass-derived alcohols. This catalyst also showed exceptional reaction specificity in HDO of furfural and m-cresol. In addition to improving HDO activity by maximizing the interfacial contact between the metal and metal oxide sites, encapsulation by the nanoporous oxide film provided a significant selectivity boost by restricting the accessible conformations of aromatics on the surface.     

Beta沸石上合成对叔丁基苯酚和2,4—二叔丁基苯酚

首次在三相条件下,在Ｂｅｔａ沸石催化剂上研究了苯酚与异丁烯烷基化合成对叔丁基苯酚和２,４－二叔丁基苯酚。通过对Ｈｂｅｔａ沸石高温焙烧和吡啶中毒试验研究了烷基化反应活性和选择性的变化规律;用ＮＨ３－ＴＰＤ和Ｐｙ－ＩＲ测定了试样的酸量和酸种类,结果表明Ｈｂｅｔａ沸石具有很好的烷基化活性,苯酚的转化率可达９２％,经１１２３Ｋ焙烧后苯酚转化率为８８％,对叔丁基苯酚和２,４－二叔丁基苯酚的选择性分别为７０～７５％和１４～２０％,中等强度的Ｂｒｎｓｔｅｄ酸是苯酚与异丁烯烷基化反应的活性中心。粘合剂含量低于３０％对烷基化活性基本无影响     

Oxidative coupling of methane over La-promoted CaO catalysts： Influence of precursors and catalyst preparation method

The oxidative coupling of methane to C2 hydrocarbons has been studied over a series of La-promoted CaO (La/Ca = 0.05) catalysts, prepared using different precursor salts for CaO and La2O3 (viz. acetates, carbonates, nitrates and hydroxides) and catalyst preparation methods (viz. physical mixing of precursors, co-precipitation using ammonium carbonate/sodium carbonate as a precipitating agent), under different reaction conditions (temperature: 700-850℃, CH4/O2 ratio: 4.0 and 8.0, and GHSV: 51360 cm3 g-1 h-1)...     

MCl2-TiO2-SnO2 (M=Mg, Ca, Sr, Ba) 催化剂甲烷氧化偶联反应性能的研究

选用不同的碱土金属氯化物为原料,采用共研磨的方法制备出了具有不同表面碱性的MCl2-TiO2-SnO2(M=Mg,Ca,Sr,Ba)催化剂,并考察了催化剂的甲烷氧化偶联反应性能.通过N2吸脱附(BET)、X-射线衍射(XRD)、X-射线光电子能谱(XPS)和CO2程序升温脱附(CO2-TPD)等技术对催化剂进行了表征.结果表明,随碱土金属元素的不同,催化剂呈现出了强弱不同的碱性吸附位.催化剂表面的碱性对活化甲烷具有促进作用,同时也带来乙烯深度氧化副反应的发生.碱量越大的弱碱性吸附位对甲烷的活化越有利,而强碱性吸附位则能导致催化剂活性降低,甚至是催化剂失活.乙烯的选择性与催化剂表面晶格氧的相对浓度密切相关.表面晶格氧的相对浓度较高的催化剂,其乙烯选择性也较大.     

Presence of lithium ions in MgO lattice: surface characterization by infrared spectroscopy and reactivity towards oxidative conversion of propane

The surface morphology of Li-promoted MgO catalysts prepared using the sol-gel method (sg) and wet impregnation procedure (imp), respectively, has been studied by low-temperature infrared spectroscopy of adsorbed CO molecules. The results show that step sites, as unselective catalytic centers, are the major features existing on the surface of pure MgO, and those are active toward the oxidative conversion of propane. However, the concentration of these sites is drastically reduced by the incorporation of lithium ions in the MgO lattice. In fact, the incorporated Li (+) ions tend to move into the surface region and occupy sites associated with lower coordination number (e.g., step sites). Li/MgO-sg catalysts are characterized by a higher concentration of incorporation of lithium compared to Li/MgO-imp. In the case of oxidative dehydrogenation/cracking of propane, Li/MgO-sg catalysts show higher activity and selectivity to olefins compared to materials prepared using wet impregnation. Catalytic performance differs strongly regarding (i) the amount of olefins formed, and (ii) the ratio of C(3)H(6)/C(2)H(4). It is shown that high density of active sites is essential for further oxidative dehydrogenation of propyl radicals to propylene and suppression of cracking reactions pathway.     

Dual Microenvironment Modulation of Pd Nanoparticles in Covalent Organic Frameworks for Semihydrogenation of Alkynes

The chemical microenvironment modulation of metal nanoparticles (NPs) holds promise for tackling the long-lasting challenge of the trade-off effect between activity and selectivity in catalysis. Herein, ultrafine PdCu₂ NPs incorporated into covalent organic frameworks (COFs) with diverse groups on their pore walls have been fabricated for the semihydrogenation of alkynes. The Cu species, as the primary microenvironment of Pd active sites, greatly improves the selectivity. The functional groups as the secondary microenvironment around PdCu₂ NPs effectively regulate the activity, in which PdCu₂ NPs encapsulated in the COF bearing −CH₃ groups exhibit the highest activity with >99 % conversion and 97 % selectivity. Both experimental and calculation results suggest that the functional group affects the electron-donating ability of the COFs, which successively impacts the charge transfer between COFs and Pd sites, giving rise to a modulated Pd electronic state and excellent catalytic performance.     

Pt-Gd/KL和Pt/GdKL分子筛的重整催化活性中心研究

通过把Ｇｄ引入Ｐｔ／ＫＬ分子筛单功能重整催化剂，研究ＰｔＧｄ／ＫＬ和Ｐｔ／ＧｄＫＬ分子筛的重整反应性能和活性中心以及催化剂的表面酸碱性。结果表明，Ｇｄ的引入方式和引进量对催化重整反应有明显影响。共浸法制备的催化剂ＰｔＧｄ／ＫＬ，其芳构活性比离子交换法制备的催化剂Ｐｔ／ＧｄＫＬ高，Ｇｄ含量为０１％的Ｐｔ０１Ｇｄ／ＫＬ芳构活性最好。弱酸性和弱碱性物质以及硫化物对ＰｔＧｄ／ＫＬ和ＰｔＧｄＫＬ催化重整反应的影响Ｇｄ小于不含Ｇｄ的Ｐｔ／ＫＬ。Ｇｄ对催化重整反应有两方面影响：其一是与金属Ｐｔ相互作用增加活性中心、加强金属功能；其二是增加催化剂的酸性和裂解产物，降低芳构选择性。     

焙烧温度对CuMgAl催化剂催化糠醛气相加氢制糠醇性能的影响

采用分步沉淀过程制得质量比m(CuO)∶m(MgO)∶m(Al_2O_3)为25∶26∶49的CuMgAl类水滑石前驱体,经过不同温度焙烧制得CuMgAl-t催化剂。通过BET、热重、XRD、H_2-TPR和CO_2-TPD对催化剂进行表征,在固定床中考察CuMgAl-t催化剂催化糠醛气相加氢制糠醇的性能。结果表明,焙烧温度影响催化剂活性、稳定性及对产物的选择性,低温焙烧的催化剂经还原后可获得较多活性中心,高温焙烧的催化剂表面具有更多的碱性位,CuMgAl催化剂经450℃焙烧表面存在适宜的活性中心和碱性位。在常压、反应温度180℃、氢醛物质的量比5∶1、糠醛体积空速0.3h~(-1)的条件下,CuMgAl-450催化剂上糠醛的转化率和糠醇的选择性分别达到98.64%和97.66%。     

ZrO2—SiO2负载Cu—Ni催化剂的CO2加氢反应性能

采用表面反应改性法,制备了ZrO2-SiO2（ZrSiO)表面复合物载体,用等体积浸渍法制备了ZrSiO担载的Cu-Ni双金属催化剂,借助BET、TPR、IR和微反等技术,研究了ZrSiO及其负载的Ni、Cu双金属催化剂的表面构造,化学吸附及催化CO2加氢的反应性能,结果表明,ZrSiO表面主要是价联型结构,ZrO2引入SiO2表面,可以有效地促进CuO和NiO的还原,在ZrSiO负载的Cu-Ni催化剂表面的Cu或Ni位,CO2发生化学 吸附形成线、剪式、卧式吸附态,在该催化剂上CO2的加氢反应产物主要是CH3OH3、CH4、CO和H2O生成CH3OH的选择性与催化剂组成及反应条件密切相关,在适当的条件,CH3OH的选择性大于90％。