用不同前驱体制备的Co/SiO2催化剂的结构及其CO2/CH4重整反应性能

 分别采用硝酸钴、醋酸钴、硫酸钴和氯化钴为前驱体制备了Co／SiO2催化剂,用XRD,TPR,SEM和H2－TPD等实验技术考察了钴盐前驱体对催化剂结构和二氧化碳重整甲烷反应性能的影响,重点考察了硝酸钴和醋酸钴的作用．结果表明,由醋酸钴制备的Co／SiO2催化剂有最佳的催化活性和稳定性,它在钴物种的存在状态、金属－载体相互作用、钴金属晶粒度及抗烧结、抗积炭能力等方面,均与由硝酸钴制备的Co／SiO2催化剂存在显著的差别．Co／SiO2催化剂的反应活性和稳定性分别与其金属分散度和抗烧结、抗积炭能力密切相关．     

碳纳米管负载的Co-Mo催化剂的HDS性能研究

应用X射线衍射(XRD)、程序升温还原(TPR)技术对等体积浸渍法制备的Co—Mo／CNT催化剂进行了表征，采用高压微反装置、以二苯并噻吩为模型化合物，对催化剂进行了HDS活性评价，XRD结果表明：260℃条件下处理催化剂，催化剂的表面物种主要是MoO3，表面物种高度分散；500℃焙烧处理的催化剂的表面物种主要是MoO2，同时在Co—Mo／CNT催化体系中出现了CoMoO3和Co2Mo3O03物种的强衍射峰，高温焙烧时催化剂活性组分在碳纳米管的表面容易聚集形成MoO2等晶体，TPR结果表明：在Co-Mo／CNT催化剂中，表面物种的还原温度低于Co—Mo／γ—Al2O3中物种的还原温度，活性评价表明：催化剂的TPR特性和加氢脱硫活性有很好的对应关系，Co—Mo／CNT具有很高的加氢脱硫选择性，并且活性明显高于Co—Mo／γ—Al2O3催化剂。     

Co助剂对稀燃NOx阱Pt/Ba-Al-O结构和性能的影响

 采用共沉淀－浸渍法制备了Pt／Co－Ba－Al－O催化剂，用X射线衍射、X射线吸收近边结构和扩展X射线吸收精细结构等手段表征了催化剂的微观结构，并在连续流动微型反应器上测定了催化剂对NOx的储存性能．载体经过800℃焙烧后，Co物种主要以四面体配位的铝酸钴相存在．在富氧条件下，高分散的小颗粒铝酸钴相促进了NO向NO2的转化，大大改善了催化剂对NOx的储存性能．铂物种则以小的金属原子簇形式存在，分散度很高．钴助剂的添加改善了氧化铝相的分散度，抑制了金属铂原子簇与载体的相互作用，使铂在催化剂表面分散得更均匀，从而有利于NOx的储存．     

磷酸盐的添加对甲烷氧化偶联反应镧基催化剂的影响

采用柠檬酸法制备了不同含量磷酸盐修饰的镧基催化剂,考察了磷酸盐的添加对镧基催化剂甲烷氧化偶联反应(OCM)活性的影响,并借助X射线衍射(XRD)、O_2-程序升温脱附(O_2-TPD)及X射线光电子能谱(XPS)等手段对催化剂的理化性质进行了表征.结果表明,随着磷酸盐加入量的增大,催化剂样品的粒径逐渐减少,催化剂的物相由La_2O_3向La_3PO_7和LaPO_4逐步转变.当催化剂的物相由La_2O_3和适量的La_3PO_7构成时,催化剂具有较多的表面缺陷位点数和较大的亲电氧物种/晶格氧物种比值,并呈现出良好的OCM反应性能.     

改性介孔 Al2O3 负载锰基催化剂的结构及其催化氧化与抗硫性能

 采用分步浸渍法分别制备了 LaCeZr 和 YCeZr 组合助剂改性的介孔 Al2O3 负载的 Mn 基系列氧化物催化剂, 用 X 射线衍射、氮气吸附-脱附、X 射线吸收精细结构、X 射线光电子能谱和程序升温还原等方法对催化剂进行了表征, 探讨了催化剂中 Mn 物种的存在形式及其还原性能, 并与样品催化 CO 和 C3H8 的氧化活性相关联. 结果表明, 样品中 Mn 物种主要以 Mn3O4 形式存在, 该物种在不同样品中与载体的作用强弱不同, 从而表现出不同的还原性能和催化活性. 助剂改性有效抑制了 Mn-Al 之间的相互作用, 提高了 Mn–O 键的活动度, 从而提高了催化剂的氧化活性. 相比于 YCeZr 助剂, LaCeZr 助剂改性更大程度上提高了 Mn 物种的还原性, 因而大大提高了催化剂的氧化性能. 650 oC 焙烧的 LaCeZr 组合助剂改性的介孔 Al2O3 负载的 Mn 氧化物催化剂, 在 0.035% SO2 存在的条件下对 CO 的氧化活性并未下降, 对 C3H8 的氧化活性下降幅度也较小, 表现出优越的抗硫性能和氧化性能.     

还原-氧化-还原过程对Co-ZrO_2共沉淀催化剂结构及其费托合成反应性能的影响

采用程序升温还原、氮吸附、X射线衍射、Raman、XPS和H2-TPD等方法研究了还原(400℃,氢还原)-氧化(室温,暴露空气中氧化)-还原(250℃或400℃,氢还原)预处理过程对Co-ZrO2共沉淀催化剂结构的影响,考察了催化剂在不同反应器中的费托反应性能。结果表明,催化剂还原氧化前后钴物种均以Co3O4形式存在,颗粒直径无明显变化;还原氧化处理后催化剂表面钴物种含量有所下降,但H2-TPD结果显示催化剂经还原-氧化-还原后氢吸附量增加。另外,还原氧化过程能够降低催化剂表层钴物种的还原温度。反应结果表明,催化剂经还原氧化还原处理后活性明显增加,甲烷选择性降低。     

氧化钡促进的Co/SiO2催化剂的还原性能和分解甲烷活性

 利用等体积浸渍法制备了氧化硅负载钴催化剂．通过程序升温还原、氢化学吸附、氧滴定和催化活性评价等手段研究了氧化钡对Co／SiO2的还原性能、钴分散度和颗粒度、分解甲烷活性及其稳定性等的影响．研究结果表明，氧化钡明显地影响Co／SiO2的还原性能；添加2％氧化钡提高了Co／SiO2在中温（450℃）条件下的还原度；氧化钡的还原对Co／SiO2还原的诱导、氧化钡与氧化硅及与氧化钴之间的相互作用是导致Co／SiO2还原性能变化的原因．氧化钡提高了Co／SiO2的初活性和钴的分散度，降低了钴的颗粒度；添加0．5％～1．5％氧化钡有利于提高Co／SiO2的稳定性．钴的分散度和颗粒度影响Co／SiO2的活性和稳定性；氧化钡的强供电效应也是提高Co／SiO2活性和稳定性的重要因素．甲烷分解生成的碳物种覆盖了钴活性中心，导致Co／SiO2初活性下降；但大部分碳物种并不沉积在钴活性中心上，可能形成了碳纤维生长在载体和钴活性中心之间．     

Co/HMS和Co/SiO2催化剂的表征及在费-托合成反应中的催化性能

 HMS介孔分子筛经水热处理得到无定形SiO2,分别以无定形SiO2和HMS为载体,用浸渍法制得了15%Co/SiO2和15%Co/HMS催化剂. 研究表明: 氧化态Co/SiO2和Co/HMS催化剂中的钴物种以Co3O4形式存在,且Co3O4晶粒粒径均较相应催化剂的孔径大,故有部分钴物种存在于催化剂外表面; 氧化态Co/HMS催化剂中的钴物种堵塞孔道较为严重; Co/HMS催化剂中存在较强的金属-载体相互作用,因此Co/HMS催化剂较Co/SiO2催化剂难还原; Co/HMS催化剂还原后具有较高的钴分散度,使其具有优异的费-托合成反应性能.     

中空介孔碳化钨微球载钯催化剂对甲酸电催化性能

采用喷雾干燥法和还原炭化处理制备具有中空介孔结构的碳化钨钴复合粉(HTCCS),其中,钴的质量含量为6%。在碳化钨钴复合粉表面的钴和氯化钯发生置换反应,得到纳米Pd/WC复合催化剂。采用X射线粉末衍射(XRD)、扫描电镜(SEM)和透射电镜(TEM)对样品的形貌和晶型结构进行了表征。结果表明, 5.0-6.0nm钯纳米粒子取代钴均匀分布在碳化钨微球表面。采用循环伏安和计时电流法研究了在酸性溶液中Pd/WC催化剂对甲酸的电催化氧化性能,结果表明,Pd/WC催化剂比Pd/C催化剂对甲酸呈现出更高的电催化氧化活性和稳定性。     

钯负载介孔氧化锆基复合催化材料的合成与表征

利用表面活性剂辅助模板及适当后处理工艺实现了少量贵金属氧化钯及稀土氧化铈在有序介孔氧化锆孔道中或孔道表面的均匀分散/负载. 借助XRD, TEM, EDS等分析手段进行样品结构表征; 同时针对不同催化体系探讨了丙烯催化氧化以及Heck反应的催化性能. 研究结果表明, 贵金属钯/稀土氧化铈负载的有序介孔氧化锆体系对丙烯氧化具有良好催化活性, 钯直接负载介孔氧化锆的体系具有优异的Heck反应催化选择性及较少的催化剂使用量.     

X-ray absorption spectroscopy of Mn/Co/TiO2 Fischer-Tropsch catalysts: relationships between preparation method, molecular structure, and catalyst performance

The effects of the addition of manganese to a series of TiO(2)-supported cobalt Fischer-Tropsch (FT) catalysts prepared by different methods were studied by a combination of X-ray diffraction (XRD), temperature-programmed reduction (TPR), transmission electron microscopy (TEM), and in situ X-ray absorption fine structure (XAFS) spectroscopy at the Co and Mn K-edges. After calcination, the catalysts were generally composed of large Co(3)O(4) clusters in the range 15-35 nm and a MnO(2)-type phase, which existed either dispersed on the TiO(2) surface or covering the Co(3)O(4) particles. Manganese was also found to coexist with the Co(3)O(4) in the form of Co(3-x)Mn(x)O(4) solutions, as revealed by XRD and XAFS. Characterization of the catalysts after H(2) reduction at 350 degrees C by XAFS and TEM showed mostly the formation of very small Co(0) particles (around 2-6 nm), indicating that the cobalt phase tends to redisperse during the reduction process from Co(3)O(4) to Co(0). The presence of manganese was found to hamper the cobalt reducibility, with this effect being more severe when Co(3-x)Mn(x)O(4) solutions were initially present in the catalyst precursors. Moreover, the presence of manganese generally led to the formation of larger cobalt agglomerates ( approximately 8-15 nm) upon reduction, probably as a consequence of the decrease in cobalt reducibility. The XAFS results revealed that all reduced catalysts contained manganese entirely in a Mn(2+) state, and two well-distinguished compounds could be identified: (1) a highly dispersed Ti(2)MnO(4)-type phase located at the TiO(2) surface and (2) a less dispersed MnO phase being in the proximity of the cobalt particles. Furthermore, the MnO was also found to exist partially mixed with a CoO phase in the form of rock-salt Mn(1-x)Co(x)O-type solid solutions. The existence of the later solutions was further confirmed by scanning transmission electron microscopy with electron energy loss spectroscopy (STEM-EELS) for a Mn-rich sample. Finally, the cobalt active site composition in the catalysts after reduction at 300 and 350 degrees C was linked to the catalytic performances obtained under reaction conditions of 220 degrees C, 1 bar, and H(2)/CO = 2. The catalysts with larger Co(0) particles ( approximately >5 nm) and lower Co reduction extents displayed a higher intrinsic hydrogenation activity and a longer catalyst lifetime. Interestingly, the MnO and Mn(1-x)Co(x)O species effectively promoted these larger Co(0) particles by increasing the C(5+) selectivity and decreasing the CH(4) production, while they did not significantly influence the selectivity of the catalysts containing very small Co(0) particles.     

Influence of the pore structure of MCM-41 and SBA-15 silica fibers on atomic layer chemical vapor deposition of cobalt carbonyl

Mesoporous high surface area MCM-41 and SBA-15 type silica materials with fibrous morphology were synthesized and used as support materials for the ALCVD (atomic layer chemical vapor deposition) preparation of Co/MCM-41 and Co/SBA-15 catalysts. Co/MCM-41 and Co/SBA-15 catalysts were prepared by deposition of Co2(CO)8 from the gas phase onto the surfaces of preheated support materials in a fluidized bed reactor. For both silica materials, two different kinds of preparation methods, direct deposition and a pulse deposition method, were used. Pure silica supports as well as supported cobalt catalysts were characterized by various spectroscopic (IR) and analytical (X-ray diffraction, Brunauer-Emmett-Teller, elemental analysis) methods. MCM-41 and SBA-15 fibers showed considerable ability to adsorb Co2(CO)8 from the gas phase. For MCM-41 and SBA-15 silicas, cobalt loadings of 13.7 and 12.1 wt % were obtained using the direct deposition method. The cobalt loadings increased to 23.0 and 20.7 wt % for MCM-41 and SBA-15 silicas, respectively, when the pulse deposition method was used. The reduction behavior of silica-supported cobalt catalysts was found to depend on the catalyst preparation method and on the mesoporous structure of the support material. Almost identical reduction properties of SBA-15-supported catalysts prepared by different deposition methods are explained by the structural properties of the mesoporous support and, in particular, by the chemical structure of the inner surfaces and walls of the mesopores. Pulse O2/H2 chemisorption experiments showed catalytically promising redox properties and surface stability of the prepared MCM-41- and SBA-15-supported cobalt catalysts.     

助剂对Co／HMS催化剂结构和F-T合成性能的影响

详细研究了钍、锆、锗及铈助剂对钴质量分数为15％的Co／HMS催化剂结构、 F-T合成CO转化率、CO2选择性及烃分布的影响,结果表明：钍能适当提高F-T合成 活性,且低温下具有较强的链增长能力;锆、锗、铈降低了催化剂CO转化率,催化 剂加氢能力变强,导致低碳烃增加较快,汽柴油馏分段减低,相应的链增长能力降 低,并以锰和铈较为明显;XRD,TPR及TG表征表明：锆和铈可提高催化剂Co还原度 ,但F-T合成反应时金属Co易披氧化,反应中金属Co量明显减少,CO转化率降低, 并以铈最为显著;Th助催化剂Co还原度稍有减低,Co分散度高于Co／HMS,且反应 中金属Co较为稳定,Co转化率得以提高;添加Mn助剂后,催化剂难以还原,反应中 活性相金属Co量较小,CO转化率较低．     

Hydrogen production through glycerol steam reforming using Co catalysts supported on SBA-15 doped with Zr,Ce and La

The steam reforming of glycerol has been studied at 500 and 600 oC using Co/SBA-15 and Co/M/SBA-15(M: Zr, Ce, or La) promoted catalysts. The prepared materials were characterized by inductively coupled plasma atomic emission spectroscopy(ICP-AES), X-ray powder diffraction(XRD), hydrogen temperatureprogramed reduction(H_2-TPR), ammonia temperature-programed desorption(NH_3-TPD), nitrogen physisorption analysis(N_2-BET), transmission electron microscopy(TEM) and thermogravimetric analysis(TGA). The incorporation of promoters like Zr, Ce and La on SBA-15 support and successive Co impregnation leaded to smaller cobalt crystallites improving metaldispersion. Besides, stronger metal-support interactions between Co species and M/SBA-15 supports were observed. Thanks to the incorporation of Zr, La and mainly Ce, promoted catalysts present higher glycerol conversion than Co/SBA-15 along 5 h of time on stream. Besides, at 600 oC, Co/M/SBA-15(M: Zr, Ce, or La) catalysts produce higher hydrogen amounts than Co/SBA-15.     

Fischer-Tropsch synthesis on anchored Co/Nb2O5/Al2O3 catalysts: the nature of the surface and the effect on chain growth

A series of Co/x%Nb2O5/Al2O3 catalysts were prepared by anchoring niobia on an Al2O3 support at different niobia concentrations. Characterization of the structure and nature of surface active sites was attempted in order to correlate the CO hydrogenation activity of these systems with those of the Co/Al2O3 and Co/Nb2O5 catalysts. The effect of the reduction temperature on the CO hydrogenation activity and selectivity was studied, showing that interaction of cobalt and niobia surface species favored the selectivity for hydrocarbon chain growth. However, this effect is less pronounced on the niobia-promoted Co/Al2O3 compared to Co/Nb2O5 catalysts. X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (DRS) results on Co/x%Nb2O5/Al2O3 showed prevailing amounts of Co2+ and Co3+ after calcination and reduction at 573 K, while, after reduction at 773 K, besides metallic cobalt, the Co2+ species still remains in contact with alumina, even for higher niobia loading. It seems that during this process formation and destruction of new interfaces involving Co0-NbOx sites takes place. Results suggest that Co0, Co0-Co2+, and Co0-NbOx are the active sites at the surface. The relative abundance of Co2+ species affects greatly the performance of the catalysts. DRIFTS and selectivity results suggest that these sites might be responsible for the reaction chain growth and therefore for the drastic change in the selectivity of CH4 and C5+ hydrocarbons mainly on the Co/Nb2O5 catalyst. DRIFTS results on Co/Nb2O5/Al2O3 showed the formation of -C=C- and -CH3- besides CHxO species. With increasing reduction temperature, the -C=C- species disappear while -CH3- fragments increased markedly, suggesting the formation of increasing amounts of hydrocarbons with higher chain length.     

钍含量对Co/HMS催化剂结构和费托合成的影响

详细研究了钍含量对15% Co/HMS催化剂结构、费托合成CO转化率和烃分布的影响, 结果表明: 钍助剂的添加降低了催化剂的钴还原度, 并可使催化剂钴晶粒减小, 且存在钍物种对钴物种的覆盖; 钴晶粒的减小、较高钍含量时催化剂里钍物种对钴物种的覆盖和钴物种还原性能的降低, 使催化剂存在最优的钍含量, 此时催化剂表面暴露的金属钴原子最多, 较好地解释了钍含量达到1.5 wt%时, 催化剂CO转化率最高的实验现象. 烃分布研究表明: 反应温度较低时钍助剂将促进产物链的增长和高碳烃选择性的增加, 但反应温度较高时难以促进产物链的增长.     

载钴分子筛的XPS研究

借助XPS技术研究了浸渍法得到的3种载钴分子筛Co/HY、Co/ZSM-5和Co/HA的表面状态和组成.结果表明,这些分子筛的表面深处都有难被还原的类CoAl₂O₄物种存在,而易被还原的钴羟基化合物覆盖于分子筛的表面.空气焙烧加快了类CoAl₂O₄物种的生成.用H₂还原实验考察了3种载钴分子筛上钴物种与分子筛之间相互作用的程度.     

有机改性二氧化硅及其负载钴催化剂的费托合成反应性能

利用硅烷化作用分别制得了甲基、二甲基和三甲基改性的SiO2载体,采用等体积浸渍法制备了质量分数为5%的一系列负载型钴催化剂.考察了有机改性对催化剂费托合成催化性能的影响.结果表明,SiO2经有机基团改性后,表面硅羟基浓度减小,削弱了钴硅之间的相互作用,促进了催化剂的还原,提高了催化剂的活性,降低了甲烷选择性.由于空间位阻不同,不同有机基团改性的SiO2的表面硅羟基浓度不同,催化剂活性随着表面硅羟基浓度的减小而提高.     

Co3O4/CeO2的氧化还原性能及反应条件对其CO氧化活性的影响

采用沉淀氧化法制备了Co₃O₄/CeO₂催化剂。运用XRD、BET和TPR表征手段,考察了不同钴铈比及焙烧温度对钴铈复合氧化物物理及化学性能的影响,并分别在干、湿条件下进行了一氧化碳氧化反应研究。结果表明,与纯的Co₃O₄相比,在不同比例的Co₃O₄/CeO₂均经723 K焙烧的各种催化剂中,钴铈原子比为9∶1的复合氧化物粒径较小,比表面积较大,说明适当比例铈的添加能使Co₃O₄具有较小的粒径。此氧化物经538 K温度焙烧制得的钴铈比为9∶1的复合氧化物中Co₃O₄平均粒径为7.2 nm, BET比表面积为167.6 m²/g。经TPR考察发现其具有最优的氧化还原性能。     

超声浸渍对费托合成Co/Zr/SiO2催化剂性能的影响

采用超声浸渍法制备了费托合成Co/Zr/SiO2催化剂,考察了超声波功率对催化剂费托反应性能的影响,并运用N2物理吸附、X射线衍射、H2程序升温脱附、H2程序升温还原和透射电子显微镜对催化剂进行了表征,结果表明,超声波处理可以增大催化剂的比表面积,减小金属Co的粒径,并使其较为均匀地分散于载体表面,其中以高功率超声波作...