载体焙烧温度对Ni/SiO2-Al2O3催化剂稳定性的影响

为了获得高水热稳定的负载Ni催化剂,延长催化剂在含水液相体系中的使用寿命,以不同温度焙烧的Si O2-Al2O3为载体,采用浸渍法制备Ni/Si O2-Al2O3催化剂,通过吡啶-原位傅立叶变换红外光谱、X射线衍射、NH3-程序升温脱附和H2-程序升温还原等方法进行表征,以水相1,4-丁炔二醇加氢为探针反应,研究载体焙烧温度对Ni/Si O2-Al2O3催化剂催化加氢性能及含水体系中稳定性的影响。结果表明,在(400~800)℃,随着载体焙烧温度升高,活性组分Ni存在状态及催化剂加氢活性变化较小,但催化剂的水热稳定性下降,造成这一现象的原因是随着载体焙烧温度升高,载体表面Si O2聚集,暴露的Al3+增加,载体水合程度增大。载体焙烧温度400℃时,Ni/Si O2-Al2O3催化剂表现出最佳的水热稳定性。     

Ni-Mn/Al_2O_3催化剂在浆态床中CO甲烷化催化性能

采用共浸渍法制备了Ni-Mn/Al2O3催化剂,考察了助剂Mn的含量对催化剂结构及浆态床CO甲烷化性能的影响。采用XRD、H2-TPR、BET、TEM、H2-化学吸附等表征对催化剂进行了测试分析,结果表明,Mn助剂的引入能够促进Ni物种在载体表面的分散,减弱Ni物种与载体的相互作用,降低催化剂的还原温度,提高催化剂的比表面积,减小活性金属Ni的晶粒尺寸。随着Mn含量的增加,Ni-Mn/Al2O3催化剂的甲烷化性能先升后降,其中以Mn含量为4%(质量分数)时的催化甲烷化性能最佳,添加过量的Mn导致活性组分Ni被部分覆盖,催化甲烷化性能下降。通过对16Ni4Mn/Al2O3催化剂样品的浆态床反应温度及反应压力的研究发现,当反应温度为280℃、反应压力为1.5 MPa时,催化剂样品16Ni4Mn/Al2O3的CO转化率及CH4选择性分别达到96.2%和88.8%。     

焙烧温度对共沉淀法制备高温甲烷化催化剂性能的影响

采用共沉淀法制备以Ni为活性组分的Ni-Mg-Al-O高温甲烷化催化剂,考察焙烧温度对催化剂性能的影响。采用N2低温吸附、XRD、H_2-TPR和H_2-化学吸附对催化剂进行表征,并将催化剂用于合成气甲烷化反应。结果表明,焙烧温度高于700℃时,催化剂预还原后织构性能参数变化幅度小。随着焙烧温度的升高,Ni晶粒增大,活性组分与载体之间相互作用增强。焙烧温度700℃时,活性组分分散度最高,催化剂具有优异的低温活性和高温稳定性。     

焙烧及还原温度对Ni-Mg甲烷化催化剂的影响

采用共沉淀-水热复合法制备Ni-Mg/Al2O3催化剂,考察焙烧和还原温度对其结构和甲烷化催化性能的影响,通过XRD,H2-TPR,TEM等表征,发现随焙烧温度升高,催化剂中NiAl2O4物相呈增多趋势,至900℃时,催化剂中镍物种完全以NiAl2O4形式存在,催化剂表面积从500℃焙烧的130m2/g降至900℃焙烧的34m2/g.针对600℃焙烧的催化剂,反应活性随还原温度升高呈现先增加后降低的趋势,其最佳还原温度为650℃,这主要是受Ni物种还原度、还原后Ni晶粒尺寸等多重因素影响.通过关联甲烷化性能与催化剂结构发现,NiO与载体之间相互作用适中,还原后表面能够形成较小的镍晶粒,催化剂具有较好的甲烷化活性和稳定性.     

丙三醇水蒸气重整制氢M/Al2O3催化剂

以Al2O3为载体,采用浸渍法制备了Cu、Co、Ni、Pt/Al2O3四种单一组分催化剂(M/Al2O3)。研究了M/Al2O3催化剂对丙三醇水蒸气重整制氢反应的适用性及反应行为;考察了制备条件及还原条件,通过活性、稳定性及抗积炭性进行了催化剂的活性评价,并对催化剂进行了TPR、XRD表征。研究发现M/Al2O3催化剂用于丙三醇水蒸气重整制氢均表现出一定活性;其中Cu/Al2O3催化剂具有一定的抗积炭性;Pt/Al2O3催化剂表现出较好的抗积炭性、高温活性,但稳定性较差;Co/Al2O3催化剂表现出较好的稳定性;Ni/Al2O3催化剂表现出较好的低温活性。     

WP/γ-Al2O3催化剂的制备及加氢脱氮性能

采用程序升温、高纯氢气还原无定形磷钨酸盐的方法制备了活性组分为磷化钨的WP／γ-A1203催化剂，考察了催化剂对吡啶加氢脱氮(HDN)反应的催化活性。结果表明，先混合后还原方法制备的WP／γ～Al2O3催化剂WP2更有利于活性组分在载体表面的分散，且稳定性比较好。该催化剂具有较好的加氢脱氮性能，340℃时吡啶加氢脱氮率为95．4％。噻吩对催化剂WP2的HDN活性有较大影响。     

Ni/SiO2催化剂的制备条件对催化间二硝基苯加氢反应性能的影响

将Ni/SiO₂催化剂应用于间二硝基苯加氢反应中,考察了该催化剂制备过程中焙烧温度和还原温度对其催化性能的影响,并通过BET、XRD、TEM、TPR等方法对催化剂进行了表征.结果表明,在实验研究范围内,随着焙烧温度的提高,Ni/SiO₂催化剂比表面积降低,NiO与载体SiO₂之间的相互作用逐渐增强,催化剂的还原温度明显提高,活性组分Ni的晶粒度增大,焙烧温度为773 K时催化剂具有最佳的催化反应性能,此时活性组分Ni以高分散状态存在.催化剂的还原温度对Ni/SiO₂催化剂的结构和催化性能影响显著,当还原温度较低时,活性组分还原不完全,催化剂活性较低;而还原温度太高会使活性组分烧结,导致催化剂活性明显降低;还原温度为723 K时催化剂表现出最佳的活性和选择性.     

共浸法制备高分散Ni/CCA催化剂及顺酐加氢性能

为获得高分散的负载型Ni基催化剂,提高催化剂加氢性能,采用共浸法制备了以炭改性Al2O3为载体(CCA)的Ni基催化剂,采用BET、XRD和H2-TPD对催化剂进行表征,以顺酐液相加氢为探针反应研究催化剂加氢性能。结果表明,通过共浸法同时引入活性组分Ni与炭助剂,经一次焙烧后即可获得活性组分Ni高度分散的负载Ni/CCA催化剂,在顺酐加氢反应中表现出高的γ-丁内酯选择性。     

MgO对Ni/Al_2O_3催化剂CO甲烷化性能的影响

采用浸渍法制备了添加MgO助剂的Ni/Al2O3催化剂,并用固定床微反装置考察了催化剂在CO甲烷化反应中的催化性能。利用N2物理吸附、X射线衍射、H2程序升温还原、H2脉冲化学吸附和热重等手段对催化剂的结构进行了表征。通过分析样品的还原特性发现,活性组分Ni与Al2O3间的强相互作用会导致催化剂上Ni物种较难还原。MgO的引入可以明显削弱Ni与载体间的强相互作用,提高催化剂的还原度,增加催化剂活性位的数目,同时MgO的存在还能促进Ni颗粒的分散,提高催化剂的抗积碳性能,进而提高催化剂的甲烷化活性。     

焙烧条件对Fe-Mo/ZSM-5催化剂上NO选择性催化还原性能的影响

采用共浸渍法制备了m(Fe):m(Mo)=1的Fe-Mo/ZSM-5催化剂,并对其在不同焙烧条件所得样品上NO选择性催化还原反应活性进行了测试。结果表明,焙烧条件对Fe-Mo/ZSM-5催化性能影响明显,600℃焙烧6 h的样品在低温范围具有较好的催化性能,随着焙烧时间或焙烧温度的增加,其NOx转化率依次向高温方向移动,在800℃焙烧后的样品催化活性明显下降。采用XRD和BET对Fe-Mo/ZSM-5样品的体相结构和表面性能进行了研究。结果表明,不同焙烧条件下Fe-Mo/ZSM-5催化剂的晶胞参数和比表面积产生了差别,特别是焙烧温度达到800℃时,其比表面积显著减小,这可能是导致Fe-Mo/ZSM-5催化性能突然下降的主要原因。焙烧过程中残留在的表面含氮物种对Fe-Mo/ZSM-5催化剂上NO选择性催化还原反应活性影响较大。     

焙烧温度对Al2O3载体的性质及其负载的煤制合成气制代用天然气镍基催化剂性能的影响

以拟薄水铝石为前驱体,经不同温度焙烧制得Al₂O₃载体,等体积浸渍法制备Ni/Al₂O₃催化剂,采用X射线衍射、N₂-物理吸附、扫描电镜、程序升温还原等对载体及催化剂进行表征,考察载体焙烧温度对Al₂O₃载体性质及其负载的镍基催化剂催化性能的影响。结果表明,随着焙烧温度的升高,Al₂O₃载体的比表面积减小,平均孔径增大,结晶度升高,晶粒度增大,晶型逐步转变为γ-Al₂O₃［(500~800) ℃］、δ-Al₂O₃［ (900~1 100) ℃］和α-Al₂O₃［(1 250) ℃］。合成气制甲烷催化剂活性变化趋势为:Ni/γ-Al₂O₃>Ni/δ-Al₂O₃>Ni/α-Al₂O₃,其中,800 ℃焙烧的γ-Al₂O₃负载的Ni基催化剂因稳定的晶型结构以及与NiO之间适当的相互作用而表现出最佳的催化活性及稳定性。     

NiO/Al_2O_3基催化剂的TPR特性研究

NiO/Al_2O_3基催化剂用于替代贵金属催化剂,被广泛应用于石油和石化领域生产过程的加氢、脱硫和脱氮。采用TPR方法,研究不同Ni含量NiO/Al_2O_3及不同载体的催化剂还原特性。结果表明,NiO/Al_2O_3催化剂在10%H_2-Ar气氛下,还原温度范围较宽,为(300~800)℃,其中,(500~600)℃还原速率最大;随着NiO含量的增加,起始还原温度降低,还原耗氢量按比例增加;以MgO为载体的NiO催化剂还原呈现双峰特征,以SiO2和TiO2为载体的NiO催化剂的初始还原温度比NiO/Al_2O_3催化剂降低(100~200)℃。     

Effects of alumina incorporation in coprecipitated NiO–Al2O3 catalysts

The effect of Al₂O₃ levels on the properties of NiO in coprecipitated NiO–Al₂O₃ samples were investigated, using samples with up to 60.7 wt.% Al₂O₃ that had been calcined in the range 300–700°C. Characterization techniques included BET surface area of fresh and reduced catalysts, X-ray diffraction analysis of structure and crystallite size, magnetic susceptibility measurements, oxidizing power, and reducibility in H₂. Only NiO was detected in samples with up to 4.1 wt.% Al₂O₃ for all sample calcination temperatures. Surface areas were similar for all fresh samples but decreased rapidly after calcination at high temperatures. The surface area loss was less for the higher Al₂O₃-containing samples. Nickel oxide crystallite sizes increased at higher calcination temperatures, but remained approximately the same for each Al₂O₃ level.

The NiO was nonstoichiometric (NiO_1+x), with x decreasing at higher calcination temperatures and increasing with small amounts of added Al₂O₃ through a maximum at about 3 wt.% Al₂O₃. However, this did not correlate well with microstrain in the NiO crystallites nor with reducibility, which decreased with Al₂O₃ addition. At higher levels of Al₂O₃ (13.6 wt.% and above), surface areas increased with higher Al₂O₃ loadings, but NiO crystallite sizes remained approximately the same, independent of both Al₂O₃ content and calcination temperature. X-ray diffraction patterns were very diffuse, and it was not possible to rule out the presence of pseudo-spinel combinations of NiO and Al₂O₃. Reducibility was more difficult than with low Al₂O₃ levels, and nonstoichiometry was low and independent of Al₂O₃ content.

Reducibilities of all samples calcined at 300°C correlated well with the final BET surface area of the reduced samples, indicating that more dispersed NiO crystallites are more difficult to reduce, a conclusion that supports a model for reduction proposed previously.     

Mg、La助剂在镍基甲烷化催化剂中的协同作用

采用浸渍法制备Ni/Al2O3、La-Ni/Al2O3、Mg-Ni/Al2O3和Mg-La-Ni/Al2O3催化剂,讨论Mg和Ni两种助剂的协同作用,通过N2低温吸附、H2-TPR、XRD和SEM等表征方法对4种催化剂进行分析。结果表明,La助剂有利于削弱NiO与载体间的相互作用,降低催化剂中γ-NiO含量,但形成活性较低的α-NiO。Mg能够抑制催化剂中NiAl2O4尖晶石的形成,但Mg的添加会导致催化剂孔道堵塞,使NiO在催化剂表面团聚。Mg能够与NiO形成固溶体,在Mg的协同作用下,可抑制La-Ni/Al2O3催化剂中α-NiO的生成。La能够促进NiO分散,克服Mg-Ni/Al2O3催化剂孔道堵塞的缺陷。活性评价实验结果表明,添加不同助剂的催化剂在不同温度区域的活性不同,La-Ni/Al2O3催化剂低温活性较好,Mg-Ni/Al2O3催化剂高温活性较好,而在Mg和La两种助剂的协同作用下,Mg-La-Ni/Al2O3催化剂活性最高。     

Effects of small MoO3 additions on the properties of nickel catalysts for the steam reforming of hydrocarbons III. Reduction of Ni-Mo/Al2O3 catalysts

Ni/Al₂O₃ catalyst modified by small amounts of Mo show unusual properties in the steam reforming of hydrocarbons. There are no data about the effect of small amounts of molybdenum on reduction of the Ni-Mo supported catalysts. The properties of these very complex systems depend on the conditions of successive preparation stages (calcination, reduction) or the process conditions.

A series of Ni/Al₂O₃ catalysts modified by Mo were prepared in order to investigate the influence of promoter amounts and preparation sequence on their properties. Temperature programmed reduction (TPR) has been employed to study the reducibility of Ni-Mo/Al₂O₃ catalysts. Catalysts were further characterized by BET area, H₂ chemisorption and X-ray diffraction measurements.

The TPR curves of Ni-Mo/Al₂O₃ catalysts are very complex. Mo addition leads to the decrease of catalysts reducibility. However, complete reduction of NiO and MoO₃ can be achieved at 800 °C. The reduction course depends on the sequence of nickel and molybdenum addition into the support. Precise measurements of Ni peaks positions in the XRD pattern of Ni/Al₂O₃ and Ni-Mo/Al₂O₃ samples show the possibility of Ni-Mo solid solution formation.     

Nano-sized Ni particles on hollow alumina ball: Catalysts for hydrogen production

Nickel nanoparticulate catalysts supported on hollow Al₂O₃ ball (<3 μm in diameter) have been prepared by spraying a mixed solution of nickel and aluminum nitrates in atmospheric pressure plasma. A wall of each ball (ca. several 10 nm in thickness) consisted of uniformly dispersed oxide bricks of ca. 30 nm sizes, which were identified as densely packed NiO, NiAl₂O₄ and Al₂O₃ crystallites. Highly dispersed Ni particles (<10 nm in diameter) have been formed on the ball surfaces by H₂ reduction of NiO crystallites, surrounded by the nano-sized oxide bricks of NiAl₂O₄ and Al₂O₃. A catalytic activity of the Ni catalyst thus prepared for methane steam reforming reaction was tested from a viewpoint of the application to fuel processors for polymer electrolyte fuel cells (PEFCs). The results showed the catalyst possessed superior performances for the reaction in the activity and the resistance to coke deposition even under a low H₂O/CH₄ molar ratio (S/C < 2) condition.     

Selective catalytic hydrogenation of naphthalene to tetralin over a NiMo/Al2O3 catalyst

The selective catalytic hydrogenation of naphthalene to high-value tetralin was systematically investigated. A series of Al₂O₃ catalysts containing different active metals (Co, Mo, Ni, W) were prepared by incipient wetness impregnation. The effects of different active metals forms (oxidation, reduction, sulfuration) and reaction conditions on naphthalene hydrogenation were investigated and the catalysts were characterized by XRD, XPS, BET, NH₃- TPD and SEM. Especially, Ni-Mo/Al₂O₃ was first used in this reactive system. The results show that the oxidative 4%NiO-20%MoO₃/Al₂O₃ is the best catalyst for the preparation of tetralin. The conversion of naphthalene and the selectivity of tetralin can reach 95.62% and 99.75% respectively at 200 ℃, 8 h and 6 MPa. Compared with reduced and sulfureted 4%NiO-20%MoO₃/Al₂O₃ catalysts, oxidative 4%NiO-20%MoO₃/Al₂O₃ has a well dispersed and uniform monolayer of the active metals, larger pore volume and size, and larger total acidity. NiO-MoO₃/Al₂O₃ has a synergistic effect between NiO activity and MoO₃ selectivity.     

过渡金属Ni对Pd/Al_2O_3催化剂甲烷催化燃烧性能的影响

考察过渡金属Ni对Pd/Al_2O_3催化剂甲烷催化燃烧活性的影响以及过渡金属负载量及循环条件对甲烷降解性能的影响,采用扫描电镜、N_2吸附-脱附以及H_2程序升温还原技术对催化剂进行表征。结果表明,过渡金属Ni的添加对催化剂在(375~475)℃下的甲烷催化燃烧活性产生影响。催化剂经多次重复使用后,催化燃烧活性提高。分析原因为经过渡金属Ni改性后,可与载体形成NiAl_2O_4尖晶石,促进活性组分形成较小晶粒,并改善活性组分分散度,提高催化剂催化活性。     

载体对镍基催化剂顺酐液相加氢性能的影响

分别以ZrO₂、SiO₂与Al₂O₃为载体,采用等体积浸渍法制备了Ni质量分数为15%的催化剂,考察了其催化顺酐液相加氢性能,并利用BET、XRD、H₂-TPR以及TPO-MS等表征手段对催化剂进行了详细表征。结果表明,随载体不同各催化剂的加氢活性及选择性存在较大差异,Ni/Al₂O₃催化剂的C=C键加氢活性最高,但其几乎没有C=O加氢活性,催化顺酐加氢主产物为丁二酸酐。Ni/ZrO₂催化剂具有最高的C=O加氢活性,催化顺酐加氢主产物为γ-丁内酯,在反应温度为483 K,氢气压力为5 MPa的条件下反应8 h时,Ni/ZrO₂催化剂的γ-丁内酯选择性达79.20%。催化剂的套用实验表明,Ni/ZrO₂与Ni/SiO₂催化剂具有高的使用稳定性,Ni/Al₂O₃催化剂则在套用过程中快速失活。顺酐加氢至γ-丁内酯的中间产物--丁二酸酐与催化剂间的相互作用是影响催化剂加氢选择性及使用稳定性的主要原因。     

Ethanol steam reforming over Ni/La–Al2O3 catalysts: Influence of lanthanum loading

Hydrogen production from ethanol reforming over nickel catalysts supported on lanthanum loaded Al₂O₃ substrates was studied. Activity results revealed the enhancement in the reforming stability of the Ni catalysts with the increase in the lanthanum loading on Al₂O₃ substrates. Catalytic behavior of Ni/La–Al₂O₃ catalysts in the ethanol steam reforming was found to be the contribution of the activity of the La–Al₂O₃ supports for the ethanol dehydration reaction and the activity of the nickel metallic phase that catalyzes both dehydrogenation and CC bond rupture. Physicochemical characterization of catalysts revealed that acidity, nickel dispersion and nickel-support interaction depend on the La-loading on Al₂O₃. The better reforming stability of catalysts with the increase in La content was explained in terms of the ability of nickel surface and/or La–Ni interactions to prevent the formation of carbon filaments.