不同粒径的Ni/SiO2催化剂上CH4和CO2吸附活化的漫反射傅里叶变换红外光谱研究

 采用原位漫反射傅里叶变换红外光谱研究了CH4和CO2在不同粒径的Ni/SiO2催化剂上的吸附及活化. 结果表明,在不同粒径的催化剂上,检测到有CH4解离生成的CHx(x=1～3)物种,以及催化剂表面吸附的CHx物种与表面-OH 作用生成的CHx-O物种. CH4的裂解强烈依赖于催化剂表面Ni颗粒的大小,在粒径8 nm左右的Ni颗粒上, CH4较易解离; CO2难以直接在Ni/SiO2催化剂表面发生解离吸附,但CH4解离生成的吸附H对CO2的解离吸附具有明显的促进作用; CH4与CO2共吸附时,较小粒径的Ni可以促进CO2与表面氧物种发生反应,生成单齿表面碳酸盐物种.     

Ni/La2O3/α-Al2O3中的高温脱附氢促进CH4/CO2重整反应的初活性

 通过H2程序升温脱附实验,在H2还原的Ni/La2O3/α-Al2O3催化剂上可以明显观察到高温脱附氢(高温氢). 动力学实验结果表明,随催化剂上高温氢含量的增加, CH4/CO2重整反应的初始活性升高,同时高温氢也可在重整反应过程中原位生成,并使重整反应的活性最终达到稳定. 脉冲实验结果表明,随催化剂上高温氢含量的增加, CH4解离后生成的活性中间体CHx物种的x值也增大,进而降低了CHx与CO2反应的活化能,提高了CHx与CO2反应的速率. La2O3助剂的添加提高了Ni/La2O3/α-Al2O3催化剂上逆水气变换反应的速率,并且对CO2的活化也有促进作用. La2O3助剂的加入对于CH4/CO2重整反应的重要作用是使高温氢的数量增多且稳定性提高,有利于保持CHx物种中较高的x值,促进重整反应.     

Rh／SiO2催化剂上甲烷部分氧化制合成气反应

 利用程序升温脱附、程序升温还原、程序升温表面反应、程序升温反应和化学捕获反应等手段，对Rh／SiO2催化剂上甲烷部分氧化制合成气反应进行了研究．结果表明，Rh／SiO2催化剂上甲烷部分氧化制合成气机理属于热解－氧化反应机理．甲烷首先在催化剂上发生解离吸附，产生具有不同H／C比的化学吸附物种CHx（x＝1～3）．其中，具有较高H／C比的CHx可能是甲烷部分氧化反应的活性物种，而具有较低H／C比的CHx可能是催化剂上积碳并导致催化剂失活的来源．活性物种CHx在活性氧物种的作用下，生成含氧中间体物种CHxO或继续脱氢．含氧中间体物种进一步分解，即生成CO和H2；CO2也可由CHx或CHxO物种进一步氧 化生成．     

透氧膜反应器内NiO/MgO催化焦炉煤气重整反应途径

对透氧膜反应器内焦炉煤气(COG)重整反应模型进行分析.通过H2+N2、CH4+N2、CO+N2和H2+CH4+N2混合气在透氧膜反应器内重整反应,以及有无催化剂下重整反应和催化剂床层厚度重整反应实验,推测焦炉煤气重整反应模型:首先焦炉煤气中H2在催化剂活性金属镍颗粒上吸附解离,解离后的氢向高活性位迁移"(三相界面")并与膜表面侧晶格氧(或O2-)反应生成H2O.同时CH4也可能在活性镍颗粒上裂解生成CH3*和H*,反应生成的H2O与膜表面催化剂上裂解的碳反应生成H2和CO.未反应完的H2O在催化剂床层内与剩余CH4反应生成H2和CO.     

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．     

Rh/SiO_2催化剂上甲烷部分氧化制合成气的反应机理

采用原位Raman光谱技术,在原料气中的O2未完全耗尽的条件下,对CH4部分氧化制合成气反应的Rh/SiO2催化剂床层前部贵金属物种的化学态以及由CH4解离所生成的碳物种进行了表征.在此基础上采用脉冲反应和同位素示踪技术,比较了CH4的部分氧化及其与H2O和CO2的重整等反应对催化剂床层氧化区内CO和H2生成的相对贡献,并将实验结果与Ra-man光谱表征结果进行了关联.结果表明,在600°C下将还原后的4%Rh/SiO2催化剂切入CH4:O2:Ar=2:1:45原料气,催化剂床层前部未检测到铑氧化物的Raman谱峰,但可清晰检测到源于CH4解离的碳物种;在700°C和接触时间小于1ms的条件下,催化剂床层的氧化区内已有大量CO和H2生成,在相同的实验条件下,CH4与H2O或CO2重整反应对氧化区内合成气生成的贡献则很小;以CH4:16O2:H218O:He=2:1:2:95为原料气的同位素示踪实验结果表明,在原料气中16O2未完全耗尽的情况下,反应产物中C16O的含量占CO生成总量的92.3%,表明CO主要来自CH4的部分氧化反应.上述结果均表明,在O2存在下Rh/SiO2催化剂上CO和H2可以通过CH4直接解离和部分氧化机理生成.     

金属-载体相互作用对CH4/CO2重整反应中Rh基催化剂抗积炭性能的影响

考察了Rh/Al2O3,Rh/SiO2和Rh/CeO2催化剂上金属-载体间相互作用对CH4/CO2重整反应抗积炭性能的影响,并与反应前后催化剂的程序升温还原和程序升温氧化(TPO)测试结果相关联.实验发现,Rh与Al2O3和SiO2载体间的相互作用越强,催化剂还原后Rh的分散度越高,晶粒越小,高分散的Rh表面生成的碳物种CHx越多,其作为活泼的反应中间体越易与CO2反应生成CO和H2.而游离态的Rh还原后晶粒较大,生成的碳物种与CO2反应能力较低,从而导致催化剂失活.TPO和CO2脉冲实验结果表明,反应过程中Rh/CeO2催化剂上反应生成的CHx物种比Rh/Al2O3和Rh/SiO2上的CHx物种更活泼.同时由于Rh-CeO2间独特的相互作用,部分CeO2还原后生成CeO2-x和氧空位,促进CO2分子的活化解离,导致生成的表面氧容易与CHx反应,从而抑制催化剂积炭.     

K2O助剂对合成碳酸二甲酯用Cu/Ni/ZrO2-SiO2催化剂的吸附和催化性能的影响

 用等体积浸渍法制备了ZrO2－SiO2（ZrSiO）表面复合氧化物负载的Cu－Ni催化剂,并用IR,TPR,TPD及微反技术考察了K2O助剂对CO2和CH3OH在Cu－Ni／ZrSiO催化剂表面上的吸附及合成碳酸二甲酯（DMC）反应性能的影响．结果表明：加入K2O助剂使CO2在催化剂表面上的吸附增强,当n（K）／n（Cu＋Ni）＝15％时,CO2在催化剂表面上吸附后生成K2CO3;CH3OH在催化剂表面上的解离吸附态（CH3O－和H＋）的吸附减弱;CO2和CH3OH在Cu－Ni／ZrSiO催化剂表面上反应的主要产物为DMC,H2O,CO和CH2O;随着K2O助剂的加入,反应转化率及DMC选择性提高,副产物（CO和CH2O）的选择性下降．根据实验结果,探讨了K2O对催化剂表面活性中心电荷分布的影响．     

水蒸气对Ni/Ce-Zr-Al-Ox催化剂上CO2重整CH4瓜的影响

采用水热合成-负载法制备了Ni/Ce-Zr-Al-Ox催化剂,测试了该催化剂上CO2重整CH4反应的活性和稳定性,并考察了添加少量水蒸气对CO2重整CH4反应的影响.结果表明,在不含水蒸气的反应气中反应198 h后CH4和CO2的转化率分别为89%和98%,H2/CO摩尔比约为1.00,且没有任何失活.添加3.2%的水蒸气后,CH4转化率提高到94%,CO2转化率不变,H2/CO摩尔比约提高0.06,同时稳定性也很好.计算结果表明,添加少量水蒸气后,CO2重整CH4被促进,逆水煤气反应被抑制,而水蒸气重整CH4没有明显变化.     

载体酸碱性对CO2／CH4重整反应用镍基催化剂的影响

考察了6种载体对镍基催化剂的CO2/CH4重整反应性能的影响,并采用CO2-TPD,H2-TPR和BET技术对催化剂进行表征.结果表明,Ni/MgO-Al203,催化剂表现出较好催化活性和较高的反应产率,且反应后催化剂的失活率最小(4.65%).载体的酸碱性和比表面积的大小直接影响到催化剂的反应性能,经碱土金属修饰的复合载体表面的碱性增强,提高了对CO2的吸附解离能力,使催化剂在重整反应中表现出较好的抗积炭能力.各催化剂的稳定性依次为:Ni/MgO-Al2O3>Ni/MCM-41>Ni/MgO>Ni/Al203>Ni/ZrO2>Ni/ZSM-5.     

Rh doping effect on coking resistance of Ni/SBA-15 catalysts in dry reforming of methane

A series of SBA-15 supported bimetallic Rh–Ni catalysts with different weight ratio of Rh/Ni in the range of 0–0.04 were prepared for carbon dioxide reforming of methane. The doping effect of Rh on catalytic activity as well as carbon accumulation and removal over the catalysts was studied. The characterization results indicated that the addition of a small amount of Rh promoted the reducibility of Ni particles and decreased the Ni particle size. During the dry reforming reaction, the carbon deposition was originated from CH4 decomposition and CO disproportionation. The Rh–Ni catalyst with small metallic particle size inhibited the carbon formation and exhibited high efficiency in the removal of coke. In comparison with bare Ni-based catalyst, the Rh–Ni bimetallic catalysts showed high activity and stability in the dry reforming of methane.     

Autothermal reforming of methane over Ni catalysts supported over ZrO2-CeO2-Al2O3

Ni catalysts supported on Al2O3, ZrO2-Al2O3, CeO2-Al2O3 and ZrO2-CeO2-Al2O3 were prepared by coprecipitation method, and their catalytic performances for autothermal reforming of methane to hydrogen were investigated. The Ni-supported catalysts were characterized by XRD, TPR and XPS. The relationship between the structures and catalytic activities of the catalysts was discussed. The results showed that the catalytic activity and stability of the Ni/ZrO2-CeO2-Al2O3 catalyst was better than those of other catalysts with the highest CH4 conversion, H2/CO and H2/COx ratio at 750 ℃. The catalyst showed a little deactivation along the reaction time during its 72 h on stream with the mean deactivation rate of 0.08%/h. The catalytic performance of the Ni/ZrO2-CeO2-Al2O3 catalyst was also affected by reaction temperature, no2 ： nCH4 molar ratio and nH2O ： nCH4 molar ratio. TPR, XRD and XPS measurements indicated that the formation of ZrO2-CeO2 solid solution could improve the dispersion of NiO, and inhibit the formation of NiAl2O3, and thus significantly promoted the catalytic activity of the Ni/ZrO2-CeO2-Al2O3 catalyst.     

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。     

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.     

Production of Hydrogen from Methane by a CO2 Emission-Suppressed Process: Methane Decomposition and Gasification of Carbon Nanofibers

Catalytic methane decomposition into hydrogen and carbon nanofibers and the oxidations of carbon nanofibers with CO₂, H₂O and O₂ were overviewed. Supported Ni catalysts (Ni/SiO₂, Ni/TiO₂ and Ni/carbon nanofiber) were effective for the methane decomposition. The activity and life of the supported Ni catalysts for methane decomposition strongly depended on the particle size of Ni metal on the catalysts. The modification of the catalysts with Pd enhanced the catalytic activity and life for methane decomposition. In particular, the supported Ni catalysts modified with Pd showed high turnover number of hydrogen formation at temperatures higher than 973 K with a high one-pass methane conversion (>70%). However, sooner or later, every catalyst completely lost their catalytic activities due to the carbon layer formation on active metal surfaces. In order to utilize a large quantity of the carbon nanofibers formed during methane decomposition as a chemical feedstock or a powdered fuel for heat generation, they were oxidized with CO₂, H₂O and O₂ into CO, synthesis gas and CO₂, respectively. In every case, the conversion of carbon was greater than 95%. These oxidations of carbon nanofibers recovered or enhanced the initial activities of the supported Ni catalysts for methane decomposition.     

CO_2 reforming of glycerol over La-Ni/Al_2O_3 catalyst:A longevity evaluative study

This paper reports on the longevity of glycerol-dry(CO2) reforming over the lanthanum(La) promoted Ni/Al2O3 catalysts.The XRD results showed that the Ni particle was well-dispersed in the presence of La promoter.In addition,via the NH3-TPD analysis,it was found that the La promoter has reduced the acidity of Ni catalyst which may have explained the mitigation of carbon laydown.It was determined that the 3.0 wt% La-promoted Ni/Al2O3 catalyst possessed the largest BET specific surface area of 97 m2 g-1.Consequently,it yielded the best catalytic longevity performance with conversion attained more than 90%,even after 72 h of reaction duration.Significantly,it can be confirmed that the presence of CO2 during the glycerol dry reforming was essential in reducing carbon deposition,most likely via gasification pathway.This has ensured a stability of catalytic activity for a long reaction period(72 h).     

Ni/Al2O3催化甲烷裂解

分别通过浸渍法和共沉淀法制备了不同Ni负载量的Ni/Al2O3催化剂。考察了Ni负载量、制备方法以及反应温度对Ni/Al2O3催化甲烷裂解性能的影响。结果表明,在550℃,浸渍法制备的Ni/Al2O3催化剂,当Ni负载量为20%(质量分数)、Ni金属平均粒径为11.25 nm时,具有最佳的甲烷催化裂解效果,其每摩尔Ni的氢气产量和每克Ni碳产量分别为164 mol和15.30 g。催化剂制备方法对Ni/Al2O3甲烷催化裂解反应有显著影响,相同Ni负载量共沉淀法制备的Ni/Al2O3甲烷催化裂解总体效果要好于浸渍法制备的Ni/Al2O3,而且反应过程中生成的碳纤维较长,管径也较均一。550℃时,共沉淀法制备的Ni负载量为41.2%(质量分数)的Ni/Al2O3催化剂在反应至350 min时,仍保持着30%以上的转化率。     

Effect of Transition Metals (Cu, Co and Fe) on the Autothermal Reforming of Methane over Ni/Ce0.2Zr0.1Al0.7Oδ Catalyst

The transition metals (Cu, Co, and Fe) were applied to modify Ni/Ce0.2Zr0.1Al0.7Oδ catalyst.The effects of transition metals on the catalytic properties of Ni/Ce0.2Zr0.1Al0.7Oδ autothermal reforming of methane were investigated. The Ni-supported catalysts were characterized by XRD, TPR and XPS.Tests in autothermal reforming of methane to hydrogen showed that the addition of transition metals (Cu and Co) significantly increased the activity of catalyst under the conditions of lower reaction temperature,and Ni/Cu0.05Ce0.2Zr0.1Al0.65Oδ was found to have the highest conversion of CH4 among all catalysts in the operation temperatures ranging from 923 K to 1023 K. TPR, XRD and XPS measurements indicated that the cubic phases of CexZr1-xO2 solid solution were formed in the preparation process of catalysts.Strong interaction was found to exist between NiO and CexZr1-xO2 solid solution. The addition of Cu improved the dispersion of NiO, inhibited the formation of NiAl2O4, and thus significantly promoted the activity of the catalyst Ni/Cu0.05Ce0.2Zr0.1Al0.65Oδ.     

掺杂助剂Ce和Zr的Ni/Al2O3催化剂的X光电子能谱分析

以Na2CO3为沉淀剂,在pH 9.0的沉淀条件下,采用并流沉淀法制备了Ni/Al2O3、Ni/CeO2-Al2O3、Ni/ZrO2-Al2O3和Ni/ZrO2-CeO2-Al2O34种催化剂,催化剂中Ni负载量(质量分数)为10%。采用XPS表征手段及常压固定床反应器对催化剂进行活性评价,考察了助剂Ce和Zr及二者的协同作用对Ni基催化剂表面物种结合能的影响以及对甲烷自热重整制氢反应性能的影响。结果表明,助剂Ce和Zr的添加及二者的协同作用对Ni基催化剂表面各物种的结合能均有一定的影响,结合评价结果可知,Ce和Zr二者的协同作用对Ni基催化剂的催化性能提高最大。     

Promoting effect of Pt in Ni-based catalysts for CH4 reforming

The effect of Pt/Ni ratio on the surface properties and catalytic behavior of bimetallic PtNi catalysts for reforming of methane with CO₂ was studied. The TPR, FTIR of adsorbed CO and XPS data showed that introduction of a small amount of Pt (0.3 – 0.5 wt.%) into the Ni catalyst leads to a decrease of the NiO size, its easy reduction and a uniform distribution of the nickel metal particles.