Study of an iron-based Fischer–Tropsch synthesis catalyst incorporated with SiO2

The effect of adding SiO₂ to a precipitated iron-based Fischer–Tropsch synthesis (FTS) catalyst was investigated using N₂ physical adsorption, H₂ differential thermogravimetric analysis, temperature-programmed reduction/desorption (TPR/TPD) and Mössbauer spectroscopy. The FTS performances of the catalysts with or without SiO₂ were compared in a fixed bed reactor. The characterization results indicated that SiO₂ facilitates the high dispersion of Fe₂O₃ and significantly influences the Fe/Cu and Fe/K contacts, which play an important role in the surface basicity, reduction and carburization behaviors, as well as the FTS performances. The incorporation of SiO₂ enhances the Fe/Cu contact, further enlarges the H₂ adsorption and promotes the reduction of Fe₂O₃ → FeO_x, while the transformation of FeO_x → Fe is suppressed probably due to the strong Fe–SiO₂ interaction. SiO₂ indirectly weakens the surface basicity and severely suppresses the carburization and CO adsorption of the catalyst. In the FTS reaction, it was found that SiO₂ decreases the FTS initial activity but improves the catalyst stability. Due to the lower surface basicity than the catalyst without SiO₂, the catalyst incorporated with SiO₂ has higher selectivity to light hydrocarbons and methane and decreased selectivity to the olefins and heavy hydrocarbons.     

助剂对铁基费托合成催化剂氧化行为的影响:H2O作用的解读

以纯Fe催化剂为研究对象,采用XRD、Raman和TPH等手段考察了催化剂的碳化程度、还原程度对H_2O氧化过程的影响,获得了H_2O氧化过程与催化剂中碳物种转变之间的相互影响规律;系统考察了典型的费托合成助剂K和SiO_2存在时对催化剂物化性质以及H_2O氧化行为的影响,发现催化剂的碳化程度越高,碳化铁的抗H_2O氧化能力越强,氧化过程使得碳物种的石墨化程度增加。适量K助剂可促进碳化铁和催化剂表面石墨碳的形成,提高了碳化铁在H_2O氧化过程中的稳定性;SiO_2助剂的加入显著抑制了催化剂的碳化,但可有效提高碳化铁以及碳物种的稳定性。     

Fe/SiO_2纳米复合物上合成气制低碳烯烃催化性能研究

分别采用一步合成法和常规共沉淀法制备了Fe/SiO2催化剂,通过N2物理吸附、X射线衍射、透射电镜、傅里叶变换红外光谱和程序升温还原等方法对催化剂进行了表征,并在固定床反应器中对其费托合成制低碳烯烃的催化性能进行了评价。结果表明,与共沉淀铁基催化剂不同,采用一步合成法制备的纳米复合物主要由Fe3O4相构成,形貌呈规则球形,平均粒径为30 nm,尺寸分布窄,更容易还原。一步合成法制得的Fe/SiO2催化剂对费托合成反应具有较高的活性和低碳烯烃选择性、较低的甲烷选择性和良好的稳定性。     

ZSM-5分子筛酸性质对甲醛合成三聚甲醛催化性能的影响

ZSM-5分子筛是合成三聚甲醛的有效催化剂。本工作通过XRF、XRD、SEM、NH₃-TPD、Py-FTIR和²⁷Al MAS NMR等手段对一系列不同SiO₂/Al₂O₃物质的量比的ZSM-5分子筛催化剂进行了表征,研究了ZSM-5分子筛中Brønsted酸中心和Lewis酸中心对其甲醛合成三聚甲醛催化性能的影响。结果表明,SiO₂/Al₂O₃物质的量比为250的ZSM-5分子筛具有合适的Brønsted酸中心用于催化甲醛缩聚为三聚甲醛的反应,同时其Lewis酸中心量极少,可有效抑制Cannizzaro或Tishchenko等副反应,提高三聚甲醛的选择性,因而具有最佳的合成三聚甲醛催化性能。寿命实验评价结果显示,SiO₂/Al₂O₃物质的量比为250的ZSM-5分子筛具有良好的催化稳定性,单程寿命长达114 h,并且可通过550℃焙烧再生恢复其催化活性。     

芬顿试剂改性ZSM-5分子筛上丙烯齐聚反应研究

采用浸渍法分别制备了芬顿试剂及其原料FeSO₄和H₂O₂改性的ZSM-5分子筛，并与未改性的母体ZSM-5分子筛进行了对比实验。通过一系列表征手段及丙烯齐聚反应考察了各催化剂的理化性质和催化性能。结果表明，芬顿试剂、FeSO₄、H₂O₂的改性处理均会引起ZSM-5分子筛脱铝，从而导致其硅铝比升高。但与FeSO₄改性相比，芬顿试剂由于其产生的大量羟基自由基更容易将Fe引入分子筛，形成新的活性中心，同时芬顿试剂改性还能使分子筛的比表面积和介孔的体积增大，调节催化剂的酸性。与母体ZSM-5相比，Fenton-ZSM-5催化剂具有优异的催化活性和稳定性。初始丙烯转化率和柴油选择性分别高达98.3%和92.4%，24 h内转化率和选择性维持在80%和82%以上。     

Pd/Co3O4纳米颗粒负载于Al2O3纳米片高效催化甲烷燃烧

We report an efficient catalyst composed of ternary components prepared by inlaying Pd/Co₃O₄ nanoparticles in alkaline Al₂O₃ nanosheets for catalytic oxidation of methane. Pd/Co₃O₄ inlaid in alkaline Al₂O₃ exhibited a higher ability to break the C-H bond of methane than Pd/Co₃O₄ supported on SiO₂, ZrO₂, CeO₂, and acidic or neutral Al₂O₃. Our results show more oxygen vacancies and higher amounts of surface adsorbed oxygen on the surface of Pd/Co₃O₄/alkaline Al₂O₃ than on other catalysts, which is responsible for methane activation and conversion. Further, the Pd/Co₃O₄/alkaline Al₂O₃ catalyst can almost restore to its initial value in the absence of water when 5% (volume fraction) vapor water was cut off, although a decrease in activity occurred when water vapor was introduced to the reaction system. Even under a condition similar to the exhaust of a lean-burn natural gas engine, the catalytic performance of the Pd/Co₃O₄/alkaline Al₂O₃ catalyst is excellent, that is, methane could be completely converted when the sample temperature in the reaction atmosphere was ramped to 400℃.     

小晶粒ZSM-5沸石的绿色、经济性合成

通过添加少量silicalite-1做为活性晶种在较宽的SiO₂/Al₂O₃比范围内制备得到了小晶粒ZSM-5沸石,对所得样品进行X射线衍射(XRD),扫描电子显微镜(SEM),透射电子显微镜(TEM),N₂吸附-脱附,氨程序升温脱附(NH₃-TPD)以及吡啶吸附红外(Py-IR)表征。研究结果表明活性晶种能有效导向生成ZSM-5沸石,避免杂晶形成并可减小所得沸石的晶粒尺寸;所得ZSM-5在低硅铝比(SiO₂/Al₂O₃ ratio = 30)时呈纳米颗粒聚集体形貌,具有多级孔道结构性质;在较高硅铝比时(SiO₂/Al₂O₃ ratio = 60–120)呈小晶粒形貌,颗粒尺寸大约200 nm。值得注意的是由胶态晶种引入的少量TPAOH不完全堵塞沸石的微孔孔道,因此所得所有沸石均无需提前焙烧除去模板剂即可进行离子交换得到具有酸性的H型ZSM-5沸石,所得酸性H型ZSM-5沸石具有和常规方法得到的相同SiO₂/Al₂O₃比的ZSM-5相似的酸类型、强度和酸量,在催化甲醇转化制备烯烃时呈现出相似的甲醇转化率和烯烃选择性。与常规ZSM-5制备方法比较,该方法能够大大减少模板剂的使用量,避免了样品离子交换前的焙烧,方法绿色清洁、成本低廉,具有很好的潜在的工业应用前景。     

沸石分子筛的生成机理与晶体生长(Ⅻ)——ZSM-5沸石生成过程中液相硅酸根离子聚合态的研究

自从1964年Lentz等人提出三甲基硅烷化(TMS)方法研究硅酸盐结构后,人们意识到这种方法能够较真按着地反映硅酸盐结构及聚合状态。又由于硅烷化所得的衍生物(硅酯)易溶于有机溶剂,可以采用多种方法进行分析鉴定。本文应用TMS-GLC及TMSGPC二种方法研究了ZSM-5沸石生成过程中液相硅酸根离子聚合状态的变化。     

Supported dichlorobis(3-hydroxi-2-methyl-4-pyrone)Ti(IV) catalysts: Evaluation on ethylene polymerization

Dichlorobis(3-hydroxi-2-methyl-4-pyrone)Ti(IV) complex was grafted on different inorganic supports, namely different kinds of SiO₂, MAO-modified silica, MCM-41, Al₂O₃, ZrO₂ and MgO. The resulting supported catalysts were shown to be active in ethylene polymerization using methylaluminoxane (MAO) as cocatalyst, most of them being even more active that the homogeneous complex. The highest catalyst activities were observed for the Ti complex supported on SiO₂ 948 activated at 450 °C, MCM-41 and Al₂O₃.     

助剂对Co/Al2O3催化剂浆态床费托合成反应性能影响

考察了ZrO₂、Ru或Pt助剂对Co/Al₂O₃催化剂结构及浆态床费托合成反应性能的影响。实验结果表明,添加ZrO₂助剂可阻止或降低难还原铝酸钴的形成、促进催化剂的还原、提高Co/Al₂O₃催化剂对费托合成反应的催化活性、降低甲烷选择性并提高C₅₊烃选择性。H₂-TPR表征结果表明,少量Ru或Pt助剂均能降低Co-ZrO₂/Al₂O₃催化剂中钴物种还原温度(Co₃O₄→CoO和CoO→Co⁰),提高催化剂的还原度,催化剂呈现出良好的CO加氢反应活性。此外,催化剂组分间浸渍次序对费托合成反应性能有重要影响,载体γ-Al₂O₃先浸渍Zr组分,可有效抑制难还原化合物形成;Co、Ru组分共浸渍加强了Co和Ru组分密切接触程度,更利于钴物种的还原;Co、Pt组分依次浸渍更利于活性组分的均匀分布,催化剂具有最佳的费托合成反应性能。     

混合碱处理制备微介孔催化剂及其噻吩烷基化催化性能

以SiO_2/Al2O3物质的量比为50的H-ZSM-5分子筛为母体,分别采用Na_2CO_3溶液处理后加入TPAOH溶液进行二次晶化法以及Na_2CO_3/TPAOH混合溶液同时处理法,制备了微孔-介孔多级孔HZSM-5催化剂,对其噻吩烷基化反应催化性能进行了研究。结果表明,采用4 mol/L的Na_2CO_3溶液处理后的催化剂在TPAOH溶液中发生了二次晶化;当TPAOH溶液浓度为0.3 mol/L、晶化温度为170℃、晶化时间为24 h时,得到的HZ(CO_2-3-TPA+,0.3-24-170)催化剂具有适宜的孔径和酸性,其噻吩烷基化转化率最高(99.1%)。而Na_2CO_3/TPAOH同时处理HZSM-5分子筛所得的催化剂,由于生成大量SiO_2堵塞了孔道,覆盖了催化剂表面,降低了催化剂的平均孔径和酸性,不适合噻吩烷基化反应。     

Selective oxidation of methane to formaldehyde over antimony oxide-loaded catalyst

A possibility of antimony oxide as a catalyst for the selective oxidation of methane with oxygen to formaldehyde was investigated. The activity measurement was carried out at an atmospheric pressure and at 873 K, where the homogeneous gas-phase reaction was negligible. Oxidized diamond (O-Dia)-supported antimony oxide catalyst produced 1.3 mmol h⁻¹ g-cat⁻¹ of formaldehyde with a formaldehyde selectivity of 23%. On the other hand, SiO₂ supported antimony oxide catalyst exhibited negligible catalytic activity. XRD and UV–vis analyses revealed that -Sb₂O₄ was formed on the oxidized diamond while Sb₆O₁₃ was formed on SiO₂. Selective oxidation of methane to formaldehyde seemed to proceed on -Sb₂O₄ with moderate activity and selectivity to formaldehyde, via a redox cycle of -Sb₂O₄ and Sb₂O_4−x. On the other hand, Sb₆O₁₃ on SiO₂ was stable under the reaction conditions and the selective oxidation occurred only slightly.     

Germanium and silicon compounds as promoters for Re2O7/SiO2-Al2O3 metathesis catalysts

The effect of replacement of R₄Sn by germanium and silicon derivatives as the promoter for the catalyst system Re₂O₇/SiO₂-Al₂O₃ in the metathesis of hex-1-ene, and the system Re₂O₇/B₂O₃/SiO₂-Al₂O₃ in the metathesis of methyl oleate, was studied. The new promoters react slowly with the rhenium oxide. An activation time of about 15 min at temperatures varying from 50 to 75 °C is required for obtaining a good catalytic activity. These promoters can replace the toxic tin compounds, although they give rise to lower turnover numbers in the metathesis of methyl oleate.     

Anaerobic oxidation of isobutane: Catalytic properties of MgV2O6 and Mg2V2O7 prepared by the molten method

The catalytic activity of MV₂O₆ and M₂V₂O₇ type oxides prepared by the molten method (MM) for anaerobic oxidation of isobutane was studied in order to construct a system for the selective oxidation of isobutene using a thin layer reactor. Isobutene, CO and CO₂ were formed by every catalyst tested. The activities for isobutene formation were CuV₂O₆ > ZnV₂O₆, NiV₂O₆, CoV₂O₆ > MgV₂O₆ > MnV₂O₆  CaV₂O₆. Isobutene was a major product over M₂V₂O₇ (MM). Co₂V₂O₇ showed the highest activity and high isobutene selectivity exceeded 90%, demonstrating that Co₂V₂O₇ is a suitable oxide for a thin layer reactor for anaerobic oxidation of isobutane. Partial substitution of Mg by Cu in Mg₂V₂O₇ (MM) improved the activity. It is shown by the oxidation at low O₂ concentration as 2–3% that two types of oxidations occurred simultaneously: isobutene formation by the lattice oxygen ions diffused from the bulk, and CO and CO₂ formation by the oxygen species derived from molecular oxygen in the gas phase.     

ZSM-5沸石大单晶的生长

ZSM-5是近十年来发展的具有广泛应用前景的高硅沸石分子筛。其骨架主要由五元环连结而成,具有十元环孔道(直径约6(?))。空间群为P_nma。大于40μm的均匀完美沸石单晶体,为晶体结构的测定以及与催化性质有密切关系的阳离子交换、扩散、吸附等重要性质的研究所必须。在通常的条件下获得大而完美的沸石单晶体是困难的。单晶的合成,有利于研究沸石晶体的形成与生长机理,是沸石结晶动力学研究的重要课题之一。     

TPAOH处理制备的微介孔催化剂物化性质与噻吩烷基化性能研究

采用不同浓度的TPAOH溶液处理不同SiO_2/Al_2O_3物质的量比的HZSM-5分子筛,制备了微孔-介孔多级孔HZSM-5催化剂。结果表明,采用不同浓度的TPAOH溶液处理不同SiO_2/Al_2O_3物质的量比的HZSM-5分子筛能够脱出HZSM-5分子筛的骨架硅而产生介孔,介孔孔径随TPAOH溶液浓度和SiO_2/Al_2O_3物质的量比的增大而增大;TPAOH溶液处理能够调变HZSM-5催化剂的酸性。采用不同浓度的TPAOH溶液处理SiO_2/Al_2O_3物质的量比分别为50、80和150的HZSM-5分子筛,其中,SiO_2/Al_2O_3物质的量比为50的HZSM-5弱中酸酸强度、相对酸量、B酸和L酸含量明显高于SiO_2/Al_2O_3物质的量比为80和150的HZSM-5分子筛。经不同浓度的TPAOH溶液处理后SiO_2/Al_2O_3物质的量比为50的HZSM-5催化剂具有最佳的噻吩烷基化反应性能。     

不同载体Ni基催化剂生物质热解气甲烷化反应性能

采用浸渍法制备了Ni金属负载在不同载体(SiO2、ZrO2、CeO2、Al2O3和Al2O3-CeO2)表面形成的催化剂,研究了水蒸气和载体对生物质热解气甲烷化反应性能的影响。结果表明,随着水蒸气量的增加CO转化率逐渐增大,而甲烷选择性呈现先增加后降低的变化趋势,当nw ater/ngas比值为0.26时达到最大。载体Al2O3相比SiO2、ZrO2和CeO2具有更大的比表面积和Ni金属分散度,促进了生物质热解气甲烷化反应活性和选择性。相比于Ni-Al2O3催化剂,Al2O3-CeO2复合载体具有更多的镍金属负载量活性金属分散度,以及最好的低温甲烷化反应性能。在300℃的低温条件下,Ni-Al2O3-CeO2催化剂的CO转化率达到97%,CH4增长率达到110%。     

Co/Fe/Al2O3/cordierite催化C3H6选择性还原NO的实验研究

采用溶胶凝胶法和浸渍法制备了负载于蜂窝陶瓷上的Co/Fe/Al₂O₃/cordierite催化剂,在陶瓷管流动反应器上对其催化C₃H₆选择性还原NO的性能进行了测试。结果表明,该催化剂表现出最优脱硝性能,在模拟烟气条件下,当反应温度为550 ℃时可实现97%的脱硝效率。Co的引入可显著增强Fe/Al₂O₃/cordierite催化剂抗SO₂和H₂O的能力。在模拟烟气中同时引入0.02% SO₂和3% H₂O后,1.5Co/Fe/Al₂O₃/cordierite的脱硝性能受影响甚微,当反应温度高于500 ℃时1.5Co/Fe/Al₂O₃/cordierite催化C₃H₆还原NO的效率均可达到90%以上;相比之下,未经Co修饰的催化剂Fe/Al₂O₃/cordierite脱硝性能受到了严重的抑制,在整个反应温度区间（200-700 ℃）内,其催化C₃H₆还原NO的效率最高不足50%。XRD和SEM表征结果表明,经过适量的Co修饰后的1.5Co/Fe/Al₂O₃/cordierite表面变得更疏松,且形成了以钴铁和钴铝双金属氧化物为主要成分的球状晶粒。H₂-TPR结果表明,相比于Fe/Al₂O₃/cordierite,1.5Co/Fe/Al₂O₃/cordierite有更好的低温还原性能。Py-FTIR结果表明,Co的引入可使催化剂表面的Lewis酸明显增加,且生成了Brønsted酸。N₂吸附-脱附表征结果表明,Co可增大催化剂的比表面积。     

负载型铂催化剂中的载体效应

本文用程序升温热脱附法和氢氧滴定法研究了SiO₂、SiO₂·Al₂O₃、Al₂O₃、SiO₂·SnO₂和Al₂O₃·SnO₂等和Pt的相互作用,表明Pt和载体作用强弱的顺序为:Al₂O₃>SiO₂·Al₂O₃>SiO₂;发现SnO₂具有强化SiO₂和Al₂O₃载体效应的作用;提出Pt和载体相互作用较强部位可能是Pt和缺氧氧化物所形成的表面络合物--Pt-[Al₂O_x]和Pt-[SnO_x]。     

耐硫甲烷化中H2S浓度对MoO3/Al2O3和CoO-MoO3/Al2O3催化剂的影响

在0 到12 mL·L^-1 (体积分数φ=0.00%-1.20%) 范围内考察了不同H₂S 浓度对25% (质量分数, w)MoO₃/Al₂O₃和5% (w) CoO-25%MoO₃/Al₂O₃催化剂甲烷化性能的影响. 结果表明, 5%CoO-25%MoO₃/Al₂O₃的甲烷化活性随H₂S浓度的增加单调上升, 而25%MoO₃/Al₂O₃对H₂S浓度并不敏感. 对比这两种催化剂发现, 只有在H₂S浓度高于0.40% (φ) 时, 在25%MoO₃/Al₂O₃中添加Co助剂才会有促进作用; H₂S浓度低于0.40% (φ)时, Co助剂会抑制25%MoO₃/Al₂O₃催化剂的甲烷化活性. 分别对反应前后的催化剂表征发现, H₂S浓度的改变不会对两种催化剂的物理结构产生明显的影响, 而是通过影响催化剂表面的金属硫化物活性位来影响催化剂的甲烷化性能. 耐硫甲烷化反应体系中较高的硫含量下Co助剂才表现出对25%MoO₃/Al₂O₃催化剂的促进作用. 该研究明确了在MoO₃/Al₂O₃催化剂中添加Co助剂的硫化氢浓度范围, 为工业上选择合适的催化剂提供了依据.