Initial steps in the production of H2 from ethanol: A FT-IR study of adsorbed species on Ni/MgO catalyst surface

Reactivity of pure ethanol and acetaldehyde on Ni/MgO catalyst at different reaction temperatures was investigated confirming that hydrogen production is ascribable to a series of consecutive and/or parallel reactions. FT-IR studies on adsorbed dry molecules (ethanol or acetaldehyde) showed that ethanol decomposition occurs on catalyst surface through formation of acetaldehyde, which is converted to acetates and then to carbonates, or decomposes to CO, C and H₂.     

有机蒙脱土负载镍催化剂上乙醇重整制氢

采用浸渍法制备了有机改性蒙脱土(OMt)负载的Ni/有机蒙脱土(Ni/OMt)催化剂,用于乙醇重整制氢;通过XRD、FT-IR、H₂-TPR、SEM、XPS和氮吸附等手段对催化剂进行了表征分析。结果表明,与未改性的蒙脱土负载的Ni催化剂(Ni/MMT)相比,有机改性可显著提高其比表面积、孔容和金属Ni的分散度,降低碳沉积量,改善Ni/MMT催化剂的稳定性。Ni/OMt催化剂表现出较高的乙醇重整制氢催化性能,在773K下反应30 h,乙醇转化率保持在100%,氢气选择性为70%;而Ni/MMT催化剂在反应10 h即开始失活,碳沉积严重,同时产生副产物乙烯和乙醛。使用十六烷基三甲基溴化铵(CTAB)改性可促进Ni高分散在MMT层板上,抑制积炭对活性金属Ni包裹,提高其乙醇重整氢气选择性、降低乙烯和乙醛的选择性。     

高活性铜催化剂无受体乙醇催化脱氢制乙醛研究

相较于Wacker工艺进行乙醛工业化生产,发展多相催化体系实现乙醇直接无氧催化脱氢制乙醛和副产氢气,从生产工艺和经济价值方面无疑是一条更加安全高效的路线.在此,我们发展了一种高效、稳固的Cu/SiO₂催化剂,用于乙醇的无受体催化脱氢.通过氨蒸发法制备得到高度分散的Cu颗粒,在没有任何平衡气体的纯乙醇进料条件下,显示出超强的热稳定性.活性组分Cu和载体SiO₂之间的强相互作用,使其具有优异的催化性能.通过反应条件优化,在250℃下实现了较高的乙醇转化率(>40%)和乙醛选择性(>95%),且催化剂在固定床连续反应过程中可稳定运行超过400 h.     

Ni-Cu/CeO2催化剂上乙醇水蒸气重整反应

 研究了Ni-Cu/CeO2催化剂在乙醇水蒸气重整反应中的催化性能. 以具有高比表面积的CeO2为载体,用沉积沉淀法制备了一系列不同担载量的Ni, Cu双组分催化剂,采用X射线衍射、程序升温还原和透射电子显微镜对催化剂的晶相组成、还原性能和形貌进行了表征. 结果表明, CuO, NiO和CeO2的相互作用明显改善了NiO的分散. 适量CuO的加入使NiO分散度增大,颗粒明显变小,从而使催化剂具有更好的催化性能,但过多CuO的加入反而降低了催化剂的活性. Ni和Cu的催化性能差异较大, Ni具有优异的断裂C-C键性能,在低温下即可实现乙醇的完全转化,而在高温区则具有很好的甲烷重整性能,可获得很高的氢气产率; Cu在低温区倾向于使乙醇脱氢生成乙醛以及进一步脱羰基生成丙酮,在高温区也具有一定的乙醇裂解性能.     

膜催化研究(Ⅲ)——无机膜反应器中乙醇脱氢制乙醛

应用Sol-gel法制备了无机氧化铝膜,其孔径大小集中分布在3～5nm间,透过率和分离系数均符合Knudsen扩散.将该膜用于乙醇脱氢制乙醛反应中,分别考察了反应温度、进料空速、内管吹扫气流对乙醇转化率及乙醛产率和选择性的影响,并与相同条件下的常规反应器中的结果作了比较.结果发现,用膜反应器后,乙醇转化率及乙醛产率均明显高于常规反应器,与相应的平衡转化率相比较,乙醛收率可提高5%～10%.     

乙醇的低温光催化氧化实验研究

利用傅里叶变换红外光谱仪(FT-IR),在间歇式反应器中研究了高浓度乙醇的低温光催化氧化特性。研究结果表明,FT-IR技术能够用来研究气态有机物的光催化降解特性;在乙醇的光催化降解过程中,有乙醛等中间产物生成,乙醇先被氧化为乙醛,再被氧化为二氧化碳;在间歇式反应器中,乙醇的循环流量对乙醇的瞬时降解速率影响不大;高浓度乙醇的低温光催化氧化过程可以用单步Langmuir-Hinshelwood 方程来描述;温度对乙醇光催化氧化的初始反应速率的影响十分显著,高浓度乙醇的初始反应速率随温度的升高而迅速提高。     

Hydrogen production via autothermal reforming of ethanol over noble metal catalysts supported on oxides

Hydrogen was produced over noble metal (Ir, Ru, Rh, Pd) catalysts supported on various oxides, including γ-Al2O3, CeO2, ZrO2 and La2O3, via the autothermai reforming reaction of ethanol (ATRE) and oxidative reforming reaction of ethanol (OSRE). The conversion of ethanol and selectivites for hydrogen and byproducts such as methane, ethylene and acetaldehyde were studied. It was found that lanthana alone possessed considerable activity for the ATRE reaction, which could be used as a functional support for ATRE catalysts. It was demonstrated that Ir/La2O3 prevented the formation of methane, and Rh/La2O3 encumbered the production of ethylene and acetaldehyde. ATRE reaction was carried out over La2O3-supported catalysts (Ir/La2O3) with good stability on stream, high conversion, and excellent hydrogen selectivity approaching thermodynamic limit under autothermal condition. Typically, 3.4 H2 molecules can be extracted from a pair of ethanol and water molecules over Ir(5wt%)/La2O3. The results presented in this paper indicate that Ir/La2O3 can be used as a promising catalyst for hydrogen production via ATRE reaction from renewable ethanol.     

镍基催化剂上乙醇水蒸气重整反应的研究

考察了载体对Ni催化剂乙醇水蒸气重整制氢反应性能的影响。结果表明,Ni/CeO2催化剂具有较好的低温活性和氢气选择性。对Ni担载量和焙烧温度考察发现,400℃焙烧的15%NiCeO2催化剂具有较好的催化性能;继续升高焙烧温度引起NiO和CeO2粒子的显著增大,导致对氢气选择性的降低。较小的Ni和CeO2粒子有利于乙醇水汽重整反应的进行,而大的粒子倾向于乙醇的分解反应。 350℃时,在反应过程中分别添加CO、CO2和CH4的结果表明没有发生CO和CO2甲烷化反应,而发生了一定程度的CH4水汽重整反应。     

Mechanism of photocatalytic oxidation of gaseous ethanol

A photocatalytic film reactor with a titanium dioxide film was used for oxidation of gaseous ethanol at 253.7 nm. The influences of partial pressures of oxygen and water vapour in different carrier gases were studied. The rate of photocatalytic oxidation of ethanol was significantly affected by the content of oxygen but water vapour had no effect. It was suggested that the photocatalytic transformation of ethanol follows a direct oxidation mechanism where the interaction of ethanol with positive hole gives first cationic free radical of ethanol, which is converted by multipathway reactions with oxygen to acetaldehyde, ethyl formate, and ethyl acetate.     

Analytical potential of enzyme-coated capillary reactors in capillary zone electrophoresis

Enzymes immobilized on the inner surface of an electrophoretic capillary were used to increase sensitivity and resolution in capillary zone electrophoresis (CZE). Sensitivity is enhanced by inserting a piece of capillary containing the immobilized enzyme into the main capillary, located before the detector, in order to transform the analyte into a product with a higher absorptivity. This approach was used to determine ethanol. In order to improve resolution, capillary pieces containing immobilized enzymes were inserted at various strategic positions along the electrophoretic capillary. On reaching the enzyme, the analyte was converted into a product with a high electrophoretic mobility, the migration time for which was a function of the position of the enzyme reactor. This approach was applied to the separation and determination of acetaldehyde and pyruvate. Finally, the proposed method was validated with the determination of ethanol, acetaldehyde, and pyruvate in beer and wine samples.     

Microcalorimetric and infrared studies of ethanol and acetaldehyde adsorption to investigate the ethanol steam reforming on supported cobalt catalysts

Microcalorimetric and infrared studies of ethanol and acetaldehyde adsorption were carried out on fresh and deactivated ZnO-supported cobalt catalysts (Co/ZnO and Co/ZnO(d), respectively) as well as on ZnO support alone. The results were used to analyze the catalytic behavior of these materials for ethanol and acetaldehyde steam-reforming reactions. The Co/ZnO(d) sample contained extensive carbon deposition as shown by Raman spectroscopy and transmission electron microscopy. On fresh Co/ZnO, the adsorption energetics of ethanol and acetaldehyde (an intermediate in the ethanol reforming reaction) were similar. Under steam-reforming conditions at low conversion values of ethanol, acetaldehyde was selectively yielded. The presence of surface acetate species was shown from IR spectra following acetaldehyde adsorption. Besides that, the Co/ZnO catalyst was active and showed a high selectivity toward the reforming products, H2 and CO2, when the steam reforming of acetaldehyde was carried out at low conversion values. In contrast, on the deactivated sample, the strongest adsorption sites of ethanol have disappeared, and acetaldehyde was adsorbed with higher energy with respect to ethanol, resulting in the blockage of the active sites; a poorer catalytic performance in both ethanol and acetaldehyde steam-reforming reactions is observed. The presence of acetate species after adsorption of acetaldehyde on Co/ZnO(d) was not shown. The polymerization of acetaldehyde over Co/ZnO(d) was related to the decomposition of acetaldehyde under reforming conditions to give CO and CH4.     

Chemical Reactions and Kinetics of the Carbon Monoxide Coupling in the Presence of Hydrogen

The chemical reactions and kinetics of the catalytic coupling reaction of carbon monoxide to diethyl oxalate were studied in the presence of hydrogen over a supported palladium catalyst in the gaseous phase at the typical coupling reaction conditions. The experiments were performed in a continuous flow fixed-bed reactor. The results indicated that hydrogen only reacts with ethyl nitrite to form ethanol, and kinetic studies revealed that the rate-determining step is the surface reaction of adsorbed hydrogen and the ethoxy radical (EtO-). A kinetic model is proposed and a comparison of the observed and calculated conversions showed that the rate expressions are of rather high confidence.     

Chemical Reactions and Kinetics of the Carbon Monoxide Coupling in the Presence of

The chemical reactions and kinetics of the catalytic coupling reaction of carbon monoxide to diethyl oxalate were studied in the presence of hydrogen over a supported palladium catalyst in the gaseous phase at the typical coupling reaction conditions. The experiments were performed in a continuous flow fixed-bed reactor. The results indicated that hydrogen only reacts with ethyl nitrite to form ethanol, and kinetic studies revealed that the rate-determining step is the surface reaction of adsorbed hydrogen and the ethoxy radical (EtO-). A kinetic model is proposed and a comparison of the observed and calculated conversions showed that the rate expressions are of rather high confidence.     

High-temperature pyrolysis of ethanol

A small, heated alumina tube was used as a pyrolysis reactor to study the thermal decomposition of ethanol at residence times of about 5 ms and temperatures from 1050 to 1275 K. The gas mixture leaving the reactor was analysed by molecular beam sampling mass spectroscopy. The products observed were ethene, water, hydrogen, methane and carbon monoxide and acetaldehyde as an intermediate. The ratio of the amounts of ethene and water formed to the other products was ca. 2:1. The experimental results are discussed in terms of a reaction mechanism and compared with other literature data. The disappearance of ethanol can be modelled by a first-order overall reaction.     

催化剂Ni/Y2O3上低温乙醇水蒸气重整制氢研究——氢气预还原对催化剂性能的影响

用浸渍－热分解－氢还原法(IHDHR)和浸渍－热分解法(IHD)分别制备了两种纳米尺寸的Ni/Y2O3催化剂，并应用X-光电子能谱、X-射线衍射、BET比表面测试等分析技术对两种催化剂的结构进行了表征和比较。采用固定床反应器对两种催化剂的催化性能进行实验测试。结果表明，氢气预还原与否对该纳米Ni/Y2O3催化剂的催化性能有一定的影响，经过氢气预还原的催化剂对低温乙醇水蒸气重整反应表现出较高的活性和稳定性，250?℃时，乙醇的转化率达到81.9%；320 ℃时，乙醇的转化率达到95.3%，对氢气的选择性为53.6%。对经过氢预还原的Ni/Y2O3催化剂进行了60 h的稳定性测试。     

Direct and Selective Production of Propene from Bio‐Ethanol on Sc‐Loaded In2O3 Catalysts

Propene, one of key building blocks for manufacturing plastics and chemicals, could be directly and stably produced from ethanol in good yields. The conversion degree of ethanol to propene reached approximately 60 mol % by using a 3 atom % scandium‐loaded indium oxide catalyst at 823 K in the presence of water and hydrogen. The introduction of Sc prevented the reduction of In₂O₃ to In metal during the reaction, and that of water decreased the coke formation. Both additions resulted in longer lifetimes of the catalysts. The hydrogen addition increased the conversion of acetone to propene. The reaction pathways are also suggested on the basis of the product distributions and the pulse experiments, ethanol→acetaldehyde→acetone→propene, which is quite different from the shape‐selective catalysis on zeolites and the dimerization‐metathesis of ethene on nickel ion‐loaded silica catalysts.     

Hydrogen production via autothermal reforming of ethanol over noble metal catalysts supported on oxides

Hydrogen was produced over noble metal (Ir, Ru, Rh, Pd) catalysts supported on various oxides, including γ-Al₂O₃, CeO₂, ZrO₂ and La₂O₃, via the autothermal reforming reaction of ethanol (ATRE) and oxidative reforming reaction of ethanol (OSRE). The conversion of ethanol and selectivites for hydrogen and byproducts such as methane, ethylene and acetaldehyde were studied. It was found that lanthana alone possessed considerable activity for the ATRE reaction, which could be used as a functional support for ATRE catalysts. It was demonstrated that Ir/La₂O₃ prevented the formation of methane, and Rh/La₂O₃ encumbered the production of ethylene and acetaldehyde. ATRE reaction was carried out over La₂O₃-supported catalysts (Ir/La₂O₃) with good stability on stream, high conversion, and excellent hydrogen selectivity approaching thermodynamic limit under autothermal condition. Typically, 3.4 H₂ molecules can be extracted from a pair of ethanol and water molecules over Ir(5wt%)/La₂O₃. The results presented in this paper indicate that Ir/La₂O₃ can be used as a promising catalyst for hydrogen production via ATRE reaction from renewable ethanol.     

Cu/ZrO2催化剂上乙醇水蒸气重整反应的研究Ⅰ催化剂性能及其制备参数的影响

研究了Cu/ZrO2催化剂在乙醇水蒸气重整反应中的催化性能。用常规沉淀法、醇凝胶法制备了ZrO2载体;用浸渍法或共沉淀法制备了Cu/ZrO2催化剂。考察了ZrO2载体的制备方法以及Cu/ZrO2的制备参数对催化剂性能的影响。采用BET、XRD、TEM及XRF等方法对催化剂的比表面积、孔容、晶相、表面形貌以及活性组分等进行了表征。同时,制备并比较了Ni/ZrO2、Cu/10MgO-90ZrO2和Cu/10CaO-90ZrO2催化剂的性能,考察了活性组分Cu、Ni的差异以及ZrO2载体的影响。在Cu/ZrO2催化剂(Cu的质量分数为8%)上,500 ℃~600 ℃乙醇转化率达到98%~100％、H2选择性为2.0~2.6（摩尔比）。 Cu/ZrO2与Ni/ZrO2机械混合有助于H2选择性的提高。在催化剂载体中添加MgO、CaO碱性物质可以使H2选择性提高1.3倍~2.0倍。浸渍法制备的Cu/ZrO2催化剂的性能优于共沉淀法。     

Pd/γ-Al2O3-TiO2催化剂上乙醇乙醛的催化氧化性能研究

采用混胶法和机械混合等方法制备了Pd质量分数为1%的Pd/γ-Al₂O₃-TiO₂催化剂,并对其催化活性、影响条件进行了考察。结果说明,由混胶法制备的Pd/γ-Al₂O₃-TiO₂催化剂对乙醇和乙醛的完全氧化表现出优异的催化性能,其活性明显高于单一载体催化剂Pd/TiO₂和Pd/Al₂O₃,150℃时乙醇和乙醛的转化率分别达到98.9%和98.5%。在较宽温度范围内和高空速条件下表现出良好的稳定性。同时运用XRD、TEM和FT-IR等技术对催化剂进行了表征。结果表明,在Pd/γ-Al₂O₃-TiO₂催化剂中Al₂O₃与TiO₂之间存在着较强的相互作用,使γ-Al₂O₃-TiO₂的比表面积和孔容积均调变到一个适中的数值,同时在催化剂表面Al₂O₃参与形成了有利于其催化活性的表面结构。     

Catalytic hydrogen transfer over MgO, VI dehydrogenation of 2-ethyl-1-hexanol

The dehydrogenation of 2-ethyl-l-hexanol to 2-ethylhexanal by hydrogen exchange with aliphatic aldehydes has been studied over MgO. As hydrogen acceptors acetaldehyde, propionaldehyde and isobutyraldehyde were used. Reaction with propionaldehyde was found to be an effective synthetic route for 2-ethylhexanal preparation, whereas during reactions with acetaldehyde and isobutyraldehyde a gradual catalyst deactivation vs. time-on-stream was observed.Part V in Stud. Surf. Sci. Catal., 78, 631 (1993) Fine Chemicals III), and references therein.