Ni-Fe/Al_2O_3催化剂催化乙醇水蒸气重整制氢研究

利用浸渍法制备了不同组成的Ni-Fe/Al2O3催化剂,对催化剂进行了X射线衍射(XRD)表征。以乙醇水蒸气重整(SRE)反应为探针,采用固定床反应器考察了催化剂组成、反应温度对活性和选择性的影响。实验结果表明,Ni-Fe/Al2O3较Ni,Fe单独担载的Ni/Al2O3,Fe/Al2O3选择性高,低温活性好,Ni是主要活性组分,Ni,Fe配比影响活性和选择性,其中Ni10Fe5性能最佳。400℃时,乙醇转化率可达100%,H2,CO和CO2选择性分别55.4%,0.86%和82.18%;450℃时,乙醇转化率为100%,H2,CO和CO2选择性分别67.18%,4.30%和91.01%,且反应温度影响SRE反应系统中各相关反应在系统中的权重。     

Steam reforming of methanol over Cu/ZnO/Al2O3 modified with hydrotalcites

Dilution of a commercial Cu/ZnO/Al₂O₃ (CZA) catalyst by well-crystallized MgAl hydrotalcite nitrate (HTNO₃) and chloride (HTCl) resulted in the formation of the modified samples CZA–HTN and CZA–HTCl, respectively. The samples were characterized by N₂ sorption and XRD measurements. The structures of the CZA–HT materials proved to be more compact than those of the pristine clays. The modified samples were investigated as catalysts for the steam reforming of methanol under steady state conditions. The catalytic activity and the long-term stability of CZA–HT were found to depend strongly on the nature of the interlamellar anion of HT. CZA–HTN exhibited a marked catalytic activity and an enhanced thermal stability. It was pointed out that dilution with HTNO₃ improved the catalytic performance of CZA by increasing the methanol conversion and decreasing the CO production. The moderate increase in the methanol conversion for CZA–HTN during time-on-stream was attributed to partial delamination of the HT structure under SRM conditions. The application of an enhanced H₂O:MeOH ratio of 1.3 for CZA–HTN was found to decrease both the methanol conversion and the CO formation to an appreciable extent.     

Steam methane reforming in a Ni/Al2O3 catalyst: Kinetics and diffusional limitations in extrudates

The true kinetics of methane steam reforming was measured in powder of Ni/Al₂O₃ catalyst (“Octolyst 1001” from Degussa) at different temperatures (733–890 K) for several operating conditions. New reaction rate constants were determined for this catalyst. The observed reaction rate was measured on catalyst extrudates to determine diffusion effects within the porous structure of the particle. A non‐isothermal model with diffusion was used to determine effectiveness factors for each reaction. The objective was to measure all necessary data to model the performance of the catalyst in a Sorption Enhanced Reaction Process (SERP) for H₂ production with in situ CO₂ capture.     

Hydrogen production from glycerol by reforming in supercritical water over Ru/Al2O3 catalyst

Supercritical water is a promising medium for the reforming of hydrocarbons and alcohols for the production of hydrogen at high pressures in a short reaction time. Water serves both as a dense solvent as well as a reactant. In this work, hydrogen is produced from glycerol by supercritical water reforming over a Ru/Al₂O₃ catalyst with low methane and carbon monoxide formation. Experiments were conducted in a tubular fixed-bed flow reactor over a temperature range of 700–800 °C, feed concentrations up to 40 wt% glycerol, all at short reaction time of less than 5 s. Glycerol was completely gasified to hydrogen, carbon dioxide, and methane along with small amounts of carbon monoxide. At dilute feed concentrations, near-theoretical yield of 7 mol of hydrogen/mol of glycerol was obtained, which decreases with an increase in the feed concentration. Based on a kinetic model for glycerol reforming, an activation energy of 55.9 kJ/mol was observed.     

Steady-state methanation kinetics over a Ni/Al2O3 catalyst

Extensive kinetic data for the methanation reaction over a Ni/Al₂O₃ catalyst were obtained in a specially designed gradientless reactor operating at steady state. The reactor pressure was 101.3 kPa, and three temperatures were used, namely, 503, 513 and 523 K. The following three-parameter phenomenological model based on a proposed Langmuir-Hinshelwood mechanism adequately describes the data: r = L² K₃ K₄^0.5 k₅ P^0.5H₂ Pco/ [1 + K₃ (k₅ / k₆)Pco + K₄^0.5 P^0.5H₂ ]² With dissociative adsorption of hydrogen and hydrogen-assisted dissociation of adsorbed carbon monoxide, the postulated mari is the CH surface group, and the rds is the hydrogenation of the surface CH group.     

Hydrogen production from ethanol steam reforming over Rh/CeO2 catalyst

Hydrogen production from ethanol steam reforming over an Rh/CeO₂ catalyst was investigated with a stoichiometric feed composition. Ethanol was entirely converted to hydrogen and C₁ products (CO, CO₂, CH₄) at 400 °C due to the remarkable C–C bond cleavage capacity of Rh species. The Rh/CeO₂ catalyst exhibited stable activity and selectivity without the obvious deactivation during 70 h on stream test. Structural analysis of the aged catalysts indicated that the strong interaction between Rh and ceria support efficiently inhibited Rh particles sintering (stable at around 2 nm) and coke formation to guarantee catalyst stability.     

Autothermal reforming of ethanol for hydrogen production over an Rh/CeO2 catalyst

Hydrogen production from ethanol by autothermal reforming over an Rh/CeO₂ catalyst was investigated with a stoichiometric feed composition. Ethanol as well as the reaction intermediates like acetaldehyde and acetone was entirely converted to hydrogen and C1 products at 673 K, and methane steam reforming and reverse water gas shift were the major reactions above 823 K. The Rh/CeO₂ catalyst exhibited stable activity and selectivity during 70 h on-stream operation at 823–923 K without obvious deactivation evidenced by the constant effluent gas composition. Structural analysis of the used catalyst revealed that CeO₂ prevented effectively the highly dispersed Rh particles with sizes of 1–3 nm from sintering and thus maintained sufficient Rh–CeO₂ interfacial areas, which facilitated coke gasification through the high oxygen storage-release capacity.     

Co-M/Al2O3上环己烷的选择性氧化研究

采用溶胶-凝胶法制备了Co-M/Al₂O₃(M=Cu，Zn，Ni)催化剂。在没有任何有机溶剂或助剂的条件下，研究了以空气为氧化剂的环己烷选择性氧化。所制备四种催化剂的活性为Co-Ni/Al₂O₃ >Co/Al₂O₃ >Co-Zn/Al₂O₃ >Co-Cu/Al₂O₃。在Co-Ni/Al₂O₃中Co、Ni的质量分数分别为4.0%和3.0%时活性最好。以Co-Ni/Al₂O₃为催化剂，在4.5 MPa、443 K下反应120 min，环己烷转化率达9.9%，环己酮和环己醇的总选择性达94.6%，n(酮)∶n(醇)为2.8。Co-Ni/Al₂O₃催化剂连续使用五次后活性基本不变。     

Transformation of cyclopentanone into cyclopentanethiol over a sulfided CoMo/Al2O3 catalyst

The transformation of cyclopentanone in the presence of H₂S/H₂ was investigated at atmospheric pressure over a sulfided CoMo/Al₂O₃ catalyst. The main reaction products were cyclopentanethiol and cyclopentene, the relative amounts of which depended on the reaction temperature and on the H₂S to cyclopentanone molar ratio. The best results were obtained at 220°C, with a 2.5 H₂S to cyclopentanone molar ratio: under these conditions, the cyclopentanethiol molar selectivity remained at about 90%, in a range of cyclopentanone conversion of 10–70%.     

Bio-template fabrication of nanoporous Ni@Al2O3: Durable catalyst for biogas reforming reaction

Following green chemistry principles and the significant role of catalysts in chemical transformations, in this study, for the first time, Ni@Al₂O₃ nanoparticles were prepared via a green, a sustainable, and practical approach using the waste management concept. To achieve this goal, the eggplant skin was employed as an abundant and green bio-template to synthesize desired materials, applying for biogas reforming (CH₄/CO₂ = 1:1) at four temperatures (600–750 °C). Synthesized materials were fully characterized and according to the findings, the bio-template was able to induce its structure on prepared materials and had a considerable effect on the activity of nickel-based alumina catalysts thanks to the high dispersion of Ni nanoparticles on the prepared materials. This catalyst could tolerate the reaction conditions even after 30 h of the catalytic run at 650 °C, along with a remarkable coke resistance (less than 4% carbon deposition).     

Steam reforming of ethanol on a Ni/Al2O3 catalyst coupled with a hydrotalcite‐like sorbent in a multilayer pattern for co2 uptake

Steam reforming of ethanol (SRE) on a Ni/Al₂O₃ catalyst was studied. The effects of the operating conditions and catalyst nature on the course of reaction were evaluated. Hydrogen was generated in the temperature range between 100 and 600°C. A mechanism was used to explain the reaction pathways. A commercial hydrotalcite‐like sorbent arranged in a multilayer pattern of catalyst and sorbent was used for CO₂‐uptake to enhance hydrogen production. The concept of sorption enhanced reaction process on SRE is illustrated by the operation of catalyst and CO₂‐sorbent at 400°C. A lower flow rate regime and multilayer pattern system enhances hydrogen production in the initial breakthrough periods. CO appears in traces in the product gas stream. © 2011 Canadian Society for Chemical Engineering     

Stable carbon dioxide reforming of methane over modified Ni/Al2O3 catalysts

CO₂ reforming of methane was studied over modified Ni/Al₂O₃ catalysts. The metal modifiers were Co, Cu, Zr, Mn, Mo, Ti, Ag and Sn. Relative to unmodified Ni/Al₂O₃, catalysts modified with Co, Cu and Zr showed slightly improved activity, while other promoters reduced the activity of CO₂ reforming. Mn-promoted catalyst showed a remarkable reduction in coke deposition, while entailing only a small reduction in catalytic activity compared to unmodified catalyst. The catalysts prepared at high calcination temperatures showed higher activity than those prepared at low calcination temperature. The Mn-promoted catalyst showed very low coke deposition even in the absence of diluent gas and the activity changed only slightly during 100 h operation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ni-Cu-Mo/Al_2O_3催化剂用于CH_4/CO_2重整的研究

甲烷和二氧化碳重整制合成气是有效利用二氧化碳资源的重要途径,对于环境保护和综合利用资源具有重大意义。文章采用浸渍法制备一系列不同镍钼质量比的Ni-Cu-Mo/Al_2O_3催化剂,通过固定床反应器考察不同Ni/Mo质量比和反应温度对催化剂性能的影响,并采用XRD,BET,SEM,CO_2-TPD技术对催化剂进行了表征。结果表明:催化剂的最佳反应温度是800℃,Ni/Mo质量比为0.75的催化剂表现出最好的催化活性。在800℃,空速182 m L/(g·min)的反应条件下,CH_4、CO_2的转化率分别为97.7%,99.1%,CO,H2的选择性分别达到94.4%,92.1%。     

Selective catalytic hydrogenation of naphthalene to tetralin over a Ni-Mo/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 °C, 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.     

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.     

甲烷催化燃烧用LaMn/Al_2O_3催化剂研究

为获得具有优良低温活性的甲烷燃烧用催化剂,采用稀土La作为助剂制备了系列Mn基催化剂,借助X射线衍射(XRD)、X射线光电子能谱(XPS)和程序升温还原(TPR)技术对催化剂的结构进行了表征,并评价了其对甲烷燃烧的低温催化性能。结果表明,La助剂的添加显著促进了活性组分MnO2的分散,使其更易于还原,且使Mn4+和晶格氧富集于催化剂表面,因而显著提高了催化剂对甲烷催化燃烧的低温活性。当La质量分数为5%时,催化活性最高,甲烷50%转化率对应的温度较未加助剂时降低了70℃,且完全转化的温度低至480℃。     

Kinetic measurements of CH4 combustion over a 10% PdO/ZrO2 catalyst using an annular flow microreactor

A kinetic study on CH₄ combustion over a PdO/ZrO₂ (10%, w/w) catalyst has been performed in a temperature range between 400 and 550 °C by means of an annular catalytic microreactor.

The role of mass transfer phenomena including diffusion in the catalyst pore, gas–solid diffusion and axial diffusion in the gas phase, has been preliminary addressed by means of mathematical modeling. Simulation results have pointed out the key role of internal diffusion showing that thicknesses of the active catalyst layer as thin as 10–15 μm are required to minimize the impact of mass transfer limitations. The thermal behavior of the reactor has been also addressed by means of catalytic combustion tests with CH₄ and CO–H₂ mixtures as fuels. The results have demonstrated the possibility to obtain nearly isothermal temperature profiles under severe conditions (up to 3% of CH₄) thanks to effective dissipation of reaction heat by radiation from the catalyst outer skin.

Finally the effect of reactants (CH₄ and O₂) and products (H₂O and CO₂) on CH₄ combustion rate has been addressed. The results have shown that both H₂O and CO₂ markedly inhibit the reaction up to 550 °C. The data have been fitted by the following simple power law expression r=k_rP_CH4P_H2O^−0.32P_CO2^−0.25 with an apparent activation energy of 108 kJ/mol.

Evidences have been found and discussed indicating a key role of the support on the extent of such inhibition effects.     

Steam effect on NO x reduction over lean NO x trap Pt–BaO/Al2O3 model catalyst

The effect of steam on NO _x reduction over lean NO _x trap (LNT) Pt–Ba/Al₂O₃ and Pt/Al₂O₃ model catalysts was investigated with reaction protocols of rich steady-state followed by lean–rich cyclic operations using CO and C₃H₈ as reductants, respectively. Compared to dry atmosphere, steam promoted NO _x reduction; however, under rich conditions the primary reduction product was NH₃. The results of NO _x reduction and NH₃ selectivity versus temperature, combined with temperature programmed reduction of stored NO _x over Pt–BaO/Al₂O₃ suggest that steam causes NH₃ formation over Pt sites via reduction of NO _x by hydrogen that is generated via water gas shift for CO/steam, or via steam reforming for C₃H₈/steam. During the rich mode of lean–rich cyclic operation with lean–rich duration ratio of 60 /20 s, not only the feed NO, but also the stored NO _x contributed to NH₃ formation. The NH₃ formed under these conditions could be effectively trapped by a downstream bed of Co²⁺ exchanged Beta zeolite. When the cyclic operation was switched into lean mode at T < 450 °C, the trapped ammonia in turn participated in additional NO _x reduction, leading to improved NO _x storage efficiency.     

镧钡改性氧化铝负载钯、铑的催化活性研究

采用纯γ-氧化铝和改性氧化铝（2.5%La2.5%Ba/Al2O3）为担体,经550 ℃,950 ℃不同温度煅烧后分别负载钯、铑,制备成系列催化活性材料,通过贵金属分散度分析、TPR氧化还原特性分析,研究了氧化铝制备条件对催化活性的影响。结果表明,改性氧化铝上的贵金属分散性优于纯γ-氧化铝,Rh3⁺与2.5%La2.5%Ba/Al₂O₃间的相互作用强于Pd²⁺,从而具有更高的分散度;钯在高温处理后的2.5%La2.5%Ba/Al₂O₃上的分散性更优,铑则相反。通过TPR还原特性分析认为,贵金属在950 ℃煅烧后的2.5%La2.5%Ba/Al₂O₃上的低温还原活性更佳,钯与2.5%La2.5%Ba/Al₂O₃结合的低温还原活性优于铑。