Methylcyclohexane dehydrogenation for hydrogen production via a bimodal catalytic membrane reactor

The dehydrogenation of methylcyclohexane (MCH) to toluene (TOL) for hydrogen production was theoretically and experimentally investigated in a bimodal catalytic membrane reactor (CMR), that combined Pt/Al₂O₃ catalysts with a hydrogen‐selective organosilica membrane prepared via sol‐gel processing using bis(triethoxysilyl) ethane (BTESE). Effects of operating conditions on the membrane reactor performance were systematically investigated, and the experimental results were in good agreement with those calculated by a simulation model with a fitted catalyst loading. With H₂ extraction from the reaction stream to the permeate stream, MCH conversion at 250°C was significantly increased beyond the equilibrium conversion of 0.44–0.86. Because of the high H₂ selectivity and permeance of BTESE‐derived membranes, a H₂ flow with purity higher than 99.8% was obtained in the permeate stream, and the H₂ recovery ratio reached 0.99 in a pressurized reactor. A system that combined the CMR with a fixed‐bed prereactor was proposed for MCH dehydrogenation. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1628–1638, 2015     

High purity hydrogen production by low temperature catalytic ammonia decomposition in a multifunctional membrane reactor

Catalytic ammonia decomposition for the generation of high purity CO_x free hydrogen has been performed in a multifunctional membrane reactor with Pd membrane walls for the hydrogen separation and a high performance Ru-carbon catalyst. By adjusting the experimental conditions an enhancement of the efficiency of the system for the hydrogen production has been achieved. The chemical thermodynamic equilibrium conversion has been exceeded using an improved catalyst, at temperatures lower than those reported in the literature. In addition, both the membrane and the catalyst components were very stable. The system showed no loss of performance after having been operated for several cycles.     

Catalytic ammonia decomposition: COx-free hydrogen production for fuel cell applications

Catalytic decomposition of ammonia has been investigated as a method to produce hydrogen for fuel cell applications. The absence of any undesirable by-products (unlike, e.g., CO_x, formed during reforming of hydrocarbons and alcohols) makes this process an ideal source of hydrogen for fuel cells. In this study a variety of supported metal catalysts have been studied. Supported Ru catalysts were found to be the most active, whereas supported Ni catalysts were the least active. The supports were found to play a profound role in the ammonia decomposition process. The activation energies for the ammonia decomposition process varied from 17 to 22 kcal/mol depending upon the catalyst employed. The activation energies of the supported Ir catalysts were found to be in excellent agreement with our recent studies addressing ammonia decomposition on single crystal Ir.     

氨分解制氢催化剂研究进展

随着环保法规日趋严格,清洁氢能的生产和应用引起关注,氨分解制氢是其中重要途径之一。综述Ru、Ni和Fe等氨分解催化剂的研究进展,Ru催化剂具有较高的催化活性,但由于资源有限和价格昂贵等因素使其在工业应用方面受到限制。以Fe和Ni为代表的非贵金属催化剂资源丰富,价格低廉,氨分解反应转化率高,具有潜在的工业应用前景。我国独创的新一代Fe_(1-x)O基新型熔铁催化剂是目前世界上活性最高的氨合成催化剂,根据微观可逆性原理,新型熔铁催化剂也是氨分解反应活性最好的制氢催化剂。     

钯膜反应器制氢研究进展

钯膜与水蒸汽重整反应器集成使反应与分离一体化,在降低装置投资成本和节能降耗方面具有明显优势和发展前景,受到研究者的青睐。综述了固定床和流化床钯膜反应器规模验证方面的研究进展,并指出钯膜反应器制氢工业化进程中可能会遇到的问题和需要解决的问题。     

电催化分解氨制氢研究进展

氢能作为一种理想的能源载体之一，近些年来受制于储存和运输的难题并未大规模发展。但随着电催化技术的成熟，在温和条件下，通过电催化分解含氢介质的制氢路线或将具备规模化开发清洁能源的潜力。氨(NH₃)具有高储氢密度(17.6%，质量分数)、运输便利、无碳等优点，被认为是合适的储氢介质之一。电催化分解氨的过程主要包括析氢反应(hydrogen evolution reaction， HER)和氨氧化反应(ammonia oxidation reaction， AOR)。重点综述了阳极电催化分解氨的反应机理及AOR催化剂的研究现状，对氨氧化技术的发展和应用进行了总结和展望，可为开发具有更高活性、稳定性的AOR催化剂和“以氨制储氢”的发展路线提供思路和指导。     

Synthesis and catalytic properties of porous Ta carbide crystallites for hydrogen production from the decomposition of ammonia

Synthesis and catalytic properties of porous tantalum carbide crystallites for hydrogen production from the decomposition of ammonia were investigated using eight different samples which have been synthesized via temperature-programmed reduction method of Ta₂O₅ with pure CH₄. The Ta carbide crystallites synthesized using two different heating rates and space velocity showed the different surface areas. These results indicated that the structural properties of these materials have been related to the preparative conditions:heating rate and space velocity employed. The O₂ uptake has a linear relation with the BET surface area of tantalum carbides. The slope of the straight line corresponds to a site density showing an oxygen capacity of 1.36 × 10¹³ O/cm². The tantalum carbide crystallites were very active for ammonia decomposition with catalytic properties that were superior to commercial Ta carbide catalysts (Aldrich). It was also observed that the tantalum carbide crystallites were as much as two orders of magnitude more active than Pt/C catalyst (Engelhard). The activity increased with the decrease of particle size, suggesting the presence of the structure-sensitivity. The highest activity in tantalum carbides was observed at an atomic ratio of C₁/Ta^δ+ = 0.85, suggesting the presence of electron transfer between Ta metals and carbon (C₁) in Ta carbide crystallites.     

Ni- and Fe-based catalysts for hydrogen and carbon nanofilament production by catalytic decomposition of methane in a rotary bed reactor

Four catalysts, consisting of Ni, Ni:Cu, Fe or Fe:Mo as the active phase and Al₂O₃ or MgO as a textural promoter, were tested for the catalytic decomposition of methane in a rotary bed reactor, obtaining both CO₂-free hydrogen and carbon nanostructures in a single step. Hydrogen yields of up to 14.4 Ndm³ H₂·(h·g_cat)^− 1 were obtained using the Ni-based catalysts, and methane conversions above 80% were observed with the Fe-based catalysts. In addition to hydrogen production, the Ni-based catalysts allowed the large-scale production of fishbone-like carbon nanofibres, whereas the use of the Fe-based catalysts promoted the production of carbonaceous filaments having a high degree of structural order, consisting of both chain-like carbon nanofibres and carbon nanotubes.     

Upgrading of a syngas mixture for pure hydrogen production in a Pd-Ag membrane reactor

Water gas shift (WGS) is a thermodynamics limited reaction and CO equilibrium conversion of a traditional reactor is furthermore reduced owing to the presence of H₂ (ca. 50%) in the feed stream coming from a reformer.The upgrading of a simulated reformate stream was experimentally investigated as a function of temperature (280-320 °C), feed pressure (up to 600 kPa), gas hourly space velocity (GHSV), etc. using a Pd-alloy membrane reactor (MR) packed with a commercial catalyst CuO/CeO₂/Al₂O₃; no sweep gas was used. The MR performance was also evaluated using new parameters such as conversion index, H₂ recovery and extraction index, etc., which evidence the advantages with respect to a traditional reactor.A Pd-based MR operated successfully overcoming the thermodynamic constraints of a traditional reactor and, specifically, the drawback introduced by the hydrogen presence. In fact, a CO conversion of 90% significantly exceeded (three times) the thermodynamics upper limit (<36%) of a traditional reactor owing to ca. 80% of hydrogen permeated through the membrane.The overall process performance was significantly improved by the presence of the Pd-based membrane and, thus, by the high reaction pressure which allowed and drove the hydrogen permeation.     

微波辐射下活性炭催化甲烷裂解制氢

采用石英管固定床反应器,在微波加热条件下分别研究了气氛条件、甲烷分压以及铁粉对活性炭催化裂解甲烷的影响,并与传统电加热方式下的甲烷裂解特性进行了对比研究。结果表明,活性炭在不同气氛条件下表现出不同的升温特性,活性炭在氮气和氢气中的升温效果优于甲烷气氛。铁粉的掺入有利于提高活性炭反应温度,从而促进甲烷的转化率。对反应前后的活性炭进行了扫描电镜和比表面积分析,结果表明甲烷裂解后产生的大量积炭覆盖在活性炭表面,导致比表面积和孔容减小,平均孔径增大。进而推测活性炭活性降低的主要原因是由于积炭堵塞了活性炭微孔,减少了甲烷与活性炭微孔中的活性中心位的接触。     

镍基氨分解制氢催化剂的制备及性能

用浸渍法制备Ni/Al_2O_3和Ni/xMo-Al_2O_3催化剂,以氨分解为模型反应,考察Ni负载量、焙烧温度、溶剂和助剂等合成条件对催化剂催化性能的影响,通过XRD和TG-DTG表征方法对催化剂进行表征。结果表明,最佳合成条件:Ni负载质量分数为16%,焙烧温度350℃,采用丙酮为溶剂制备的Ni/Al_2O_3催化剂具有较好的催化活性。500℃添加质量分数3%的助剂Mo可以使Ni/Al_2O_3催化剂的活性显著提高39%,Ni/3%Mo-Al_2O_3催化剂的氨分解率达93.5%。     

氨分解制氢催化剂改性研究进展

在氨分解制氢技术中催化剂的选取尤为重要,其组成、形貌结构、载体、助剂等均能影响催化剂活性发挥。本文综述了近几年国内外氨分解制氢催化剂的改性研究现状,对催化剂的形貌结构变化、不同载体的影响、助剂的添加、矿石及工业废品在氨分解中的应用进行了详细的介绍,指出有效发挥催化剂和载体、助剂等之间的协同作用,改善外部条件,对于实现氨分解制氢具有很好的潜在实用价值,进一步设计出低压、低温、高活性氨分解的新型催化剂,降低能量消耗是未来氨分解催化剂的研究方向。     

甲烷催化裂解制氢和碳纳米材料研究进展

甲烷通过催化裂解反应可生成不含碳氧化合物（CO_x）的高纯氢和碳纳米材料（如碳纤维或碳纳米管等）,对我国能源结构的调整及新材料的应用具有重要意义。与其他制氢工艺相比,甲烷催化裂解制氢工艺具有反应过程简单、产物清洁无污染、反应成本低等优点,因此该工艺具有重要的工业应用前景。本文重点阐述了催化剂（活性组分、催化剂载体、制备方法等）以及反应条件（催化剂还原条件、空速、反应温度等）对甲烷转化率、氢气产率和碳纳米材料（形貌和产量）的影响并对甲烷催化裂解反应机理、催化剂的失活与再生进行了概述。甲烷催化裂解反应目前仍处于实验室研究阶段,高效催化剂的研制以及流化床反应器的优化是该反应实现工业化应用的必要前提。     

Integrated membrane system for pure hydrogen production: A Pd-Ag membrane reactor and a PEMFC

In this work, an integrated system consisting of single stage hydrogen production and a commercial PEMFC was investigated experimentally. The CO-free hydrogen fed to the PEMFC was produced in a Pd-Ag membrane reactor (MR), upgrading a syngas stream with a composition similar to that coming out of a reformer (CO 45%; H₂ 50%; CO₂ 4%; N₂ balance, on dry basis). The performance of the MR was evaluated in terms of CO conversion and H₂ recovery as a function of the feed pressure (up to 600 kPa) and space velocity; no sweep gas was used for promoting the H₂ permeation, since this role was assigned exclusively to the feed pressure.Special attention was paid to the analysis of the integrated system, focusing on the influence of the Pd-Ag MR operating conditions on the electrical performance of the PEMFC. The PEMFC internal crossover was also considered to have an effect on the electrical performance and this was taken into account estimating the PEMFC actual efficiency. Furthermore, the chemical efficiency of the integrated membrane plant was evaluated, considering the H₂ converted into electricity with respect to the total amount of H₂ contained in the feed mixture. An interesting performance was shown by the integrated system since the PEMFC performance was close to the power nominal value.     

温和条件下水合肼催化分解制氢研究进展

水合肼（N2H4?H2O）的氢质量分数高达8.0%,完全分解时副产物仅为N2,且在温和条件下物理化学性质较为稳定,因此可以作为一种理想的移动氢源,在一些特殊场合为燃料电池提供氢气。本文概述了温和条件下水合肼分解制氢反应所使用的催化体系,具体包括金属纳米粒子、复合氧化物及负载型催化剂。简要介绍了肼分解过程的机理,并分析了影响水合肼分解制氢选择性的因素,包括催化剂中活性金属的特性、反应条件及助剂的性质对催化剂选择性的影响。总结了现阶段水合肼分解制氢催化剂的优缺点,为进一步开发高效、高选择性的水合肼分解制氢催化剂提供借鉴,并为涉及N—H键及N—N键断裂的其他反应催化剂设计提供参考。     

氨硼烷分解制氢及其再生的研究进展

氨硼烷具有储氢密度高（152.9g/L）、放氢条件温和、无毒以及常温下为稳定的固体而易于储运等特点而成为最有前景的储氢材料之一。本文综述了近年来氨硼烷在不同催化剂作用下,通过热解、醇解和水解这3种方式制氢以及分解后的副产物循环再生氨硼烷的研究进展。分析讨论了氨硼烷的热解制氢研究主要集中在降低温度和抑制气态副产物的生成这两方面,而水解或醇解制氢的研究热点是二元或三元非贵金属纳米核壳或负载型催化剂。与氨硼烷的热解相比,水解或醇解由于条件温和、制氢速度快而更具实用性。指出氨硼烷作为储氢材料最大的挑战是其再生问题,氨硼烷分解脱氢后的副产物不能直接氢化而再生氨硼烷,需要通过一系列反应来进行间接的离线再生,因此氨硼烷的再生将是今后的重点研究方向。     

Simulation of autothermal reforming in a staged‐separation membrane reactor for pure hydrogen production

Steam methane reforming with oxygen input is simulated in staged‐separation membrane reactors. The configuration retains the advantage of regular membrane reactors for achieving super‐equilibrium conversion, but reaction and membrane separation are carried out in two separate units. Equilibrium is assumed in the models given the excess of catalyst. The optimal pure hydrogen yield is obtained with 55% of the total membrane area allocated to the first of two modules. The performance of the process with pure oxygen input is only marginally better than with air. Oxygen must be added in split mode to reach autothermal operation for both reformer modules, and the oxygen input to each module depends on the process conditions. The effects of temperature, steam‐to‐carbon ratio and pressure of the reformer and the area of the membrane modules are investigated for various conditions. Compared with a traditional reformer with an ex situ membrane purifier downstream, the staged reactor is capable of much better pure hydrogen yield for the same autothermal reforming operating conditions.     

Effect of hydrogen combustion reaction on the dehydrogenation of ethane in a fixed-bed catalytic membrane reactor

A two-dimensional non-isothermal mathematical model has been developed for the ethane dehydrogenation reaction in a fixed-bed catalytic membrane reactor. Since ethane dehydrogenation is an equilibrium reaction, removal of produced hydrogen by the membrane shifts the thermodynamic equilibrium to ethylene production. For further displacement of the dehydrogenation reaction, oxidative dehydrogenation method has been used. Since ethane dehydrogenation is an endothermic reaction, the energy produced by the oxidative dehydrogena-tion method is consumed by the dehydrogenation reaction. The results show that the oxidative dehydrogenation method generated a substantial improvement in the reactor performance in terms of high conversions and significant energy saving. It was also established that the sweep gas velocity in the shell side of the reactor is one of the most important factors in the effectiveness of the reactor.     

Computer modelling and numerical analysis of hydrodynamics and heat transfer in non-porous catalytic reactor for the decomposition of ammonia

Chemical reactors exhibit very complex behaviours such as multiple steady states, oscillations, etc. resulting from complex linkage between the transport processes and the non-linear chemical reaction kinetics. Ammonia is a potential hydrogen source for a number of fuel cell applications for small scale power generation useful for portable equipments. In the present work, we analyse the fluid dynamics and heat transfer in catalytic microreactor systems for the decomposition of ammonia over a monolayer Ni non-porous catalyst. The overall model for this convective-diffusive-reactive system consists of a flow model, a mass transport model, an energy conservation model and a reaction kinetics model for ammonia decomposition. The flow model is described by the Stokes equation for a creeping flow regime. The mass transport and energy conservation models are based on convective-diffusion equations. The rate of ammonia decomposition can be measured as a function of the catalyst activity and ammonia concentration. A standard Galerkin finite element technique has been applied for the solution of the flow equations. A slightly perturbed form of the mass continuity equation is used to satisfy the Ladyzhenskaya-Babuška-Brezzi stability criterion. For the solution of convection-diffusion equations, a streamline inconsistent upwind finite element scheme has been chosen to avoid any spurious oscillations. C⁰-continuous 9-noded Lagrangian biquadratic isoparametric finite elements are used for the approximation of the field variables. A second-order Taylor-Galerkin time-stepping scheme has been chosen for the temporal discretisation of the flow equations whilst an implicit theta method has been used for convection-diffusion equations. The results are presented in the form of velocity vectors and concentration, temperature contours and are examined for stability, convergence and theoretical consistency.     

氨分解制氢镍基催化剂研究进展

氨分解制氢清洁高效,易于工业化使用,是一种极具前景的便携式制氢方法。镍作为氨分解非贵金属催化剂中性能最好、应用最广的催化剂,但仍存在低温活性低、易烧结等问题亟需改进。本文概括了氨分解反应的反应机理、动力学和热力学,综述了近年来国内外氨分解镍基催化剂的研究现状。研究者从镍金属活性中心调控出发进行研究,发现调节镍粒子尺寸、加入第二金属(Fe、Co、Mo等)、载体(Al₂O₃、SiO₂、分子筛等)、助剂(碱土金属、稀土金属等)以及设计核壳结构进行调控,可提高镍金属的分散性和抗烧结能力。本文在以上基础上提出了镍基催化剂的改进措施和未来发展方向,以期为进一步设计出低温高活性镍基催化剂提供依据。