Hydrogen production from steam reforming of methanol over CuO/ZnO/Al_2O_3 catalysts: Catalytic performance and kinetic modeling

A series of CuO/ZnO/Al_2O_3, CuO/ZnO/ZrO_2/Al_2O_3 and CuO/ZnO/CeO_2/Al_2O_3 catalysts were prepared by coprecipitation and characterized by N_2 adsorption, XRD, TPR, N_2O titration and HRTEM. The catalytic performances of these catalysts for the steam reforming of methanol were evaluated in a laboratory-scale fixed-bed reactor at 0.1 MPa and temperatures between 473 and 543 K. The results showed that the catalytic activity depended greatly on the catalyst reducibility and the specific surface area of Cu. An approximate linear correlation between the catalytic activity and the Cu surface area was found for all catalysts investigated in this study.Compared to CuO/ZnO/Al_2O_3, the ZrO_2-doped CuO/ZnO/Al_2O_3 exhibited higher activity and selectivity to CO,while the CeO_2-doped catalyst displayed lower activity and selectivity. Finally, an intrinsic kinetic study was carried out over a screened CuO/ZnO/CeO_2/Al_2O_3 catalyst in the absence of internal and external mass transfer effects. A good agreement was observed between the model-derived effluent concentrations of CO(CO_2) and the experimental data. The activation energies for the reactions of methanol-steam reforming, water-gas shift and methanol decomposition over CuO/ZnO/CeO_2/Al_2O_3 were 93.1, 85.1 and 116.5 k J·mol^(-1), respectively.

High-efficient solar-driven hydrogen production by full-spectrum synergistic photo-thermo-catalytic methanol steam reforming with in-situ photoreduced Pt-CuO_(x) catalyst

Synergy between the intrinsic photon and thermal effects from full-spectrum sunlight for H_(2) production is considered to be central to further improve solar-driven H_(2) production.To that end,the photo-thermocatalyst that demonstrates both photoelectronic and photothermal conversion capabilities have drawn much attention recently.Here,we propose a novel synergistic full-spectrum photo-thermo-catalysis technique for high-efficient H_(2) production by solar-driven methanol steam reforming(MSR),along with the Pt-Cu Oxphoto-thermo-catalyst featuring Pt-Cu/Cu_(2)O/CuO heterojunctions by Pt-mediated in-situ photoreduction of Cu O.The results show that the H_(2) production performance rises superlinearly with increasing light intensity.The optimal H_(2) production rate of 1.6 mol g^(-1) h^(-1) with the corresponding solar-to-hydrogen conversion efficiency of 7%and the CO selectivity of 5%is achieved under 15×sun full-spectrum irradiance(1×sun=1 k W m^(-2))at 180°C,which is much more efficient than the previously-reported Cu-based thermo-catalysts for MSR normally operating at 250~350°C.These attractive performances result from the optimized reaction kinetics in terms of intensified intermediate adsorption and accelerated carrier transfer by long-wave photothermal effect,and reduced activation barrier by short-wave photoelectronic effect,due to the broadened full-spectrum absorbability of catalyst.This work has brought us into the innovative technology of full-spectrum synergistic photothermo-catalysis,which is envisioned to expand the application fields of high-efficient solar fuel production.

Reaction parameters influence on the catalytic performance of copper-silica aerogel in the methanol steam reforming

Steam reforming of methanol was carried out on the copper-silica aerogel catalyst.The effects of reaction temperature,feed rate,water to methanol molar ratio and carrier gas flowrate on the H_2 production rate and CO selectivity were investigated.M ethanol conversion was increased considerably in the range of about 240-300,after which it increased at a slightly lower rate.The used feed flowrate,steam to methanol molar ratio and carrier gas flowwere 1.2-9.0 m L/h,1.2-5.0 and 20-80 m L/min,respectively.Reducing the feed flowrate increased the H_2 production rate.It was found that an increase in the water to methanol ratio and decreasing the carrier gas flowrate slightly increases the H2production rate.Increasing the water to methanol ratio causes the lowest temperature in which CO formation was observed to rise,so that for the ratio of 5.0 no CO formation was detected in temperatures lower than 375℃.In all conditions,by approaching the complete conversion,increasing the main product concentration,increasing the temperature and contact time,and decreasing the steam to methanol ratio,the CO selectivity was increased.These results suggested that CO was formed as a secondary product through reverse water-gas shift reaction and did not participate in the methanol steam reforming reaction mechanism.

Kinetics of steam regeneration of SAPO-34 zeolite catalyst in methanol-to-olefins(MTO) process

Methanol-to-olefins(MTO)is industrially applied to produce ethylene and propylene using methanol converted from coal,synthetic gas,and biomass.SAPO-34 zeolites,as the most efficient catalyst in MTO process,are subject to the rapid deactivation due to coke deposition.Recent work shows that steam regeneration can provide advantages such as low carbon dioxide emission and enhanced light olefins yield in MTO process,compared to that by air regeneration.A kinetic study on the steam regeneration of spent SAPO-34 catalyst has been carried out in this work.In doing so,we first investigated the effect of temperature on the regeneration performance by monitoring the crystal structure,acidity,residual coke properties and other structural parameters.The results show that with the increase of regeneration temperature,the compositions of residual coke on the catalyst change from pyrene and phenanthrene to naphthalene,which are normally considered as active hydrocarbon pool species in MTO reaction.However,when the regeneration temperature is too high,nitrogen oxides can be found in the residual coke.Meanwhile,as the regeneration temperature increases,the quantity of residual coke reduces and the acidity,BET surface area and pore structure of the regenerated samples can be better recovered,resulting in prolonging catalyst lifetime.We have further derived the kinetics of steam regeneration,and obtained an activation energy of about 177.8 kJ·mol^(-1).Compared that with air regeneration,the activation energy of steam regeneration is higher,indicating that the steam regeneration process is more difficult to occur.

Simulation Studies of the Hydrogen Production from Methanol Partial Oxidation Steam Reforming by a Tubular Packed-bed Catalytic Reactor

Hydrogen production by partial oxidation steam reforming of methanol over a Cu/ZnO/Al2 O3 cata lyst has been paid more and more attention. The chemical equilibria involved in the methanol partial oxidation steam reforming reaction network such as methanol partial oxidation, methanol steam reforming, decomposition of methanol and water-gas shift reaction have been examined over the ranges of temperature 473-1073 K under normal pressure. Based on the detailed kinetics of these reactions over a Cu/ZnO/Al2O3 catalyst, and from the basic concept of the effectiveness factor, the intraparticle diffusion limitations were taken into account. The effec tiveness factors for each reaction along the bed length were calculated. Then important results were offered for the simulation of this reaction process.

Methanol Steam Reforming Reactions on CuZn(Zr)AlO Catalyst

The catalytic performances of methanol steam reforming reactions on CuZn(Zr)AIO catalysts were studied. When the ZrO2 promoter was added to a CuZnAIO catalyst, its methanol conversion, H2 production and H2 selectivity improved greatly. By using the (?)COPZr-2 catalyst as an example, which exhibited the best catalytic performance, the optimized reaction conditions were established to be: 250℃, 0.1 MPa, H2O/MeOH=1.3, WHSV=3.56 h-1, and without carrier gas. A 150 h stability test of the (?)COPZr-2 catalyst showed that the catalyst had good stability, as the methanol conversion and H2 production could be kept at 88% and 83% respectively. Moreover, outlet H2 and CO contents were>63% and 0.20%-0.31%, respectively.

Methanol Steam Reforming Catalysts for Fuel Cell Driven Electric Vehicles

Cu/ZnAlO catalysts derived from hydroxycarbonate precursors containinghydrotalcite-like layered double hydroxides (LDHs) were studied. The influence on the performanceof the catalysts was also studied when the Al in the Cu/ZnAlO catalyst was partly or completelyreplaced by Zr or Ce.

Study on Performance of Laminated Porous Metal Fiber Sintered Felt as Catalyst Support for Methanol Steam Reforming Microreactor

In this study, the laminated porous metal fiber sintered felt(PMFSF) functioning as catalyst support was used in a cylindrical methanol steam reforming(MSR) microreactor for hydrogen production. The PMFSF was fabricated by the low temperature solid-phase sintering method using metal fibers such as copper fibers and aluminum fibers which are obtained by the multi-tooth cutting method. The two-layer impregnation method was employed to coat Cu/Zn/Al/Zr catalyst on the PMFSF. The effect of fiber material, uniform porosity and gradient porosity on the performance of methano steam reforming microreactor was studied by varying the gas hourly space velocity(GHSV) and reaction temperature. Our results showed that the loading strength of porous copper fiber sintered felt(PCFSF) was better than porous aluminum fiber sintered felt(PAFSF). Under the same reaction conditions, the PCFSF showed higher methanol conversion and more H_2 output than PAFSF. Moreover, the gradient porosity(Type 5: 90%×80%×70%) of PMFSF used as the catalyst support in microreactor demonstrated a best reaction performance for hydrogen production.

High-performance Cu/Zn O/Al_(2)O_(3) catalysts for methanol steam reforming with enhanced Cu-ZnO synergy effect via magnesium assisted strategy

Methanol steam reforming(MSR) is an attractive approach to produce hydrogen for fuel cells.Due to the limited catalyst loading volume and frequent start-ups and shut-downs on board,it is highly desired to develop an extremely active and robust catalyst.Herein,on the basis of industrial Cu/ZnO/Al_(2) O_(3) catalysts,a series of CuZnAl-xMg catalysts with enhanced Cu-ZnO synergy were synthesized via magnesium assisted strategy.The incorporation of magnesium was found to be beneficial to the enhancement of catalytic activity and stability of catalyst.A combination of complementa ry characterizations(e.g.XRD,H_(2)-TPR,N_(2) O chemisorption,TEM,XPS analysis etc.) proves that isomorphous substitution of Cu^(2+)in malachite phase gives rise to more dispersive Cu and ZnO NPs,and the increased Cu^(+)/Cu~0 ratio indicates the strengthened Cu-ZnO synergy effect,which leads to the boosted stability during the thermal treatment.

Methanol Steam Reforming over Na-Doped ZnO-Al2O3 Catalysts

In this study, the catalyst composition in binary ZnO-Al2O3 catalyst was initially evaluated and optimized for methanol steam reforming. Then different Na contents were loaded by an incipient wetness impregnation method onto the optimized ZnAl catalyst. It was found that the activity was greatly enhanced by the modification of Na, which depended on the Na content in the catalyst. The methanol conversion was 96% on a 0.1 Na/0.4 ZnAl catalyst (GHSV = 14,040 h-1, S/C = 1.4, 350°C), which was much higher with respect to a Na-free 0.4 ZnAl catalyst (74%). The remarkable improvement of activity was attributed to a weakening of the C-H bonds and clear of hydroxyl group by the Na dopant leading to an accelerated dehydrogenation of the reaction intermediates formed on ZnAl2O4 spinel surface and thus the overall reaction.

Cu-Al尖晶石氧化物缓释催化剂表面重构对促进甲醇重整反应性能的研究

Cu-Al尖晶石氧化物作为甲醇水蒸气重整制氢缓释催化剂,在反应过程中逐渐释放活性Cu,其催化行为与催化剂的表面结构密切相关。本研究采用酸碱溶液对固相球磨法合成的Cu-Al尖晶石催化剂进行表面处理,以期通过表面组成及结构的修饰来提高其催化性能。研究结果表明,硝酸、氨水、氢氧化钠溶液与催化剂的作用差别极大,酸处理去除了催化剂表面的Cu和Al物种,氢氧化钠溶液处理则主要去除了Al物种,氨水溶液处理作用最弱,去除了极少量的Cu和Al。伴随着Cu、Al物种的流失,催化剂表面结构重组和铜物种再分布改变了铜的缓释行为。反应性能评价结果表明,硝酸和氨水处理改善了缓释催化性能,其中,硝酸处理后的催化剂表现出更优异的催化稳定性;而氢氧化钠溶液处理不利于缓释催化性能的提高。结合反应后催化剂表征结果,阐明缓释Cu粒径大小和Cu晶粒微观结构应变对催化性能发挥着重要作用。当前工作为提高缓释催化提供了一种切实可行的方法。

光热协同甲醇水蒸气重整制氢实验和微观机理研究

针对太阳能光热化学甲醇重整制氢中光热耦合效应及微观机理尚不清楚的问题,采用光热化学和热化学反应对比的研究方式,与微观实验相结合,研究了光热化学甲醇重整中光和热的耦合效应,探究了光和热在微观产物转化中的反应路径。研究结果表明:在较低温度下,光对氢气产率的提升具有促进作用,当其与热化学达到相同氢气产率时,光热化学反应温度降低,造成这种现象的原因是光促进了水的分解、吸附态HCOO*的生成以及碳酸盐的分解,其中水在反应中的作用通过不同水醇比的实验得到了进一步验证;随着温度的升高,固定辐照度下光的促进作用逐渐降低,这是因为光对碳酸盐物质分解的促进作用随温度升高而减弱。研究阐明了光和热的耦合效应,分析了对应的微观机理,为理解光热协同机理提供了理论基础。

Cu-Mn-Al三元尖晶石催化甲醇重整反应特性

以硝酸铜为铜源、拟薄水铝石为铝源、柠檬酸为添加剂,以乙酸锰为第三组分部分取代铜,采用球磨法制备了Cu_(0.7)Mn_(0.3)Al_(2.5)三元固溶体尖晶石催化剂;借助XRD、BET、H_(2)-TPR和XPS等表征技术,对Cu_(0.7)Mn_(0.3)Al_(2.5)的晶相结构、织构性质、还原性质及表面阳离子状态及分布进行研究,并在甲醇水蒸气重整制氢(MSR)反应中考察其缓释催化性能。结果表明,与Cu Al_(2.5)、Cu_(0.7)Zn_(0.3)Al_(2.5)相比,Cu_(0.7)Mn_(0.3)Al_(2.5)的晶粒最小,比表面积最大,且晶胞收缩最大,晶胞常数最小;该催化剂呈富铝状态,但表面尖晶石相Cu^(2+)占比更高,H_(2)气氛下还原难度增大,在MSR反应中表现出较好的缓释催化性能;在温度为265℃、n(H_(2)O)/n(CH_(3)OH)=2、质量空速为2.25 h^(-1)的条件下反应40 h,甲醇转化率高达84%。该研究为研发高效铜基缓释催化剂提供了数据参考。

试验数据驱动的MSRFC系统分析与仿真

甲醇重整高温质子交换膜燃料电池(MSRFC)是一种以甲醇为燃料的清洁高效能源转换装置。建立了目标功率为3.5 kW的MSRFC试验平台,系统测量和分析了高温燃料电池(HT-PEMFC)电堆功率阶跃期和稳定期甲醇燃料供给、重整气组分、电堆性能以及重整器、燃烧器和电堆温度等动态响应特征。基于试验数据研究了样本空间和不同机器学习方法对HT-PEMFC电堆性能预测的准确性和适用性,最终训练了高斯过程回归HT-PEMFC电堆电压预测模型。通过Simulink构建了耦合机器学习电压预测模型和MSRFC子系统能量守恒方程的系统仿真方法,可以准确预测MSRFC系统阶跃期和稳定期的功率、温度和响应时间,相对误差分别控制在1%和3%以内。试验结果和系统仿真模型可以为MSRFC系统优化和放大提供数据支撑。

CuO/ZnO/Al_(2)O_(3)不锈钢纤维毡结构整体催化剂的甲醇水蒸气重整制氢性能

以切削法制备的商用多孔不锈钢纤维毡为催化剂载体,采用浸渍法制备CuO/ZnO/Al_(2)O_(3)结构整体催化剂,研究其对甲醇水蒸气重整制氢性能的影响。采用扫描电镜(SEM)对多孔不锈钢纤维毡结构整体催化剂进行微观形貌分析。通过改变反应空速和反应温度,考察结构整体反应器与固定床反应器的制氢性能。结果表明:相比于固定床反应器,填充不锈钢纤维毡结构整体催化剂的反应器可强化反应过程的传质和传热,在反应温度为280℃时,氢气流量为0.55 mol/h,甲醇转化率为95.07%;不锈钢纤维毡结构整体催化剂可降低甲醇水蒸气重整制氢的反应温度,减少反应系统的能量消耗。

Performance assessment of a spiral methanol to hydrogen fuel processor for fuel cell applications

A novel design of plate-type microchannel reactor has been developed for fuel cell-grade hydrogen production.Commercial Cu/Zn/Al2O3 was used as catalyst for the reforming reaction,and its effectiveness was evaluated on the mole fraction of products,methanol conversion,hydrogen yield and the amount of carbon monoxide under various operating conditions.Subsequently,0.5 wt% Ru/Al2O3 as methanation catalyst was prepared by impregnation method and coupled with MSR step to evaluate the capability of methanol processor for CO reduction.Based on the experimental results,the optimum conditions were obtained as feed flow rate of 5mL/h and temperature of 250℃,leading to a low CO selectivity and high H2 yield.The designed reformer with catalyst coated layer was compared with the conventional packed bed reformer at the same operating conditions.The constructed fuel processor had a good performance and excellent capability for on-board hydrogen production.

Highly controlled structured catalysts for on-board methanol reforming

The on-board methanol steam reforming(MSR) has long been considered as an effective approach to insitu produce hydrogen for fuel cell vehicles(FCVs). However, the conventional MSR catalyst pellets suffer from easy breakage during the vehicle movement, leading to increased pressure drop and reduced system stability. Herein, we introduce an integrated method to prepare the highly controlled structured catalysts based on coupled processes: direct prototyping the structured substrate using digital light processing(DLP) 3D printing technology, in-situ dynamic crystallization of active components assisted by magnetic resonance imaging(MRI) and calcination. The synthesized catalyst owns a gradient layer of active component, and exhibits better MSR performance, higher mechanical strength, reduced pressure drop, higher Cu dispersion and better adhesion of active compounds when compared with the conventional powder and pellet catalysts. The demonstrated successful application proves the feasibility of developed method,which has great potential to be used for preparing precisely other monolithic catalysts with customized structures.

干凝胶蒸汽辅助晶化构筑包覆结构ZSM-5及其甲醇制芳烃性能

煤基甲醇经催化转化制苯、甲苯和二甲苯是煤炭高效清洁转化的重要技术。由于其反应步骤复杂,单一结构催化剂上难以调控反应过程,实现高的芳烃选择性。采用干凝胶蒸汽辅助晶化方法将硅铝比(Si/Al)约为50的ZSM-5原粉放入硅铝比为220的干凝胶中进行晶化制备包覆结构ZSM-5,以催化耦合甲醇制烯烃和烯烃芳构化两步反应,提升芳烃选择性。考察不同硅包覆比对甲醇制芳烃性能的影响发现,硅包覆比小于0.5时,凝胶中硅铝物种可于原粉表面成功包覆。外部的高硅铝比包覆结构促进了甲醇到低碳烯烃的转化,进而强化了甲醇分步芳构化过程,总芳烃选择性可从原粉的12.9%增加至14.5%,轻质芳烃在芳烃中的选择性也由原粉的61.8%增加至66.5%.当硅包覆比继续增加到2,部分硅铝物种在原粉外围独立成核形成小晶粒ZSM-5.虽然芳烃选择性增加到15.2%,但小晶粒也促进了芳烃的烷基化,使C9+芳烃选择性增加,抑制了轻质芳烃的形成。

水热时间对CuO/CeO_(2)催化甲醇水蒸气重整制氢的影响

以六水合硝酸铈和尿素为原料,通过改变水热时间制备了CeO_(2)-X(X为水热时间,X=3、6、12、24 h)载体,对其进行等体积浸渍法负载活性组分Cu获得CuO/CeO_(2)-X催化剂,将其应用于甲醇水蒸气重整制氢(MSR)反应中。通过XRD、BET、H2-TPR等表征手段,探索水热时间对CeO_(2)-X载体、CuO/CeO_(2)-X催化剂的结构和物化性质的影响,并考察了CuO/CeO_(2)-X催化剂在MSR反应中的催化性能。结果表明,CuO/CeO_(2)-6催化剂在MSR反应中展现出较好的催化活性;在反应温度为280℃、水醇物质的量比为1.2、甲醇气体体积空速(GHSV)为800 h-1的条件下,甲醇转化率可达92.8%。