Ni/KZSM-5催化剂的生物乙醇水蒸气重整制氢催化性能

采用浸渍法制备了Ni/γ-Al_2O_3,Ni/HZSM-5和Ni/KZSM-5 3种负载型催化剂,利用XRD,XPS,BET,NH3-TPD,CO2-TPD和H2-TPR等手段对催化剂的晶相、比表面积、酸/碱性等物化特性进行了表征,并通过固定床反应器对比考察了不同载体的Ni基负载型催化剂对乙醇水蒸气重整制氢的催化性能。实验结果表明:由于HZSM-5的酸性较强,Ni/HZSM-5催化剂不能有效催化乙醇水蒸气重整制氢,主要产物为乙烯;由于KZSM-5具有一定的碱性并有较高的比表面积,Ni/KZSM-5催化剂对乙醇水蒸气重整制氢表现出了较高的催化活性,当反应温度为450℃时,乙醇转化率为100%,氢气选择性达到65.0%,且反应积碳率仅为3.0%;由于载体的碱性较弱,导致产物中含有部分乙烯,降低了氢气选择性,从而Ni/γ-Al_2O_3催化剂的活性低于Ni/KZSM-5催化剂。     

Cu/La2O3/Al2O3催化剂上甲醇水蒸气重整制氢反应

研究以并流共沉淀法制备Cu/La2 O3 /Al2 O3 系列催化剂催化甲醇水蒸气重整制氢反应过程 ,考察了La2 O3含量、反应温度、水醇比、液体空速 (WHSV)等因素对催化剂活性的影响。结果表明 :催化剂表现出较好的低温活性、高氢气选择性和稳定性。La2 O3 质量分数为 15 % ,在 2 5 0℃反应时 ,催化剂活性表现最佳 ,甲醇摩尔转化率为94 .5 % ,氢气选择性为 10 0 % ,CO摩尔分数为 1.0 5× 10 -7。     

整体式催化剂上甘油水蒸气重整制氢

为改善甘油重整制氢反应在转化率、氢产率以及抑制积碳方面都与热力学平衡存在较大差距的问题,设计开发了整体式重整催化剂.考察了涂层组分、比例对整体式催化剂理化特性及其在甘油水蒸气重整制氢反应中催化性能的影响.通过考察Ce-Zr物质的量比及La的添加对催化剂活性的影响,确定了Ce-Zr-La物质的量比为1∶1∶1为最优条件.整体式催化剂的活性得到明显改善,在甘油质量分数为10%,空速为3.07,h-1时,在温度考察范围内甘油完全转化为气相产物,氢气选择性递增,并趋于平稳,最高可达90.85%;随着空速增大,甘油质量分数的增加,氢气选择性减小,甘油气相转化率降低,但仍可保持较好的转化效果.     

掺钾硅酸锂吸附强化乙醇水蒸气重整制氢

针对吸附强化乙醇水蒸气重整(SE-SRE)制氢技术,通过热力学分析和制氢实验,研究了硅酸锂加入乙醇重整的效果,并结合多种表征手段分析了掺杂K对硅酸锂的影响,进一步用实验方法探究了多种工艺条件对以掺钾硅酸锂为吸附剂的SE-SRE系统的影响及该系统的循环稳定性.结果表明,硅酸锂加入乙醇重整提高了氢气产率,适量掺钾能改善硅酸锂的结晶度和孔隙特性,提升其吸附性能.SE-SRE系统的最佳工艺条件是:温度为525℃,空速为0.9 m L/(g·h),水醇体积比为8∶1,催化剂与吸附剂配比为1∶3,经过10次循环后SE-SRE系统仍能保持较高的二氧化碳吸附活性和氢气产率.     

多组分生物油吸附强化重整制氢的热力学分析

文章采用HSC Chemistry软件进行多组分生物油重整制氢(包括普通重整和吸附强化重整)过程的热力学分析,研究反应温度、S/C和Ca/C对氢气浓度和氢气产率等指标的影响。研究结果表明:两种重整制氢过程的氢气产率和氢气浓度均随着S/C的增大而增大,但在S/C3后增幅不再明显;当S/C=3时,普通重整制氢过程的氢气产率和氢气浓度均仅为70%左右,最佳重整反应温度高达830℃;加入吸附剂CaO后,吸附强化重整过程的氢气产率和氢气浓度较普通重整制氢过程有大幅提升,且最佳重整反应温度显著下降,当S/C=3时,最佳重整反应温度为480℃,氢气产率和氢气浓度分别为97.2%和99.7%。     

木炭催化甘油重整制氢研究

以木炭为催化剂,在固定床反应器中对甘油水蒸气重整制氢进行研究。结果表明:随着空速的增大,氢产率、潜在氢产率和碳转化率逐渐减小;随着温度的升高,氢产率、潜在氢产率和碳转化率增大;S/C的增大在一定程度上有助于促进氢产率、潜在氢产率和碳转化率的增大。在温度为800℃,S/C为4∶1,空速为1.5 h~(-1)时,氢气产率、潜在氢产率分别为114.31 g/kg和128.30 g/kg,碳转化率为89.08%。     

乙酸水蒸气重整制氢中载体组成对催化剂性能的影响

采用溶胶–凝胶法结合湿浸渍法制备了Ni/ZrO2、Ni/La2O3-ZrO2和Ni/La2O3催化剂,采用XRD、BET、TG及 H2-TPR等方法对催化剂的结构和性质进行了表征。通过生物油模型物乙酸水蒸气重整反应,探讨了载体组成对催化剂性能和积炭形成的影响。载体组分不同的Ni催化剂具有不同的Ni颗粒尺寸、孔结构和Ni–载体相互作用,这对乙酸水蒸气重整反应路径有重要影响。催化剂Ni/70wt%La2O3-ZrO2在乙酸水蒸重整反应中表现出较好的催化性能和稳定性,在反应时间10 h内,氢气产率保持在76.05%以上;同时,TG和XRD分析结果表明,Ni/70wt%La2O3-ZrO2具有较好的抗烧结能力和较低的积炭率。     

反应吸附强化模拟沼气蒸汽重整制氢的计算和实验研究

文章对反应吸附强化模拟沼气-水蒸气重整制氢技术(Re SER-Biogas)进行了热力学计算和实验研究。首先,建立甲烷蒸汽重整反应耦合氧化钙与二氧化碳反应的制氢反应模型,对CO2和CH4体积比(α)分别为0.25,0.43和0.67的模拟沼气进行改变CO2移除率(ζ)、反应温度(T)、水碳摩尔比(β)对甲烷转化率和氢气浓度影响规律的模拟计算。计算结果表明,提高ζ,T和β值能有效强化重整反应,当P=0.1 MPa,ζ=0.95,T=600℃,β=4时,甲烷转化率可达94%,产物中氢气的浓度可达96%。其次,采用镍系催化剂与纳米Ca O基CO2吸附剂,在固定床反应器中进行模拟沼气Re SER-Biogas制氢实验,改变T,β以及α值得到不同反应条件下的甲烷转化率与产品氢气浓度,从实验层面上验证模拟计算结果和反应条件影响规律的可靠性。实验结果表明,在P=0.1 MPa,ζ=0.95,T=600℃,β=4和α=0.43的实验条件下,产物中氢气的浓度高达93%,CO的浓度低至0.32%。和传统无吸附强化的沼气蒸汽重整制氢工艺相比,Re SER-Biogas技术能够在更低的温度条件下直接制取低CO浓度的高纯氢气产品,对开发高效,节能的沼气制氢新技术具有重要的实际意义。     

HYDROGEN PRODUCTION RESERACH BY STEAM REFORMING OF ETHANOL OVER Ni-Cu/SrCeO3 CATALYST

利用固定床反应器对一系列自制催化剂Ni-Cu/SrCe03在乙醇水蒸气重整制氢反应中的催化性能进行考察,研究活性金属Ni的负载量、反应温度、水醇比对催化剂活性的影响.实验结果表明,Ni负载量为10％(质量分数)的催化剂Ni-Cu/SrCe03在乙醇重整制氢中表现出最佳催化活性,当反应温度为650℃,水醇比为8时,氢选择性达到最大值87.3％.     

La2O3改进Ni/γ-Al2O3催化剂上沼气重整制氢

为了寻求制备氢气的可再生资源及减少沼气的排放量,用浸渍法制备了不同La2O3含量的Ni/La2O3/γ Al2O3催化剂,用CH4/CO2体积比为1的混合气体模拟沼气,考察了还原温度、反应温度、空速等操作条件对该催化剂上沼气重整制氢性能的影响.并运用H2-TPR、TEM、TG-DSC等对催化剂进行了表征.结果表明:La2O3含量为6%的催化剂具有较好的综合性能;载体中掺杂适量La2O3能增加金属Ni的分散性,提高催化剂的可还原性及载体对CO2的吸附能力,从而改善了催化剂的活性及抗积炭性,使催化剂具有较好的稳定性.在100h的稳定性实验中,CH4及CO2转化率、H2及CO的选择性、H2/CO比平均值分别约为87.4%、88.8%、87.3%、93.8%及0.92.催化剂表面积炭速率非常低,仅为0.7279mg/(gcat·h).     

Catalytic steam reforming of bio-oil

Hydrogen and synthesis gas can be produced in an environmentally friendly and sustainable way through steam reforming (SR) of bio-oil and this review presents the state-of-the-art of SR of bio-oil and model compounds hereof. The possible reactions, which can occur in the SR process and the influence of operating conditions will be presented along with the catalysts and processes investigated in the literature.     

Thermodynamic analysis of steam reforming and oxidative steam reforming of propane and butane for hydrogen production

Thermodynamic analyses of cracking, partial oxidation (POX), steam reforming (SR) and oxidative steam reforming (OSR) of butane and propane (for comparison) were performed using the Gibbs free energy minimization method under the reaction conditions of T = 250–1000 °C, steam-to-carbon ratio (S/C) of 0.5–5 and O₂/HC (hydrocarbon) ratio of 0–2.4. The simulations for the cracking and POX processes showed that olefins and acetylene can be easily generated through the cracking reactions and can be removed by adding an appropriate amount of oxygen. For SR and OSR of propane and butane, predicted carbon formation only occurred at low S/C ratios (<2) with the maximum level of carbon formation at 550–650 °C. For the thermal-neutral conditions, the TN temperatures decrease with the increase of the S/C ratio (except for O/C = 0.6) and the decrease of the O/C ratio. The simulated results for SR or OSR of propane and butane are very close under the investigated conditions.     

Microwave-activated methanol steam reforming for hydrogen production

Methanol steam reforming (MSR) was carried out in a catalytic packed bed reactor under electrical and microwave heating using the two most common catalysts for this process-CuZnO/Al₂O₃ and PdZnO/Al₂O₃. Significant two-dimensional temperature gradients were found, especially in the latter case. Our results show that for the same average bed temperature, methanol conversion is higher under microwave heating (>10%). On the other hand, the product distribution is not affected by the heating mode. We demonstrate that even in cases where the maximum temperature along the entire height of the bed is significantly higher under electrical heating, conversion is either higher in the microwave case or approximately the same between the two heating modes. Finally, our experimental data indicate that a given methanol conversion can be achieved with lower net heat input to the reactor under microwave heating. This does not mean lower total energy consumption in the microwave process due to the limitations in the magnetron efficiency and the reflected power. However, it may be an implicit indication of higher temperature at metal sites than in bulk phase (microscale hot spot formation) due to the selective heating principle.     

Bio-oil steam reforming,partial oxidation or oxidative steam reforming coupled with bio-oil dry reforming to eliminate CO2 emission

Biomass is carbon-neutral and utilization of biomass as hydrogen resource shows no impact on atmospheric CO₂ level. Nevertheless, a significant amount of CO₂ is always produced in biomass gasification processes. If the CO₂ produced can further react with biomass, then the biomass gasification coupled with CO₂ reforming of biomass will result in a net decrease of CO₂ level in atmosphere and produce the chemical raw material, syngas. To achieve this concept, a “Y” type reactor is developed and applied in bio-oil steam reforming, partial oxidation, or oxidative steam reforming coupled with CO₂ reforming of bio-oil to eliminate the emission of CO₂. The experimental results show that the reaction systems can efficiently suppress the emission of CO₂ from various reforming processes. The different coupled reaction systems generate the syngas with different molar ratio of CO/H₂. In addition, coke deposition is encountered in the different reforming processes. Both catalysts and experimental parameters significantly affect the coke deposition. Ni/La₂O₃ catalyst shows much higher resistivity toward coke deposition than Ni/Al₂O₃ catalyst, while employing high reaction temperature is vital for elimination of coke deposition. Although the different coupled reaction systems show different characteristic in terms of product distribution and coke deposition, which all can serve as methods for storage of the carbon from fossil fuels or air.     

Ethanol oxidative steam reforming over Ni-based catalysts

Oxidative steam reforming of ethanol for hydrogen production in order to feed a solid polymer fuel cell (SPFC) has been studied over several catalysts at on board conditions (a molar ratio of H₂O/EtOH and of O₂/EtOH equal to 1.6 and 0.68 respectively) and a reforming temperature between 923 and 1073 K. Two Ni (11 and 20 wt.%)/Al₂O₃ catalysts and five bimetallic catalysts, all of them supported on Al₂O₃, were tested. The bimetallic catalysts were Ni (approximately 20 wt.%) based catalysts doped with Cr (0.65 wt.%), Fe (0.6 wt.%), Zn (0.7 wt.%) or Cu (0.6 and 3.1 wt.%). The results in terms of H₂ production and CO₂/CO_x ratio obtained over Ni-based catalysts supported on Al₂O₃ are compared with those obtained over Ni–Cu/SiO₂ and Rh/Al₂O₃ catalysts reported in our previous works. Tendencies of the product selectivities are analyzed in the light of the reaction network proposed.     

Toluene steam reforming over nickel based catalysts

Steam reforming of toluene (SRT) has been studied initially in eight nickel-based catalysts where nickel (10 wt%) was incorporated in different supports (olivine, Al2O3, MgO, LDH, ZrO₂, CeO₂ and natural sepiolite) by the incipient wetness impregnation method. Among them, nickel catalyst based on sepiolite exhibited a promising catalytic performance, with a high conversion of toluene (16%), high selectivity to hydrogen (68.4%) and low production of undesired by-products (CO, CH₄, ethylene and benzene) at low temperature (500 °C). On the other hand, the incorporation of Ni in the sepiolitic material by precipitation (PP) has been considered as alternative method to the incipient wetness impregnation method (IWI). PP method allowed to prepare a Ni-based catalyst with a very high activity (conversion of toluene ~100%), high selectivity to hydrogen (73%) and lower production of undesirable by-products (5% CO, 2% CH₄ and 0% C₆H₆) at 575 °C. In addition, catalytic deactivation due to coke deposition and nickel sinterization was clearly lower for the catalyst synthesized by PP. Characterization by different physicochemical techniques (XRD, TEM, BET surface area, ICP-OES, TPR and EA) showed that PP method allowed to obtain a sepiolite-based catalyst containing Ni with larger external surface area and smaller, highly dispersed and easily reducible Ni metal particles. The results here discussed show that the Ni incorporation method has a clear influence in the preparation of nickel catalyst supported on sepiolite with improved catalytic performance in the steam reforming of toluene.     

Effect of pollutants on biogas steam reforming

This study reports the influence of biogas poisoning on a Ni based catalyst working under steam reforming conditions (atmospheric pressure, T = 1073 K and H₂O/CH₄ = 2 mol/mol). A biogas stream composed by CH₄ and CO₂ with a ratio 55/45 vol.%, added with different chemical species (H₂S, hydrocarbons mixture and D5) as contaminants, was used as inlet gas stream.First, effect of poisoning on Ni catalyst were separately evaluated and the boundary concentrations for each contaminants were revealed (0.4 ppm, 200 ppm and 0.5 ppm for H₂S, hydrocarbons and D5 respectively) to assure Ni stable performances on time on stream (100 h at 50,000 h^?1 of GHSV). Successively, a comparison between Ni catalytic behaviors in presence of two combined poisoning in the biogas (H₂S + Hydrocarbons and Hydrocarbons + D5) was carried out.It was found that the effect of combined poisoning, even though it considered in moderate concentration, is harmful for Ni catalyst activity. Methane conversion on time on stream was reduced from 86% to 40% after 50 h, when the couple of poisoning Hydrocarbons + D5 was added to the inlet gas stream, while a lower deactivation pattern (about 73%) was leaded by couple H₂S + Hydrocarbons. Both poisoning mixtures promoted coke deposition on Ni catalyst surface (about ≥0.5 mgC/g_cat·h) independently by poisoning chemical characteristics probably due to adsorption/deposition of contaminants on catalytic sites.     

Ethanol steam reforming over Ni-based spinel oxide

The Ni-based spinel-type oxides, NiB₂O₄ (B = Al, Fe, Mn), were investigated for their catalysis of the ethanol steam reforming reaction. Ethanol conversion over spinel-type oxides without reduction treatment was comparable to that over γ-alumina-supported Ni catalyst with reduction. The spinel oxide of NiAl₂O₄ showed extremely stable performance for 48 h, while the activity of NiFe₂O₄ and NiMn₂O₄ catalysts was reduced by carbon deposition. Catalyst stability for reforming reaction was closely related to the stability of the nickel metal dispersed on the catalyst surface and the spinel structure. Differences in crystallinity and surface area among the catalysts were not crucial factors for determining ethanol conversion for NiAl₂O₄ calcined between 800 °C and 1100 °C. The catalyst calcined at 900 °C exhibited the highest activity for the reforming reaction.     

Availability of steam impacts coke properties in steam reforming of acetic acid

Steam to carbon ratio (S/C) determines the availability of oxygen-containing species during steam reforming, which not only affect the amount of coke formed, but also might impact physicochemical properties of the coke generated. In this study, the effect of S/C on the coke formation in steam reforming of acetic acid was assessed. The results indicated that dissociative absorption of acetic acid generated the intermediates containing both CO and CC groups even at 100 °C. At low S/C, the insufficient 1OH reacted with carbonaceous intermediates such as CH_x to form more carbonyl species, leading to significant coking and lower gas yields. Sufficient 1OH at high S/C facilitated transformation of the carbonyl-containing species into gases, minimizing coking. The varied amount of coke showed significant effect on the diffraction of metallic nickel phase, the particle size of Ni and the absorption for the Si–O–Si functional groups on spent catalysts. The coke formed at low S/C was more aromatic with high thermal stabilities, while the coke formed at high S/C was more aliphatic with low thermal stabilities. The involvement 1OH species in coking process determined not only properties but also morphologies of the coke. The coke formed at low S/C showed bamboo-like, dendritic or twisted rope-like structure. While the higher S/C favored the generation of the carbon nanotubes with smooth outer surface.     

Comparative analysis on sorption enhanced steam reforming and conventional steam reforming of hydroxyacetone for hydrogen production: Thermodynamic modeling

The chemical thermodynamics of sorption enhanced steam reforming (SESR) of hydroxyacetone for hydrogen production were investigated and contrasted with hydroxyacetone steam reforming (SR) by means of Gibbs free energy minimization principle and response reactions (RERs) method. Hydrogen is mainly derived methane steam reforming reaction from and water gas shift reaction. The former reaction contributes more than the latter one to hydrogen production below 550 °C and at higher temperature the latter one tends to dominate. The maximum hydrogen concentration is 70% in SR, which is far below hydrogen purities required by fuel cells. In SESR, hydrogen purities are over 99% in 525–550 °C with a WHMR greater than 8 and a CHMR of 6. The optimum temperature for SESR is approximately 125 °C lower than that for SR. In comparison with SR, SESR has the advantage of almost complete inhibition of coke formation in 200–1200 °C for WHMR ≥ 3.