Ni基生物质焦油重整催化剂的研究进展

Ni基催化剂对生物质气化过程中生成焦油的催化裂解重整具有较好的催化活性,但在催化反应中存在容易积炭进而失活的现象。如何提高Ni基催化剂的催化活性和抗积炭能力是Ni基催化剂研究中的难点。本文从催化剂的活性组分、载体和助催化剂3个方面入手,详细综述了近几年关于提高Ni基生物质焦油重整催化剂催化活性和抗积炭能力的研究进展,讨论了催化剂的活性组分、载体和助催化剂对催化剂催化活性的影响。指出Ni-Fe、Ni-Co、Ni-Cu催化剂均表现出比Ni基催化剂更好的催化活性,助剂的加入有利于提高吸附剂的抗积炭能力和抗烧结能力;催化剂载体方面,钙钛矿型混合金属氧化物载体、煤焦和生物质焦载体具有较好的研究前景。     

助剂对镍基生物质焦油重整催化剂性能影响的研究进展

分别以碱及碱土金属、过渡金属以及稀土金属3种常见助剂类型,探讨了不同助剂对镍基催化剂催化生物质裂解及气化重整制氢催化活性、催化剂物化特性及催化剂失活特性的影响。添加碱金属组分后,生物质热解反应速率会大幅上升,生物质焦的水蒸气气化反应得到促进,并且达到最大热解速率所需的温度也有所降低,热解产物趋向于小分子量产物;过渡金属对生物质气化过程中生成焦油的催化裂解重整具有较好的催化活性;稀土元素对甲醇水蒸气重整等催化反应有着重要的作用,镍基催化剂中加入Ce和Pr能提高甲醇转化率、改善产气组分、提高H₂的选择性。结合国内外的研究情况发现钴、镧等金属助剂有利于提升镍基催化剂重整制氢活性,催化剂积炭及表面活性颗粒的聚集是造成催化剂失活的主要原因。     

生物质焦油重整催化剂的研究进展

生物质热解制备富氢合成气是当前的研究热点,催化重整生物质焦油不仅能够有效地去除焦油,而且可以增加气相中H₂和CO的含量。本文综述了近几年关于生物质焦油重整催化剂的研究,讨论了镍基催化剂、非镍过渡金属催化剂和碱金属催化剂的优劣势。镍基催化剂使用时通常需要载体,虽然具有较高的催化活性,但是易通过积炭和镍烧结而失活。非镍过渡金属催化剂中的贵金属催化剂虽然具有极高的活性和稳定性,但是价格昂贵。碱金属催化剂易挥发而永久失活。     

乙酸蒸汽催化重整制氢的研究进展

通过生物油蒸汽重整制备氢气可以减少环境污染,降低对化石燃料的依赖,是一种极具潜力的制氢途径。乙酸是生物油的主要成分之一,常作为模型化合物进行研究。镍基催化剂是乙酸蒸汽重整过程中常用的催化剂,但容易因积炭失去活性,降低了制氢过程的经济性。本文首先分析了影响乙酸蒸汽重整制氢过程的各种因素,阐述了在这一过程中镍基催化剂的积炭原理,讨论了优化镍基催化剂的方法,包括优化催化剂的预处理过程、添加助剂和选择合适的载体,最后对乙酸蒸汽重整制氢的热力学分析研究进展进行了总结。未来应重点研究多种助剂复合使用时对镍基催化剂积炭与活性的影响,分析多种助剂的协同作用机理,得到一种高活性、高抗积炭能力的用于生物油蒸汽重整制氢的镍基催化剂。     

钴基费托合成催化剂失活机理及再生研究进展

综述了钴基费托合成催化剂的失活机理、催化剂再生工艺及如何延长催化剂寿命的研究进展,通过分析催化剂失活原因,认为中毒、Co颗粒烧结、积炭、氧化、固相反应、晶相重构、表面阻塞和催化剂磨损等因素造成催化剂不同程度失活,其中积炭和Co颗粒烧结是催化剂失活的最主要原因,延长催化剂寿命的关键是提高催化剂的抗烧结能力和抑制积炭生成。增强活性金属Co和载体间的相互作用,保持Co晶粒分布均一或采用包覆、限域等策略可提高催化剂的抗烧结能力,通过添加助剂、调整氢碳比和空速等工艺参数亦可抑制积炭的生成。采用氢处理、脱蜡-氧化-还原和脱蜡-氧化-溶液处理-还原等工艺可实现催化剂的再生,对催化剂进行再生时要结合催化剂失活的主要原因,选择合适的再生工艺来最大限度地恢复催化剂活性。今后,提高催化剂的稳定性以及开发催化剂再生工艺技术路线是提高钴基费托合成技术竞争力的关键。     

凹凸棒石黏土负载Ni催化裂解生物质焦油

利用浸渍法制备了凹凸棒石黏土(palygorskite,PG)Ni基催化剂(Ni/PG),探究了不同Ni负载量以及反应温度对凹凸棒石镍基催化剂催化裂解生物质焦油的影响,利用透射电镜、X射线粉末衍射、总碳等分析手段对催化剂的形貌、物相和积炭量进行表征.结果表明:活性组分高负载量有利于提高焦油去除率和氢产率;高温条件也有利...     

负载型Co基F-T合成催化剂中贵金属助剂促进作用的研究进展

在负载型Co基催化剂中添加少量贵金属助剂能显著影响催化剂活性、选择性与稳定性。贵金属助剂的添加提高了Co活性组分的还原度与分散度,增加了催化剂表面的活性位数目,改变了催化剂的几何结构和电子结构,影响CO、H₂或中间产物的吸附活化行为,抑制催化剂积炭和金属Co小粒子的再氧化。综述贵金属助剂对催化剂活性中心性质、反应物的吸附活化行为和催化剂反应稳定性的影响。     

生物质气化焦油裂解催化剂研究进展

将生物质气化转化为气体燃料或化工合成气原料,是生物质清洁高效利用的有效途径之一,焦油是气化的副产物,影响产气品质和气化效率,催化剂对生物质催化气化及焦油裂解效果明显,得到广泛应用。综述了天然催化剂、无机盐催化剂及合成催化剂对生物质气化过程焦油催化裂解效果、反应条件、催化机理。进一步分析了不同催化剂的生物质催化气化性能及研究进展。同时指出对天然矿石催化剂进行改性或大力发展合成类催化剂对生物质气化焦油降解有着良好的前景。     

生物质催化气化实验研究

在常压流化床上进行了生物质在水蒸气条件下的实验研究。实验装置主体由常压流化床反应器和固定床催化裂解反应器组合而成。生物质原料为木屑,焦油裂解催化剂分别选用煅烧白云石和镍基重整催化剂。实验结果表明,H2/CO(H/C)的摩尔比随着气化温度、水蒸气质量/生物质质量（S/B）的升高迅速增加,但催化裂解温度变化对H/C的影响较小。另外,在催化裂解反应器中使用催化剂种类不同,H/C也不同。本文采用两段催化裂解,一段催化剂采用煅烧白云石,二段采用镍基催化剂,焦油裂解率达到96.70％。采用两段催化裂解,不但可以提高焦油的裂解率,增加了H2和CO收率,净化生物质裂解气,而且可以防止镍基重整催化剂失活,延长其使用寿命。     

催化重整生物质焦油的Ni基催化剂中常见助剂和载体的研究进展

Ni基催化剂作为催化重整生物质焦油过程中一种高效的催化剂,仍然存在易烧结、易积炭等问题,使得其活性和稳定性难以得到保证。通过添加合适的助催化剂和使用催化剂载体可有效缓解Ni基催化剂的烧结与积炭问题。介绍了稀土元素Ce、磁性元素Fe和Co、碱土金属Ca和Mg作为助催化剂,以及天然矿物材料白云石和橄榄石、天然加工材料煅烧贝壳和稻壳炭、合成材料β-Al₂O₃和SBA-15作为载体的Ni基催化剂的研究进展,并展望了今后的研究方向。     

Effects of promoters on biomass gasification using nickel/dolomite catalyst

Metallic nickel has been selected as a catalyst for biomass gasification because of its activity in biomass steam gasification and tar reduction. The effects of types of promoters such as platinum, cobalt, and iron on biomass gasification were evaluated. The area of interest was the effects of preparation methods, which were impregnation and coprecipitation. Catalyst preparation by the impregnation method showed superior performance. The conclusion can be drawn from the experiments that the platinum promoter enhanced the reforming reaction, iron promoted a water-gas shift reaction, and the cobalt promoter favored a methanation reaction. Moreover, the addition of noble metal reduced carbon deposition on Ni/dolomite.     

Steam reforming of tar from a biomass gasification process over Ni/olivine catalyst using toluene as a model compound

A Ni/olivine catalyst, previously developed for biomass gasification and tar removal during fluidized bed steam gasification of biomass, was tested in a fixed bed reactor in toluene steam reforming as a tar destruction model reaction. The influence of the catalyst preparation parameters (nickel precursor, calcination temperature and nickel content) and operating parameters (reaction temperature, steam to carbon S/C ratio and space-time) on activity and selectivity was examined showing a high toluene conversion and a low carbon formation compared to olivine alone. The steam reforming of toluene was found to be of zero order for water and first order for toluene. Activation energy required for Ni/olivine was determined to be about 196 kJ mol⁻¹ in accordance with literature. Catalyst activity and stability and its resistance against carbon formation were discussed on the basis of X-ray diffraction (XRD), transmission electron microscopy (TEM) and temperature programmed oxidation (TPO) results. Characterization before test (XRD, temperature programmed reduction (TPR), Mössbauer spectroscopy) have shown the presence of NiO–MgO solid solution, formed on the surface of olivine support, which explains the efficiency of the catalyst calcined at 1100 °C. After test, Ni–Fe alloys were observed (TEM, Mössbauer spectroscopy). It was suggested that magnesium oxide enhanced steam adsorption, facilitating the gasification of surface carbon and that Ni–Fe alloys prevented carbon deposition by dilution effect.     

Steam reforming of tar in hot syngas cleaning by different catalysts: Removal efficiency and coke layer characterization

Syngas produced by biomass and waste gasification processes must be adequately clean of tar compounds before being utilized in value-added applications. Syngas cleaning by tar cracking at high temperatures is a promising technique that can utilize different kinds of catalysts. However, their use is limited by the deposition of coke layers, which induces a masking phenomenon on the active surface, and, consequently, the rapid deactivation of the catalyst. This study addresses how the temperature (750 and 800°C) and the steam concentration (0% and 7.5%) can affect the extent of water–gas and reforming reactions between steam and coke deposits. Two catalysts were used: a market-available activated carbon and an iron-based alumina catalyst. The tests showed better performance of the Fe/γ-Al₂O₃ catalyst. A mass increase of the bed was measured in tests with both the catalysts, which confirms the deposition of the coke layer produced by tar dehydrogenation and carbonization. Scanning electronic microscopy-energy-dispersive X-ray analysis (SEM-EDX) and Raman spectroscopy were utilized to investigate the nature of coke layers over the catalyst surface, with the aim of acquiring information about their reactivity towards the water gas reaction. SEM-EDX observations indicate that the thickness of these carbon layers is less than 2 μm. Raman spectra suggest a negligible effect of the reaction temperature in the tested range and, in particular, that the amorphous nature of coke layers deposited in the presence of steam is relatively more graphitic than that obtained without steam.     

Catalytic reforming of tar during gasification. Part I. Steam reforming of biomass tar using ilmenite as a catalyst

Ilmenite, a natural iron-containing mineral, has been investigated as an inexpensive catalyst for the steam reforming of volatiles (tar) from the pyrolysis of mallee woody biomass. The results indicate that ilmenite has good activity for the steam reforming of tar into gases due to its highly dispersed iron-containing species. The supply of external steam, in addition to the H₂O and CO₂ produced during the pyrolysis of biomass, plays an important role in minimising the formation of coke on the catalyst surface and thus the catalyst activity. The catalyst deactivation due to coke formation has more adverse effects on the reforming of larger aromatic ring system with steam than that of smaller ones. In addition, the supply of additional oxygen at low concentration changed the outcomes of tar reforming mainly because oxygen activated the smaller aromatic ring systems and polymerised them into larger aromatic ring systems in the gas phase.     

Partial oxidation reforming of biomass fuel gas over nickel-based monolithic catalyst with naphthalene as model compound

With naphthalene as biomass tar model compound, partial oxidation reforming (with addition of O₂) and dry reforming of biomass fuel gas were investigated over nickel-based monoliths at the same conditions. The results showed that both processes had excellent performance in upgrading biomass raw fuel gas. Above 99% of naphthalene was converted into synthesis gases (H₂+CO). About 2.8 wt% of coke deposition was detected on the catalyst surface for dry reforming process at 750 °C during 108 h lifetime test. However, no coke deposition was detected for partial oxidation reforming process, which indicated that addition of O₂ can effectively prohibit the coke formation. O₂ can also increase the CH₄ conversion and H₂/CO ratio of the producer gas. The average conversion of CH₄ in dry and partial oxidation reforming process was 92% and 95%, respectively. The average H₂/CO ratio increased from 0.95 to 1.1 with the addition of O₂, which was suitable to be used as synthesis gas for dimethyl ether (DME) synthesis.     

Development of new nickel based catalyst for tar reforming with superior resistance to sulfur poisoning and coking in biomass gasification

Gasification of tar by catalytic steam reforming was examined in the gasification process of biomass, such as dried sewage sludge and wood chips. The tar reforming characteristics of the newly-developed Ni/MgO–CaO (based on dolomite) catalyst which was doped with WO₃ as a sulfur-resistant promoter, was investigated using a simulated gas containing naphthalene as tar. The result has confirmed that the developed catalyst shows a high naphthalene reforming activity and is stable even in gas containing hydrogen sulfide. The catalyst also exhibited superior resistance to coking as well as sulfur poisoning compared to several commercial steam-reforming catalysts.     

Olivine catalysts for methane- and tar-steam reforming

The removal of tar and lower hydrocarbons is a vital technological barrier hindering the development of biomass gasification. The present work evaluates four olivine catalysts (three untreated of different origin and one calcined) for lowering the amount of these compounds in biomass derived syngas by reforming model compounds (naphthalene, toluene, and methane). Treatments prior to reaction were shown to largely impact the catalytic activity and physiochemical properties of the olivine catalysts depending on its origin. The formation of free Fe phases following decomposition of a Fe-bearing serpentine phase ((Mg,Fe)₃Si₂O₅(OH)₄) near the surface of untreated olivine catalysts proved most important for facilitating higher activity compared to olivine catalysts with little or no serpentine phase initially. The most active catalyst was efficient at naphthalene removal (90% conversion at 800 °C), but more active catalysts are needed for applications where methane removal is required. Additionally, carbon deposition during naphthalene-steam reforming as well as Fe clustering during naphthalene-steam reforming and exposure to reducing conditions suggested stability may be a liability.