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。     

Low-temperature steam reforming ofn-butane over Rh and Ru catalysts supported on ZrO2

In the 500 ° C steam reforming reaction ofn-butane, Rh and Ru catalysts supported on ZrO₂ exhibited high catalytic activities for hydrogen production at a low steam-to-carbon ratio with little activity decline.     

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.     

Low-temperature reforming of ethanol over CeO2-supported Ni-Rh bimetallic catalysts for hydrogen production

A new series of Ni-Rh bimetallic catalysts with different Ni and Rh loadings on a high-surface-area CeO₂ was developed for the reforming of bio-ethanol at low-temperature (below 450 °C) to produce H₂-rich gas for on-site or on-board fuel cell applications. Oxidative steam reforming of ethanol (OSRE) over a Ni-Rh/CeO₂ catalyst containing 5 wt% Ni and 1 wt% Rh was found to be more efficient offering about 100% ethanol conversion at 375 °C with high H₂ and CO₂ selectivity and low CO selectivity compared to the steam reforming of ethanol (SRE) reaction which required a higher temperature of about 450 °C to achieve 100% ethanol conversion. The high temperature SRE reaction favors the formation of large amount of CO, which would make the downsteam CO cleanup more complicated for polymer electrolyte membrane fuel cell (PEMFC). The presence of O₂ in the feed gas was found to greatly enhance the conversion of ethanol to produce H₂ and CO₂ as major products. Increase in Ni content above 5 wt% in the catalyst formulation decreased the H₂ selectivity while the selectivity of undesirable CH₄ and acetaldehyde increased. The 1 wt% Rh/CeO₂ catalyst was twice as active as 10 wt% Ni/CO₂ catalyst in terms of ethanol conversion and acetaldehyde selectivity and this indicated that Rh was more effective in C–C bond cleavage than Ni. The reaction was found to proceed through the formation of acetaldehyde intermediate, which subsequently underwent decomposition to produce a mixture of CO and CH₄ or reforming with H₂O and O₂ to produce CO, CO₂ and H₂. The role of Rh is mainly to cleave the C–C and C–H bonds of ethanol to produce H₂ and COx while Ni addition helps converting CO into CO₂ and H₂ by WGS reaction under the conditions employed.     

Steam reforming of CH4 over Ni-Ru catalysts supported on Mg-Al mixed oxide

Ni_0.5/Mg_2.5(Al)O catalyst prepared from hydrotalcite precursors showed high and stable activity in the CH₄ steam reforming, but was severely deactivated in the daily start-up and shut-down (DSS) operation under steam purging. The addition of Ru drastically improved the behavior of Ni_0.5/Mg_2.5(Al)O catalyst for the DSS operation. During the wet Ru loading on the Ni_0.5/Mg_2.5(Al)O catalyst, the reconstitution of hydrotalcite took place by “memory effect,” resulting in the formation of Ru-Ni alloy as well as the strong interaction between Ru and Ni after the calcination followed by reduction. This provided the catalyst with high sustainability probably by suppressing the oxidation of Ni metal by steam by hydrogen spillover from Ru. Only 0.05 wt% of Ru loading was enough to effectively suppress the deactivation.     

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.     

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 II. Char as a catalyst or as a catalyst support for tar reforming

Char, char-supported catalysts and ilmenite were investigated for the steam reforming of biomass tar derived from the pyrolysis of mallee wood in situ. Special attention was given to the reforming of aromatic ring systems in tar. The results indicated that the char-supported iron/nickel catalysts exhibited much higher activity for the reforming of tar than the char itself. Ilmenite and the char-supported iron catalyst contained similar active phase but showed different tar reforming activities. Kinetic compensation effects demonstrated that the reaction pathways on the char-supported catalysts were similar but were different from those on ilmenite. The proprieties of support could play important roles for the activities of the catalysts and the reaction pathways on the catalysts. Char would not only disperse the catalysts but also interact with the catalysts to enhance their activity for the steam reforming of tar.     

The Effect of Modifiers on the Performance of Ni/CeO2 and Ni/La2O3 Catalysts in the Oxy–Steam Reforming of LNG

This work interrogates for the first time the catalytic properties of various monometallic Ni catalysts in the oxy-steam reforming of LNG. Various research techniques, including X-ray diffraction (XRD), specific surface area and porosity analysis (BET method), scanning electron microscopy with X-ray microanalysis (SEM-EDS), temperature-programmed desorption of ammonia (TPD-NH₃), temperature-programmed reduction (TPR-H₂) and the FTIR method, were used to study their physicochemical properties. The mechanism of the oxy-steam reforming of LNG is also discussed in this paper. The high activity of monometallic catalysts supported on 5% La₂O₃–CeO₂ and 5% ZrO₂–CeO₂ oxides in the studied process have been proven and explained on the basis of their acidity, specific surface area, sorption properties in relation to the reaction products, the crystallite size of the metallic nickel and their phase composition.     

Ni nanoparticles supported on carbon as efficient catalysts for steam reforming of toluene (model tar)

This paper investigated the influences of surface properties of carbon support and nickel precursors (nickel nitrate,nickel chloride and nickel acetate) on Ni nanoparticle sizes and catalytic performances for steam reforming of toluene.Treatment with nitric acid helped to increase the amount of functional groups on the surface and hydrophilic nature of carbon support,leading to a homogeneous distribution of Ni nanoparticles.The thermal decomposition products of nickel precursor also played an important role,Ni nanoparticles supported on carbon treated with acid using nickel nitrate as the precursor exhibited the smallest mean diameter of 4.5 nm.With the loading amount increased from 6 wt％ to 18 wt％,the mean particle size of Ni nanoparticles varied from 4.5 nm to 9.1 nm.The as-prepared catalyst showed a high catalytic activity and a good stability for toluene steam reforming:98.1％ conversion of toluene was obtained with the Ni content of 12 wt％ and the S/C ratio of 3,and the conversion only decreased to 92.0％ after 700 min.Because of the high activity,good stability,and low cost,the as-prepared catalyst opens up new opportunities for tar removing.     

Fe/生物质焦预重整在Ni基催化重整生物油中的作用

低温预重整能够经济节能地提高Ni基催化剂重整生物油的效果。为研究廉价易得的Fe/生物质焦预重整催化剂对重整效果的影响及机理,设计了Fe/生物质焦催化剂和Ni-Ca/γ-Al₂O₃催化剂不同组合方式在不同的预重整温度（350～600℃）下的重整实验,并用紫外荧光分光光度计（UV）和气相色谱-质谱联用仪（GC-MS）分析重整焦油,用气相色谱仪（GC）对重整气进行定性和定量分析。实验结果表明：Fe/生物质焦优化了预重整产生的挥发分,将原本挥发分中分子量较大的苯系物、萘系物及多环芳香化合物转化为结构简单、更易重整为气体的呋喃类、酚类及非芳香化合物,从而有效提高下段Ni基催化剂重整的合成气（H₂、CO）产率。预重整温度增加能有效抑制积炭生成。另外,Fe/生物质焦在较高预重整温度（550～600℃）下能够抑制Ni基催化剂表面积炭生成。     

Combined catalytic partial oxidation and CO2 reforming of methane over supported cobalt catalysts

The combined partial oxidation and CO₂ reforming of methane to synthesis gas was investigated over the reduced Co/MgO, Co/CaO, and Co/SiO₂ catalysts. Only Co/MgO has proved to be a highly efficient and stable catalyst. It provided about 94–95% yields to H₂ and CO at the high space velocity of 105000 mlg^–1h^–1 and for feed ratios CH₄/CO₂/O₂=4/2/1, without any deactivation for a period of study of 110 h. In contrast, the reduced Co/CaO and Co/SiO₂ provided no activity for the formation of H₂ and CO. The structure and reducibility of the calcined catalysts were examined using X-ray diffraction and temperature-programmed reduction, respectively. A solid solution of CoO and MgO, which was difficult to reduce, was identified in the 800°C calcined MgO-supported catalyst. The strong interactions induced by the formation of the solid solution are responsible for its superior activity in the combined reaction. The effects of reaction temperature, space velocity, and O₂/CO₂ ratio in the feed gases (while keeping the C/O ratio constant at 1/1) were investigated over the Co/MgO catalyst. The H₂/CO ratio in the product of the combined reaction increased with increasing O₂/CO₂ ratio in the feed.     

低镍/ZnO-TiO2催化剂的乙醇水蒸气重整制氢

为考察低镍负载量对乙醇水蒸气重整制氢催化剂性能的影响,利用沉积-沉淀法(DP)制备了镍负载最质量分率为0.5%～5.0%的Ni/ZnO-TiO2催化剂,并在内径14 mm的固定床管式反应器中对低镍催化剂进行了性能评价.结果表明,低镍/ZnO-TiO2催化剂具有较好的乙醇水蒸气重整制氢性能.在水醇物质的量比为13:1及反...     

Comparative study of atmospheric and high pressure CO2 reforming of methane over Ni/MgO-AN catalyst

Catalytic activity of Ni/MgO-AN prepared from alcogel derived MgO was studied for the dry reforming of methane under atmospheric as well as high pressure (1.5 MPa). Different catalytic performances are observed in the atmospheric and high-pressure reactions; while the catalyst was highly active and extremely stable under atmospheric pressure it shows a self-stabilization process under high pressure. The self-stabilization process was characterized initially by a decrease in deactivation rate with increasing the reaction time-on-stream (TOS) up to ca. 12 h and then by a thereafter stabilization during the reaction. Characterizations of the coked catalyst with TPO, TEM, SEM, TPH and XRD techniques detected very little carbon deposits (ca. 0.2 wt% of the catalyst charge) on the used catalyst under atmospheric pressure. In contrast, large amount of whisker carbon deposit (ca. 100 wt% of the catalyst charge) were formed on the used catalyst under high pressure. In the high-pressure reaction, the activity decline during the initial stage was closely related to the amount of carbon deposits on the catalyst, which also became stabilized after the catalyst had served the reaction for ca. 12 h. The carbon deposits on the used catalyst in the high-pressure reaction contained two different components (-carbon and -carbon) while the carbon deposits in the atmospheric pressure reaction were in the form of -carbon. No notable sintering of metallic nickel was detected by XRD on the used catalyst in the reaction under atmospheric pressure whereas unavoidable sintering of metallic Ni particles happened within the very first hours of the high-pressure reaction.     

Cu-Ni/Al2O3-SiO2催化剂上乙醇水蒸气重整制氢

采用共沉淀法、热分解和氢还原等步骤制备了纳米晶载体催化剂Cu-Ni/Al2O3-SiO2,应用X射线衍射、x射线光电子能谱、扫描电镜对催化剂的体相和表面结构进行了测定,采用固定床反应器考察了催化剂对乙醇水蒸气重整制氢反应的催化性能。实验结果表明,5%Cu-Ni/Al2O3-SiO2催化剂对乙醇的低温水蒸气重整反应表现出较高的催化活性,350℃时乙醇的转化率已达到100%。在650℃时氢气的选择性可达78.5%。增加铜含量对增加催化剂的活性没有帮助。     

Steam reforming of n-hexadecane over noble metal-modified Ni-based catalysts

Steam reforming of n-hexadecane, a main constituent of diesel, over noble metal-modified Ni-based hydrotalcite catalyst was carried out in a temperature range of 700–950 °C, at an atmospheric pressure with space velocity of 10,000–100,000 h⁻¹ and feed molar ratio of H₂O/C = 3.0. The catalysts were prepared by a co-precipitation and dipping methods. The noble metal-modified Ni-based hydrotalcite catalyst displayed higher resistance for the sintering of active metal than the Ni-based hydrotalcite catalyst prepared by the conventional method. It was found that the Rh-modified Ni-based catalysts showed high resistance to the formation of carbon compared to Ni-based catalysts. The results suggest that Rh-modified Ni-based catalyst can be applied for the steam reforming (SR) reaction of diesel.     

Cu-Ni/Al_20_3-SiO_2催化剂上乙醇水蒸气重整制氢

采用共沉淀法、热分解和氢还原等步骤制备了纳米晶载体催化剂Cu-Ni/Al203-SiO2,应用X射线衍射、x射线光电子能谱、扫描电镜对催化剂的体相和表面结构进行了测定,采用固定床反应器考察了催化剂对乙醇水蒸气重整制氢反应的催化性能。实验结果表明,5%Cu-Ni/Al203-SiO2催化剂对乙醇的低温水蒸气重整反应表现出较高的催化活性,350℃时乙醇的转化率已达到100%。在650℃时氢气的选择性可达78.5%。增加铜含量对增加催化剂的活性没有帮助。     

新型镍基镁渣催化重整松木热解挥发分焦油析出特性研究

采用过量浸渍法制备了镍基镁渣催化剂,并在小型气流床气化炉上开展了松木热解挥发分的催化重整研究。评估了煅烧/催化温度、镍含量和水碳比对焦油组分的影响,同时在不同煅烧/催化温度下与Ni/γ-Al₂O₃催化剂进行了裂解焦油性能的对比。采用比表面积测试（BET）、X射线衍射（XRD）、扫描电镜（SEM）和透射电镜（TEM）对催化剂进行了表征。结果表明,当镍含量为3%,煅烧/催化温度为800℃,水碳比为0.5时,镍基镁渣催化剂表现出最优异的催化裂解焦油能力：大幅度降低了重质多环芳烃的相对含量,并且焦油转化率达到95.69%,同时焦油露点温度降至40.2℃。XRD结果表明,Ni、Fe、Ca、Mg相互作用可以形成多种活性中心,进而协同提高催化剂活性。     

镍基乙醇水汽重整催化剂:机理、失活与构效关系

为了应对潜在的氢能利用需求,乙醇水汽重整反应受到了越来越多的关注。镍基催化剂因其高活性、高选择性以及成本优势而极具应用前景,同时在提高催化剂稳定性、降低反应温度、提高氢气收率等方面仍然有进一步发展的空间。更深入认识反应机理、失活机制和催化剂的构效关系是开发高效催化剂的关键。本文对近年来镍基乙醇重整催化剂的研究进展进行了整理总结,首先介绍了通过原位光谱、动力学以及理论计算等手段取得对反应中间物种与反应机理的新认识,分析了催化剂失活的主要原因,并且讨论了镍基催化剂的活性相、尺寸效应、助剂效应,双金属效应等问题,最后简单介绍了得益于基础研究进展的催化剂合成方面的成果,并提出对镍基乙醇水蒸气重整（ESR）剂未来发展的看法：在线/原位表征技术和理论计算将有助于真正理解镍基ESR催化剂的构效关系和反应机理,而新材料,如碳化钼的应用可能在提高催化剂反应性能方面起到作用。