CH4 reforming with CO2 for syngas production over La2O3 promoted Ni catalysts supported on mesoporous nanostructured γ-Al2O3

Nanostructured γ-Al₂O₃ with high surface area and mesoporous structure was synthesized by sol-gel method and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by XRD, N₂ adsorption-desorption, TPR, TPO, TPH, NH₃-TPD and SEM techniques. The BET analysis showed a high surface area of 204 m²·g⁻¹ and a narrow pore-size distribution centered at a diameter of 5.5 nm for catalyst support. The BET results revealed that addition of lanthanum oxide to aluminum oxide decreased the specific surface area. In addition, TPR results showed that addition of lanthanum oxide increased the reducibility of nickel catalyst. The catalytic evaluation results showed an increase in methane conversion with increasing lanthanum oxide to 3 mol% and further increase in lanthanum content decreased the catalytic activity. TPO analysis revealed that the coke deposition decreased with increasing lanthanum oxide to 3 mol%. SEM and TPH analyses confirmed the formation of whisker type carbon over the spent catalysts. Addition of steam and O₂ to dry reforming feed increased the methane conversion and led to carbon free operation in combined processes.     

Mo/HZSM-5催化剂上甲烷无氧芳构化反应中积炭的研究

 对经过程序升温表面甲烷无氧芳构化反应后的Mo／HZSM－5催化剂上的积炭进行程序升温加氢反应和程序升温二氧化碳反应,并对相应的催化剂上的积炭进行程序升温氧化反应和热重实验,以研究催化剂上的不同积炭物种．结果表明,甲烷无氧芳构化反应后有两类烧炭峰,一类是低温烧炭峰,另一类是高温烧炭峰;H2主要对高温烧炭峰发生作用,对低温烧炭峰几乎没有影响;CO2可同时对两种烧炭峰产生影响．由此推论,甲烷在无氧条件下直接转化生成芳烃的反应过程中,沉积在Mo／HZSM－5催化剂上的积炭有三种形式,即：能够与H2反应的积炭,能够与CO2反应的积炭和可能以Mo2C形式存在的物种．     

甲烷无氧芳构化反应中Co助剂对Mo／HZSM-5

 甲烷在Co－Mo／HZSM－5催化剂上进行无氧芳构化反应的评价结果表明，Co的添加大大提高了Mo／HZSM－5催化剂在反应过程中的稳定性．BET实验证明，反应后的积炭对Co－Mo／HZSM－5催化剂孔道堵塞的程度较小．对积炭催化剂进行的一系列程序升温表面反应（如TPH，TPCO2和TPO）结果表明，TPO谱上有两个峰温明显不同的烧炭峰，Co的添加明显抑制了高温积炭的生成．H2主要与高温积炭发生反应，这部分积炭是催化剂失活的主要原因；CO2对低温积炭的影响则尤为明显．TEM结果表明，积炭催化剂上存在丝状积炭物种．碳丝不能与H2反应，但能被CO2除去．Co的添加促进了丝状积炭物种的生成，碳丝并不是导致催化剂失活的因素．     

Rh doping effect on coking resistance of Ni/SBA-15 catalysts in dry reforming of methane

A series of SBA-15 supported bimetallic Rh–Ni catalysts with different weight ratio of Rh/Ni in the range of 0–0.04 were prepared for carbon dioxide reforming of methane. The doping effect of Rh on catalytic activity as well as carbon accumulation and removal over the catalysts was studied. The characterization results indicated that the addition of a small amount of Rh promoted the reducibility of Ni particles and decreased the Ni particle size. During the dry reforming reaction, the carbon deposition was originated from CH4 decomposition and CO disproportionation. The Rh–Ni catalyst with small metallic particle size inhibited the carbon formation and exhibited high efficiency in the removal of coke. In comparison with bare Ni-based catalyst, the Rh–Ni bimetallic catalysts showed high activity and stability in the dry reforming of methane.     

Syngas Production by Methane Reforming with Carbon Dioxide on Noble Metal Catalysts

A series of noble metal catalysts (Ru, Rh, Ir, Pt, and Pd) supported on alumina-stabilized magnesia (Spinel) were used to produce syngas by methane reforming with carbon dioxide. The synthesized catalysts were characterized using BET, TPR, TPO, TPH, and H2S chemisorption techniques. The activity results showed high activity and stability for the Ru and Rh catalysts. The TPO and TPH analyses indicated that the main reason for lower activity and stability of the Pd catalyst was the formation of the less reactive deposited carbon and sintering of the catalyst.     

Study on the Reaction Mechanism for Carbon Dioxide Reforming of Methane over supported Nickel Catalyst

The adsorption and dissociation of methane and carbon dioxide for reforming on nickel catalyst were extensively investigated by TPSR and TPD experiments. It showed that the decomposition of methane results in the formation of at least three kinds of surface carbon species on supported nickel catalyst, while CO2 adsorbed on the catalyst weakly and only existed in one kind of adsorption state. Then the mechanism of interaction between the species dissociated from CH4 and CO2 during reforming was proposed.     

Catalytic performances of Ni/mesoporous SiO_2 catalysts for dry reforming of methane to hydrogen

Several mesoporous silicas with different morphologies were controllably prepared by sol-gel method with adjustable ratio of dual template,and they were further impregnated with aqueous solution of nickel nitrate,followed by calcination in air.The synthesized silica supports and supported nickel samples were characterized using N_2-adsorption/desorption,X-ray diffraction(XRD),H_2 temperature-programmed reduction(H_2-TPR),Scanning electron microscope(SEM),Transmission electron microscope(TEM) and thermo-gravimetric analysis(TGA-DTG) techniques.The Ni nanoparticles supported on shell-like silica are highly dispersed and yielded much narrower nickel particle-size than those on other mesoporous silica.The methane reforming with dioxide carbon reaction results showed that Ni nanoparticles supported on shell-like silica carrier exhibited the better catalytic performance and catalytic stability than those of nickel catalyst supported on other silica carrier.The thermo-gravimetric analysis on used nickel catalysts uncovered that catalyst deactivation depends on the type and nature of the coke deposited.The heterogeneous nature of the deposited coke was observed on nickel nanoparticles supported on spherical and peanut-like silica.Much narrower and lower TGA derivative peak was founded on Ni catalyst supported on the shell-like silica.     

程序升温技术研究Mo/HZSM-5催化剂上甲烷无氧芳构化反应积炭的化学特性

对经过程序升温表面甲烷无氧芳构化反应(TPSR)后的Mo/HZSM-5催化剂上的积炭进行了程序升温加氢反应(TPH)和程序升温CO₂反应(TPCO₂),并对相应催化剂上的积炭进行了程序升温氧化反应(TPO)和热重(TG)实验.TPH实验及TPCO₂实验表明,H₂主要对高温烧炭峰发生作用.CO₂则可同时对这两种烧炭峰产生影响,对低温峰积炭的影响尤其明显.对不同Mo含量的催化剂进行上述实验的结果表明,Mo担载量的变化及不同的实验过程都会影响催化剂上两种温峰的积炭在总积炭量中所占的比例.由TG实验数据计算出的动力学结果说明,无论是TPH还是TPCO₂实验都可以降低烧炭过程的一级反应起始温度,并减少其活化能.此外,催化剂中Mo担载量的变化也会对开始温度和烧炭活化能产生明显影响.     

Co/Al2O3催化剂上积炭的研究

甲烷的二氧化碳重整制合成气是近年来甲烷催化转化的一个重要方面,而所用催化剂的积炭问题仍是影响催化剂活性和寿命的主要因素之一．近年来,对催化剂表面的积炭形式有一些报道［１］,但对积炭的种类及其与催化剂活性的关系很少有报道．本文从经低温焙烧的Ｃｏ／Ａｌ２...     

甲烷干重整催化剂Ni/Al2O3表面积炭表征与分析

用蒸发法制备了Ni/Al2O3催化剂及浸渍法制备了Ni/α-Al2O3和Ni/γ-Al2O3催化剂, 并与商品天然气水蒸气重整催化剂Z118Y一起进行了甲烷干重整实验, 考察了各催化剂上表面积炭行为. 通过H2程序升温还原(H2-TPR)、BET(Brunauer-Emmett-Teller)比表面积分析、X射线衍射(XRD)、透射电镜(TEM)、热重-差式扫描量热(TG-DSC)、程序升温氢化(TPH)等表征手段对催化剂表面沉积炭的特性进行了表征. 结果表明, 各催化剂上至少存在三种形式的碳物种: 无定形碳、丝状碳及石墨碳. 由于载体性质不同, 各催化剂上沉积炭的种类及其含量有所差别. Z118Y、Ni/Al2O3及Ni/α-Al2O3催化剂上主要沉积丝状炭, 而Ni/γ-Al2O3催化剂上则主要是石墨碳. Ni/γ-Al2O3催化剂中金属Ni颗粒较小(小于15 nm)、粒径分布范围较窄、分散性较好, 能减少催化剂表面炭的沉积, 有效地抑制丝状碳的生长.     

CO2 reforming of methane over nickel catalysts supported on nanocrystalline MgAl2O4 with high surface area

In this paper dry reforming of methane (DRM) was carried out over nanocrystalline MgAl2O4-supported Ni catalysts with various Ni loadings. Nanocrystalline MgAl2O4 spinel with high specific surface area was synthesized by a co-precipitation method with the addition of pluronic P123 triblock copolymer as surfactant, and employed as catalyst support. The prepared samples were characterized by X-ray diffraction (XRD), N2 adsorption, H2 chemisorption, temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), temperature- programmed desorption (TPD) and transmission and scanning electron microscopies (TEM, SEM) techniques. The obtained results showed that the catalyst support has a nanocrystalline structure (crystal size: about 5 nm) with a high specific surface area (175 m2 g-1) and a mesoporous structure. Increasing in nickel content decreased the specific surface area and nickel dispersion. The prepared catalysts showed high catalytic activity and stability during the reaction. SEM analysis revealed that whisker type carbon deposited over the spent catalysts and increasing in nickel loading increased the amount of deposited carbon. The nickel catalyst with 7 wt% of nickel showed the highest catalytic activity.     

Effect of CO2/CO Addition in Dehydroaromatization of Methane on Zeolite-Supported Mo and Re Catalysts Towards Hydrogen, Benzene and Naphthalene

High activity and high formation selectivity for aromatics in the dehydrocondensation reaction of methane were realized only on selected catalysts. The requisites of a metal and a zeolite support as the selected catalyst were described. However, the catalytic activity steadily declined even on the selected catalysts with time on stream because of coke accumulation. A stable catalytic activity was obtained when CO₂ or CO was added into methane feed due to effective removal of coke from the catalyst surface by CO or CO₂. The route from methane to aromatics and the formation process of active phase of catalyst were discussed.     

Effect of CO2/CO Addition in Dehydroaromatization of Methane on Zeolite-Supported Mo and Re Catalysts Towards Hydrogen, Benzene and Naphthalene

High activity and high formation selectivity for aromatics in the dehydrocondensation reaction of methane were realized only on selected catalysts. The requisites of a metal and a zeolite support as the selected catalyst were described. However, the catalytic activity steadily declined even on the selected catalysts with time on stream because of coke accumulation. A stable catalytic activity was obtained when CO₂ or CO was added into methane feed due to effective removal of coke from the catalyst surface by CO or CO₂. The route from methane to aromatics and the formation process of active phase of catalyst were discussed.     

Optimizing the parameters of the steam-carbon dioxide conversion of methane by Gibbs energy minimization

The thermodynamic equilibrium for the steam-carbon dioxide conversion of methane was studied by Gibbs energy minimization. The degree of coke formation, the content of methane and carbon dioxide in the synthesis gas, and the synthesis gas H₂/CO ratio were plotted as functions of the molar ratios of CO₂/CH₄ and H₂O/CH₄ in the initial mixture at different temperatures and pressures. The regions of the optimum CH₄/CO₂/H₂O molar ratios for steam-carbon dioxide conversion were discovered, with no coke formation taking place in these regions. The optimized CH₄/CO₂/H₂O molar fractions characterized by the minimum content of methane and carbon dioxide in the synthesis gas were found for each region.     

Studies on the Adsorption and Dissociation of Methane and Carbon Dioxide on Nickel

The adsorption and dissociation of methane and carbon dioxide for reforming on nickel catalysts were extensively investigated by TPSR, TPD, XPS and pulse reaction methods. These studies showed that the decomposition of methane results in the formation of at least three kinds of surface carbon species on supported nickel catalysts. Carbidic Cα, carbonaceous Cβ and carbidic clusters Cγ surface carbon species formed by the decomposition of methane demonstrated different surface mobility, thermal stability and reactivity. Carbidic Cα is a very active and important intermediate in carbon dioxide reforming with methane, and the carbidic clusters Cγ species might be the precursor of surface carbon deposition. The partially dehydrogenated Cβ species can react with H2 or CO2 to form CH4 or CO. On the other hand, it was proven that CO2 can be weakly adsorbed on supported nickel catalysts, and only one kind of CO2 adsorption state is formed. The interaction mechanism between the species dissociated from CH4 and CO2 during reforming was then hypothesized.     

甲烷干重整反应用Ni-Ru/MgAl类水滑石催化剂的研究

采用焙烧记忆法分别制备Ni/Mg Al O和NiRu/Mg Al O类水滑石催化剂用于甲烷干重整反应.利用XRD、TPR、TG、XPS、CO2-TPD、TEM等表征催化剂的结构及失活特征,发现在Ni/Mg Al O中添加Ru,有利于增加催化剂表面Ni含量,并促进Ni2+的还原.不同Mg/Al比双金属催化剂中,7Ni-0.15Ru/Mg2.5Al催化剂具有较高的催化活性,这归结为该催化剂适宜的碱性、较高表面Ni含量以及小尺寸的Ni0物种.添加Ru明显抑制Ni/Mg Al O催化剂表面的丝状碳的形成.而7Ni-0.15Ru/Mg2.5Al较强的抗积碳性能与其较小Ni0晶粒尺寸及适宜催化剂碱性有关.     

等离子体条件下甲烷在CO_2存在下的脱氢偶联(英文)

在常温常压下,利用脉冲电晕等离子体研究了甲烷和二氧化碳的转化。在等离子体一催化反应装置上,测试了Ｐｄ／γ－Ａｌ２Ｏ３对甲烷偶联的催化活性。实验发现,在脉冲电晕等离子体作用下,甲烷和二氧化碳被转化为Ｃ２烃、ＣＯ、Ｈ２、Ｏ２、少量积碳和高碳烃;在等离子体条件下引入Ｐｄ／γ－Ａｌ２Ｏ３催化剂,能够有效地改善甲烷偶联产物Ｃ２烃的分布,有利于生成更高附加值的乙烯。     

Dry reforming reaction over nickel catalysts supported on nanocrystalline calcium aluminates with different CaO/Al2O3 ratios

Nanocrystalline calcium aluminates with different CaO/Al2O3 ratios were prepared by a facile co-precipitation method using Poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-PPG-PEG, MW: 5800) as a surfactant. They were employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by X-ray diffraction (XRD), N2 adsorption (BET), temperature-programmed reduction and oxidation (TPR-TPO), and scanning electron microscopy (SEM) techniques. Catalysts showed a relatively high catalytic activity and stability. TPR analysis revealed that the catalysts with higher CaO content are more difficult to be reduced. TPO analysis showed that the 5 wt%Ni/CA and 5 wt%Ni/C12A7 catalysts with higher CaO amount were effective against coke deposition.     

Nickel catalysts supported on MgO with different specific surface area for carbon dioxide reforming of methane

In this paper, three kinds of MgO with different specific surface area were prepared, and their effects on the catalytic performance of nickel catalysts for the carbon dioxide reforming of methane were investigated. The results showed that MgO support with the higher specific surface area led to the higher dispersion of the active metal, which resulted in the higher initial activity. On the other hand, the specific surface area of MgO materials might not be the dominant factor for the basicity of support to chemisorb and activate CO₂, which was another important factor for the performance of catalysts. Herein, Ni/MgO(CA) catalyst with proper specific surface area and strong ability to activate CO₂ exhibited stable catalytic property and the carbon species deposited on the Ni/MgO(CA) catalyst after 10 h of reaction at 650 °C were mainly activated carbon species.     

Hydrogenation of Carbon Dioxide on Iron Manganese Catalysts

The synthesis of hydrocarbons from hydrogenation of carbon dioxide has been studied on a series of coprecipitated iron-manganese catalysts. Kinetic measurements, X-ray diffraction, Mössbauer spectroscopy, and temperature-programmed reaction of adsorbed species were used for activity tests and catalyst characterizations. The results showed that the yields of low-carbon olefins decrease, whereas the amount of methane increases with increasing manganese content in catalysts. The conversion to hydrocarbons is suppressed by the reverse water-gas shift (RWGS) reaction equilibrium. Mössbauer spectra and XRD patterns of catalysts after reaction indicate that catalysts are severely oxidized; it is speculated that the olefin producing surface structure in CO hydrogenation may be destroyed by this oxidation. A pulse-reactor study of the Boudouard reaction showed that manganese has the effect of suppressing CO dissociation and thus decreasing carbon content on catalysts. For CO₂ hydrogenation, the affinity to carbon on catalysts is important; therefore manganese is not a good promoter. Among all catalysts tested, pure iron has the best selectivity to olefinic and long-chain hydrocarbons.