Insights into the intrinsic interaction between series of C1 molecules and surface of NiO oxygen carriers involved in chemical looping processes

Understanding and modulating the interaction between various reactive molecules and oxygen carriers are the key issue to achieve process intensification of chemical looping technology. C1 chemical molecules play an important role in many reactions involved with chemical looping processes. However, up to now, there is still a lack of systematic and in-depth understanding of the adsorption mechanism of C1 molecules on the surface of oxygen carriers (OCs). In this work, the intrinsic interaction between a series of C1 molecules composed of CH₄, CO, CO₂, CH₃OH, HCHO and HCOOH and surface of NiO OCs in the chemical looping process have been studied using density functional theory calculations. Various adsorption configurations of C1 molecules and also different adsorption sites of NiO have been considered. The structural features of stable configuration of C1 molecules on the surface of NiO OCs have been obtained. Further, the interacted sites, types and strengths of C1 molecules on the surface of NiO have been directly pictured by the independent gradient model methods. Also, the nature of the interaction between C1 molecule and NiO surface has been investigated with the aid of energy decomposition analysis from a quantitative view.     

Catalytic combustion of methane over a highly active and stable NiO/CeO2 catalyst

In the last decades, many reports dealing with technology for the catalytic combustion of methane (CH₄) have been published. Recently, attention has increasingly focused on the synthesis and catalytic activity of nickel oxides. In this paper, a NiO/CeO₂ catalyst with high catalytic performance in methane combustion was synthesized via a facile impregnation method, and its catalytic activity, stability, and water-resistance during CH₄ combustion were investigated. X-ray diffraction, low-temperature N₂ adsorption, thermogravimetric analysis, Fourier transform infrared spectroscopy, hydrogen temperature programmed reduction, methane temperature programmed surface reaction, Raman spectroscopy, electron paramagnetic resonance, and transmission electron microscope characterization of the catalyst were conducted to determine the origin of its high catalytic activity and stability in detail. The incorporation of NiO was found to enhance the concentration of oxygen vacancies, as well as the activity and amount of surface oxygen. As a result, the mobility of bulk oxygen in CeO₂ was increased. The presence of CeO₂ prevented the aggregation of NiO, enhanced reduction by NiO, and provided more oxygen species for the combustion of CH₄. The results of a kinetics study indicated that the reaction order was about 1.07 for CH₄ and about 0.10 for O₂ over the NiO/CeO₂ catalyst.     

二价铬/钼/镍空配位MOFs的CH4/N2吸附分离研究

基于金属有机骨架材料中金属空配位对气体的强吸附作用,利用具有较高活性的二价金属Cr²⁺/Mo²⁺/Ni²⁺与均苯三酸（H₃BTC）配位合成了HKUST-1（Cu-BTC）同构系列材料M-BTC（M=Cr、Mo、Ni）,并与Cu-BTC对比分析了该类型材料中不同金属空配位对甲烷和氮气的吸附性能。实验结果显示,此三种材料均具有较好的甲烷选择吸附性,其中含Ni²⁺金属空位的Ni-BTC以其尤为突出的甲烷吸附热值而呈现较好的CH₄/N₂分离潜力;Cr²⁺空配位虽具有较强活性,但是对于甲烷的选择性吸附性能却低于含Cu²⁺空位的Cu-BTC材料。结合吸附选择性IAST计算分析得到此三种含较高活性不饱和金属空配位的MOFs材料对于甲烷选择性吸附作用能顺序为：Ni-BTC > Mo-BTC > Cu-BTC > Cr-BTC。     

化学链燃烧过程Fe2O3/Al2O3载氧体表面CH4反应：ReaxFF-MD模拟

借助ReaxFF-MD方法,对化学链燃烧过程Al₂O₃负载Fe₂O₃载氧体（Fe₂O₃/Al₂O₃）表面CH₄反应过程模拟,探究Al₂O₃惰性载体对Fe₂O₃-CH₄体系燃烧过程的调控机制。研究发现添加Al₂O₃惰性载体改变了化学链燃烧过程中Fe₂O₃载氧体反应性和Fe₂O₃/Al₂O₃-CH₄反应体系的热力学和动力学行为。主要是促进了Fe₂O₃载氧体表面CH₄氧化,并对CH₄反应过程、中间体、产物及其反应速率和放热量等均具有显著促进和调控作用。原因在于Al₂O₃惰性载体对Fe₂O₃活性相中晶格氧的活化作用促进了晶格氧的迁移-扩散-释放。添加惰性载体增强了Fe₂O₃载氧体在化学链燃烧过程晶格氧释放速率和释放量,有利于CH₄氧化燃烧向合成气的高效、清洁转化,强化了化学链燃烧过程,满足当前能源高效转化和碳减排目标。     

化学链燃烧过程Fe2O3/Al2O3载氧体表面CH4反应：ReaxFF-MD模拟

借助ReaxFF-MD方法,对化学链燃烧过程Al₂O₃负载Fe₂O₃载氧体（Fe₂O₃/Al₂O₃）表面CH₄反应过程模拟,探究Al₂O₃惰性载体对Fe₂O₃-CH₄体系燃烧过程的调控机制。研究发现添加Al₂O₃惰性载体改变了化学链燃烧过程中Fe₂O₃载氧体反应性和Fe₂O₃/Al₂O₃-CH₄反应体系的热力学和动力学行为。主要是促进了Fe₂O₃载氧体表面CH₄氧化,并对CH₄反应过程、中间体、产物及其反应速率和放热量等均具有显著促进和调控作用。原因在于Al₂O₃惰性载体对Fe₂O₃活性相中晶格氧的活化作用促进了晶格氧的迁移-扩散-释放。添加惰性载体增强了Fe₂O₃载氧体在化学链燃烧过程晶格氧释放速率和释放量,有利于CH₄氧化燃烧向合成气的高效、清洁转化,强化了化学链燃烧过程,满足当前能源高效转化和碳减排目标。     

碱/碱土金属修饰Ni基催化剂的CO2吸附与甲烷化性能

采用分步浸渍法制备了碱/碱土金属修饰Ni基催化剂Ni-M/Al₂O₃ (M=K₂CO₃, Na₂CO₃, MgO, CaO)。探究了碱/碱土金属的添加对改性Ni基催化剂CO₂吸附和甲烷化性能的影响。研究发现,碱/碱土金属的添加提高了Ni/Al₂O₃催化剂表面的碱性活性位点密度,强化了其CO₂吸附性能。碱/碱土金属类型影响Ni-M/Al₂O₃催化剂碱性活性位点的分布、NiO物相的转化及Ni的分散度,进而影响其甲烷化性能。MgO添加使NiO物相转化为与载体呈强相互作用的β型和γ型NiO,降低了催化剂表面的强碱性活性位点比例,有利于CO₂吸附活化。Ni-MgO/Al₂O₃的CO₂吸附容量最高为0.68mmolCO₂/g,其CO₂转化率和CH₄选择性分别高达58.4%和95.4%,其在烟气CO₂捕集与原位甲烷化中极具应用前景。     

Ce1-xNixOy氧载体在化学链甲烷重整耦合CO2还原中的应用

化学链甲烷重整耦合CO₂还原技术既能生产合成气还可以还原CO₂生成CO。采用共沉淀法制备不同Ce/Ni摩尔比的系列Ce_1-xNi_xO_{y（x = 0,0.2,0.4,0.6,0.8,1）氧载体。通过XRD、BET、XPS及CH4-TPR等表征对氧载体的理化性质进行了研究。系统考察了Ce1-xNixOy氧载体在化学链甲烷重整耦合CO2还原反应中的反应性能。与单一金属氧化物NiO和CeO2相比,Ce1-xNixOy复合氧载体在该反应中具有更高的活性和热稳定性。在甲烷部分氧化阶段,Ce0.2Ni0.8Oy和Ce0.4Ni0.6Oy氧载体具有较高的CH4转化率。经历了20次redox循环实验,Ce0.2Ni0.8Oy氧载体的CO2转化率几乎保持不变,表明Ce0.2Ni0.8Oy氧载体具有较高的热稳定性。}     

Investigation of the redox performance of pyrite cinder calcined at different temperature in chemical looping combustion

As an industrial solid waste, pyrite cinder exhibited excellent reactivity and cycle stability in chemical looping combustion. Prior to the experiment, oxygen carriers often experienced a high temperature calcination process to stabilize the physico-chemical properties, which presented significant influence on the redox performance of oxygen carriers. However, the effect of calcination temperature on the cyclic reaction performance of pyrite cinder has not been studied in detail. In this work, the effect of calcination temperature on the redox activity and attrition characteristic of pyrite cinder were studied in a fluidized-bed reactor using CH₄ as fuel. A series of pyrite cinder samples were prepared by controlling the calcination temperature. The redox activity and attrition rate of the obtained pyrite cinder samples were investigated deeply. The results showed that calcination temperature displayed significant impact on the redox performance of pyrite cinder. Considering CH₄ conversion (80%–85%) and attrition resistance, the pyrite cinder calcined at 1050?℃ presented excellent redox properties. In the whole experiment process, the CO₂ selectivity of the pyrite cinder samples were not affected by the calcination temperature and were still close to 100%. The results can provide reference for optimizing the calcination temperature of pyrite cinder during chemical looping process.     

Synthesis of C2H4 by partial oxidation of CH4 over LiCl/NiO

Alkali halide added transition metal oxides produced ethylene selectively in oxidative coupling of methane. The role of alkali halides has been investigated for LiCl-added NiO (LiCl/NiO). In the absence of LiCl the reaction over NiO produced only carbon oxides (CO₂ + CO). However, addition of LiCl drastically improved the yield of C₂ compounds (C₂H₆ + C₂H₄). One of the roles of LiCl is to inhibit the catalytic activity of the host NiO for deep oxidation of CH₄. The reaction catalyzed by the LiCl/NiO proceeds stepwise from CH₄ to C₂H₄ through C₂H₆ (2CH₄ → C₂H₆ → C₂H₄). The study on the oxidation of C₂H₆ over the LiCl/NiO showed that the oxidative dehydrogenation of C₂H₆ to C₂H₄ occurs very selectively, which is the main reason why partial oxidation of CH₄ over LiCl/NiO gives C₂H₄ quite selectively. The other role of LiCl is to prevent the host oxide (NiO) from being reduced by CH₄. The catalyst model under working conditions was suggested to be the NiO covered with molten LiCl. XPS studies suggested that the catalytically active species on the LiCl/NiO is a surface compound oxide which has higher valent nickel cations (Ni^(2+δ)+ or Ni³⁺). The catalyst was deactivated at the temperatures>973 K due to vaporization of LiCl and consumption of chlorine during reaction. The kinetic and CH₄---CD₄ exchange studies suggested that the rate-determining step of the reaction is the abstraction of H from the vibrationally excited methane by the molecular oxygen adsorbed on the surface compound oxide.     

Kinetic studies of CH4 oxidation over Pt–NiO/δ-Al2O3 in a fluidised bed reactor

The oxidation of CH₄ over Pt–NiO/δ-Al₂O₃ has been studied in a fluidised bed reactor as part of a major project on an autothermal (combined oxidation–steam reforming) system for CH₄ conversion. The kinetic data were collected between 773 and 893 K and 101 kPa total pressure using CH₄ and O₂ compositions of 10–35% and 8–30%, respectively. Rate–temperature data were also obtained over alumina-supported monometallic catalysts, Pt and NiO. The bimetallic Pt–NiO system has a lower activation energy (80.8 kJ mol⁻¹) than either Pt (86.45 kJ mol⁻¹) and NiO (103.73 kJ mol⁻¹). The superior performance of the bimetallic catalyst was attributed to chemical synergy. The reaction rate over the Pt–NiO catalyst increased monotonically with CH₄ partial pressure but was inhibited by O₂. At low partial pressures (<30 kPa), H₂O has a detrimental effect on CH₄ conversion, whilst above 30 kPa, the rate increased dramatically with water content.     

Catalytic reduction of NO by CO over NiO/CeO2 catalyst in stoichiometric NO/CO and NO/CO/O2 reaction

A new catalyst composed of nickel oxide and cerium oxide was studied with respect to its activity for NO reduction by CO under stoichiometric conditions in the absence as well as the presence of oxygen. Activity measurements of the NO/CO reaction were also conducted over NiO/γ-Al₂O₃, NiO/TiO₂, and NiO/CeO₂ catalysts for comparison purposes. The results showed that the conversion of NO and CO are dependent on the nature of supports, and the catalysts decreased in activity in the order of NiO/CeO₂ > NiO/γ-Al₂O₃ > NiO/TiO₂. Three kinds of CeO₂ were prepared and used as support for NiO. They are the CeO₂ prepared by (i) homogeneous precipitation (HP), (ii) precipitation (PC), and (iii) direct decomposition (DP) method. We found that the NiO/CeO₂(HP) catalyst was the most active, and complete conversion of NO and CO occurred at 210 °C at a space velocity of 120,000 h⁻¹. Based on the results of surface analysis, a reaction model for NO/CO interaction over NiO/CeO₂ has been proposed: (i) CO reduces surface oxygen to create vacant sites; (ii) on the vacant sites, NO dissociates to produce N₂; and (iii) the oxygen originated from NO dissociation is removed by CO.     

Simulation study on the gasification process of Ningdong coal with iron-based oxygen carrier

Chemical looping gasification (CLG) of Ningdong coal by using Fe₂O₃ as the oxygen carriers (OCs) was studied, and the gasification characteristics were obtained. A computation fluid dynamics (CFD) model based on Eulerian‐-Lagrangian multiphase framework was established, and a numerical simulation the coal chemical looping gasification processes in fuel reactor (FR) was investigated. In addition, the heterogeneous reactions, homogeneous reactions and Fe₂O₃ oxygen carriers' reduction reactions were considered in the gasification process. The characteristics of gas flow and gasification in the FR were analyzed and it was found that the experiment results were consistent with the simulation values. The results show that when the O/C mole rate was 0.5:1, the gasification temperature was 900 ℃ and the water vapor volume flow rate was 2.2 ml·min^-1, the mole fraction of syngas reached a maximum value of the experimental result and simulation value were 71.5% and 70.2%, respectively. When the O/C mole rate was 0.5:1, the gasification temperature was 900 ℃, and the water vapor volume flow was 1.8 ml·min^-1; the gasification efficiency reached the maximum value was 62.2%, and the maximum carbon conversion rate was 84.0%.     

NiFeAlO4载氧体制备及煤化学链燃烧反应特性

铁基载氧体是一种具有工业应用前景的载氧体,但存在氧利用率低、在高温下易烧结等问题。虽可通过制备双金属复合载氧体或添加惰性组分改进其性能,但均存在一定缺陷。若将活性组分和惰性材料融入到一个晶体结构制备尖晶石结构载氧体,则可实现利用双金属协同作用提高载氧体活性的同时,利用Al3+提高载氧体的稳定性。采用共沉淀法和溶胶凝胶法制备了具有尖晶石结构的NiFeAlO₄载氧体,考察了制备方法、载氧体与煤质量比对NiFeAlO₄载氧体化学链燃烧特性和循环稳定性的影响,并分析了载氧体对煤转化过程的作用。结果表明,溶胶凝胶法制备的NiFeAlO₄载氧体具有更好的反应性,载氧体与煤质量比为20∶1时,碳转化率为86.7%,远高于煤单独热解时的碳转化率(34%),此时CO₂体积分数为93.6%。对反应前后NiFeAlO₄载氧体晶相结构和形貌进行分析,表明循环过程中经“还原-氧化”后生成的NiO和载氧体颗粒团聚是导致载氧体活性下降的主要原因。相较于载热作用,NiFeAlO₄载氧体在煤化学链燃烧中主要起供氧作用,其不仅会促进挥发分向煤气的转化,且NiFeAlO₄载氧体与焦炭之间也存在固-固反应,利于更多CO₂的生成。     

Mg修饰Fe/Al载氧体煤化学链制氢

目前化学链过程常用的Fe₂O₃/Al₂O₃载氧体会形成FeAl₂O₄,因热力学限制很难与水反应制氢。为了抑制FeAl₂O₄的形成,本文向Fe/Al载氧体中添加Mg,在固定床上进行煤化学链制氢（CLHG）,深入分析Mg的作用机理并探究其对实验结果的影响。XRD结果表明,Mg质量分数从1%增加到26.5%时,MgAl₂O₄特征峰增强,FeAl₂O₄特征峰逐渐消失,说明Mg减弱了Fe和Al之间的相互作用。SEM显示Mg添加后载氧体颗粒减小,耐烧结性能优异。对比不同煤/载氧体质量比的实验,质量比为0.5/15时碳转化率和产氢量最高。在不同Mg含量的载氧体中,Fe40Mg20Al40具备最好的反应性能,碳转化率和产氢量为81.75%和1.7182L/g,比Fe40Al60分别增加10.2%和58.5%。Fe40Mg20Al40经10次循环,表面仅有轻微烧结,碳转化率和产氢量均在78%和1.52L/g以上,循环性能良好。添加Mg可以有效抑制FeAl₂O₄的生成,显著增强蒸汽氧化过程的反应活性,大幅提高氢气产量,十分适用于煤化学链制氢。     

铁基移动床化学链技术进展

在日益增长的能源需求与日益严峻的全球气候变化带来的双重压力下,清洁、高效且经济的能源利用方法显得尤为重要。将化学链概念用于传统化石能源的转化是一种前景广阔的新技术。化学链燃烧利用载氧体间接转化含碳燃料,同时实现二氧化碳的捕集。俄亥俄州立大学研发了采用铁基载氧体和移动床反应器的化学链技术,可实现天然气、煤、生物质等多种燃料向电力、氢、液体燃料等产品的零排放转化。目前,合成气化学链（syngas chemical looping,SCL）和煤直接化学链（coal direct chemical looping,CDCL）技术两套25 kW_th级小试装置已成功运行总计超过850 h,一套250 kW_th级的高压SCL装置即将投入示范运行。     

CuO修饰的赤泥载氧体废弃活性炭化学链燃烧

以拜耳法赤泥为基体,采用浸渍法制备了CuO修饰的赤泥载氧体（Cu0.5RM1、Cu1RM1）。利用SEM-EDSmapping、XRD对其进行物化表征,并在高温流化床反应器及热重分析仪中考察了赤泥载氧体的废弃活性炭化学链燃烧特性。结果表明,浸渍法可准确制备定量CuO修饰的赤泥载氧体;相比于纯赤泥载氧体,CuO修饰的赤泥载氧体具有化学链燃烧载氧体与化学链氧解耦燃烧载氧体的双重特性,能够加快碳转化速率,有效提高出口气体中CO₂浓度;Cu1RM1反应活性较高,875℃为其较优的反应温度,此时t₉₅为28min,出口气体中CO₂浓度为92.9%（体积分数）,燃烧效率达93.0%。10次循环实验表明Cu1RM1载氧体具有相对稳定的循环反应特性。     

CH4在PVDF中渗透行为及机理的分子模拟研究

采用巨正则蒙特卡洛法(GCMC)和分子动力学法(MD)相结合的方法模拟研究了典型气体CH4在聚偏氟乙烯(PVDF)中的吸附扩散行为,探讨了温度及压力对气体吸附扩散能力的影响,分析了CH4在PVDF中的吸附位点及扩散轨迹.模拟结果表明,CH4在PVDF中的溶解系数、渗透系数随温度的升高先增大后减小,随压力的升高而增大;扩...     

LaMn1-x-yFexCoyO3-δ钙钛矿载氧体用于化学链部分氧化

采用溶胶-凝胶法制备了B位Fe和Co共取代的LaMn_1-x-yFe_xCo_yO_3-δ钙钛矿型复合氧化物,并用于化学链甲烷部分氧化制合成气。X射线衍射（XRD）结果表明Fe和Co均进入了LaMnO₃的晶格形成钙钛矿晶相,活性和稳定性测试表明LaMn_1/3Fe_1/3Co_1/3O_3-δ载氧体具有最佳的化学链甲烷部分氧化性能。CH₄程序升温还原（CH₄-TPR）表征发现LaMn_1/3Fe_1/3Co_1/3O_3-δ具有比LaBO₃（B=Co, Mn, Fe）更高的甲烷活化能力和晶格氧迁移性能。甲烷恒温脉冲反应（CH₄-pulse reaction）进一步证实了B位离子的协同作用可以提高LaBO₃（B=Co, Mn, Fe）的表面反应速率。程序升温氢气还原（H₂-TPR）表明,LaMn_1/3Fe_1/3Co_1/3O_3-δ中晶格氧具有适中的氧化还原能力,适合用于化学链甲烷部分氧化。     

Characterization of catalysts for methane-coupling by means of temperature programmed desorption

The technique of temperature programmed desorption has been employed to study the adsorptive behaviour of CaO and Na₂O/CaO towards the reactants and products of the methane-coupling reaction. Two forms of adsorbed O₂ can exist on CaO, and they desorb at intermediate temperatures: the first corresponds to the sites for adsorption and desorption without reaction of CH₄, while the second to sites for desorption with total oxidation of CH₄ itself. At the temperatures of the activity runs for methane coupling (750–800 °C), no adsorbed species is therefore stable on the surface of CaO. 7% Na₂O/CaO shows different features, because the desorption of O₂ produces only a large broad peak at very high temperatures, corresponding to sites for adsorption and desorption with total oxidation of CH₄. (On the other hand a desorption peak of CH₄ at intermediates temperatures is also present, which seems to be due to a species, adsorbed undissociatively and desorbed without reaction). At the temperatures of the activity experiments, adsorbed species are therefore stable on the surface of Na₂O/CaO. A conclusion is therefore drawn on the necessity for the intervention of the gas phase O₂ during the methane coupling reaction in order to produce C₂-hydrocarbons, and on the greater importance of the surface reactions in the presence of Na₂O, in comparison to the case of CaO.     

LaMn1-x-yFexCoyO3-δ perovskite based oxygen carriers for chemical looping partial oxidation

LaMn_1-x-yFe_xCo_yO_3-δ perovskite-type composite oxides co-substituted with B-site Fe and Co were prepared by the sol-gel method, and used for the chemical looping partial oxidation of methane to syngas. The XRD results suggest that Fe and Co were incorporated into the lattice of LaMnO₃ and formed perovskite phase. Reactivity and stability tests show that LaMn_1/3Fe_1/3Co_1/3O_3-δ oxygen carrier has the best reaction performance. CH₄-TPR results indicate that LaMn_1/3Fe_1/3Co_1/3O_3-δ has higher methane activation and lattice oxygen migration rates than those of LaBO₃ (B=Co, Mn, Fe). CH₄-pulse reaction further confirms that the synergistic effect of B-site ion substitution can improve the surface reaction rate of LaBO₃ (B=Co, Mn, Fe). H₂-TPR results show that the lattice oxygen in LaMn_1/3Fe_1/3Co_1/3O_3-δ has moderate redox capacity, which is suitable for partial oxidation of methane.