The effect of the nature of the support on catalytic properties of ruthenium supported catalysts in partial oxidation of methane to syn-gas

The effect of the carrier on catalytic properties of ruthenium supported catalysts in partial oxidation of methane (POM) was investigated. A variety of supports differed in texture and reducibility (Al₂O₃, SiO₂, TiO₂, Cr₂O₃, CeO₂ and Fe₂O₃) were used. The catalyst activity is governed by ruthenium phase formation (RuO₂ → Ru⁰), and it depends on redox properties of the support as well as support-ruthenium phase interaction. The activity of Ru supported catalysts decreases in the order Al₂O₃ ≈ SiO₂ > Cr₂O₃ > TiO₂ > CeO₂ > Fe₂O₃. No significant effects of the specific surface area and porosity of catalysts on the methane conversion and selectivity of CO formation were found. The selectivity of CO₂ formation (total oxidation of CH₄) under conditions of POM (a ratio of CH₄/O₂ = 2) is associated with the contribution of reducible support oxides into the catalytic performance.     

Microwave effect on partial oxidation of methane to syngas

In this paper the results of the partial oxidation of methane over Ni-based and Co-based catalysts activated by two different heating modes (conventional and microwaves) are reported. Compared with a conventional heating mode, the temperature of the catalytic bed is much lower and there is a higher selectivity of CO and H₂ with microwave irradiation.     

Modeling of microreactor for syngas production by catalytic partial oxidation of methane

Fixed-bed reactors for the catalytic partial oxidation of methane (CPOM) to produce synthesis gas still pose hot spots problems. Microreactor is a good alternative reactor proposed to resolve these problems. In this paper, synthesis gas (hydrogen and carbon monoxide) production was investigated by a two-dimensional numerical model of single microchannel. CFD modeling with detailed chemistry was conducted to understand the CPOM on platinum (Pt) catalyst. Gas inlet velocity, microchannel pressure, and fuel to air ratio (F/A) are selected as the effective parameters on microchannel performance. Study results show that Reynolds number has considerable effect on methane conversion, hydrogen to carbon monoxide ratio (H2/CO), and product distribution. Increasing gas inlet velocity causes all the above parameters to decrease. It is noted that increasing microchannel pressure and decreasing the ratio of fuel to air cause the decrease of the H2/CO ratio.     

Coke formation during high pressure catalytic partial oxidation of methane to syngas

Summary Carbonization of the surface of alumina-based catalysts has been studied with respect to the composition of the catalysts and conditions of the propionitrile ammonolysis. It was shown that the surface concentration of carbon increases with the increase in temperature and with time of the reaction and depends on the catalysts nature in the order: Al-Zr(5)-O < Al-Zr(40)-O < Al-O < Al-Mg-O. The surface concentration of the Brönsted acidic sites follows the same sequence.     

The role of pressure in partial oxidation of methane

Analysis of experimental data and results of kinetic simulation throw light on the reasons for which the pressure exerts influence on the partial oxidation of methane to methanol. Among the most important factors are a crucial transition of the reaction to the steady-state chain-branched regime, an increase in the role of nonlinear gas-phase reactions, and a change in the relative contribution of heterogeneous transformations to the overall process.     

Kinetics of catalytic oxidation of methane

A kinetic model for methane oxidation in sulfur dioxidecontaining gaseous mixtures at 640–830 °C with Al₂O₃ as catalyst is suggested.     

Monolithic reactors for experimental studies of the catalytic partial oxidation of methane to synthesis gas

Monoliths containing 0.1 wt.% Pt and Rh have been used for the partial oxidation of methane to synthesis gas. Two different impregnation methods for making Pt and Rh (and Ni) monoliths are described and discussed. The studies were carried out at conditions with incomplete conversion of O₂ and with product distributions far from equilibrium. The two metals show different activities.     

State of supported rhodium nanoparticles for methane catalytic partial oxidation (CPO): FT-IR studies

The effect of pretreatments as well as of rhodium precursor and of the support over the morphology of Rh nanoparticles were investigated by Fourier transform infrared (FT-IR) spectroscopy of adsorbed CO. Over a Rh/alumina catalyst, both metallic Rh particles, characterized by IR bands in the range 2070-2060 cm-1 and 1820-1850 cm-1, and highly dispersed rhodium species, characterized by symmetric and asymmetric stretching bands of RhI(CO)2 gem-dicarbonyl species, are present. Their relative amount changes following pretreatments with gaseous mixtures, representative of the catalytic partial oxidation (CPO) reaction process. The Rh metal particle fraction decreases with respect to the Rh highly dispersed fraction in the order CO approximately CO/H2 > CH4/H2O, CH4/O2 > CH4 > H2. The metal particle dimensions decrease in the order CH4/O2 > H2 > CH4/H2O > CO > CO/H2. Grafting from a carbonyl rhodium complex also increases the amount and the dimensions of Rh0 particles at the catalyst surface. Increasing the ratio (extended rhodium metal particles/highly dispersed Rh species) allows a shorter conditioning process. The surface reconstruction phenomena going on during catalytic activity are related to this effect.     

Temperature dependence of catalytic cyclohexane partial oxidation in a polytetrafluoroethylene reactor

Polymer-supported Co(II) catalyst was prepared and its activity and selectivity in the partial oxidation of cyclohexane was determined at several temperatures in a polytetrafluoroethylene reactor (PTFE). The catalyst was characterized by means of SEM-EDX, FTIR, diffuse reflectance UV-Vis, N₂ sorption, and mecury porosimetry. Activation energies were determined under steady state conditions for the net production of cyclohexanone and cyclohexanol and for cyclohexane and oxygen net consumption. Some activation energies were lower than the ones reported for the uncatalyzed process, indicating that the catalyst played an important role in the initiation of the free-radical reaction. The text was submitted by the authors in English.     

The impact of a dielectric barrier discharge on the catalytic oxidation of methane over Ni-containing catalyst

Methane oxidation with air was studied over a Ni-containing catalyst in a dielectric barrier discharge (DBD) at temperatures above 625 K. The DBD increases the methane conversion and shifts the process towards partial oxidation. This effect is related to a catalyst heating by the discharge. This revised version was published online in August 2006 with corrections to the Cover Date.     

甲烷直接氧化制甲醇研究进展概述

目前,天然气转化为高附加值化工产品的应用越来越受到人们关注.甲烷作为天然气的主要成分,其转化和应用是天然气化工领域的重要研究方向.而甲烷直接氧化制甲醇长久以来一直是研究重点.甲烷直接氧化制甲醇与传统的甲烷二步法间接转化相比,有节能和工艺简化的突出特点.然而,甲醇直接氧化制甲醇过程所面临的主要问题有：(1)甲烷分子的活化能很高,需要苛刻的操作条件才能活化参与反应;(2)反应进行的程度难以控制,生成的甲醇会进一步被氧化生成较多副产物,大大降低甲醇收率.因此,高效活化甲烷分子和抑制甲醇深度氧化是促进该过程工业化的重要研究内容.本文主要论述了非均相、气相均相和液相体系中甲烷直接氧化制甲醇的研究进展.在甲烷非均相氧化过程中,采用过渡金属氧化物作为催化剂在高温条件下催化甲烷部分氧化反应,其中,钼系和铁系催化剂的研究最为广泛.研究表明, MoO3可作为催化剂的主要活性组分,尤以 MoO3/Ga2O3催化剂性能最好,得到甲醇收率最高.在铁系催化剂中, Fe-ZSM-5 催化反应的甲醇选择性和收率都相对较高;但是每次反应后催化剂都需要重新活化,这种间歇性操作会增加成本,不利于工业化应用.总之,甲烷的非均相氧化过程存在易形成金属聚集体、催化剂选择性低以及甲醇收率低(5%)等问题,需要深入系统地研究解决.然而,与非均相氧化过程相比,操作较为简单的甲烷气相均相氧化作为目前最有工业前景的过程受到越来越多关注.在此过程中,影响反应的主要因素有反应器、反应条件(反应压力、反应温度和反应时间等)以及添加的介质等.反应器的特殊设计需要考虑的方面有反应产物的分离与转移、反应热的移除以有效提高甲烷的转化率,比如膜反应器对物质的分离作用.反应压力对反应过程的影响较为复杂.基于动力学因素,提高反应压力可以较大幅度地增加甲醇收率,同时最佳反应温度降低,但是,当压力高于8.0 MPa时,设备成本消耗大幅增加.另外,研究表明,进料中加入 NOx作为添加介质可以提高甲烷转化率和甲醇选择性,同时降低初始反应温度.与前两个氧化体系相比,液相均匀氧化过程能够获得较高的甲烷转化率与甲醇选择性.但是液相体系中强腐蚀性介质的使用增加了设备成本,阻碍了该过程工业化的应用进程.因此,促进液相体系工业化的关键就是开发绿色高效的催化剂.     

Effects of surface states over core-shell Ni@SiO_2 catalysts on catalytic partial oxidation of methane to synthesis gas

In the present work, core-shell Ni@Si O2 catalysts were investigated in order to evaluate the relevance of catalytic activity and surface states of Ni core as well as Ni nanoparticles size to catalytic partial oxidation of methane(POM). The catalysts were characterized by N2 adsorption,H2-TPR, XRD, TEM and XPS techniques. The catalytic performance of the core-shell catalysts was found to be dependent on the surface states of catalyst, which influenced the formation of products. It was considered that carbon dioxide formed on the oxidized nickel sites(Ni O)and carbon monoxide produced on the reduced sites(Ni). The surface states of active metal in the dynamic were influenced both by the size of Ni core and the porosity of silica shell. However, the catalytic activity would be debased when the size of Ni core was under a certain extent,which can be ascribed to the fact the carbon deposition increased with the increasing content of Ni O. The effects of surface states of Ni@Si O2 catalyst on the catalytic performance were discussed and the reaction pathway over Ni core encapsulated inside silica shell was proposed.     

Influence of mechanical activation of molybdenum oxide on its catalytic activity in the reaction of the partial oxidation of methanol

The influence of mechanical activation on the structure and catalytic activity of MoO₃ was studied. It was established that as a result of mechanical treatment grinding, secondary aggregation of particles and accumulation of materials from the grinding machine occurred. An increase in the catalytic activity was observed in the oxidation of methanol to formaldehyde.     

Catalytic partial oxidation of methane to synthesis gas over a ruthenium catalyst: the role of the oxidation state

The catalytic partial oxidation of methane to synthesis gas over ruthenium catalysts was investigated by thermogravimetry coupled with infrared spectroscopy (TGA-FTIR) and in situ X-ray absorption spectroscopy (XAS). It was found that the oxidation state of the catalyst influences the product formation. On oxidized ruthenium sites, carbon dioxide was formed. The reduced catalyst yielded carbon monoxide as a product. The influence of the temperature was also investigated. At temperatures below the ignition point of the reaction, the catalyst was in an oxidized state. At temperatures above the ignition point, the catalyst was reduced. This was also confirmed by the in situ XAS spectroscopy. The results indicate that both a direct reaction mechanism as well as a combustion-reforming mechanism can occur. The importance of knowing the oxidation state of the surface is discussed and a method to determine it under reaction conditions is presented.     

2D-mapping of the catalyst structure inside a catalytic microreactor at work: partial oxidation of methane over Rh/Al2O3

Tremendous changes of the structure of Rh particles occurred during partial methane oxidation to hydrogen and carbon monoxide over a 2.5 wt % Rh/Al(2)O(3) catalyst upon ignition of the catalytic reaction. Furthermore, near the ignition temperature a variation in the Rh-valence state along the catalyst bed was observed. By combining hard X-ray absorption spectroscopy (X-ray absorption near edge structure, XANES) with a charged coupled device (CCD) camera and using a suitable spectroscopic cell with gas supply and on-line mass spectrometry, we demonstrate that 2D-mapping of the Rh-oxidation state in a catalyst bed can be achieved during the catalytic reaction. For this purpose, X-ray images were recorded with the CCD camera at each energy around the Rh K-edge with and without the spectroscopic cell. This resulted effectively in the transmitted and incident intensity at each energy and at each pixel of the spectroscopic cell. Reconstruction of the full Rh K-edge XANES spectra at each pixel revealed the local distribution of oxidized and metallic Rh-species in the catalyst bed. Along the catalyst bed, structural changes were found with a steep gradient within less than 100 microm. Furthermore, a characteristic cone toward the inlet of the spectroscopic cell was observed.     

在非平衡等离子体中甲烷直接氧化成甲醛的研究

非平衡等离子体能使几乎所有的分子激发、电离、自由基化,以至达到高活化状态.如果在化学反应发生的瞬时使产物脱离等离子体区,或迅速将产物捕获,实现高的反应选择性和得率是可能的.本文报道不用引发剂,在非平衡等离子体中甲烷直接氧化成甲醛的反应.     

助剂对甲烷部分氧化制合成气镍基催化剂性能的影响

考察了添加助剂铈、镧和钙对镍基催化剂反应性能的影响，发现助剂对以α-Al2O3为载体的镍基催化剂的调变作用比以γ-Al2O3为载体的镍基催化剂好，且助剂铈对催化剂的性能改善最好。在此基础上，研究了不同载量的铈对催化剂性能的影响。结果表明，铈的质量分数为1%时对催化剂的性能改善最好。同时采用XRD、XPS、TG等技术，研究了助剂铈对10％Ni/γ-Al2O3催化剂的改性作用。XRD分析表明，铈负载量较低时，催化剂中的CeO2高度分散在催化剂表面，铈负载量较高时，CeO2形成微晶颗粒，降低了催化活性。     

氟修饰的含Ni类水滑石在甲烷部分氧化制合成气中的应用研究

通过共沉淀法合成了含Ni/Mg/Al的类水滑石,并利用水滑石的"重构性能"将F^-引入到水滑石层间。焙烧该类水滑石后得到Ni/Mg/Al/O-F催化剂,采用XRD、SEM、CO₂-TPD、H₂-TPR、N₂吸附-脱附等手段对其结构进行了表征。结果表明,焙烧后的催化剂为方镁石结构,并具有丰富的介孔,Ni/Mg/Al/O-F较之不含F^-的复合氧化物Ni/Mg/AlO具有更小的比表面积、颗粒粒径和结晶度,但是碱密度明显增大,并且在甲烷部分氧化(POM)反应中表现出更高的活性和稳定性,反应120h后,活性没有下降。这是因为F^-的引入提高了催化剂碱性和活性组分Ni的分散,从而改善了催化剂的抗积炭和烧结能力。     

Temporal decay of the catalytic oxidation of methane over palladium supported on silica

The temporal decay of the oxidation of methane(CH4-O2reaction)over palladium supported on silica is determined experimentally at different temperatures,comparing the results with those of various classical models which show the behavior of the adsorbed phase as the cause of the phenomenon.This effect is visualized through Monte Carlo simulations of the CH4-O2reaction on a mixed lattice whose partial poisoning,due to the configuration of the OH groups on the surface of the adsorbate,is translated into a gradual decay of the reaction’s activity.