CeO_2 as the Oxygen Carrier for Partial Oxidation of Methane to Synthesis Gas in Molten Salts: Thermodynamic Analysis and Experimental Investigation

A new technique -- the direct partial oxidation of methane to synthesis gas using lattice oxygen in molten salts medium has been introduced. Using CeO2 as the oxygen carrier, thermodynamic data were calculated in the reaction process, and the results indicated that direct partial oxidation of methane to synthesis gas using lattice oxygen of cerium oxide is feasible in theory. In a stainless steel reactor, the effects of temperature and varying amounts of γ-Al2O3 supported CeO2 on cn4 conversion, H2 and CO selectivity, were investigated, respectively. The results show that 10% CeO2/γ-Al2O3 has the maximal reaction activity at a temperature of 865 ℃ and above, the H2/CO ratio in the gas that has been produced reaches 2 and the CH4 conversion, H2 and CO selectivity reached the following percentages： i.e. 61%, 89%, and 91% at 870 ℃, respectively. In addition, increase of reaction temperature is favorable for the partial oxidation of methane.

Methane Oxidation to Synthesis Gas Using Lattice Oxygen of La_(1-x)Sr_xMO_(3-λ)(M =Fe,Mn) Perovskite Oxides Instead of Molecular Oxygen

In this paper, the partial oxidation of methane to synthesis gas using lattice oxygen of La1- SrxMO3-λ (M=Fe, x Mn) perovskite oxides instead of molecular oxygen was investigated. The redox circulation between 11% O2/Ar flow and 11% CH4/He flow at 900℃ shows that methane can be oxidized to CO and H2 with a selectivity of over 90.7% using the lattice oxygen of La1- SrxFeO3-λ (x≤0.2) perovskite oxides in an appropriate reaction condition, while the lost lattice x oxygen can be supplemented by air re-oxidation. It is viable for the lattice oxygen of La1- SrxFeO3-λ (x≤0.2) perovskite x oxides instead of molecular oxygen to react with methane to synthesis gas in the redox mode.

Hydrate capture CO_2 from shifted synthesis gas, flue gas and sour natural gas or biogas

CO2 capture by hydrate formation is a novel gas separation technology, by which CO2 is selectively engaged in the cages of hydrate and is separated with other gases, based on the differences of phase equilibrium for CO2 and other gases. However. rigorous temperature and pressure, high energy cost and industrialized hydration separator dragged the development of the hydrate based CO2 capture. In this paper, the key problems in CO2 capture from the different sources such as shifted synthesis gas, flue gas and sour natural gas or biogas were analyzed. For shifted synthesis gas and flue gas, its high energy consumption is the barrier, and for the sour natural gas or biogas （CO2/CH4 system）, the bottleneck is how to enhance the selectivity of CO2 hydration. For these gases, scale-up is the main difficulty. Also, this paper explored the possibility of separating different gases by selective hydrate formation and reviewed the progress of CO2 separation from shifted synthesis gas, flue gas and sour natural gas or biogas.

Oscillations during partial oxidation of methane to synthesis gas over Ru/Al_2O_3 catalyst

Oscillations in temperatures of catalyst bed as well as concentrations of gas phase species at the exit of reactor were observed during the partial oxidation of methane to synthesis gas over Ru/Al2O3 in the temperature range of 600 to 850℃. XRD, H2-TPR and in situ Raman techniques was used to characterize the catalyst. Two types of ruthenium species, i.e. the ruthenium species weakly interacted with Al2O3 and that strongly interacted with the support, were identified by H2-TPR experiment. These species are responsible for two types of oscillation profiles observed during the reaction. The oscillations were the result of these ruthenium species switching cyclically between the oxidized state and the reduced state under the reaction condition. These cyclic transformations, in turn, were the result of temperature variations caused by the varying levels of the strongly exothermic CH4 combustion and the highly endothermic CH4 reforming （with H2O and CO2） reactions （or the less exothermic direct partial oxidation of methane to CO and H2）, which were favored by the oxidized and the metallic sites, respectively. The major pathway of synthesis gas formation over the catalyst was via the combustion-reforming mechanism.

Characterization and catalytic performance of CeO_2-Co/SiO_2 catalyst for Fischer-Tropsch synthesis using nitrogen-diluted synthesis gas over a laboratory scale fixed-bed reactor

The surface species of CO hydrogenation on CeO2-Co/SiO2 catalyst were investigated using the techniques of temperature programmed reaction and transient response method. The results indicated that the formation of H2O and CO2 was the competitive reaction for the surface oxygen species, CH4 was produced via the hydrogenation of carbon species step by step, and C2 products were formed by the polymerization of surface-active carbon species （-CH2-）. Hydrogen assisted the dissociation of CO. The hydrogenation of surface carbon species was the rate-limiting step in the hydrogenation of CO over CeO2-Co/SiO2 catalyst. The investigation of total pressure, gas hourly space velocity （GHSV）, and product distribution using nitrogen-rich synthesis gas as feedstock over a laboratory scale fixed-bed reactor indicated that total pressure and GHSV had a significant effect on the catalytic performance of CeO2-Co/SiO2 catalyst. The removal of heat and control of the reaction temperature were extremely critical steps, which required lower GHSV and appropriate CO conversion to avoid the deactivation of the catalyst. The feedstock of nitrogen-rich synthesis gas was favorable to increase the conversion of CO, but there was a shift of product distribution toward the light hydrocarbon. The nitrogen-rich synthesis gas was feasible for F-T synthesis for the utilization of remote natural gas.

Synthesis gas production using oxygen storage materials as oxygen carrier over circulating fluidized bed

A novel process for synthesis gas production over Circulating Fluidized Bed （CFB） using oxygen storage materials as oxygen carder was reported. First, oxygen in the air was chemically fixed and converted to lattice oxygen of oxygen storage materials over regenerator, and then methane was selectively oxidized to synthesis gas with lattice oxygen of oxygen storage materials over riser reactor. The results from simulation reaction of CFB by sequential redox reaction on a fixed bed reactor using lanthanum-based perovskite LaFeO3 and La0.8Sr0.2Fe0.9CO0.1O3 oxides prepared by sol-gel, suggested that the depleted oxygen species could be regenerated, and methane could be oxidized to synthesis gas by lattice oxygen with high selectivity. The partial oxidation of methane to synthesis gas over CFB using lattice oxygen of the oxygen storage materials instead of gaseous oxygen should be possibly applicable.

Transformation of methane to synthesis gas over metal oxides without using catalyst

This article reviews a new developing method in the field of metal oxide reduction in chemical and metallurgical processes, which uses methane as a reducing agent. Commonly, coal is used as the reducing agent in the reduction of metal oxide and other inorganic materials; Metal producing factories are among the most intensive and concentrated source of greenhouse gases and other pollutants such as heavy metals, sulfur dioxide and fly ash. Thermodynamically, methane has a great reducing capability and can be activated to produce synthesis gas over a metal oxide as an oxygen donor. Metal oxide reduction and methane activation, two concurrent thermochemical processes, can be combined as an efficient and energy-saving process; nowadays this kind of technologies is of great importance. This new reduction process could improve energy efficiencies and significantly decrease greenhouse gas emission compared to the conventional process; furthermore, the produced gases are synthesis gas that is more valuable than methane. In this paper, thermodynamic studies and advantages of this promising method were discussed. The major aim of this article is to introduce methane as a best and environmentally friendly reducing agent at low temperature.

Effect of CeO_2 Promoter on the Performance of Catalyst for CH_4, CO_2with O_2 to Synthesis Gas

In the reaction of mathane, carbon dioxide with oxygen to synthesis gas, conversion ofCH4 was increased, but CO selectivity was reduced when CeO2 was added to Ni/CaO-Al2O3catalyst The characterization of TPR, XPS. XRD and H2-TPD exhibited that, on one hand, theCeO2 promoter decreased the reduction temperature of catalyst. On the other hand, addition ofCeO2 resulted in an increase in the electron density of active component Ni, and as a result,reduced the ability of CH4 deep cracking and enhanced the resistance to carbon-deposition ofcatalyst. In addition, the existence of CeO2 was beneficial to decrease the Ni crystal particle size.

Reaction of nitrous oxide with methane to synthesis gas:A thermodynamic and catalytic study

The aim of the present study is to explore the coherence of thermodynamic equilibrium predictions with the actual catalytic reaction of CH4 with N2O,particularly at higher CH4 conversions.For this purpose,key process variables,such as temperature(300℃-550℃) and a molar feed ratio(N2O/CH4 = 1,3,and 5),were altered to establish the conditions for maximized H2yield.The experimental study was conducted over the Co-ZSM-5 catalyst in a fixed bed tubular reactor and then compared with the thermodynamic equilibrium compositions,where the equilibrium composition was calculated via total Gibbs free energy minimization method.The results suggest that molar feed ratio plays an important role in the overall reaction products distribution.Generally for N2O conversions,and irrespective of N2O/CH4feed ratio,the thermodynamic predictions coincide with experimental data obtained at approximately 475℃-550℃,indicating that the reactions are kinetically limited at lower range of temperatures.For example,theoretical calculations show that the H2 yield is zero in presence of excess N2O(N2O/CH4= 5).However over a Co-ZSM-5 catalyst,and with a same molar feed ratio(N2O/CH4) of 5,the H2yield is initially 10%at 425℃,while above450℃ it drops to zero.Furthermore,H2yield steadily increases with temperature and with the level of CH4 conversion for reactions limited by N2O concentration in a reactant feed.The maximum attainable(from thermodynamic calculations and at a feed ratio of N2O/CH4=3) H2yield at 550℃ is 38%,whereas at same temperature and over Co-ZSM-5,the experimentally observed yield is about 19%.Carbon deposition on Co-ZSM-5 at lower temperatures and CH4 conversion(less than 50%) was also observed.At higher temperatures and levels of CH4conversion(above 90%),the deposited carbon is suggested to react with N2O to form CO2.

Partial Oxidation of Methane to Synthesis Gas over Hexaaluminates LaMAl_(11)O_(19-δ) catalysts

A series of M-substituted hexaaluminates LaMAl11O19-δ （M=Fe, Co, Ni, Mn, and Cu） were prepared and characterized by XRD, XPS, TPR and TGA techniques, respectively. They exhibited different reducibility and catalytic activity for partial oxidation of methane （POM） to synthesis gas. Among the LaMAl11019-δ samples, LaNiAl11O19-δ showed the best catalytic activity for the topic reaction and selectivity for synthesis gas at 780 ℃ for 2 h. The conversion of CH4 was over 99.2%, and the product selectivity for both CO and H2 was above 90.3%.

Co-Generation of C_2 Hydrocarbons and Synthesis Gases from Methane and Carbon Dioxide: a Thermodynamic Analysis

This paper deals with thermodynamic chemical equilibrium analysis using the method of direct minimization of Gibbs free energy for all possible CH4 and CO2 reactions. The effects of CO2/CH4 feed ratio, reaction temperature, and system pressure on equilibrium composition, conversion, selectivity and yield were studied. In addition, carbon and no carbon formation regions were also considered at various reaction temperatures and CO2/CH4 feed ratios in the reaction system at equilibrium. It was found that the reaction temperature above 1100 K and CO2/CH4 ratio=1 were favourable for synthesis gas production with H2/CO ratio unity, while carbon dioxide oxidative coupling of methane （CO2 OCM） reaction to produce ethane and ethylene is less favourable thermodynamically. Numerical results indicated that the no carbon formation region was at temperatures above 1000 K and CO2/CH4 ratio larger than 1.

Visualizing the importance of oxide-metal phase transitions in the production of synthesis gas over Ni catalysts

Synthesis gas, composed of H2 and CO, is an important fuel which serves as feedstock for industrially relevant processes, such as methanol or ammonia synthesis. The efficiency of these reactions depends on the H2: CO ratio, which can be controlled by a careful choice of reactants and catalyst surface chemistry.Here, using a combination of environmental scanning electron microscopy(ESEM) and online mass spectrometry, direct visualization of the surface chemistry of a Ni catalyst during the production of synthesis gas was achieved for the first time. The insertion of a homebuilt quartz tube reactor in the modified ESEM chamber was key to success of the setup. The nature of chemical dynamics was revealed in the form of reversible oxide-metal phase transitions and surface transformations which occurred on the performing catalyst. The oxide-metal phase transitions were found to control the production of synthesis gas in the temperature regime between 700 and 900 ℃ in an atmosphere relevant for dry reforming of methane(DRM, CO2: CH4=0.75). This was confirmed using high resolution transmission electron microscopy imaging, electron energy loss spectroscopy, thermal analysis, and C18O2 labelled experiments.Our dedicated operando approach of simultaneously studying the surface processes of a catalyst and its activity allowed to uncover how phase transitions can steer catalytic reactions.

Purification Influence of Synthesis Gas Derived from Methanol Cracking on the Performance of Cobalt Catalyst in Fischer-Tropsch Synthesis

Synthesis gas derived from methanol cracking （SGMC） was applied as simulating feedstock of Fischer-Tropsch synthesis （FTS） in laboratory. With MS and GC detector, a trifle of sulfur compounds, a small amount of oxygenates including H2O, CH3OH, DME and CO2 as well as a few of low carbon alkanes were found in the SGMC. After purification, the sulfur compounds, H2O, CH3OH and DME could be eliminated efficiently from the SGMC while CO2 and the low carbon alkanes were partly removed. When the unpurified SGMC, the desufurized SGMC and the totally purified SGMC were sequentially applied in cobalt-based FTS, the catalytic performance of Co/ZrO2/SiO2 catalyst was gradually improved corresponding to the degree of purification. The untreated SGMC led to the serious deactivation of the cobalt catalyst, the partially treated SGMC slowed down the deactivation rate and the totally purified SGMC resulted in little deactivation of the catalyst, which was similar to what the pure synthesis gas （the mixture of pure H2 and CO） did. The results indicated that the SGMC should be purified and the purification course used in this paper was effective for the SGMC. Furthermore, the totally purified SGMC could substitute for the pure synthesis gas in cobalt FTS.

Research activities and recent progresses on synthesis gas conversion

Five catalytic processes and their catalysts will be introduced in my talk. Firstly,the demonstration test(3000 ton/a)results using a novel catalyst Co/SiO2 with egg-shell structure and the strategies for this catalyst preparation based on the issues from the mass transfer of produced wax from F-T synthesis will be discussed. Recent progresses on C2-oxygenate synthesis from syngas over a Rh/SiO2 catalyst and a 10 thousands ton/a demonstration test facility in China will be built in 2010 will be reported in the second section. A naphtha and diesel distillate which cut off the heavier end of S-F-A distribution direct synthesis with low methane selectivity from syngas over a Co/AC1 catalyst and a 10000 ton/a demonstration test with a bubble column slurry reactor will be talked about in this speech. A high α-alcohols of C2-C18 direct synthesis with more than 50 wt% selectivity and low methane and methanol selectivities from syngas over a Co2C/AC2 catalyst,a 3000 ton/a demonstration test with a bubble column slurry reactor and the primary fundamental understandings will be detailedly discussed in the forth section. In situ formation of homogeneous active sites on the surface of supported Rh heterogeneous catalysts and their application in hydroformylation of olefins will be introduced in fifth section.

Determination of Air/Fuel and Steam/Fuel Ratio for Coal Gasification Process to Produce Synthesis Gas

In this study, a coal gasification model is developed based on nine simultaneous reactions. For given gasification temperature and pressure, the air/fuel and water vapor/fuel ratio are optimized for maximum H2/CO ratio by parametric study. Furthermore, the cold gas efficiency and higher heating value of the synthesis gas produced are computed for each case. Optimum locations of investigated parameters are also searched for maximizing cold gas efficiency and higher heating value of the synthesis gas.

Production of Synthesis Gases from Ethanol Steam Reforming Process

In this study, the production of synthesis gases has been purposed under between 250oC - 700oC and 1 - 2 bars pressures. The research was conducted over a commercial BASF catalyst and a laboratory prepared catalyst. The catalyst has a content of different substances including basically NiO/Al2O3 and some additionals (Ca, Mg, Cr, Si). The experimental measurements were carried out within a recently developed experimental equipment which can be operated up to 1200o and 1 to 3 bars pressures. The study was conducted over a commercial BASF catalyst and a laboratory prepared catalyst under different ethanol/water ratios, temperatures, and catalyst loads. Under the condition when ethanol/water ratios were decreased from 1/2 to 1/10, it was observed that hydrogen ratios increased in exit gas composition of the reactor. With increments in catalyst loads from 1 to 5 grammes, hydrogen ratios in exit gas composition gradually increased. Reaction of ethanol-steam reforming started nearly at 300oC, and when temperature increments continued further up to 700oC, hydrogen yields in exit gas compositions of the reactor increased significantly to a range of 70% - 80%. In the case of using commercial BASF catalyst, hydrogen ratios in exit gas composition were found slightly higher than laboratory prepared catalyst. According to our observations, life time of laboratory prepared catalyst was found higher than the commercial BASF catalyst. In this study which kinetic measurements were applied, some kinetic parameters of ethanol-steam reaction were calculated. The mean activation energy of ethanol consumptions at 573oK - 973oK was found as 26.87 kJ/mol, approximately. All kinetic measurements were analyzed with a first order reaction rate model. In this study, some diffusion limitations existed, however, overall reaction was chemically controlled.

Auto-ignition of biomass synthesis gas in shock tube at elevated temperature and pressure

Ignition delay times of multi-component biomass synthesis gas （bio-syngas） diluted in argon were measured in a shock tube at elevated pressure （5, 10and 15 bar, 1 bar = 105 Pa）, wide temperature ranges （1,100-1,700 K） and various equivalence ratios （0.5, 1.0, 2.0）. Additionally, the effects of the variations of main constituents （H2：CO = 0.125-8） on ignition delays were investigated. The experimental results indicated that the ignition delay decreases as the pressure increases above certain temperature （around 1,200 K） and vice versa. The ignition delays were also found to rise as CO concentration increases, which is in good agreement with the literature. In addition, the ignition delays of bio-syngas were found increasing as the equivalence ratio rises. This behavior was primarily discussed in present work. Experimental results were also compared with numerical predictions of multiple chemical kinetic mechanisms and Li＇s mechanism was found having the best accuracy. The logarithmic ignition delays were found nonlinearly decrease with the H2 concentration under various conditions, and the effects of temperature, equivalence ratio and H2 concentration on the ignition delays are all remarkable. However, the effect of pressure is rela- tively smaller under current conditions. Sensitivity analysis and reaction pathway analysis of methane showed that R1 （H ＋O2= O -9 OH） is the most sensitive reaction promot- ing ignition and R13 （H ＋O2 （＋M） = HO2 （＋M））, R53（CH3＋H （＋M）= CH4 （＋M））, R54 （CH4＋H= CH3 ＋ H2） as well as R56 （CH4 ＋ OH = CH3 ＋ H2O） are key reactions prohibiting ignition under current experimental conditions. Among them, R53 （CH3 ＋ H （＋M） = CH4 （＋M））, R54 （CH4 ＋ H = CH3 ＋ H2） have the largest posi- tive sensitivities and the high contribution rate in rich mixture. The rate of production （ROP） of OH of R1 showed that OH ROP of R1 decreases sharply as the mixture turns rich. Therefore, the ignition delays become longer as the equiva- lence ratio increases.

Gold modified cobalt-based Fischer-Tropsch catalysts for conversion of synthesis gas to liquid fuels

The addition of Au as a promoter/modifier for alumina supported Co catalyst has been studied by combined in-situ high temperature, high pressure Fourier transform infrared （FTIR） and on-line gas chromatography. The combination of these tools permitted the state of the active catalyst surface to be monitored while following the elution of reaction products during the first 5-7 h on stream of the catalyst. The catalysts under study were a 10%Co/ A1203 and a 2.5%Au/10%Co/A1203. Samples were characterised before use using Raman and temperature programmed reduction （TPR）. During the initial stages of reaction, hydrocarbons were built up on the surface of the catalyst as monitored by FTIR and the nature and amount of these species were assessed in terms of CH2/CH3 ratio and the density of these alkyl fragments by employing absorption coefficients for the individual components. The nature and reducibility of the Co particles were modified by the presence of Au while the later also shifted the CO/ H2 balance by acting as an effective water-gas shift catalyst during the early stages of reaction. This characteristic was lost during reaction as a consequence of redistribution of the two metallic phases.

Synthesis, Crystal Structure and Gas Adsorption of a Two-fold Interpenetrated Three-dimensional Framework {[Cd(2-NO_2-BDC)(4,4？-DPA)]·(DMF)}_n

The reaction of Cd（NO_3）_2·4H_2O with 4,4？-dipyridylacetylene（4,4？-DPA） and 2-nitroterephthalic acid（2-NO_2-H_2BDC） in DMF/H_2O mixed solvent has afforded a compound {[Cd（2-NO_2-BDC）（4,4？-DPA）]·（DMF）}_n（1）. Compound 1 has been characterized by single-crystal X-ray diffraction, powder X-ray diffraction, thermogravimetry analysis, and IR spectrum. Compound 1 crystallizes in the monoclinic system, space group P21/n, with a = 12.1488（3）, b = 14.6689（3）, c = 13.1615（3） ？, β = 111.809（3）o, V = 2177.63（9） ？~3, Z = 4, C_（23）H_（18）N_4O_7 Cd, M_r = 574.81, D_c = 1.753 g/cm^3, μ = 8.523 mm^（-1）, F（000） = 1152, the final R = 0.0411 and wR = 0.1064 for 3589 observed reflections with I 〉 2s（I）. In compound 1, the Cd（Ⅱ） ions are linked by the carboxylate groups of 2-NO_2-BDC ligands to give a two-dimensional layered structure based on the centrosymmetric dinuclear Cd_2（COO）_2 units, which are further connected by the 4,4？-DPA ligands to produce a three-dimensional framework with pcu topology. Careful examination revealed that compound 1 is a 2-fold interpenetrating framework. Furthermore, the gas adsorption properties of 1 for N_2 and CO_2 have also been investigated.

Progress in studies of natural gas conversion in China

Progress in natural gas conversion in China is presented in this paper, including processes of natural gas to synthesis gas （syngas）, syngas to liquid hydrocarbons, oxygenates synthesis, methanol to olefins （MTO）, methane to aromatics and oxidative coupling of methane （OCM）.