Water Gas Shift Equilibrium Research Articles

Boundaries of High-Temperature Co-Electrolysis Towards Direct CO2-Electrolysis

High-temperature co-electrolysis of CO2 and H2O at elevated temperatures between 700 °C and 900 °C valorises CO2 to produce a mixture of carbon monoxide (CO) and hydrogen (H2), called syngas. Co-electrolysis has the great advantage over conventional processes, that the desired syngas ratios of downstream processes can be realized by varying process parameters such as temperature and feed gas composition accordingly in a one step process. Co-electrolysis can also play a vital role in counteracting power fluctuations of renewable energy sources by storing temporarily unused electricity through conversion to other energy resources like chemicals or heat for later use.The underlying processes in co-electrolysis for CO production are direct electrochemical CO2 reduction and reverse water gas shift equilibrium (RWGS). Their specific significance has not been clarified in detail yet and was controversially discussed in literature up to this day [1,2].The impact of the equilibrium partial pressure of H2O on the physical processes in the transition boundary of co-electrolysis towards direct CO2-electrolysis was investigated by AC and DC measurements for various gas compositions. The analysis led to identifying the role of the underlying electrochemical processes during co-electrolysis, in particular the electrochemical CO2 reduction compared to the conversion of CO2 in the reverse water-gas shift reaction and the electrochemical H2O reduction. The area specific resistance (ASR) was, amongst others, taken as an indicator to determine, which of the reduction reactions (H2O or CO2 reduction) is dominant depending on the gas composition. The experiments were conducted using commercially available cathode-supported full cells (Elcogen) made of Ni-8YSZ/8YSZ/CGO/LSC.Results as seen in Figure 1 show that the ASR for an equilibrium concentration of 5 % H2O is considerably larger than for higher H2O contents. Above 15 % H2O, the ASR shows no dependency on the gas composition and is comparable to pure H2O-electrolysis [3]. These observations underline the hypothesis that CO2-electrolysis becomes pre-dominant compared to H2O-electrolysis for low H2O content during co-electrolysis. With increasing H2O content, CO2-electrolysis becomes less significant and carbon dioxide is converted in the reverse water gas shift equilibrium. The origin of the discrepancy in literature was found to be the different operating H2O concentrations. A threshold has been established for the perception of CO2-electrolysis during co-electrolysis experiments.figure caption: Arrhenius plot of ASROCV for different steam concentrations at 6 l·h-1.[1] C. Stoots, J. O'Brien, J. Hartvigsen, Int. J. Hydrogen Energy 2009, 34, 4208.[2] S. D. Ebbesen, R. Knibbe, M. Mogensen, J. Electrochem. Soc. 2012, 159, F482-F489.[3] L. Dittrich, M. Nohl, E. E. Jaekel, S. Foit, L.G.J. (Bert) de Haart, R.-A. Eichel J. Electrochem. Soc. 2019, 166, F971-F975. Figure 1

Numerical modelling of a three-zone combustion for heavy fuel oil in inert porous media reactor

Numerical model for heavy fuel oil and air mixtures combustion is presented to simulate the behavior of the fuel in an inert porous medium reactor for hydrogen production. Three-zone combustion of oil and petroleum cokes separated by temperature ranges starting from ambient temperature to 560 K, from 560 K to 673 K, and above 673 K, is presented. Hydrogen production is achieved using water gas shift equilibrium reaction on the combustion products at different temperatures. Results show a high enthalpy contribution due to coke combustion formed in the low temperature oxidation reaction, being the most important reaction in relation to its zone size. Simulations increasing filtration velocity (from 0.05 to 0.9 m/s) has a favorable effect on the maximum temperature and the combustion front velocity. The effect of the simplified combustion model lowers computational time, with acceptable results for temperature as well as hydrogen production in contrast to laboratory tests and other software simulation such as COMSOL Multiphysics.

Effect of biomass fuel ash and bed material on the product gas composition in DFB steam gasification

Gasification is a thermochemical process that transforms carbonaceous matter into a gaseous secondary energy carrier, referred to as product gas. This product gas can be used for heat and power generation but also for syntheses. One possible gasification technology suitable for further synthesis is dual fluidised bed (DFB) steam gasification. The H2:CO ratio, which determines the suitability of the product gas for further synthesis, is influenced by the catalytic activity inside the gasification reactor. Eleven DFB steam gasification experiments were performed comparing the catalytic activity for various bed material and fuel combinations. The bed materials used were K-feldspar, fresh and layered olivine, and limestone, and the fuels gasified were softwood, chicken manure, a bark–chicken manure mixture and a bark-straw-chicken manure mixture. The water-gas-shift (WGS) equilibrium deviation was used to evaluate the catalytic activity inside the gasification reactor. It was shown that both the fuel ash and bed material have an effect on the catalytic activity during gasification. Scanning electron microscopy and energy dispersive X-ray spectrometry showed the initial layer formation for experiments with ash-rich fuels. Isolated WGS experiments were performed to further highlight the influence of bed material, fuel ash and fuel ash layers on the WGS equilibrium.

On the basic effects on the gas composition governed by the water-gas shift equilibrium

The water-gas shift (WGS) reaction plays an important role in various syngas processes but also in gasification and fuel-rich combustion. In this paper, graphical representations of the key equations describing the gas composition governed by the WGS equilibrium are provided from a combustion perspective, and analytic solutions for the product ratios are given. These representations and solutions are helpful to distinguish and illustrate the basic effects of stoichiometry (molar H/C ratio and oxygen availability) and thermodynamics (temperature) on the WGS equilibrium composition. The developed graphical representations and analytical solutions are also useful for studying catalytic processes in which the WGS plays an important role. As an essential basis for this study, new simple correlations for the WGS equilibrium constant are proposed for different temperature ranges and compared with other correlations and data reported in literature.

The impact of gasification temperature on the process characteristics of sorption enhanced reforming of biomass

Especially carbon-intensive industries are interested in a decarbonization of their processes. A technology, which can contribute to a significant reduction of the carbon footprint, is the so-called sorption enhanced reforming process. The sorption enhanced reforming process uses a dual fluidized bed reactor system with limestone as a bed material for the thermochemical conversion of biomass into a valuable nitrogen-free product gas. This product gas can be used for further synthesis processes like methanation. The dependency of the product gas composition on the gasification temperature is already a well-known fact. Nevertheless, detailed investigations and models of the effect on elemental balances (especially carbon) of the process are missing in the literature and are presented in this work. Therefore, previously published data from different pilot plants is summarized and is discussed on a mass balance. Based on this information, investigations on the product gas equilibrium composition are presented and conclusions are drawn: it can be shown that the sorption enhanced reforming process can be divided into two sub-processes, namely “carbonation dominated sorption enhanced reforming” and “water-gas shift dominated sorption enhanced reforming.” The sub-process carbonation dominated SER is characterized by a high deviation from the water-gas shift equilibrium and a nearly constant CO content in the product gas over gasification temperature (< 700 °C). The sub-process water-gas shift dominated SER can be identified by a steep increase of the CO content in the product gas over temperature and nearly equilibrium state of the water-gas shift reaction (700–760 °C).

Biogas to high purity hydrogen by methane dry reforming in TZFBR+MB and exhaustion by Steam-Iron Process. Techno–economic assessment

A techno-economic study has been carried out with the aim of analyzing the performance (product distribution and energy yields) and estimating the production costs of high purity hydrogen obtained from biogas. For such purpose and taking advantage of empirical data developed in our laboratory, it has been proposed a system consisting of a two-zone fluidized bed reactor aided by a system of permselective (Pd/Ag) metallic membranes inserted in the fluidized bed (TZFBR+MB), and a battery of several fixed bed reactors operating cycles of reduction and oxidation (Steam-Iron Process -SIP-). The feed has always been an equimolar mixture of CH4 and CO2 simulating a sweetened biogas. The first reactor (TZFBR+MB) can produce a stream of pure hydrogen (i.e. PEMFC quality) as permeated flow through the MB, and a retentate stream rich in all species resulting from the methane dry reforming reaction (MDR) and the water gas shift equilibrium (WGS). The singularity of this kind of complex reactors is that regeneration of the catalyst is performed in the same reactor and simultaneously to the MDR reaction because of the two-zone. Due to the reductive behavior of the retentate stream, it can be fed to a bed of solid where up to two different oxygen carriers (iron oxide with additives and cobalt ferrite) can be reduced to their metallic state. Once the solid has been completely reduced, it can be reoxidized with steam releasing a high purity hydrogen stream. Both reactors (i.e. TZFBR+MB and SIP) have been coupled in different degrees. A performance (hydrogen and energy yields) as well as costs analysis (fixed assets and operating costs) have been performed with the aid of Aspen HYSYS v9.0, used for dimensioning the equipment needed to process up to 1350 kg/h of biogas. On this way, the integrated process enhances the efficiencies of every single process allowing pure hydrogen yields up to 68% at 575 °C in the TZFBR+MB and an overall energy efficiency greater than 45%. Production costs have been found to be in the range from 4 to 15 €/kg, still high but not so far away from the target of DOE fixed in 2 $/kg by 2020.

Entrained flow gasification Part 1: Gasification of glycol in an atmospheric-pressure experimental rig

Three coordinated papers are presented concerning entrained flow gasification of a liquid fuel under atmospheric conditions. The work is based on a detailed mapping of process parameters inside the entrained flow gasifier and at the gasifier outlet. In this paper the experimental setup and the experimental data are reported. Mono ethylene glycol (MEG) is used as a well-defined surrogate fuel for biogenic oils. The overall performance of the reactor is evaluated by measuring the gas-phase composition at the reactor outlet; radial profiles of gas-phase composition (CO2, CO, H2, CH4, hydrocarbons) and temperature at 300 and 680 mm distances from the burner are measured to describe the mixing and reaction pattern in the gasifier. Global and local species balances are used to derive data that are not accessible by measurement. Characteristic parameters, i.e. stoichiometry, carbon conversion and water gas shift temperature, are derived to assess consistency of the measured data. Droplet size distribution and droplet velocity at the burner nozzle are reported based on atomization test rig experiments and direct measurements in the burner near field under gasification conditions. The experiments show a free jet with a strong outer recirculation zone as core gasification pattern. The measured species concentrations and temperatures provide an insight into both the mixing and the reactions in the burner near field. The water gas shift equilibrium is reached for a temperature of 1495 K upstream of the gasifier outlet. Hydrocarbons are not completely converted due to the low temperatures near the gasifier outlet.The research work has been conducted within the research cooperation of the Helmholtz Virtual Institute HVIGasTech.

Effects of oxygen coverage on rates and selectivity of propane-CO2 reactions on molybdenum carbide

Mo2C catalyzes propane dehydrogenation and hydrogenolysis at 823 K; carbon selectivity can be tuned to >95% propylene via dehydrogenation in absence of H2, >95% CH4 via hydrogenolysis with H2 co-feed, or >80% CO via reforming pathways with H2 and CO2 co-feed. The changes in selectivity are mediated by an evolution in the coverage of oxidized (O∗) and carbidic (∗) surface sites which results in an evolution of O∗O∗, O∗∗, and ∗∗ site pairs that catalyze propane dehydrogenation. The fraction of O∗ in relation to ∗ was assessed from measured CO2/CO ratios because reverse water gas shift equilibrium exists under H2/CO2 co-feed steady state reaction conditions. Kinetic models based on the two-site dehydrogenation mechanism could be used to quantitatively describe measured rates of propane dehydrogenation at steady state with or without H2 and/or CO2 co-feed and the transient evolution in dehydrogenation rates upon removing H2 or CO2 in the influent stream to note that O∗∗ site pairs exhibit the highest rate per gram. This model also provides a rationale for O∗ inhibition of H-activated hydrogenolysis pathways and for promotion of oxidative dehydrogenation rates with the introduction of hydrogen into CO2-propane influent streams. This study extends concepts developed for examining the catalytic effects of O∗ coverage on oxidative light alkane conversion from transition metal catalysts to also include carbidic formulations.

Structural and Catalytic Properties of Ag- and Co3O4-Impregnated Strontium Titanium Ferrite SrTi0.7Fe0.3O3−δ in Methanol Steam Reforming

The catalytic performance of Ag- and Co3O4-impregnated strontium titanium ferrite (SrTi0.7Fe0.3O3-δ, STF) has been assessed in methanol steam reforming as a test reaction and accordingly correlated with spectroscopic and structural characterization after each step of a catalytic cycle including pre-oxidation and pre-reduction. After pre-reduction in hydrogen at 400 °C, metallic silver and oxidized Co in the form of Co3O4 are present. As for catalysis, it was observed that both Ag and Co3O4 are strongly promoting the methanol chemistry with respect to pure STF already at low temperatures (230 °C for both materials). As a consequence, the selectivity towards carbon monoxide is strongly enhanced in comparison to pure STF. On Co3O4-STF, the catalytic profile is basically dominated by a temperature-dependent complex interplay between methanol steam reforming, methanol dehydrogenation and the water-gas shift equilibrium. The results also prove that despite the obvious inadequacy of H2-prereduced Ag-STF to act a...

Consequences of Surface Oxophilicity of Ni, Ni-Co, and Co Clusters on Methane Activation.

This study describes a new C-H bond activation pathway during CH4-CO2 reactions on oxophilic Ni-Co and Co clusters, unlike those established previously on Ni clusters. The initial C-H bond activation remains as the sole kinetically relevant step on Ni-Co, Ni, and Co clusters, but their specific reaction paths vary. On Ni clusters, C-H bond activation occurs via an oxidative addition step that involves a three-center (H3C···*···H)⧧ transition state, during which a Ni-atom inserts into the C-H bond and donates its electron density into the C-H bond's antibonding orbital. Ni-Co clusters are more oxophilic than Ni; thus, their surfaces are covered with oxygen adatoms. An oxygen adatom and a vicinal Co-atom form a metal-oxygen site-pair that cleaves the C-H bond via a σ bond metathesis reaction, during which the Co inserts into the C-H bond while the oxygen abstracts the leaving H-atom in a concerted, four-center (H3C···*···H···O*)⧧ transition state. Similarly, Co clusters also catalyze the σ bond metathesis step, but much less effectively because of their higher oxophilicities, much stronger binding to oxygen, and less effective hydrogen abstraction than Ni-Co clusters. On Ni-Co and Co clusters, the pseudo-first-order rate coefficients are single-valued functions of the CO2-to-CO ratio (or H2O-to-H2 ratio), because this ratio prescribes the oxygen chemical potentials and the relative abundances of metal-oxygen site-pairs through the water-gas shift equilibrium. The direct involvement of reactive oxygen in the kinetically relevant step leads to more effective CH4 turnovers and complete elimination of coke deposition on Ni-Co bimetallic clusters.

Observation of water–gas shift equilibrium in diffusion flames

The kinetic behavior of the water–gas shift (WGS) sub-system has been studied computationally for hydrocarbon diffusion flames in the counterflow geometry. Of specific interest was the spatial domain in which the reactions in the WGS-complex exhibit characteristics that lead to species concentrations approaching those expected from equilibrium. Two scenarios were observed for WGS equilibrium:(1)full equilibrium in which every step of the WGS-mechanism is nearly in equilibrium;(2)“apparent” equilibrium, which is achieved via opposing but coherent shifts away from equilibrium for the two key elementary reactions that constitute the WGS reaction. This interesting phenomenon is caused by the supply of the H radical, which participates in the forward reaction of one step and the reverse reaction of the other. This new form of apparent equilibrium differs from well-known “quasi” equilibrium, which is typically caused by the combination of a fast reversible step and slow irreversible step.Parametric domains were found in which these two scenarios are observed. For a given fuel type it was shown that the two scenarios can be separated by the location of stoichiometry. On the oxidizer side, the full equilibrium of the overall WGS reaction is achieved, while on the fuel side, apparent equilibrium can occur.

Metastable Corundum-Type In2O3: Phase Stability, Reduction Properties, and Catalytic Characterization

The phase stability, reduction, and catalytic properties of corundum-type rhombohedral In2O3 have been comparatively studied with respect to its thermodynamically more stable cubic In2O3 counterpart. Phase stability and transformation were observed to be strongly dependent on the gas environment and the reduction potential of the gas phase. As such, reduction in hydrogen caused both the efficient transformation into the cubic polymorph as well as the formation of metallic In especially at high reduction temperatures between 573 and 673 K. In contrast, reduction in CO suppresses the transformation into cubic In2O3 but leads to a larger quantity of In metal at comparable reduction temperatures. This difference is also directly reflected in temperature-dependent conductivity measurements. Catalytic characterization of rh-In2O3 reveals activity in both routes of the water–gas shift equilibrium, which gives rise to a diminished CO2-selectivity of ∼60% in methanol steam reforming. This is in strong contrast to its cubic counterpart where CO2 selectivities of close to 100% due to the suppressed inverse water–gas shift reaction, have been obtained. Most importantly, rh-In2O3 in fact is structurally stable during catalytic characterization and no unwanted phase transformations are triggered. Thus, the results directly reveal the application-relevant physicochemical properties of rh-In2O3 that might encourage subsequent studies on other less-common In2O3 polymorphs.

A novel development of mixed catalyst–sorbent pellets for steam gasification of coal chars with in situ CO2 capture

The main purpose of this research was the development of a mixed catalyst–sorbent for gasification and in situ CO2 capture; therefore, novel mixed catalyst–sorbent (composite) pellets were prepared with different contents of potassium carbonate and calcium oxide as the catalyst and sorbent, respectively. The pellets were used in steam gasification experiments of two different types of coal. The maximum hydrogen yield of 80% was obtained with 50% of the catalyst in the composite pellets and lignite Boundary Dam (BD) coal at 700°C. Use of the catalyst enhanced the gasification and water–gas shift (WGS) reaction rates, while the capture of carbon dioxide (CO2) shifted the WGS equilibrium forward, favoring hydrogen production. Trace amounts of CO2 and carbon monoxide were detected. In terms of maximum achievable hydrogen yield, the pellets containing 50% catalyst demonstrated the best performance. As expected, BD coal (a low-rank coal) showed a higher reactivity than the Genesee sub-bituminous (a medium-rank coal) samples. Ultimate analyses and burn-off tests were performed on the residues to determine the amounts of unconverted carbon, and the results of these tests also confirmed the best performance of the pellets with a catalyst content of 50%. Despite the decreasing trend of pore surface area with increasing catalyst percentage, increasing the catalyst content of composite pellets to a certain level had a positive effect on hydrogen production. This indicates that the performance of pellets is almost independent of the pore surface area. Indeed, the optimal ratio is the result of the trade-off among pore surface area, dispersion, formation of a bimetallic solid phase, and the concentration of active catalyst sites on the pellets.

Co-gasification of biomass and plastics: pyrolysis kinetics studies, experiments on 100 kW dual fluidized bed pilot plant and development of thermodynamic equilibrium model and balances.

Thermo-gravimetric analysis (TGA) of volatilization reaction kinetics for 50 wt.% mixtures of plastics (PE) and biomass (wood pellets) as well as for 100 wt.% plastics was conducted to predict decomposition times at 850°C and 900°C using iso-conversional model method. For mixtures, agreement with residence time of dual fluidized bed (DFB) reactor, treated as continuous stirred-tank reactor (CSTR), was obtained at large conversions. Mono-gasification of plastics and its co-gasification with biomass were performed in DFB pilot plant, using olivine as heterogeneous catalyst and heat transfer agent. It was found that co-gasification led to successful thermochemical conversion of plastics as opposed to mono-gasification. Unknown flow rates were determined applying nonlinear regression to energy and mass balances acknowledging combustion fuel, air, steam, feedstock, but also exiting char, tar, steam and other components in DFB gasification unit. Water-gas shift equilibrium and methanol synthesis requirements were incorporated into gasification model, based on measurements.

CO 2 hydrogenation to hydrocarbons over iron nanoparticles supported on oxygen-functionalized carbon nanotubes

Hydrogenation of CO2 to hydrocarbons over iron nanoparticles supported on oxygen-functionalized multi-walled carbon nanotubes was studied in a fixed-bed U-tube reactor at 25 bar with a H2:CO2 ratio of 3. Conversion of CO2 was approximately 35% yielding C1–C5 products at 360 ∘C with methane and CO as major products. The CO2 equilibrium conversion for temperatures in the range of 320 ∘ to 420∘C was analysed by using CHEMCAD simulation software. Comparison between experimental and simulated degrees of CO2 conversion shows that reverse water gas shift equilibrium had been achieved in the investigated temperature range and that less than 47% of CO2 can be converted to CO at 420∘C.

Influence of fuel feeding positions on gasification in dual fluidized bed gasifiers

An in-bed and an on-bed feeding system are implemented in a dual fluidized bed gasifier in order to investigate the influence of the fuel feeding position on the gasification process. Two bed materials, fresh and used olivine, are used because of their varying catalytic activity. The comparison of in-bed and on-bed feeding of wood pellets shows that in-bed feeding is more favorable, because lower tar concentrations are achieved and the gas composition is closer to water–gas shift equilibrium. Better mixing of bed material and fuel particles occurs with in-bed feeding. The residence time of the gas phase in the fluidized bed is longer in the case of in-bed feeding, and therefore better performance of the gasifier is achieved. Sufficient residence time of the fuel in the bubbling bed is important when a less active bed material is used. More active bed material is capable of compensating for the shorter residence time of the gas phase in contact with bed material during on-bed feeding.

Parametric study of methane steam reforming to syngas in a catalytic microchannel reactor

The aim of this work is the parametric investigation of methane steam reforming (MSR) to synthesis gas (syngas, CO + H 2) in a wall-coated catalytic microchannel reactor. Methane conversion and CO selectivity on coated Rh, Ru, Pt and Ni catalysts, all supported on Al 2O 3, are compared in the parameter ranges of 12.86–77.14 ms residence time, 600–800 °C temperature and 0.5–3.0 M steam-to-carbon ratio at the reactor inlet. Among the active metals, Rh is the best one in terms of both methane conversion and productivity (rate of methane consumption per weight of catalyst). Productivity decreases in the order of Rh > Ru > Pt ≈ Ni. For all catalysts, conversion increases with residence time, temperature and steam-to-carbon ratio. CO selectivity is highest in all cases on Rh, and increases with increasing temperature and decreasing steam-to-carbon ratio. However, in the range of residence times considered, a maximum CO selectivity for each catalyst is encountered where the water–gas shift equilibrium becomes significant, and converts more of the CO produced by MSR to CO 2. Time-on-stream runs conducted on Rh and Ni show that the former has excellent chemical and mechanical stability for 72 h even at extreme conditions such as steam-to-carbon ratio of 0.5 and residence time of 12.86 ms. Activity of Ni starts to decrease after 20 h even though it is operated at a steam-to-carbon ratio of 3.0. Comparative tests conducted between microchannel and packed-bed reactors show that the former outperforms the packed bed in terms of productivity and CO selectivity.

Simultaneous utilization of two different membranes for intensification of ultrapure hydrogen production from recuperative coupling autothermal multitubular reactor

The potential of simultaneous hydrogen production and in situ water removal in a thermally coupled multitubular two-membrane reactor (TCTMR) were studied numerically. Methanol synthesis is carried out in exothermic side with H-SOD membrane and supplies the necessary heat for the endothermic side. Dehydrogenation of cyclohexane is carried out in endothermic side with hydrogen-permselective Pd/Ag membrane wall. Therefore, the proposed reactor consists of two membranes, one for separation of pure hydrogen from endothermic side and another one for separation of water from exothermic side. The motivation for in situ H 2O removal during methanol synthesis by using H-SOD membranes is to displace the water–gas shift equilibrium to enhance conversion of CO 2 to improve methanol productivity. A steady-state heterogeneous model is developed to analyze the operation of the coupled methanol synthesis. The proposed model has been used to compare the performance of a TCTMR with conventional reactor (CR) and thermally coupled membrane reactor (TCMR) at identical process conditions. This comparison shows that TCTMR in addition to possessing advantages of a TCMR has a more favorable profile of temperature and increased productivity compared with other reactors. Furthermore, lower water production rate in TCTMR reduces catalyst re-crystallization.

Sorption-enhanced dimethyl ether synthesis—Multiscale reactor modeling

As an opportunity for the attenuation of atmospheric CO 2 emissions, conversion of carbon dioxide into valuable oxygenates as fuel additives or fuel surrogates was explored conceptually in terms of a potentially feasible dimethyl ether (DME) conversion process. Incentives for application of conventional CO 2–DME conversion process are insufficient due to low CO 2 conversion, and DME yield and selectivity. In-situ H 2O removal by adsorption (sorption-enhanced reaction process) can lead to the displacement of the water gas shift equilibrium and therefore, the enhancement of CO 2 conversion into methanol and the improvement of DME productivity. A two-scale, isothermal, unsteady-state model has been developed to evaluate the performance of a sorption-enhanced DME synthesis reactor. Modeling results show that under H 2O removal conditions, methanol and DME yields and DME selectivity are favoured and the methanol selectivity decreases. The increase of methanol and DME yields and DME selectivity becomes more important at higher CO 2 feed concentration because a relatively large amount of water is produced followed by a large quantity of water removed from the system. Also, the drop in the fraction of unconverted methanol becomes more important when CO 2 feed concentration is higher and the dehydration reaction is favoured. Therefore, application of the sorption-enhanced reaction concept allows the use of CO 2 as a constituent of the synthesis gas as the in-situ H 2O removal accelerates the reverse water gas shift reaction.

ChemInform Abstract: Hydrogen Formation in Propane Oxidation on Pt-Rh/CeO2/Al2O3 Catalysts.

Temperature-programmed oxidation (TPO) of propane (200–550°C) was carried out on PtRh/CeO2/ Al2O3 catalysts with oxygen-deficient C3H8/O2 mixtures. On these TPO profiles, two regions of reaction can be observed. ForT 350 ° C, there are two distinct zones in the catalyst bed: total oxidation catalyzed by platinum at the bed inlet and steam reforming catalyzed by rhodium in the outlet zone. Steam reforming is the slow step in the formation of hydrogen. Gas composition (H2, CO, CO2) is always very close to that predicted by the water-gas shift equilibrium, here this reaction being very rapid.