This chapter mainly deals with the various catalysts investigated for the low-temperature water gas shift reaction (WGSR). This chapter deals with Cu, Ni, Pt, Au. This paper discusses some aspects of the water-gas shift, which is a reversible, exothermic chemical reaction, usually assisted by a catalyst, and is the reaction. ABSTRACT: Density functional theory (DFT) is employed to study the water−gas shift (WGS) reaction in the gas phase for two complexes.
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LT sweet shifting catalysts are extremely sensitive to sulfur and chloride poisoning and are normally not used in coal gasification plants.
Water-gas shift reaction
Sweet shift is normally not used for coal gasification applications, given the problems of sulfur and chloride poisoning as mentioned above, in addition to the inefficiency of having to cool the syngas before sulfur removal, which water gas shift reaction out all of the moisture gained in the water scrubber, and then reheating and re-injecting the steam into the treated gas after H2S removal to provide moisture for shift.
However, in the production of hydrogen it is an essential post-gasification operation water gas shift reaction used to convert all CO present in the syngas to CO2, yielding the maximum possible amount of hydrogen.
Due to the different reaction conditions, different catalysts must be employed at each stage to ensure optimal activity.
The commercial HTS catalyst is the iron oxide—chromium oxide catalyst and the LTS catalyst is a copper-based catalyst.
Hydrogen Production from the Water-Gas Shift Reaction on Iron Oxide Catalysts
The order proceeds from high to low temperature due to the susceptibility of the copper catalyst to poisoning by sulfur that may remain after the steam reformation process. Conversely, the iron used in the HTS reaction is generally more robust and resistant toward poisoning by sulfur compounds.
The function of ZnO is to provide structural support as water gas shift reaction as prevent the poisoning of copper by sulfur. The Al2O3 prevents dispersion and pellet shrinkage.
The upper temperature limit is due to the susceptibility of copper to thermal sintering.
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These lower temperatures also reduce the occurrence of side reactions that are observed in the case of the HTS. The elaborated solids were water gas shift reaction characterized by means of techniques of analysis, X-ray powder diffraction, CO2 and NH3 adsorptions calorimetry, and the diffuse reflectance infrared Fourier transform spectroscopy.
Differential heats of adsorption were measured in a heat flow Setaram HT microcalorimeter linked to a volumetric adsorption system.
Successive small doses of CO2 or NH3 were sent over the catalytic surface. From the calorimetric and volumetric data, the differential heats of adsorption versus coverage and the corresponding water gas shift reaction are plotted. The reaction was performed in a high temperature Spectratech cell equipped with a ZnSe window.
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Results and Discussions 3. Three methods of preparation of iron-chromium oxides, described obviously in [ 3 ], are chosen to study their catalytic activities in WGS reaction.
The Fe-Cr prepared by substituting Fe by Cr stays almost inactive for all the duration of the study, while Fe-Cr prepared by the coprecipitation technique provides the highest values of H2 after 90 min of reaction time and Fe-Cr prepared via impregnation method exhibits an intermediate performance.
In turn, the Fe-only catalyst presents very high initial activity which decreased significantly with water gas shift reaction reaction time to values one more active than the promoted catalyst Fe-Cr water gas shift reaction via impregnation method.
Journal of Catalysts
This loss of activity and stability can be related to the sintering of the iron oxide phase. It has been proved that the addition of chromium oxide to Fe2O3 slows the deactivation of the iron oxide [ 14 ].
Fe-Mg Systems The aim of this part of the study is to promote the iron oxide-based catalyst by replacement of the water gas shift reaction oxide by MgO which can be apt to improve the catalytic activity of the intermediate active catalyst, in the occurrence Fe-Cr prepared via impregnation method see Figure 1.
The WGS reaction results of Fe-Mg catalysts, expressed by water gas shift reaction hydrogen production and the X-ray diffraction patterns of the magnesium promoted catalyst, are given in Figures 2 and 3respectively. Temperature dependence of the H2 generation from WGS reaction of the samples: X-ray diffraction patterns of the magnesium promoted Fe-Mg catalysts.
Water gas shift |
The H2 production is also found to increase with the rise of reaction temperature. The analysis of XRD patterns reveals that the Fe2O3 crystalline phase was detected in the unsupported solid.
Iron oxide did not appear on the Fe-supported solids.