Water Gas Shift WGS

In the WGS reaction, CO is activated to nucleophilic attack by water. Clearly cationic complexes are well suited to this task, and it is not surprising 

It is not yet clear if the system remains cationic throughout the catalytic cycle added base does not suppress the reaction. 

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Furthermore, the application of the SOD membrane in a FT reaction has been investigated. The advantages of water removal in a FT reaction are threefold (i) reduction of H20-promoted catalyst deactivation, (ii) increased reactor productivity, and (iii) displaced water gas shift (WGS) equilibrium to enhance the conversion of CO2 to hydrocarbons [53]. Khajavi etal. report a mixture of H2O/H2 separation factors 10000 and water fluxes of 2.3 kg m h under... 

The optimization of heat transfer in a heat-exchanger reactor was also the objective of the work of TeGrotenhuis et al. [165]. Specifically, the exothermic water-gas shift (WGS) reaction ... 

Step 4 Side reaction such as CO dissociation (Eqn. 6), the Boudouard reaction (Eqn. 7) or the water gas shift (WGS) reaction (Eqn. 8, with surface OH species) may also occur ... 

Once particulate matter is removed, the syngas passes through a two stages catalytic reactor, where CO reacts with steam to produce C02 and further yield H2 water-gas-shift (WGS) reaction. 

Figure 3.4 and Table 3.3 show that C02 selectivity over the 15% Co/Si02 catalyst is quite low, less than 0.4% regardless of the calcination procedure used, indicating a small extent of the water-gas shift (WGS) reaction over the catalysts. However, as shown in Table 3.3, a slightly lower average C02 selectivity was observed over the NO calcined 15% Co/Si02 catalyst compared to the air calcined one (0.19 vs. 0.29%), another indication that the NO calcination benefited FTS performance. 

CO can be converted into either hydrocarbon products and water (via FTS) or C02 and Fl2 via the water-gas shift (WGS) reaction. The reversible WGS reaction accompanies FTS over the iron-based catalyst only at high temperature conditions. The individual rates of FTS (rFTS) and the WGS reaction (rWGS) can be calculated from experimental results as rWGS = r(,and rFTS = rco-rc02, where rCo2 is the rate of C02 formation and rco is the rate of CO conversion. 

In this chapter a two a selectivity model is proposed that is based on the premise that the total product distribution from an Fe-low-temperature Fischer-Tropsch (LIFT) process is a combination of two separate product spectrums that are produced on two different surfaces of the catalyst. A carbide surface is proposed for the production of hydrocarbons (including n- and iso-paraffins and internal olefins), and an oxide surface is proposed for the production of light hydrocarbons (including n-paraffins, 1-olefins, and oxygenates) and the water-gas shift (WGS) reaction. This model was tested against a number of Fe-catalyzed FT runs with full selectivity data available and with catalyst age up to 1,000 h. In all cases the experimental observations could be justified in terms of the model proposed. 

For the development of a selectivity model it is helpful to have a picture of the surface of the catalyst to ht the explanation of how the product spectrum is formed. The fundamental question regarding the nature of the active phase for the FT and water-gas shift (WGS) reactions is still a controversial and complex topic that has not been resolved.8 Two very popular models to describe the correlations between carbide phase and activity are the carbide9 and competition models.10 There are also proposals that magnetite and metallic iron are both active for the FT reaction and carbides are not active11. These proposals will not be discussed in detail and are only mentioned to highlight the uncertainty that is still present on the exact phase or active site responsible for the FT and WGS reactions. 

In this contribution, the steady-state isotopic transient kinetic analysis-diffuse reflectance Fourier transform spectroscopy (SSITKA-DRIFTS) method provides further support to the conclusion that not only are infrared active formates likely intermediates in the water-gas shift (WGS) reaction, in agreement with the mechanism proposed by Shido and Iwasawa for Rh/ceria, but designing catalysts based on formate C-H bond weakening can lead to significantly higher... 

Transition metal compounds in various form such as metal carbonyls 0), carbonyl clusters (2), Pt(II) chloride/tin chloride (3) PtLn (L=PR3) (4), etc. have been proposed as homogeneous catalysts for the water gas shift (wgs) reaction (eq. 1). Some of them are reportedly active at relatively low temperature (<150°)... 

The large body of examples discussed in the previous section indicates that SCFs, and in particular scC02, offer a broad potential for applications in hydrogenation reactions. Very little is known, however, about possible interactions between the catalytically active species and the reaction medium in such systems. In particular, two possible transformations of C02 in the presence of hydrogen must be considered, which are also transition metal-catalyzed (Scheme 39.8). The water gas shift (WGS) reaction can lead to the formation of CO, and has... 

In some applications water-gas-shift (WGS) is coupled with other reactions. For example, the steam reforming of methane to produce hydrogen is one example where both the forward and reverse reaction may be involved. However, this reaction is accomplished at high temperatures and the reaction is usually considered to be at equilibrium at the high temperatures used. In the following these high temperature processes will not be covered only those instances where the WGS reaction is the dominant reaction that is used to produce and/or purify hydrogen is considered. 

The water-gas-shift (WGS) reaction (HzO + CO -> H2 I C02) on MgO, ZnO, and Rh/CeOz is another example of a surface catalytic reaction that is assisted by gas-phase molecules. It is known that the WGS reaction proceeds via surface formate intermediate (HCOO-), which can be monitored by FT-IR. The behavior of the surface intermediates (HCOO-) (Cat-X in Figure 8.1a) is remarkably influenced by weakly coadsorbed water molecules (A in Figure 8. lb). The characteristic aspect of the WGS reactions on ZnO and Rh/Ce02 are as follows ... 

Depending on the reason for converting the produced gas from biomass gasification into synthesis gas, for applications requiring different H2/CO ratios, the reformed gas may be ducted to the water-gas shift (WGS, Reaction 4) and preferential oxidation (PROX, Reaction 5) unit to obtain the H2 purity required for fuel cells, or directly to applications requiring a H2/CO ratio close to 2, i.e., the production of dimethyl ether (DME), methanol, Fischer-Tropsch (F-T) Diesel (Reaction 6) (Fig. 7.6). 

Steam methane reforming (SMR) is the most widely practiced commercial process for the production of syngas and hydrogen almost 50% of the world s hydrogen production comes from natural gas. Two equilibrium reactions, steam reforming and the water-gas shift (WGS) reaction, are at the heart of the hydrogen production process ... 

Exposure of the reaction mixture to reduced carbon monoxide pressure in the flash-tank has implications for catalyst stability. Since the metal catalyst exists principally as iodocarbonyl complexes (e.g. [Rh(CO)2l2] and [Rh(CO)2l4]" for the Rh system), loss of CO ligands and precipitation of insoluble metal species (e.g. Rhl3) can be problematic. It is found that catalyst solubility is enhanced at high water concentrations but this results in a more costly separation process to dry the product. The presence of water also results in occurrence of the water gas shift (WGS) reaction (Eq. 6), which can be catalysed by Rh and Ir iodocarbonyls, in competition with the desired carbonylation process, resulting in a lower utilisation of CO ... 

The main unit is the catalytic primaiy process reactor for gross production, based on the ATR of biodiesel. After the primary step, secondary units for both the CO clean-up process and the simultaneous increase of the concentration are employed the content from the reformated gas can be increased through the water-gas shift (WGS) reaction by converting the CO with steam to CO and H. The high thermal shift (HTS) reactor is operating at 575-625 K followed by a low thermal shift (LTS) reactor operating at 475-535 K (Ruettinger et al., 2003). A preferential oxidation (PROX) step is required to completely remove the CO by oxidation to COj on a noble metal catalyst. The PROX reaction is assumed to take place in an isothermal bed reactor at 425 K after the last shift step (Rosso et al., 2004). 

Figure 8.2 Catalytic cycle for the rhodium-catalyzed water gas shift (WGS) reaction.

Figure 8.3 (a) Catalytic cycle for the iridium-catalyzed methanol carbonylation (b) catalytic cycle for the iridium-catalyzed water gas shift (WGS) reaction. Both as originally proposed by D. Forster (adapted from Ref [25]). 

SR of methane/natural gas is one of the largest catalytic processes in the world and is by far the most important method for producing industrial hydrogen today. The process is well described in literature and it is typically carried out at 800-950 °C over nickel-based catalysts." The main reactions are methane SR (11) and water-gas-shift (WGS) (12). 

Water-gas shift reaction. The water-gas shift (WGS) reaction (reaction (2)) made by particles composed of a promoter element close to a supported cobalt particle leads to a change in the local CO/H2 ratio, which may affect the surface coverage of cobalt. As a result, both the activity and the selectivity of the catalyst can be altered. Some transition metal oxides are known to act as WGS reagents. 

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