Catalyst methanol steam reforming

The catalytic combustor provides heat for the endothermic reforming reaction and the vaporization of liquid fuel. The endothermic reforming reaction is carried out in a parallel flow-type micro-channel of the reformer unit. It is well known that the methanol steam reforming reaction for hydrogen production over the Cu/ZnO/AbOs catalyst involves the following reactions [10]. Eq. (1) is the algebraic summation of Eqs. (2) and (3). 

In this study, we developed microchannel PrOx reactor to control CO outlet concentrations less than 10 ppm from methanol steam reformer for PEMFC applications. The reactor was developed based on our previous studies on methanol steam reformer [5] and the basic technologies on microchaimel reactor including design of microchaimel plate, fabrication process and catalyst coating method were applied to the present PrOx reactor. The fabricated PrOx reactor was tested and evaluated on its CO removal performance. 

Pfeifer, P., Fichtner, M., Schubert, K., Liauw, M. a., Emig, G., Micro-structured catalysts for methanol-steam reforming, in Ehrfeld, W. (Ed.), Microreaction Techndogy 3rd Intematiorud Conference on Microreaction Technology, Proc. of IMRET 3, pp. 372-382, Springer-Verlag, Berlin (2000). 

P., Detailed characterization of various porous alumina based catalyst coatings within microchannels and their testingfor methanol steam reforming, Chem. Eng. Res. Des., special issue on Chemical Reaction Engineering (2003) submitted for publication. 

Mann, Thurgood, and coworkers—Langmuir-Hinshelwood kinetic model for methanol steam reforming and WGS over Cu/Zn. Mann et al.335 published a complex Langmuir-Hinshelwood model for CuO/ZnO catalysts based on what one would encounter for a methanol steam reformer (MSR) for fuel cell applications. The water-gas shift rate, containing all MSR terms, was determined to be ... 

It is worthy to note that numerous researchers have recently observed high catalytic activity for methanol steam reforming over Pd/Zn and Pt/Zn catalysts,528-534 and it would seem that these catalysts likely have potential for low temperature water-gas shift activity. 

Figure 3 in Ref. 217, reproduced on the right, shows SIMS spectra from a CuO/Ce02/ y-Al2 03 catalyst before and after a methanol steam reforming reaction. Assign the main peaks in the spectra, and provide an interpretation for the changes seen in the catalyst after reaction. 

DME hydration occurs over acid catalysts, whereas the methanol steam reforming reaction proceeds over metal catalysts. Consequently, DME steam reforming requires a multi-component catalyst. Two approaches have been proposed in the literature (a) physical mixtures of a DME hydrolysis catalyst and a methanol steam reforming catalyst (b) supported catalysts that combine the DME hydrolysis and methanol steam reforming components into a single catalyst. 

DME hydrolysis is an equilibrium-limited reaction and is considered as the rate-limiting step of overall DME steam reforming. The equilibrium conversion of hydration of DME is low at low temperatures (e.g. about 20% at 275 °C). However, when methanol formed in the first step is rapidly converted into H2 and CO2 by methanol steam reforming catalysts, high DME conversion is expected. Therefore, enhancement of DME hydrolysis is an important factor to obtain high reforming conversion. 

Reuse et al. [24] applied a reactor carrying micro structured plates for methanol steam reforming over commercial copper-based low-temperature water-gas shift catalyst from Sud-Chemie. The reactor took up 20 plates made of FeCrAl alloy of size 20 mm x 20 mm x 0.2 mm. The channel size was 200 pm x 100 pm (Figure 2.5). The catalyst was conditioned by oxygen and hydrogen treatment. 

The experiments were carried out at a pressure of 1.5 bar and a flow rate of 80-270 Ncm3 min-1. At 200 °C no deactivation of the catalyst was observed. As the rate of reaction was found to show a linear dependence on the residence time, differential conditions were assumed for the measurements. Because of the determined high activation energy of 5 6 kj mol-1, mass transport limitations were excluded. A power law kinetic expression of the following form was determined for methanol steam reforming ... 

Ziogas et al. [28] performed catalyst screening with this reactor with catalysts coatings, which were made of various base aluminas such as corundum, boehmite and y-alumina. Testing of Cu/Cr and Cu/Mn catalysts based on the different coatings for methanol steam reforming revealed differences in activity which were ascribed... 

Development of Catalyst Coatings for Methanol Steam Reforming in Micro Channels... 

A commercial Cu0/Zn0/Al203 catalyst was coated on quartz and fused silica capillaries by Bravo et al. [29] for methanol steam reforming and compared with packed-bed catalysts. The coatings had a thickness of 25 pm and showed 97% conversion and 97% selectivity towards carbon dioxide at 230 °C reaction temperature, a water/methanol molar feed composition of 1.1 and a space velocity of 45 kgcat s moh1 (methanol). 

In a later study, Pfeifer et al. [30] prepared Pd/Zn catalysts by both pre- and postimpregnation of wash-coated zinc oxide particles with palladium and compared their performance in methanol steam reforming. The catalytic performance of the samples was tested at a 250 °C reaction temperature, 3 bar pressure, a S/C ratio of two and 250 ms residence time. The WHSV amounted as 0.3 Ndm3 (min gcat) 1. The thickness of the coatings was calculated to 20 pm. The formation of the PdZn alloy was proven to occur at temperatures exceeding 200 °C by XRD measurements. 

Chin et al. [31] studied Pd/ZnO catalysts for methanol steam reforming, heading for a 10-50 W micro structured fuel processor. The catalysts under investigation contained 4.8, 9.0 and 16.7 wt.% Pd deposited on ZnO powder by impregnation. The catalysts were thoroughly characterized by thermogravimetry (TG), TPR, XRD and TEM. 

A detrimental effect of excess nitric acid on the ZnO support was observed, resulting in a reduced ZnO particle size and losses of surface area. This excess was present in the palladium nitrate solution that was applied for catalyst impregnation. Additionally it was found that the PdZn alloy was not only formed during the initial reduction step but also in situ in the hydrogen-rich reaction mixture of methanol steam reforming. 

The [MSR 6] reactor type (see below) was applied for methanol steam reforming over Cu/Ce02/Al203 catalysts by Men et al. [34, 35], Wash coating of the alumina was performed, followed by subsequent impregnation steps with ceria and copper salt solutions. At 250 °C reaction temperature and a water/methanol molar ratio of 0.9, the copper/ceria atomic ratio was varied from 0 to 0.9, revealing the lowest conversion for pure ceria and a sharp maximum for a ratio of 0.1 (see Figure 2.13). 

Dudfield et al. [88] presented results generated in the scope of the Mercatox program funded by the European Community aimed at a combined methanol steam reformer/combustor with consecutive CO clean-up by PrOx. First, various catalysts were tested for the reaction as micro spheres in a test reactor which was similar to a macroscopic shell-and-tube heat exchanger (Figure 2.57). 

The [PrOx 3] reactor (see Section 2.6.2) and an improved second version of it carrying also a different ratio of platinum and ruthenium on the catalyst were tested separately and switched in series by Dudfield et al. [88] prior to combining it with a 20 kW methanol steam reformer. The reactors had dimensions of 46 mm height, 56 mm width and 170 mm length, which corresponds to a volume of 0.44 dm3 and a weight of 590 g. They contained 2 g of catalyst each. 

Reuse et al. [68] combined endothermic methanol steam reforming with exothermic methanol combustion. The reactor consisted of a stack of 40 foils, 20 dedicated to each reaction (see Figure 2.77). The total length of the foils was 78 mm and their thickness was 200 pm. The foils carried 34 S-shaped channels each with a length of 30 mm, a depth of 100 pm and a width of 310 pm. A special plate in the center of the stack allowed for temperature measurements. The plates were made of FeCrAlloy and an a-alumina film 5 pm thick was generated on their surface by temperature treatment at 1000 °C for 5 h to improve the adherence of the catalyst coatings (see Section 2.10.7). 

Catalysts from Slid Chemie were applied for methanol steam reforming by Stimming et al. [121], G66-MR, a general-purpose catalyst containing 11% Al, 37% Cu and 52% Zn with 121 m2 g 1 surface area, and C18-HA, a catalyst optimized for methanol synthesis containing 2-3% Al, 50-60% Cu and 25-35% Zn with... 

Bravo et al. [29] dealt with the coating of a commercial CuO/ZnO catalyst on quartz and fused-silica capillaries for future application in micro channels. The catalyst was mixed with boehmite as binder and water at a mass ratio of44 11 100. The boehmite was treated with hydrochloric or nitric acid before. The capillaries were pretreated with a hot sulfuric acid/solid oxidation step before coating. The capillaries were filled with the catalyst/binder suspension and then cleared with air. In this way, catalyst coatings up to 25 pm thick were obtained. The coatings were applied to methanol steam reforming (see Section 2.4.1). 

Wash coats made of various source aluminas were prepared by applying this procedure (Figure 2.96) [147]. The catalysts obtained after subsequent impregnation were applied to methanol steam reforming [25, 28], propane steam reforming [52], water-gas shift [84] and preferential oxidation [89], to name but a few reaction systems. 

L., Renken, A., Catalyst coating in microreactors for methanol steam reforming kinetics, in Matlosz, M., Ehrfeld, W., Baselt, J. P. (Eds.), Microreaction Technology - IMRET 5 Proc. of the 5th International Conference on Microreaction Technology, Springer-Verlag, Berlin, 2001, 322-331. 

G. P., Datye, A., Wall coating of a CuO/ Zn0/Al203 methanol steam reforming catalyst for micro channel reformers, Chem. Eng.J. 2004, 101, 113-121. 

Chin, Y.-H., Wang, Y., Dagle, R. A., Li, X. S., Methanol steam reforming over Pd/ZnO catalyst preparation and pretreatment studies, Fuel Process. 

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