Abstract
A comparison between the effect of different highly thermal conductive carriers on the performance of Pt/CeO2/Al2O3-based structured catalysts in a water–gas shift reaction, was reported. The structured catalysts were prepared by means of washcoating two carriers, a flow through aluminum monolith and an open cell aluminum foam, with the same contact surface and the same chemical composition of the washcoat. The experiments were carried out under stressful conditions (no dilution and high space velocity), so as to minimize the thermal dispersions and to highlight the effect of the thermal conductivity of the carriers and the material transport phenomena. Both of the catalysts showed a substantially flat thermal profile, while the carbon monoxide conversion was higher with the foam-based catalyst, as a result of the higher temperatures reached. The experimental results were validated with a computational fluid dynamics (CFD) simulation by using the finite elements software, COMSOL Multiphysics®. Through the simulation results, it was also possible to investigate the effects of transport phenomena on the two catalytic systems, such as mass and heat transfer.
Highlights
The water–gas shift process (WGS) plays a crucial role in modulating the H2 /CO ratio in the syngas [1]; it can be considered as the first purification step of the reformate gas to produce pure hydrogen, reducing the percentage of carbon monoxide
The WGS process is normally performed in two steps, with an intermediate cooling; in the high temperature shift (HTS) [10] more than 90% of the CO is quickly converted [11], exploiting the high reaction rates, while in the low temperature shift (LTS), it is possible to reach more than 99% of CO conversion [12], exploiting the favorable thermodynamic equilibrium
We showed the results of a comparative study on the WGS reaction, between two structured catalysts, characterized by two different carriers (i.e., aluminum monolith (PtCeWM) and aluminum foam (PtCeWF10)); the reaction system was developed with the aim of reducing the thermal dispersions under stressful operative conditions for the catalyst
Summary
The water–gas shift process (WGS) plays a crucial role in modulating the H2 /CO ratio in the syngas [1]; it can be considered as the first purification step of the reformate gas to produce pure hydrogen, reducing the percentage of carbon monoxide. The heat of the reaction causes a thermal gradient on the catalytic bed, which depresses the kinetics at the inlet of the bed, where the temperature is lower, disadvantaging the CO conversion at the outlet of the bed, where the temperature is higher To overcome these limitations, the WGS process is normally performed in two steps, with an intermediate cooling; in the high temperature shift (HTS) [10] more than 90% of the CO is quickly converted [11], exploiting the high reaction rates, while in the low temperature shift (LTS), it is possible to reach more than 99% of CO conversion [12], exploiting the favorable thermodynamic equilibrium. The multi-stage approach has several disadvantages, namely: the intermediate cooling
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