Perovskites for the Water-Gas Shift Reaction

For the WGS reaction, the temperature strongly influences the achieved CO conversion, since this is a reversible and exothermic reaction. In addition, the reaction rate is limited by kinetics at low temperatures thus, catalysts with high performance are necessary to provide the adequate activity [61,62]. 

Maluf et al. [67] evaluated the catalytic performance of La2 Ca cCu04 perovskites on the low-temperature WGS reaction. They observed that all studied perovskites are active at 290 °C, and a promoter effect of Ca is described. They found that the partial substitution of La by Ca enhanced the stability of the perovskites and increased their reduction temperature. The calcium amount 

The same authors performed a kinetic study of the WGS reaction over a Lao.7Ceo.2Fe03 perovskite-hke catalyst in the temperature range of 550-600 °C [70]. It was found a power-law rate expression (Eq. (20.4)), which involved six variables and correlates with the experimental data with good accuracy  

T is the temperature, R is the universal gas constant, and R, is the partial pressure of gas component i. As expected, the presence of both reactants and products has an effect on the overall WGS reaction rates. 

Among the possible reaction mechanism proposed in the literature, the regenerative mechanism is generally the most accepted to describe the WGS reaction, in which water molecules are adsorbed and dissociated on reduced sites to generate hydrogen while oxidizing the site (Eq. (20.5)). Subsequently, CO is oxidized to CO2 and reduces the oxidized site to complete the catalytic cycle (Eq. (20.6)), 

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