LAUSR

In the present study, Cu/Zn/Mg/Al nanocatalysts were synthesized using the urea homogeneous co-precipitation method. The obtained powders were then formed in cylindrical (6 mm × 6 mm and 12 mm × 3 mm) shapes. The morphology and structure of powdered and formed catalysts were characterized, using XRD, SEM and BET analysis. The particle size of the powdered, 6 mm × 6 mm, and 12 mm × 3 mm catalyst samples were found as 30, 50–100 and more than 100 nm. The powdered and formed catalysts were subjected to water gas shift reactions in a fixed bed reactor. The limiting factors and their dominating conditions as a controller of reaction rate for CO conversion were analyzed employing Thiele modulus (Φ) and effectiveness factor (η) definitions. In this regard, the effects of the size and shape of the catalyst on reaction rate controller mechanism were investigated. Characterizing the Thiele modulus, it was found that pore diffusion could not be the reaction rate controller for the powdered type nanocatalyst under the studied temperatures (473–673 K). In contrast, the diffusion mechanism was the controlling factor of the reaction rate in 6 mm × 6 mm, and 12 mm × 3 mm formed catalysts at 673 and 623–673 K. The prediction model for 6 mm × 6 mm cylindrical catalyst was in good agreement with the experimental data. However, for the 12 mm × 3 mm catalyst, a deviation between the prediction and experimental values was observed. The latter result would be perhaps due to the side channeling of reactants between the large cylindrical catalysts.