Statistical optimization by response surface methodology for water-gas shift reaction in a H 2-rich stream over Cu–Zn–Fe composite-oxide catalysts

Abstract

The catalytic performance of Cu–Zn–Fe composite-oxide catalysts prepared by the urea–nitrate combustion (UNC) method for the WGS reaction was investigated in this study. The catalysts were characterized by means of X-ray diffraction (XRD), X-ray fluorescence (XRF), and the Brunauer–Emmet–Teller (BET) method. In order to reduce the total number of experiments to achieve the optimal condition of CO conversion in the reaction and to reveal the interactions among the factors, two sets of statistical designs of experiments were carried-out. Initially, a full 2 5 factorial design with three central points was done. Increased CO conversion is obtained when increasing the H 2O concentration and the O 2 concentration in the influent, the W/ F ratio, and the reaction temperature. On the other hand, the CO conversion is decreased with increasing Cu/(Cu + Zn + Fe) molar ratio, increasing interaction between O 2 concentration in the influent and reaction temperature, and increasing interaction between Cu/(Cu + Zn + Fe) molar ratio and reaction temperature. In order to continue the optimization, the application of the face-centered central composite design (FCCCD) falling under response surface methods was done. Two independent factors were selected from the five main factors. Based on the important variabilities in the conversion, the O 2 concentration in the feedstream and the reaction temperature were then selected to achieve the optimal conditions for CO conversion. The maximum CO conversion of 0.87 was obtained when adding 0.10% O 2 and 30% H 2O in the feedstream at a reaction temperature of 333 °C, a W/ F ratio of 0.24 g s cm −3, and a Cu/(Cu + Zn + Fe) molar ratio of 0.30. After optimizing CO conversion by statistical design of the experiments, validation of the model was performed. The estimated values of the statistical response surface analysis were well fitted with the observed ones. This elucidated that the response surface methodology with appropriate experimental design can be effectively applied to the optimization of CO conversion in the WGS reaction.