Preparation of mesoporous nanocrystalline alkali promoted chromium free catalysts (Fe2O3–Al2O3–NiO) for a high temperature water gas shift reaction

Abstract

The water gas shift reaction is one of the oldest heterogeneous catalytic reactions operating in industry for H₂ production with high purity and CO removal from syngas. Typical industrial catalyst for high temperature water gas shift (HTS) reactions is Fe–Cr–Cu, but has environmental and safety concerns related to chromium content, which has been regarded as a hazardous material. In this study, the effect of the addition of alkali metal oxide promoters to chromium free Fe₂O₃–Al₂O₃–NiO catalyst was investigated in HTS reaction. Nanocrystalline promoted chromium free catalysts with mesoporous structure were synthesized by coprecipitation and impregnation methods. Brunner–Emmett–Teller (BET), X-ray diffraction (XRD), temperature-programmed reduction (TPR) and desorption (TPD), scanning and transmission electron microscopic (SEM, TEM) techniques were performed to elucidate the HTS catalytic activity based on the influence of the addition of promoters on the catalyst structure. The results indicated that the addition of alkali promoters was effective in suppressing methanation, as well as in promoting HTS reaction activity for CO removal, which was related to the increment of the number of weakly basic sites through the addition of promoter. The results revealed that the Fe₂O₃–Al₂O₃–NiO (FAN) catalyst promoted by Na exhibited the highest catalytic activity and the lowest methanation among the investigated catalysts under a low steam/gas molar ratio, which favored methane formation. Furthermore, this catalyst presented higher CO removal activity than the commercial catalyst, which contains chromium. Moreover, the effect of Na content on the structural and catalytic properties of the FANNa catalysts was investigated and the results indicated that the catalyst with 3 wt% Na showed high activity and stability during 50 h time on stream.