Preparation of mesoporous nanocrystalline iron based catalysts for high temperature water gas shift reaction: Effect of preparation factors

摘要

Mesoporous nanocrystalline iron based catalysts were synthesized by coprecipitation method and employed in high temperature water gas shift reaction. The effects of several process parameters such as pH, aging temperature, aging time, concentration of the precursors solution and calcination temperature on the structural and catalytic properties of the prepared catalysts were investigated. The catalysts were characterized by powder X-ray diffraction (XRD), N2 adsorption (BET), temperature programmed reduction (TPR), transmission and scanning electron microscopies (TEM, SEM) techniques. The results revealed that the prepared samples showed mesoporous structure with different pore size distributions depending on the process parameters chosen. It was found that the increase in pH value and decrease in the concentration of the precursors solution and calcination temperature caused an increase in the specific surface area, whereas for aging time and aging temperature there was an optimum point. Variation of these process factors varied the specific surface area of the prepared catalysts from 28.2 to 91.1 m~2/g. The results indicated that the higher pH value could favor the catalytic activity and the catalyst prepared at pH = 10 possessed the highest activity. The TEM analysis showed a nanostructure for this sample with a crystallite size less than 20 nm. This catalyst showed high stability during 100 h time on stream. Moreover, the effect of GHSV and steam/gas ratio on the catalytic performance of this catalyst was investigated.