Preparation of iron oxide nanoparticles doped by chromium for application in water–gas shift reaction

Abstract

An efficient preparation method of chromium-doped iron oxide nanoparticles of controlled size, chromium content and catalytic activity was developed. The catalysts were synthesized in an acidic hydrolysis of ferric chloride in order to obtain suspensions of spherical iron oxide nanoparticles with an average size of 10 and 100nm. After purification, the suspensions were transformed into powders. Afterwards, by a wet-impregnation and calcination chromium cations were incorporated to the nanoparticle structure without changing their size. The catalysts were characterized by powder X-ray diffraction (XRD), Raman spectroscopy, N2 adsorption (BET) and scanning electron microscopy (SEM). The activity of obtained samples was tested in a high temperature water gas shift reaction (HT-WGS) and compared with the results gained for chromium-free nanoparticles of similar sizes. The analysis of Raman spectra revealed that at elevated temperature iron hydroxyoxides are transformed to hematite (α-Fe2O3) and then, under catalytic conditions, to magnetite (Fe3O4) which is an active phase in the HT-WGS reaction. The chromium incorporated into the nanoparticles prevented a thermal sintering of nanocrystals, leading to an efficient catalyst performance. It was also shown that chromium-doped α-Fe2O3 nanoparticles of the size of 100nm, after the transformation to the magnetite phase, allowed to obtain a high carbon oxide conversion approaching the thermodynamic limit for temperatures above 500°C .