Membrane reactors are a promising alternative to the currently used two-stage Water Gas Shift (WGS) conversion processes. The catalytic systems that are being tested for membrane reactors are based on those used for high temperature WGS, modified with other metals to keep the activity in the new operation conditions (higher CO₂ and lower H₂O concentrations). In this context, the objective of this work is the development of new formulations for high temperature WGS catalysts to adapt them to membrane reactor conditions.

Magnetite based catalysts were promoted with Cr, Mo, Cu or Co, obtaining three different formulations: Fe₃O₄-Cr₂O₃-CuO, Fe₃O₄-MoO₃-CuO, Fe₃O₄-Cr₂O₃-CoO. Catalysts were prepared by oxidation-precipitation of an aqueous solution of FeCl₂ and CrCl₃, (NH₄)₆Mo₇O₂₄, CuCl₂ or CoCl₂ adding the appropriate Fe/promoter molar ratio. Catalysts were characterized by X-ray diffraction, X-ray fluorescence, transmission electron microscopy (TEM), nitrogen adsorption/desorption at 77 K and temperature programmed reduction (TPR).

TEM results showed that Fe₃O₄-Cr₂O₃-CuO material was composed of Fe₃O₄ crystals surrounded by smaller high chromium containing particles. On the contrary, Mo was incorporated into magnetite lattice in Fe₃O₄-MoO₃-CuO catalyst. TPR results showed that addition of Mo increases thermal stability of the magnetite active phase and prevents metallic iron formation when catalyst is reduced. The cobalt doped sample exhibited higher reducibility than Fe₃O₄-MoO₃-CuO but lower than that detected in the classical Fe₃O₄-Cr₂O₃-CuO material.

In conclusion, modified high temperature WGS catalysts were prepared by oxidation-precipitation directly in the active phase, incorporating metal promoters to improve thermal stability.