Study of iron-promoted Cu/SiO₂ catalyst on high temperature reverse water gas shift reaction

The reverse water gas shift reaction over Cu/SiO₂ catalysts with and without iron promoter was studied by means of CO₂ hydrogenation, temperature programmed reduction (TPR), temperature programmed desorption (TPD) and X-ray diffraction (XRD). By addition of a small amount of iron (0.3% Fe to 10% Cu/SiO₂), the catalytic activity and stability of Cu/SiO₂ at high temperatures were effectively improved. The Cu/SiO₂ catalyst had low copper surface area when it was calcined and reduced at 600°C. Due to the addition of iron, Cu-Fe catalysts provided high copper surface area, even if these catalysts were pretreated at high temperatures. At 600°C and atmospheric pressure, the Cu-Fe catalysts exhibited high and constant catalytic activity up to 120h. In contrast, the 10% Cu/SiO₂ catalysts without Fe additives deactivated rapidly. Loss of copper surface area and oxidation of copper are the main factors causing the decay of catalytic activity of Cu/SiO₂ at high temperatures. The new active species located at the interface between Cu and Fe particles is proposed to be an important factor in enhancing catalytic activity. On the other hand, Fe in Cu-Fe catalysts surprisingly inhibits the sintering and oxidation of Cu and elevates the catalytic stability of Cu-Fe catalysts. The formation of small particles of iron species around Cu particles effectively prevents sintering of Cu at high temperatures. Oxygen releasing from the reaction on Cu can rapidly diffuse to Fe surfaces to form Fe oxides through a spillover process. This keeps Cu in its reduced state. Iron also offers similar promotions in catalytic activity, thermal stability and prevention of copper oxidation for Cu/Al ₂O₃ and commercial Cu/Zn/Al catalysts.