CO₂ reforming of methane over Ni_xMg_6−xAl₂ catalysts: Effect of lanthanum doping on catalytic activity and stability

Ni_xMg_6−xAl₂ and Ni_xMg_6−xAl_1.8La_0.2 (x = 2, 4 or 6) catalysts were prepared via a co-precipitation method and calcined under an air flow at 800 °C. X-ray diffraction (XRD) results showed that the Ni_xMg_6−xAl_1.8La_0.2 catalysts contained different lanthanum oxide species after calcination. Fourier Transform Infrared Spectroscopy (FTIR) spectra demonstrated that the lanthanum doped catalysts adsorbed more CO₂ compared to the lanthanum free solids. This improved basicity was verified in the CO₂-TPD profiles. Temperature programmed reduction (TPR) analyses proved that the addition of lanthanum affected nickel species distribution in the catalysts and strengthened NiO-MgO interactions inside the solid matrix. The CO₂ reforming of methane reaction (Ar/CO₂/CH₄:60/20/20; GHSV 60000 mL g⁻¹ h⁻¹) was carried out over the different catalysts in the temperature range of 600 °C–800 °C. Lanthanum addition improved the catalytic activity particularly by favoring the methane dry reforming reaction over all the other secondary reactions in addition to the creation of more basic sites that enhanced CO₂ adsorption and contributed to the removal of carbon deposits. The most active lanthanum containing catalyst kept a constant catalytic performance for 14 h on stream despite the formation of carbon deposits. These carbon deposits can be removed under an oxidative atmosphere at moderate temperature due to the presence of lanthanum oxide species in the catalyst.