Intercorrelation of structure and performance of Ni–Mg/Al2O3 catalysts prepared with different methods for syngas methanation

Abstract

Ni–Mg/Al₂O₃ catalysts prepared with methods of co-precipitation (CP), homogeneous precipitation (HP) and acid–base pairing (ABP) were tested for syngas methanation at 623–923 K in a stainless steel fixed bed reactor and further characterized to justify their performances. The Ni–Mg/Al₂O₃ catalysts prepared with CP using NH₄OH, NaOH and Na₂CO₃ as the precipitants followed an activity order of NaOH > NH₄OH > Na₂CO₃. Comparing further with the samples prepared by HP and ABP resulted in an activity order of HP > ABP > CP (NaOH) for syngas methanation under 0.1 MPa. For CO conversion, a transition of reaction control from kinetic dominance to thermodynamic dominance was observed at about 780 K. Performing 20 h continuous tests at 773 K and under 0.1 and 2.5 MPa further verified the stability of the HP, ABP and CP (NaOH) catalysts for syngas methanation. Analyzing the catalysts via H₂-TPR clarified that a lower amount of free NiO and a stronger interaction between the dispersed NiO and Al₂O₃ or MgO ensured better catalytic performance for methanation. The study also identified two types of carbon deposited on the surface of the spent catalysts.