Effect of citric acid on CoO-MoO3/Al2O3 catalysts for sulfur-resistant methanation

CoO-MoO3/AO(2)O(3) catalysts with different contents of citric acid were prepared by the simultaneous impregnation method and were tested for sulfur-resistant methanation. The catalysts were characterized with N-2-physisorption, XRD, scanning electron microscopy (SEM), H-2-TPR, Raman spectroscopy, ultraviolet-visible spectroscopy, and XPS. The N-2-physisorption and SEM results indicated that the addition of citric acid could increase the BET surface area and the amount of smaller particles in catalysts, improving the monolayer loading capacity. It would result in the better dispersion of metal active components (Co, Mo species). The combined results of various characterization suggested that the addition of citric acid could avoid the formation of crystalline CoMoO4 while the Mo-CA complex was found in the Raman spectrum. As the mole ratio of n(CA)/n(Mo) increased up to 2.0, the catalysts showed the highest activity in sulfur-resistant methanation as there were the most MoS2 on the surface of Al2O3 supports according to the results of XPS.