Influence of preparation method on the structure of NiCo/MgO catalyst and its performance in the reforming of CH₄ with CO₂

To enhance the performance of nickel-based catalysts in the reforming of CH₄ with CO₂ and alleviate the coke deposition, a series of NiCo/MgO catalysts were prepared by different methods, viz., deposition-precipitation (DP), co-precipitation method (CP) and co-impregnation (CI); the influence of preparation method on the structure and performance of NiCo/MgO catalyst was then investigated. The results show that during the deposition-precipitation process, CO(NH₂)₂ as the precipitant could created an alkaline atmosphere for the complete hydrolysis of Ni²⁺ and Co²⁺ ions, leading to a relatively fast nucleation and growth of active species; however, oversaturation may occur during the co-precipitation process with NaOH and Na₂CO₃ as the precipitants. In comparison with the catalysts prepared by CP and CI, the NiCo/MgO-DP catalyst is provided with superior reduction capacity, smaller particle size (9.7 nm), higher Ni/Co dispersion (10.4%) and larger specific surface area (68.1 m²/g) and then exhibits better resistance to coke deposition. Over the DP catalyst, the conversions of CH₄ and CO₂ at 800 ℃ reach 88% and 92%, respectively, much higher than those over the CP and CI catalysts; moreover, the DP catalyst also gives much higher yield of H₂ and CO as well as better stability for methane reforming with CO₂.