Additives affect the physiochemical properties of the catalyst as well as the evolution of the reaction intermediates produced during the reaction process such as the methanation of CO₂. In this study, Co/Al₂O₃ catalysts modified with Na, K, Mg or Ca were prepared and the reaction intermediates formed during CO₂ methanation were investigated. The results showed that Na, K or Mg species reacted with alumina, forming Al(OH)₃ or MgAl₂O₄ spinel structure, leading to the re-structure of the catalysts and a remarkable decrease of the specific surface area. The increased alkalinity of the catalyst did not promote the catalytic activity for methanation but promoted CO formation. The addition of Na or K enhanced the affinity of the catalyst to the reaction intermediates of HCOO* and CO₃²⁻, slowing down their further reduction to CH₄ and leading to the lower catalytic activity. The evolution of HCOO* and CO₃²⁻ species strongly correlated with the catalytic activity, while the direct correlation between the capability for the absorbance of CO₂* as well as the C–O functionality and the catalytic activity was not found. In addition, the addition of Na or K to Co/Al₂O₃ could also induce the formation of a significant amount of the coke species in the nanotube form.

添加剂影响催化剂的物理化学性质以及在反应过程中产生的反应中间体的演化，例如CO ₂的甲烷化。在这项研究中，制备了用Na，K，Mg或Ca改性的Co / Al ₂ O ₃催化剂，并研究了在CO ₂甲烷化过程中形成的反应中间体。结果表明，Na，K或Mg物质与氧化铝反应，形成Al（OH）₃或MgAl ₂ O _4。尖晶石结构，导致催化剂的重组和比表面积的显着降低。催化剂碱度的提高不会促进甲烷化的催化活性，但会促进一氧化碳的形成。Na或K的添加增强了催化剂对HCOO *和CO ₃ ^2-的反应中间体的亲和力，减慢了它们进一步还原成CH _{4的速度，}并导致较低的催化活性。HCOO *和CO ₃ ^2-的释放与催化活性密切相关，而CO ₂吸收能力之间的直接相关*以及C–O官能度和催化活性均未发现。另外，将Na或K添加到Co / Al ₂ O _3中还可以诱导以纳米管形式形成大量的焦炭物质。