Carbon dioxide (CO₂) is regarded as a main contributor to the greenhouse effect. As a potential strategy to mitigate its negative impacts, the reduction of CO₂ is environmentally critical, economically meaningful and scientifically challenging. Being both thermodynamically and kinetically unfavored, CO₂ reduction requires catalysts as a crucial component irrespective of the reaction modes, be it electrocatalytic, photoelectrocatalytic or photocatalytic. In an effort to systematically review the types of catalysts that have been studied for CO₂ reduction, we categorize them into two major groups: those being activated by external sources and those being photoexcited and activated themselves. Attention is focused on the detailed mechanisms for each group by which the reduction of CO₂ proceeds, yielding a summary of the guiding principles for catalyst designs. This review highlights the importance of mechanistic studies, which permits us to discuss our perspectives on potential directions of catalyst investigation for future catalytic CO₂ reduction research.

二氧化碳（CO ₂）被认为是造成温室效应的主要因素。作为减轻其负面影响的一种潜在策略，减少CO _2对环境至关重要，在经济上有意义并且在科学上具有挑战性。由于在热力学和动力学上均不利，所以CO ₂还原需要催化剂作为关键组分，而与反应模式无关，无论其是电催化的，光电催化的还是光催化的。为了系统地审查已针对CO ₂研究的催化剂类型还原，我们将它们分为两大类：那些由外部来源激活的和那些由光激发并自身激活的。注意力集中在每组减少CO ₂进行的详细机理上，从而总结了催化剂设计的指导原则。这篇综述突出了机理研究的重要性，这使我们能够讨论我们对未来催化CO ₂还原研究的催化剂研究潜在方向的看法。