Hydrogen gas is a storable form of chemical energy that could complement intermittent renewable energy conversion. One of the main disadvantages of hydrogen gas arises from its low density, and therefore, efficient handling and storage methods are key factors that need to be addressed to realize a hydrogen-based economy. Storage systems based on liquids, in particular, formic acid and alcohols, are highly attractive hydrogen carriers as they can be made from CO₂ or other renewable materials, they can be used in stationary power storage units such as hydrogen filling stations, and they can be used directly as transportation fuels. However, to bring about a paradigm change in our energy infrastructure, efficient catalytic processes that release the hydrogen from these molecules, as well as catalysts that regenerate these molecules from CO₂ and hydrogen, are required. In this review, we describe the considerable progress that has been made in homogeneous catalysis for these critical reactions, namely, the hydrogenation of CO₂ to formic acid and methanol and the reverse dehydrogenation reactions. The dehydrogenation of higher alcohols available from renewable feedstocks is also described. Key structural features of the catalysts are analyzed, as is the role of additives, which are required in many systems. Particular attention is paid to advances in sustainable catalytic processes, especially to additive-free processes and catalysts based on Earth-abundant metal ions. Mechanistic information is also presented, and it is hoped that this review not only provides an account of the state of the art in the field but also offers insights into how superior catalytic systems can be obtained in the future.

中文翻译：

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均相催化在甲酸和乙醇中可持续储氢

氢气是化学能的一种可存储形式，可以补充间歇性可再生能源的转化。氢气的主要缺点之一是其密度低，因此，有效的处理和储存方法是实现氢基经济所需要解决的关键因素。基于液体（尤其是甲酸和醇）的存储系统是极具吸引力的氢载体，因为它们可以由CO ₂制成或其他可再生材料，它们可用于固定式蓄电装置（例如加氢站）中，并可直接用作运输燃料。但是，为了在我们的能源基础设施中带来范式的变化，需要从这些分子释放氢的有效催化过程，以及从CO ₂和氢再生这些分子的催化剂。在这篇综述中，我们描述了在这些关键反应（即CO ₂的氢化）的均相催化方面已取得的重大进展。以甲酸和甲醇逆向进行脱氢反应。还描述了可得自可再生原料的高级醇的脱氢。分析了催化剂的关键结构特征以及许多系统所需的添加剂的作用。特别注意可持续催化方法的进展，尤其是无添加剂的方法和基于地球上丰富的金属离子的催化剂。还提供了机械信息，希望这篇综述不仅可以介绍该领域的技术现状，还可以为将来如何获得优质的催化体系提供一些见识。