Recent advances in carbon dioxide hydrogenation to formic acid

<p indent="0mm">The massive utilization of fossil resources, such as coal, petroleum and natural gas, has spurred rapid societal advancement, however, it has also led to excessive carbon dioxide (CO₂) emissions. In 2022, global atmospheric CO₂ concentrations reached <sc>417.9±0.2 ppm,</sc> and marking a new record high over the past two million years. This substantial in CO₂ levels contributes to intensified greenhouse effects and widespread environmental issues. By 2023, the annual average temperature increased to 1.45±0.12°C above pre-industrial levels, further approaching the 1.5°C temperature control target set by the Paris Agreement, resulting in notable significant negative economic and social consequences. Mitigating CO₂ emissions and controlling atmospheric CO₂ levels have thus become urgent global priorities. Given that CO₂ is a clean abundant carbon resource, it can be catalytically hydrogenated into valuable C₁ compounds, such as methane (CH₄), methanol (CH₃OH), formic acid (HCOOH) and carbon monoxide (CO), as well as C₂₊ products, such as like alkenes, aromatics, gasoline, diesel and liquefied petroleum gas (LPG) etc. The conversion of CO₂ into value-added products helps reduce atmospheric CO₂ content and provides a sustainable pathway for producing essential chemicals. Amongst these products, formic acid stands out as a fundamental organic chemical feedstock with extensive applications in leather production, pharmaceutical, textile printing, dyeing, agriculture, paper manufacturing and chemical industries. In addition, formic acid serves as a crucial hydrogen energy, carrier with a hydrogen storage capacity of up to <sc>53 g L⁻¹.</sc> It exhibits low toxicity and flammability, making it safe and practical for storage and transportation. Consequently, the selective conversion of CO₂ to formic acid holds promise for mitigating the global greenhouse effect, while enabling synthesis of valuable chemical precursors. Nevertheless, this reaction has a significant challenge that cannot be overlooked, the hydrogenation of CO₂ to formic acid necessitates simultaneous activation of two stable gas molecules-H₂ and CO₂, which is subject to obvious thermodynamic limitations and usually requires reaction conditions of high temperature and pressure. Therefore, designing an effective catalytic system is critical to lower the substantial energy barrier involved in hydrogen dissociation and C=O bond hydrogenation. Current catalytic approaches for CO₂ hydrogenation to formic acid mainly include both homogeneous and heterogeneous systems. Although homogeneous catalysts demonstrate exceptional catalytic activity for formic acid/formate production, their practical application is limited by the high costs of organic ligands and challenges associated with separating and recycling metal complexes, making industrialization difficult. Conversely, heterogeneous catalysts are particularly appealing owing to their low preparation costs, good stability and ease of separation and recycling. Among these, metal-supported catalysts are the most commonly utilised heterogeneous catalysts for CO₂ hydrogenation to formic acid/formate reaction. However, the activity of such catalysts rapidly decreases during reactions, primarily due to metal site agglomeration and loss. To enhance the catalytic stability of metal-supported catalysts, strengthening the metal–support interaction is essential. This can be achieved by tailoring the surface geometry and electronic structure of the support material. In this review, we present a comprehensive evaluation of the catalytic performance of various metal-supported catalysts, including zeolites, mesoporous silicas, metal-organic frameworks and metal oxides, for CO₂ hydrogenation to formic acid/formate. In addition, we assess the impact of support structure, morphology and exposed crystal surfaces on the activity in formic acid/formate formation. We hope this work may provide some guidance for the design of high-performance catalysts for CO₂ hydrogenation to formic acid.