With the increasing global population, the demands for fuels and chemicals are greater than ever. Greenhouse gas (GHG) emissions from the use of fossil fuel-based conventional feedstocks are also a matter of great concern. A revolution is needed to replace the conventional feedstocks, processes, and the materials that enable these processes with more sustainable alternatives such as renewable biomass, recycled carbon, and carbon dioxide (CO₂). In fact, we are at the verge of witnessing a shift from conventional fossil fuel-based petrochemical conversion to more sustainable processes that utilize unconventional feedstocks. Specifically, CO₂ can be viewed as a renewable source of carbon, which can be used as a C1 building block to valuable chemicals. Replacing petrochemical-based hydrocarbons would require massive sourcing of renewable hydrogen and carbon. Advances are underway in producing so-called “green” hydrogen, as the costs of renewable energy has significantly reduced in recent times. However, major renewable energy sources, such as solar and wind, are distributed with intermittent supply and spatiotemporal variability and uncertainty. Natural gas-based hydrogen generation is mature, but we must remove CO₂ to make it sustainable. Significant scientific and research challenges need to be resolved in the areas of hydrogen generation, separation, storage, and utilization to envision a sustainable future hydrogen economy. On the other hand, CO₂ capture and utilization/storage (CCUS) not only shows great promise for decarbonizing the hydrogen, energy and manufacturing sectors, it allows one to tap into large volumes of CO₂ that are available from stationary/point sources (e.g., fossil power plants, cement, iron and steel, agricultural processing, etc.) and from air via direct air capture. CO₂ capture remains expensive, and the associated parasitic energy penalty remains high. CO₂ is a stable gas that is mostly available as a combustion product after we burn fossil fuels. The energetics of CO₂ utilization is a key challenge. We need novel materials, methods, and multiscale approaches before we envision large-scale implementation of CO₂ as a primary resource for fuels and chemicals. Biomass and recycled plastics can constitute a major portion of a future feedstock portfolio for both hydrogen and carbon toward meeting our increasing demands for hydrocarbons. To that end, the concepts of integrated biorefineries and circular economy require further work in terms of resource utilization, materials development, and process intensification, among others. To overcome the intrinsic thermodynamic stability of CO₂, a large amount of chemical energy is required. Thermocatalytic CO₂ conversion is a known pathway for CO₂ upgrading and, for the ACS Sustainable Chemistry & Engineering (ACS SCE) journal, we pay attention to the wording used in the submitted papers. For example, the hydrogenation of CO₂ to methane implies the consumption of H₂, so it should not be presented as a process that allows “upgrading CO₂” on its own but as a reaction that allows “converting a CO₂ + H₂ mixture into methane (and water)”. This point is crucial because the large majority of the hydrogen production worldwide is still by steam reforming of natural gas (a large CO₂ emitter). For a net positive utilization of CO₂, the hydrogen must be obtained from renewable resources. Thus, the implementation of any significant development made on the front of catalytic CO₂ hydrogenation will rely on our ability to develop effective, cheap, and sustainable means to produce “green hydrogen”. As the GHG potential of methane is much higher than CO₂, one also needs to factor the net sustainability gain when methane is used as a fuel or reagent as part of chemical production. Another aspect of CO₂ utilization that is often overlooked is the nature of the CO₂ feed. While academic studies are usually carried out on pure CO₂ streams, it should be kept in mind that the CO₂ has to be mined (from gas effluents or possibly directly from air), and then, the solid adsorbent or the liquid absorbent used for capture has to be regenerated to produce a concentrated CO₂ stream. This step is known to be energy consuming. The energy requirement and cost of CO₂ capture vary significantly with the source CO₂ composition, flow rate, required purity of captured CO₂ to meet the pipeline specifications (typically >95%), and extent of separation (i.e., CO₂ recovery).(22) Therefore, CO₂ capture itself is a key challenge toward CO₂-based sustainable feedstocks. This is why efforts are being made to develop combined processes,(1,2) where capture and transformation are being carried out synergistically on nonpure CO₂ streams (ideally targeting the gas effluents of point sources such as incinerators or cement factories). ACS SCE welcomes manuscripts that propose an integrated discussion on the transformation of CO₂ and on its sourcing (capture and purification). The electrification of the chemical industry concept is gaining momentum both academically and industrially.(3) New reaction concepts that use electricity should enable renewable energy sources (e.g., wind and solar) to power chemical transformations and promote sustainability in the chemical industry. A core pillar of this transformation will be the electrochemical conversion of CO₂. Electrochemical CO₂ reduction offers a promising strategy to reduce the atmospheric CO₂ concentration and produce value-added chemicals and fuels at the same time. The reaction environment is friendly with ambient pressure and temperature. The electrochemical CO₂ conversion offers advantages such as benign conditions, controlled reaction conditions via applied potentials and/or currents, and easy coupling with renewable energies such as solar or wind with no extra CO₂ emission. In electrochemical CO₂ conversion processes, the electrocatalyst is key to overcome the high kinetic barriers for CO₂ activation, suppress the competitive reaction (e.g., hydrogen evolution reaction), and increase the selectivity toward the wanted products. Currently, the electrocatalysts used for CO₂ electrolysis can be generally classified into four groups including (i) non-Cu metal materials, (ii) carbon materials, (iii) molecular materials, and (iv) Cu-based catalysts. Electrolyzers for CO₂ conversion to CO and/or formic acid are reaching the pilot scale.(4) More valuable C₂₊ products, such as ethanol, ethylene, and acetate, can only be generated over the Cu-based materials, as well as several heteroatom-doped carbon materials. Beyond the electrocatalysts, the cell and reactor designs become significant in CO₂ conversion processes. Traditionally, the reaction occurs in a H-type electrochemical cell where the catalyst is fully immersed into electrolytes, while CO₂ gas is generally bubbled into the electrolyte. However, these conventional electrochemical systems suffer from low CO₂ reduction rates, especially with water as the solvent. This is because CO₂ solubility in water at ambient operating pressures is very low (34 mmol/L) and can be increased with pressure only moderately, according to Henry’s law. Such low solubilities limit achievable CO₂ reduction rates, regardless of the intrinsic activity of the electrocatalysts used. Thus, process intensification is needed for industrially relevant electrochemical CO₂ conversion. A variety of strategies are being pursued to alleviate CO₂ starvation at electrode surfaces. One example is gas-diffusion electrode-based flow cells, including a three-electrodes flow cell and membrane electrode assembly, to overcome these limitations and significantly enhance electrocatalytic performance. These vapor-fed systems are ripe for additional research on understanding the complexity of the three-phase boundary and myriad of interfaces on the micrometer and nanometer scales. In addition to vapor-feed systems, organic-based CO₂-rich systems can also provide significant process intensification.(5) Under ambient conditions, CO₂ is close to its critical temperatures, and when it is mildly compressed to few tens of bars at ambient temperatures, its density transitions from a gas-like to liquid-like form. Thus, in its compressed state, the solubilities of CO₂ in most organic solvents increase dramatically, and the volume of the liquid phase expands, resulting in a CO₂-expandedliquid. These CO₂-expanded liquids can also be paired with supporting electrolytes (hence referred to as CO₂-expanded electrolytes) to enable electrochemical CO₂ conversion at multimolar liquid-phase CO₂ concentrations. This provides process intensification, but further work is needed on developing larger-scale flow reactors using condensed CO₂. However, it is anticipated that highly efficient and selective electrocatalysts used together with well-designed flow cells hold great promise for electrochemical CO₂ conversion in the industry in the near future. As we continue to develop new approaches to utilize unconventional feedstocks for the chemical process industry, we also need to keep in mind the increased competition, stringent environmental regulations, and volatile markets. In recent times, these factors have contributed to renewed interest in process intensification methods to drastically reduce the size, cost, CO₂ emissions, and energy consumption. Process intensification synergistically combines multiple operations, such as separation, conversion, and intermittent storage, within a single piece of equipment. However, it is not trivial to identify the hotspots for process intensification to achieve sustainability goals. Another long-standing problem is to be able to systemically obtain out-of-the-box process solutions (an example is integrated CO₂ capture and conversion(2) with significantly less equipment and energy requirement). To that end, advances are made in computer-aided process intensification techniques. One example is the sustainable process design and intensification technique using the SPICE (synthesis and process intensification of chemical enterprises) framework.(6) SPICE departs from the classic unit operation-based representation of chemical processes and uses a new building block-based representation to achieve a seamless transition from the phenomena scale to the task/equipment scale to the flowsheet scale. SPICE enables “systematic innovation”, which is to say that process designers and process engineers now can systematically discover out-of-the-box and optimal design/retrofitting solutions without exhaustively enumerating all plausible alternatives. Significant progress in the development of homogeneous and heterogeneous catalysts for CO₂ hydrogenation to C1 products (e.g., formic acid, carbon monoxide, methane, and methanol) and C₂₊ products (chemicals containing two or more carbons) has been achieved. CO₂ hydrogenation by homogeneous (molecular) catalysts primarily produces methanol, formic acid/formate, and formamides.(7) Homogenous catalysts featuring phosphine, carbene, pincer, and proton-responsive bidentate ligands coordinated to platinum group metals like Ir, Ru, and Rh are known for CO₂ hydrogenation to formate. For example, an Ir^III trihydride pincer complex, [IrH3(PNP)](8) (PNP = 2,6-bis(di-isopropylphosphinomethyl)pyridine, has the highest activity in CO₂ hydrogenation to formate at 3,500,000 turnover numbers (TON) and 150,000 h^–1 turnover frequency (TOF). Another Ru^II pincer complex [RuH(Cl)(CO)(PNP′)](9) (PNP′ = 2,6-bis(di-tert-butylphosphinomethyl)pyridine) has remarkable performance at TOF of 1,100,000 h^–1 in an environmentally friendly solvent–aqueous media. The structure of pincer ligands impart high stability to the catalyst leading to high activities; notably, in some bifunctional systems, the metal and ligand work cooperatively, resulting in improved activities.(10) However, high operating temperatures and pressures (≥120 °C and 40 bar) mean an undesirable energy-intensive process from a scale-up viewpoint. A prominent class of CO₂ hydrogenation homogeneous catalysts are the half-sandwich Ir, Rh, and Ru complexes bearing bidentate N,N ligands with proton-responsive groups. The Ir version achieves a high activity in basic aqueous solution, at just 50 °C (TON = 153,000, pH 8.4). This system also converts CO₂ to formate at 25 °C and atmospheric pressure, albeit at low productivity (32 h^–1).(11) Even though some of these systems operate efficiently in aqueous media, the use of milder operating conditions (ambient temperature and pressure are ideal), elimination of additives such as bases and acids, and recyclable catalysts are important for achieving sustainability. CO₂ to MeOH is most efficient when alcohols or amines are used first to convert CO₂ to formamides, alkyl formates, or carbamates, which are further reduced to obtain methanol. Generally, homogeneous catalysts are not as highly active in hydrogenation beyond the process leading to formate; however, some Ru^II complexes exhibit activity in amine-assisted methanol synthesis from CO₂(12) and in direct CO₂ conversion to methanol.(13) Further catalyst development is required, particularly those that exhibit high activity at mild operating conditions and are derived from abundant sources or waste metals recovered from mine tailings or e-waste. The quest to develop efficient and inexpensive catalysts based on earth-abundant metals has led to several catalysts, including Fe, Mn, Co, and Cu, with promising activities in CO₂ hydrogenation to formate, methanol, and formamides.(14,15) Some catalysts show greater activities than known noble metal catalytic systems.(16) Although several catalytic systems show high activity, further development of highly active catalytic systems into chemical processes is less explored. If the main goal is to create innovative homogeneous catalytic hydrogenation systems that might lead to practical schemes for recycling CO₂, efforts should also be directed toward process design such as in the following examples: (1) the continuous-flow hydrogenation of supercritical CO₂ to produce pure formic acid in a single process that incorporates easy separation of the solvent, product, and catalyst(17) and (2) the synthesis of formamides in a miniplant scale catalyzed by a Ru pincer complex. The hydrogenation of CO₂ into CO, CH₄, CH₃OH, dimethyl ether, olefins, aromatics, hydrocarbons, and higher alcohols has been extensively studied in the field of heterogeneous catalysis. Numerous catalysts based on metals, oxides, and their alloys, such as Cu, Ru, Rh, Pt, Pd, Au, Ir, Co, Fe, Ni, Re, and In, have been developed for the CO₂ hydrogenation reaction, especially targeting higher activity and selectivity. CO₂ conversion is limited by the thermodynamics, but the product selectivity can be fine-tuned by catalyst design to avoid the thermodynamically most stable product methane(18) and by chosen operating conditions, such as low temperature and high pressure to increase methanol yield under supercritical flow conditions.(19) The classical methanol synthesis (from CO/H₂) catalysts, based on Cu/ZnO/Al₂O₃, have also been investigated and improved for the direct hydrogenation of CO₂ to methanol, while a remarkably productive process for the synthesis of methanol was achieved at high pressure and by increasing the H₂/CO₂ feed ratio.(20) Combined with zeolites, one-step integrated processes for the CO₂ conversion into dimethyl ether and other liquid products are achievable. Several studies have not only addressed the catalysts and process-technical aspects but also provide insightful views on the reaction thermodynamics, mechanism, and kinetics from theoretical studies. The literature is vast, but development of efficient catalysts to break the thermodynamic barriers of CO₂ hydrogenation reaction continues to be of extreme importance. Lastly, as we continue to develop new catalysts, solvents, adsorbents, membranes, and other materials toward utilizing CO₂ and renewable or recycled carbon as primary feedstocks for sustainable future, we foresee new challenges in terms of operability, safety, controllability, flexibility, resilience, and system integration of new processes and plant configurations that will use these materials.(21) Process system engineering methods and tools will play important roles in balancing the trade-offs between various economic, environmental, and sustainability goals. Specifically, we need to be cognizant about the variability, uncertainty, and spatiotemporal distribution associated with CO₂ sources. The selection of appropriate CCUS materials, processes, and technologies will largely depend on the CO₂ source compositions and flow rates and the distances between sources and utilization sites.(22) Synergistic integration of renewables and flexible carbon capture with individual fossil power plants will need to be considered. Furthermore, just focusing on converting CO₂ to chemicals will not be economically sustainable in the long term, since the large volume of available CO₂ is likely to saturate the chemical market quickly. A more sustainable pathway would involve combining CO₂ with renewable hydrogen toward producing alternatives to liquid transportation fuels and plastics. Overall, a holistic approach with a systems perspective will be necessary to determine the optimal pathways following informed decisions through systematic technoeconomic and life cycle analysis (TEA and LCA). Model-based and computer-aided multiscale design, simulation, and optimization of molecules, processes, and supply chains will be useful, all in conjunction with experimental synthesis and scale up. This article references 22 other publications.

中文翻译：

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二氧化碳和可再生碳能否成为可持续燃料和化学品的主要资源？

随着全球人口的增加，对燃料和化学品的需求比以往任何时候都大。使用基于化石燃料的常规原料产生的温室气体 (GHG) 排放也是一个非常令人担忧的问题。需要进行一场革命，用更可持续的替代品（例如可再生生物质、回收碳和二氧化碳 (CO ₂ )）取代传统的原料、工艺和材料，使这些工艺成为可能。事实上，我们即将见证从基于化石燃料的传统石化转化到利用非常规原料的更可持续的过程的转变。具体而言，CO ₂可被视为碳的可再生来源，可用作有价值化学品的 C1 构建块。替换基于石化的碳氢化合物将需要大量采购可再生氢和碳。由于近来可再生能源的成本已显着降低，因此在生产所谓的“绿色”氢方面取得了进展。然而，太阳能和风能等主要可再生能源的分布具有间歇性供应和时空可变性和不确定性。天然气制氢成熟，但必须去除CO ₂使其可持续。需要解决氢气产生、分离、储存和利用领域的重大科学研究挑战，以设想可持续的未来氢经济。另一方面，CO ₂捕获和利用/储存 (CCUS) 不仅在氢、能源和制造业脱碳方面显示出巨大的前景，它还允许人们利用固定/点源提供的大量 CO ₂（例如，化石发电厂、水泥、钢铁、农业加工等）和通过直接空气捕获从空气中提取。CO ₂捕获仍然很昂贵，并且相关的寄生能量损失仍然很高。CO ₂是一种稳定的气体，在我们燃烧化石燃料后主要作为燃烧产物使用。CO ₂利用的能量学是一个关键挑战。在我们设想大规模实施 CO ₂作为燃料和化学品的主要资源之前，我们需要新的材料、方法和多尺度方法。生物质和再生塑料可以构成未来氢和碳原料组合的主要部分，以满足我们对碳氢化合物日益增长的需求。为此，综合生物炼制和循环经济的概念需要在资源利用、材料开发和工艺集约化等方面进一步开展工作。克服 CO ₂固有的热力学稳定性，需要大量的化学能。热催化 CO ₂转化是 CO ₂升级的已知途径，对于ACS 可持续化学与工程( ACS SCE ) 期刊，我们会注意提交论文中使用的措辞。例如，CO ₂加氢为甲烷意味着消耗 H ₂，因此不应将其呈现为允许“升级 CO ₂ ”自身的过程，而应呈现为允许“将 CO ₂ + H ₂转化”的反应。混合成甲烷（和水）”。这一点至关重要，因为全球大部分氢气生产仍然是通过天然气（大型 CO ₂排放源）的蒸汽重整。对于 CO ₂的净正利用，氢必须从可再生资源中获得。因此，在催化 CO ₂加氢方面取得的任何重大进展的实施都将取决于我们开发有效、廉价和可持续的方法来生产“绿色氢”的能力。由于甲烷的温室气体潜力远高于 CO ₂，因此当将甲烷用作燃料或试剂作为化学生产的一部分时，还需要考虑净可持续性收益。CO _{2 的}另一方面经常被忽视的利用是 CO ₂进料的性质。虽然学术研究通常是对纯 CO ₂流进行的，但应该记住的是，必须开采CO ₂（来自气体流出物或可能直接来自空气），然后是固体吸附剂或液体吸收剂用于必须再生捕获以产生浓缩的 CO ₂流。众所周知，这一步是耗能的。CO ₂捕获的能量需求和成本随源 CO ₂组成、流速、捕获的 CO ₂所需纯度以满足管道规格（通常 > 95%）和分离程度（即 CO ₂(22) 因此，CO ₂捕获本身是对基于CO ₂的可持续原料的关键挑战。这就是为什么正在努力开发联合工艺，(1,2) 在非纯 CO ₂流上协同进行捕获和转化（理想情况下针对点源，如焚化炉或水泥厂的废气）。ACS SCE欢迎提交关于 CO ₂转化的综合讨论的手稿及其来源（捕获和纯化）。化学工业概念的电气化在学术和工业上都获得了动力。(3) 使用电力的新反应概念应该使可再生能源（例如风能和太阳能）能够为化学转化提供动力并促进化学工业的可持续性。这种转变的核心支柱将是 CO ₂的电化学转化。电化学 CO ₂还原提供了一种有前景的策略，可以降低大气中的 CO ₂浓度并同时生产具有附加值的化学品和燃料。反应环境友好，常压常温。电化学 CO ₂转换提供了一些优势，例如良性条件、通过施加的电位和/或电流控制反应条件，以及易于与可再生能源（如太阳能或风能）耦合而不会排放额外的 CO ₂。在电化学 CO ₂转化过程中，电催化剂是克服 CO ₂活化的高动力学障碍、抑制竞争反应（例如析氢反应）和提高对所需产物的选择性的关键。目前，用于CO ₂电解的电催化剂大致可分为四类，包括(i)非Cu金属材料、(ii)碳材料、(iii)分子材料和(iv)Cu基催化剂。CO ₂电解槽(4) 更有价值的 C ₂₊产品，如乙醇、乙烯和醋酸盐，只能在 Cu 基材料以及几种杂原子的基础上产生。掺杂碳材料。除了电催化剂之外，电池和反应器的设计在 CO ₂转化过程中也变得很重要。传统上，反应发生在 H 型电化学电池中，其中催化剂完全浸入电解质中，而 CO ₂气体通常鼓泡到电解质中。然而，这些传统的电化学系统的 CO ₂还原率低，尤其是用水作为溶剂时。这是因为 CO ₂根据亨利定律，在环境操作压力下，其在水中的溶解度非常低 (34 mmol/L)，并且只能随压力适度增加。无论所用电催化剂的内在活性如何，这种低溶解度限制了可实现的 CO ₂还原速率。因此，工业相关的电化学CO ₂转化需要过程强化。正在采取各种策略来缓解 CO ₂电极表面饥饿。一个例子是基于气体扩散电极的流通池，包括三电极流通池和膜电极组件，以克服这些限制并显着提高电催化性能。这些蒸汽供给系统已经成熟，可以进行进一步研究，以了解三相边界的复杂性以及微米和纳米尺度上的无数界面。除了蒸汽进料系统，富含有机物的 CO ₂系统也可以提供显着的过程强化。(5) 在环境条件下，CO ₂接近其临界温度，当它在环境温度下轻微压缩到几十巴时，它的密度会从类似气体的形式转变为类似液体的形式。因此，在其压缩状态下，CO ₂在大多数有机溶剂中的溶解度急剧增加，并且液相体积膨胀，导致 CO ₂膨胀液体。这些CO ₂ -expanded液体也可以与支持电解质配对（因此被称为CO ₂ -expanded电解质），以使电化学CO ₂在multimolar液相CO转化₂浓度。这提供了工艺强化，但需要进一步的工作来开发使用冷凝 CO _{2 的}更大规模流动反应器。然而，预计在不久的将来，与设计良好的流通池一起使用的高效和选择性电催化剂对电化学 CO ₂转化具有广阔的前景。随着我们继续开发利用非常规原料用于化学加工行业的新方法，我们还需要牢记日益激烈的竞争、严格的环境法规和动荡的市场。最近，这些因素重新激发了人们对工艺强化方法的兴趣，以大幅降低尺寸、成本、CO ₂排放和能源消耗。过程集约化将分离、转换和间歇存储等多种操作协同组合在一个设备中。然而，确定过程强化的热点以实现可持续发展目标并非易事。另一个长期存在的问题是能够系统地获得开箱即用的工艺解决方案（一个例子是集成的 CO ₂捕获和转化（2），设备和能源需求显着减少）。为此，计算机辅助过程强化技术取得了进展。一个例子是使用 SPICE（化工企业的合成和过程集约化）框架的可持续过程设计和集约化技术。 (6) SPICE 脱离了化学过程的经典基于单元操作的表示，并使用了一种新的基于构建块的表示来实现从现象尺度到任务/设备尺度再到流程尺度的无缝过渡。SPICE 实现了“系统创新”，也就是说，工艺设计师和工艺工程师现在可以系统地发现开箱即用的最佳设计/改造解决方案，而无需详尽列举所有可能的替代方案。₂加氢为C1 产物（例如甲酸、一氧化碳、甲烷和甲醇）和C ₂₊产物（含有两个或多个碳的化学品）已经实现。均相（分子）催化剂对CO ₂加氢主要产生甲醇、甲酸/甲酸盐和甲酰胺。 (7) 均相催化剂具有与铂族金属如 Ir、Ru 和Rh已知用于将CO ₂氢化成甲酸盐。例如，Ir ^{III 三}氢化物钳形复合物 [IrH3(PNP)](8) (PNP = 2,6-双(二异丙基膦甲基)吡啶)在 CO _{2 中的}活性最高以 3,500,000 周转数 (TON) 和 150,000 h ^–1周转频率 (TOF)加氢生成甲酸。另一种 Ru ^II钳形配合物 [RuH(Cl)(CO)(PNP')](9) (PNP' = 2,6-bis(di- tert - butylphosphinomethyl)pyridine) 在 TOF 为 1,100,000 h ^–1 in一种环保的溶剂-水介质。钳形配体的结构赋予催化剂高稳定性，从而导致高活性；值得注意的是，在一些双功能系统中，金属和配体协同工作，从而提高了活性。(10) 然而，高操作温度和压力（≥120 °C 和 40 bar）意味着从放大来看是不希望的能源密集型过程观点。一类突出的 CO ₂氢化均相催化剂是带有质子响应基团的双齿 N,N 配体的半夹心 Ir、Rh 和 Ru 配合物。Ir 版本在碱性水溶液中实现了高活性，温度仅为 50 °C（TON = 153,000，pH 8.4）。该系统还在25 °C 和大气压下将 CO ₂转化为甲酸盐，尽管生产率较低 (32 h ^–1 )。(11) 尽管其中一些系统在水性介质中有效运行，但使用较温和的操作条件（环境温度和压力是理想的），消除碱和酸等添加剂以及可回收催化剂对于实现可持续性很重要。当首先使用醇或胺来转化 CO ₂时，CO ₂到 MeOH 的效率最高为甲酰胺、甲酸烷基酯或氨基甲酸酯，进一步还原得到甲醇。通常，均相催化剂在除导致甲酸盐的过程之外的加氢过程中没有那么高的活性；然而，一些 Ru ^II配合物在胺辅助的 CO ₂甲醇合成(12) 和 CO ₂直接转化为甲醇中表现出活性。 (13) 需要进一步开发催化剂，特别是那些在温和操作条件下表现出高活性并且来源于丰富的资源或从尾矿或电子垃圾中回收的废金属。开发基于地球丰富金属的高效且廉价的催化剂的探索导致了几种催化剂，包括 Fe、Mn、Co 和 Cu，在 CO _{2 中}具有良好的活性加氢生成甲酸、甲醇和甲酰胺。(14,15) 一些催化剂显示出比已知贵金属催化系统更高的活性。 (16) 虽然几种催化系统显示出高活性，但对将高活性催化系统进一步开发到化学过程中的探索较少. 如果主要目标是创建创新的均相催化加氢系统，这可能会导致回收 CO _{2 的}实用方案，则还应致力于工艺设计，例如以下示例：（1）超临界 CO ₂的连续流加氢在单个过程中生产纯甲酸，该过程包含溶剂、产物和催化剂的轻松分离 (17) 和 (2) 由 Ru 钳络合物催化的小型工厂规模的甲酰胺合成。CO ₂加氢为CO、CH ₄、CH ₃ OH、二甲醚、烯烃、芳烃、烃类和高级醇在多相催化领域得到了广泛的研究。许多基于金属、氧化物及其合金的催化剂，如 Cu、Ru、Rh、Pt、Pd、Au、Ir、Co、Fe、Ni、Re 和 In，已被开发用于 CO ₂加氢反应，特别是以更高的活性和选择性为目标。CO ₂转化率受热力学限制，但产品选择性可以通过催化剂设计进行微调，以避免热力学上最稳定的产品甲烷 (18) 和选择的操作条件，如低温和高压，以增加超临界流下的甲醇产率(19)基于 Cu/ZnO/Al ₂ O ₃的经典甲醇合成（来自 CO/H ₂）催化剂也被研究和改进用于将 CO ₂直接加氢为甲醇，同时具有显着的生产率合成甲醇是在高压下实现的，通过增加 H ₂ /CO ₂(20) 结合沸石，可实现将CO ₂转化为二甲醚和其他液体产品的一步集成工艺。多项研究不仅涉及催化剂和工艺技术方面，而且还从理论研究中提供了对反应热力学、机理和动力学的深刻见解。文献很多，但开发有效催化剂以打破 CO ₂加氢反应的热力学障碍仍然非常重要。最后，随着我们继续开发新的催化剂、溶剂、吸附剂、膜和其他材料以利用 CO ₂和可再生或回收的碳作为可持续未来的主要原料，我们预见到将使用这些材料的新工艺和工厂配置的可操作性、安全性、可控性、灵活性、弹性和系统集成方面的新挑战。 (21) 工艺系统工程方法和工具将在平衡各种经济、环境和可持续性目标之间的权衡方面发挥重要作用。具体而言，我们需要了解与 CO ₂源相关的可变性、不确定性和时空分布。选择合适的 CCUS 材料、工艺和技术在很大程度上取决于 CO ₂(22) 需要考虑可再生能源和灵活碳捕获与单个化石发电厂的协同整合。此外，从长远来看，仅仅专注于将 CO ₂转化为化学品在经济上是不可持续的，因为大量可用的 CO ₂可能会很快使化学品市场饱和。更可持续的途径将包括结合 CO ₂使用可再生氢生产液体运输燃料和塑料的替代品。总体而言，通过系统的技术经济和生命周期分析（TEA 和 LCA），有必要采用具有系统视角的整体方法来确定明智决策后的最佳途径。分子、过程和供应链的基于模型和计算机辅助的多尺度设计、模拟和优化将非常有用，所有这些都与实验合成和放大相结合。本文引用了 22 篇其他出版物。