Bio-inspired sulfide nanocatalysts: From proof of concept to 'real' catalysis

可持续能源和气候变化是全球社会关注的领域，这是RCUK通过其能源计划(由EPSRC管理)公认的战略优先领域。此外，催化是大量工业过程的关键，这些过程有助于维持全球财富和健康，并在开发环境和经济可持续的过程中发挥关键作用。尽管二氧化碳具有高度的热力学稳定性，但生物系统能够激活分子并将其转化为一系列有机分子，所有这些都是在适度的条件下进行的。显然，如果我们能够模仿大自然，在不需要极端反应条件的情况下，成功地将二氧化碳转化为燃料或有用的化学中间体，好处将是巨大的：导致气候变化的主要气体之一将成为燃料、化工和制药行业的重要原料！在太古代洋底温暖的碱性泉水中形成的铁镍硫化物薄膜越来越被认为是导致生命出现的一系列化学反应的早期催化剂。醋酸盐、甲醛、氨基酸和核酸碱基--生命的有机前体分子--的厌氧生产被认为是由小立方烷(Fe，Ni)S簇合物(例如Fe5NiS8)催化的，这些簇合物在结构上与当今硫化物矿物如闪锌矿(Fe3S4)和麦基纳维石(FeS)的表面相似。现代证实硫化物簇合物作为催化剂的重要性是由许多现代厌氧生命形式所必需的蛋白质提供的，如铁氧还蛋白、氢酶、一氧化碳脱氢酶或乙酰辅酶A合成酶(ACs)，所有这些蛋白质都保留了Cubane(Fe，A)合成酶在本项目的第一阶段，我们综合运用计算、合成和电化学的专业知识，模拟自然界，制备了Fe-S和Ni掺杂的Fe-S纳米粒子，用于催化二氧化碳的转化。对通过新的合成路线制备的计算机设计的材料进行的仔细和灵敏的测试明确表明，纳米颗粒具有吸附二氧化碳并将其还原为甲酸的能力--一种有用的化学中间体。一个特别有希望的方面是，二氧化碳的催化转化是在常压和温度下进行的，而且是在可以从太阳能获得的低电压下进行的，因此使其成为一个可持续的过程。在取得这一成功之后，在该项目的第二阶段，我们的目标是优化催化剂，以提高产量并适应进一步的产品形成，例如甲醇、乙酸酯，最终是二甲醚(DME)--所有这些都是燃料和精细化学品的已被证明的前体--并开发足够坚固的材料和工艺，以在“真实”条件下运行。这一领域的工作与一些工业伙伴合作，需要实验和计算的鸽尾相互作用，以设计、合成、表征和催化测试潜在的过渡金属-硫化物纳米催化剂，然后在工业环境中扩大纳米粒子的生产和评价。第二阶段结束时的目标是创建一个商业上可行的二氧化碳减排催化系统，该系统在工业相关的环境中运行。

Sustainable energy and climate change are areas of global societal concern, which is a recognised strategic priority area of the RCUK through their Energy Programme, managed by EPSRC. Catalysis, moreover, is the lynchpin of a large number of industrial processes, which are instrumental in maintaining global wealth and health, as well as playing a key role in developing processes that are both environmentally and economically sustainable.Despite the high thermodynamic stability of CO2, biological systems are capable of both activating the molecule and converting it into a range of organic molecules, all of which under moderate conditions. It is clear that, if we were able to emulate Nature and successfully convert CO2 into fuel or useful chemical intermediates without the need for extreme reaction conditions, the benefits would be enormous: One of the major gases responsible for climate change would become an important feedstock for the fuel, chemical and pharmaceutical industries!Iron-nickel sulfide membranes formed in the warm, alkaline springs on the Archaean ocean floor are increasingly considered to be the early catalysts for a series of chemical reactions leading to the emergence of life. The anaerobic production of acetate, formaldehyde, amino acids and the nucleic acid bases - the organic precursor molecules of life - are thought to have been catalyzed by small cubane (Fe,Ni)S clusters (for example Fe5NiS8), which are structurally similar to the surfaces of present day sulfide minerals such as greigite (Fe3S4) and mackinawite (FeS).Contemporary confirmation of the importance of sulfide clusters as catalysts is provided by a number of proteins essential to modern anaerobic life forms, such as ferredoxins, hydrogenases, carbon monoxide dehydrogenase (CODH) or acetylcoenzyme A synthetase (ACS), all of which retain cubane (Fe,Ni)S clusters with a greigite-like local structure, either as electron transfer sites or as active sites to metabolise volatiles such as H2, CO and CO2.In Phase 1 of the project, we have used a comprehensive combination of computational, synthetic and electrochemical expertise to mimic Nature and produce Fe-S and Ni-doped Fe-S nanoparticles to catalyse the conversion of CO2. Careful and sensitive testing of the computationally designed materials, prepared through novel synthesis routes, has shown unequivocably that the nanoparticles have the power to adsorb CO2 and reduce it to formic acid - a useful chemical intermediate. A particularly promising aspect is that the catalytic conversion of CO2 takes place at room pressure and temperature and at the sort of low voltages that could be obtained from solar energy, thus making it a sustainable process. Following this success, in Phase 2 of the project we aim to optimise the catalysts to improve yield and adapt for further product formation e.g. methanol, acetate and, eventually, dimethyl ether (DME) - all proven pre-cursors to fuels and fine chemicals - and to develop materials and processes that are robust enough to perform under 'real' conditions. Work in this area, in collaboration with a number of industrial partners, requires the dove-tailed interplay of experiment and computation to design, synthesise, characterise and catalytically test the potential transition metal-sulfide nano-catalysts, followed by scale-up of the nanoparticle production and evalulation in an industrial environment. The aim at the end of Phase 2 is to have created a commercially viable catalytic system for CO2 reduction, that performs in an industrially relevant environment.