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，催化是许多工业过程的关键，有助于维护全球财富和健康，并在开发环境和经济可持续的过程中发挥关键作用。尽管CO2具有很高的热力学稳定性，但生物系统能够激活分子并将其转化为一系列有机分子，所有这些都是在温和的条件下。很明显，如果我们能够模仿大自然，成功地将二氧化碳转化为燃料或有用的化学中间体，而不需要极端的反应条件，那么好处将是巨大的：造成气候变化的主要气体之一将成为燃料，化学和制药行业的重要原料！在大西洋海底温暖的碱性温泉中形成的硫化铁镍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。厌氧生产乙酸，甲醛，氨基酸和核酸碱基-生命的有机前体分子-被认为是由小立方烷（Fe，Ni）S簇催化的（例如Fe 5 NiS 8），其在结构上类似于当今硫化物矿物的表面，例如硼硅镁石（Fe 3S 4）和镁钠石（FeS），硫化物簇作为催化剂的重要性的当代确认由现代厌氧生命形式所必需的许多蛋白质提供，例如铁氧化还原蛋白、氢化酶、一氧化碳脱氢酶（CODH）或乙酰辅酶A合成酶（ACS），所有这些都保留了立方烷（Fe，Ni）S簇合物，具有类似于灰英石的局部结构，作为电子转移位点或作为代谢挥发物如H2，CO和CO2的活性位点。在该项目的第一阶段，我们使用了计算，合成和电化学专业知识，以模仿自然和生产Fe-S和Ni掺杂的Fe-S纳米颗粒，以催化CO2的转化。通过新的合成路线制备的计算设计材料的仔细和敏感的测试已经明确表明，纳米颗粒具有吸附CO2并将其还原为甲酸的能力-甲酸是一种有用的化学中间体。一个特别有前途的方面是，二氧化碳的催化转化在室温和室温下进行，并且在可以从太阳能获得的低电压下进行，从而使其成为一个可持续的过程。在此成功之后，在项目的第二阶段，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，乙酸酯和最终的二甲醚（DME）-所有经过验证的燃料和精细化学品的前体-并开发足够强大的材料和工艺，以在“真实的”条件下运行。在这一领域的工作，与一些工业合作伙伴合作，需要实验和计算的相互作用，以设计，合成，催化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颗粒的生产和评估。第2阶段结束时的目标是创建一个用于CO2还原的商业上可行的催化系统，该系统在工业相关环境中运行。

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.