Functional bionanomaterials and novel processing for targeted catalytic applications

商业催化剂通常基于金属纳米颗粒，由于其表面原子的比例高于埋藏原子，因此具有不同寻常的高活性性质。催化反应发生在表面上或表面下，借助于晶体表面的缺陷和扭结。扭结的精确结构有助于催化剂和底物之间的分子识别，并有助于在其镜像“双胞胎”上形成特定形式的产物分子（称为对映体）。工业需要对映体的选择性，也需要更好的制造C-C键的方法；使用一种基于细菌的新型纳米颗粒，这两种方法都将成为可能。用化学方法制造纳米粒子是很困难的，因为它们想要聚集。当这种情况发生时，特殊属性就会丢失。通常需要“辅助”化学物质（“钝化配体”）。细菌可以克服这种需要。他们可以利用酶制造纳米颗粒，也可以通过提供自己的钝化剂来支持纳米颗粒。催化生物纳米粒子可以用作催化剂，方法是将金属化的细菌作为悬浮的小（~2微米）体（它们可以使用磁铁回收），或者首先将它们作为生物膜生长在（例如）珠子或单体上，然后将其金属化以形成催化纳米涂层。生物纳米晶体的表面结构尚不清楚，但它们是极好的催化剂。通过我们的工业合作伙伴的新工艺，我们希望制造一种全新的材料（超级生物催化剂）。我们将在4个有强烈工业需求的重要反应中测试这些，例如(a)对映体选择和(b)通常需要高温高压的反应。(a)通常使用贵金属催化剂和(b)使用基于铁的催化剂；在纳米世界中，这两种方法通常可以互换使用（或一起使用），因为涉及到相同的原子尺度过程。这种影响可以在磁性（以及催化）特性（一种非常有用的诊断探针）中看到，而另一方面是通过纳米晶体和实验者之间的电化学“对话”来揭示的。当细菌产生“双金属”（结合两种金属）时，这些变得更加有趣；这些通常具有大大增强的特性。我们将研究生物双金属的催化作用，以及作为燃料电池的催化剂来制造清洁能源。含铁催化剂的反应是特殊的。它们取决于所用铁的确切类型（矿物相）；细菌可以制造特定的矿物相。催化反应使用活化形式的氢，通常只发生在高温下；小颗粒的氧化铁被活性氢部分还原成一些铁金属（催化剂，通过磁检测）。商业上，氢是由“裂解”天然气制成的，但这种氢含有微量的催化剂毒物。生物制造的氢是无毒的，使用Bio-H也有助于延长催化剂的寿命。我们将制造新的、坚固的、优越的催化材料，但更重要的是，我们还将把新的晶体和纳米结构与改进的功能联系起来，应用全方位的固态分析方法来补充磁性和电化学方法。通过了解纳米世界中关键的分子过程，我们也可以为其他商业应用设计更好的催化剂。

Commercial catalysts are often based on metallic nanoparticles which have unusual and highly reactive properties due to their high proportion of surface atoms as compared to buried ones. Catalytic reactions occur at or just below surfaces and are helped by the crystal surface having defect sites and kinks. The exact architecture of the kinks can help in molecular recognition between the catalyst and its substrate, and help to make a particular form of the product molecule (called an enantiomer) over its mirror image 'twin'. Industry needs enantiomeric selectivity, and also better ways to make C-C bonds; both would become possible using a new type of nanoparticle based on bacteria. It is difficult to make nanoparticles chemically as they want to aggregate. When this happens the special properties are lost. Usually 'helper' chemicals ('passivant ligands') are needed. Bacteria can overcome this need. They can biomanufacture nanoparticles using enzymes and also support the nanoparticles by providing their own passivants. The catalytic bionanoparticles can be employed as catalysts by using the metallised bacteria as small (~2 microns) bodies in suspension (they can be recovered using a magnet), or by growing them first as a biofilm on (e.g) beads or monoliths and then metallising to form a catalytic nano-coating. Nothing is known yet about the surface structures of the bionanocrystals but they are excellent catalysts. Using novel processing by our industrial partner, we hope to make a completely new class of materials(superbionanocatalysts). We will test these in 4 important reactions where there are strong industrial needs, e.g. (a) enantiomeric selections and (b) a reaction which normally require high temperature and pressures. (a) Usually uses precious metal catalysts and (b) uses a catalyst based on iron; in the nanoworld these can often be used interchangeably (or together) because the same atomic-scale processes are involved. Effects of this are seen in magnetic (as well as catalytic) properties (a very useful diagnostic probe), while another facet is unravelled via an electrochemical 'dialogue' between the nanocrystal and the experimenter. These become even more interesting when the bacteria make 'bimetallics' (combining 2 metals); these often have greatly enhanced properties. We will look at bio-bimetallics for catalysis and also as fuel cell catalysts to make clean energy. Reactions involving Fe catalysts are special. They depend on the exact type of Fe used (the mineral phase); bacteria can make specific mineral phases to order. The catalytic reaction uses an activated form of hydrogen which normally only happens at high temperatures; small particles of ferric oxide are partially reduced by the active H to give some Fe metal (the catalyst; detected magnetically). Commercially, H is made from 'cracking' natural gas but this H contains traces of catalyst poisons. Biologically-made H is poison-free and the use of Bio-H will also help to extend catalyst life. We will make new, robust, superior, catalytic materials but, importantly, we will also relate the new crystal and nano structures to improved functions, applying a full range of solid state analytical methods to complement the magnetic and electrochemical ones. By understanding pivotal molecular processes in the nanoworld we can then design better catalysts for other commercial applications too.