Functional bionanomaterials and novel processing for targeted catalytic applications

商用催化剂通常基于金属纳米粒子，由于其表面原子的比例比埋入的原子高，因此具有不寻常的高活性。催化反应发生在表面或恰好在表面之下，并受到具有缺陷位置和扭结的晶体表面的帮助。这种扭结的精确结构有助于催化剂和其底物之间的分子识别，并有助于在其镜像的双胞胎上生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C-C键形成方法；使用一种新型的基于细菌的纳米颗粒，这两种方法都将成为可能。很难用化学方法制造纳米颗粒，因为它们想要聚集在一起。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求。他们可以使用酶来生物制造纳米颗粒，也可以通过提供自己的钝化剂来支持纳米颗粒。催化生物纳米颗粒可以用作催化剂，方法是将金属化的细菌作为悬浮的小(~2微米)物体(它们可以用磁铁回收)，或者首先将它们作为生物膜生长在(例如)珠子或整体上，然后金属化以形成催化纳米涂层。目前还不知道这些生物纳米晶体的表面结构，但它们是很好的催化剂。使用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类别(超生物催化材料)。我们将在有强烈工业需求的4个重要反应中测试这些反应，例如(A)对映体选择和(B)通常需要高温和压力的反应。(A)通常使用贵金属催化剂；(B)使用以铁为基础的催化剂；在纳米世界中，这些催化剂通常可以互换使用(或一起使用)，因为涉及相同的原子尺度过程。这一点的影响可以在磁性(以及催化)特性(一个非常有用的诊断探针)中看到，而另一个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，这些就变得更加有趣；这些往往具有极大的增强性质。我们将研究用于催化的生物双金属材料，以及用于制造清洁能源的燃料电池催化剂。涉及铁催化剂的反应是特殊的。它们取决于所使用的铁的确切类型(矿物相)；细菌可以按顺序制造特定的矿物相。催化反应使用活化形式的氢，这通常只在高温下发生；小颗粒的三氧化二铁被活性H部分还原，得到一些金属铁(催化剂；通过磁性检测)。在商业上，氢气是由“裂解”天然气制成的，但这种氢气含有微量的催化剂毒物。生物制造的H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、优质的催化材料，但重要的是，我们还将把新的晶体和纳米结构与改进的功能联系起来，应用全面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的关键分子过程，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.