New Route to Zero Carbon Hydrogen

为了减少人类对环境的影响，我们需要迅速摆脱使用化石燃料来生产能源和化学品。氢现在正被用作替代能源载体，因为它的使用产生水作为副产品（与使用化石燃料时产生的二氧化碳相反）。因此，挑战在于我们如何获得分子氢（即，H2）以碳中性的方式。氢气生产的传统途径被称为蒸汽重整。该方法传统上使用化石燃料（即，天然气）作为原料，并且是能量密集型工艺，因此导致相当大的二氧化碳排放。水分解（2 H2O = 2 H2 + O2）长期以来一直被视为制氢的替代选择，但仍面临一些挑战，如工艺成本。因此，非常需要开发用于氢气生产的进一步方法。在这个项目中，我们从大自然中汲取灵感，并考虑如何使用大自然的催化剂（酶）来帮助生产零碳氢。为了实现这一点，两个不同的过程必须协调工作：步骤1：通过酶促脱氢将氢从底物转移到辅因子。步骤2：从辅因子释放氢，以便它可以再循环回步骤1。步骤1中的“底物”是一个分子，它将被酶作为质子（H+）和氢化物（H-）去除两个氢原子。然后，氢化物将被转移到辅因子（称为NAD+）以产生NADH，其暂时保持氢化物。为了使系统是循环的，因此能够去除氢化物使得NAD+辅因子再生是至关重要的，并且在这样做的过程中，将产生氢（通过氢化物和质子的重组）。因此，本项目将探索使用催化剂来实现这一特定步骤。非均相催化剂（即，固体催化剂）是优选的。首先，这些材料被相对较好地研究和理解，易于放大。其次，由于许多催化剂是基于使用昂贵的金属（例如，铂、铑、金等），重要的是能够分离和再利用催化剂以降低成本，并且这对于多相/固体催化剂来说更加可行。为了使上述方法为零碳，重要的是仔细选择所谓的底物（其转化为副产物）。将被探索的底物将来自可再生来源（即，天然产生的醇、醛、酸、糖和多元醇等）并且选择副产品以使其本身是增值化学品。换句话说，该项目将同时以零碳的方式生产关键的能源载体H2，同时还为某些化合物提供无化石燃料的路线。

In order to decrease the environmental impact of humanity we need to rapidly move away from the use of fossil fuels both for energy and chemical production. Hydrogen is now being pursued as an alternative energy carrier since its use yields water as a by-product (as opposed to the carbon dioxide produced when a fossil fuel is used). The challenge is therefore how we obtain molecular hydrogen (i.e., H2) in a carbon neutral manner. The conventional route for hydrogen production is known as steam reforming. This process traditionally uses a fossil fuel (i.e., natural gas) as feedstock and is an energy intensive process and so results in considerable carbon dioxide emissions. Water splitting (2H2O = 2H2 + O2) has long been viewed as an alternative option for hydrogen production but still faces some challenges, such as the process cost. It is therefore highly desirable to develop further methods for hydrogen production. In this project, we are taking inspiration from nature and considering how the use of nature's catalysts (enzymes) can assist in the production of zero-carbon hydrogen. In order to achieve this, two distinct processes must work in harmony:Step 1: Hydrogen transfer from substrate to a cofactor by enzymatic dehydrogenation.Step 2: Release of hydrogen from the cofactor so that it can be recycled back into Step 1.The 'substrate' in Step 1 is a molecule which will have two hydrogen atoms removed as a proton (H+) and a hydride (H-) by an enzyme. The hydride will then be transferred to a cofactor (known as NAD+) to yield NADH, which temporarily holds the hydride. In order for the system to be cyclic, it is therefore vital to be able to remove the hydride so that the NAD+ cofactor is regenerated and in doing so, hydrogen will be produced (via the recombination of hydride and proton). This project will therefore look to explore the use of a catalyst for this particular step. A heterogeneous catalyst (i.e., a solid catalyst) is preferred for a number of reasons. Firstly, these materials are relatively well studied and understood, easy for scaling up. Secondly, since many catalysts are based on the use of expensive metals (e.g., platinum, rhodium, gold etc) it is important to be able to separate and reuse the catalyst to decrease cost and this is far more feasible with a heterogeneous/solid catalyst.In order for the process described above to be zero-carbon it is important that the so-called substrate (which is converted into a by-product) is chosen carefully. The substrates that will be explored will be from renewable sources (i.e., naturally produced alcohols, aldehydes, acids, sugars, and polyols, etc.) and chosen such that the by-product is in its own right a value-added chemical. In other words, this project will simultaneously target the production of the key energy carrier H2 in a zero-carbon manner whilst also offering a fossil fuel free route to certain chemical compounds.