New Route to Zero Carbon Hydrogen

为了减少人类对环境的影响，我们需要迅速摆脱将化石燃料用于能源和化学生产。氢现在被用作一种替代能源载体，因为它的使用会产生水作为副产品(而不是使用化石燃料时产生的二氧化碳)。因此，挑战是我们如何以碳中性的方式获得分子氢(即H2)。传统的制氢方法被称为水蒸气重整。这一过程传统上使用化石燃料(即天然气)作为原料，是一个能源密集型过程，因此会产生相当大的二氧化碳排放量。长期以来，水裂解(2H2O=2H2+O2)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，开发更多的制氢方法是非常可取的。在这个项目中，我们从自然中获得灵感，并考虑如何使用自然的催化剂(酶)来帮助生产零碳氢气。为了实现这一点，两个不同的过程必须协调工作：步骤1：通过酶脱氢将氢从底物转移到辅因子。步骤2：从辅因子中释放氢，使其可以循环回到步骤1。步骤1中的底物是一个分子，它将有两个氢原子被酶去除，作为质子(H+)和氢化物(H-)。然后氢化物将被转移到辅因子(称为NAD+)以产生NADH，NADH暂时保持氢化物。因此，为了使体系具有循环性，必须能够去除氢化物，以便再生NAD+辅因子，并在这样做的过程中(通过氢化物和质子的复合)产生氢气。因此，该项目将探索在这一特定步骤中使用催化剂。出于许多原因，多相催化剂(即固体催化剂)是首选的。首先，这些材料比较容易研究和理解，易于放大。其次，由于许多催化剂都是以贵金属(如铂、铑、金等)的使用为基础的，因此能够分离和重复使用催化剂以降低成本是很重要的，对于多相/固体催化剂来说这是更可行的。为了使上述过程是零碳的，重要的是仔细选择所谓的底物(被转化为副产品)。将探索的底物将来自可再生来源(即自然产生的醇、醛、酸、糖和多元醇等)。并进行选择，使副产品本身就是一种增值化学品。换句话说，该项目将同时以零碳方式生产关键能源载体H2，同时还提供一条不含化石燃料的路线来生产某些化合物。

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.