Development of real-time Kerr-gated Raman Spectroscopy for the interrogation of the role of hydrocarbon pool species in catalytic reaction mechanisms

拉曼光谱法是一种特别强大的技术，用于研究反应条件下的催化剂，但通常会受到样品中杂质的影响，导致荧光淹没散射信号。这可以通过使用替代的激发波长来规避，尽管是以对催化重要物质的敏感性为代价的，催化重要物质通常受益于与可见光激发的共振增强。因此，我们建议进一步发展时间分辨的应用，（时间分辨率为几分钟）使用ULTRA@CLF设备的拉曼散射（@Harwell）作为皮秒激光源与克尔门光谱仪结合以“规避”荧光[1]，因此，为了检查用于催化剂的具有各种拓扑结构的一系列沸石样品的催化烃库物质随时间的重要性，甲醇转化为烃（MTH，根据沸石拓扑结构产生轻质烯烃和/或芳族化合物）和用于来自快速生物质热解（FBP）的蒸气的催化升级。先前在MTH反应（最近商业化的替代燃料/散装化学品生产技术）之后对H-ZSM-5沸石进行的拉曼研究已经证明了“取代的芳族化合物”的存在，其可能是C6烃产物的原因。然而，最近的研究表明，“多烯机制”可能是轻烃形成的原因。[2]这两种途径的重要性一直处于争论之中，这仅仅是因为不可能在适当的工艺条件下进行拉曼测量并与形成的催化产物相关联。我们最近对经历MTH的沸石进行了这种原理证明、时间分辨的克尔门拉曼研究，对这种关系产生了前所未有的且良好相关（与催化活性）的见解[3];见图1。请注意，当不应用门控时，不可能记录这样的信号，1064 nm FT-拉曼仪器也不可能记录这样的信号。虽然我们最初的研究是成功的，但所使用的linkam反应器单元存在死体积问题和样品长度上的梯度。此外，液体输送系统倾向于脉冲输送而不是提供液体的连续输送。因此，该项目的目标将是首先开发和调试一个石英毛细管流反应器和气体输送系统，能够在高达873 K的温度下运行。随后，系统应配置为使用蠕动输送/加热输送管线的组合输送高于468 K的汽化液体。待研究的体系将包括1D - 3D沸石拓扑结构，如ZSM-5、SSZ-13、SAPO-35、-39，用于MTH和更探索性的FBP，初步研究表明，通过多烯机制可以获得酚类化合物，更好地了解这一点将有助于进一步优化这种可持续技术[4]离线测试将在研究中心和约翰逊万丰技术中心（JMTC）进行。该项目与哈威尔研究中心和STFC的战略保持一致，特别及时，因为它建立在一些非常探索性但非常成功的初步研究基础上。此外，它与新的利益相关者（JMTC比灵厄姆，CLF@STFC）谁目前没有参与赞助博士生@ UCL化学-他们将贡献50%的学生奖学金的成本。

Raman spectroscopy is a particularly powerful technique for studying catalysts under reaction conditions although can often be compromised by impurities in the sample leading to fluorescence swamping the scattered signal. This can be circumvented by using an alternative excitation wavelength although at the expense of sensitivity to the catalytically important species which often benefit from resonance enhancement with visible excitation. We propose therefore to develop further the application of time-resolved (with time resolution in the order of a few minutes) Raman scattering using the ULTRA@CLF facility (@Harwell) as a picosecond laser source in combination with a Kerr-Gated spectrometer to 'circumvent' fluorescence [1], so to examine the significance of the catalytic hydrocarbon pool species with time for a series of zeolite samples with various topologies used for the conversion of methanol-to-hydrocarbons (MTH, producing light olefins and/or aromatics depending on zeolite topology) and for catalytic upgrading of vapors from fast biomass pyrolysis (FBP). Previous Raman studies performed on H-ZSM-5 zeolites after the MTH reaction (a recently commercialised alternative fuel/bulk chemical production technology), have demonstrated the presence of 'substituted aromatics', likely responsible for C6 hydrocarbon products. However, recent research has suggested that a 'polyene mechanism' maybe responsible for light hydrocarbon formation. [2] The significance of these two pathways has been under debate simply because it has not been possible to perform the Raman measurements under proper process conditions and to correlate with the evolving catalytic products. We recently performed such proof-of-principle, time resolved Kerr-gate Raman studies on zeolites undergoing MTH which yielded unprecedented and well correlated (with catalytic activity) insight into this relationship [3]; see Fig. 1. Note that when no gating is applied it is not possible to record such signals nor is it with 1064 nm FT-Raman instrument.Although our initial studies were successful, the linkam reactor cell used suffers from dead volume problems and gradients across the sample length. In addition, the liquid delivery system tended to pulse rather than provide a continuous delivery of liquid. The project aims will therefore be in the first instance to develop and commission a quartz capillary flow reactor and gas delivery system capable of operating at temperatures up to 873 K. Subsequently the system should be configured to deliver vapourised liquids above 468 K using a combination of peristaltic delivery/heated transfer lines. Systems to be studied would include both 1D - 3D zeolite topologies such as ZSM-5, SSZ-13, SAPO-35, -39 both for MTH and the more exploratory FBP, where initial studies have shown a possible route to phenolic compounds via a polyene mechanism and where a better understanding of this will help in further optimising this sustainable technology [4].Offline tests will be performed at the Research Complex and Johnson Matthey Technology Centres (JMTC). The project is well aligned with the strategies of the Research Complex at Harwell and the STFC and is particularly timely as it builds on some very exploratory but highly successful initial studies. Furthermore, it engages with new stakeholders (JMTC Billingham, CLF@STFC) whom are not currently involved in the sponsorship of PhD students @ UCL Chemistry - they will contribute 50 % each to the cost of the studentship.