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

拉曼光谱是研究反应条件下催化剂的一种特别强大的技术，尽管样品中的杂质经常会导致荧光淹没散射信号。这可以通过使用另一种激发波长来避免，尽管以牺牲对催化重要物质的灵敏度为代价，这些物质通常受益于可见激发的共振增强。因此，我们建议使用ULTRA@CLF设备（@Harwell）作为皮秒激光源，结合kerr门控光谱仪，进一步开发时间分辨（以几分钟的时间分辨）拉曼散射的应用，以“规避”荧光[1]，从而检查催化烃库物种随时间的意义，用于甲醇转化为碳氢化合物（MTH）的一系列具有不同拓扑结构的沸石样品。生产轻质烯烃和/或芳烃（取决于沸石的拓扑结构），以及快速生物质热解（FBP）蒸汽的催化升级。先前对H-ZSM-5沸石进行的拉曼研究表明，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，存在“取代芳烃”，可能是C6烃产品的原因。然而，最近的研究表明，“多烯机制”可能是轻烃形成的原因。这两种途径的意义一直存在争议，因为不可能在适当的工艺条件下进行拉曼测量，也不可能与进化的催化产物相关联。我们最近对沸石进行了原理验证，时间解决的Kerr-gate拉曼研究，对这种关系产生了前所未有的和良好相关的（与催化活性）见解[3]；见图1。请注意，当没有门控应用时，不可能记录这样的信号，也不可能使用1064nm ft -拉曼仪器。虽然我们最初的研究是成功的，但linkam反应器电池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而不是提供连续的液体输送。因此，该项目的目标是首先开发和调试能够在高达873 K的温度下运行的石英毛细管流反应器和气体输送系统。随后，系统应配置为使用蠕动输送/加热输送管线组合输送468 K以上的汽化液体。待研究的系统将包括用于MTH和更具探索性的FBP的1D - 3D沸石拓扑，如ZSM-5、SSZ-13、SAPO-35、-39，其中初步研究已经显示了通过多烯机制产生酚类化合物的可能途径，并且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庄信万丰技术中心（JMTC）进行。该项目与哈维尔研究中心和STFC的战略非常一致，并且特别及时，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，它还与新的利益相关者（JMTC Billingham, CLF@STFC）合作，这些利益相关者目前没有参与赞助伦敦大学学院化学学院的博士生，他们将为每个学生贡献50%的学费。

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.