Methane oxidation over oxide-supported Pd nanoparticles observed in-situ by ambient-pressure XPS

对工作条件下多相催化的基本微观理解是催化剂设计和化学过程控制进一步发展的关键。多相催化发生在催化剂表面；因此，我们需要有关所研究表面的化学成分和分子排列的有意义的实验数据。一般来说，基于电子的光电子能谱（如x射线光电子能谱（XPS））最能提供表面特异性信息。使电子成为理想表面探针的特性是它们在固体物质中只有几个原子层的穿透深度很短。然而，当这些系统要在毫巴或更高的实际压力环境下进行研究时，这就提出了一个大问题。电子的平均自由程只有几毫米或更少，传统的电子能量分析仪不能再使用了。通常在高反应物压力下甚至在溶液中发生的传统电子能谱和实际催化反应之间的所谓“压力间隙”在某种程度上通过“近环境压力电子分析仪”来弥补。这种仪器最近才在同步辐射设施，如美国伯克利的先进光源（ALS）中可用。申请人正在寻求资助前往伯克利ALS，在反应条件下对氧化负载的Pd纳米颗粒催化剂进行近环境压力光发射实验，用于甲烷的部分氧化。这个反应产生合成气，一种一氧化碳和氢气的混合物，用作一系列有用的散装化学品的基础。计划中的实验的意义在于，它们涉及的是真正的工业催化剂，而不是模型催化剂。因此，研究结果可以更直接地用于化工厂的改进。

A fundamental microscopic understanding of heterogeneous catalysis under working conditions is key to further developments in catalyst design and control of chemical processes. Heterogeneous catalysis happens at the catalyst surface; we therefore need meaningful experimental data about the chemical composition and molecular arrangement at the surfaces under investigation. In general, surface-specific information is best provided by electron-based photoemission spectroscopy such as X-ray photoelectron spectroscopy (XPS). The property that makes electrons ideal surface probes is their short penetration depth of only a few atomic layers in solid matter. This poses, however, a big problem when these systems are to be studied under realistic pressure environments in the range of millibar or higher. The mean free path of electrons is then only a few millimetres or less and conventional electron energy analysers cannot be used anymore.This so-called "pressure gap" between conventional electron spectroscopy and actual catalytic reactions, which usually take place at high reactant pressures or even in solution, is bridged to some extent by "near-ambient pressure electron analysers". Such instruments have become available very recently at synchrotron radiation facilities, such as the Advanced Light Source (ALS) in Berkeley, USA.The applicant is seeking funding for travelling to ALS in Berkeley in order to perform near-ambient pressure photoemission experiments on oxide-supported Pd nanoparticle catalysts for partial oxidation of methane under reaction conditions. This reaction produces syn-gas, a mixture of carbon monoxide and hydrogen which is used as basis for a whole range of useful bulk chemicals. The significance of the planned experiments is that they involve real industrial catalysts as opposed to model catalysts. Therefore the results can be fed into improvement of chemical plants much more directly.