Antonio Emma N, Wicking Christianne, Filip Sorin, Ryan Mary P, Heutz Sandrine
Department of Materials, Imperial College London, SW7 2AZ London, U.K.
London Centre for Nanotechnology, Imperial College London, SW7 2AZ London, U.K.
ACS Appl Mater Interfaces. 2020 Apr 22;12(16):19140-19152. doi: 10.1021/acsami.9b22983. Epub 2020 Apr 7.
Interactions between iron surfaces and hydrocarbons are the basis for a wide range of materials synthesis processes and novel applications, including sensing. However, in diesel engines these interactions can lead to deposit formation that reduces performance, lowers efficiency, and increases emissions. Here, we present a global study to understand deposition at iron-hexadecane interfaces. We use a combination of spectroscopy, microscopy, and mass spectrometry to investigate surface reactions, bulk chemistry, and deposition processes. A dynamic equilibrium between the oxidation products, both at the surface and in solution, determines the deposition at the surface. Considering the solution and the surface in parallel, we find that the iron speciation affects the morphology, composition, and quantity of the deposit at the surface, as well as the oxidation of hexadecane. Fe(II) and Fe(III) both promote the decomposition of peroxides-intermediates in the oxidation of hexadecane-but through noncatalytic and catalytic mechanisms, respectively. In contrast, Fe(0) is proposed to initiate hexadecane autoxidation during its oxidation to Fe(III). We find that in all cases, the surfaces exclusively contain Fe(III) following heat treatment with hexadecane. Upon subsequent exposure at room temperature, Fe(III) species are found to promote oxidation; this finding is particularly concerning for hybrid vehicles where longer time periods are expected between engine operation. Our work provides a foundation for the development of strategies that disrupt the role of iron in the degradation of hexadecane to ultimately reduce oxidation and deposition in diesel engines.
铁表面与碳氢化合物之间的相互作用是广泛的材料合成过程和新型应用（包括传感）的基础。然而，在柴油发动机中，这些相互作用会导致沉积物形成，从而降低性能、降低效率并增加排放。在此，我们开展了一项全面研究，以了解铁 - 十六烷界面处的沉积情况。我们结合使用光谱学、显微镜和质谱技术来研究表面反应、整体化学性质和沉积过程。表面和溶液中的氧化产物之间的动态平衡决定了表面的沉积情况。综合考虑溶液和表面，我们发现铁的形态会影响表面沉积物的形态、组成和数量，以及十六烷的氧化。Fe(II) 和 Fe(III) 都能促进十六烷氧化过程中过氧化物中间体的分解，但分别通过非催化和催化机制。相比之下，有人提出 Fe(0) 在氧化成 Fe(III) 的过程中引发十六烷的自氧化。我们发现，在所有情况下，用十六烷进行热处理后，表面仅含有 Fe(III)。在随后的室温暴露过程中，发现 Fe(III) 物种会促进氧化；这一发现对于预计发动机运行间隔时间更长的混合动力汽车尤其令人担忧。我们的工作为制定策略奠定了基础，这些策略旨在破坏铁在十六烷降解中的作用，从而最终减少柴油发动机中的氧化和沉积。
