Mechanism and kinetics of the thermal decomposition of Fe(C5H5)2 in inert and reductive atmosphere: A synchrotron-assisted investigation in a microreactor

Abstract

The decomposition and reduction of ferrocene, an important precursor for iron CVD and catalyst for nanotube synthesis, was investigated with a versatile and sensitive experimental method. The gas-phase reactive intermediates are detected to understand the underlying chemistry by using a microreactor coupled to a synchrotron light source. Utilizing soft photoionization coupled with photoelectron-photoion coincidence detection enables to characterize elusive intermediates isomer-selectively. We propose a reaction mechanism for the ferrocene decomposition, which proceeds as a two-step process. Initially, the molecule decomposes in a homogeneous surface reaction at temperatures < 900 K, leading to products such as cyclopentadiene and cyclopentadienyl radicals that are immediately released to the gasphase. At higher temperatures, ferrocene rapidly decomposes in the gas-phase, losing two cyclopentadienyl radicals in conjunction with iron. The addition of hydrogen to the reaction mixture reduces the decomposition temperature, and changes the branching ratio of the products. This change is mainly attributed to the H-addition of cyclopentadienyl radicals on the surface, which leads to a release of cyclopentadiene into the gas-phase. On the surface, ligand fragments may also undergo a series of catalytic H-losses leading most probably to a high carbon content in the film. Finally, Arrhenius parameters for both global reactions are presented.