SiO2-supported Fe & FeMn colloids—Fischer-Tropsch synthesis on 3D model catalysts

Mohammadhassan Dad,Remco J Lancee,Matthys Janse Van Vuuren,Jan Van De Loosdrecht,J.W Hans Niemantsverdriet,Hans O.A Fredriksson

doi:10.1016/j.apcata.2017.02.023

Abstract

A well-defined model catalyst constituting a compromise between high surface area, porous, industrial catalysts and a planar model catalyst has been developed. It allows for measurements of catalytic activity in micro reactors, where diffusion problems are kept at a minimum, while characterization both by surface science techniques and by bulk techniques can be applied. Monodisperse, non-porous SiO2 microspheres with diameter 875±25nm have been synthesized, serving as the large area model support. These where then impregnated with pre-formed, monodisperse, colloidal Fe and FeMn nanoparticles resulting in a three-dimensional equivalent of a flat, Fe(-Mn)/SiO2 model catalysts. Characterization with electron microscopy (SEM and TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), before and after catalytic testing was performed. It was shown that the model catalysts can be used in Fischer-Tropsch synthesis experiments under industrially relevant conditions. The FTS experiments reveal that compared to the pure Fe catalyst, FeMn shows more stable activity, higher selectivity towards olefins and lower selectivity toward CH4 and CO2. Significant amounts of hydrocarbons on the catalyst surfaces and some minor indications of sintering were detected after the reaction. Formation of FeCx was detected for the Fe catalyst while no significant amounts could be seen on the Mn-promoted catalyst.

Highlights

A typical heterogeneous catalyst consists of a variety of metal nanoparticles dispersed in the pores of a support particle
It allows for measurements of catalytic activity in micro reactors, where diffusion problems are kept at a minimum, while characterization both by surface science techniques and by bulk techniques can be applied
Our measurements show that our model catalysts can be used to perform catalytic testing of both fast and slow reactions and that the catalysts can be characterized with SEM, TEM, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Attenuated total reflectance infrared spectroscopy (ATR-IR), while still retaining the high definition of a flat model catalyst

Summary

Introduction

A typical heterogeneous catalyst consists of a variety of metal nanoparticles dispersed in the pores of a support particle. Some of the most relevant properties for a catalyst’s activity are the geometry, morphology, structure and chemistry of the metal nanoparticles. Since these are concealed inside the support pores, it is hard to perform an exhaustive characterization of such catalysts. A common method to overcome these difficulties is to study flat model catalysts or single crystals [1]. This allows for in depth characterization by different surface science techniques, under conditions ranging from ultra-high vacuum and liquid nitrogen temperature to more representative high pressure and temperatures.

Results

Discussion

Conclusion