Abstract
This work presents multi-scale approaches to investigate 3D printed structured Mn–Na–W/SiO2 catalysts used for the oxidative coupling of methane (OCM) reaction. The performance of the 3D printed catalysts has been compared to their conventional analogues, packed beds of pellets and powder. The physicochemical properties of the 3D printed catalysts were investigated using scanning electron microscopy, nitrogen adsorption and X-ray diffraction (XRD). Performance and durability tests of the 3D printed catalysts were conducted in the laboratory and in a miniplant under real reaction conditions. In addition, synchrotron-based X-ray diffraction computed tomography technique (XRD-CT) was employed to obtain cross sectional maps at three different positions selected within the 3D printed catalyst body during the OCM reaction. The maps revealed the evolution of catalyst active phases and silica support on spatial and temporal scales within the interiors of the 3D printed catalyst under operating conditions. These results were accompanied with SEM-EDS analysis that indicated a homogeneous distribution of the active catalyst particles across the silica support.
Highlights
In the results presented in this work, in the ex situ set-up the gas mixture was fed into the reactor from the top of the tube while the same gas mixture was fed from the bottom of the set-up in the in situ study
9.2 m2 /g, about one order of magnitude lower, still almost an order of magnitude higher than the as-received pressed pellets supplied by Johnson Matthey
This allowed for a better understanding of the structure-activity relationships and of whether the silica support and Mn species exert an effect on the catalyst behavior under operating conditions
Summary
The most widespread method for ethylene production is naphtha steam cracking, which is one of the most energy consuming processes. The oxidative coupling of methane (OCM) has been attracting interest for years as a promising route for the direct conversion of methane to ethylene [3]. In contrast to naphtha steam cracking, OCM offers the potential for simplifying the production process and enabling an important reduction of the environmental impact of manufacturing commercial olefins. The direct conversion of CH4 is challenging due to the high C-H bond strengths and requires high temperature conditions which can be reduced with a careful selection of transition metals as catalysts. Since the 1980s there have been numerous studies on OCM reactions revolving around finding a suitable and stable catalyst composition based on variations of rare-earth oxides or mixed oxides and transition metals
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