A Study of Deactivating Carbon Species during Methanation on a Ni/Al2O3 Catalyst

Research output: Book/ReportPh.D. thesis – Annual report year: 2017Research

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This Ph.D. thesis describes the research and ndings from experimental testing of a methanation catalyst and the characterisation of said catalyst. Methanation is the conversion of syngas (CO and H2) typically from coal or biomass to methane and water. Methane is the biggest constituent of natural gas and as the infrastructure is already in place for natural gas, it is an attractive alternative to depleting oil resources. Catalysts based on nickel are the most common choice within industry due to the relatively low price of nickel and its acceptable performance. However, nickel catalysts are prone to deactivate due to sintering and carbon deposition. The latter process is not well understood and thus, this work attempted to further the research in low temperature carbon formation. In order to obtain fundamental knowledge, the experimental setup had to be free of impurities and great care was taken to eliminate potential sources. Experiments designed for that purpose established that the influence of sulfur was negligible. Through a series of experiments of temperature programmed hydrogenation (TPH) - methanation - TPH, the carbon build-up during the methanation was studied by the second TPH. Four types of carbon were identified and especially one was found to be the main cause of deactivation. Through x-ray diffraction (XRD) it was established that part of the carbon dissolved into the nickel particles expanding the crystal structure. No carbon was observed during transmission electron microscopy (TEM). Yet by scanning transmission electron microscopy (STEM) energy dispersive spectroscopy (EDS) carbon was discovered in proximity to the nickel particles. However, this was not as well-defined shells and thus, it was deduced that the particles were not encapsulated by carbon. Instead, the carbon was likely very inhomogeneously
distributed across the nickel surface, which was supported by remaining activity observed during the methanation tests. Preliminary results on the effect of particle size, temperature and total pressure of methanation showed that especially temperature greatly affected the types of carbon deposited.
Original languageEnglish
PublisherDepartment of Physics, Technical University of Denmark
Number of pages132
Publication statusPublished - 2017

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