R.L. Vander Wal, M.M. Nkiawete, J.W. Heim II
Penn State University,
United States
Keywords: thermo-catalytic decomposition, hydrogen, natural gas, carbon catalyst
Summary:
Thermo-catalytic decomposition is well-suited for the generation of hydrogen from natural gas. In a decarbonization process for fossil fuel—pre-combustion—solid carbon is produced, with potential commercial uses including energy storage. Metal catalysts have the disadvantages of coking and deactivation, whereas carbon materials as catalysts offer resistance to deactivation and poisoning. Many forms of carbon have been tested with varied characterization techniques providing insights into the catalyzed carbon deposition. The breadth of studies testing carbon materials motivated this review. Thermo-catalytic decomposition (TCD) rates and active duration vary widely across carbons tested. Regeneration remains rarely investigated but does appear necessary in a cyclic TCD–partial oxidation sequence. Presently, studies making fundamental connections between active sites and deposit nanostructures are few. The review begins with the motivating factors for TCD, followed by a description of deposited carbon characterization—for structure via XRD, XPS, Raman and texture. Across studies, differences are observed over time as carbon deposition continues—signaling both differences between the depositing carbon and the original carbon catalyst, but more importantly, an evolution of the depositing carbon structure. This bears implications for longevity of TCD operation and timing for interleaved regeneration processes. Notably, few studies have utilized TEM for analysis of the deposited carbon nanostructure—though it would provide insights into the depositing carbon nanostructure. Results with other natural gas components or mixtures are sorely absent despite being the feedstock for TCD at scale. The article concludes with directions for fundamental studies critical to the mechanistic understanding of TCD and catalyst activity. Thermo-catalytic decomposition (TCD) of methane can produce COX-free hydrogen for PEM fuel cells, oil refineries, ammonia and methanol production. Recent research has focused on enhancing the production of hydrogen by the direct thermo-catalytic decomposition of methane to form elemental carbon and hydrogen as an attractive alternative to the conventional steam reforming process. Hybrid solar-fossil thermochemical processes that make use of an external source of concentrated solar radiation for supplying process heat, offer viable and efficient routes for fossil fuel decarbonization and CO2 sequestration. It prepares the path to the hydrogen economy, as it represents a mid-term transition from fossil fuel to renewable hydrogen energy systems.