Inelastic neutron scattering study on the influence of after-treatments on different technical cokes of varying impurity level and their sp2/sp3 character Original Research Article

Technical cokes from the surfaces of Pd/SiO2 and Pt/Al2O3 catalysts obtained from large scale chemical reactors, waste products, diesel soot and pyrocarbon containing different amounts of inorganic/metallic contaminants or corrosion products were compared utilizing the inelastic incoherent neutron scattering (INS) technique. Different sensitivities of material from high speed coking and low speed coking towards a treatment with hydrogen were observed dependent on the relative amounts of inorganic contaminants throughout the coke. Metallic contaminants are of a pronounced catalytic relevance not only during the deposition of these cokes by means of a chemical vapour deposition process and catalytic transformations of the carbon structure but also in the first interactions between coke and hydrogen in a controlled decomposition process. The internetwork linking between sp2 and sp3 type carbonaceous entities was affected and degraded in after-treatments using hydrogen or air. The sp2 entities themselves remained largely unaffected. However, the formation of new metal–organic structures was observed only after a first hydrogasification step. A species similar to [Fe(H2O)Cl5]2− is an important intermediate in dew point corrosion. As expected, methane-derived pyrocarbon from Pt/Al2O3 catalysts showed a much higher resistance to the influence of hydrogen than soot particles from diesel fuel or various low temperature cokes. INS is useful to improve the understanding of catalyst deactivation under industrial conditions by the formation of coke together with the occurrence and properties of corrosion products.