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The coke gasification performance of synthesized Mn−Cr−O catalysts, as well as MnO x , Cr 2 O 3 , and α-Al 2 O 3 , is evaluated in the presence of steam and steam−hydrogen mixtures. Radical coke is deposited in situ onto the catalysts via ethylene pyrolysis at an elevated temperature. Raman spectroscopy analysis reveals that the coke deposited on the various catalysts is similar in nature across all catalysts. Rates of coke gasification are determined from thermogravimetric analysis (TGA) using different gas/vapor feeds including inert/steam and steam/hydrogen mixtures. Addition of hydrogen to a steam feed results in a considerable reduction in reaction rates, suggesting that hydrogen inhibits the production of surface oxygen that is needed for coke gasification. Active Mn 3+ species on the surface of Mn-rich spinel (Mn 1.5 Cr 1.5 O 4 ) and MnO catalysts are hypothesized to be responsible for the significantly higher reaction rates and lower apparent activation barriers for coke gasification under mixed steam−hydrogen conditions.

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A CeO2/α‐Al2O3 bilayer was coated on a high temperature alloy (Incoloy 800H) by sol–gel dip‐coating and was evaluated for its potential as an anticoking barrier and coke oxidation catalyst. The bilayer effectively functioned as a barrier to metal surface catalyzed coking. The film prevented filamentous catalytic coking via blocking surface active metallic sites on the Incoloy substrate. Furthermore, the bilayer reduced the oxidation temperature of pyrolytic coke deposited on the film surface as compared to a bare oxidized Incoloy substrate, mostly owing to the oxidation catalytic activity of the CeO2 layer. Finally, it is demonstrated that the presence of the α‐Al2O3 buffer layer is critically important to the overall performance. Without the α‐Al2O3 layer, a CeO2 layer nearly completely lost both its barrier and oxidation catalytic functions. It is presumed that metallic species migrating from the substrate during high temperature treatments are responsible for the CeO2 deactivation, likely by blocking catalytic sites on the CeO2 surface. © 2018 American Institute of Chemical Engineers AIChE J, 64: 4019–4026, 2018