Enhanced Coke Gasification Activity of the Mn_1.5Cr_1.5O₄ Spinel Catalyst during Coking in Ethylene–Steam Mixtures

Abstract

Mn–Cr–O spinel catalysts (MnCr2O4 and Mn1.5Cr1.5O4) and single oxides of Mn and Cr are coked under ethylene and ethylene–steam mixtures to simulate reaction conditions occurring in steam cracker furnaces. The coking rates are measured using thermogravimetric analysis, and the Mn1.5Cr1.5O4 catalyst displayed considerably less coke deposition (an order of magnitude) under ethylene–steam flow. Analysis of the outlet gas flow suggests the Mn1.5Cr1.5O4 catalyst gasified the radically formed coke into carbon oxides without significantly affecting ethylene conversion. The anticoking performance of the Mn1.5Cr1.5O4 catalyst is attributed to the presence of Mn3+ species in the spinel phase structure that are active for coke gasification in the presence of steam. No significant changes in structure or performance are observed for the Mn1.5Cr1.5O4 catalyst across several coking and decoking cycles. The Mn–Cr–O spinel oxide with higher Mn content is suggested to have desirable activity and stability to limit coke deposition during steam cracking.