Transient and Steady-State Light-Off Features during Co-Oxidation of CO and HCS in Doc

Date

2017-12

Authors

Dadi, Karthik Venkata Rama Krishna

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Abstract

We present expressions for the width of the dynamic hysteresis loop as a function of the ramp rate, solid to gas heat capacity ratio, space time and the heat Peclet number, for the limiting cases of pseudo-homogeneous and two phase plug flow models with negligible heat effects. We demonstrate the combined impact of steady-state and dynamic hysteresis. We study the light-off behavior and dynamic hysteresis during the co-oxidation of CO+C₂H₆ mixture on Pt/Al₂O₃.

Ignition and extinction behavior of pure CO, C2H6 and C3H6 and of their mixtures on a Pt/Al2O3 diesel oxidation catalyst is investigated. A single S-shaped bifurcation diagram is obtained during the co-oxidation of all feed mixtures of CO and C3H6 because the activation energies of CO and C3H6 are close to each other. A double-S shaped bifurcation diagram is obtained when hysteresis exists for both CO and C2H6 during the co-oxidation. CO inhibits propylene oxidation. However, it reduces the light-off temperature of ethane by generating the exotherm.

A detailed kinetic model is investigated to study the oxidation and co-oxidation of H2, CO, C3H6 and C2H6 on Pt/Al2O3 monolithic catalyst. The kinetic parameters are obtained using data describing the transient behavior of the catalyst. The model provides insights into the enhanced CO conversion in the presence of H2 and the inverse hysteresis phenomena during co-oxidation of CO and C3H6 on Pt/Al2O3.

A global kinetic model is used to study the light-off behavior of a mixture of CO and HCs (C₂H₄, C₇H₈, C₆H₁₄ & C₂H₆) on Pt, Pd and combined catalysts. There is a considerable difference in the light-off behavior of dual layer and dual brick configurations at high space velocities. The difference in the light-off behavior of dual layer and bimetallic catalyst is almost negligible at practical space velocities.

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Keywords

Light-off, Hysteresis, Washcoat, Oxidation

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