Modeling of Hydrogen Production from Catalytic Partial Oxidation of Ethanol over a Platinum–Rhodium-Supported Catalyst

Abstract

With the aim of designing an onboard hydrogen production system for automotive applications, this work numerically obtained in-depth knowledge of the catalytic partial oxidation of ethanol (ECPOX). The simulation was developed based on a two-dimensional, non-isothermal, and single-channel monolithic catalyst. By combining a novel microkinetic approach with the classical Langmuir–Hinshelwood method, a surface reaction mechanism for ECPOX over platinum–rhodium coated on an alumina catalyst was formulated. The mechanism consisted of (i) partial oxidation of ethanol, (ii) oxidation of hydrogen, (iii) ethanol steam reforming, (iv) oxidation of carbon monoxide, (v) formation of acetaldehyde, (vi) formation of methane, and (vii) water–gas shift. Essential parameters, such as equilibrium constants for the adsorption process and activation energies, were estimated using transition state theory (TST) and the theory of unity bond index-quadratic exponential potential (UBI-QEP), respectively. The developed mechanism was optimized and validated against experimental data. The model predicted products produced from ECPOX (e.g., H2, CO, CO2, H2O, CH3CHO, and CH4) and the temperature profile inside the monolith channel as a function of the ethanol content and the oxygen-to-ethanol molar ratio. The hot spot position and temperature were accurately calculated by the model. The oxidation of ethanol dominated the first 7 mm of the catalyst, while steam reforming was active over the whole catalyst length. The reverse water–gas shift showed a small effect in the oxidation zone and approached equilibrium in the reforming zone. The model indicated that carbon monoxide adsorbed on the catalyst surface (CO*) was the most abundant reaction intermediate (MARI).