Low-Temperature CO Oxidation over Rh/Al2O3 in a Stagnation-Flow Reactor

Nawaf Alghamdi, Ribhu Gautam, Jorge Gascon, Dionisios G. Vlachos, Mani Sarathy

Research output: Contribution to journalArticlepeer-review

Abstract

Anthropogenic activities are responsible for nearly half of the total CO emissions in the US. A significant amount of CO is emitted by the transportation sector. Three-way catalytic converters are widely employed to treat CO emissions from gasoline engines; however, current kinetic mechanisms for CO oxidation and the water-gas shift (WGS) reaction on Rh are limited and were built based on data collected over a narrow range of conditions. To fill in this gap, we conducted low-temperature CO oxidation and WGS experiments on 5 wt. % Rh/Al2O3 in a stagnation-flow reactor, which allows for reducing the problem to one dimension and simplifies the development of accurate kinetic models. We characterized the catalyst via N2-physisorption, ICP, XRD, H2-chemisorption, H2-TPR, STEM and EELS. We studied the effects of pressure, temperature, flowrate, and the presence of H2O on the conversion of CO to CO2 and on the WGS reaction over the temperature range relevant to aftertreatment systems. The total operating pressure affected the resolution of the experimental measurements. Higher temperatures resulted in higher CO2 production due to faster kinetics. Investigating the reaction order with respect to O2 showed three distinct kinetic regimes, where the order is positive below the stoichiometric ratio, beyond which a negative order was observed which decreased with increasing O2 content. With respect to CO, the order was positive below the stoichiometric ratio, beyond which the order was negative. When increasing and reducing the O2 content, we observed bistability manifested as a hysteresis behavior, which is attributed to the oxidation (by O2) and reduction (by CO) of the metal. This thorough experimental study aids in developing accurate and versatile CO oxidation on Rh kinetic mechanisms that predict reactivity over a wide range of conditions.
Original languageEnglish (US)
JournalReaction Chemistry & Engineering
DOIs
StatePublished - Oct 12 2022

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