Abstract
The rhodium (Rh) component in automotive three way catalysts (TWC) experiences severe thermal deactivation during fuel shutoff, an engine mode (e.g., at downhill coasting) used for enhancing fuel economy. In a subsequent switch to a slightly fuel rich condition, in situ catalyst regeneration is accomplished by reduction with H2 generated through steam reforming catalyzed by Rh0 sites. The present work reports the effects of the two processes on the activity and properties of 0.5% Rh/Al2O3 and 0.5% Rh/CexOy-ZrO2 (CZO) as model catalysts for Rh-TWC. A very brief introduction of three way catalysts and system considerations is also given. During simulated fuel shutoff, catalyst deactivation is accelerated with increasing aging temperature from 800 °C to 1050 °C. Rh on a CZO support experiences less deactivation and faster regeneration than Rh on Al2O3. Catalyst characterization techniques including BET surface area, CO chemisorption, TPR, and XPS measurements were applied to examine the roles of metal-support interactions in each catalyst system. For Rh/Al2O3, strong metal-support interactions with the formation of stable rhodium aluminate (Rh(AlO2)y) complex dominates in fuel shutoff, leading to more difficult catalyst regeneration. For Rh/CZO, Rh sites were partially oxidized to Rh2O3 and were relatively easy to be reduced to active Rh0 during regeneration.
Highlights
When the gasoline engine is operated around the stoichiometric air-to-fuel ratio (14.6 wt.%, ±2%), a three way catalyst (TWC) allows simultaneous conversions (~98%) of CO, HCs and NOx to innocuous compounds [1]
Fuel shutoff was simulated by aging fresh catalysts in flowing air at high temprature (800 °C, 950 °C, or 1050 °C) for a short period (5 min), while catalyst regeneration was performed by exposing the aged catalysts to a reducing atmosphere (500 vppm propane, 10% steam, 8% CO2, and N2 balance at 550 °C for 1 h), simulating a slightly rich exhaust composition which is close to normal engine operation
The results indicate that Rh in fresh Rh/Al2O3 was already partially oxidized with a H2 consumption peak at 90 °C
Summary
When the gasoline engine is operated around the stoichiometric air-to-fuel ratio (14.6 wt.%, ±2%), a three way catalyst (TWC) allows simultaneous conversions (~98%) of CO, HCs and NOx to innocuous compounds [1]. Rh-support interactions; and (2) regenerating the deactivated catalyst after fuel shutoff by operating engine at the fuel rich (λ < 1) condition [2,15,36,37,38,39,40,41,42]. The second approach returns the operational mode to slightly fuel rich at ~500 °C, which allows the creation of a reducing engine exhaust atmosphere for partially reversing catalyst deactivation [2,45]. Fuel shutoff was simulated by aging fresh catalysts in flowing air at high temprature (800 °C, 950 °C, or 1050 °C) for a short period (5 min), while catalyst regeneration was performed by exposing the aged catalysts to a reducing atmosphere (500 vppm propane, 10% steam, 8% CO2, and N2 balance at 550 °C for 1 h), simulating a slightly rich exhaust composition which is close to normal engine operation. The paper highlights the maintenance of catalyst performance through cyclic fuel shutoff-fuel rich operation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
