Pd Model Catalysts: Effects of Aging Environment, Aging Duration and Interrupting Aging with Brief Air Pulses on Lean Pd Redispersion.

Palladium;Redispersion;Catalyst reactivation;Catalyst deactivation;Chemical Engineering;Engineering;Chemical Engineering

Lupescu, Jason AaronGraham, George W ;

University of Michigan

关键词: Palladium;    Redispersion;    Catalyst reactivation;    Catalyst deactivation;    Chemical Engineering;    Engineering;    Chemical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/133379/batjase_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The goals of this investigation were to determine how automotive catalyst characteristics were affected by prolonged exposure to a simulated engine exhaust gas environment, and identify opportunities to limit or reverse catalyst deactivation that correlate with conditions achievable on a vehicle.Model Palladium-based powder catalysts supported on ceria-zirconia (Pd/CZO) and 4wt% La2O3 stabilized γ-Al2O3 (Pd/Al) were selected since these are the primary washcoat components of an automotive catalytic converter.The catalysts were deactivated by constant exposure at 700°C in three different aging environments, oxidizing (lean-only), reducing (rich-only) or a 10 minute cycling of each (redox), for up to three different aging durations, 20 minutes, 2 hours or 16 hours.We determined the aging environment severity ranking of these samples aged for 2 hours or more was as follows: redox > rich-only >> lean-only.The reducing aging environment caused strong metal-support interactions (SMSI) that limited gas-phase access to the Pd surface and dramatically lower catalyst activity, which was much more severe for Pd/CZO catalysts than for Pd/Al catalysts.Dry air treatments applied for 2 hours at 550°C or 700°C showed various degrees of success at reversing SMSI effects, and restoring the fresh-like Pd particle size and catalyst activity depending on the support material, aging duration and dry air temperature.Catalysts with larger average Pd particle size caused by a longer aging duration showed diminishing effects from post-aging dry air treatments, indicating that air should be applied before 20 minutes of aging while the Pd particles were still small.These changes were then made to the redox aging cycle by intermittant replacment of the aging gas with dry air to interrupt the Pd sintering mechanism.Interrupting air pulses on the time scale of a common engine 10 second fuel cut were shown to maintain fresh-like Pd particle size after 16 hours for Pd/Al catalysts, but Pd/CZO catalysts required 10 minute air pulses to achieve the same effect.The insight gained from this work could be used to develop engine control and aftertreatment systems to actively intervene and regenerate a catalyst that is designed to be capable of rapid Pd redispersion.