Spatiotemporal behavior of Pt/Rh/CeO2/BaO catalyst during lean–rich cycling

Abstract

The experimental system that utilized an optical fiber and a spatially resolved capillary inlet mass spectrometer to study the dynamic oxygen storage capacity of ceria containing LNT catalyst during periodic lean (oxygen)–rich (propylene) operation. • Combined measurement of intrachannel temperature and concentration. • Detailed insight about the dynamics of a transient exothermic catalytic reaction. • Oxidation and reduction chemistry with ceria plays important role during cycling. • Ceria enables a more efficient oxidation to total oxidation products. • Cycling leads to much higher production of partial oxidation products H 2 and CO. Experiments were conducted to determine the impact of key operating variables (ceria loading, space velocity, cycle time, and rich pulse intensity) on the oxygen storage and release process of a Pt/Rh/CeO 2 /BaO monolithic catalyst during periodic lean (oxygen)–rich (propylene) operation. The concentrations were measured by spatially-resolved capillary inlet mass spectrometry (SpaciMS), and the temperature profile was measured by coherent optical frequency domain reflectometry (c-OFDR), providing detailed insight into the spatio-temporal features of the reaction system. The experiments revealed that the addition of ceria increased the breakthrough time of the propylene during a lean-to-rich transition due to an increased oxidation rate. Hydrogen was formed in the upstream and was consumed in the downstream section of the catalyst by reaction with ceria. Increasing the space velocity increased the upstream hydrogen formation rate and decreased its downstream oxidation rate. Increasing the lean and rich durations (while keeping their duration ratio constant) increased the oxygen uptake but resulted in propylene breakthrough and decreased the solid temperature. Increasing the rich period (at a fixed rich feed and total cycle time) allowed the catalyst to release more oxygen. A comparison of the ceria-containing catalyst to one without ceria revealed a more efficient complete oxidation for the former, while a comparison of the periodic to stationary operation revealed that less than half the propylene was converted to CO 2 by the former.