The Effective-Double-Layer as an Efficient Tool for the Design of Sinter-Resistant Catalysts

Activity and Thermal Aging Stability of La1−xSrxMnO3 (x = 0.0, 0.3, 0.5, 0.7) and Ir/La1−xSrxMnO3 Catalysts for CO Oxidation with Excess O2

“…This sufficient stabilization against oxidative thermal sintering of Ir NPs at temperatures as high as 750 °C is an important result for practical applications, considering that iridium in its oxidation state (IrO 2 ) is one of the most sensitive elements of the noble metal series, with a high aggregation propensity even at temperatures as low as ~450 °C [ 37 , 59 , 60 ], and the fact that such high temperatures are commonly reached in practice, e.g., in automotive emissions control systems [ 2 , 7 , 23 , 46 ] and methane-reforming processes [ 3 , 27 , 28 , 34 , 35 ]. These results indicate the operation of antisintering mechanisms protecting the catalysts’ nanostructure and the sensitive IrO 2 nanoparticles, most likely on the basis of the model recently demonstrated in a series of studies [ 28 , 37 , 38 , 40 , 41 ] evidencing that the high OSC values of the catalysts’ supports can sufficiently induce such stabilization phenomena; the LSMx perovskites studied herein indeed have high OSC values ( Table 1 ).…”

“…It is noteworthy that the aged Ir/LSM00, Ir/LSM30 and Ir/LSM50 catalysts show a slightly better CO oxidation light-off behavior than their fresh counterparts. This is likely due to some slight redispersion of the Ir nanocrystallites during the oxidative thermal aging, as we recently observed to occur when the particles are dispersed in carriers that have a high population of surface oxygen vacancies and explained consistently via a model we developed [ 40 , 41 ]. According to this model, surface oxygen vacancies on catalyst supports can act as traps for atomic species detached from metal nanoparticles, eliminating their attachment from larger nanoparticles, leading to particles’ agglomeration via the Ostwald ripening (OR) mechanism.…”

“…The stability of performance of the Ir/LSMx catalysts on CO oxidation reaction, after their exposure to two consecutive oxidative thermal aging stages, was investigated, with the aim of determining whether the perovskites characterized by high values of oxygen storage capacity (OSC) and O 2− mobility are able, as supports, to stabilize the catalytic behavior of the Ir nanoparticles that are prone to agglomerating, as it was recently found to be the case with high OSCs CeO 2 -based supports [ 28 , 35 , 37 , 38 , 40 , 41 ].…”

“…After purging the line by He flow for 10 min, the TPR experiment was conducted using a 15 mL/min flow of 1% H 2 /He and a heating rate of 10 °C/min up to ~750 °C. The H 2 -TPR profiles showing the reducibility characteristics of the materials and the total area of the H 2 consumption peaks versus time were then used to determine the oxygen storage capacity (OSC) of the materials [ 27 , 28 , 37 , 41 ].…”

“…However, the main inhibiting factor for Ir use as a catalyst in such practical applications is its high aggregation propensity under oxidizing environments and elevated temperatures [ 28 , 35 , 37 , 38 ]. Nevertheless, we have recently reported an efficient method to stabilize Ir nanoparticles, which is based on the use of supports with a high lattice oxygen storage capacity (OSC) and O 2− ion mobility values [ 40 , 41 ]. Perovskites as catalytic supports that possess these characteristics are potential candidate materials that could impart resistance properties to the sintering of noble or other metal nanoparticles dispersed on their surface.…”