Kinetic Synergy between Supported Ir Single Atoms and Nanoparticles during CO Oxidation Light-Off

Abstract

Supported metal single-atom catalysts often exhibit different reactivities than their nanoparticle analogues. Such differences provide unique opportunities in terms of their practical applications. However, single atoms and nanoparticles often coexist under reaction conditions. In this work, we modeled the CO oxidation on a MgAl2O4 supported Ir with different mixtures of single atoms and nanoparticles. We demonstrate the pitfalls in determining reaction parameters for isolated systems if a minority species is present. More importantly, we show a kinetic synergy between single atoms and nanoparticles for CO oxidation light-off and we present optimization strategies to increase the catalyst activity. Specifically, we optimize the ratio of the single atoms and nanoparticles and mass of catalyst to increase activity for established reaction conditions. The optimization results show that the temperature required for 99% conversion can be decreased or a lower metal weight can be used to achieve the same conversion. The results highlight how the different mechanisms and kinetics on single atoms and nanoparticles can be advantageous to optimize the catalyst performance for practical applications, such as their use in catalytic converters.

Synergy Between Supported Metal Single Atoms and Nanoparticles and their Relevance in Catalysis

“…Considering the difficulty of this task, it might be interesting to use physical mixtures of pure metal SAC and pure supported NP catalyst. [19] Although in that case the communication between the species can be degraded since the two species are not on the same support, this approach offer the possibility to mix or not (dual beds of catalysts) the two species.…”

“…[20] [18] (b) Evaluation of the individual reaction steps of cyclohexanol dehydrogenation over Rh SA + NP /C catalysts and the illustration of proposed reaction pathways. [19] from FA, followed by reduction to o-phenylenediamine under the action of Co NP and Co SA . Then, the two intermediate products, o-phenylenediamine and furfural, undergo CÀ N coupling cyclization to rapidly generate 2-substituted benzimidazole on ZnO sites (alkaline local environment).…”

“…Although the approach is interesting, very few studies are still dealing with the use of physical mixtures of catalysts (one containing SAs and the other NPs). [19] When considering the possible synergy between SAs and NPs on the same support, the question of communication between these two species should be taken into account. Some type of synergy does not involved communication, such as synergy in parallel for cascade reactions (Figure 1a).…”

“…In fact, a growing number of articles have appeared in recent years promoting cooperative catalysis between SAs and NPs present on the same support, [18] and structure‐activity relationships are under discussion in literature. Although the approach is interesting, very few studies are still dealing with the use of physical mixtures of catalysts (one containing SAs and the other NPs) [19] …”

Precise Synthesis at the Atomic Scale

“…Some experimental and theoretical results showed that the catalytic performance of SASC was still not satisfactory in some specific reactions. The dynamic phenomena occurring during the catalytic process may lead to the synergy interaction between SASC and nanoparticles. − Thereby, tuning the geometric configuration and electronic structure of the SASC with the coexistence of nanoparticles offers another promising approach to improving their catalytic performance. − It was shown in the case of Ir particles and Ir single atom sites (Ir NP @Ir SA –N–C) for the hydrogen oxidation reaction (HOR) and CO electro-oxidation reaction (COOR) . Yang et al reported a two-step carbonization approach to fabricate a catalyst comprising both Ir particles and Ir single-atom sites, marked as Ir NP @Ir SA –N–C.…”