Facet‐Dependent Oxidative Strong Metal‐Support Interactions of Palladium–TiO₂ Determined by In Situ Transmission Electron Microscopy

Abstract

The strong metal-support interaction (SMSI) is widely used in supported metal catalysts and extensive studies have been performed to understand it. Although considerable progress has been achieved, the surface structure of the support, as an important influencing factor,isusually ignored. We report af acet-dependent SMSI of Pd-TiO 2 in oxygen by using in situ atmospheric pressure TEM. Pd NPs supported on TiO 2 ( 101) and (100) surfaces showed encapsulation. In contrast, no such cover layer was observed in Pd-TiO 2 (001) catalyst under the same conditions.This facet-dependent SMSI, which originates from the variable surface structure of the support, was demonstrated in ap robe reaction of methane combustion catalyzedb yP d-TiO 2 .O ur discovery of the oxidative facet-dependent SMSI gives direct evidence of the important role of the support surface structure in SMSI and provides anew way to tune the interaction between metal NPs and the support as well as catalytic activity.

Dynamic interplay between metal nanoparticles and oxide support under redox conditions

“…The system thus equilibrated by reverting to an oxygen-induced SMSI state, which was formed in this case directly, without prior initialization through the wellknown high-temperature reduction route. This nonclassical, oxygen-induced SMSI state was recently observed by Tang et al (20).…”

“…This work provides an explanation for the observed particle restructuring and directed particle migration on the support. Furthermore, it provides additional evidence for a nonclassical SMSI state that is observed in oxidizing conditions ( 17 , 20 , 48 ).…”

“…Similar encapsulation effects have also been reported for Co ( 12 ), Ni ( 13 , 14 ), Au ( 15 ), and Cu ( 16 ) NPs. More recently, it was shown that high-temperature oxidative treatment can also lead to NP encapsulation ( 15 , 17 – 20 ). Potential benefits of SMSI encapsulation include enhanced resistivity against both NP coalescence and Ostwald ripening ( 21 – 23 ).…”

Stable Cu Catalysts Supported by Two‐dimensional SiO2 with Strong Metal–Support Interaction

“…[ 36 ] Classical SMSI refers to the physical coverage/encapsulation of metal nanoparticles with oxide overlayers to prevent the migration. [ 37 , 38 , 39 , 40 , 41 ] To aid the encapsulation by SiO 2 , previous arts regarding the synthesis of stable Cu/SiO 2 catalysts with SMSI required evaporation of the corrosive ammonia, careful regulation of pH, and surfactants. [ 36 , 42 , 43 ] Moreover, most of these Cu catalysts were tested at mild temperatures below 350 ℃, so their stability for those reactions performed at high temperature and high conversion is still a mystery.…”

The Significant Role of the Atomic Surface Structure of Support in Strong Metal‐Support Interaction

“…[9] Extensive coverage of the NPs is detrimental for the catalytic performance due to blockage of active sites. [11] However, these formed suboxides can change the local electronic structure of the metal surface promoting the activation of reactants and, importantly, improving the catalytic performance. [12] Furthermore, the suboxides covering the NPs with a few atomic layers may possess dynamic structures under different gas atmospheres.…”