Strong Metal–Support Interaction in Heterogeneous Catalysts

Abstract

too strong of a metal-support interaction would trigger Ostwald ripening, whereas too weak of that would lead to particle migration and coalescence. Therefore, the metal-support binding energy serves as a descriptor to predict the growth rates of supported NPs in this case. [14] Strong metal-support interaction (SMSI) is a special form of interaction that is typically observed between metal NPs and reducible supports. [15][16][17] In 1978, Tauster et al. first discovered that the chemisorption abilities of TiO 2 -supported Group VIII noble metals toward small gas molecules, such as CO and H 2 , suddenly disappeared after a reduction treatment at 500 °C. [15] In this case, the term SMSI was proposed to describe this phenomenon that was once believed to be caused by the electronic perturbation due to the formation of PtTi bond. [16,[18][19][20] Later, subsequent investigations confirmed the encapsulation of metal NPs by migrated support species. [21][22][23][24] In 1986, Sakellson et al. provided direct evidences of the SMSI in Rh-TiO 2 using extended X-ray absorption fine structure spectroscopy (EXAFS)-the RhTi bond formed between Rh NPs and TiO 2 support was apparently shorter than that in RhTi intermetallic compounds due to the cationic nature of Ti n+ in TiO 2 . [25] This highlights the meaning of "strong" in "SMSI". On that occasion, Tauster emphasized that the SMSI should be referred to as the formation of such strong interfacial metalmetal bonds rather than its subsequent consequences. [17] However, considering the difficulty in detecting the relatively small amounts of interfacial bonds in supported metal NPs, SMSI is still identified by the apparent change of physicochemical behaviors including encapsulation, loss of chemisorption ability, etc.Later, similar phenomena were observed when other reducible metal oxides were used as the supports including CeO 2 , [26,27] Nb 2 O 5 , [28,29] etc. Moreover, such a reduction-induced SMSI can be eliminated after oxidation treatment at elevated temperatures. Recently, the SMSI has been observed between some new components beyond the typical Group VIII noble metals and reducible metal oxide supports. [30][31][32] The development of advanced material characterization technologies, in situ high-resolution transmission electron microscopy (HRTEM) for example, [33][34][35][36] has also brought new insights into understanding SMSI behaviors. More importantly, owing to its intriguing behaviors, SMSI brings about new principles for designing and modulating advanced heterogeneous catalysts toward thermocatalysis and electrocatalysis. [27,[37][38][39] Meanwhile, it should also be noted that the concept of SMSI has been usedStrong metal-support interaction (SMSI) in supported metal catalysts, typically accompanied by the formation of encapsulation layers over metal nanoparticles, has drawn intense research attention owing to a variety of intriguing behaviors. In particular, recent years have witnessed enormous progress in constructing SMSI between novel components as well as...

Engineering Heterogeneous Catalysis with Strong Metal–Support Interactions: Characterization, Theory and Manipulation

“…[13] Lately, Luo et al reviewed the advances in SMSI and discussed the applications in both thermocatalysis and electrocatalysis systems. [14] Nonetheless, we point out that the rationalization of SMSI research requires answering the three fundamental questions: (i) How to properly define and characterize the SMSI state? (ii) How do first-principle calculations bring insights into the modeling and mechanisms of SMSI?…”

Design of the Synergistic Rectifying Interfaces in Mott–Schottky Catalysts

“…Recently, the possible catalyst support candidates for metal centers have been further extended from transition metal oxides as typical reducible catalyst supports in SMSI systems to carbon materials, , the metal–organic frameworks (MOFs), polymers, etc. The strong metal–support interaction between the metal and reducible oxide supports is usually accompanied by the redispersion or reconstruction of metal particles and increased surface coverage of the oxides, resulting in special contact zones with promoted absorption capacity and/or catalytic activity at the interface. , The electronic perturbation of the metal atoms via contact and even the formation of interfacial bonds with the oxide surface also exhibit a great influence on the final catalytic performance of the dyadic interface . The effect of a strongly coupled interface could be further enhanced or tuned in the confined sheath of two-dimensional materials, including but not limited to active oxide phases, carbon nanotubes, graphene, boron nitride (BN), − and MoS 2 .…”

Design strategies of Pt-based electrocatalysts and tolerance strategies in fuel cells: a review

“…Besides, other transition metal oxides, such TiO 2 , CeO 2 , and Co 3 O 4 , were used as the optimal alternatives due to their strong metal-support interactions (SMSI). [110][111][112][113] Among these metal oxides, TiO 2 carriers could x Pt NPs on its surface, and tune the d-band center of Pt due to its wide band gap. More importantly, hydrophilic TiO 2 carriers are conducive to the formation of OH ad in both acid and alkaline media.…”