Operando Surface Studies on Metal-Oxide Interfaces of Bimetal and Mixed Catalysts

Abstract

The formation of metal-oxide interfaces in catalytic systems exhibits a synergistic phenomenon between metal and reducible oxides, often referred to as the strong metal−support interaction (SMSI). This unusual characteristic has been connected to the origin of highly enhanced catalytic performance for decades, but the mechanistic explanation of SMSI remains a long-standing issue in heterogeneous catalysis. To understand this matter at the molecular level, geometric and electronic functions of metal-oxide interfaces during catalytic reactions should be clearly interpreted using advanced microscopic and spectroscopic analysis techniques. In this Review, we highlight recently performed investigations at metal-oxide interfaces by operando characterization tools to identify active sites in working conditions. We introduce two kinds of catalysts, platinum-based bimetallic alloys and mixed metal-oxide catalysts. Selected operando techniques reveal their atomic-scale morphology, surface electronic structure, and charge transfer/transport at surfaces under oxidation, reduction, and gas mixture environments. With bimetallic model catalysts, topographic morphology observations present critical evidence for the structural modulation between the topmost layer and the subsurface lattice in oxygen conditions. For the mixed metal-oxide catalysts, we note that metal nanoparticles on reducible oxides demonstrate the catalytic activity enhancement, which is obviously influenced by the change of oxidation states at the metal-oxide interface. Environmental transmission electron microscopy images unveil the atomic-scale redox behaviors at the nanoparticle interfaces with evolutions of the reducible oxide under the catalytic reaction. The important role of reactive interfaces between the transition metal atom and oxide-support explains the surface chemistry and heterogeneous catalysis over active sites on well-defined single crystal model surfaces, as well as nanoparticle catalysts. Overall, operando studies for metal-oxide interfaces can shed light on mechanistic insights into the tuning of catalytic activity at the molecular level and on improving catalytic performance by the SMSI effect.

Breaking the Activity–Selectivity Trade-Off for Simultaneous Catalytic Elimination of Nitric Oxide and Chlorobenzene via FeVO4–Fe2O3 Interfacial Charge Transfer

“…Charge transfer between a metal oxide and support could tune the chemical property of the metal oxide (such as redox ability), thereby modulating its reactivity . The XPS peak of O 1s (Figure a) was analyzed to figure out the state of oxygen species.…”

“…Charge transfer between a metal oxide and support could tune the chemical property of the metal oxide (such as redox ability), thereby modulating its reactivity. 43 The XPS peak of O 1s (Figure 3a) was analyzed to figure out the state of oxygen species. The peaks at 531−532 eV (O α ) were assigned to reactive oxygen generated by the adsorption and dissociation of O 2 molecule near the oxygen vacancy, while the peaks at 529−531 eV (O β ) were assigned to lattice oxygen.…”

Microemulsion Antisolvent Extraction Strategy to Realize Adjacent Coprecipitation of Copper Acetate and Zinc Acetate for Preparing Highly Efficient Dual Site Catalysts

“…The specific activity of the EA-10% sample was about 1.5 times that of the IM-10% sample. The formation of metal-oxide interfaces exhibits a synergistic phenomenon between metals and oxides. − According to the above characterization analysis, the difference in the catalytic performance comes from the difference in crystallinity, morphology, and distribution of the two active components. The proposed preparation strategy effectively adjusts the crystallinity, morphology, and uniformity of the distribution of the two active site components, thereby improving the catalytic performance of the final catalysts …”

Synergy between Ru and WOx Enables Efficient Hydrodeoxygenation of Primary Amides to Amines

“…It has been recognized that the synergy between the two components in a bifunctional catalyst is critically dependent on the interface structure, which is a multivariant function such as the dimension of the respective individuals and the proximity between them. − In our previous work, we found that Pt–W bimetallic NPs supported on alumina were highly active and selective for HDO of glycerol to 1,3-propanediol when Pt was highly dispersed on submonolayer WO x structures . Motivated by the success of HDO of biomass-derived polyols with Re- and W-based bifunctional catalysts, ,,− herein, we develop a Ru–W bimetallic catalyst with a well-controlled interfacial structure, which enables highly active and selective HDO of primary amides to the corresponding amines.…”