Synthesis, catalysis, surface chemistry and structure of bimetallic nanocatalysts

Abstract

Bimetallic catalysts are one of the main categories of metal catalysts due to the tunability of electronic and geometric structures through alloying a second metal. The integration of a second metal creates a vast number of possibilities for varying the surface structure and composition of metal catalysts toward designing new catalysts. It is well acknowledged that the surface composition, atomic arrangement, and electronic state of bimetallic catalysts could be different from those before a chemical reaction or catalysis based on ex situ studies. Thanks to advances in electron-based surface analytical techniques, the surface chemistry and structure of bimetallic nanoparticles can be characterized under reaction conditions and during catalysis using ambient pressure analytical techniques including ambient pressure XPS, ambient pressure STM, X-ray absorption spectroscopy and others. These ambient pressure studies revealed various restructurings in the composition and arrangement of atoms in the surface region of catalysts under reaction conditions or during catalysis compared to that before reaction. These restructurings are driven by thermodynamic and kinetic factors. The surface energy of the constituent metals and adsorption energy of reactant molecules or dissociated species on a metal component are two main factors from the point of view of thermodynamics. Correlations between the authentic surface structure and chemistry of catalysts during catalysis and simultaneous catalytic performance were built for understanding catalytic mechanisms of bimetallic catalysts toward designing new catalysts with high activity, selectivity, and durability.

Charge distribution and Fermi level in bimetallic nanoparticles

“…In recent years, bimetallic nanoparticles have received increasing attention due to their promising electrocatalytic, [1][2][3] catalytic, [4][5][6][7][8] magnetic, 4,9,10 and optical properties. 4,11 The interaction of nanoparticles with their environment can, sometimes drastically, shift the Fermi level of electrons in the nanoparticles, influencing their chemical and electrochemical properties, as highlighted in a recent review.…”

Electrochemical Surface Processes and Opportunities for Material Synthesis

“…Metallic monolayers and alloys based on precious metals are extensively used in a variety of heterogeneous (electro)catalysis processes; alloys in particular exhibit quite different properties from those of the parent metals, often providing synergistic effects; in addition, they exhibit tunable properties, achieved by gradually varying the composition [121]. Catalytic properties of alloy surfaces are determined both by electronic effects, whereby heteroatom bonds change the local electronic environment with respect to the pure elements, and by geometric (ensemble) effects, where definite atomic arrangements provide suitable adsorption sites for the reactive species, and, in parallel, strain effects may arise.…”

Design of a new reactor-like high temperature near ambient pressure scanning tunneling microscope for catalysis studies

“…Atoms in surface layer and even nearly surface layers are significantly impacted by the existence of environment. [2][3][4][5][6] The complexity is largely enhanced when the catalyst functions at a high temperature.…”

“…This difference has been demonstrated in recent studies. 2,3,5 In addition, structure and chemistry of the catalyst surface upon removal of a catalytic or reaction condition could be different from that during catalysis since catalyst surface could be maintained only when the reactant mixture with certain pressure around the catalyst is remained at a high temperature. Figure 1 presents three potential surface phases of a catalyst upon removal of the catalytic condition after catalysis.…”