The genesis and importance of oxide–metal interface controlled heterogeneous catalysis; the catalytic nanodiode

Abstract

Much of the research by KonradHayek's group is focused on the influence of oxide-metal interfaces in heterogeneous catalysis. In this paper, we show that electronic excitations at the metal surface induced by exothermic catalytic reactions lead to the generation of energetic (hot) electron flows. We detected the flow of hot electrons during oxidation of carbon monoxide using Pt/ TiO 2 Schottky diodes. The thickness of the Pt film used as the catalyst was 5 nm, less than the electron mean free path, resulting in the ballistic transport of hot electrons through the metal. The electron flow was detected as a chemicurrent if the excess electron kinetic energy generated by the exothermic reaction was larger than the effective Schottky barrier formed at the metalsemiconductor interface. We found that heat generated by the reaction caused a negligible increase of temperature in our experimental range, suggesting that this thermal effect is not responsible for the generation of hot electron flow. We tested the stability and reversibility of chemicurrent generated during CO oxidation at 413$573 K. The activation energy calculated from the measurement of chemicurrent is quite close to that of the turnover rate of chemical reaction, which indicates that the generation mechanism of hot electrons is closely correlated with the chemical reaction. This correlation suggests that hot electron flow could be a new tool to probe the role of oxide-metal interfaces in heterogeneous catalysis.

Colloid Science of Metal Nanoparticle Catalysts in 2D and 3D Structures. Challenges of Nucleation, Growth, Composition, Particle Shape, Size Control and Their Influence on Activity and Selectivity

“…Also, when vibrationally excited molecules strike another surface they are rapidly deexcited because of hot electron formation [42][43][44] . We fabricated a catalytic nanodiode where catalytically reactive platinum thin films were deposited on an oxide to form a Schottky barrier and we made contact to both sides of this barrier of Pt or Pd on TiO x or GaN [45][46][47] . Figure 18a shows the typical I-V curves measured on Pd/TiO x diode.…”

Concepts, instruments, and model systems that enabled the rapid evolution of surface science

“…As the surface becomes less positively charged, the acetonitrile orientation flips 180° with the CH 3 group pointing toward the surface. We constructed a so called catalytic nanodiode (59)(60)(61), which is composed of a metal of thickness less than the mean free path of hot electrons, deposited on a semiconductor surface, as shown in Figure 8a. When exothermic catalytic chemical reactions occur, we find that the heat transferred is converted to a hot electron flow that can pass through the metal film into the semiconductor which has a Schottky barrier (62; 63), which allows the passing of energetic electrons in one direction but not in the other direction.…”

Probing Hot Electron Flow Generated on Pt Nanoparticles with Au/TiO2Schottky Diodes during Catalytic CO Oxidation

“…The oxide-metal interface is one of the major factors which determines the activity and selectivity of the heterogeneous catalysts [19][20][21] . It was observed that during certain reactions the oxide onto which the metal nanoparticles are deposited can dramatically change activity and selectivity even though the oxide itself is not active in catalysis 22,23 .…”