Wolkenstein’s Model of Size Effects in CO Oxidation by Gold Nanoparticles

Nigora Turaeva,Herman Krueger

doi:10.3390/catal10030288

Abstract

The Wolkenstein’s theory of catalysis and the d-band theory of formation chemical bonds between transition metal catalysts and adsorbates were used to develop the approach applied to the kinetics of CO oxidation by gold nanoparticles. In the model, within the framework of the mechanism of the reaction going through dissociative adsorption of oxygen molecules and reaction with gas-phase CO molecules, weak and strong chemisorption states of intermediates (O, CO2) were taken into account in the kinetic equations by introducing reversible electronic steps corresponding to electron transfers between the intermediates and the catalyst. As a result, we obtain the expression for the reaction rate, which exhibits a volcano-shape dependence upon the size of the gold nanoparticles at the conditions when the intermediates fractions are not small compared to the empty active sites of the catalyst. It is supposed that the approach can be also applied to the Langmuir-Hinshelwood mechanism.

Highlights

Remarkable opportunities that nanotechnologies offer to the science and industry include a possibility of tuning properties of materials by their size and shape at the nanometer scale instead of replacement of materials by new ones to achieve desirable properties [1]
We will investigate the possibility of obtaining a volcano-shape size dependence of the reaction rate by combining the Wolkenstein’s theory of catalysis [26,27] based on a regulatory role of the Fermi level of catalysts and d-band model [28,29] establishing the origin of the chemical bonds between intermediates and transition metal catalysts
The volcano-shape size dependence of the reaction rate for CO oxidation observed in experiments can be interpreted by the changing of adsorption and desorption of molecules at changing the size of gold nanoparticles, as the Fermi level of the particles moves down at decreasing the size

Summary

Introduction

Remarkable opportunities that nanotechnologies offer to the science and industry include a possibility of tuning properties of materials by their size and shape at the nanometer scale instead of replacement of materials by new ones to achieve desirable properties [1]. A very good example is gold, which is inert at the bulk but chemically active at the nanometer scale to catalyze many redox reactions at low temperatures [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23] One of such reactions catalyzed by gold nanocatalysts is the environmentally important CO oxidation reaction.

Wolkenstein’s Approach

Jellium Model

D-Band Model

Theoretical Model

Discussion

Conclusions