Ab Initio Density Study of N and O Coadsorption on PT(100) and PT(111)

Ab Initio Density Study of N and O Coadsorption on PT(100) and PT(111).

ABSTRACT

We have used ab initio density functional theory to study the coadsorption of N and O on Pt(100) and Pt(111) surfaces.

Our calculations show that on Pt(100) the most favourable site is the hollow site for N and the bridge site for O, while for Pt(111) there are different possible N and O coadsorption geometries.

On both surfaces the interaction between N and O is repulsive
in nature.

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TABLE OF CONTENTS

1 Introduction 1
2 BACKGROUND LITERATURE 4
2.1 DENSITY FUNCTIONAL THEORY . . . . . . . . . . . . . . 4
2.1.1 Local Density Approximation . . . . . . . . . . . . . . 8
2.1.2 Generalized Gradient Approximation . . . . . . . . . . 8
2.2 INFINITE PERIODIC SYSTEM . . . . . . . . . . . . . . . . 9
2.3 PSEUDOPOTENTIAL . . . . . . . . . . . . . . . . . . . . . . 10
2.3.1 Pseudopotential Approximation . . . . . . . . . . . . . 13
2.3.2 Ultra-Soft (Vanderbilt) pseudopotentials . . . . . . . . 14
2.3.3 Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.4 Surface Modelling . . . . . . . . . . . . . . . . . . . . . . . . . 17
3 Methodology and Test Calculations 19
3.1 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.2 Test Calculations . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.2.1 Determination of Augumented Charge Density cutoff
(Ecutrho) . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.2.2 Determination of plane wave cut off (Ecutwfc) . . . . . 20
3.2.3 k-point mesh . . . . . . . . . . . . . . . . . . . . . . . 21
3.2.4 Test for Pseudopotential . . . . . . . . . . . . . . . . . 22
4 RESULTS 26
4.1 Clean Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.1.1 Pt(100) . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.1.2 Pt(111) . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.2 Adsorption of atomic N and O on Pt surfaces . . . . . . . . . 28
4.2.1 On Pt(100) . . . . . . . . . . . . . . . . . . . . . . . . 29
4.2.2 On Pt(111) . . . . . . . . . . . . . . . . . . . . . . . . 30
4.3 Coadsorption of N and O on Pt surfaces . . . . . . . . . . . . 31
4.3.1 On Pt(100) . . . . . . . . . . . . . . . . . . . . . . . . 32
4.3.2 On Pt(111) . . . . . . . . . . . . . . . . . . . . . . . . 34
5 Conclusion 40

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INTRODUCTION

Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself but alters the rate of chemical reaction. The catalyst may participate in multiple chemical transformations.

Generally, catalysts are transition metals which have different number of d-electrons which play an important role in the performance of the catalyst. Heterogeneous catalysts are those which are in different phases than the reactants.

Most heterogeneous catalysts are in solid phase while the reactants and products are in liquid or in gaseous phase. Diverse mechanisms for reactions on surfaces are known, depending on how the adsorption takes place (Langmuir-Hinshelwood and Eley-Rideal)[25].

Intensive studies on the adsorption of small molecules on metallic surfaces have been carried out due to their potential applica tions in several technological proceses, such as heterogeneous catalysis, corrosion, lasers and gas sensors.

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BIBLIOGRAPHY

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