Comparison between Iron and Cobalt Clusters in Terms of Chemical Catalysis

 

Faycal Baira1, Yamina Benkrima2*, Mohammed Elbar Soudani3, Abdelkader Souigat2,

Afif benameur4, Zineb korichi2, Djamel Eddine Belfennache5

1Faculty of Technology University of Batna2

2Ecole Normale Supérieure de Ouargla, 30000 Ouargla, Algeria.

3Laboratoire de Développement des Energies Nouvelles et Renouvelables dans les Zones Arides et Sahariennes, Faculté des Mathématiques et des Sciences de la Matière, Université Kasdi Merbah Ouargla, Ouargla 30000.

4Faculty of Science and Technology, University Mustapha Stambouli of Mascara, 29000, Algeria.

5Research Center in Industrial Technologies CRTI, P.O. Box 64, Cheraga, 16014 Algiers, Algeria.

*Corresponding Author E-mail: benkrimayamina1@gmail.com

 

ABSTRACT:

The low-energy geometry and electronic structures of each of the nickel (Fen) and (Con) clusters were arrived at, where the number of n atoms that make up these groups ranges from 2 to 10 and this is based on the use of density functional theory (DFT) using generalized gradient approximation (GGA) taken from the method SIESTA. By searching for clusters with low-energy structures, new structures with low-energies were obtained. For each cluster size, the average bond length, binding energy, Vertical Ionization Potential (VIP) was calculated by this method. Low-energy structures of clusters are even for values n > 6 being linear in the plane, while stability showed that the clusters Fe10 and Co10 have the highest value of the binding energy. The VIP, show clear oscillations at odd and even values, indicating that Fe 2, 6,8,10 and Co 3,7,9 clusters have a higher stability compared to their neighboring clusters. In this research we have succeeded in studying some groups of iron and cobalt using DFT, and addressing their structural aspects in addition to their catalytic properties.

 

Keywords: Density functional theory (DFT), Fen and Con clusters, binding energy, Stability structure, vertical ionization potential (PIV), chemical catalysis.

 


INTRODUCTION

The physics and chemistry of nano clusters have been among the most intriguing sciences over the past two decades, with researchers conducting several investigations in order to search for the unique properties of these clusters, and their unique structure between molecule and size (bulk) has been the main reason for the theoretical researcher to delve into the understanding of the transition from atom to clusters, molecule and finally to solid state. In recent years, researchers have focused on the structural, electronic, optical and catalytic properties of metallic clusters of minerals. This type of cluster is very important thanks to the possibility of using it according to special requests.

 

Nano sized mono- and bi-metallic clusters have received a lot of attention due to their unique and promising applications in optics, magnetism and catalysis1,2 Because it has physical and chemical properties that change by changing the size as a result of the surface change in size, Metal nano clusters, especially Fen and Con nano clusters, are attractive catalysts3-5.The physical and chemical properties of bimetal clusters depend not only on size and shape, but also on the atomic composition of the two metal elements6. The new structural and electronic variables that clusters have become enjoying due to their new size are therefore being studied7. Some results showed that some of the characteristics can change significantly by comparing the clusters before and after modification on their surface8.

 

Both iron and cobalt particles have wide uses in organic chemistry, as they play an important role in protein delivery9, as well as an important role in cancer treatment10-12, cobalt (II) chloride in enhancing hypoxia inducible Factor-1α expression of gingival derived mesenchymal stem cells in vitro13. Iron particles are also included in the catalytic oxidation of blue carbon and in the general electrochemical behaviours of safe compounds and generally in many applications in other fields14, Synthesis of novel iron nanoparticles derived from beta vulgaris extract also acted against enterobacteriaceae, anti-inflammatories and housefly15.

 

DETAIL OF CALCULATIONS:

I have performed the calculations on the principles of sine polarization density functional theory (DFT)16. In terms of interchangeability and functional correlation, we chose to implement the generalized gradient approximation (GGA) function according to the suggestions of Perdew, Burke, and Ernzerhof (PBE)17. The improvements in the geometries of the obtained clusters have been made by the first density functional principle simulation technique, which is rooted in the scalar atomic orbit method according to the application of the SIESTA code18. The structures were also confirmed by using the¢clusters MATERIAL STUDIO software code. The extended wave functions occurred in the planar wave fundamental groups using a 300 eV kinetic energy cutoff. This was applied to all the systems studied in our work. The Monkhorst-Pack network containing proprietary K-point networks was used to implement Brillouin area integrations. As for the implementation of self-consistent field calculations, a criterion of convergence of 10-5 to the total power was used for this. In fact, 0.05 Å was the maximum tolerance value for the displacement of ions in the mass. I obtained the optimized structures when the atomic forces were less than 0.005 eV/Å. Geometric optimizations have been initiated from many primary candidate geometries, which range from the open structured arrangement of  Fe and Co atoms to the close-packed one. Z-matrices in the Q-Chem program output provided the optimized electronic structure for each cluster.

 

 

RESULTS AND DISCUSSION:

1.     Structural properties of clusters Fenand Con (n=2-10):

1.1 Structural characteristics:

The electronic structures of iron (Fe) and cobalt (Co) metal clusters have been reached, starting from the cluster consisting of two atoms to the cluster consisting of 10 atoms, using the simulated annealing application. Figure 1 show the most stable structures of the studied iron clusters, while Figure 2 show the most stable structures of the studied cobalt clusters

 

Figure 1. The most stable structures of Fen (n=2-10) clusters.

 

Figure 2. The most stable structures of Con (n=2-10) clusters.

 

It is noticeable from the two figures that cluster of two and three atoms are open linear chains; it also has an average bond length of 2.67 Å, 2.48 Å, 2.55 Å, and 2.30 Å for each of the clusters Fe2, Fe3, Co2 and Co3 respectively, while the most stable structures of the metallic clusters of iron and cobalt, which consist of four and five atoms it has a trapezoidal shape, we find that the two clusters Fe4 and Co4 have an average bond length of 2.57 Å, 2.42 Å respectively.

 

The average bond length between the atoms of clusters of each metal is calculated through the process of adding all the bond lengths between the cluster atoms and dividing them by the number of bonds that make up it. The average bond length between the atoms of iron and cobalt clusters has been extracted from the XCRYSDEN program and the results are represented in the table 1.


Table 1. The average bond length for of iron (Fen) and cobalt (Con) clusters.

 

cluster

2

3

4

5

6

7

8

9

10

Average bond      length (Å)

Fe

2.67

2.48

2.57

2.64

2.63

2.696

2.70

2.689

2.68

Co

2.55

2.30

2.42

2.45

2.55

2.49

2.53

2.58

2.57

 


Figure 3. The average bond length of the Fen and Con (n=2-10) clusters

 

The results of Table 1 have also been translated into Figure 3.

 

It is noticed from Figure 3, which represents a graphic curve of the average bond length for clusters of iron and cobalt minerals in terms of cluster size that the average bond length increases with the increase in cluster size, and that starts from the cluster consisting of two atoms to the cluster consisting of 10 atoms, where we recorded the largest value for it in each of the clusters Fe8 and Fe7, respectively, with an estimated value of 2.70 Å and 2.696 Å, As for cobalt metal clusters, we recorded the largest value for it at each of Co6 and Co10, respectively, with an estimated value of  2.58 Å and 2.57 Å, while some exceptional cases were recorded that recorded a decrease in the value of the average bond length in each of the clusters Fe3, Fe4, Co3 and Co4.

 

As a result of the analysis of  Figure 3, we conclude that the greater the average bond length between the atoms of each metal cluster, the more stable the system, and from it the iron (Fen) clusters are more stable than the cobalt (Con) clusters.

 

1.2. binding energy:

To study the stability of metal clusters of iron and cobalt, we perform a calculation of the binding energy, where we notice a strong relationship between each of the cluster structure and its binding energy, because the cluster is always looking for its optimal stability, here we find that large clusters are the most stable, and iron clusters are the most stable compared to cobalt clusters because they record greater values of binding energy.

 

The binding energy between the atoms of clusters of iron and cobalt is calculated based on the knowledge of the total energy of the cluster and the energy of one atom in the free state, according to the following relationship:

 

Ebin (kn) = Etot (kn) –nEat (kn)/n                             (1)

where it represents:

Eat is the energy of one atom in the free state, Etot is the total energy of the cluster, n is the number of atoms in the cluster, kn is cluster code.

 

 

Figure 4: Binding energy of Fen and Con clusters as a function of cluster size

 

The binding energy values are represented in Figure 4.

 

From Figure 4, the binding energy of iron and cobalt metal clusters is increasing compared to the increase in the size of the cluster, where we find for the Fe2 cluster the value of the binding energy is estimated at: 1.86 eV, while the value of the binding energy for the Fe10 cluster is 3.46 eV, As for cobalt metal clusters, we recorded the same observation in terms of the increase in the value of the binding energy. For cluster Co2, the value of binding energy was estimated at 2.50 eV, while for cluster Co10, the value of binding energy was estimated at: of 5.13 eV.

 

2.     vertical ionization potential (PIV):

The vertical ionization potential is calculated from the difference between the cation energy and the element energy, through the following relationship:

= E(kn*) – E(kn)                                                   (2)

Where it represents:

E (kn*) is cation energy, E(kn) is element energy. 

 

Figure 5: The vertical ionization potential of Fen and Con clusters as a function of cluster size

It can be seen from Figure 5 that the column ionization potential decreases as the cluster size increases for iron and cobalt, where we find that the largest value of it for iron metal clusters was recorded at the Fe2 cluster, which was estimated at 8.21 eV, while at the Fe10 cluster for example, the vertical ionization value was estimated at 5.65 eV, while we record the largest value of the vertical ionization potential for cobalt metal clusters at the Co2 cluster, which was estimated at 7.23 eV, while at the Co10 cluster, the vertical ionization value was recorded, which was estimated at 5.26 eV.

 

We also note that there is an identical in the value of the vertical ionization potential, which is estimated at 7.47 eV, 6.11 eV, 7.42 eV and 6.16 eV, for clusters Fe3, Fe5, Co3, and Co5 respectively, while we record the high value of the vertical ionization potential for the two clusters of platinum metal Co7 and Co9 With an estimated value of 5.91 eV and 5.56 eV, respectively, compared to the Fe7 and Fe9 cluster, which was estimated at 5.40 eV and 5.18 eV respectively.

 

The vertical ionization potential is one of the variables that highlights the stability of the elements. We find that the greater the value of the vertical ionization indicates greater stability. When a comparison is made between clusters of iron and cobalt, we find that the clusters of iron metal are characterized by greater values, so it is considered it is the most stable metal compared to cobalt metal and from it the latter is more chemically active where it can be used as a chemical catalyst.

 

CONCLUSION:

In this work, we have theoretically studied iron and cobalt metal clusters, in order to determine the structural and catalytic properties, where we relied in our calculations on the siesta program, which is based on the density function theory (DFT) based on the generalized gradient approximation (GGA) .

The results obtained can be summarized as follows:

·       The difference in cluster size leads to a difference in the electronic structure of iron and cobalt metal clusters.

·       There is a direct relationship between the cluster size and the average bond length between the atoms of clusters of iron and cobalt, where the larger the cluster size, the greater the average bond length, and from it can be said that iron clusters are more stable than cobalt clusters because they have greater values for this variable.

·       There is a direct relationship between the cluster size and the binding energy, as the larger the cluster size, the higher the binding energy. And as it is known that the higher the binding energy, the more stable the system, and accordingly, the iron clusters are more stable than the cobalt clusters.

·       There is an inverse relationship between the cluster size for both minerals and the values of the vertical ionization potential, as the larger the cluster size the lower the values of the vertical ionization potential, and from it we conclude that the iron-metal clusters are the most stable compared to the cobalt-metal clusters, while the iron-metal clusters are less active in terms of Chemical which makes cobalt clusters very important in the field of catalysis.

 

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Received on 07.11.2022                    Modified on 15.02.2023

Accepted on 17.04.2023                   ©AJRC All right reserved

Asian J. Research Chem. 2023; 16(3):225-229.

DOI: 10.52711/0974-4150.2023.00036