Chemical Reactions Catalysts

Introduction

In chemical reactions catalysts are used in order to speed up the reaction. Their ability is to decrease the activation energy of the reaction while they are not used within the reaction. Catalysts usually consist of one or more active components imposed on surface of an oxidation material referred as catalyst support. Support material acting as building block for catalysts has many advantages such as:

- Maximizing the surface area of the active components [1]

- Achieving a good dispersion of active components

- Stabilizing the active components against sintering[2]

Among catalysts, heterogeneous catalysis is focused as they are very important in the development of environmentally sustainable technologies such as oil refining, petrochemicals and power generation. Among them Hydrodesulphurisation (HDS) catalysts are those which are used to reduce the sulphur content of fuels. The most industrially used component in this field is Cobalt-Molybdenum supported on Alumina (Co-Mo/ Al2O3) which consists of active phase of MoS2 promoted by Co both imposed on Ɣ-Al2O3 as the catalyst support.[3] Ɣ-Al2O3 represents a support with high surface area (15-300 m2/g) and high thermal stability from which the surface acidity can be controlled.[1]

The catalytic performance of a catalyst depends on its different components, such as support and active metal. Usually, the behavior of the active phase is influenced by the type of support material; thus, it becomes necessary to select an optimum support material according to the criteria of interaction with active phases, acid-base properties (inertness), textural properties, stability, extrusion properties, and cost at commercial scale. The major component of these supports remains γ-alumina due to its outstanding mechanical properties, nature of interaction with active phases (Mo, W, Co, Ni), and cost. (S. K. Maity, 2007)

The most commercially and industrially used alumina catalysts are high surface area aluminas. High surface area aluminas are defined as aluminas with a surface area greater than 100m2/g.[4]

• talk about other types

Catalyst Preparation

The preparation of a catalyst which can be used in industry is like an art. A hydroprocessing catalyst composed of sulphided active metals (Cobalt and Molybdenum in this preview) on the surface of a support (γ-Al2O3). The overall catalyst preparation process can be subdivided into support preparation, active metal impregnation and its drying and calcinations. Every basic property of each catalyst is influenced by changing the conditions of each stage. (S. K. Maity, 2007)

• Preparation of γ-Al2O3

The main characteristics of catalysts, which