Heterogeneous Catalysis and Surface Reactions

The definition of a catalyst, as per the International Union of Pure and Applied Chemistry (IUPAC), is that a catalyst is a substance that increases the rate of a reaction without modifying the overall standard Gibbs energy change in the reaction [1], The chemical process of increase of the reaction rate is called catalysis and the catalyst is both a reactant and a product of the reaction. That is, the catalyst is restored after each catalytic act. Besides, the catalyst does not influence the final equilibrium composition after the cessation of the reaction. 

Catalysis can be classified as homogeneous catalysis, in which only one phase is involved, and heterogeneous catalysis, the case of interest here, in which the reaction occurs at or near an interface between phases [1], 

Since the start of the development of the science and technology of catalysis, it has become an important operation in the chemical industry. In this regard, catalytic technologies are extremely significant for the economic development and expansion of the chemical industry. Heterogeneous catalysts offer numerous inherent benefits over their homogeneous counterparts, such as simplicity of product separation and catalyst reuse. 

In this chapter, the basic principles of heterogeneous catalysis and surface reactions, and chemical, sustainable energy, and pollution abatement applications of heterogeneous catalysts are described [3-5], 

---

Other reactions at surfaces (heterogeneous catalysis and reduction reactions)... 

The fields of heterogeneous catalysis and surface science have long been intertwined. Whether it is the studies of Faraday on oxidation reactions over platinum surfaces, Langmuir s studies of the surface properties of catalysts, or even work performed in the present day on the abilities of different surfaces to act as catalysts, advances in surface science often lead to the development of new... 

Coadsorption phenomena in heterogeneous catalysis and surface chemistry quite commonly consider competitive effects between two reactants on a metal surface [240,344]. Also cooperative mutual interaction in the adsorption behavior of two molecules has been reported [240]. Recently, this latter phenomenon was found to be very pronounced on small gas-phase metal cluster ions too [351-354]. This is mainly due to the fact that the metal cluster reactivity is often strongly charge state dependent and that an adsorbed molecule can effectively influence the metal cluster electronic structure by, e.g., charge transfer effects. This changed electronic complex structure in turn might foster (or also inhibit) adsorption and reaction of further reactant molecules that would otherwise not be possible. An example of cooperative adsorption effects on small free silver cluster ions identified in an ion trap experiment will be presented in the following. 

In this section the nature of a series of simple intermediates will be considered. In catalysis and surface reactions in general it is usually organic species which form these intermediates and the following discussion will itemise a few of the main types of species which have been well studied by surface science methods. The bonding and stability of such species is often crucial for the efficiency of heterogeneous catalysis. 

Ammonia synthesis catalyst with Fes04 as precursor has been studied widely and deeply in the past one century. " These results have greatly promoted the development of heterogeneous catalysis and surface science. Ammonia synthesis reaction is a green chemical reaction without side reaction and with molecular efficiency and selectivity of 100%. It is used as the ideal model reaction in heterogeneous catalysis, and all general concepts of catalysis were developed and formulated in relation to ammonia synthesis. So ammonia synthesis catalyst is also called textbook catalyst. ... 

Studies of surfaces and surface properties can be traced to the early 1800s [1]. Processes that involved surfaces and surface chemistry, such as heterogeneous catalysis and Daguerre photography, were first discovered at that time. Since then, there has been a continual interest in catalysis, corrosion and other chemical reactions that involve surfaces. The modem era of surface science began in the late 1950s, when instmmentation that could be used to investigate surface processes on the molecular level started to become available. 

Nonstoichiometric oxide phases are of great importance in semiconductor devices, in heterogeneous catalysis and in understanding photoelectric, thermoelectric, magnetic and diffusional properties of solids. They have been used in thermistors, photoelectric cells, rectifiers, transistors, phosphors, luminescent materials and computer components (ferrites, etc.). They are cmcially implicated in reactions at electrode surfaces, the performance of batteries, the tarnishing and corrosion of metals, and many other reactions of significance in catalysis. ... 

In heterogeneous catalysis, solids catalyze reactions of molecules in gas or solution. As solids - unless they are porous - are commonly impenetrable, catalytic reactions occur at the surface. To use the often expensive materials (e.g. platinum) in an economical way, catalysts are usually nanometer-sized particles, supported on an inert, porous structure (see Fig. 1.4). Heterogeneous catalysts are the workhorses of the chemical and petrochemical industry and we will discuss many applications of heterogeneous catalysis throughout this book. 

---