Introduction to Catalysis and Industrial Catalytic Processes

Robert J. Farrauto, Lucas Dorazio, C. H. Bartholomew

• Publisher: Wiley-AIChE
• Year: 2020
• ISBN:
  9781119101673
• Edition: 1
• Topic: Tecnología e ingeniería
• Subtopic: Ingeniería química y bioquímica

Introduces major catalytic processes including products from the petroleum, chemical, environmental and alternative energy industries

• Provides an easy to read description of the fundamentals of catalysis and some of the major catalytic industrial processes used today
• Offers a rationale for process designs based on kinetics and thermodynamics
• Alternative energy topics include the hydrogen economy, fuels cells, bio catalytic (enzymes) production of ethanol fuel from corn and biodiesel from vegetable oils
• Problem sets of included with answers available to faculty who use the book

Review:
"In less than 300 pages, it serves as an excellent introduction to these subjects whether for advanced students or those seeking to learn more about these subjects on their own time...Particularly useful are the succinct summaries throughout the book...excellent detail in the table of contents, a detailed index, key references at the end of each chapter, and challenging classroom questions..." (GlobalCatalysis.com, May 2016)

CHAPTER 1
CATALYST FUNDAMENTALS OF INDUSTRIAL CATALYSIS

1.1 INTRODUCTION

Chemical reactions occur by breaking the bonds of reactants and forming new bonds and new compounds. Breaking stable bonds requires the absorption of energy, while making new bonds results in the liberation of energy. The combination of these energies results in either an exothermic reaction in which the conversion of reactants to products liberates energy or an endothermic process in which the conversion process requires energy. In the former case, the energy of the product is lower than that of the reactants with the difference being the heat liberated. In the latter case, the product energy is greater by the amount that must be added to conserve the total energy of the system. Under the same reaction conditions, the heat of reaction (ΔH) being a thermodynamic function does not depend on the path or rate by which reactants are converted to products. Similarly, ΔG of the reaction is not dependent on the reaction path since it too is a thermodynamic state function. This will be emphasized once we discuss catalytic reactions. The rate of reaction is determined by the slowest step in a conversion process independent of the energy content of the reactants or products.

1.2 CATALYZED VERSUS NONCATALYZED REACTIONS

In the most basic sense, the purpose of the catalyst is to provide a reaction pathway or mechanism that has a lower activation barrier compared to the noncatalyzed (E_nc) pathway, as illustrated in Figure 1.1. Also shown is the catalyzed barrier (E_Mn). In any reaction, catalyzed or noncatalyzed, the reaction sequence occurs through a series of elementary steps. In a noncatalyzed reaction, the species that participate in the reaction sequence are derived solely from the reactants. In a catalyzed reaction, the catalyst is simply an additional species that participates in the reaction sequence by lowering the activation energy and hence enhances the kinetics of the reaction. Finally, during the catalyzed reaction sequence, the catalyst species returns to its original state. It is the regeneration of the catalyst species to its original state that makes a catalyst a “catalyst” and not a “reactant.” Thus, a catalyst is a species that participates in the reaction sequence—it interacts with the “reactants” to form an intermediate species that undergoes further reaction to form the “product” with the catalyst returning to its original state. This basic sequence of events is illustrated in Figure 1.2.

Figure 1.1 Catalyzed and uncatalyzed reaction energy paths illustrating the lower energy barrier (activation energy) associated with the catalytic reaction compared with the noncatalytic reaction. (Reproduced from Chapter 1 of Heck, R.M., Farrauto, R.J., and Gulati, S.T. (2009) Catalytic Air Pollution Control: Commercial Technology, 3rd edn, John Wiley & Sons, Inc., New York.)

Figure 1.2 Illustration of catalyzed versus noncatalyzed reactions.

1.2.1 Example Reaction: Liquid-Phase Redox Reaction

Let us consider the simple redox reaction between Fe²⁺ and Ce⁴⁺ in aqueous solution. The reaction below excludes the H₂O present in the coordination sphere for each species since it does not directly participate in the reaction.

Figure 1.3 Catalytic Fe–Ce redox reaction catalyzed by Mn.

(1.1a)

(1.1b)

This reaction involves a direct electron transfer from the Fe²⁺ to the Ce⁴⁺ and by itself occurs very slowly because the electron transfer process occurs slowly. However, in the presence of Mn⁴⁺ species, the rate dramatically increases because the electron transfer is now facilitated through the Mn⁴⁺/Mn²⁺ couple. The Mn⁴⁺ species is a catalyst, not a reactant. While it does directly participate in the reaction, the reaction pathway results in no overall change in the chemical state of the Mn ion (Figure 1.3).

The reaction profile of both the catalyzed and noncatalyzed reactions can be described kinetically by the Arrhenius profile in which reactants convert to products by surmounting the energy barrier called the activation energy. According to the Arrhenius expression (Equation 1.2), the rate of reaction is proportional to the exponential of absolute temperature (T) and inversely proportional to the exponential of the activation energy (E)....