Chapter 1

Heterogeneous Catalysts

Abstract

The merits of industrial chemistry as a production activity and the role of heterogeneous catalysis are briefly reviewed. A summary of the families of solid catalysts is proposed. Some information on the industrial catalyst production and international publications on catalysts and catalysis is given.

Kewords

Industrial chemistryheterogeneous catalysiscatalytic materialscatalyst producerscatalysis journals

Chapter Outline

1.1 Introduction?1

1.1.1 On the merits of industrial chemistry as a production activity?1

1.1.2 Catalysis and its role in industrial chemistry?2

1.1.3 Why solid catalysts??3

1.1.4 Industrial catalytic materials?5

References?7

Introduction

On the merits of industrial chemistry as a production activity

At the beginning of the third millennium, few disciplines such as industrial chemistry are in a difficult situation and, together, transformation with exciting prospects. Public opinion attributes to chemistry, and not without a few good reasons, the environmental degradation, with its harmful consequences. However, the merits of chemistry as an industrial activity are actually largely unknown to people and neglected by experts that would know them. In fact, industrial chemistry is a service activity, allowing in particular the production of materials and molecules that are strictly needed by other activities to obtain their goals. It is well evident, for example, that the exponential growth and improving of information and telecommunication technologies are largely dependent from the development of suitable materials made available by the product and process developments of industrial chemistry. It is sufficient to think about the number of chemical components (constituting conducting electrodes, insulating components, dyes, polymers) involved in the i-phone touch screens, and to understand how chemistry and industrial chemistry contributed to the development of electronic technologies. By analogy, we can say that, without the past development of industrial chemistry and processes, the cars, aircraft, household electrical appliances and equipments, etc., of today would not be available. Similarly, part of the development of medicine is due to the development, at the research level, of new active drug molecules as well as, at the industrial level, of efficient synthesis processes, allowing them to be obtained at moderate costs. Medicine also takes advantage of instrumentations in part, based on chemical analytical techniques, as well as of materials and chemicals that become unique. An example is polyvinyl chloride, which is the main component of hospital wastes, proving its very large application in the medical equipment. Another example is that of sodium hypochlorite, which is universally considered today as a unique disinfecting agent. Both these chemical species have been the object of criticism due to safety and environmental concerns in their preparation and end-of-life destiny. However, both of them proved to have unique and irreplaceable behavior, while safety and environmental concerns have been addressed and largely (if not completely) resolved technologically. Another important and disputed example is that of crop protection technology, which includes the developments of processes allowing the large scale production of pesticides, herbicides, insecticides, fungicides, etc. These chemical products help control the thousands of weed species, harmful insects and numerous plant diseases that afflict crops. The development of these molecules and of the processes for their production allowed millions of people to be fed and a number of lethal illnesses to be reset. Chemical activities are usually considered to be responsible for environmental degradation. This is largely true, but it is quite evident that this is right as a result of the initial development of chemical technologies at their childhood level, mixed with (at times) a still poor knowledge of several natural phenomena and of some chemical phenomena too. A better knowledge of environmental chemistry and biochemistry reached in more recent years allowed to actually resolve most of environmental issues of chemical production technologies. Today, and sometimes also earlier, environmental problems arise from the lack of application of technologies that have been developed just to reduce and sometimes neutralize any environmental concern. On the other hand, it is evident that chemistry and industrial chemistry are leading actors in the environment remediation too. In spite of the evident concerns associated with the environment degradation, it is without any doubt that industrial chemistry has been a major leading actor in the exponential technological development that occurred in the last 150 years, allowing a very high level of wealth reached today by most of the populations of the developed countries. It is certainly a pity, and a dishonor for our civilization, that this high level of wealth did not catch up with most of the populations of less developed countries and also with a large part of the inhabitants of our industrialized countries. But this is a matter of politics more than of that of science and technology.

Catalysis and its role in industrial chemistry

As first recognized by the Swedish chemist J.J. Berzelius in 1835, catalysis is a phenomenon allowing a chemical reaction occurring faster when a nonreactant species is present. In spite of the apparent limited interest of doing a reaction faster, catalysis gives rise to very relevant practical effects. In fact, the increase of the rate of a reaction can in practice result in many cases in its practical feasibility. The acceleration of a desirable chemical conversion, in fact, frequently allows it to be realized instead of other competitive reactions, less desirable, being definitely slower. Thus, finding an appropriate catalyst to make the desired reaction faster than the competitive ones, as well as allowing it to perform with high efficiency, is crucial in developing industrial processes. Thus, since maybe 180 years (the contact process for sulfuric acid production was developed in 1831), heterogeneous catalysis is a keystone in industrial chemistry.1 For this reason, catalysts are also important products of the chemical industry itself and their industrial production represents a big business, like 13 billion dollars per year.

Why solid catalysts?

In practice, a large majority of industrial chemical processes (likely 85%2) are catalyzed and most of them are catalyzed by solids. The main reasons to use catalysts are synthetically the following: 1. The catalyst allows the desired reaction to become faster than competitive reactions thus allowing the desired reaction to be actually realized. 2. For exothermic equilibrium reactions: the catalyst allows the reaction to be performed also at lower temperature, where it would be kinetically hindered without it. Thus, it allows the reaction to be realized in conditions where thermodynamics is more favorable. 3. For endothermic equilibrium reactions: the catalyst allows the reaction to be performed also at moderately high temperatures, where it would be kinetically hindered without it. Thus, it allows the reaction to be realized in conditions where thermodynamics is already quite favorable with lower energy waste and allowing cheaper materials to be used for the reactor. 4. For exothermic nonequilibrium reactions: the catalyst allows reactions less favored by thermodynamics and kinetics (without it) to be realized instead of more favored and otherwise faster reactions. 5. A better catalyst allows reactions to be performed in smaller flow reactors with the same performances, or with better performances and lower recycles of unconverted reactants in the same reactor, or even with shorter times in batch reactors. Solid catalysts are usually preferred in the industry with respect to liquid catalysts because of their easier separation from the reaction fluid. On the other hand, solid catalysts are frequently more environmentally friendly than liquid catalysts and their manipulation far safer. A typical example is that of acid catalysts for refinery and petrochemistry. Protonic zeolites substituted for liquid acids catalysts in some important processes. In practice, dangerous corrosive liquids characterized by unsafe manipulation procedures, difficult regeneration and unappropriate disposal, like sulfuric acid, and AlCl3-based Friedel Crafts type liquid acid, and very toxic and volatile acids like hydrofluoric acid have been substituted by environmentally friendly silicoaluminates. Additionally, catalyst performances have also been improved.

Table 1.1

Summary of Some Most Relevant Families of Industrial Catalysts

Bulk single oxide Alcohol dehydration to olefins ?-Al2O3 Lewis acidic catalyst Bulk mixed oxide Aldol condensation MgO–Al2O3 calcined hydrotalcite Basic catalyst Propane to...