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Chapter

Cover The Basis and Applications of Heterogenuous Catalysis

Catlytic materials and their preparation  

This chapter evaluates catalytic materials and their preparation. Catalysts can take a broad range of forms and this is reflected in the range of materials produced, and used, by the chemical industry and by nature. Thus, they can range from solid materials to biological enzymes, from gas phase molecules to liquid coatings on surfaces. The chapter highlights the important types of applied industrial catalysts, including metals and oxides. There is a wide range of properties of a catalyst that are required in order for it to be an efficient one for any particular reaction. The foundations of catalyst production are the correct kinetic reaction parameters, that is, high product yield per unit time, and so the correct active phase is the basis of catalyst preparation. The chapter then looks at catalyst design methods, as well as the making of catalysts.

Chapter

Cover Applied Organometallic Chemistry and Catalysis

Olefin oligomerization and polymerization  

This chapter describes the polymerization of olefins, which is the main industrial use of organometallic catalysts. It looks first at polyketones, which can be produced by the co-polymerization of olefins with carbon monoxide. Polyketones are of particular interest as specialty polymers in the context of their superior material performance properties. The chapter also outlines the metallocene complexes of the early transition metals and the complexes of the later transition metals, which are the two types of high-activity polymerization catalysts. The chapter explains how the olefin growth reactions involved in oligomerization and polymerization are governed by a sequence of initiation, propagation, and termination steps. It talks about the distribution of chain lengths for the growth reaction that can be derived mathematically from the Schulz-Flory distribution.

Chapter

Cover Physical Chemistry for the Life Sciences

The values of rate constants  

This chapter considers the properties of rate constants. First, it distinguishes between the rate at which reactants encounter each other from the rate at which they undergo change once they have met. The very important feature of the latter step is the dependence of the relevant rate constant on temperature, which is found in most cases to obey an expression in terms of two parameters. These considerations inspire an expression for the rate at which reactants pass over an energy barrier and become products and clarifies one of the roles of enzymes acting as catalysts. The expression also inspires the introduction of parameters that resemble those used in thermodynamics. With those parameters established it is possible to see how factors other than temperature, specifically isotopic substitution and ionic strength, affect the rates of reactions.

Chapter

Cover Making the Transition to University Chemistry

Transition Metals 2  

This chapter focuses on the first row of transition metals ranging from tin to copper. It clarifies how scandium and zinc are not transition metals due to their oxidation states and d subshells. The group has d-block elements with at least one stable ion that has a partially-filled d subshell. Transition metals showcase variable oxidation states. An acidic solution with a reductant can reduce a transition metal ion, while an alkaline solution with an oxidant could oxidize a transition metal. The stability of the high oxidation states can be significantly increased in alkaline solutions. The chapter also notes how transition metals are often used as catalysts.

Chapter

Cover Atkins’ Physical Chemistry

Examples of reaction mechanisms  

This chapter cites examples of reaction mechanisms. It provides a description of a special class of reactions in the gas phase that depend on the collisions between reactants and the formation of polymers. It shows how the kinetics of their formation affects their properties and examines the general mechanism of action of enzymes, which are biological catalysts. It also analyses some important reactions that have complex mechanisms and need special treatment in order to demonstrate how to make and implement assumptions about the relative rates of the steps in a mechanism. The chapter assesses the steady-state approximation that can often be used to derive rate laws for proposed mechanisms. It highlights the setting up and testing of a rate law by proposing a mechanism and applying the steady-state approximation.

Chapter

Cover The Basis and Applications of Heterogenuous Catalysis

Changing the reactivity of catalytic surfaces  

This chapter examines the process of changing the reactivity of catalytic surfaces. If we consider any particular reaction then, in principle, it is possible to manipulate the properties of a catalyst for that reaction by any process that alters the properties of its surface. The chapter then looks at the effects of engineering the active phase of the material by placing additives at the surface. In practice, most industrial processes have additives that act as modifiers to the chemistry at the surface. Promoters can be classed as substances which, when added to a catalyst as a minor component, improve one or more of the properties of the material with respect to product formation. Meanwhile, poisons tend to be electronegative elements. At the simplest level, they block sites on the surface and so reduce the total number of centres of activity. The chapter then discusses the process of alloying.

Chapter

Cover Applied Organometallic Chemistry and Catalysis

Organometallic chemistry and catalysis  

This chapter provides a background on the vital role that catalysis plays in the production of fuels, commodity chemicals, fine chemicals, and pharmaceuticals, including as a means for strengthening environmental safeguards all over the world. It mentions the rapid development of organometallic chemistry and applications in catalytic processes, including technology based on organometallic catalysis such as olefin polymerization. It also discusses heterogenous catalysts which are used for the production of large-scale commodity chemicals, such as methanol and ammonia, and in the production of high-octane gasoline from petroleum. The chapter talks about the significance of homogeneous catalysts in the manufacture of both commodity and fine chemicals in high purity. It gives a comparison between homogeneous and heterogeneous catalysis.

Chapter

Cover Making the Transition to University Chemistry

Hydrocarbons: Arenes  

This chapter discusses arenes, a type of hydrocarbon. Benzene is known to be the archetypal arene as it features the original Kekulé structure with alternating double and single bonds. The electrophilic substitution reactions of benzene go in line with the high electron density above and below the benzene ring. Nitration is a particularly vital reaction undergone by benzene. This involves a nitrating mixture of concentrated nitric acid and sulfuric acid. Additionally, the electrophilic substitution of Friedel–Crafts acylation involves reagents of acyl chloride and aluminium chloride , the latter which acts as a Lewis acid. On the other hand, the electrophilic substitution of halogenation pertains to how benzene needs a catalyst for halogenation.

Chapter

Cover Organic Chemistry

Equilibria, rates, and mechanisms  

This chapter studies a number of thermodynamic principles, looking at equilibria, rates, and mechanisms. At any one particular temperature, the equilibrium constant is just that: constant. This provides a means of forcing the equilibrium to favour the products (or reactants) since the ratio between them must remain constant. One way to make esters in the laboratory is to use a large excess of the alcohol and remove water continually from the system as it is formed, for example by distilling it out. This means that in the equilibrium mixture there is a tiny quantity of water, lots of the ester, lots of the alcohol, and very little of the carboxylic acid; in other words, we convert the carboxylic acid into the ester. The acid catalyst does not alter the position of the equilibrium; it simply speeds up the rate of the reaction, allowing equilibrium to be reached more quickly.

Chapter

Cover Organic Chemistry

Reactions of unsaturated compounds  

This chapter assesses reactions of unsaturated compounds, focusing on electrophilic addition. In general, electrophilic addition reactions occur between an electrophile and an alkene, though other groups possessing π-bonds may also react in this way. Electrophilic addition results in the π-bond breaking with the formation of two new σ bonds, with the electrophile 'adding' to the alkene to form a new, larger, molecule. The chapter shows an example electrophilic addition in which hydrogen bromide 'adds' to an alkene π-bond. Common reagents which undergo electrophilic addition to alkenes are hydrogen halides, alcohols, and water. Acid catalysts are often used which act as an electrophile, reacting with the alkene in the first instance to form a carbocation, which is then attacked by a nucleophile.

Chapter

Cover Physical Chemistry for the Life Sciences

Enzyme action  

This chapter defines reaction rates and shows how to set up the expressions for the rate laws when enzymes are involved. Enzymes are biological catalysts that work by providing a pathway with a lower activation energy than the uncatalysed reaction. They are essential for life because the chemical reactions that have been selected by cells are inherently slow. Enzymes control these reactions in space and time. Here, the chapter introduces the Michaelis–Menten mechanism, which provides a chemical kinetics framework for describing simple enzymatic reactions. The chapter also establishes a way of assessing the efficiency of an enzyme in carrying out its role.

Chapter

Cover Elements of Physical Chemistry

Response to conditions  

This chapter addresses a very important question in chemistry, which is how to influence the yield of a reaction by increasing the equilibrium constant by changing the conditions, especially the temperature, at which the reaction takes place. Le Chatelier's principle states that when a system at equilibrium is subjected to a disturbance, the composition of the system adjusts so as to tend to minimize the effect of the disturbance. The variation of an equilibrium constant with temperature is expressed by the van 't Hoff equation. The chapter then differentiates between an endothermic reaction and an exothermic reaction. When a system at equilibrium is compressed, the composition of a gas-phase equilibrium adjusts so as to reduce the number of molecules in the gas phase. Meanwhile, the equilibrium constant of a reaction is independent of the presence of a catalyst and is independent of the pressure.

Chapter

Cover Elements of Physical Chemistry

Homogeneous catalysis  

This chapter explores homogeneous catalysis. A catalyst lowers the activation energy of a reaction, thereby accelerating it, by providing an alternative path that avoids the slow, rate-determining step of the uncatalysed reaction. A homogeneous catalyst is a catalyst in the same phase as the reaction mixture. Enzymes are very selective homogeneous catalysts that regulate the rates of biological processes. One of the earliest descriptions of the action of enzymes is the Michaelis–Menten mechanism. The chapter then considers how an inhibitor supresses the action of an enzyme. In competitive inhibition, the inhibitor competes for the active site and reduces the ability of the enzyme to bind the substrate. In non-competitive inhibition, the inhibitor attaches to another part of the enzyme molecule, thereby distorting it and reducing its ability to bind the substrate.

Chapter

Cover Inorganic Chemistry

Hydrogen  

This chapter looks at hydrogen, the most abundant element in the universe and the tenth most abundant by mass on Earth. It discusses reactions of hydrogen species that are particularly interesting in terms of fundamental chemistry as well as important applications, including energy. The chapter describes how hydrogen is produced in the laboratory, on an industrial scale from fossil fuels, and on its possible production through increasing use of renewable resources in the future. It also tackles how hydrogen bonding stabilizes the structures of water and DNA. It then summarizes the synthesis and properties of binary compounds that range from volatile, molecular compounds to salt-like and metallic solids. Furthermore, the chapter considers how the hydrogen molecule is activated by binding to catalysts, the processes that can produce hydrogen from water using solar energy.

Book

Cover Introduction to Protein Science
Introduction to Protein Science firstly outlines the topics ahead. The first main topic is protein structure and protein structure determination. The next subject the text considers is bioinformatics of protein sequence and structure. Proteins as catalysts is examined after that. This discussion particularly looks at enzyme structure, kinetics, and mechanisms. The text then moves on to describe proteins with partners, the evolution of protein structure and function, and protein folding and design. Finally, it looks at proteomics and systems biology.

Chapter

Cover The Basis and Applications of Heterogenuous Catalysis

The reactive interface  

This chapter provides a background of catalysis, which is an extremely important phenomenon for the modern industrial economy. It is a process whereby a reaction occurs faster than the uncatalysed reaction, the reaction being accelerated by the presence of a catalyst. Industrial catalysis can be divided into two broad types: heterogeneous and homogeneous. Most large-scale, industrially catalysed processes are of the former type, and the widespread recent application of catalysis to car emission control uses such solid catalysts in contact with the gas phase exhaust stream. For these kinds of reaction, the nature of the interface is crucial for the efficiency of the process. The nature of the top layer of atoms determines how fast a catalytic reaction takes place and small amounts of additives can reduce or enhance the reaction. The chapter then details the catalytic cycle and the adsorption on surfaces.

Chapter

Cover The Basis and Applications of Heterogenuous Catalysis

The effect of surface structure on reactivity  

This chapter discusses the effect of the surface structure on reactivity. Since the nature of the surface involved in heterogeneous catalysis is crucial to performance, it is important to consider the structure as a starting point for the discussion of catalytic properties. Generally speaking, surfaces with lower coordination surface atoms have the highest surface free energy, the highest reactivity for adsorption, and the strongest binding for the adsorbate (high adsorption heat). Because the surface is a region of high energy, thermodynamics dictates that there will be a tendency to minimise this energy. In nature, this occurs in several ways, including surface relaxation, surface reconstruction, sintering, and adsorption. The chapter then considers the surface structure of catalysts, as well as the structure dependence and independence of catalytic reactions. The best evidence for the influence of structure on a reaction comes from studies using model catalysts, namely single crystals.

Chapter

Cover The Basis and Applications of Heterogenuous Catalysis

Measurement of catalytic properties  

This chapter assesses the measurement of catalytic properties. The most accurate measure of the productivity of a catalyst is an industrial plant. However, industrial plants are inflexible, work in a very narrow window of temperature, pressure, and flow rate, and the catalyst cannot be readily changed. For these reasons, scaled down versions of reactors are used for catalyst testing, and the smallest of these is usually referred to as a microreactor. There are wide range of industrial reactors for heterogeneous reactions, including fixed bed reactors, multitubular reactors, fluidised bed reactors, batch reactors, and flowing bed reactors. The total surface area and pore volume are also important properties of a catalyst that determine how active it is. These can be measured by X-ray diffraction, electron microscopy and particle size distributions, and EXAFS (extended X-ray absorption fine structure). The chapter then looks at the techniques for measuring surface structure.

Book

Cover The Mechanisms of Reactions at Transition Metal Sites
The Mechanisms of Reactions at Transition Metal Sites provides an introduction to this topic. Understanding the mechanisms of the reactions at transition metal sites is a key component in designing synthetic methods, developing industrial homogeneous catalysts, and investigating metalloenzymes. The chapters here provide a broad-based and systematic guide through the fundamentals of transition-metal mechanistic chemistry. Chapters in this book cover substitution reactions, electron transfer reactions, and ligand-based reactions.

Chapter

Cover The Mechanisms of Reactions at Transition Metal Sites

Substitution mechanisms at transition metal sites  

This chapter starts off by looking at the substitution process, which is relevant to several areas of chemistry, such as the binding of substrates to the active site in both metalloproteins and homogeneous catalysts, and many electron transfer reactions. It refers to the discussion about substitution mechanisms in terms of coordination number, which proposes that each coordination type has a particular group of mechanisms that are different to those observed with other coordination numbers. It also refers to associative and dissociative mechanisms that are established in four-, five-, six-, and seven-coordinate complexes. The chapter looks at the three classes of substitution mechanisms, namely the associative mechanism, dissociative mechanism, and interchange mechanism. It analyses variations to the identity of the reaction mechanism that are associated with the relative heights of the barriers.