Academic literature on the topic 'Platinum. Substitution reactions. Oxidation-reduction reaction'

For most purposes, inorganic reactions can be classified as either substitution reactions or oxidation-reduction reactions. The latter involve the transfer of at least one electron from the reducing agent to the oxidizing agent. Such reactions are widely used in analytical procedures and are important in many biological processes. One of the mechanistic types in this area is unique in having a fairly simple theoretical basis for predicting rate constants in solution from measurable input parameters. Oxidation-reduction reactions have been classified in two general ways; the first, historically, is by stoichiometry and the second is by mechanism. The Stoichiometric classification only requires a knowledge of the reaction stoichiometry but has limited kinetic applicability. The change in oxidation state of the reducing agent is the same as the change in oxidation state of the oxidizing agent.

In ligand substitution reactions, one or more ligands around a metal ion are replaced by other ligands. In many ways, all inorganic reactions can be classified as either substitution or oxidation-reduction reactions, so that substitution reactions represent a major type of inorganic process. Some examples of substitution reactions follow: The operational approach was first expounded in 1965 in a monograph by Langford and Gray. It is an attempt to classify reaction mechanisms in relation to the type of information that kinetic studies of various types can provide. It delineates what can be said about the mechanism on the basis of the observations from certain types of experiments. The mechanism is classified by two properties, its stoichiometric character and its intimate character. The Stoichiometric mechanism can be determined from the kinetic behavior of one system. The classifications are as follows: 1. Dissociative (D): an intermediate of lower coordination number than the reactant can be identified. 2. Associative (A): an intermediate of larger coordination number than the reactant can be identified. 3. Interchange (I): no detectable intermediate can be found. The intimate mechanism can be determined from a series of experiments in which the nature of the reactants is changed in a systematic way. The classifications are as follows: 1. Dissociative activation (d): the reaction rate is more sensitive to changes in the leaving group. 2. Associative activation (a): the reaction rate is more sensitive to changes in the entering group. This terminology has largely replaced the SN1, SN2 and so on type of nomenclature that is still used in physical organic chemistry. These terminologies are compared and further explained as follows: Dissociative [D = SN1 (limiting)]: there is definite evidence of an intermediate of reduced coordination number. The bond between the metal and the leaving group has been completely broken in the transition state without any bond making to the entering group. Dissociative interchange (1d= SN1): there is no definite evidence of an intermediate. In the transition state, there is a large degree of bond breaking to the leaving group and a small amount of bond making to the entering group.

The copper-chlorine (Cu-Cl) thermochemical cycle uses both heat and electricity to carry out a series of chemical and electrochemical reactions with the net reaction being the splitting of water into hydrogen and oxygen. The process forms a closed loop with all intermediate chemicals being recycled. All of the chemical and electrochemical reactions can be carried out at temperatures that do not exceed about 530°C. Thus, the heat requirement of this process can be satisfied by intermediate temperature nuclear reactors such as the Super Critical Water Reactor (SCWR) developed in Canada by Atomic

The catalyst layer (CL) in polymer electrolyte membrane (PEM) fuel cells is one of the key components regulating the overall performance of the cell. In PEM fuel cells, there are two CLs having identical composition for hydrogen oxidation (HO) and oxygen reduction (OR) reactions. There are four phases inside the CL, namely: carbon, Pt particles, ionomer and voids. In this work, a micro-model of the cathode CL has been developed mathematically using finite volume (FV) technique to investigate the transport phenomena of reactants and product species, ions and electrons by incorporating the above