The chemical process accompanying the hydrogenation of fats I. Geometrical isomerization
Summary1. It has been shown for numerous examples that the catalytic hydrogenation of fats is accompanied by the cis-trans isomerization of the radicals of the unsaturated acids.2. A scheme is proposed which explains the mechanism of the isomerization through a process of the hydrogenation-dehydrogenation of the olefinic compounds.
Modern State of the Multiplet Theor of Heterogeneous Catalysis
Publisher Summary This chapter reviews the modern state of the multiplet theory of heterogeneous catalysis. The multiplet theory deals with numerical values of bond lengths and bond energies, as well as with the geometrical form of reacting molecules and the crystal lattices of catalysts. This allows definite results to be obtained for many reactions on an atomic level. This is how the multiplet theory differs from a number of other theories on catalysis. The theory of the structure of matter is based on both electronic theory and quantum mechanics—the basis for the multiplet theory. Bond lengths and energies represent a stable complex of electronic properties essential for catalysis. The multiplet theory proceeds from the premise that catalysis is a chemical phenomenon and that covalent bonds require catalytic activation.
On the catalytic dehydrogenation of naphthenes I. Kinetic study
The kinetics of the dehydrogenation of naphthenes over a chromium oxide supported on alumina catalyst at temperatures of 400° C and above has been investigated. Cyclohexene has been detected and estimated in the products from cyclohexane, and it has been shown that side reactions producing olefine other than cyclohexene proceed at only 0.01 of the speed of the main reaction at 450° C. If the contact time is sufficiently long a stationary concentration of olefine is established. The linear nature of the plot of the reciprocal of the rate against the reciprocal of the pressure for cyclohexane and methyl cyclohexane has been demonstrated experimentally for the stationary state conditions, while the intercepts and slopes have been identified with functions of the rate constants. As a result of the study of the rate of dehydrogenation of cyclohexene it is concluded that the loss of the first pair of hydrogen atoms from cyclohexane is the slow step in the reaction. An activation energy of 36 kcal./g. mol. has been obtained for this step. The variation of the stationary olefine concentration with temperatures indicates that for cyclohexane and methyl cyclohexane the loss of the first pair of hydrogen atoms is the step with the highest activation energy. The variation of rate with pressure and the behaviour when nitrogen and benzene are mixed with the reactants all prove that benzene and hydrogen act mainly as diluents. Evidence is presented from the failure to attain thermodynamic equilibrium between ethyl benzene, styrene and hydrogen during the dehydrogenation of ethyl cyclohexane for a stepwise mechanism in which a large proportion of the molecules evaporate from the surface after the loss of the first pair of hydrogen atoms.