Der magnetokatalytische Effekt der Ortho-Para-Wasserstoff-Konversion an Nickelkatalysatoren

Abstract

In a preceding paper Justi and Vieth investigated the influence of external magnetic fields upon the catalytic activity of ferromagnetic substances. The reaction p-H₂ →η-H₂ was chosen for this study because it cannot lead to secondary chemical products which might be deposited upon the catalyst, thereby altering its surface. In spite of this elimination of systematic experimental errors a considerable margin of errors still persisted owing to seemingly uncontrollable temporal fluctuations of the activity of the catalyst caused by the necessary interruptions of the gas stream. These fluctuations may, in the relatively long time intervals lapsing between consecutive withdrawals of samples for static analysis, simulate spurious systematic effects. Therefore the thermal method for measuring and registering the concentrations of p- and o-hydrogen was further developed thus that the values are measured and registered in so short time intervals that a practically continuous curve is obtained which no longer needs any arbitrary interpolation. The increase of accuracy thus achieved was used in the first instance for a renewed study of the Hedvall effects, i. e. the alterations of the activity of nickel in the Curie interval. The diagrams obtained show with great certainty that the activation energy and the frequency factor of the p-n-H₂-conversion are smaller above than below the Curie temperature of nickel. This result is in line with the known behaviour of the adsorption of hydrogen in the transition from para- to ferromagnetism. When studying other reactions, e. g. decomposition of N₂O and formic acid, Hedvall et al. have observed an increase of the activation energy and of the temperature coefficient when transgressing the Curie temperature. This difference between their and our findings is nevertheless quite in line with Hedvalls perception of the basic changes in the catalyst underlying the phenomena observed and becomes understandable if the results of Suhrmann and Sachtler are considered, who show that alterations of the energy of electron emission may have widely differing effects upon the activation of reactions with electronegative and electropositive adsorbates respectively.