No abstract

A carbon supported Pd catalyst is used in the liquid phase hydrogenation of the aromatic cyanohydrin mandelonitrile (C6H5CH(OH)CH2CN) to afford the primary amine phenethylamine (C6H5CH2CH2NH2).

Structure/function relationships in heterogeneous catalysis play an important role in catalyst design strategies. The combination of chemisorption of suitable probe molecules alongside application of infrared spectroscopy is an established technique for providing information on the metal crystallite morphology of supported metal catalysts. Following a review of key literature on this topic, a variety of experimental arrangements that may be adopted for this task are examined. Specifically, the adsorption of CO over a 5wt% Pd/Al2O3 catalyst is investigated using transmission and diffuse reflectance sampling options and two research grade spectrometers. Although comparable spectra are obtained on all the platforms examined, differences are noted. In particular, temperature-programmed IR spectroscopy on one platform enables resolution of two features assigned to linear CO bound to the Pd particles. The relevance of this sub-division of terminal sites with respect to selective hydrogenation reactions is briefly considered.

Tyramine hydrogen sulphate is produced via the heterogeneously catalysed selective hydrogenation of 4-hydroxybenzyl cyanide within a three-phase reactor.

The liquid phase hydrogenation of benzonitrile over a 5 wt % Pd/C catalyst using a stirred autoclave is investigated. The reaction conforms to a consecutive reaction sequence: first benzonitrile is hydrogenated to produce benzylamine, which subsequently undergoes a hydrogenolysis step to form toluene. Benzonitrile hydrogenation obeys first-order kinetics with an activation energy of 27.6 kJ mol–1. In contrast, the benzylamine hydrogenolysis stage obeys zero-order kinetics and exhibits an activation energy of 80.1 kJ mol–1. A 1 wt % Pd/Al2O3 catalyst is additionally examined, which is also seen to support hydrogenolysis activity alongside the hydrogenation pathway. Gas phase transmission infrared spectroscopic measurements of the hydrogenation of benzonitrile and benzylamine over the 1 wt % Pd/Al2O3 catalyst utilizing hydrogen and deuterium are undertaken, which enable reaction schemes incorporating adsorption geometries of intermediate adsorption complexes to be proposed.