Stephen Robert Tennison

Metal-support interactions in heterogeneous catalysis

Abstract This paper considers the range over which a catalyst support can be expected to influence the electron density of states of a metal particle. Nickel on carbon is chosen as a model system and calculations are reported for (111) nickel layers in epitaxial relationship with the graphite basal plane. Atoms are described by a spherically symmetrical Wakoh potential and the calculations use a Green function method. They show that, with only two intervening layers of nickel, the effect of the carbon support on the metal density of states is vanishingly small. The effect of the support on catalyst reactivity is therefore very localised. It is shown that such a short range effect would lead to a strong influence of catalyst dispersion (D) on reactivity, which will be proportional to D5 for spherical particles and approximately to D2 for hemispheres. A further set of calculations also indicate that the poisoning effect of an adsorbed carbon atom on a Ni(100) layer is localised to nearest neighbour nickel atoms.

The Genesis and Development of the Commercial BP Doubly Promoted Catalyst for Ammonia Synthesis

In the 1970s BP started developing a new catalyst for ammonia synthesis which in final form comprises ruthenium, two promoters and a graphitised carbon support. This became the first new catalyst for ammonia synthesis to be commercialised since Fritz Haber’s promoted iron catalyst. The catalyst is commercialised in the KBR Advanced Ammonia Process (KAAP). We describe the development of the catalyst, starting in the 1960s with studies to elucidate the mechanism of selective hydrogenation catalysts using nickel single crystals and LEED. These identified a phenomenon dubbed surface reorientation, in which an adsorbate such as sulphur causes the structure of the surface monolayer of a metal to change e.g. from fcc [111] to [100]. These ideas led to discovery of an active platinum/alkali metal/carbon catalyst for the dehydrocyclisation of hexane. That catalyst was not commercial, but it led in turn to the identification of highly active ruthenium/alkali metal/carbon catalysts for ammonia synthesis. The best new catalyst is about 20 times more active than a commercial Haber catalyst. The special carbon support is mesoporous and graphitic. Scale up of catalyst production and testing are described briefly, as are some process considerations.Graphical Abstract

The use of carbons produced from phenolic resins for flue gas desulphurization

Abstract Novel high-performance carbon adsorbents were produced by heat-treatment and carbonization of phenolic resin. They were compared with conventional activated carbons for the removal of SO 2 from combustion gases, and the nature of the interactions occurring on the carbon surface was clarified. Using a gas Chromatographic technique, isotherms for the physisorption of SO 2 were determined at appropriate temperatures for flue gas treatment. Selected carbons were then evaluated in a flow system and the effect of oxygen and water was studied. The new carbons exhibited a superior performance under all conditions, providing enhanced SO 2 uptake and easier regeneration. Measurement of the proportion of SO 2 and CO 2 present during regeneration also revealed less adsorbent wastage due to oxidation, implying that complete conversion of adsorbed SO 2 to sulphuric acid did not occur.