CATALYTIC PROPERTIES OF 0.3-PERCENT PT/AL2O3 (EUROPT-3) AND OF 0.3-PERCENT PT-0.3-PERCENT RE/AL2O3 (EUROPT-4)

The catalysts, 0.3% Pt/Al2O3 (EUROPT-3) and 0.3% Pt-0.3% Re/Al2O3 (EUROPT-4), have been studied in a number of European laboratories in order to construct a profile of their performance, especially in structure-sensitive reactions of alkanes. Both are exceedingly active for the hydrogenation of ethene; sub-ambient temperatures had to be used to achieve conversions less than 100% under typical flow conditions, but deactivation was rapid. Hydrogenation of ethyne and of butadiene was conveniently followed between 273 and 400 K, but deactivation was again severe. Results are presented to show the normal sample-to-sample and batch-to-batch reproducibility of rates and product selectivities in propane hydrogenolysis. While this is satisfactory for the monometallic Pt/Al2O3, considerable variation is encountered with bimetallic Pt-Re/Al2O3. Extensive results are tabulated for the hydrogenolysis of ethane, propane and n-butane, as well as for n-hexane, 2- and 3-methylpentanes, methylcyclopentane (MCP) and n-octane. It is demonstrated that rates and product selectivities both depend sensitively on the pretreatment afforded to the catalysts, and on the state of surface cleanliness in respect of 'carbonaceous residues'. The sensitivity to pretreatment is understandably greater with the bimetallic catalyst, since the surface Pt/Re ratio may vary and a pure Re or Re-rich phase may be sometimes formed; unlike the Pt catalyst, however, deactivation does not lead to changes in product selectivities. With multipath reactions (e.g. of n-hexane) the effect of these factors is even more visible, and results show wide divergences. This study emphasises the overriding importance of very full control over activating pretreatments, to a degree not yet commonly practised, and of definition of reaction conditions and of surface cleanliness, if measurements of fundamental significance are to result.