Pt-Ir, the rational scientific design

While there appears to be an element of serendipity in the success of Pt-Re formulations, the invention of Pt-Ir catalysts is an example of engineering desirable properties by rational scientific design.8 

Sinfelt and coworkers91 demonstrated the potential benefits of Ir-alumina, especially in dehydrocyclisation, where it was more than twice as active as Pt, nearly twice as active as Pt-Re, and significantly more stable in hydrocarbon conversion. Ir aids spillover.7 Exxon patented its use in 1972.94 Somorjai134 found that Pt2lr foil was three times more active than the equivalent Pt foil in the cyclisation of iso-hexane to methyl cyclopentane. Very low Ir suppresses carbon deposition in an essentially Pt-like catalyst.135 This levels may be the philosophy behind IFP s RG 432 catalyst.127 

In a comparison between with Pt and Pt-Re, Pt-Ir catalysts have the following characteristic performance, when suitably moderated by sulphur.91 138 

Barbier demonstrated that Pt, Pt-Re and Pt-Ir catalyst all exhibit plateau behaviour for benzene hydrogenation and C/Ptacc ratio as a function of time.139 

There is little doubt that Pt-Re is the industrial standard for S/R technology, possibly because the interaction is reversible and achievable in-situ due to the mobility of Re in an oxidising environment, leading to an apparent reproducibility of repeated regenerations. Conversely there is an element of irreversibility in the Pt-Ir formulation under similar conditions. 

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