Molecular metal carbonyl clusters and volatile organometallic compounds for tailored mono and bimetallic heterogeneous catalysts

Specific studies carried in Milan laboratory in the application of metal carbonyl clusters to preparation of supported catalysts are reviewed. Examples are reported of catalysis by heterogeneous organometallic surface species, such as 1-butene isomerisation catalysed by silica-anchored osmium carbonyl species, or of catalysis by very small metal particles produced under catalytic conditions, such as ethylene hydroformylation using silica supported [Rh-12(CO)(30)](2-) as precursor. Highly active bimetallic FeIr/MgO catalysts for methanol synthesis, have been prepared by controlled reductive decomposition of physisorbed [Et(4)N](2)[Fe2Ir4(CO)(16)] and [Et(4)N](2)[Fe2Ir2(CO)(12)] clusters. In these examples, evidence of the nature of the catalytic entities is reached by in situ DRIFTS characterisation under catalytic conditions or using EXAFS measurements. Metal particles deposited inside the zeolitic cavities have been obtained by mild reduction conditions of entrapped organometallic compounds introduced by chemical vapour deposition (CVD). In this way, non-acidic Pt/KL, Pd/NaY catalysts for hydrocarbon reforming have been prepared. Bimetallic Pt/Re and Rh/Mn particles, entrapped inside a NaY zeolite, have been easily obtained by CVD of M(2)( CO)(10) carbonyls (M = Re, Mn) on pre-reduced metal particles.