Highly dispersed rhodium/polyphosphine metal catalysts: Catalytic activity for ethylene hydrogenation

Rhodium metal catalysts dispersed on polyphosphine supports were employed in the hydrogenation of ethylene. The reaction was studied in a flow reactor at 395 K and 1 atm. Turnover numbers ranged between 5.8 × 10-3 and 145 × 10-3 (molecules/sec surface atom) depending on phosphorus content. Reaction orders for olefin and hydrogen were about 0.0 and 1.0, respectively. Correlations between specific activity N and phosphorus content for various samples are reported and suggest the existence of a strong phosphorus rhodium interaction which controls the catalytic activity. This was confirmed by chemisorption measurements and activation energy data. Typical activation energy values were 5 kcal/mol for phosphinated samples and 12 kcal/mol for nonphosphinated ones.