THE BENEFICIAL EFFECT OF ALKALI-METAL SALT ON SUPPORTED AQUEOUS-PHASECATALYSTS FOR OLEFIN HYDROFORMYLATION

Alkali metal salt modified SAP (supported aqueous-phase) rhodium catal ysts prepared by coimpregnation method using alkali metal chloride wer e found to be active and selective for olefin hydroformylation. The sa lt addition promoted the formation of aldehydes with high selectivity, the aldehyde yield being increased more than 2.5 times at a proper sa lt/Rh ratio. Changes in stretching frequency of the carbonyl species w ere detected during ethene hydroformylation, which appeared at ca. 162 5 cm-1 on the non-modified SAP catalyst sample, while at ca. 1586 cm-1 on the KCl-modified one, as shown by in situ IR spectroscopy. The res ults of a deuterium isotope effect experiment showed that the hydrofor mylation rate for aldehyde formation on SAP rhodium catalyst under atm ospheric pressure of CO/D2 was about 1.3 times faster than that under CO/H2, implying that the rate-determining step involved in aldehyde fo rmation is most probably a step related with hydrogen. The role of the alkali metal salt is discussed in relation with the reaction mechanis m.