Selective hydrogenation of cinnamaldehyde over Raney cobalt catalysts modified with salts of heteropolyacids

The hydrogenation of cinnamaldehyde to cinnamyl alcohol was carried out ove r Raney cobalt catalysts modified by Cu3/2PMo12O40 It was found that the co nversion of cinnamaldehyde decreases substantially with increases in the am ount of Cu3/2PMo12O40 deposited on Raney cobalt catalysts. The maximum yiel d of cinnamyl alcohol varies with the amount of deposited Cu3/2PMo12O40 The more the deposited modifier, the higher the attainable maximum yield of ci nnamyl alcohol. With 2.8% Cu3/2PMo12O40 modified Raney cobalt, the selectiv ity fbr cinnamyl-alcohol does not change with reaction temperature and reac tion time. Thus, it is likely that the selectivity of ca. 80% for cinnamyl alcohol represents a specific value which is related to the nature of the s urface modifier, Cu3/2PMo12O40 The influences of the heteropolyanions and t he competitive cations on the conversion and the selectivity were also inve stigated. It was found that copper salts of different heteropolyacids actin g as the modifier of the catalyst bring about different enhancements in the selectivity for cinnamyl alcohol. The order of enhancement of selectivity in terms of heteropolyacid anion is PMo12O403- > SiMo12O404- > PW12O403-. T here is little difference in selectivity by modification with (NH4)(6)Mo7O2 4 and Cu2SiMo12O40. Raney cobalt catalyst modified by different 12-molybdop hosphate containing cations of alkali, alkaline earth and transition metals gives a similar selectivity of about 75%. Among all of the 12-molybdophosp hates, that containing the cation Cu2+ is the best in improving the selecti vity of the catalysts. A selectivity as high as 83% was attained when an am ount of 2.8% Cu3/2PMo12O40 was deposited on the catalyst. (C) 1999 Elsevier Science B.V. All rights reserved.