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

摘要

The hydrogenation of cinnamaldehyde to cinnamyl alcohol was carried out over Raney cobalt catalysts modified by Cu_3/2PMo_(12)O_(40) deposited on Raney cobalt catalysts. The maximum yield of cinnamyl alcohol varies with the amount of deposited Cu_(3/2)PMO_(12)O_(40). The more the deposited modifier, the higher the attainable maximum yield of cinnamyl alcohol. With 2.8% Cu_(3/2)PMo_(12)O_(40) modified Raney cobalt, the selectivity for cinnanyl alcohol does not change with reaction temperature and reaction 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 surface modifier, Cu_(3/2)PMo_(12)O_(40). The influences of the heteropolyanions and the competitive cations on the conversion and the selectivity were also investigated. It was found that copper salts of different heteroployacids acting 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 heteroployacid anion is PMo_(12)O~(3+)_(40) >SiMo_(12)O~4-_(40) > PW_12O~3-_(40) > PW_(12)O~(3-)_(40). There is little difference in selectivity by modification with (NH_4)_6Mo_7O_24 and Cu_2SiMo_(12)O_(40). Raney cobalt catalyst modified by different 12-molybdophosphate containing cations of alkali, alkaline earth and transition metals gives a similar selectivity of about 75%. Among all of the 12-molybdophosphates, that containing the cation Cu~(2+) is the best in improving the selectivity of the catalysts. A selectivity as high as 83% was attained when an amount of 2.8% Cu_(3/2)PMo_(12)O_(40) was deposited on the catalyst.