Catalysis of Organic..

362Synthesis of PseudoiononesTable 3 Catalytic activity data obtained on Li-promoted MgO samples aCatalystInitial citralconversion rate0rcit(µmol/min m 2 )Initial PSformation rate0rPS(µmol/min m 2 )PS Yield b , η PS (%)CisisomerTransisomerMgO 6.3 6.2 49.2 32.5Li/MgO-1 7.8 7.6 48.5 36.7Li/MgO-2 15.4 14.9 51.5 39.8Li/MgO-3 21.2 20.5 51.1 41.9Li/MgO-4 16.6 16.6 47.6 40.9Li/MgO-5 15.2 15.2 32.7 25.5a 0At T = 353 K, nDMK= 0.8 moles, nb At 6 h reaction time.0cit= 0.016 moles, W Cat. = 0.5 gamounts of Li improve the MgO activity for the formation of pseudoionones;however, Li concentrations higher than about 0.5 wt. % are detrimental becausecause the η PS to decrease. In order to explain these results, and also in an attempt torelate the catalytic behavior of the samples with their surface base properties, wecompared the catalyst activity data of Table 3 with the base site densities given inTable 2. We obtained a good correlation between the initial PS formation rate andthe density of strong base sites (n O ) as it is shown in Fig. 6. In contrast, a poor0correlation was found when rPSwas plotted against the density of weak (n OH ) or100η PS (Carbon atom %)908070600 0.4 0.8 1.2 1.6 2.0 2.4 2.8Li + loading (wt. %)Figure 5. Effect of Li amount in Li/MgO samples on pseudoionone yield