Liquid-phase Knoevenagel reactions over modified basic microporous titanosilicate ETS-10

Al- and Ga-incorporated ETS-10, designated as ETAlS-10 and ETGaS-10, respectively, were synthesized by using P25 titania as a Ti source. The isomorphous substitution of Al and Ga for framework Si at the (4Si) environment was confirmed by ²⁹Si MASNMR measurements. ETS-10 was more active in the Knoevenagel condensation than Y-type zeolites. The introduction of Al and Ga into ETS-10 enhanced the activity, due to the increase of the ion-exchange sites, which act as Brønsted base sites. The ion exchange of Na and K in ETS-10 for larger alkali cations such as Rb or Cs caused an increase in the activity for the Knoevenagel reaction of the less reactive and less bulky substrates. ETS-10 selectively promoted the Knoevenagel condensation product compared to homogeneous amine catalysts, which produced the undesired self-condensed products of active methylene compounds.