Highly effective Cu-HMS catalyst for hydroxylation of phenol

Abstract

Transition metals copper and titanium substituted mesoporous silicas (Cu-HMS and Ti-HMS) were synthesized at ambient temperature by using dodecylamine (DDA) surfactant as templating agent. XRD measurements prove that incorporating titanium and especially copper into the mesostructures causes the d100 peaks of mesoporous silicas to become shifted to lower angles, indicating progressive expansion of the lattice d-spacings upon heteroatoms Ti and especially Cu incorporating. FT-IR measurements indicate that the calcined Cu-HMS and Ti-HMS samples all exhibit a weaker absorption band near 960 cm-1 which may be rather a fingerprint of the heteroatom on the matrix of [SiO4] units whatever its crystallization state. Cu-HMS possesses relatively high catalytic activity for the hydroxylation of phenol with 30% aq. H2O2 in aqueous solution (about 36% phenol conversion and more than 95% selectivity for dihydroxybenzene isomers), but Ti-HMS has no catalytic activity under the same reaction conditions. The product distribution obtained from Cu-HMS is completely different from that of the microporous titanium silicalite zeolites (TS zeolites). This is attributed to the porous structural differences between Cu-HMS and TS zeolites. The catalytic activity of the Cu-HMS is strongly dependent on the nature of the solvent; the Cu-HMS does not have any catalytic activity in the presence of organic solvents such as methanol or acetone instead of water. A reusing test of the recovered Cu-HMS indicates that the recovered catalyst suffers almost loss of activity and must be regenerated by calcination in air at 873 K in order to recover its activity.