Synthesis of mesoporous iron-incorporated silica-pillared clay and catalytic performance for phenol hydroxylation

Fe-incorporated silica-pillared clays (Fe-SPCs) with ordered interlayer mesoporous structure have been synthesized through a new two-step procedure including the modification of the silica nano-pillars with potassium ferricyanide (K3Fe(CN)6) and successive calcination. X-ray diffraction, nitrogen adsorption–desorption, Fourier transform infrared spectra, X-ray fluorescence analyses, diffuse reflectance UV–vis spectra and X-ray absorption near-edge structure spectra were used to characterize the structures and the synthesizing mechanism of Fe-SPCs. Results show that all iron species were tetrahedrally coordinated with the interlayer silica nano-pillars, and the cationic surfactant molecule plays an important role in the intercalation of tetraethoxysilane and the introduction of iron into the intragallery silica framework. Moreover, the structural parameters of Fe-SPC can be adjusted by controlling the concentration of K3Fe(CN)6, as the concentration of K3Fe(CN)6 increases from 1 M to 2 M, the gallery height of Fe-SPC increases from 2.51 to 2.66 nm, while the Brunauer–Emmett–Teller (BET) surface area, pore volume and Barrett–Joyner–Halenda (BJH) pore size decrease from 856 to 794 m2/g, 0.75 to 0.69 cm3/g, and 2.2 to 2.0 nm, respectively. The Fe-SPCs show good catalytic activity in phenol hydroxylation using H2O2 as oxidant (phenol:H2O2 = 1:1, water), specifically, the phenol conversion is 46.2%, and the selectivity of dihydroxybenzenes is 70.6% at 343 K.