Insights into the effects of modifying factors on the solvent-free synthesis of FeAPO-5 catalysts towards phenol hydroxylation

Abstract

A modified solvent-free method has been developed to synthesize FeAPO-5 zeolite catalysts with hierarchical porous structure as well as high crystallinity and iron content. The effects of mechanochemical and low-temperature pretreatment, as well as the addition of hydrogen peroxide and seed crystals on the synthesis of FeAPO-5 were studied in detail. The composition and structural features of relatively pure resultant products were deeply analyzed by XRD, SEM, ICP-AES, CHN analysis, TG–DTA, UV–Vis diffuse reflectance spectroscopy and N2 physisorption. Most importantly, low-temperature pretreatment towards H2O2-containing precursor mixtures can to a great degree improve the crystallinity of FeAPO-5 molecular sieve. Significantly, compared to the conventional micron-sized microporous FeAPO-5 zeolite, the hierarchical FeAPO-5 catalysts created by this modified solvent-free method show superior performance in phenol hydroxylation, in which the one with a high content of framework iron species exhibits the best catalytic performance, giving phenol conversion of about 40% and dihydroxybenzene selectivity of up to 80% at 50 °C within 3 h reaction time.