A Novel Synthesis Method of Al/Cr Pillared Clay and its Application in the Catalytic Wet Air Oxidation of Phenol

Abstract

Natural bentonite clay was pillared with Al and Cr polycations (Al-PILCs and Cr-PILCs) as well as with both Al and Cr mixed polycations (Al/Cr-PILCs) at different Al/Cr molar ratios. The structural and textural properties of the pillared clay catalysts were characterized by various techniques, such as high resolution scanning electron microscopy with energy dispersive system, powder X-ray diffraction, adsorption–desorption of N2 at − 196 °C, Fourier transform infrared spectroscopy, thermogravimetric analysis, cation exchange capacity and zeta potential. The obtained results showed that the intercalation of polycations in the interlamellar space of clay led to changes in the clay properties, basal spacing and specific surface area of a mixed PILCs were higher compared to single PILCs. Moreover, diffractograms of the Cr-PILCs confirmed the presence of a Cr2O3 phase. The catalytic wet air oxidation (CWAO) of the phenol was studied in a batchwise slurry reactor, at the experimental conditions of 100 °C temperature, 10 bar oxygen (O2) partial pressure, at pH 3.0, 100 mg/L concentration and 0.4 g of catalyst. All catalysts were analysed to determine the conversion of phenol and removal of total organic carbon (TOC). The results showed that, Al-PILCs displayed higher removal of phenol and TOC conversion than Cr-PILCs. In the case of mixed Al/Cr-PILCs, maximum removal values of phenol and TOC conversion were achieved with Al/Cr molar ratio of 1:1. Moreover, aromatic intermediate products as catechol, hydroquinone and benzoquinones which are identified in the beginning of the phenol oxidation oxidized into short-chain carboxylic acids such as oxalic acid, maleic acid, formic acid, acetic acid and malonic acid. The obtained results demonstrate the potential of Al/Cr-PILCs catalyst as robust and cheap catalyst for CWAO of phenol under mild reaction conditions.