Optimization of the MnCeOx system for the catalytic wet oxidation of phenol with oxygen (CWAO)

A class of MnCeOx catalysts has been synthesized via the new redox-precipitation route in alternative to the conventional co-precipitation technique. The effects of preparation method, composition and calcination temperature on catalyst texture, dispersion and reduction pattern properties have been addressed. Redox-precipitated systems exhibit high surface area (SA, 120–170 m2/g), large pore volume (PV, 0.4–0.5 cm3/g) and a “narrow” pore size distribution (PSD) in a wide range of the Mn/Ce ratio (1/3–3/1). A quasi-molecular dispersion markedly improves oxide-support interactions and reducibility of the active phase. Redox-precipitated systems show a superior performance in the catalytic wet oxidation of phenol with oxygen (CWAO) at 373 K in terms of substrate and total organic carbon (TOC) elimination and mineralization (i.e., CO2 formation) selectivity. Carbon mass-balance from TG-DSC data of used catalysts and CO2 selectivity values signal that the CWAO of phenol proceeds via a L–H reaction path, the oxidation of C-containing species being the rate limiting step (r.l.s.). Then, an optimum average pore diameter (APD, 10–15 nm) enhances the rate of the adsorption step, while a straight relation between CO2 selectivity and reducibility prove that dispersion and redox properties of the active phase control the mineralization activity of the MnCeOx system.