On the optimization of activated carbon-supported iron catalysts in catalytic wet peroxide oxidation process

Different homemade iron-activated carbon catalysts (Fe/AC) have been studied in the CWPO of phenol at mild conditions (atmospheric pressure and 50 degrees C). Both iron content and the way to introduce iron active phase in Fe/AC catalysts were analyzed to select the most stable and efficient activated carbon-supported iron catalyst. The major differences were found on their surface properties, mainly those related to iron distribution and iron particle size. Catalysts prepared by two-consecutive steps of impregnation, regardless of iron content, always presented lower leaching phenomena of iron to the reaction medium than those prepared by one-step wetness impregnation. This higher stability could be indicating an improved metal-support interaction as a consequence of the two-step methodology used to incorporate the iron, which leads to the formation of small iron particles very homogeneous in size (approximate to 3 nm). The best performance balanced between activity and stability was obtained with 2% iron 2-steps catalyst (2sFe/CN) which gave rise to complete removal of phenol after 60 min, maximal reduction of TOC content and optimal use of the stoichiometric amount of H2O2 added during batch experiments at 50 degrees C, atmospheric pressure, 500 mg L-1 catalyst loading, 100 mg L-1 and 500 mg L-1 of phenol and hydrogen peroxide concentrations, respectively, at pH(0) = 3. The study of H2O2 decomposition in the presence of an excess of MeOH, a well-known (OH)-O-center dot scavenger, has been an useful tool to analyze the behavior of heterogeneous catalysts in CWPO reactions. 2sFe/CN catalyst led to a better and efficient use of H2O2 with higher hydroxyl radical yield in the presence of phenol instead of methanol, as a consequence of phenol adsorption onto the catalyst surface which minimizes the inefficient decomposition of H2O2 at the same operating conditions. (C) 2015 Elsevier B.V. All rights reserved.