Low-cost Fe/SiO2 catalysts for continuous Fenton processes

Fe2O3/SiO2 materials were prepared using a simple sol-gel method and subsequent agglomeration to yield macroscopic particles of catalyst. The influence of silica source as well as the iron content in their physicochemical properties were studied and related with the catalytic performance and stability in a continuous intensified Fenton process. Likewise, the properties of these iron-containing silica materials were benchmarked with Fe2O3-SBA-15 as pelletized composite material of iron oxides particles embedded into a mesostructured silica support. The use of tetraethyl orthosilicate (TEOS) led to catalysts with specific surface areas around 250 m(2)/g that is ten times higher than that obtained when using sodium silicate as silica source. Additionally, the size of crystalline hematite nanoparticles in Fe2O3/SiO2 materials varied from ca. 2-100 nm when the iron content was increased from theoretical 5-20 wt.%. Similar catalytic activity in terms of phenol and TOC removals were obtained with all the agglomerated materials, being phenol and TOC removals higher than 90 and 50% under steady conditions, respectively. However, the stability of the iron species was different depending of the silica source and the iron loading. Thus, Fe2O3/SiO2 materials prepared with sodium silicate instead of TEOS exhibited higher stability. Concerning the iron composition, the increased of the iron loading yielded to Fe2O3/SiO2 materials with iron species less susceptible to be leached-out. The Fe2O3/SiO2 material prepared with sodium silicate and a theoretical iron loading of 20 wt.% achieved the highest resistance to the iron leaching. This material provided an expected lifetime of 760 h under continuous operation in the intensified Fenton system that is quite superior to that calculated for the Fe2O3/SBA-15 catalysts. Likewise, the production cost is only 20% of that of the Fe2O3/SBA-15 catalyst due to the absence of expensive structure direct agents as well as lower energetic requirements. (C) 2016 Elsevier B.V. All rights reserved.