Solid-State Kinetic Investigations of Nonisothermal Reduction of Iron Species Supported on SBA-15

Iron oxide catalysts supported on nanostructured silica sba-15 were synthesized with various iron loadings using two different precursors. structural characterization of the as-prepared fexoy/sba-15 samples was performed by nitrogen physisorption,x-ray diffraction,dr-uv-vis spectroscopy,and mössbauer spectroscopy. an increasing size of the resulting iron species correlated with an increasing iron loading. significantly smaller iron species were obtained from (fe(iii),nh4)-citrate precursors compared to fe(iii)-nitrate precursors. moreover,smaller iron species resulted in a smoother surface of the support material. temperature-programmed reduction (tpr) of the fexoy/sba-15 samples with h2 revealed better reducibility of the samples originating from fe(iii)-nitrate precursors. varying the iron loading led to a change in reduction mechanism. tpr traces were analyzed by model-independent kissinger method,ozawa,flynn,and wall (ofw) method,and model-dependent coats-redfern method. jmak kinetic analysis afforded a one-dimensional reduction process for the fexoy/sba-15 samples. the kissinger method yielded the lowest apparent activation energy for the lowest loaded citrate sample (ea ≈ 39 kj/mol). conversely,the lowest loaded nitrate sample possessed the highest apparent activation energy (ea ≈ 88 kj/mol). for samples obtained from fe(iii)-nitrate precursors,ea decreased with increasing iron loading. apparent activation energies from model-independent analysis methods agreed well with those from model-dependent methods. nucleation as rate-determining step in the reduction of the iron oxide species was consistent with the mampel solid-state reaction model. © 2017 n. s. genz et al.