Fe-PILC

Oxidation intermediates and reaction pathways of wet hydrogen peroxide oxidation of p-coumaric acid over (Al-Fe)PILC catalyst... 

In the present study, we have focused our attention on the catalytic wet peroxide oxidation of p-coumaric acid over (Al-Fe)PILC. This phenolic molecule was chosen as a representative of the biologically recalcitrant polyphenolic compounds present in olive oil processing and wine distillery wastewaters. 

The intercalant solution was prepared by titration of an Al3+/ Fe3+cationic solution with 0.2 molL"1 NaOH. The cationic solution contained 0.18 and 0.02 molL"1 of A1C13 and FeCl3, respectively. The NaOH solution was slowly added to the cationic solution at 70°C until the OH/cation molar ratio was equal to 1.9. The intercalant solution was added to the clay suspension under stirring. The final ( Al+Fe) /clay ratio was equal to 3.8 mmol/g of dry clay. After aging for 24h, the pillared clay precursor was washed until total elimination of chloride ions, dried at 60°C and finally calcined at 500°C for 5h. The resulting material is (Al-Fe)PILC. 

Fig 1 shows the rate of p-coumaric acid solution (500ppm) and TOC removals during the phenolic compound oxidation over (Al-Fe)PILC catalyst (0.5g/l), as well as the uncatalysed reaction in slurry at 70°C. 

It can be seen that p-coumaric acid was slowly oxidised without catalyst, only 20% of substrate was converted and 5% of TOC was removed in 4hours of reaction. The use of (Al-Fe)PILC catalyst remarkably increased the rates of both p-coumaric acid and TOC removals in the reaction mixture under mild reaction conditions (temperature of 70°C, atmospheric pressure, [H2O2]=2.10"2M). The fact that the fast removal of p-coumaric acid was accompanied by a rather slower TOC reduction implies that intermediates which are stable and resistant to further total oxidation had been formed. 

Figure 2. Concentration profile of p-Coumaric acid (A) p-hydroxybenzoic acid ( ) and p-hydroxybenzaldehyde ( ). ([p-coumaric] = 500 ppm, pHi= 3.5, T=343 K, [H202] = 2xl0 2 M, 0.5g/l (Al-Fe)PILC).

The unmodified and modified pillared clays, synthesized using amines or with mixed pillars, have an intermediate hydrophylic-hydrophobic character and thus have some potential for the removal of chlorinated hydrocarbons. In Figure 12, the adsorption isotherms of some hydrocarbons on different pillared clays are compared to the adsorption isotherm on Na-montmorillonite (79). In all cases, the adsorption capacity of the mixed Fe-/Zr-PILC is a factor 4 higher than that of the pure Fe-PILC. Besides the adsorption capacity, the isotherm type also changes. 

Table 6 Porosity and Adsorption Characteristics (N2 and O2 at 273 K on Al- and Zr-PILC and at 194 K on Fe-PILC) of Pillared Clays, Prepared Without and With Templates...

Oxides Bentonite Zr-PILC Al-PILC Cr-PILC Fe-PILC Ti-PILC... 

Fig. 6. Illustration of some pillaring precursors for Al-PILC (A), Zr-PILC (B), Ti-PILC (C) and Fe-PILC (D)...

As an example, Heylen et al. showed that the incorporation of chromium in iron oxide pillars has a positive effect on the adsorption affinity for cyclohexane, CCI4 (Peq=4.7x 10 Pa), and CO2 (P,q=4.7x 10 Pa) at 273 K [33]. An improvement of the selectivity as well as the capacity was noticed for the mixed Fe/Cr-PILC in comparison to the parent Fe-PILC. 

Heylen et al. reported a surface area and a micropore volume which was 2.5 times higher for an Fe-PILC synthesized with butylammonium as template, in comparison to the unmodified Fe-PlLC [27]. An important increase in the adsorption capacity towards Nj, Oj and CO at 194 K (Pgq=4.5x 10 Pa) has been observed after the modification. Adsorption capacities of 0.23 mmol/g, 0.17 mmol/g and 0.30 mmol/g for, respectively, Nj, O2 and CO were reached for the modified BuA-Fe-PILC. When compared to the adsorption on the unmodified Fe-PILC, the following capacities were obtained 0.00 mmol/g N2, 0.03 mmol/g O2 and 0.27 mmol/g CO. Also, it is proven that ammonium templates can be used to optimize the Zr-pillaring of laponite leading to enhanced pore volumes and surface areas. 

Catrinescu, C., Arsene, D., Apopei, P., and Teodosiu, C. (2012) D radation of 4-chlorophenol from wastewater through heterogeneous Fenton and photo-Fenton process, catalyzed by A1 Fe PILC. Appl. 

The latter species are those active in the total phenol oxidation by hydrogen peroxide. These species are also rather stable against leaching. The authors reported long-time (350 h) catalytic experiments in a continuous flow reactor that showed the high stabihty of the Al-Fe-PILC. However, stabihty in continuous flow reactor experiments has not been reported in other studies of WHPCO reactions. This is the critical problem for the industrial development of the process. 

The isotherms of Al-PILC and Zr-PILC are of type I, indicating the small dimensions of the pillars. The shape of the adsorption isotherm of Fe-PILC resembles a type II isotherm (nonporous). The isotherm of Ti-PILC is close to type IV, but with a distortion in the relative pressure range 0.05-0.5 followed by capillary condensation. The distortion is due to the presence of pores on the border region between micro- and mesopores (1.5-3.5 nm). Isotherms of intermediate shape can also be observed, for example, alumina PILC doped with lanthania (LaAl-PILC) (31). For some PILC materials, the presence of a large hysteresis loop in the isotherm might be observed, indicating the importance of mesopores in the structure. From the adsorption isotherm data, several parameters describing the porosity can be quantitatively derived. 

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