Pillared clays from natural resources as catalysts for catalytic wet peroxide oxidation: Characterization and kinetic insights

Abstract

Pillared clays with Zr and Fe/Cu/Zr polycations have been prepared from natural clays found in large deposits of Kazakhstan and assessed as catalysts for the catalytic wet peroxide oxidation (CWPO), using 4-nitrophenol (4-NP) as model compound. The performance of the catalysts was followed by measuring the concentration of 4-NP, H2O2 and the total organic carbon (TOC), considering C4-NP = 5 g L-1 , CH 2 O 2 = 17.8 g L-1 , Ccat = 2.5 g L-1 , initial pH = 3.0 and T = 50°C. At those selected conditions, the pillared clays showed higher activity than natural clays in the CWPO of 4-NP. The conversion of the model pollutant was complete when Fe/Cu/Zr-PILCs were used, with the TOC removal reaching 78.4% after 24 h with the best Fe/Cu/Zr-PILC. The H2O2, 4-NP and TOC time-evolution was well described by a kinetic model based on TOC lumps in three blocks, considering the initial TOC (corresponding to 4-NP), the production of oxidizable intermediates and the formation of refractory products.

The pH effect on the kinetics of 4-nitrophenol removal by CWPO with doped carbon black catalysts

“…Small aliquots were periodically withdrawn from the reactor to determine 4-NP, its oxidized intermediates and H 2 O 2 concentration by HPLC and a colorimetric method, as previously described [34,38]. Briefly, 4-NP and its aromatic oxidation products (hydroquinone, 1,4benzoquinone, 4-nitrocatechol, catechol and phenol), low molecular weight carboxylic acids (formic, acetic, oxalic, malonic, maleic and malic acids) and nitrates, were determined by using a Jasco HPLC system at wavelengths of 318, 277 and 210 nm (UV-2075 Plus detector), respectively.…”

“…Within this context, catalytic wet peroxide oxidation (CWPO) appears more advantageous AOP [30,31], since run with a heterogeneous catalyst which can be recovered after the process [11,32,33]. However, most of the studies regarding the CWPO of 4-NP deals with the development of catalysts containing iron, such as hybrid magnetic graphitic nanocomposites [34], nano-magnetite [35], fly ash [36], ferrous hydroxide colloids [37], Fe/Cu/Zr-clays [38], or carbon nanotubes produced onto iron catalysts [34][35][36][37]39]. In those studies, high conversions of 4-NP were achieved, but generally ascribed to an homogenous contribution, as consequence of iron leaching to the reaction media, which results in an additional contamination.…”

Wet Peroxide Oxidation of Paracetamol Using Acid Activated and Fe/Co-Pillared Clay Catalysts Prepared from Natural Clays

“…The acid activated clay (KO-A) is able to adsorb more nitrogen, resulting in the sample with the best textural properties (Table 1), namely the highest BET surface area and total pore volume (28 m 2 g −1 and 94.6 mm 3 g −1 , respectively). The development of porosity by the acid activation of natural clays could be expected to be higher than observed, but natural clays used in this work possess high amount of impurities in the form of quartz (>45%), limiting the porous development [21]. The pillarization of these clays does not result in an increment of the specific surface area or pore volume, also as a consequence of the quartz content of the natural clays employed, as discussed in previous works [21].…”

“…The development of porosity by the acid activation of natural clays could be expected to be higher than observed, but natural clays used in this work possess high amount of impurities in the form of quartz (>45%), limiting the porous development [21]. The pillarization of these clays does not result in an increment of the specific surface area or pore volume, also as a consequence of the quartz content of the natural clays employed, as discussed in previous works [21]. Figure 2 gathers the XRD diffractograms of the Kokshetau and Karatau based samples.…”

“…Although this technology represent an interesting alternative, it has been scarcely studied so far for micropollutants abatement [18,20]. Clays play a prominent role as a catalyst in the field of organic pollutants removal by CWPO [21][22][23][24][25]. In this regard, natural clays can be chemically modified to increase their performance by different methods, such as activation or pillarization.…”