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Abstract: A ferromagnetic γ-Al2O3-supported iron catalyst has been prepared and its activity and stability in catalytic wet peroxide oxidation (CWPO) have been compared with those of a previous iron-based conventional catalyst using the same support. Both catalysts were characterized by nitrogen adsorption–desorption isotherms, ICP, TXRF, XRD, XPS, elemental analysis and Mössbauer spectroscopy. The behavior of these catalysts in CWPO of chlorophenols has been related with the nature of the dominant iron species (magnetite or hematite). The results showed that the magnetic catalyst improved significantly the decomposition of H2O2 leading to an increased degradation and mineralization of chlorophenols. Complete conversion of those target pollutants and more than 75% TOC reduction were achieved after 4h under stoichiometric H2O2 dose, 100mgL−1 initial chlorophenol concentration, 1gL−1 catalyst, pH 3 and 50°C temperature. Moreover, complete dechlorination of all the chlorophenols tested was achieved, being the residual organic by-products short-chain acids without significance in terms of ecotoxicity. The catalyst showed a remarkable stability in long-term continuous experiments with limited Fe leaching, below 5% of the initial loading after 100h on stream. An additional clear advantage of the new catalyst is its easy separation and recovery from the reaction medium by applying an external magnetic field. [Copyright &y& Elsevier]

Abstract: Hydrodechlorination of 4-chlorophenol using Pd/A2O3 as catalyst at mild conditions (30°C, 1atm) was carried out in plain water, buffered (CH3COOH/NaCH3COO, NaH2PO4/Na2HPO4 and NaHCO3/Na2CO3) and alkaline NaOH media at different pH. The highest reaction rate was achieved when the process was carried out at alkaline NaOH solution of pH=8.5. Continuous long term experiments (τ: 5.4kgcat h/mol) were performed in plain water and alkaline medium using Pd/Al2O3 and Pd/AC as catalysts. The former showed an appreciable loss of activity upon time on stream, which was associated with the formation of palladium chloride complexes. However, a residual activity remained practically stable, reaching very similar 4-chlorophenol conversion (36%) in both reaction media. The Pd/AC catalyst maintained a constant activity at a 70% 4-chlorophenol conversion once the steady state was reached. This suggests that the AC supported catalyst is less susceptible to the chloride poisoning produced during the reaction. [Copyright &y& Elsevier]

Abstract: We have examined the catalytic action of 1mol% Au/TiO2 and Ag/TiO2 in the continuous gas phase hydrogenation of a series of para-substituted (–H, –OH, –OCH3, –CH3, –Cl and –NO2) nitroarenes. Both catalysts promoted exclusive –NO2 group reduction, resulting in the sole formation of the corresponding amino-compound. The catalysts have been characterized in terms of temperature-programmed reduction (TPR), H2 chemisorption, BET area, diffuse reflectance UV–vis, X-ray diffraction and HRTEM measurements. The formation of zero valent Au and Ag is established post-TPR. Au/TiO2 showed a narrower metal particle size (1–10nm) distribution than Ag/TiO2 (1–15nm) but both catalysts exhibited a similar surface area weighted mean size (6–7nm). A time-invariant nitroarene conversion has been established where Au/TiO2 delivered higher specific hydrogenation rates. We associate this response to an enhanced reactant activation on Au/TiO2 to generate a negatively charged intermediate, consistent with a nucleophilic mechanism. The presence of electron-withdrawing substituents is shown to enhance –NO2 reduction rate. This effect is quantified in terms of the Hammett relationship where a linear correlation between the substituent constant (σ i ) and rate is established and a higher reaction constant (ρ) was recorded for Au/TiO2 (0.93) relative to Ag/TiO2 (0.22). The data generated provide the first direct comparison of the catalytic action of supported Au and Ag in the hydrogenation of substituted nitroarenes and establish the viability of both catalysts to promote selective –NO2 group reduction. [Copyright &y& Elsevier]

In this work, polymer-based spherical activated carbon (PBSAC) (dp = 500 μm) has been used as support to synthesize several Pd/PBSAC (1% wt.) catalysts. These catalysts have been tested in the hydrodechlorination (HDC) of 4‐chlorophenol (4-CP) in aqueous phase under ambient-like conditions (30 °C, 1 atm) at [4-CP] 0 = 3.9 mmol L −1 ; [catalyst] 0 = 1 g L −1 and 50 N mL H 2 min −1 . A sequential calcination (200 °C, air atmosphere) − reduction (80 °C, H 2 atmosphere) treatment was required to obtain active HDC catalysts with a convenient proportion of zero-valent and electrodefficient Pd species. This catalyst allowed to achieve complete conversion of 4-CP in 90 min reaction time, giving rise to phenol as main reaction product. An expanded kinetic model accounting for both consecutive reaction and sorption processes was used to successfully fit the experimental data. The values obtained for the effective rate constant of 4-CP disappearance (3.26–10.88 × 10 −4 s −1 ) and apparent activation energy (31.6 kJ mol −1 ) were close to the previously reported for powdered supported Pd catalysts. Remarkably, the catalyst showed a high stability in long-term continuous application (100 h on stream). [ABSTRACT FROM AUTHOR]