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The activity of monometallic (Pd or Rh) and bimetallic (iron-bearing) catalysts has been tested in the HDC of 4-chlorophenol (4-CP) in aqueous phase. The catalysts were prepared by a simple procedure consisting of incipient wetness impregnation followed by calcination and reduction at different temperatures. This allowed controlling the size, dispersion and oxidation state of the metallic nanoparticles. Increasing the temperature of calcination led to a higher dispersion of the active phase (from 21 to 46% by increasing the calcination temperature from 200 to 400 °C) and a higher ratio of zerovalent to electrodefficient palladium (M 0 /M n + values from 1.15 to 2.17) in the case of the Pd-catalysts. Those calcined in air at 400 °C and reduced with H 2 at 350 °C yielded the highest values of the pseudo-first-order rate constant of 4-CP dechlorination (16.2 L h −1 g cat −1 ). The introduction of iron reduced the metal dispersion of both Pd and Rh but the catalysts maintained their dechlorination activity and showed magnetic properties useful for further separation from the liquid phase. [ABSTRACT FROM AUTHOR]

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]