Catalytic removal of pharmaceutical compounds in water medium under an H2 stream over various metal-supported catalysts: A promising process

All rights reserved.Abstract: To date, very few prescriptive studies have been reported in the literature concerning the catalytic removal of pharmaceutical substances in wastewater using H2 in the presence of O2 for the in situ formation of H2O2, while the mechanism of the reaction has not been studied in detail yet. Hydrogen peroxide is a potent oxidizing agent used extensively in catalytic wet air oxidation (CWAO) applications and can be used for the elimination of pharmaceuticals from waste water. In the present work, an attempt has been made to elucidate the actual effects of the in situ production of hydrogen peroxide on the CWAO of pharmaceuticals. Therefore, the effects of the nature of the active phase (Pd, Pt, and Rh), as well as the feed gas composition have been examined toward the reaction at hand. The results showed that 1% Pd/Al2O3 and 1% Rh/Al2O3 are the most effective catalysts for the elimination of paracetamol from the reaction medium using hydrogen-rich streams, having a conversion of up to 70% in 2 h. A maximum conversion of paracetamol of 90% was obtained in just 30 min of reaction over 1 wt.% Rh/Al2O3, when using pure hydrogen in the feed. Total organic carbon measurements performed over the latter catalyst showed that practically no organic carbon is removed from the liquid phase, indicating the conversion of paracetamol to a different organic (probably aromatic) compound, through hydrogenation. Toxicity tests that followed showed a dramatic decrease in the toxicity of the products solution, indicating that paracetamol hydrogenation might be a promising method for the elimination of its toxicity

Novel catalytic and mechanistic studies on wastewater denitrification with hydrogen

Presented at: IWA Regional Conference on Waste and Wastewater Management, Science and Technology, 2013, Limassol, Cyprus, 26-28 JuneThe present work reports up-to-date information regarding the reaction mechanism of the catalytic hydrogenation of nitrates in water media. In the present mechanistic study, an attempt is made, for the first time, to elucidate the crucial role of several catalysts and reaction parameters in the mechanism of the NO3-/H2 reaction. Steady-state isotopic transient kinetic analysis (SSITKA) experiments coupled with ex situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were performed on supported Pd-Cu catalysts for the NO3-/H2 and NO3-/H2/O2 reactions. The latter experiments revealed that the formation and surface coverage of various adsorbed active intermediate N-species on the support or Pd/Cu metal surface is significantly favored in the presence of TiO2 in the support mixture and in the presence of oxygen in the reaction's gaseous feed stream. The differences in the reactivity of these adsorbed N-species, found in the present work, adequately explain the large effect of the chemical composition of the support and the gas feed composition on catalyst behaviour (activity and selectivity). The present study leads to solid mechanistic evidence concerning the presence of a hydrogen spillover process from the metal to the support. Moreover, this study shows that Cu clusters are active sites for the reduction of nitrates to nitrites

The effect of several parameters on catalytic denitrification of water by the use of H2 in the presence of O2 over metal supported catalysts

The present paper involves a detailed study of the selective catalytic reduction of nitrates in aqueous mediums by the use of H2 in the presence of O2 over monometallic and bimetallic supported catalysts. In this study, an attempt has been made to improve the denitrification efficiency (XNO3-, SN2) of several catalysts by regulating some experimental parameters that are involved in the process. Therefore, the effects of the type of reactor (semi-batch reactor vs continuous flow reactor), the nature of the active phase (Pd, Cu, and Pd-Cu) and the particle size of γ-Al2O3 spheres (particle diameter= 1.8 mm and 3 mm) on catalytic activity and reaction selectivity, as well as the adsorption capacity of γ-Al2O3 spheres for nitrates, were examined. As the review indicates, most of the research has so far been conducted on batch or semi-batch reactors. This study successfully demonstrates the benefits of using a continuous flow reactor in terms of catalytic activity (XNO3-, %) and reaction selectivity (SN2, %). Another important aspect of this study is the crucial role of bimetallic Pd-Cu clusters for the prevention of NH4+ formation. Moreover, the use of 1.8 mm diameter γ-Al2O3 spheres as a support was proved to significantly enhance the catalytic performance of bimetallic Pd-Cu catalysts towards nitrate reduction compared to 3 mm diameter γ-Al 2O3 spheres. This difference may be attributed to mass (NO3-, OH-) transfer effects (external mass transfer phenomena)

New insights into the antimicrobial treatment of water on Ag‐supported solids

BACKGROUND: Silver (Ag) has been long known to be a strong antimicrobial agent and has been used as such either as AgNO3 or in the form of nanoparticles. The antimicrobial activity of nanosilver is believed to be due to free metal ion toxicity, the consequent generation of excess reactive oxygen species and inhibition of gene expression in several cells. RESULTS: The antimicrobial activity of Ag/Al2O3 spheres was studied after suppression of free Ag ions by using a suitable complexing agent (Ag+ scavenger). It was found that Ag/Al2O3 retained its antimicrobial activity even after the addition of the Ag+ complexing agent, which is in contrast to the behaviour of an AgNO3 solution which became completely inactive. Initial/preliminary transmission electron microscopy and Fourier transform infrared studies indicate possible phospholipid residues on the Ag-supported solid surface. •OH radicals were confirmed to be formed during the antimicrobial process. CONCLUSIONS: The present work provides strong evidence that the antimicrobial property of Ag-supported solids is not exclusively due to the dissolution of surface silver (free Ag+). A possible simplified mechanism is proposed in which the initiation of the antimicrobial reaction is proposed to be a heterogeneous intersurface process, which might include the interaction between the partially positively charged, surface silver atoms and the negatively charged outer membrane (OM) of microbes, and the subsequent activation of a free radical mechanism. Further study and confirmation of the above findings might be decisive for the development of novel Ag-supported solids with limited metal surface dissolution but strong antimicrobial activity useful for the confrontation of particular environmental challenges