Sonochemical degradation of ofloxacin in aqueous solutions

The use of low frequency (20 kHz), high energy ultrasound for the degradation of the antibiotic ofloxacin in water was investigated. Experiments were performed with a horn-type ultrasound generator at varying applied power densities (130-640 W/L), drug concentrations (5-20 mg/L), hydrogen peroxide concentrations (0-100 mM) and sparging gases (air, oxygen, nitrogen and argon). In general, conversion (which was assessed following sample absorbance at 288 nm) increased with increasing ultrasound energy and peroxide concentration and decreasing initial drug concentration. Moreover, reactions under an argon atmosphere were faster than with diatomic gases, possibly due to argon's physical properties (e.g. solubility, thermal conductivity and specific heat ratio) favoring sonochemical activity. Overall, low to moderate levels of ofloxacin degradation were achieved (i.e. it never exceeded 50%), thus indicating that radical reactions in the liquid bulk rather than thermal reactions in the vicinity of the cavitation bubble are responsible for ofloxacin degradation

A Novel Catalyst Ag/MgO-CeO2-Al2O3 for the Low-temperature Ethanol- SCR of NO Under Lean de-NOx Conditions

The present work reports data on a novel catalyst having excellent activity, selectivity and stability for the selective reduction of nitric oxide to nitrogen in the presence of ethanol or ethanol/hydrogen mixture as reducing agent, in the low temperature range of 150-300°C and in the presence of excess oxygen, H2O and SO2 in the feed. The novelty of the present catalyst compared to other patented ones, for the reaction at hand, lies upon the simplicity and the remarkably low Ag loading (wt%) used, characteristics that are required for a practical application. In addition, the latter catalyst shows significant activity (rate of NO reduction) at much lower temperatures (below 300°C) compared to other already patented catalysts. The present inventive catalyst consists of silver crystals that are in contact with a mixed oxide support comprised of MgO, CeO2 and Al2O3 in 1:1:2 wt% ratio. This novel catalyst presents high activity in terms of NO conversion (XNO = 60-90%) and high selectivities towards N2 (SN2 = 92-95%) and CO2 (SCO2 > 97%) in the range of 150-400°C, at a GHSV of 40,000 h-1 and using a feed stream of 0.05vol% NO, 0.1vol% EtOH, 5vol% O2 and 5vol% H2O. To our knowledge, this is the highest selectivity towards N2 and CO2 ever reported. In addition, the current catalyst shows remarkable stability with time on stream and in the presence of 5 vol% H2O and 50 ppm SO2 in the feed stream. After 48 h on stream the patented catalyst retains its stability expressed in high activity (XNO > 80%) and selectivities to N2 (SN2 > 95%) and CO2 (SCO2 > 97%)

A novel highly selective and stable Ag/MgO-CeO2-Al2O3 catalyst for the low-temperature ethanol-SCR of NO

The selective catalytic reduction of NO by ethanol under strongly oxidizing conditions (ethanol-SCR) in the wide-temperature range of 150–400 °C has been studied over Ag supported on a series of metal oxides (e.g., MgO, Y2O3, CuO, CeO2, SiO2, MgO-CeO2-Al2O3). The Ag/MgO, Ag/CeO2 and Ag/Al2O3 solids showed the best catalytic behavior with respect to N2 and CO2 yield and the widest temperature window of operation compared with the other single metal oxide-supported Ag solids. An optimum 25 wt% MgO-25 wt% CeO2-Al2O3 support composition was found in terms of specific reaction rate of N2 production (mol N2/gcat s) and CO2 selectivity. High NO conversions (60–90%), N2 selectivities (95–99%) and CO2 selectivities (>97%) were also obtained in the 150–400 °C range at a GHSV of 40,000 h−1 with the low 0.1 wt% Ag loading and using a feed stream of 0.05 vol% NO, 0.1 vol% ethanol, 5 vol% O2, 5 vol% H2O and He as balance gas. Moreover, the latter catalytic system exhibited a high stability in the presence of 50 ppm SO2 in the feed stream. N2 selectivity values higher than 98% and CO2 selectivities higher than 97% were obtained over the 0.1 wt% Ag/MgO-CeO2-Al2O3 catalyst in the 150–400 °C range in the presence of water and SO2 in the feed stream. The above-mentioned results led to the submission of a patent application for the commercial exploitation of Ag/MgO-CeO2-Al2O3 catalyst towards a new NOx control technology in the low-temperature range of 150–250 °C using ethanol as reducing agent. DRIFTS studies after adsorption of NO, and transient titration of the adsorbed surface intermediate NOx species with H2 experiments, have revealed some preliminary important information towards the understanding of basic mechanistic issues of the present catalytic system (e.g., number and location of possible active NOx intermediate species)

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)