Preventing maritime transport of pathogens: The remarkable antimicrobial properties of silver-supported catalysts for ship ballast water disinfection

Ship ballast water (SBW) antimicrobial treatment is considered as a priority issue for the shipping industry. The present work investigates the possibility of utilizing antimicrobial catalysis as an effective method for the treatment of SBW. Taking into account the well-known antimicrobial properties of ionic silver (Ag+), five silver-supported catalysts (Ag/gamma-Al2O3) with various loadings (0.05, 0.1, 0.2, 0.5, and 1 wt%) were prepared and examined for the antimicrobial treatment of SBW. The bactericidal activity of the aforementioned catalysts was investigated towards the inhibition of Escherichia coli (Gram-negative) and Escherichia faecalis (Gram-positive) bacteria. Catalytic experiments were conducted in a three-phase continuous flow stirred tank reactor, used in a semi-batch mode. It was found that using the catalyst with the lowest metal loading, the inhibition of E. coli reached 95.8% after 30 minutes of treatment of an E. coli bacterial solution, while the inhibition obtained for E. faecalis was 76.2% after 60 minutes of treatment of an E. faecalis bacterial solution. Even better results (100% inhibition after 5 min of reaction) were obtained using the catalysts with higher Ag loadings. The results of the present work indicate that the prepared monometallic catalysts exert their antimicrobial activity within a short period of time, revealing, for the first time ever, that the field of antimicrobial heterogeneous catalysis using deposited ionic silver on a solid support may prove decisive for the disinfection of SBW

The new concept of antimicrobial catalysis: disinfection of ships ballast water

The present paper introduces the new concept of antimicrobial catalysis towards the disinfection/treatment of ships ballast water (SBW), which is considered as a priority issue for the shipping industry. Taking into account the well-known antimicrobial properties of ionic silver (Ag+), five silver supported catalysts (Ag/γ-Al2O3) with various loadings (0.05 wt%, 0.1 wt%, 0.2 wt%, 0.5 wt%, and 1 wt%) were prepared and examined for the antimicrobial treatment of ships ballast water. The bactericidal activity of the aforementioned catalysts was investigated towards the inhibition of E. coli and E. faecalis bacteria. Catalytic experiments were conducted in a three-phase continuous flow stirred tank reactor, used in a semibatch mode. It was found that using the catalyst with the lowest metal loading, the inhibition of E. coli reached 95.8% after 90 min of treatment of an E. coli bacteria containing solution, while the inhibition obtained for E. faecalis was 76.2% after 60 min of treatment of an E. faecalis bacterial solution. The results of the present work indicate that the prepared monometallic catalysts exert their antimicrobial activity within a short period of time, revealing, for the first time ever, that the field of antimicrobial heterogeneous catalysis using deposited ionic silver on a solid support may prove decisive for the disinfection of SBW

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)