A photocatalytic HC/SCR system has been developed and its high deNOx performance (54.0-98.6% NOx conversion) at low temperatures (150-250 °C) demonstrated by using a representative diesel fuel hydrocarbon (dodecane) as the reductant over a hybrid SCR system of a photocatalytic reactor (PCR) and a dual-bed HC/SCR reactor. The PCR generates highly active oxidants such as O3 and NO2 from O2 and NO in the feed stream, followed by the subsequent formation of highly efficient reductants such as oxygenated hydrocarbon (OHC), NH3, and organo-nitrogen compounds. These reductants are the key components for enhancing the low temperature deNOx performance of the dual-bed HC/SCR system containing Ag/Al2O3 and CuCoY in the front and rear bed of the reactor, respectively. The OHCs are particularly effective for both NOx reduction and NH3 formation over the Ag/Al2O3 catalyst, while NH3 and organo-nitrogen compounds are effective for NOx reduction over the CuCoY catalyst. The hybrid HC/SCR system assisted by photocatalysis has shown an overall deNOx performance comparable to that of the NH3/SCR, demonstrating its potential as a promising alternative to the current urea/SCR and LNT technologies. Superior durability of HC/SCR catalysts against coking by HCs has also been demonstrated by a PCR-assisted regeneration scheme for deactivating catalysts.
The effects of hydrocarbons (HCs) on a combined selective catalytic reduction (SCR) system by NH3 and mixed HCs for simulated exhaust over five different types of Cu2+-exchanged zeolite catalysts have been systematically examined according to the reaction temperature. CuSSZ-13 with three-dimensional (3D) small pores and CuFER with 2D medium- and small-pore channels showed good resistance to poisoning by heavy HCs such as dodecane (C12H26) and m-xylene (C8H10), while they were not tolerant to poisoning by short-chain HCs such as propylene (C3H6). The deNOx activities of CuZSM-5 and CuBEA containing 3D medium- and large-pore channels, respectively, were significantly decreased by the inclusion of C12H26 in the reaction feed stream. Another large-pore channel-based zeolite catalyst, CuMOR, showed a peculiar behavior of NOx reduction by the combined SCR: complete conversions of NO and NH3 without any side reactions in the medium-temperature region, probably due to small-pore side pockets alongside straight large-pore channels. The NH3/SCR performances of the catalysts tested varied depending on the structural features of the zeolite supports, while there were somewhat common features according to the reaction temperatures. Inhibition of surface NO oxidation by adsorbed HCs was the primary cause of the decrease in NH3/SCR performance at low temperature. In the medium-temperature region, NH3 reacted with HCs to form nitrile compounds through ammoxidation, resulting in a further decrease in deNOx activity due to a shortage of NH3 for NOx reduction. On the other hand, deNOx activity increased at high temperature due to NOx reduction by HCs present in the feed stream.
Antimiciobials were evaluated in thioglycollate broth at pH 6.5 for the ability to inhibit growth and toxin production by C. botulinum 12885A and ATCC 7949 (Type B). Methyl, ethyl, propyl, and butyl parabens (0.1%) and sorbic acid (0.2%) were effective in inhibiting growth of C. botulinum 12885A and ATCC 7949 in broth. Ethyl, propyl, and butyl parabens (0.1%) and sorbic acid (0.2%) inhibited toxin production by both strains in culture medium. Ethyl, propyl, butyl parabens (0.1%) and sorbic acid (0.2%) were individually added to a comminuted pork slurry having salt and sugar, with or without 40 ppm sodium nitrite. Cans were inoculated with a mixture of C. botulinum 12885A and ATCC 7949 spores. The canned product was abused by holding at 27°C and was observed over a 3‐month period for swollen cans. Swollen cans were examined for botulinal toxin by the mouse bioassay. Propyl and butyl paraben did not inhibit or delay toxin production. Ethyl paraben with or without nitrite delayed toxin production for 4 wk. Sorbic acid inhibited toxin for 3 wk; when 40 ppm nitrite was added to the sorbic acid treatment, toxin production was delayed for 4 wk.
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