ABSTRACT
Three different types of NH3 species can be simultaneously present on Cu(2+)-exchanged CHA-type zeolites, commonly used in Ammonia Selective Catalytic Reduction (NH3-SCR) systems. These include ammonium ions (NH4(+)), formed on the Brønsted acid sites, [Cu(NH3)4](2+) complexes, resulting from NH3 coordination with the Cu(2+) Lewis sites, and NH3 adsorbed on extra-framework Al (EFAl) species, in contrast to the only two reacting NH3 species recently reported on Cu-SSZ-13 zeolite. The NH4(+) ions react very slowly in comparison to NH3 coordinated to Cu(2+) ions and are likely to contribute little to the standard NH3-SCR process, with the Brønsted groups acting primarily as NH3 storage sites. The availability/reactivity of NH4(+) ions can be however, notably improved by submitting the zeolite to repeated exchanges with Cu(2+), accompanied by a remarkable enhancement in the low temperature activity. Moreover, the presence of EFAl species could also have a positive influence on the reaction rate of the available NH4(+) ions. These results have important implications for NH3 storage and availability in Cu-Chabazite-based NH3-SCR systems.
Subject(s)
Ammonia/chemistry , Copper/chemistry , Organometallic Compounds/chemistry , Zeolites/chemistry , Catalysis , Models, Molecular , Oxidation-Reduction , Surface Properties , TemperatureSubject(s)
Breast Feeding , Hospital Departments , Infant Care , Obstetrics and Gynecology Department, Hospital , Rooming-in Care , Female , Humans , Infant, Newborn , Norway , Pregnancy , Time FactorsABSTRACT
A 24-year-old gravida 1 with benign molar pregnancy, which was evacuated after 12 weeks of amenorrhea, developed ovarian cysts that reached the costal margin. Afterwards, she developed thrombosis, which occluded the superior vena cava as well as the right axillary vein. Treatment with streptokinase, followed by heparin and warfarin sodium, apparently resulted in a clinically complete cure. The ovarian cysts regressed spontaneously, and regular menstrual cycles recurred.
