Preparation of ceria-zeolite catalysts by different techniques and its effect on selective catalytic reduction of NO with NH3 at high space velocities

Topics in Catalysis - Several zeolite-based catalysts containing Ce3+ and/or CeO2 were prepared by a variety of catalyst preparation techniques like ion exchange, solid-state ion exchange,...     

Selective Catalytic Reduction of NO with NH3 over Fe-ZSM-5 Catalysts Prepared by Sublimation of FeCl3 at Different Temperatures

Fe-ZSM-5 catalysts were prepared by subliming FeCl₃ into H-ZSM-5. The method used allowed Fe-ZSM-5 catalyst preparation by FeCl₃ exchange at a desired sublimation temperature and was found to be more precise. The sublimation of FeCl₃ into H-ZSM-5 was carried out at 320 and 700 °C. Fe-ZSM-5 prepared by sublimation of FeCl₃ at 320 °C followed by rapid heating to 700 °C and the catalyst prepared by subliming FeCl₃ at 700 °C were found to be more active for NO reduction with NH₃ in the presence of simulated exhaust gases containing water vapor than catalysts prepared by subliming FeCl₃ at 320 °C. To determine the active sites, the catalysts were characterized by H₂-TPR, in situ DRIFTS of NO adsorption, NH₃-TPD, XRD and chemical analysis methods. The observed NO conversion differences in selective catalytic reduction using NH₃ could be correlated to the iron cation species present at different locations determined from diffuse reflectance infrared spectroscopy. Enhanced NO reduction activity was obtained when positions in Fe-ZSM-5, corresponding to Fe²⁺(NO) band at 1877 cm^-1 in DRIFTS, were preferentially occupied.     

Functions of OECD Water Governance Principles in assessing water governance practices: assessing the Dutch Flood Protection Programme

ABSTRACT

The OECD Principles on Water Governance aim to contribute to good water governance. Learning and change through assessments are useful ways to strengthen water governance systems. This article presents a methodology for a learning assessment based on the OECD principles. The methodology has been applied to the Dutch Flood Protection Programme. The analysis revealed various functions of the OECD principles, from enhancing understanding to reforming the agenda, reflection and informed action. Recommendations are given on how the OECD principles can be used to come to meaningful action-oriented water governance assessments; they include contextualization, multiple methods, inclusiveness and periodic assessments.     

Preparation of Ceria-Zeolite Catalysts by Different Techniques and Its Effect on Selective Catalytic Reduction of NO with NH3 at High Space Velocities

Several zeolite-based catalysts containing Ce³⁺ and/or CeO₂ were prepared by a variety of catalyst preparation techniques like ion exchange, solid-state ion exchange, impregnation and physical mixing and are characterised. Selective catalytic reduction was evaluated using simulated exhaust gas containing NO _x , NH₃, O₂ and H₂O at high space velocities (>180000 h^–1) in the temperature window 150–600 °C. The activity and selectivity in NO _x reduction was found to strongly depend on the charge compensating ions, crystallite size of the zeolite and CeO₂ content in the catalyst. CeO₂ mixed with zeolite having H⁺ or Ce³⁺ co-cations showed benificial effect and increased the NO _x conversion and selectivity. Among the different zeolite materials studied, the structure and the strength and amount of Brønsted acidity did not influence the NO _x conversion.