P.M. Lugt

Selective reduction of NOx with ammonia over cerium-exchanged mordenite

Abstract Cerium-exchanged sodium-type mordenite (CeNa-MOR) was studied in comparison with a non-redox lanthanide mordenite (LaNa-MOR) and an acid-type mordenite (H-MOR) for nitric oxide reduction with ammonia in the presence of excess oxygen. The activity of CeNa-MOR was found to be high over a wide temperature range of 250–560°C. LaNa-MOR showed a similar nitric oxide conversion profile versus temperature as H-MOR, becoming substantially active only above 400°C. Bronsted acid sites are assumed to be responsible for the catalysis by LaNa-MOR, while over CeNa-MOR, two plausible reaction pathways involving the redox couple (Ce III /Ce IV ) are proposed and discussed.

Selective reduction of NOx with ammonia over cerium exchanged zeolite catalysts: Towards a solution for an ammonia slip problem

Abstract Cerium-exchanged ZSM-5 and modenite showed a high NO conversion (> 70%) and a high selectivity to N2 (>97%) at 300–600 °C for NO reduction with ammonia in the presence of oxygen. Ammonia was found to be oxidized by oxygen over these cerium zeolite catalysts exclusively towards N2 without production of N2O and NO. NO reduction with up to 30% excess of ammonia exhibited a high NO conversion and complete conversion of NH3 at 300–500 °C at a gas space velocity of 12,000 h−1. This offers a possible solution for the ammonia slip problem in a selective catalytic reduction (SCR) system with NH3. Strong NH3 adsorption up to 600°C and a high amount of adsorbed reactive NO species in associated with the redox property of cerium (CeIII/CeIV) are assumed to be responsible for the high NO reduction activity of cerium exchanged zeolite catalysts.

Catalytic removal of NOx from total energy installation flue-gases: process design and development

The flue-gases from total energy installations can be used for CO2 fertilization in greenhouses. However, the gases contain too much toxic chemicals to be led into the greenhouses untreated. At Delft University of Technology a process has been developed for the removal of these toxins. This so called ‘Delft NOx/urea process’ has been tested successfully downstream of a natural gas fired engine. Our group has described that the process could be well used for so called lean-bum engines. However, for non-lean-burn engines, which have a very high NOx output (1500 ppm), the required NOx conversion was not reached. Which was caused by high NOx concentration. Hence, the process should be optimized further for this purpose. Especially, the decomposition of urea should be given more attention. This paper focuses on this aspect. The decomposition has been investigated both theoretically and experimentally.

Catalytic removal of NOx from total energy installation flue-gases for carbon dioxide fertilization in greenhouses

Abstract A catalytic process, based on urea as a reactant to remove NOx from the exhaust gases of total energy installations driven by gas engines has been developed. A prototype has been successfully tested using a commercial gas engine.

Selective catalytic reduction of NOx in diesel exhaust gases with NH3 over Ce & Cu mordenite and V2O5/TiO2/WO3 type catalysts: Can Ce solve the NH3 slip problem?

The performance of two zeolite type catalysts on their NOx-SCR activity and their SO2 oxidative activity is compared to a vanadium type catalyst. Home made CeC selectivity decline above 450°C and SO3 formation above 400°C. However, the Ce mordenite catalyst showed high temperature (>400°C) activity without oxidation of SO2 to SO3 and NH3 to NO; a large excess of NH3 resulted only in a limited NH3 slip.

NOx reduction with ammonia over cerium exchanged mordenite in the presence of oxygen. An ir mechanistic study

Summary An IR mechanistic study of NO reduction with ammonia in the presence of oxygen was performed over cerium-exchanged mordenite (CeNa-MOR) and compared with lanthanum-exchanged mordenite (LaNa-MOR), which does not possess redox properties. The formation of NO x − (x = 2 or 3) species was observed upon NO adsorption, which was obviously enhanced in the presence of oxygen over both mordenites. These NO x − species were found to be reactive towards ammonia over cerium already at 300°C, while the same species remained unreacted over lanthanum. The importance of redox properties in this reaction is indicated.