Search

The tightening emission regulations have led to the development of commercial DOCs with zoned or layered formulations allowing to cover a wide range of functionalities (i.e. CO, HC and NO oxidation as well as HC or NOx trap). Aging phenomena in such complex formulations are not well understood. To shed light on material deactivation, this study compares phosphorus poisoning and thermal sintering of two DOC monoliths with related formulations: (1) a commercial monolith comprising two catalytic layers where the top layer is rich in Pt, and (2) a model monolith containing only the top layer of the commercial monolith. The activity and characterisation (elemental analysis, microscopy and N2-physisorption) results are used to deconvolute the deactivation process of the two layers and should serve to rationalize the aging in layered catalyst formulations. [ABSTRACT FROM AUTHOR]

Polyoxymethylene dimethyl ethers (OME) produced from methanol are considered as potential substitutes of Diesel fuel. Emissions of formaldehyde and other components have been observed, particularly under cold-start conditions in engine test-bench experiments with OME fuel. In this study, the reactivity of OME3 (CH3O(CH2O)3CH3) and its decomposition products was studied in the temperature range 80–450 °C in a model gas test bench over V2O5/WO3/TiO2 and Cu-CHA SCR catalysts, a platinum-coated V2O5/WO3/TiO2 ammonia slip catalyst (ASC) and two diesel oxidation catalysts (DOC), based on platinum and platinum-palladium. Already at 80 °C, OME3 was largely hydrolyzed to methanol and formaldehyde over all catalysts. At temperatures above 150 °C, V2O5/WO3/TiO2 oxidized methanol and formaldehyde to CO via formic acid as intermediate. The platinum ASC showed a similar behavior but oxidized the decomposition products to CO2. Whereas Cu-CHA hydrolyzed OME3 quantitatively to methanol and formaldehyde, it did not show oxidation activity in the studied temperature range. The data indicate that the release of significant amounts of OME from a catalytic converter can be virtually ruled out under cold start conditions, but also that low temperature hydrolysis produces formaldehyde and methanol emissions. [ABSTRACT FROM AUTHOR]

Copyright of Grundwasser is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Increasing the use of natural gas engines is an important step to reduce the carbon footprint of mobility and power generation sectors. To avoid emissions of unburnt methane and the associated severe greenhouse effect of lean-burn engines, the stability of methane oxidation catalysts against steam-induced sintering at low temperatures (<500 °C) needs to be improved. Here we demonstrate how the combination of catalyst development and improved process control yields a highly efficient solution for complete methane oxidation. We design a material based on palladium and hierarchical zeolite with fully sodium-exchanged acid sites, which improves the support stability and prevents steam-induced palladium sintering under reaction conditions by confining the metal within the zeolite. Repeated short reducing pulses enable the use of a highly active transient state of the catalyst, which in combination with its high stability provides excellent performance without deactivation for over 90 h in the presence of steam. [ABSTRACT FROM AUTHOR]

The original article can be found online at https://doi.org/10.1007/s11244-022-01725-z. B Figure 1 b Formaldehyde (green), methanol (red), OME3 (blue), formic acid (orange), CO2 (black), methyl formate (yellow), sum of C1 carbon components (- - -). [Extracted from the article]

Catalytic methane oxidation is used in exhaust gas after treatment to reduce methane emissions in stationary combustion processes as well as in natural gas vehicles. Pd/zeolite catalysts provide higher activity than the commonly used Pd/AlO, but suffer from rapid deactivation under reaction conditions and in the presence of steam. This work presents a detailed study of deactivation of 1 wt% Pd/H-ZSM-5 catalyst in reaction conditions in dry and wet feed including characterization of both the active phase and the support. Initially well-dispersed PdO particles are not stable and sinter immediately after the exposure to the reaction mixture even in dry feed and stabilize at lower dispersion level. Despite the reasonable methane oxidation activity exhibited by the large particles, the initial PdO particles could potentially provide a 40 °C lower methane oxidation temperature. In the presence of water in the feed at moderate temperature (450 °C), support degradation governs the deactivation of the catalyst, which is evidenced by a significant decrease in BET surface area and generation of extra-framework aluminium species. These results suggest that active and stable catalysts could be obtained by careful choice and design of the support material with the aim to guarantee high dispersion of PdO. [ABSTRACT FROM AUTHOR]

Posttranslational modification of the neural cell adhesion molecule (NCAM) by polysialic acid (polySia) is crucial for nervous system development and brain plasticity. PolySia attachment is catalyzed by the polysialyltransferases (polySTs) ST8SIA2 and ST8SIA4, two enzymes with distinct but also common functions during neurodevelopment and in the adult brain. A growing body of evidence links aberrant levels of NCAM and polySia as well as variation in the ST8SIA2 gene to neuropsychiatric disorders, including schizophrenia. To investigate whether polyST deficiency might cause a schizophrenia-like phenotype, St8sia2 mice, St8sia4 mice and their wildtype littermates were assessed neuroanatomically and subjected to tests of cognition and sensorimotor functions. St8sia2 but not St8sia4 mice displayed enlarged lateral ventricles and a size reduction of the thalamus accompanied by a smaller internal capsule and a highly disorganized pattern of fibers connecting thalamus and cortex. Reduced levels of the vesicular glutamate transporter VGLUT2 pointed towards compromised glutamatergic thalamocortical input into the frontal cortex of St8sia2 mice. Both polyST-deficient lines were impaired in short- and long-term recognition memory, but only St8sia2 mice displayed impaired working memory and deficits in prepulse inhibition. Furthermore, only the St8sia2 mice exhibited anhedonic behavior and increased sensitivity to amphetamine-induced hyperlocomotion. These results reveal that reduced polysialylation in St8sia2 mice leads to pathological brain development and schizophrenia-like behavior. We therefore propose that genetic variation in ST8SIA2 has the potential to confer a neurodevelopmental predisposition to schizophrenia. [ABSTRACT FROM AUTHOR]

An analysis method was developed for the quantification of gaseous urea in model exhaust gases by FT-IR spectroscopy. The method was applied for the investigation of the catalytic thermolysis of urea, which is used as ammonia storage compound in the selective catalytic reduction of NO in diesel engines. [ABSTRACT FROM AUTHOR]

Aqueous solutions of NH-precursor compounds (i.e. urea and methanamide) were catalytically hydrolyzed in the liquid phase by applying a pressure of 50 bar during contact with the catalyst in a heated tube. Methanamide could be hydrolyzed on an Au/TiO catalyst to yield not only NH, but also H. Decomposition of urea under high pressure in the liquid phase could even be achieved without the addition of a catalyst. Due to the large excess of water present during decomposition, side products could be avoided. As the reactor tube is electrically heated, the presented method provides a possibility to reliably transform NH-precursor compounds into gaseous NH independent of the engine exhaust gas temperature. The NH-flow can be added to the main exhaust duct to enable the selective catalytic reduction of NO at the light-off of the SCR catalyst. [ABSTRACT FROM AUTHOR]

The catalytic activity of soot samples for the selective catalytic reduction (SCR) of NO with NH was investigated in dependence of the NO, NO and NH concentration in the temperature range between 200 and 350 °C. The highest NO reduction of up to 25 % was measured in the presence of both NO and NO at a GHSV of 35,000 h. Decreasing space velocities resulted in an increase of the SCR activity. In the absence of NO, NO reduction was not observed. Carbon oxidation and SCR reaction occurred in parallel due to the presence of NO and O, but hardly influenced each other, which suggested that in the NO reduction on soot most probably physisorbed species were involved. The observed stoichiometries indicated the action of the fast SCR reaction in the presence of NO and the NO SCR reaction in the absence of NO, while the observed gas phase and surface species pointed at reaction steps similar to those on classical SCR catalysts. [ABSTRACT FROM AUTHOR]

A new catalyst WO/ZrO-CeZrO (15 wt % WO/ZrO:CeZrO = 50:50) has been developed for the selective catalytic reduction of NO with NH. The redox component CeZrO was dispersed on the surface of acidic WO/ZrO by the solution combustion method showing the best NO reduction efficiency among the catalysts prepared by various modes of mixing of the components. The catalyst has been characterized by XRD, Raman spectroscopy and NH-TPD. A NO reduction efficiency of more than 90 % was obtained between 300 and 500 °C at α = NH/NO = 1. The catalyst showed stable NO reduction efficiency after hydrothermal ageing at 700 °C. Sulfur poisoning promoted the NO reduction efficiency at high temperatures at the expense of a reduced activity at lower temperatures, but the catalyst could be fully regenerated by heating in O at 650 °C. [ABSTRACT FROM AUTHOR]

thermogravimetric analyzer and a Fourier-transform infrared (FTIR) spectrometer were combined and redesigned for investigations with corrosive and condensable reactive gases. The standard gas inlet and outlet of the thermogravimetric analyzer were changed in order to heat the gas tubes, which are lead through the flanges, and avoid condensation in these parts of the system. Furthermore, all tubes upstream and downstream of the thermogravimetric analyzer were trace heated up to 180 °C. The gas measuring cell of the FTIR spectrometer was designed such that an optimum compromise between the small flow rates through the thermogravimetric analyzer and a short residence time of the gases in the gas measuring cell could be achieved. The gas supply allows the dosage of different gas compositions containing nitrogen, oxygen, water, NH, and NO, for example. The system was validated by analyzing the composition of a diesel particulate matter (PM) sample with a temperature-programmed desorption followed by oxidation (TPD/O) experiment, which showed good agreement with the established analysis methods. The reactivity of the PM sample was investigated by temperature-programmed oxidation (TPO) experiments with different reactive gas mixtures of oxygen, water, and NO in nitrogen. By adding NO, the soot oxidation started at lower temperatures and the addition of water lead to a shift of the maxima of the carbon oxidation rates to lower temperatures. The ratio of formed CO and CO was shifted to higher values by the addition of NO and water whereby the influence of water was much more pronounced. [ABSTRACT FROM AUTHOR]

In selective catalytic reduction (SCR) systems for diesel vehicles the injected urea solution decomposes to ammonia and isocyanic acid (HNCO), which reacts with water to another ammonia molecule and carbon dioxide over the SCR catalyst or a special urea decomposition catalyst. The second reaction step, i.e. the catalytic hydrolysis of HNCO was studied on the anatase TiO2(101) surface and Al2O3(100) surface with ab initio density functional theory (DFT) calculations using a cluster model as well as with in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS) investigations and kinetic experiments. The following mechanistic pathway has been identified to be most feasible: HNCO dissociatively adsorbs on the metal oxide surface as isocyanates, which are attacked by water, thereby forming carbamic acid at the surface. In a further step this intermediate is transformed to a carbamate complex, which leads to CO2 desorption and consequently NH3 formation. The comparison between the sum of the theoretical vibrational spectra of the reaction intermediates with the in situ DRIFT spectra also strongly supports the accuracy of the second reaction pathway. This mechanism holds also for the HNCO hydrolysis over γ-Al2O3 and the reactivity compared to TiO2 was found to be consistent with the heights of the barriers in the energy diagrams. Based on these promising preliminary results a computational screening has been started in order to predict the most active metal oxides and surfaces for this reaction. [ABSTRACT FROM AUTHOR]

In selective catalytic reduction (SCR) systems for diesel vehicles the injected urea solution decomposes to ammonia and isocyanic acid (HNCO), which reacts with water to another ammonia molecule and carbon dioxide over the SCR catalyst or a special urea decomposition catalyst. The second reaction step, i.e. the catalytic hydrolysis of HNCO was studied on the anatase TiO2(101) surface and Al2O3(100) surface with ab initio density functional theory (DFT) calculations using a cluster model as well as with in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS) investigations and kinetic experiments. The following mechanistic pathway has been identified to be most feasible: HNCO dissociatively adsorbs on the metal oxide surface as isocyanates, which are attacked by water, thereby forming carbamic acid at the surface. In a further step this intermediate is transformed to a carbamate complex, which leads to CO2 desorption and consequently NH3 formation. The comparison between the sum of the theoretical vibrational spectra of the reaction intermediates with the in situ DRIFT spectra also strongly supports the accuracy of the second reaction pathway. This mechanism holds also for the HNCO hydrolysis over γ-Al2O3 and the reactivity compared to TiO2 was found to be consistent with the heights of the barriers in the energy diagrams. Based on these promising preliminary results a computational screening has been started in order to predict the most active metal oxides and surfaces for this reaction. [ABSTRACT FROM AUTHOR]

The adsorption of HNCO on Fe-ZSM5 was investigated in detail by DRIFT spectroscopy and compared to the adsorption on H-ZSM5, Al2O3, SiO2, Fe2O3/Al2O3 and Fe2O3/SiO2. At 150 °C, HNCO adsorbs dissociatively on Fe-ZSM5 producing principally isocyanate species (–NCO) adsorbed on Al and Fe sites. In the presence of water the hydrolysis of the –NCO groups to NH3 was observed. Comparison of the DRIFT results with measurements of the catalytic activity of coated cordierite monoliths suggests that –NCO groups are likely intermediate species in the hydrolysis of HNCO over Fe-ZSM5. [ABSTRACT FROM AUTHOR]

The influence of the combustion products of different lubrication oil additives and impurities in fuel or urea solution on the activity and selectivity of V2O5/WO3-TiO2 catalysts in the selective catalytic reduction (SCR) of nitrogen oxides by ammonia was investigated. Focusing on the deactivation by calcium, phosphate, and potassium, the DeNO x activity followed the order K ? Ca >PO4. This trend was investigated on the structural level of the catalyst by means of temperature programmed desorption of ammonia (NH3-TPD) and a DRIFT characterization of the adsorbed ammonia species. The results suggest that the studied elements strongly reduce the acidity of the SCR catalyst in the order K ? Ca >PO4 by mainly affecting the Brønsted acidity of the surface. [ABSTRACT FROM AUTHOR]

Soot oxidation on potassium nitrate impregnated cerium oxide and manganese cerium mixed oxide was investigated using TG-FTIR. It was found, that potassium nitrate promotes the soot oxidation by enhancing the contact between the soot and the catalyst, as soot ignition temperature corresponds to the melting point of potassium nitrate for both the individual and the mixed oxide. Since potassium nitrate is easier sulfatized than cerium or manganese, the susceptibility of the catalyst to sulfur poisoning is considerably decreased. [ABSTRACT FROM AUTHOR]

A DeNOx demonstration system for a diesel engine used in construction machineries and mobile cranes was setup. In preliminary experiments various extruded and coated SCR catalysts were evaluated with and without oxidizing pre-catalyst. The data from stationary tests with two selected catalysts were used to establish various model-based control algorithms for the optimum dosage of urea in the ESC and ETC. A NOx conversion of >93% at <10 ppm average ammonia slip could be achieved at a converter-to-swept volume ratio of <2.0. [ABSTRACT FROM AUTHOR]