Enzyme activity of Chromic Luvisols under different degree of erosion and land use

Soil erosion is a serious environmental problem and a threat to the sustainable agriculture production. Little information is available on enzyme activities of eroded soils in Bulgaria, especially on their relations to the degree of erosion and soil properties. In this work, slightly, moderately and severely eroded Chromic Luvisols under different land use (pasture, crop field and virgin) were studied. Enzyme activities (invertase, catalase and phosphatase), total nitrogen, total carbon, available phosphorus contents and soil particle distribution were determined and possible relations between them were examined. Data showed that enzyme activities tended to lower with increasing the degree of erosion. This was better pronounced for invertase and phosphatase in pasture and virgin soils. Depending on land use, all enzyme activities decreased in the order pasture > virgin > crop field soils, showing positive impact of soil cover and negative effect of cultivation practices. Soil invertase and phosphatase activities were in close relations with soil carbon content. The activities of catalase and phosphatase correlated positively with soil clay. Invertase only was in positive relation with soil silt and in negative relation with the sand content. Data obtained are intended to contribute to development of biological indicators of eroded soils

Interzeolite Conversion of FAU Type Zeolite into CHA and its Application in NH3-SCR

In this work we studied the potential feasibility to synthesize small pore zeolites, such as chabazite (CHA) via interzeolite conversion of FAU type zeolite. We have thereafter used CHA as the starting material to obtain Cu-CHA. When CHA in NH4 (+) form was used to prepare Cu-CHA, the large size of the potassium cation present in the structure caused pore blockage in the chabazite framework, and diminished the adsorption and exchange capacity. However, Cu-CHA with comparable Selective Catalytic Reduction performance to the commercial catalyst was obtained via ion exchange if Cu-exchange was performed from H+-CHA form. Still, the main challenge was to fully eliminate K+ from the zeolite structure in order to further improve its catalytic performance and high temperature stability

Improved low-temperature SCR activity for Fe-BEA catalysts by H2-pretreatment

A series of iron-exchanged zeolite beta catalysts (0.5 - 4 wt.-% Fe) have been prepared by incipient wetness impregnation and tested for selective catalytic reduction (SCR) of NOx with ammonia as reductant. The catalysts were characterized using BET, NH3-TPD and XPS before and after H2-pretreatment at 650\ub0C for 5 h. The NH3-SCR activity tests show that the samples pretreated by hydrogen exhibit higher low-temperature SCR activity compared to the fresh samples, while the high-temperature activity remains almost constant. The results clearly show that the high-temperature H2-treatment has a significant influence on the extent of different iron species formed in the zeolite. Furthermore, H2-treatment of hydrothermally aged samples can recover some of the initial activity, although not completely due irreversible dealumination during the ageing. By H2-pretreatment SCR catalysts with high iron loading and high activity can be prepared

Mechanistic investigations of the promoting role of Rh on the NSR performance of NOx storage BaO-based catalysts

To determine the promoting effect of Rh on the overall NOx storage and reduction (NSR) performance, the studies in the current work were directed toward investigating the storage and release ability over Rh NOx storage BaO-based catalysts compared to Pt. In terms of the metal surface dispersion and the ability of the noble metals to release oxygen at lower temperatures, the synthesized catalysts were characterized by means of dynamic CO chemisorption (RT) and N2O dissociation (RI - 773 K). The NOx storage capacity and the thermal stability of the NOx adsorbed species formed on the surface were analyzed via NOx storage tests and temperature programmed desorption (TPD) without and in the presence of CO2 and H2O. In addition, experiments with lean and rich cycling were conducted at 473,573 and 673 K. The results from the N2O dissociation experiments showed the superior ability of Rh/Al and Rh/Ba/Al catalysts compared to Pt toward O-2 release from the catalytic surface at lower temperatures. In this work, we show that the presence of Rh into the BaO/gamma-Al2O3 system has a considerable effect on the spill-over process of NOx to the precious metal, controlling the subsequent desorption of NOx to occur at lower temperatures in comparison with that of the Pt catalysts. It is suggested a mechanism of NOx desorption where the lower temperature of O-2 release from the surface of Rh catalysts could leave a significant number of noble metal sites accessible for adsorption. Thus this could facilitate the rate of spill-over of NOx from the storage site (the surface sites on gamma-Al2O3 and those on BaO) to the noble metal and their desorption at lower temperatures. The limited NOx storage ability of the Rh-based BaO/gamma-Al2O3 catalysts under lean-burn conditions was found to originate from both low NO oxidation activity and NOx reduction activity, while the main limiting factor for the low NSR performance of the Pt-based catalysts was the limited regeneration ability during rich period

Experimental evidence of the mechanism behind NH3 overconsumption during SCR over Fe-zeolites

Isotope labeled (NO)-N-15 was used to investigate the mechanism of the unusual overconsumption of NH3 during standard SCR over Fe-zeolite, under conditions during which NH3 oxidation with O-2 alone (without NO) was unfavorable. When the Fe-BEA catalyst was exposed to the (NO)-N-15 + (NH3)-N-14 + O-2 gas mixture at 250 and 300 degrees C, the resulting products included (NO)-N-14, a product of (NH3)-N-14 oxidation under SCR conditions. However, (NO)-N-14 was not detected when Fe-BEA was exposed to (NH3)-N-14 + O-2. Since the only source of N-14 derives from (NH3)-N-14, with the labeled gas mixture used, the (NO)-N-14 during SCR must have originated from oxidation of (NH3)-N-14. Furthermore, twice as much (NN)-N-14-N-14 was observed at 300 degrees C under SCR conditions in comparison with NH3 oxidation using O-2 alone. Under SCR conditions, the (NO)-N-14 formed through the unusual oxidation route further reacted with (NH3)-N-14 to produce N-14(2). Thus, for the first time, we have experimental evidence for the unusual overconsumption of ammonia during SCR over Fe-zeolites

Influence of hydrothermal ageing on NH3-SCR over Fe-BEA -Inhibition of NH3-SCR by ammonia

The decay in ammonia adsorption capacity and the amount of active iron sites are important to consider in order to understand the deactivation processes of Fe-BEA as NH3-SCR catalyst. NH3 and NO storage capacity experiments together with kinetic modeling have been used to evaluate ammonia inhibition during NH3-SCR before and after hydrothermal treatment of H-BEA and Fe-BEA. The kinetic model shows that at least four types of acid sites for H-BEA and one additional site for Fe-BEA are required to predict the NH3 desorption well. NH3-TPD experiments together with simulations show that the strongest adsorption sites are the sites that are most affected by the hydrothermal treatment. For H-BEA a clear correlation between the ammonia storage capacity and the improved NOX conversion after NH3 cut-off during NH3-SCR is observed. However, Fe-BEA show an inhibiting effect of ammonia after NH3 cut-off but no significant difference (i.e. increased NOX conversion time) between fresh and aged samples can be observed, indicating that the inhibiting effect is unaffected by the hydrothermal treatment