Strikingly Distinctive NH3-SCR Behavior over Cu-SSZ-13 in the Presence of NO2

Commercial Cu-exchanged small-pore SSZ-13 (Cu-SSZ-13) zeolite catalysts are highly active for the selective catalytic reduction (SCR) of NOx with NH3, but distinct from other catalyst systems, their activity is unexpectedly inhibited in the presence of NO2. Here, we combined kinetic experiments, in-situ/operando X-ray absorption spectroscopy, and density functional theory (DFT) calculations to obtain direct evidence that under reaction conditions, strong oxidation by NO2 forces Cu ions to exist mainly as fixed framework Cu2+ species (fw-Cu2+), which impede the formation of dynamic binuclear Cu+ species that serve as the main active sites for the standard SCR (SSCR) reaction. As a result, the SSCR reaction is significantly inhibited by NO2 in the zeolite system, and the NO2-involved SCR reaction occurs with an energy barrier higher than that of the SSCR reaction on dynamic binuclear sites. Moreover, the NO2-involved SCR reaction tends to occur at the Brønsted acid sites (BAS) rather than the fw-Cu2+ sites. This work clearly explains the strikingly distinctive selective catalytic behavior in the zeolite system.

Early Identification of Acute Kidney Injury in the Icu With Real-time Urine Output Monitoring: A Clinical Investigation

BackgroundThe inconsistencies in classifying AKI according to the KDIGO (Kidney Disease: Improving Global Outcomes) urine output (UO) criteria have prevented an accurate assessment of the role this easily available biomarker can play in the early identification of AKI. Study goal: To assess and compare the performance of the two KDIGO criteria (SCr and UO) for early identification of AKI in the intensive care unit (ICU) by comparing the standard SCr criteria to real-time, consecutive, electronic urine output measurements. Methods95 catheterized patients in the GICU of Hadassah Medical Center, Israel were connected to The RenalSense™ Clarity RMS™ sensor kit to monitor UO electronically (UOelec). UOelec and SCr were recorded between 24-48 hours and up to one week, respectively, after ICU admission. ResultsReal-time consecutive UO measurements identified significantly more AKI patients than SCr in the patient population, 57.9% (N=55) versus 26.4% (N=25), respectively (P<0.0001). In 20 patients that had AKI according to both criteria, time to AKI identification was significantly earlier by the UOelec criteria as compared to the SCr criteria (P<0.0001). Among this population, the median (IQR) identification time of AKI UOelec was 12.75 (8.75, 26.25) hours from ICU admission and 39.06 (25.8, 108.64) hours for AKI SCr. ConclusionApplication of KDIGO criteria for AKI using continuous electronic monitoring of UO identifies more AKI patients, and identifies them earlier, than using the SCr criteria alone. This application can enable the clinician to set protocol goals for earlier intervention of the treatment of AKI.

Alternate pathway for standard SCR on Cu-zeolites with gas-phase ammonia

Redox mechanisms have been theorized for the selective catalytic reduction (SCR) of NOx over small-pore Cu-zeolites.

Inhibitory role of excessive NH3 in NH3-SCR on CeWOx at low temperatures

An inhibitory effect of excessive NH3 on NH3-SCR on CeWOx at low temperatures was found, and H2O rendered the inhibitory effect insignificant for standard SCR.

Detection of key transient Cu intermediates in SSZ-13 during NH3-SCR deNOx by modulation excitation IR spectroscopy

Protagonists in the standard SCR reaction have been caught in the act by modulation excitation IR & XAFS spectroscopy.

Effect of the NH4NO3 Addition on the Low-T NH3-SCR Performances of Individual and Combined Fe- and Cu-Zeolite Catalysts

We have measured NOx conversions and N2O productions over Fe-BEA and Cu-SAPO catalysts and over their sequential arrangements under Enhanced SCR conditions, resulting from the addition of an aqueous solution of ammonium nitrate (AN) to the typical Standard SCR feed stream, and we have compared them to those observed under Standard and Fast SCR conditions. The expected strong enhancement of the poor low temperature activity of the Fe-BEA catalyst was confirmed: both NH3 and NOx conversions and N2O formations similar to those of the Fast SCR reaction were achieved when cofeeding ammonium nitrate. On the other hand, the Cu-SAPO efficiency was drastically decreased by the addition of AN at low temperatures, possibly due to trapping of the ammonium nitrate salt within the SAPO zeolite, characterized by smaller pores than those of the BEA zeolite. The Cu-SAPO performances were recovered only at T > 250 °C with a huge release of N2O due to the thermal decomposition of AN. The combined system with the Fe-zeolite sample placed upstream of the Cu-zeolite also exhibited outstanding low temperature deNOx performances, with even lower N2O production than over the Fe-zeolite only at the same Enhanced SCR (E-SCR) conditions.

Reaction mechanism and chemical kinetics of NH3-NO/NO2-SCR system with vanadium-based catalyst under marine diesel exhaust conditions

As one of the most effective NOx emission removing technologies to meet the Tier III limitation by International Maritime Organization, urea-selective catalytic reduction (SCR) technology is starting to be used in two-stroke marine diesel engines. Based on the two-cycle catalytic mechanism proposed by Topsoe, in combination with the exhaust characteristics of the marine diesel, expansion studies on detailed SCR reaction model were carried out in this paper. According to the temperature dependence of reaction pathway, SCR reaction model was divided into three parts: low temperature reaction pathway, standard SCR reaction pathway, and high temperature oxidation pathways, and an expanded NH3-NO/NO2-SCR reaction model for V2O5 catalyst was proposed in the paper. In order to verify the accuracy of the expanded SCR reaction model, simulating and testing studies of SCR reaction under marine diesel conditions were carried out with a commercial extruded V2O5/TiO2 catalyst. The simulation values are agreed well with experimental values at 150–500 ℃, and kinetics characteristics of SCR reaction process under V2O5/TiO2 catalyst can be predicted accurately with the expanded NH3-NO/NO2-SCR reaction model.

Catalyst systems for selective catalytic reduction + NOx trapping: from fundamental understanding of the standard SCR reaction to practical applications for lean exhaust after-treatment

Physical mixtures of NOx adsorbers and SCR catalysts both for fundamental studies and for abatement of cold start NOx emissions.

Adaptive Sampling for Spatial Capture-Recapture: An efficient sampling scheme for rare or patchily distributed species

Rare species present challenges to data collection, particularly when the species is spatially clustered over large areas, such that the encounter frequency of the organism is low. Sampling where the organism is absent consumes resources, and offers relatively low-quality information which are often difficult to model using standard statistical methods. In adaptive sampling, a probabilistic sampling method is employed first, and additional effort is allocated in the vicinity of sites where some measured index variable - assumed to be proportional to local population size - exceeds an a priori threshold. We applied this principle to the spatial capture-recapture (SCR) analytical framework in a Bayesian hierarchical model incorporating capture-recapture (CR) and index information from unsampled sites to estimate density. We assessed the adaptively sampled SCR model (AS-SCR) by simulating CR data and compared performance with a standard SCR baseline (F-SCR), adaptive SCR discarding index information (AS-SCR–), and standard SCR applied at a simple random sample of sites. Under AS-SCR, we observed minimal bias and comparable variance with respect to parameter estimates provided by the standard F-SCR model and sampling implementation, but with substantially reduced effort and significant cost saving potential. This represents the first application of adaptive sampling to SCR.