NOx Removal Catalysis

This paper surveys the most important catalytic emission control technologies being employed or near commercialization for the removal of nitrogen oxides (NOx) from the exhausts of mobile sources under lean conditions. Urea/Ammonia-SCR systems and NOx Storage/Reduction (NSR) catalysts will be addressed, with particular attention to the specific demands related to the mobile applications. In the first part of the paper the transient kinetics of standard de-NOx SCR reaction over commercial V-W/Ti SCR catalysts and the dynamic model of the honeycomb reactor will be addressed. Then the validation of the dynamic model with integral reactor measurements and full-scale transients in vehicles will be illustrated. The second part presents a complete and quantitative understanding of the NOx storage chemistry of a Pt-Ba/Al2O3 “Lean NOx Trap” catalyst

Labeled 15NO Study on N2 and N2O Formation Over Pt–Ba/Al2O3 NSR Catalysts

Mechanistic aspects involved in the formation of N2 and of N2O during the reduction of NO, stored nitrites and stored nitrates in the presence of NO are investigated in this work by means of isotopic labeling experiments over a model PtBa/Al2O3 NSR catalyst. The reduction of gaseous labeled NO with unlabelled NH3 leads to the formation of N2O at low temperature (below 180 °C), and of N2 at high temperature. All N2 possible isotopes are observed, whereas only labeled molecules have been detected in the case of N2O. Hence the formation of nitrous oxide involves undissociated NO molecules, whereas that of N2 can be explained on the basis of the statistical coupling of 15N- and 14N-adatoms on Pt. However, due to a slight excess of the mixed 15N14N isotope, a SCR-like pathway likely operates as well. The reduction of the stored labelled nitrates is very selective to N2 and all isotopes are observed, confirming the occurrence of the recombination pathway. However also in this case a SCR-like pathway likely occurs and this explains the abundance of the 14N15N species. When the reduction of the stored nitrates is carried out in the presence of NO, this species is preferentially reduced pointing out the higher reactivity of gaseous NO if compared to the nitrates

Inactivation of palladium-based oxygen scavenger system by volatile sulphur compounds present in the headspace of packaged food

An oxygen scavenger based on a catalytic system with palladium (CSP) was recently developed to remove oxygen in food packagings. Although the CSP worked with various types of food, with some foods, an inhibition of the CSP was observed. Because such catalytic systems are susceptible to poisoning by sulfurcontaining compounds, the aim of this study was to understand the inactivation of palladium-based catalysts in presence of foods containing volatile sulfur compounds (VSCs). To achieve this, the oxygen scavenging activity (OSA) of the CSP was evaluated in presence of selected food products. Afterwards, VSCs mainly present in these foods were exposed to the CSP, and the influence on the OSA was evaluated. Finally, headspace analysis was performed with the diluted VSCs and with the packaged food products using proton transfer reaction time-of-flight mass spectrometry. It was found that the catalytic activity of the CSP was inhibited when VSCs were present in the headspace in concentrations ranging between 10.8–36.0 ppbv (dimethyl sulfide, DMS), 1.2–7.2 ppbv (dimethyl disulfide), 0.7–0.9 ppbv (dimethyl trisulfide), 2.1–5.8 ppbv methional) and 4.6–24.5 ppbv (furfuryl thiol). It was concluded that in packaged roast beef and cheese, DMS may be the compound mainly responsible for the inactivation of the CSP. In packagings containing ham, the key compounds were hydrogen sulfide and methanethiol; in peanuts, it was methanethiol; and in par-baked buns, an accumulation of methional, DMS, butanethiol and methionol. When potato chips were packaged, it was demonstrated that when VSCs are present in low concentrations, oxygen can still be scavenged at a reduced OSA

Pyrazolate-Bridged NHC Cyclometalated [Pt2] Complexes and [Pt2Ag(PPh3]+ Clusters in Electroluminescent Devices

he ionic transition metal complexes (iTMCs) [{Pt(C∧C*)(μ-Rpz)}2Ag(PPh3)]X (HC∧C* = 1-(4-(ethoxycarbonyl)phenyl)-3-methyl-1H-imidazole-2-ylidene, X = ClO4/PF6; Rpz = pz 1a/2a, 4-Mepz 1b/2b, and 3,5-dppz 1c/2c) were prepared from the neutral [{Pt(C∧C*)(μ-Rpz)}2] (Rpz = pz A, 4-Mepz B, and 3,5-dppz C) and fully characterized. The “Ag(PPh3)” fragment is in between the two square-planar platinum units in an “open book” disposition and bonded through two Pt–Ag donor–acceptor bonds, as shown by X-ray diffraction (dPt–Ag ∼ 2.78 Å, 1a–1c). 195Pt{1H} and 31P{1H} NMR confirmed that these solid-state structures remain in solution. Photoluminescence studies and theoretical calculations on 1a, were performed. The diphenylpyrazolate derivatives show the highest photoluminescence quantum yield (PLQY) in the solid state. Therefore, 2c and its neutral precursor C were selected as active materials on light-emitting devices. OLEDs fabricated with C showed a turn-on voltage of 3.2 V, a luminance peak of 21,357 cd m–2 at 13 V, and a peak current efficiency of 28.8 cd A–1 (9.5% EQE). They showed a lifetime t50 of 15.7 h. OLEDs using 2c showed a maximum luminance of 114 cd m–2, while LECs exhibited a maximum luminance of 20 cd m–2 and a current efficiency of around 0.2 cd A–1, with a t50 value of 50 min

Application of V2O5/WO3/TiO2 for Resistive-Type SO2 Sensors

A study on the application of V2O5/WO3/TiO2 (VWT) as the sensitive material for resistive-type SO2 sensor was conducted, based on the fact that VWT is a well-known catalyst material for good selective catalytic nitrogen oxide reduction with a proven excellent durability in exhaust gases. The sensors fabricated in this study are planar ones with interdigitated electrodes of Au or Pt. The vanadium content of the utilized VWT is 1.5 or 3.0 wt%. The resistance of VWT decreases with an increasing SO2 concentration in the range from 20 ppm to 5,000 ppm. The best sensor response to SO2 occurs at 400 °C using Au electrodes. The sensor response value is independent on the amount of added vanadium but dependent on the electrode materials at 400 °C. These results are discussed and a sensing mechanism is discussed

Organic Light-Emitting Diodes Combining Thick Inorganic Perovskite Hole Transport Layers and Ultrathin Emitting Layers

[EN] Organic light-emitting diodes have a huge gain in popularity over the past 25 years for display and lighting applications, but the production of low-cost efficient devices remains a challenge. OLEDs using sub-nanometer undoped emissive layers are a route to fabricate cost-effective devices but, as they are inherently thin, it opens to issues with variation in thickness and shunting paths. At the same time, lead chloride perovskites are currently being investigated as charge transport materials in light-emitting devices owing to their wide bandgap, and remarkable high carrier mobility. In this work, for the first time, OLEDs that combine vacuum-processed thick cesium lead chloride perovskite hole transport layers with ultrathin Ir complex-based emissive layers are reported. Defects on the perovskite film are suppressed and the thickness of the emitting layer is optimized. Semitransparent devices are also fabricated with an average visible transmittance of over 50%. The results show extraordinarily thick devices (>1 mu m) with low turn-on voltage (3.3 V), high luminance (>15 000 cd m(-2)) and efficiencies (up to 54.1 cd A(-1)), and a negligible efficiency roll-off in the display applications luminance region.M.F. and S.-H.C. contributed equally to this work. The authors acknowledge financial support of the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant Agreement No. 834431) and by the European Union's Horizon 2021 research and innovation programme under grant agreement No. 101073045 (TADFsolutions). The authors also acknowledge financial support from the Comunitat Valenciana (CIGE/2021/027 and CISEJI/2022/43).Forzatti, M.; Chin, S.; Hernández Fenollosa, MDLÁ.; Sessolo, M.; Tordera, D.; Bolink, HJ. (2024). Organic Light-Emitting Diodes Combining Thick Inorganic Perovskite Hole Transport Layers and Ultrathin Emitting Layers. Advanced Optical Materials. https://doi.org/10.1002/adom.20240106

The oxycoal process with cryogenic oxygen supply

Due to its large reserves, coal is expected to continue to play an important role in the future. However, specific and absolute CO2 emissions are among the highest when burning coal for power generation. Therefore, the capture of CO2 from power plants may contribute significantly in reducing global CO2 emissions. This review deals with the oxyfuel process, where pure oxygen is used for burning coal, resulting in a flue gas with high CO2 concentrations. After further conditioning, the highly concentrated CO2 is compressed and transported in the liquid state to, for example, geological storages. The enormous oxygen demand is generated in an air-separation unit by a cryogenic process, which is the only available state-of-the-art technology. The generation of oxygen and the purification and liquefaction of the CO2-enriched flue gas consumes significant auxiliary power. Therefore, the overall net efficiency is expected to be lowered by 8 to 12 percentage points, corresponding to a 21 to 36% increase in fuel consumption. Oxygen combustion is associated with higher temperatures compared with conventional air combustion. Both the fuel properties as well as limitations of steam and metal temperatures of the various heat exchanger sections of the steam generator require a moderation of the temperatures during combustion and in the subsequent heat-transfer sections. This is done by means of flue gas recirculation. The interdependencies among fuel properties, the amount and the temperature of the recycled flue gas, and the resulting oxygen concentration in the combustion atmosphere are investigated. Expected effects of the modified flue gas composition in comparison with the air-fired case are studied theoretically and experimentally. The different atmosphere resulting from oxygen-fired combustion gives rise to various questions related to firing, in particular, with regard to the combustion mechanism, pollutant reduction, the risk of corrosion, and the properties of the fly ash or the deposits that form. In particular, detailed nitrogen and sulphur chemistry was investigated by combustion tests in a laboratory-scale facility. Oxidant staging, in order to reduce NO formation, turned out to work with similar effectiveness as for conventional air combustion. With regard to sulphur, a considerable increase in the SO2 concentration was found, as expected. However, the H2S concentration in the combustion atmosphere increased as well. Further results were achieved with a pilot-scale test facility, where acid dew points were measured and deposition probes were exposed to the combustion environment. Besides CO2 and water vapour, the flue gas contains impurities like sulphur species, nitrogen oxides, argon, nitrogen, and oxygen. The CO2 liquefaction is strongly affected by these impurities in terms of the auxiliary power requirement and the CO2 capture rate. Furthermore, the impurity of the liquefied CO2 is affected as well. Since the requirements on the liquid CO2 with regard to geological storage or enhanced oil recovery are currently undefined, the effects of possible flue gas treatment and the design of the liquefaction plant are studied over a wide range

Study of N2O formation over Rh- and Pt-based LNT catalysts

In this paper, mechanistic aspects involved in the formation of N2O over Pt-BaO/Al2O3 and Rh-BaO/Al2O3 model NOx Storage-Reduction (NSR) catalysts are discussed. The reactivity of both gas-phase NO and stored nitrates was investigated by using H2 and NH3 as reductants. It was found that N2O formation involves the presence of gas-phase NO, since no N2O is observed upon the reduction of nitrates stored over both Pt- and Rh-BaO/Al2O3 catalyst samples. In particular, N2O formation involves the coupling of undissociated NO molecules with N-adspecies formed upon NO dissociation onto reduced Platinum-Group-Metal (PGM) sites. Accordingly, N2O formation is observed at low temperatures, when PGM sites start to be reduced, and disappears at high temperatures where PGM sites are fully reduced and complete NO dissociation takes place. Besides, N2O formation is observed at lower temperatures with H2 than with NH3 in view of the higher reactivity of hydrogen in the reduction of the PGM sites and onto Pt-containing catalyst due to the higher reducibility of Pt vs. Rh

Organic light-emitting diodes comprising an undoped thermally activated delayed fluorescence emissive layer and a thick inorganic perovskite hole transport layer

Funding: The authors thank K.P.S. Zanoni for acquiring AFM images. This project has been partly funded by the European Union Horizon 2021 research and innovation program under grant agreement No. 101073045 (TADF solutions) and the EPSRC grant EP/X026175/1. H.B. acknowledges financial support of the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Grant Agreement No. 834431).Organic light-emitting diodes (OLEDs) hold potential for next-generation displays and lighting solutions, but current OLED displays rely on the use of scarce metals or fluorescent emitters. Thermally activated delayed fluorescence (TADF) compounds kickstarted a new, promising class of OLEDs as organic TADF emitters do not contain scarce platinoid elements yet remain highly efficient. However, similarly to phosphorescent emitters, their incorporation into devices typically requires complicated doping techniques when vacuum processed. Lowering the mass production costs of high-performing OLEDs using simpler fabrication techniques remains a challenge. Here, we report OLEDs comprising a thermally evaporated CsPbCl3 perovskite transport layer and a TADF-based single-component emitting layer by exploring different approaches to obtain efficient undoped OLEDs, both solution- and vacuum-processed. We first demonstrated the compatibility of the perovskite layer with the solution processing of a TADF dendrimer for host-free, thick emitting layers, with an efficiency of 15 cd A–1 well over a luminance of 1000 cd m–2. Then, we employed a TADF small molecule as the emitter and reduced its layer’s thickness to the subnanometer regime, while the incorporation of the perovskite increased the required total device thickness. The resulting devices showed a low turn-on voltage of 3.3 V, a high luminance of 11 152 cd m–2, and a high efficiency of 67.6 cd A–1, equaling that of 20 times thicker emissive layers. These findings highlight the versatility of using a perovskite as a transport layer and the potential of combining it with an undoped TADF emitting layer for fabricating simple, cost-effective, and efficient OLEDs.Peer reviewe