Pd/Al2O3 and Pd/CeO2 catalysts were investigated for methane oxidation at conditions typical for the exhaust of lean burn gas engines. The results show that catalyst prereduction significantly ...increases the catalytic activity during the light-off irrespective of the gas composition. Operando X-ray absorption spectroscopy revealed a fully reduced catalyst state after the reductive pretreatment, which is reoxidized with increasing temperature in a lean reaction mixture, resulting in bulk PdO formation at 350 °C. The correlation of catalytic activity with oxidation state during light-off tests led to the conclusion that PdO is a mandatory species for methane oxidation. We attribute the increased conversion after prereduction to the slight sintering of Pd particles and higher reactivity of the formed PdO surface species. Additionally, the H2O inhibition effect was found to be retarded under dry conditions due to the relatively slow palladium reoxidation. The results presented are in particular relevant for the activity of methane oxidation catalysts at low temperature and under dynamic conditions.
Pt-CeO2-Al2O3 catalysts play an important role in diesel oxidation and three-way catalysis. In this study, the fast structural dynamics of both platinum and ceria in a 1 wt %Pt/5 wt %CeO2-Al2O3 ...catalyst prepared by flame spray pyrolysis have been systematically investigated under reducing and oxidizing conditions to elucidate the role of the Pt–CeO2 interface for CO oxidation and fast oxygen storage/release of ceria. The catalyst showed enhanced catalytic activity, particularly after application of a reducing/oxidizing conditioning step at 250 °C, with a pronounced dependence on the reducing agent (C3H6 < H2 < CO). In situ time-resolved X-ray absorption spectroscopy (XAS) at the Ce L3-edge unraveled a dependence of the reduction extent of ceria during temperature-programmed reduction on the noble metal constituent and the applied reducing agent. Dynamic reducing/oxidizing cycling (2% H2 ↔ 10% O2 or 2% CO ↔ 10% O2) at various temperatures (150, 250, and 350 °C) showed that the reducibility of ceria increased at higher temperature and by using a more strongly reducing reaction mixture. This coincides with the trend in catalytic activity. Time-resolved XAS data recorded at the Pt L3-edge and Ce L3-edge during redox cycling revealed a close relationship between the Pt oxidation state and the ceria redox response. The formation of reduced Pt particles was found to induce variations in ceria reducibility under transient conditions and was identified as a decisive prerequisite for ceria reduction at low temperatures. Variations in the extent of ceria reduction during the reducing/oxidizing cycles indicate an evolution of the Pt–ceria interface from an inactive state toward an optimal activated state due to reduction and slight sintering of the noble metal particles. Further growth of Pt particles leads to a decrease in ceria reduction rate due to the smaller Pt–CeO2 interface perimeter. A schematic model illustrating the role of Pt for ceria reducibility is developed and the optimal Pt particle size derived. The results are relevant for various applications, particularly for catalysts operated at low temperature under highly dynamic reaction conditions such as exhaust gas catalysts.
Composite materials are of increasing interest in aircraft and spacecraft structures, and carbon fiber reinforced polymers (CFRP) have emerged as materials meeting quality standards for structural ...applications in the aircraft industry. Despite their high mechanical properties, CFRPs are associated with high production costs. Building on recent research by the authors, this paper investigates the use of ply-level hybridization to reduce manufacturing costs while maintaining the mechanical perfonnance of the manufactured material. Focusing on the causes of nonlinear response under off-axis tensile loading, the paper involves cyclic load-unload (LU) tensile tests conducted at off-axis angles of 15°, 30°, and 45° to predict mechanical characteristics and damage evolution. Residual strains are directly extracted from load-unload stress-strain responses. Three distinct methods for estimating cycle modulus are employed and compared for damage variable fonnulation. The research findings reveal dependencies of both the damage variable and residual strains on the off-axis angle. Furthennore, the method used to assess the modulus during cycling loading significantly influences the damage variable estimation. Encouragingly, the hybrid laminates exhibit reduced internal damage and matrix plasticity compared to reference counterparts, indicating a positive effect on the mechanical perfonnances of hybridized CFRPs in addition to the cost reduction.
A dynamic structural behavior of Pt nanoparticles on the ceria surface under reducing/oxidizing conditions was found at moderate temperatures (<500 °C) and exploited to enhance the catalytic activity ...of Pt/CeO2‐based exhaust gas catalysts. Redispersion of platinum in an oxidizing atmosphere already occurred at 400 °C. A protocol with reducing pulses at 250–400 °C was applied in a subsequent step for controlled Pt‐particle formation. Operando X‐ray absorption spectroscopy unraveled the different extent of reduction and sintering of Pt particles: The choice of the reductant allowed the tuning of the reduction degree/particle size and thus the catalytic activity (CO>H2>C3H6). This dynamic nature of Pt on ceria at such low temperatures (250–500 °C) was additionally confirmed by in situ environmental transmission electron microscopy. A general concept is proposed to adjust the noble metal dispersion (size, structure), for example, during operation of an exhaust gas catalyst.
Under control: The low temperature oxidation activity of diesel oxidation catalysts was improved by unraveling the dynamic structural behavior of Pt nanoparticles on ceria using operando X‐ray absorption spectroscopy (XAS) and environmental transmission electron microscopy (ETEM). This led to a general concept to finely adjust the size and structure of noble metal particles on strongly interacting supports during real operation.
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•A supported Pt/Al2O3 catalyst was studied during stable CO oxidation oscillations.•Operando IR thermography was used to identify active catalyst in fixed bed reactor.•Dynamics of Pt ...oxidation state and atomic coordination was probed by operando XAS.•Correlation of structure and activity ascribed high activity to metallic Pt.•A schematic mechanism is proposed to explain the observed CO oscillations.
A comprehensive approach was applied to investigate oscillatory CO oxidation over a Pt/Al2O3-based diesel oxidation catalyst with small Pt particles (about 1.5nm diameter) in a fixed-bed microreactor under relevant reaction conditions by combining spatially and time-resolved operando X-ray absorption spectroscopy, infrared thermography, and online mass spectrometry. The catalyst-bed zone responsible for the oscillatory behavior and the emerging hot spot was identified by means of IR thermography. Oscillations of the Pt oxidation state and the hot spot region evolved simultaneously and moved from the end toward the beginning of the catalyst bed with increasing reaction temperature. The changes in CO oxidation activity during oscillations can be unambiguously correlated with dynamic structural changes of the Pt particles. The applied operando approach is complementary to surface science studies and also studies on model Pt particles. Surface oxidation of small Pt nanoparticles leads to a fast deactivation of the catalyst, which is regenerated in a slow reduction step. The presence of metallic Pt is required for high activity of the catalyst.
The emerging field of artificial intelligence (AI) will probably affect the practice for the next generation of doctors. However, the students' views on AI have not been largely investigated.
An ...anonymous electronic survey on AI was designed for medical and dental students to explore: (1) sources of information about AI, (2) AI applications and concerns, (3) AI status as a topic in medicine, and (4) students' feelings and attitudes. The questionnaire was advertised on social media platforms in 2020. Security measures were employed to prevent fraudulent responses. Mann-Whitney
-test was employed for all comparisons. A sensitivity analysis was also performed by binarizing responses to express disagreement and agreement using the Chi-squared test.
Three thousand one hundred thirty-three respondents from 63 countries from all continents were included. Most respondents reported having at least a moderate understanding of the technologies underpinning AI and of their current application, with higher agreement associated with being male (
< 0.0001), tech-savvy (
< 0.0001), pre-clinical student (
< 0.006), and from a developed country (
< 0.04). Students perceive AI as a partner rather than a competitor (72.2%) with a higher agreement for medical students (
= 0.002). The belief that AI will revolutionize medicine and dentistry (83.9%) with greater agreement for students from a developed country (
= 0.0004) was noted. Most students agree that the AI developments will make medicine and dentistry more exciting (69.9%), that AI shall be part of the medical training (85.6%) and they are eager to incorporate AI in their future practice (99%).
Currently, AI is a hot topic in medicine and dentistry. Students have a basic understanding of AI principles, a positive attitude toward AI and would like to have it incorporated into their training.
The structure of copper sites in Cu-SSZ-13 during NH3-SCR was unravelled by a combination of novel operando X-ray spectroscopic techniques. Strong adsorption of NH3 on Cu, its reaction with weakly ...adsorbed NO from the gas phase, and slow re-oxidation of Cu(I) were proven. Thereby the SCR reaction mechanism is significantly different to that observed for Fe-ZSM-5.
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