In Situ X-ray Absorption Spectroscopic Study of Nanoparticle Catalysts

X-ray absorption spectroscopy (XAS) is sensitive to the oxidation state and coordination environment of an element and places few constraints on the samples, thus it is a useful technique for the characterization of metal nanoparticles with short-range order. With recent advances in XAS techniques, it is now possible to study materials under in situ conditions. As the synthesis and many catalytic reactions involving nanoparticles occur in solution, in situ XAS is a powerful technique to study the structures and speciation of nanoparticles under real reaction conditions. Fe@FexOy core@shell nanoparticles have been widely studied for environmental remediation and catalysis due to their low cost, relatively low toxicity and magnetic recovery advantages. Using in situ XAS, this thesis details investigations into the oxidation mechanisms of Fe@FexOy nanoparticles, the formation of Fe@FexOy/Pd and Fe@FexOy/Cu nanoparticles, the penetrability of hollow Fe oxide shells via galvanic exchange reactions between the Fe(0) core within the hollow Fe oxide shell and Pd(II) salts, and the metal speciation in these nanoparticles during catalytic reactions. First, Fe@FexOy nanoparticles were synthesized by the reduction of Fe salts in methanol or water/methanol mixtures using a NaBH4 reducing agent under nitrogen gas. Polyvinylpyrrolidone stabilizers and different volume ratios of methanol to water were used to control the sizes of the resulting Fe@FexOy nanoparticles. The relative oxidation kinetics of these different sizes of Fe@FexOy nanoparticles were monitored by in situ Fe K-edge X-ray absorption near-edge structure (XANES) spectra. These Fe@FexOy nanoparticles were also applied as catalysts for the hydrogenation of a variety of alkenes, and their catalytic abilities were compared with Fe nanoparticles synthesized in a tri(hexyl)tetradecylphosphonium chloride ionic liquid. Then, Fe@FexOy nanoparticles were reacted with different molar ratios of Pd(II) and Cu(II) by galvanic exchange reactions to form Fe@FexOy/Pd and Fe@FexOy/Cu bimetallic nanoparticles with different morphologies. The reduction processes of Pd(II) and Cu(II) toward the formation of Fe@FexOy/Pd and Fe@FexOy/Cu bimetallic nanoparticles were studied through using in situ Pd L3-edge and Cu K-edge XANES spectra. In situ XANES results also show that these Fe@FexOy nanoparticles can re-reduce oxidized Pd in Suzuki-Miyaura cross-coupling reactions. As catalysts for the hydrogenation of 2-methyl-3-buten-2-ol, Fe@FexOy/Pd nanoparticles are shown to have a higher catalytic activity in ethanol compared to water for hydrogenation reactions, and in situ XANES experiments reveal that these nanoparticles are more stable in ethanol solutions, whereas further oxidation of the Fe cores occurs in the presence of water. 50:1 or 20:1 Fe@FexOy/Pd nanoparticles could also be used as magnetically recoverable catalysts. Finally, Fe nanoparticles were also obtained by thermal decomposition of Fe pentacarbonyl in the presence of air-free 1-octadecene with oleylamine at 180 °C. Starting with these Fe nanoparticles, in situ high temperature Fe K-edge XANES spectroscopy was used to monitor the formation of hollow Fe oxide nanoparticles from Fe nanoparticles. The core-void-shell Fe-FexOy intermediates during the formation of hollow Fe oxide nanoparticles were captured. Utilizing the incompletely oxidized Fe cores in these core-void-shell structures to reduce Pd(II) to Pd(0), the penetrability of hollow Fe oxide shells was studied

Fischer-Tropsch synthesis using CO2-containing syngas mixture over cobalt and iron based catalysts

Recently, engineers have devoted a great deal of research to developing a Fischer–Tropsch synthesis (FTS) process with high carbon utilization efficiency and low CO2 emissions. This is desirable not only to improve the process and make it more economical, but also to promote its industrial sustainability. Because CO2 is produced in both syngas preparation and the FTS step, it may be a significant component in the syngas or in the FT tailgas that may be recycled back to the FT reactor. With the aim of providing new insights into the process that would help engineers to design FT plants with high overall carbon utilization efficiency, we investigated FTS using CO2-containing syngas mixtures over cobalt- and iron-based catalysts. During the course of our research, we conducted a large number of experiments on CO/H2, CO2/H2 and CO/CO2/H2 syngas mixtures for FTS under different reaction conditions over both cobalt- and iron-based catalysts. The results elicited the following information: No apparent catalyst deactivation was observed when we co-fed CO2 into the feeds during FTS over both cobalt- and iron-based catalysts under the reaction conditions we conducted. The rate of hydrocarbon production was maximized at an intermediate composition of the CO/CO2/H2 mixtures for a cobalt-based catalyst. The hydrocarbon product formation rate reached a maximum and then maintained this value, even at a high concentration of CO2 in the H2/CO/CO2 feed, over an iron-based catalyst. Most of the products for CO2-rich syngas were short chain paraffins with high CH4 selectivity and high molar paraffin to olefin (P/O) ratios. The product distribution followed a typical one-alpha Anderson–Schulz–Flory (ASF) distribution with low alpha values with carbon number n>2. C2 selectivity lay on or close to the ASF distribution line. However, CH4 selectivity was far above the line. For CO-rich feeds, the product composition shifted to an FT-type product (mainly long chain hydrocarbons) with a low P/O ratio, and followed a two-alpha ASF distribution with high alpha values for carbon number n>3. Furthermore the composition of C2 was plotted below the ASF distribution line, while for CH4 was above it

Watching Iron Nanoparticles Rust: An In Situ X-ray Absorption Spectroscopic Study

NSERCPeer ReviewedIron nanoparticles and iron oxide nanoparticles are among the most commonly studied nanomaterials because of their applications in fields ranging from catalysis to ferrofluids. However, many synthetic methods give iron nanoparticles with large size distributions, and it is difficult to follow the kinetics of iron nanoparticle oxidation reactions and the relative speciation of iron oxidation states in real time. Herein, we introduce a simple approach of controlling the sizes of Fe@FexOy nanoparticles and a novel method for following Fe@FexOy nanoparticle oxidation in situ in liquid solutions by Fe K- and L-edge X-ray absorption near-edge structure (XANES) spectroscopy. XANES results show that these Fe@FexOy nanoparticles have similar XANES spectra before exposure to air. In situ XANES measurements allow for quantitative oxidation kinetics of different nanoparticle sizes to be followed; results show that the rate of Fe(0) oxidation increases with a decrease in average nanoparticle size. However, the rate of Fe core size depletion was found to be ca. 0.02 nm/min for all the nanoparticle systems studied. This suggests similar oxidation mechanisms are at work for all the particle sizes studied. This work shows that in situ liquid cell XANES can be used to follow oxidation state and coordination environment changes in Fe NP dispersions

Impact of drug-eluting stents with different coating strategies on stent thrombosis: A meta-analysis of 19 randomized trials

Background: Whether drug-eluting stents with biodegradable polymers (BP-DES) improve safety, especially with respect to stent thrombosis (ST) compared with permanent polymers DES (PP-DES), remains uncertain. We aimed to compare the short- and long-term outcomes and the ST risk in patients treated with BP-DES vs. PP-DES.Methods: We searched Medline, Embase, Web of science, CENTRAL databases, and conferenceproceedings/abstracts for randomized controlled trials (RCTs) comparing BP-DES with PP-DES. The primary endpoint was to compare the risks of overall and different temporalc ategories of definite/probable ST. Other clinical outcomes were target lesion revascularization (TLR), myocardial infarction (MI), and all-cause death in short-term (≤ 1 year) and long-term follow-up. The meta-analyses were performed by computing odds ratios (ORs) with 95% confidence intervals (CIs) using a random-effects model.Results: Nineteen RCTs including 20,229 patients were analyzed. Overall, BP-DES significantly decreased the risks of very late definite/probable ST (OR 0.33; 95% CI 0.16–0.70), and TLR in long-term follow-up (OR 0.70; 95% CI 0.52–0.95) compared with PP-DES. There were no significant differences between the groups regarding MI incidence and mortality during both short and long follow-up periods. In stratified analyses, the long-term superiority of BP-DES was maintained only by using first-generation DES as the comparators.Conclusions: The present meta-analysis indicated that BP-DES were more efficacious than PP-DES at reducing the risks of very late ST and long-term TLR, but it could vary by heterogeneities in the use of PP-DES comparators. Additional rigorous RCTs with longer follow-up periods are warranted to verify these very promising long-term endpoints.

High Throughput Screening for CO2 Capture by Mof Pressure Swing Adsorption Based on Maximum Economic Benefit

The seriousness of the greenhouse effect has forced more and more national and international institutions to actively develop carbon dioxide separation technologies, capture and storage technologies to control CO2 emissions. Among the many CO2 separation technologies, adsorption separation is a common method used in mixed gas separation technology at present. Pressure swing adsorption (PSA) has less regeneration time and less energy consumption, so is used more widely than temperature swing adsorption (TSA) and vacuum swing adsorption (VSA), which are the other two types of adsorption separation technologies. However, the adsorption capacity and adsorption selectivity of the existing adsorbents are poor, resulting in high energy consumption. This study is based on the results of industrial process simulation of flue gas from power plants [Sai et al. 2022], when the economic benefits of CO2 / N2 mixed gas PSA separation process are optimal, the adsorption capacity of MOF material is within a certain range. More than 4000 computation-ready, experimental metal-organic frameworks (CoRE MOFs) were calculated using Grand Canonical Monte Carlo (GCMC) high-throughput simulation, the PSA process of 1bar and a temperature of 298K, obtained 142 MOFs with potential performance

A Cross-Scale Neutral Theory Approach to the Influence of Obesity on Community Assembly of Human Gut Microbiome

Background: The implications of gut microbiome to obesity have been extensively investigated in recent years although the exact mechanism is still unclear. The question whether or not obesity influences gut microbiome assembly has not been addressed. The question is significant because it is fundamental for investigating the diversity maintenance and stability of gut microbiome, and the latter should hold a key for understanding the etiological implications of gut microbiome to obesity.Methods: In this study, we adopt a dual neutral theory modeling strategy to address this question from both species and community perspectives, with both discrete and continuous neutral theory models. The first neutral theory model we apply is Hubbell's neutral theory of biodiversity that has been extensively tested in macro-ecology of plants and animals, and the second we apply is Sloan's neutral theory model that was developed particularly for microbial communities based on metagenomic sequencing data. Both the neutral models are complementary to each other and integrated together offering a comprehensive approach to more accurately revealing the possible influence of obesity on gut microbiome assembly. This is not only because the focus of both neutral theory models is different (community vs. species), but also because they adopted two different modeling strategies (discrete vs. continuous).Results: We test both the neutral theory models with datasets from Turnbaugh et al. (2009). Our tests showed that the species abundance distributions of more than ½ species (59–69%) in gut microbiome satisfied the prediction of Sloan's neutral theory, although at the community level, the number of communities satisfied the Hubbell's neutral theory was negligible (2 out of 278).Conclusion: The apparently contradictory findings above suggest that both stochastic neutral effects and deterministic environmental (host) factors play important roles in shaping the assembly and diversity of gut microbiome. Furthermore, obesity may just be one of the host factors, but its influence may not be strong enough to tip the balance between stochastic and deterministic forces that shape the community assembly. Finally, the apparent contradiction from both the neutral theories should not be surprising given that there are still near 30–40% species that do not obey the neutral law

Low titers of measles antibody in mothers whose infants suffered from measles before eligible age for measles vaccination

<p>Abstract</p> <p>Background</p> <p>Resurgence or outbreak of measles recently occurred in both developed and developing countries despite long-standing widespread use of measles vaccine. Measles incidence in China has increased since 2002, particularly in infants and in persons ≥ 15 years of age. It is speculated that infants may acquire fewer measles IgG from their mothers, resulting in the reduced duration of protection during their early months of life. This study aimed to clarify the reason of increased susceptibility to measles in young infants in China. Measles IgG in 24 measles infants ≤ 9 months of age and their vaccinated mothers was quantitatively measured. The mean measles neutralizing titer in the vaccinated mothers and in 13 age-match women with the histories of clinical measles were compared.</p> <p>Results</p> <p>All the mothers were confirmed to be vaccinated successfully by the presence of measles IgG. Six vaccinated mothers were positive for measles IgM and had high concentrations of measles IgG and the neutralizing antibody, indicating underwent natural boosting. The mean measles neutralizing titer in 18 vaccinated mothers without natural boosting were significantly lower than that in 13 age-match women with the histories of clinical measles (1:37 vs 1:182, <it>P </it>< 0.05).</p> <p>Conclusions</p> <p>Our results suggest that infants born to mothers who acquired immunity to measles by vaccination may get a relatively small amount of measles antibody, resulting in loss of the immunity to measles before the vaccination age. Measures to improve the immunity in young infants not eligible for measles vaccination would be critical to interrupt the measles transmission in China.</p

Atypical Frontotemporal Connectivity of Cognitive Empathy in Male Adolescents With Conduct Disorder

Background: It has been suggested that adolescents with conduct disorder (CD) may have a deficit in the affective and cognitive domains empathy, but studies exploring networks within the key brain regions of affective and cognitive empathy in adolescents with CD are lacking.Methods: Functional connectivity (FC) analyses among key brain regions of the affective and cognitive empathy with resting-state functional magnetic resonance imaging (fMRI) were conducted in 30 adolescent boys with CD and 33 demographically matched healthy controls (HCs).Results: Atypical FC within the key brain regions of affective empathy was not observed in CD adolescents. However, we found that CD adolescents showed decreased frontotemporal connectivity within the key brain regions of cognitive empathy in relation to HCs, that is, the FCs between right temporoparietal junction and ventromedial prefrontal cortex as well as dorsomedial prefrontal cortex.Conclusion: These findings may provide insight into neural mechanism underlying a cognitive empathy deficiency of CD adolescents from the perspective of FC