The First Very Long Baseline Interferometry Image of 44 GHz Methanol Maser with the KVN and VERA Array (KaVA)

We have carried out the first very long baseline interferometry (VLBI) imaging of 44 GHz class I methanol maser (7_{0}-6_{1}A^{+}) associated with a millimeter core MM2 in a massive star-forming region IRAS 18151-1208 with KaVA (KVN and VERA Array), which is a newly combined array of KVN (Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry). We have succeeded in imaging compact maser features with a synthesized beam size of 2.7 milliarcseconds x 1.5 milliarcseconds (mas). These features are detected at a limited number of baselines within the length of shorter than approximately 650 km corresponding to 100 Mlambda in the uv-coverage. The central velocity and the velocity width of the 44 GHz methanol maser are consistent with those of the quiescent gas rather than the outflow traced by the SiO thermal line. The minimum component size among the maser features is ~ 5 mas x 2 mas, which corresponds to the linear size of ~ 15 AU x 6 AU assuming a distance of 3 kpc. The brightness temperatures of these features range from ~ 3.5 x 10^{8} to 1.0 x 10^{10} K, which are higher than estimated lower limit from a previous Very Large Array observation with the highest spatial resolution of ~ 50 mas. The 44 GHz class I methanol maser in IRAS 18151-1208 is found to be associated with the MM2 core, which is thought to be less evolved than another millimeter core MM1 associated with the 6.7 GHz class II methanol maser.Comment: 19 pages, 3 figure

Size-dependent Oxygen Reduction Property of Octahedral Pt–ni Nanoparticle Electrocatalysts

The size effect on the electrocatalytic property of octahedral Pt–Ni alloy nanoparticles in the oxygen reduction reaction (ORR) was studied by making particles with different sizes and conducting electrochemical measurements. Octahedral Pt–Ni nanoparticles on carbon support (Pt–Ni/C) were produced using a facile and surfactant-free solid-state chemistry method. Two groups of octahedral Pt–Ni/C, including Pt3Ni/C and Pt1.5Ni/C, with particle size ranging from around 4 to 8 nm were prepared. Both the ORR activity and the stability of the two group catalysts were studied, which exhibited varying dependence over the particle size. The different relationships between the Pt–Ni size and the ORR property were investigated and attributed to alterations in the particle electronic/geometric structure and the Ni leaching behaviour

Carbon Monoxide in Controlling the Surface Formation of Group Viii Metal Nanoparticles

Group VIII metal nanoparticles with variant morphologies were synthesized under a carbon monoxide atmosphere. The important roles of CO in determining the surface formation of growing particles were studied both by experiment and density functional theory (DFT) calculations, which suggest different growth mechanisms for these metals

Solid-State Chemistry-Enabled Scalable Production of Octahedral Pt–Ni Alloy Electrocatalyst for Oxygen Reduction Reaction

Although octahedral Pt–Ni alloy nanoparticles possess an excelling property in oxygen reduction reaction (ORR) and are of great potential as an electrocatalyst for polymer electrolyte membrane fuel cells (PEMFCs), mass production of the materials at low cost remains a big challenge. By combining the advantages of both solid-state chemistry and wet synthetic chemistry, we developed one scalable, surfactant-free, and cost-effective method for producing octahedral Pt–Ni alloy nanoparticles on carbon support. The octahedral Pt–Ni samples were prepared with different compositions and studied for the ORR property. They exhibit a much improved reaction activity compared to the commercial catalyst. The experiments demonstrate an innovative strategy for preparing shaped metal nanoparticles and make significant progress in the ORR catalyst research

Pre-Treatment Methods for Regeneration of Spent Activated Carbon

Spent activated carbon (SAC) usually exhibits a low specific surface area due to its high ash contents. In this study, pre-treatments, such as heat and acid treatments, were optimized to improve this feature. The heat pre-treatment did not reduce the ash content, nor did it increase the surface area. Because metallic ions adsorbed in SACs turn into ash upon the heat treatment. In the acid pre-treatment, the volatiles and fixed carbon were increased with decreasing ash contents. In this study, it was found that the surface area increase was correlated with the ratio between fixed carbon and ash. Among the pre-treatment methods, the combined heat and acid pre-treatment method highly increased the ratio, and therefore led to the surface area increase. Additionally, the acid pre-treatment was carried out using different types of acid (organic and inorganic acids) solutions to further improve the surface areas. The organic acid treatment caused a significant structural collapse compared to the inorganic acid treatment, decreasing the surface area. In particular, H3PO4 effectively removed ashes adsorbed on the activated carbon surface and regenerated the exhausted activated carbon. Both the heat and acid pre-treatments before chemical activation resulted in the positive effects such as strong desorption of pollutants and ashes within the internal structure of the activated carbon. Therefore, the regeneration introduced in this study is methodically the best method to regenerate SAC and maintain a stable structure

A Generic Wet Impregnation Method for Preparing Substrate-Supported Platinum Group Metal and Alloy Nanoparticles with Controlled Particle Morphology

Mass production of shape-controlled platinum group metal (PGM) and alloy nanoparticles is of high importance for their many fascinating properties in catalysis, electronics, and photonics. Despite of successful demonstrations at milligram scale using wet chemistry syntheses in many fundamental studies, there is still a big gap between the current methods and their real applications due to the complex synthetic procedures, scale-up difficulty, and surface contamination problem of the made particles. Here we report a generic wet impregnation method for facile, surfactant-free, and scalable preparation of nanoparticles of PGMs and their alloys on different substrate materials with controlled particle morphology and clean surface, which bridges the outstanding properties of these nanoparticles to practical important applications. The underlying particle growth and shape formation mechanisms were investigated using a combination of ex situ and in situ characterizations and were attributed to their different interactions with the applied gas molecules

Hydrogen Production via Hydrazine Decomposition on Model Platinum–Nickel Nanocatalyst with a Single (111) Facet

Model octahedral Pt–Ni/C nanocatalyst with different particle composition (0.5 ≤ Pt/Ni ≤ 4) was prepared and researched in hydrazine decomposition for hydrogen generation. The experiments discovered dependency of the catalyst activity, selectivity, durability, and stability on both the particle composition and morphology, with the octahedral PtNi/C being found to be the most active and 100% selective, with superior durability and stability. Mechanistic studies and discussions on the reaction mechanism and kinetics were conducted by collecting the kinetic data and deriving the rate law. The finding suggests both the synergistic effect between Pt and Ni active sites and the morphology-originated geometric effect, which play crucial roles in determining the catalyst property

The Effects of Methane Storage Capacity Using Upgraded Activated Carbon by KOH

In this study, a feasible experiment on adsorbed natural gas (ANG) was performed using activated carbons (ACs) with high surface areas. Upgraded ACs were prepared using chemical activation with potassium hydroxide, and were then applied as adsorbents for methane (CH4) storage. This study had three principal objectives: (i) upgrade ACs with high surface areas; (ii) evaluate the factors regulating CH4 adsorption capacity; and (iii) assess discharge conditions for the delivery of CH4. The results showed that upgraded ACs with surface areas of 3052 m2/g had the highest CH4 storage capacity (0.32 g-CH4/g-ACs at 3.5 MPa), which was over two times higher than the surface area and storage capacity of low-grade ACs (surface area = 1152 m2/g, 0.10 g-CH4/g-ACs). Among the factors such as surface area, packing density, and heat of adsorption in the ANG system, the heat of adsorption played an important role in controlling CH4 adsorption. The released heat also affected the CH4 storage and enhanced available applications. During the discharge of gas from the ANG system, the residual amount of CH4 increased as the temperature decreased. The amount of delivered gas was confirmed using different evacuation flow rates at 0.4 MPa, and the highest efficiency of delivery was 98% at 0.1 L/min. The results of this research strongly suggested that the heat of adsorption should be controlled by both recharging and discharging processes to prevent rapid temperature change in the adsorbent bed