Rare-earth-platinum alloy nanoparticles in mesoporous zeolite for catalysis.

Platinum is a much used catalyst that, in petrochemical processes, is often alloyed with other metals to improve catalytic activity, selectivity and longevity1-5. Such catalysts are usually prepared in the form of metallic nanoparticles supported on porous solids, and their production involves reducing metal precursor compounds under a H2 flow at high temperatures6. The method works well when using easily reducible late transition metals, but Pt alloy formation with rare-earth elements through the H2 reduction route is almost impossible owing to the low chemical potential of rare-earth element oxides6. Here we use as support a mesoporous zeolite that has pore walls with surface framework defects (called 'silanol nests') and show that the zeolite enables alloy formation between Pt and rare-earth elements. We find that the silanol nests enable the rare-earth elements to exist as single atomic species with a substantially higher chemical potential compared with that of the bulk oxide, making it possible for them to diffuse onto Pt. High-resolution transmission electron microscopy and hydrogen chemisorption measurements indicate that the resultant bimetallic nanoparticles supported on the mesoporous zeolite are intermetallic compounds, which we find to be stable, highly active and selective catalysts for the propane dehydrogenation reaction. When used with late transition metals, the same preparation strategy produces Pt alloy catalysts that incorporate an unusually large amount of the second metal and, in the case of the PtCo alloy, show high catalytic activity and selectivity in the preferential oxidation of carbon monoxide in H2.

Densification Mechanism of Soft Magnetic Composites Using Ultrasonic Compaction for Motors in EV Platforms.

In this paper, the densification mechanism of ultrasonic compaction was analyzed using a force balance model. Ultrasonic compaction is quite a promising way to solve the lower mechanical property problem of green compact in the compaction process, although it has some obstacles to overcome for its various applications. Our model proposes that the resultant density is achieved as the applied and resistance forces reach the equilibrium state. Based on the proposed model, the ultrasonic compaction increases the density of green compact by reducing the internal friction between the powder and compaction die, as well as the internal friction among particles themselves. It was also found that during the powder compaction, the ultrasonic vibration mostly contributes to slipping and the rearrangement of the particles.

Designed Synthesis of Mesoporous Solid-Supported Lewis Acid-Base Pairs and Their CO2 Adsorption Behaviors.

Conventional amines and phosphines, such as diethylenetriamine, diphenylpropylphosphine, triethylamine, and tetramethylpiperidine, were grafted or impregnated on the surface of metalated SBA-15 materials, such as Ti-, Al-, and Zr-SBA-15, to generate air-stable solid-supported Lewis acid-base pairs. The Lewis acidity of the metalated materials before and after the introduction of Lewis bases was verified by means of pyridine adsorption-Fourier transform infrared spectroscopy. Detailed characterization of the materials was achieved by solid-state 13C and 31P MAS NMR spectroscopy, low-temperature N2 physisorption, X-ray photoelectron spectroscopy, and energy-dispersive X-ray mapping analyses. Study of their potential interactions with CO2 was performed using CO2 adsorption isotherm experiments, which provided new insights into their applicability as solid CO2 adsorbents. A correlation between solid-supported Lewis acid-base pair strength and the resulting affinity to CO2 is discussed based on the calculation of isosteric enthalpy of adsorption.

Nanoscale glassification of gold substrates for surface plasmon resonance analysis of protein toxins with supported lipid membranes.

Surface plasmon resonance (SPR) spectroscopy, a powerful tool for biosensing and protein interaction analysis, is currently confined to gold substrates and the relevant surface chemistries involving dextran and functional thiols. Drawbacks of using self-assembled monolayers (SAMs) for SPR-related surface modification include limited stability, pinhole defects, bioincompatibility, and nonspecific protein adsorption. Here we report the development of stable nanometer-scale glass (silicate) layers on gold substrates for SPR analysis of protein toxins. The nanoscale silicate layers were built up with layer-by-layer deposition of poly(allylamine hydrochloride) and sodium silicate, followed by calcination at high temperature. The resulting silicate films have a thickness ranging from 2 to 15 nm and demonstrate outstanding stability in flow cell conditions. The use of these surfaces as a platform to construct supported bilayer membranes (SBMs) is demonstrated, and improved performance against protein adsorption on SBM-coated surfaces is quantified by SPR measurements. SBMs can be formed reproducibly on the silicate surface via vesicle fusion and quantitatively removed using injection of 5% Triton X-100 solution, generating a fresh surface for each test. Membrane properties such as lateral diffusion of the SBMs on the silicate films are characterized with photobleaching methods. Studies of protein binding with biotin/avidin and ganglioside/cholera toxin systems show detection limits lower than 1 microg/mL (i.e., nanomolar range), and the response reproducibility is better than 7% RSD. The method reported here allows many assay techniques developed for glass surfaces to be transferred to label-free SPR analysis without the need for adaptation of protocols and time-consuming synthetic development of thiol-based materials and opens new avenues for developing novel bioanalytical technologies for protein analysis.