Tuning the Selectivity in the Nonoxidative Alkane Dehydrogenation Reaction by Potassium-Promoted Zeolite-Encapsulated Pt Catalysts.

The significance of the nonoxidative dehydrogenation of middle-chain alkanes into corresponding alkenes is increasing in the context of the world's declining demands on transportation fuels and the growing demand for chemicals and materials. The middle-chain alkenes derived from the dehydrogenation reaction can be transformed into value-added chemicals in downstream processes. Due to the presence of multiple potential reaction sites, the reaction mechanism of the dehydrogenation of middle-chain alkanes is more complicated than that in the dehydrogenation of light alkanes, and there are few prior studies on elucidating their detailed structure-reactivity relationship.

Reactant-Induced Structural Evolution of Pt Catalysts Confined in Zeolite.

Reactant-induced structural evolutions of heterogeneous metal catalysts are frequently observed in numerous catalytic systems, which can be associated with the formation or deactivation of active sites. In this work, we will show the structural transformation of subnanometer Pt clusters in pure-silica MFI zeolite structure in the presence of CO, O, and/or HO and the catalytic consequences of the Pt-zeolite materials derived from various treatment conditions. By applying the appropriate pretreatment under a reactant atmosphere, we can precisely modulate the size distribution of Pt species spanning from single Pt atoms to small Pt nanoparticles (1-5 nm) in the zeolite matrix, resulting in the desirably active and stable Pt species for CO oxidation.

Unraveling the molecular mechanism for enhanced gas adsorption in mixed-metal MOFs via solid-state NMR spectroscopy.

The incorporation of multiple metal ions in metal-organic frameworks (MOFs) through one-pot synthesis can induce unique properties originating from specific atomic-scale spatial apportionment, but the extraction of this crucial information poses challenges. Herein, nondestructive solid-state NMR spectroscopy was used to discern the atomic-scale metal apportionment in a series of bulk MgCo-MOF-74 samples via identification and quantification of eight distinct arrangements of Mg/Co ions labeled with a C-carboxylate, relative to Co content. Due to the structural characteristics of metal-oxygen chains, the number of metal permutations is infinite for MgCo-MOF-74, making the resolution of atomic-scale metal apportionment particularly challenging.

Generation of Subnanometer Metal Clusters in Silicoaluminate Zeolites as Bifunctional Catalysts.

Zeolite-encapsulated subnanometer metal catalysts are an emerging class of solid catalysts with superior performances in comparison to metal catalysts supported on open-structure solid carriers. Currently, there is no general synthesis methodology for the encapsulation of subnanometer metal catalysts in different zeolite structures. In this work, we will show a general synthesis method for the encapsulation of subnanometer metal clusters (Pt, Pd, and Rh) within various silicoaluminate zeolites with different topologies (MFI, CHA, TON, MOR).

Ternary PtZrNi nanorods for efficient multifunctional electrocatalysis towards oxygen reduction and alcohol oxidation.

Pt-based alloys with precise structure and composition design have been considered to be effective and robust novel electrocatalysts for fuel cells. Whereas, the sluggish kinetics of oxygen reduction reaction (ORR) and low intrinsic activity of Pt limited their real application on a large scale. Herein, a novel ternary PtZrNi nanorods (PtZrNi NRs) was synthesized via a facile wet-chemical method to achieve high electrocatalytic performance for both ORR and alcohol oxidation reaction owing to the synergism of chosen three elements and prominent one-dimensional morphology.

HPTLC screening of saccharin in beverages by densitometry quantification and SERS confirmation.

As a widely used artificially synthesized sweetener, saccharin faced numerous disputes associated with food safety. Therefore, its fast analysis in food is of crucial importance. In this study, an analytical method for the fast and reliable screening of saccharin in various beverages was established and validated, by combining HPTLC with densitometry and surface enhanced Raman spectroscopy.

Collision-mediated ultrafast decay of N fluorescence during fs-laser-induced filamentation.

We investigate experimentally spatiotemporal characteristics of fluorescence emission from fs-laser-induced filaments in air. Emissions accompanying the transitions of N (CΠ-BΠ) and N 2+ (BΣu+-XΣg+) are dominant. The decay dynamics of fluorescence from different radial positions and longitudinal sections of a filament column are obtained along with high resolution spectra.

Characteristics of plasma plume in ultrafast laser ablation with a weakly ionized air channel.

We report the influence of femtosecond (fs) laser weakly ionized air channel on characteristics of plasma induced from fs-laser ablation of solid Zr metal target. A novel method to create high temperature, low electron density plasma with intense elemental emission and weak bremsstrahlung emission was demonstrated. Weakly ionized air channel was generated as a result of a non-linear phenomenon.

Laser Ablation Molecular Isotopic Spectrometry for Molecules Formation Chemistry in Femtosecond-Laser Ablated Plasmas.

Recently, laser ablated molecular isotopic spectrometry (LAMIS) has expanded its capability to explore molecules formation mechanism in laser-induced plasma in addition to isotope analysis. LAMIS is a powerful tool for tracking the origination of atoms that is involved in formation of investigated molecules by labeling atoms with their isotopic substitution. The evolutionary formation pathways of organic molecules, especially of C dimers and CN radicals, were frequently reported.

Femtosecond laser ablation molecular isotopic spectrometry for zirconium isotope analysis.

Laser ablation molecular isotopic spectrometry (LAMIS) for rapid isotopic analysis of zirconium at atmospheric pressure was studied with a femtosecond-laser system operated under high repetition rate (1 kHz) and low pulse energy (160 μJ). The temporal evolution of zirconium neutral-atomic and ionic lines, as well as zirconium oxide molecular bands, were studied. Six molecular bands, belonging to the d(3)Δ-a(3)Δ (i.

Temperature measurement of laser-induced plasmas from the intensity ratio of two lines emitted from different elements with the same ionization degree.

A new laser induced plasma temperature measuring method with two lines emitted from different elements with the same ionization degree is proposed, assuming local thermodynamic equilibrium condition of the plasma. The influence of measurement error on deduced temperature accuracy was simulated in theory. A solution containing Cu, K, and Cr elements was used as the sample.

Quantitative determination of manganese in aqueous solutions and seawater by laser-induced breakdown spectroscopy (LIBS) using paper substrates.

The detection of manganese (Mn) in industrial wastewater and seawater plays an important role in pollution monitoring and the investigation of geochemical and biological processes in the ocean. An approach has been introduced in this work to improve the detection sensitivity of Mn in liquids by laser-induced breakdown spectroscopy with a filter paper as solid substrate. The calibration curves of Mn in aqueous solutions were obtained with the detection of a Czerny-Turner spectrometer and an echelle spectrometer, respectively.

The origin of high electrolyte-electrode interfacial resistances in lithium cells containing garnet type solid electrolytes.

Dense LLZO (Al-substituted Li7La3Zr2O12) pellets were processed in controlled atmospheres to investigate the relationships between the surface chemistry and interfacial behavior in lithium cells. Laser induced breakdown spectroscopy (LIBS), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, synchrotron X-ray photoelectron spectroscopy (XPS) and soft X-ray absorption spectroscopy (XAS) studies revealed that Li2CO3 was formed on the surface when LLZO pellets were exposed to air. The distribution and thickness of the Li2CO3 layer were estimated by a combination of bulk and surface sensitive techniques with various probing depths.

[The measurement of methane dissolved in water using raman spectroscopy assisted with CCl4 extraction].

While under laboratory conditions, the concentration of methane dissolved in water is too low to be detected because of the low solubility of methane using Raman spectroscopy. In the present paper, a novel approach based on CCl4 extraction was introduced, and used in the measurement of methane dissolved in water using Raman spectroscopy under laboratory conditions. Saturated aqueous solution of CH4, CCl4 solution after extraction of CH4 from the saturated aqueous solution and the saturated CCl4 solution of CH4 were prepared, and the Raman spectra of three samples were obtained.

[Study of cuttings identification using laser-induced breakdown spectroscopy].

Cutting identification is one of the most important links in the course of cutting logging which is very significant in the process of oil drilling. In the present paper, LIBS was used for identification of four kinds of cutting samples coming from logging field, and then multivariate analysis was used in data processing. The whole spectra model and the feature model were built for cuttings identification using PLS-DA method.

[Time-resolved evaluation of self-absorption in laser induced plasma from nickel sample].

Laser induced breakdown spectroscopy (LIBS) has been shown to be a promising technique for element analysis. However, self-absorption effect deeply influences the LIBS measurements. In the present paper, a Q-switched Nd:YAG laser operated at 1 064 nm was used to generate nickel plasmas in air.

[Experimental investigation of Pb in soil slurries by laser induced breakdown spectroscopy].

Laser induced breakdown spectroscopy (LIBS) has been shown to be a promising technique for element analysis with many advantages including on-line, real time, standing off and multi-element detection capability. In the present paper, the LIBS experiments for Pb in slurry samples were carried out with the motivation of developing an in-situ sensor for monitoring heavy metal. A Q-switched Nd : YAG laser operating at 532 nm with repetition frequency of 10 Hz was utilized to generate plasma on the prepared slurry samples, which were doped with same weight manganese as reference and varied concentration of lead.