Effect of Cage Size on the Selective Conversion of Methanol to Light Olefins

Zeolites that contain eight-membered ring pores but different cavity geometries (LEV, CHA, and AFX structure types) are synthesized at similar Si/Al ratios and crystal sizes. These materials are tested as catalysts for the selective conversion of methanol to light olefins. At 400 °C, atmospheric pressure, and 100% conversion of methanol, the ethylene selectivity decreases as the cage size increases. Variations in the Si/Al ratio of the LEV and CHA show that the maximum selectivity occurs at Si/Al = 15–18. Because lower Si/Al ratios tend to produce faster deactivation rates and poorer selectivities, reactivity comparisons between frameworks are performed with solids having a ratio Si/Al = 15–18. With LEV and AFX, the data are the first from materials with this high Si/Al. At similar Si/Al and primary crystallite size, the propylene selectivity for the material with the CHA structure exceeds those from either the LEV or AFX structure. The AFX material gives the shortest reaction lifetime, but has the lowest amount of carbonaceous residue after reaction. Thus, there appears to be an intermediate cage size for maximizing the production of light olefins and propylene selectivities equivalent to or exceeding ethylene selectivities

Liquid phase oxidation of cyclohexane using bimetallic Au-Pd/MgO catalysts

A detailed study of the selective oxidation of cyclohexane has been performed using bimetallic gold–palladium catalysts supported on magnesium oxide. Mono-metallic supported gold or palladium catalysts show limited activity for cyclohexane oxidation. However, a significantly enhanced catalytic performance is observed when supported gold–palladium alloy catalysts are used for this particular reaction. This synergy is observed for alloys spanning a wide range of gold-to-palladium molar ratios. Mechanistic studies reveal a promotion effect that occurs from alloying palladium with gold on the supported catalyst, which significantly improves the homo-cleavage of the O–O bond in cyclohexyl hydroperoxide, an important intermediate species in cyclohexane oxidation

Crystalline tin disulfide by low-temperature plasma-enhanced atomic layer deposition as an electrode material for Li-Ion batteries and CO2 electroreduction

Abstract: Tin disulfide (SnS2) is a promising candidate for electrochemical applications, showcasing improved performance via tailored structure and morphology. This study discusses a plasma-enhanced atomic layer deposition (PE-ALD) method for depositing crystalline SnS2 thin films using the tetrakis(dimethylamino)tin(IV) precursor and H2S plasma at temperatures of 80 and 180 \ub0C. X-ray diffraction confirms a layered hexagonal crystal structure and strong c-axis-oriented film growth, with the alignment of the basal planes mainly parallel to the substrate. At 80 \ub0C, the film surface consists of continuous grain-like structures, whereas at 180 \ub0C, the smooth film surface during the initial growth evolves to out-of-plane oriented structures when more SnS2 is deposited. The influence of crystallinity and surface morphology on the electrochemical performance of crystalline SnS2 thin films deposited by the PE-ALD process is evaluated for Li-ion battery and electrochemical CO2 reduction applications. A comparison is made with those of amorphous SnS2 thin films deposited by the corresponding thermal ALD process. As an anode material in Li-ion batteries, the SnS2 thin film with out-of-plane oriented structures outperforms the other films with 77% capacity retention after 100 charge/discharge cycles despite its lower initial capacity. In contrast, the crystalline SnS2 with grain-like morphology and amorphous SnS2 retain only 65 and 34%, respectively, of the initial capacity after 100 charge/discharge cycles regardless of their higher initial capacity. In a similar fashion, the SnS2 thin films with out-of-plane oriented structures exhibit lower Faradaic efficiencies for formate production by CO2 electroreduction at 100 mA cm\u20132 as compared to SnS2 with grains (i.e., 64 vs 80%) albeit at lower overpotentials (i.e., 260 mV less negative) and maintaining a better structural and electrochemical stability. The amorphous SnS2 thin film showed similar Faradaic efficiencies (i.e., 80%), stability, and overpotentials (i.e., 120.84 V vs RHE) compared to the crystalline SnS2 thin film with a grain-like morphology

Continuous-Flow Microelectroextraction for Enrichment of Low Abundant Compounds

We present a continuous-flow microelectroextraction flow cell that allows for electric field enhanced extraction of analytes from a large volume (1 mL) of continuously flowing donor phase into a micro volume of stagnant acceptor phase (13.4 μL). We demonstrate for the first time that the interface between the stagnant acceptor phase and fast-flowing donor phase can be stabilized by a phaseguide. Chip performance was assessed by visual experiments using crystal violet. Then, extraction of a mixture of acylcarnitines was assessed by off-line coupling to reversed phase liquid chromatography coupled to time-of-flight mass spectrometry, resulting in concentration factors of 80.0 ± 9.2 times for hexanoylcarnitine, 73.8 ± 9.1 for octanoylcarnitine, and 34.1 ± 4.7 times for lauroylcarnitine, corresponding to recoveries of 107.8 ± 12.3%, 98.9 ± 12.3%, and 45.7 ± 6.3%, respectively, in a sample of 500 μL delivered at a flow of 50 μL min(-1) under an extraction voltage of 300 V. Finally, the method was applied to the analysis of acylcarnitines spiked to urine, resulting in detection limits as low as 0.3-2 nM. Several putative endogenous acylcarnitines were found. The current flowing-to-stagnant phase microelectroextraction setup allows for the extraction of milliliter range volumes and is, as a consequence, very suited for analysis of low-abundant metabolites.Analytical BioScience