Reductive Treatment of Pt Supported on Ti0.8Sn0.2O2-C Composite: A Route for Modulating the Sn-Pt Interactions

The composites of transition metal-doped titania and carbon have emerged as promising supports for Pt electrocatalysts in PEM fuel cells. In these multifunctional supports, the oxide component stabilizes the Pt particles, while the dopant provides a co-catalytic function. Among other elements, Sn is a valuable additive. Stong metal-support interaction (SMSI), i.e., the migration of a partially reduced oxide species from the support to the surface of Pt during reductive treatment is a general feature of TiO2-supported Pt catalysts. In order to explore the influence of SMSI on the stability and performance of Pt/Ti0.8Sn0.2O2-C catalysts, the structural and catalytic properties of the as prepared samples measured using XRD, TEM, XPS and electrochemical investigations were compared to those obtained from catalysts reduced in hydrogen at elevated temperatures. According to the observations, the uniform oxide coverage of the carbon backbone facilitated the formation of Pt-oxide-C triple junctions at a high density. The electrocatalytic behavior of the as prepared catalysts was determined by the atomic closeness of Sn to Pt, while even a low temperature reductive treatment resulted in Sn-Pt alloying. The segregation of tin oxide on the surface of the alloy particles, a characteristic material transport process in Sn-Pt alloys after oxygen exposure, contributed to a better stability of the reduced catalysts.

A Study of the Conversion of Ethanol to 1,3-Butadiene: Effects of Chemical and Structural Heterogeneity on the Activity of MgO-SiO2 Mixed Oxide Catalysts

The ethanol-to-butadiene (ETB) transformation proceeds through consecutive reactions, involving hydrogenation/dehydrogenation, C-C coupling, and dehydration. Uniform active sites are needed to attain high catalytic selectivity. It is a challenge to generate...

Nitrogen doped carbonaceous materials as platinum free cathode electrocatalysts for oxygen reduction reaction (ORR)

Comparison of physicochemical properties and electrocatalytic behavior of different N-doped carbonaceous materials as potential catalysts for oxygen reduction reaction (ORR) was attended. Ball-milling of graphite with melamine and solvothermal treatment of graphite oxide, graphene nanoplatelets (GNP) with ammonia were used as preparation methods. Elemental analysis and N2 physisorption measurements revealed the synthesis of N-doped materials with strongly different morphological parameters. Contact angle measurements proved that all three samples had good wettability properties. According to analysis of XRD data and Raman spectra a higher nitrogen concentration corresponded to a smaller size of crystallites of the N-doped carbonaceous material. Surface total N content determined by XPS and bulk N content assessed by elemental analysis were close, indicating homogenous inclusion of N in all samples. Rotating disc electrode tests showed that these N-doped materials weremuch less active in acidic medium than in an alkaline environment. Although the presence of in-plane N species is regarded to be advantageous for the ORR activity, no particular correlation was found in these systems with any type of N species. According to Koutecky–Levich analysis, both the N-containing carbonaceous materials and the reference Pt/C catalyst displayed a typical one-step, four-electron ORR route. Both ball-milled sample with high N-content but with low SSA and solvothermally synthesized N-GNP with high SSA but low N content showed significant ORR activity. It could be concluded that beside the total N content other parameters such as SSA, pore structure, structural defects, wettability were also essential for achieving high ORR activity.

Electrocatalytic Properties of Mixed-Oxide-Containing Composite-Supported Platinum for Polymer Electrolyte Membrane (PEM) Fuel Cells

TiO2-based mixed oxide–carbon composite supports have been suggested to provide enhanced stability for platinum (Pt) electrocatalysts in polymer electrolyte membrane (PEM) fuel cells. The addition of molybdenum (Mo) to the mixed oxide is known to increase the CO tolerance of the electrocatalyst. In this work Pt catalysts, supported on Ti1−xMoxO2–C composites with a 25/75 oxide/carbon mass ratio and prepared from different carbon materials (C: Vulcan XC-72, unmodified and functionalized Black Pearls 2000), were compared in the hydrogen oxidation reaction (HOR) and in the oxygen reduction reaction (ORR) with a commercial Pt/C reference catalyst in order to assess the influence of the support on the electrocatalytic behavior. Our aim was to perform electrochemical studies in preparation for fuel cell tests. The ORR kinetic parameters from the Koutecky–Levich plot suggested a four-electron transfer per oxygen molecule, resulting in H2O. The similarity between the Tafel slopes suggested the same reaction mechanism for electrocatalysts supported by these composites. The HOR activity of the composite-supported electrocatalysts was independent of the type of carbonaceous material. A noticeable difference in the stability of the catalysts appeared only after 5000 polarization cycles; the Black Pearl-containing sample showed the highest stability.

Interspecies Comparisons of the Effects of Potential Antiviral 3-Amidinophenylalanine Derivatives on Cytochrome P450 1A2 Isoenzyme

In vitro models of animals vulnerable to SARS-CoV-2 infection can support the characterization of effective antiviral drugs, such as synthetic inhibitors of the transmembrane protease serine 2 (TMPRSS2). Changes in cytochrome P450 (CYP) 1A2 activities in the presence of the potential TMPRSS2/matriptase inhibitors (MI) were measured using fluorometric and luminescent assays. Furthermore, the cytotoxicity of these inhibitors was evaluated using the MTS method. In addition, 60 min-long microsomal stability assays were performed using an UPLC-MS/MS procedure to elucidate depletion rates of the inhibitors. CYP1A2 was influenced significantly by MI-463 and MI-1900 in rat microsomes, by MI-432 and MI-482 in beagle microsomes, and by MI-432, MI-463, MI-482, and MI-1900 in cynomolgus monkey microsomes. The IC50 values in monkey microsomes were 1.30 ± 0.14 µM, 2.4 ± 1.4 µM, 0.21 ± 0.09 µM, and 1.1 ± 0.8 µM for inhibitors MI-432, MI-463, MI-482, and MI-1900, respectively. The depletion rates of the parent compounds were lower than 50%, independently of the investigated animal species. The host cell factor TMPRSS2 is of key importance for the cross-species spread of SARS-CoV-2. Studies of the in vitro biotransformation of TMPRSS2 inhibitors provide additional information for the development of new antiviral drugs.

In vitro interaction of potential antiviral TMPRSS2 inhibitors with human serum albumin and cytochrome P 450 isoenzymes

The interactions of four sulfonylated Phe(3-Am)-derived inhibitors (MI-432, MI-463, MI-482 and MI-1900) of type II transmembrane serine proteases (TTSP) such as transmembrane protease serine 2 (TMPRSS2) were examined with serum albumin and cytochrome P450 (CYP) isoenzymes. Complex formation with albumin was investigated using fluorescence spectroscopy. Furthermore, microsomal hepatic CYP1A2, 2C9, 2C19 and 3A4 activities in presence of these inhibitors were determined using fluorometric assays. The inhibitory effects of these compounds on human recombinant CYP3A4 enzyme were also examined. In addition, microsomal stability assays (60-min long) were performed using an UPLC-MS/MS method to determine depletion percentage values of each compound. The inhibitors showed no or only weak interactions with albumin, and did not inhibit CYP1A2, 2C9 and 2C19. However, the compounds tested proved to be potent inhibitors of CYP3A4 in both assays performed. Within one hour, 20%, 12%, 14% and 25% of inhibitors MI-432, MI-463, MI-482 and MI-1900, respectively, were degraded. As essential host cell factor for the replication of the pandemic SARS-CoV-2, the TTSP TMPRSS2 emerged as an important target in drug design. Our study provides further preclinical data on the characterization of this type of inhibitors for numerous trypsin-like serine proteases.

Effect of the Microstructure of the Semiconductor Support on the Photocatalytic Performance of the Pt-PtOx/TiO2 Catalyst System

The influence of the semiconductor microstructure on the photocatalytic behavior of Pt-PtOx/TiO2 catalysts was studied by comparing the methanol-reforming performance of systems based on commercial P25 or TiO2 from sol-gel synthesis calcined at different temperatures. The Pt co-catalyst was deposited by incipient wetness and formed either by calcination or high-temperature H2 treatment. Structural features of the photocatalysts were established by X-ray powder diffraction (XRD), electron spin resonance (ESR), X-ray photoelectron spectroscopy (XPS), optical absorption, Raman spectroscopy and TEM measurements. In situ reduction of Pt during the photocatalytic reaction was generally observed. The P25-based samples showed the best H2 production, while the activity of all sol-gel-based samples was similar in spite of the varying microstructures resulting from the different preparation conditions. Accordingly, the sol-gel-based TiO2 has a fundamental structural feature interfering with its photocatalytic performance, which could not be improved by annealing in the 400-500 °C range even by scarifying specific surface area at higher temperatures.

Propylene synthesis via isomerization–metathesis of 1-hexene and FCC olefins

Highly efficient conversion of 1-hexene and FCC mixture to propylene via isomerization–metathesis (ISOMET) catalyzed by a HBEA–MoOx/Al2O3 system.

Interaction of carbon monoxide with Au(111) modified by ion bombardment: a surface spectroscopy study under elevated pressure

Gold based model systems exhibiting the structural versatility of nanoparticle ensembles and being accessible for surface spectroscopic investigations are expected to provide new information about the adsorption of carbon monoxide, a key process influencing the CO oxidation activity of this noble metal in nanoparticulate form. Accordingly, in the present work the interaction of CO is studied with an ion bombardment modified Au(111) surface by means of a combination of photoelectron spectroscopy (XPS and UPS), sum frequency generation vibrational spectroscopy (SFG), and scanning tunneling microscopy (STM). While no adsorption was found on intact Au(111), data collected on the ion bombarded surface at cryogenic temperatures indicated the presence of stable CO adsorbates below 190 K. A quantitative evaluation of the C 1s XPS spectra and the surface morphology explored by STM revealed that the step edge sites created by ion bombardment are responsible for CO adsorption. The identification of the CO binding sites was confirmed by density functional theory (DFT) calculations. Annealing experiments up to room temperature showed that at temperatures above 190 K unstable adsorbates are formed on the surface under dynamic exposure conditions that disappeared immediately when gaseous CO was removed from the system. Spectroscopic data as well as STM records revealed that prolonged CO exposure at higher pressures of up to 1 mbar around room temperature facilitates massive atomic movements on the roughened surface, leading to its strong reordering toward the structure of the intact Au(111) surface, accompanied by the loss of the CO binding capacity.

Modification of multi-walled carbon nanotubes by Diels-Alder and Sandmeyer reactions

Random (L) and aligned (A) multi-walled carbon nanotubes (MWNTs) were modified by Diels-Alder (DA) [4+2] cycloaddition, Sandmeyer (SM) reaction and by catalytic oxidation (OX). The properties of modified carbon nanotubes were studied by dispersability tests, elemental analysis, thermogravimetry/mass spectrometry, X-ray photoelectron spectroscopy, and NMR spectroscopy. The cycloaddition reaction could only be successfully performed with the L-MWNTs in molten and in solution state by using an aluminum chloride homogeneous catalyst. The efficiency and thermal stability of the solution phase cycloaddition were much higher than in the case of modification in the molten phase. The functionalization of both types of MWNTs by Sandmeyer reaction was carried out by copper(I) and iron(ll) ions that helped in the radical decomposition of diazonium salts. Successful functionalization of nanotubes is achieved by a long decomposition time of the thermally activated diazonium salts. To the contrary, in the case of radical decomposition of diazonium salts, the time is not a decisive parameter. The dispersability tests have proved the changes in the physical features of modified carbon nanotubes depending on the hydrophobic and hydrophilic character of the solvents. The presence of the modifying groups and their fragments from the functionalized MWNTs has been demonstrated by thermogravimetry/mass spectrometry (TG/MS). Relatively high concentration of sulfur atoms was detected by X-ray photoelectron spectroscopy in nanotubes modified by sulfur substituent groups. In the case of catalytic oxidation, the X-ray photoelectron spectroscopic signal of oxygen bound to nanotubes showed considerable change as compared to pristine nanotubes. Due to the high thermal stability of modified multi-walled carbon nanotubes, the functionalized derivatives are applicable in several industrial fields.