Enhancement of the catalytic performances and lifetime of Ni/γ-Al2O3 catalysts for the steam toluene reforming via the combination of dopants: inspection of Cu,Co, Fe,Mn, and Mo species addition

In this work, the influence of metallic dopant addition in 10 wt % Ni/γ-Al₂O₃ catalyst on the material physico-chemical properties and catalytic activity for the toluene steam reforming was studied. Seventeen doped Ni/γ-Al₂O₃ catalysts were synthesized by the sol–gel process. The aim of this study was to determine which elements were the most suitable for the doping of 10 wt % Ni/γ-Al₂O₃ catalysts. The influence of the dopants was studied through different physico-chemical techniques. It appeared that some dopants showed lower catalytic performances due to high carbon deactivation. On the contrary, some dopants increased the resistance to coking while also improving the catalytic activity. Different mechanisms were proposed to explain these modifications of catalytic behavior. Among all doped Ni/γ-Al₂O₃ catalysts, the samples that combined Mn + Mo or Co + Mo dopants showed the best catalytic performances at 650 °C. Both samples showed high toluene reforming activity and low amounts of carbon deposit.     

Polycyclic heteroaromatics via hydrazine-catalyzed ring-closing carbonyl–olefin metathesis

The use of hydrazine-catalyzed ring-closing carbonyl–olefin metathesis (RCCOM) to synthesize polycyclic heteroaromatic (PHA) compounds is described. In particular, substrates bearing Lewis basic functionalities such as pyridine rings and amines, which strongly inhibit acid catalyzed RCCOM reactions, are shown to be compatible with this reaction. Using 5 mol% catalyst loadings, a variety of PHA structures can be synthesized from biaryl alkenyl aldehydes, which themselves are readily prepared by cross-coupling.

Hydrazine catalysis enables the ring-closing carbonyl–olefin metathesis (RCCOM) to form polycyclic heteroaromatics, especially those with basic functionality.

Polycyclic heteroaromatic (PHA) structures comprise the core framework of many valuable compounds with a diverse range of applications (Fig. 1A).¹ For example, polycyclic azines (e.g. quinolines) are embedded in many alkaloid natural products, including diplamine² and eupolauramine³ to name just a few. These types of structures are also of interest for their biological activity, such as with the inhibitor of the Src-SH3 protein–protein interaction shown in Fig. 1A.⁴ Many nitrogenous PHAs are also useful as ligands for transition metal catalysis, as exemplified by the widely used ligand 1,10-phenanthroline.⁵ Meanwhile, chalcogenoarenes⁶ such as dinaphthofuran⁷ and benzodithiophene⁸ have attracted high interest for both their medicinal properties⁹ and especially for their potential use as organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), and organic field-effect transistors (OFETs).¹⁰ These and numerous other examples have inspired the development of a wide variety of strategies to construct PHAs.^1,11–14 Although these approaches are as varied as the structures they target, the wide range of molecular configurations within PHA chemical space and the challenges inherent in exerting control over heteroatom position and global structure make novel syntheses of these structures a topic of continuing interest.Open in a separate windowFig. 1(A) Examples of PHAs. (B) RCCOM strategy for PHA synthesis. (C) Lewis base inhibition for Lewis acid vs. hydrazine catalyzed RCCOM. (D) Hydrazine-catalyzed RCCOM for PHA synthesis.One potentially advantageous strategy for PHA synthesis is the use of ring-closing carbonyl–olefin metathesis¹⁵ (RCCOM) to forge one of the PHA rings, starting from a suitably disposed alkenyl aldehyde precursor 2 that can be easily assembled by cross-coupling (Fig. 1B). In related work, the application of RCCOM to form polycyclic aromatic hydrocarbons (PAHs) was reported by Schindler in 2017.¹⁶ In this case, 5 mol% FeCl₃ catalyzed the metathesis of substrates to form phenanthrenes and related compounds in high yields at room temperature. This method was highly attractive for its efficiency, its use of an earth-abundant metal catalyst, and the production of benign acetone as the only by-product. Nevertheless, one obvious drawback to the use of Lewis acid activation is that the presence of any functionality that is significantly more Lewis basic than the carbonyl group can be expected to strongly inhibit these reactions (Fig. 1C). Such a limitation thus renders this method incompatible with a wide swath of complex molecules, especially PHAs comprised of azine rings. This logic argues for a mechanistically orthogonal RCCOM approach that allows for the synthesis of PHA products with a broader range of ring systems and functional groups.We have developed an alternative approach to catalytic carbonyl–olefin metathesis that makes use of the condensation of 1,2-dialkylhydrazines 5 with aldehydes to form hydrazonium ions 6 as the key catalyst–substrate association step.^17–19 This interaction has a much broader chemoorthogonality profile than Lewis acid–base interactions and should thus be much less prone to substrate inhibition than acid-catalyzed approaches. In this Communication, we demonstrate that hydrazine-catalyzed RCCOM enables the rapid assembly of PHAs bearing basic functionality (Fig. 1D).For our optimization studies, we chose biaryl pyridine aldehyde 7 as the substrate (20 salt 11 was also productive (entry 2), albeit somewhat less so. Notably, iron(iii) chloride generated no conversion at either ambient or elevated temperatures (entries 3 and 4). Trifluoroacetic acid (TFA) was similarly ineffective (entry 5). Meanwhile, a screen of various solvents revealed that, while the transformation could occur in a range of media (entries 6–9), THF was optimal. Finally, by raising the temperature to 90 °C (entry 10) or 100 °C (entry 11), up to 96% NMR yield (85% isolated yield) of adduct 8 could be obtained in the same time period.Optimization studies^a

Etude par Spectrométrie Infrarouge et Raman des Phases Cristallines Basses Temperatures de (NH4)3H(SO4)2

The Raman and infrared spectra of (NH₄)₃H(SO₄)₂ crystal were investigated in the range 20–300 K. An assignment of bands due to internal and external vibrations is given. The crystalline phases designated II, III, V and VII were identified and characterized spectroscopically. Hydrogen bonding, the nature and degree of structural (dis)order and the mechanisms of the phase transitions are discussed. The NH₄⁺ ions show an important orientational disorder and become fully ordered in phase VII only. They are involved in all transitions and seem the main cause of the ferroelectricity at low temperature.     

Oxygen chemisorption and the carbon monoxide-oxygen interaction on Ru(101)

The adsorption of oxygen and the interaction of carbon monoxide with oxygen on Ru(101) have been studied by LEED, Auger spectroscopy and thermal desorption. Oxygen chemisorbs at 300 K via a precursor state and with an initial sticking probability of ~0.004, the enthalpy of adsorption being ~300 kJ mol^?1. As coverage increases a well ordered ¦11,30¦ phase is formed which at higher coverages undergoes compression along [010] to form a ¦21,50¦ structure, and the surface eventually saturates at 0 ~ $\text{8}\text{9}$. Incorporation of oxygen into the subsurface region of the crystal leads to drastic changes in the surface chemistry of CO. A new high; temperature peak (γ CO, E_d ~ 800 kJ mol^?1) appears in the desorption spectra, in addition to the α and β CO peaks which are characteristic of the clean surface. Coadsorption experiments using ¹⁸O₂ indicate that γ CO is not dissociatively adsorbed, and this species is also shown to be in competition with β CO for a common adsorption site. The unusual temperature dependence of the LEED intensities of the ¦11,30¦-O phase and the nature of α, β, and β CO are discussed. Oxygen does not displace adsorbed CO at 300 K and the converse is also true, neither do any Eley-Rideal or Langmuir-Hinshelwood reactions occur under these conditions. Such processes do occur at higher temperatures, and in particular the reaction CO(g) + O(a) → CO₂(g) appears to occur with much greater collisional efficiency than on Ru(001). The oxidation of CO has been examined under steady state conditions, and the reaction was found to proceed with an apparent activation energy of 39 kJ mol^?. This result rules out the commonly accepted explanation that CO desorption is rate determining, and is compared with the findings of other authors.     

Positive Operator Majorization and <Emphasis Type="Italic">p</Emphasis>-hyponormality

In this note we examine the relationships between p-hyponormal operators and the operator inequality . This leads to a method for generating examples of p-hyponormal operators which are not q-hyponormal for any . Our methods are also shown to have implications for the class of Furuta type inequalities.     

Femtosecond dynamics of electron transfer in a neutral organic mixed-valence compound

In this article we report a femtosecond time-resolved transient absorption study of a neutral organic mixed-valence (MV) compound with the aim to gain insight into its charge-transfer dynamics upon optical excitation. The back-electron transfer was investigated in five different solvents, toluene, dibutyl ether, methyl-tert-butyl ether (MTBE), benzonitrile and n-hexane. In the pump step, the molecule was excited at 760 nm and 850 nm into the intervalence charge-transfer band. The resulting transients can be described by two time constant. We assign one time constant to the rearrangement of solvent molecules in the charge-transfer state and the second time constant to back-electron transfer to the electronic ground state. Back-electron transfer rates range from 1.5 × 10¹² s⁻¹ in benzonitrile through 8.3 × 10¹¹ s⁻¹ in MTBE, around 1.6 × 10¹¹ s⁻¹ in dibutylether and toluene and to 3.8 × 10⁹ s⁻¹ in n-hexane.     

Stereoelectronic effects on 1H nuclear magnetic resonance chemical shifts in methoxybenzenes

Investigation of all O-methyl ethers of 1,2,3-benzenetriol and 4-methyl-1,2,3-benzenetriol (3-16) by 1H NMR spectroscopy and density-functional calculations disclosed practically useful conformational effects on 1H NMR chemical shifts in the aromatic ring. While the conversion of phenol (2) to anisole (1) causes only small positive changes of 1H NMR chemical shifts (Delta delta < 0.08 ppm) that decrease in the order Hortho > Hmeta > Hpara, the experimental O-methylation induced shifts in ortho-disubstituted phenols are largest for Hpara, Delta delta equals; 0.19 +/- 0.02 ppm (n = 11). The differences are due to different conformational behavior of the OH and OCH3 groups; while the ortho-disubstituted OH group remains planar in polyphenols due to hydrogen bonding and conjugative stabilization, the steric congestion in ortho-disubstituted anisoles outweighs the conjugative effects and forces the Ar-OCH3 torsion out of the ring plane, resulting in large stereoelectronic effects on the chemical shift of Hpara. Conformational searches and geometry optimizations for 3-16 at the B3LYP/6-31G** level, followed by B3LYP/6-311++G(2d,2p) calculations for all low-energy conformers, gave excellent correlation between computed and observed 1H NMR chemical shifts, including agreement between computed and observed chemical shift changes caused by O-methylation. The observed regularities can aid structure elucidation of partly O-methylated polyphenols, including many natural products and drugs, and are useful in connection with chemical shift predictions by desktop computer programs.     

Access to Nitriles from Aldehydes Mediated by an Oxoammonium Salt

A scalable, high yielding, rapid route to access an array of nitriles from aldehydes mediated by an oxoammonium salt (4‐acetylamino‐2,2,6,6‐tetramethylpiperidine‐1‐oxoammonium tetrafluoroborate) and hexamethyldisilazane (HMDS) as an ammonia surrogate has been developed. The reaction likely involves two distinct chemical transformations: reversible silyl‐imine formation between HMDS and an aldehyde, followed by oxidation mediated by the oxoammonium salt and desilylation to furnish a nitrile. The spent oxidant can be easily recovered and used to regenerate the oxoammonium salt oxidant.     

Mixed electrolytes in hydrophobic interaction chromatography†

An essential part of the modulation of protein‐binding capacity in hydrophobic interaction chromatography is the buffer‐salt system. Besides using “single” electrolytes, multicomponent electrolyte mixtures may be used as an additional tool. Both the protein solubility and the binding capacity depend on the position of a salt in the so‐called Hofmeister series. Specific interactions are observed for an individual protein‐salt combination. For salt mixtures, selectivity, recovery, and binding capacity do not behave like for the single salts that are positioned in between the two mixed components in the Hofmeister series, as the continuous correlation would suggest. Thus, finding strategies for mixed salts could potentially lead to improved capacities in hydrophobic interaction chromatography. Mixtures of ammonium sulfate, sodium citrate, sodium sulfate, sodium chloride, sodium acetate, and glycine were used to investigate the binding capacities for lysozyme and a monoclonal antibody on various hydrophobic resins. Resin capacity for two investigated proteins increases when mixtures consisting of a chaotropic and a kosmotropic salt are applied. It seems to be related to the rather basic isoelectric points of the proteins.