Effects of pore size, mesostructure and aluminum modification on FDU-12 supported NiMo catalysts for hydrodesulfurization

A series of NiMo/FDU-12 catalysts with tunable pore diameters and mesostructures have been controllably synthesized by adjusting the synthetic hydrothermal temperature and applied for the hydrodesulfurization of dibenzothiophene and its derivative. The state-of-the-art electron tomography revealed that the pore sizes of FDU-12 supports were enlarged with the increase in the hydrothermal temperature and the mesostructures were transformed from ordered cage-type pores to locally disordered channels. Meanwhile, the MoS2 morphology altered from small straight bar to semibending arc to spherical shape and finally to larger straight bar with the change of support structures. Among them, FDU-12 hydrothermally treated at 150 °C possessed appropriate pore diameter and connected pore structure and was favorable for the formation of highly active MoS2 with curved morphology; thus, its corresponding catalyst exhibited the best HDS activity. Furthermore, it was indicated that the isomerization pathway could be significantly improved for HDS of 4,6-dimethyldibenzothiophene after the addition of aluminum, which was expected to be applied to the removal of the macromolecular sulfur compounds. Our study sheds lights on the relationship between support effect, active sites morphology and HDS performance, and also provides a guidance for the development of highly active HDS catalysts.

The Photoisomerization Pathway(s) of Push-Pull Phenylazoheteroarenes

<div> <p>Azoheteroarenes are the most recent derivatives targeted to further improve the properties of azo-based photoswitches. Their light-induced mechanism for trans-cis isomerization is assumed to be very similar to that of the parent azobenzene. As such, they inherited from the controversy about the dominant isomerization pathway (rotation<i> vs.</i> inversion) depending on the excited state (nπ* <i>vs.</i> ππ*). While the controversy seems settled in azobenzene, the extent to which the same conclusions apply to the more structurally-diverse family of azoheteroarenes is unclear. Here, we unravel by means of non-adiabatic molecular dynamics, the photoisomerization mechanism of three prototypical phenyl-azoheteroarenes with an increasing push-pull<i> </i>character. The evolution of the rotational and inversion conical intersection energies, the preferred pathway, and the associated kinetics upon both nπ* and ππ* excitations can be linked directly with the push-pull substitution effects. Overall, we clarify the working conditions of this family of azo-dyes and identify a possibility to exploit push-pull substituents to tune their photoisomerization quantum yield.</p> </div> <br>

The Photoisomerization Pathway(s) of Push-Pull Phenylazoheteroarenes

<div> <p>Azoheteroarenes are the most recent derivatives targeted to further improve the properties of azo-based photoswitches. Their light-induced mechanism for trans-cis isomerization is assumed to be very similar to that of the parent azobenzene. As such, they inherited from the controversy about the dominant isomerization pathway (rotation<i> vs.</i> inversion) depending on the excited state (nπ* <i>vs.</i> ππ*). While the controversy seems settled in azobenzene, the extent to which the same conclusions apply to the more structurally-diverse family of azoheteroarenes is unclear. Here, we unravel by means of non-adiabatic molecular dynamics, the photoisomerization mechanism of three prototypical phenyl-azoheteroarenes with an increasing push-pull<i> </i>character. The evolution of the rotational and inversion conical intersection energies, the preferred pathway, and the associated kinetics upon both nπ* and ππ* excitations can be linked directly with the push-pull substitution effects. Overall, we clarify the working conditions of this family of azo-dyes and identify a possibility to exploit push-pull substituents to tune their photoisomerization quantum yield.</p> </div> <br>

Production of Sorbitol via Catalytic Transfer Hydrogenation of Glucose

Sorbitol production from glucose was studied through catalytic transfer hydrogenation (CTH) over Raney nickel catalysts in alcohol media, used as solvents and hydrogen donors. It was found that alcohol sugars, sorbitol and mannitol, can be derived from two hydrogen transfer pathways, one produced involving the sacrificing alcohol as a hydrogen donor, and a second one involving glucose disproportionation. Comparison between short-chain alcohols evidenced that ethanol was able to reduce glucose in the presence of Raney nickel under neutral conditions. Side reactions include fructose and mannose production via glucose isomerization, which occur even in the absence of the catalyst. Blank reaction tests allowed evaluating the extension of the isomerization pathway. The influence of several operation parameters, like the temperature or the catalyst loading, as well as the use of metal promoters (Mo and Fe-Cr) over Raney nickel, was examined. This strategy opens new possibilities for the sustainable production of sugar alcohols.

Exploring Machine Learning Tools for the Prediction of the Stability of New Togni-type Reagents

In the context of the prediction of the (in-)stability of chemical compounds using machine learning tools, we are often confronted with a basic issue: Whereas much information is available on stable (existing) compounds, little is known about compounds that might well exist, but that have not yet been successfully synthesized, or compounds that are inherently unstable (kinetically and thermodynamically). In the search for Togni-type reagents, many of them kinetically instable, the stability of the prospects can be assessed based on the transition state for the conversion to their non-hypervalent inactive isomer. In earlier work, we determined the barriers of conversion for over one-hundred reagents, still not enough information to train a tool such as a vector support machine. Here, instead, we focus on the early intermediate structures expressed along the isomerization pathway, i.e. transition state searches are replaced by finding (local) minima. Based on an array of 382 Togni-type reagents whose behaviour was known in advance, we show that it is possible to have the machine predict the intermediate form expressed. The approach introduced here can be used to make predictions on the stability and possibly also the reactivity of Togni-type reagents in general.

C n ( n =2−4): current status

The major aspects of the C 2 , C 3 and C 4 elemental carbon clusters are surveyed. For C 2 , a brief analysis of its current status is presented. Regarding C 3 , the most recent results obtained in our group are reviewed with emphasis on modelling its potential energy surface which is particularly complicated due to the presence of multiple conical intersections. As for C 4 , the most stable isomeric forms of both triplet and singlet spin states and their possible interconversion pathways are examined afresh by means of accurate ab initio calculations. The main strategies for modelling the ground triplet C 4 potential are also discussed. Starting from a truncated cluster expansion and a previously reported DMBE form for C 3 , an approximate four-body term is calibrated from the ab initio energies. The final six-dimensional global DMBE form so obtained reproduces all known topographical aspects while providing an accurate description of the C 4 linear–rhombic isomerization pathway. It is therefore commended for both spectroscopic and reaction dynamics studies. This article is part of the theme issue ‘Modern theoretical chemistry’.