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Graphical abstract Highlights • Base-free transfer hydrogenation of menthone by primary and secondary alcohols as a hydrogen donor under sub- and sc conditions. • The similar H -donor activity of all alcohols under non-catalytic sc conditions. • Only secondary alcohols demonstrate a high H -donor activity in the presence of Raney® Ni under subcritical conditions. • A quasi-equilibrium of isomeric menthone/isomenthone mixture reached via enolization under sc conditions. Abstract The base-free transfer hydrogenation (THR) of menthone with six aliphatic alcohols as hydrogen source has been developed under sub- and supercritical conditions. Under sc conditions (at 350 °C and 78–210 atm) without any catalyst, all alcohols demonstrated the similar H -donor activity, which was high enough. The menthone conversion was about 64 ± 5% for 5 h of the reaction, whereas the selectivity on menthol reached 92–99% for all alcohols except MeOH (73%). The non-catalytic THR at 250 °C was very slow and the conversion in the most active 2-PrOH was only 7.0–7.5% for 9 h of the reaction. Under subcritical conditions at 150 °C, the non-catalytic menthone reduction was negligible in all alcohols. But in secondary 2-PrOH and 2-BuOH, the base-free THR catalyzed by Raney® nickel results in excellent conversion and selectivity of menthol at 150 °C, whereas no conversion of menthone was observed in primary alcohols under the same reaction conditions. A quasi-equilibrium of isomeric menthone/isomenthone mixture reached via enolization was evaluated under sub- and supercritical conditions and the Gibbs energies of the isomerization in each alcohol were calculated. [ABSTRACT FROM AUTHOR]

Highlights: [•] Different forms of SiO2 react slowly with methanol at 350°C to give mainly TMOS. [•] Some N-unsubstituted benzazoles increase considerably the amount of reacted SiO2. [•] The key role of heterocycles is nucleophilic assistance to the reaction. [•] Azole ring of heterocycles is methylated by MeOH during the reaction. [•] Both SiO2-surface and TMOS catalyze the methylation of benzazole. [ABSTRACT FROM AUTHOR]

In this work ZrO 2 –SiO 2 aerogels with ZrO 2 content of 3, 6 and 10 mol. % in the form of transparent blocks were synthesized using the sol-gel method. The possibility of introducing ZrO 2 into a SiO 2 aerogel without considerable decline of the optical characteristics of the material was shown for the first time. Aerogel samples were studied by several techniques including UV–Vis, ATR-FTIR spectroscopy and nitrogen adsorption, the refractive index was determined using beam tests ("Extracted beams" of the VEPP-4M complex). It was shown that the addition of ZrO 2 to SiO 2 aerogel increases the refractive index without increasing of the aerogel density. For the first time, the possibility of obtaining highly transparent ZrO 2 –SiO 2 aerogel blocks with acceptable optical characteristics for radiator in Cherenkov detectors has been demonstrated. This result makes it possible to achieve high refractive indices in the production of aerogel blocks for Cherenkov detectors to increase their performance. [ABSTRACT FROM AUTHOR]

• The Al-Si oxides were synthesized for the first time via supercritical antisolvent precipitation of Al-Si-containing sols. • The alumina and silicon-doped alumina obtained by the SAS method were shown to be mesoporous and thermal stable materials. • The alumina composed of X-ray amorphous particles (2-5 nm) forming a narrow pores size distribution (3-5 nm). A method of alumina and silica sols precipitation in supercritical CO 2 has been developed for the first time to prepare alumina and silica doped alumina. The silicon content of samples is varied within the range from 0 to 30 mol. %. The approach suggested can be considered as a development of supercritical antisolvent (SAS) method that is widely used to prepare powders from solutions but not sols. The alumina and silicon-doped alumina obtained are shown to be mesoporous materials with narrow size distribution in the range of 3–5 nm. The high-temperature treatment of the sample containing 10 mol. % of Si results in the formation of γ-Al 2 O 3 phase followed by its transition into the δ -Al 2 O 3 phase at 1200 °C without α-Al 2 O 3 phase formation. It is demonstrated that the gradual introduction of silica into the alumina allows one to fine-tune the strength and amount of acid sites existing in oxides. [ABSTRACT FROM AUTHOR]

The Si/Al ratio is a key parameter of acid-base, structural, textural and, consequently, catalytic properties of amorphous crystalline (micro- and mesoporous) aluminosilicates. The changes of structural and textural characteristics of Al-Si aerogels with gradual increase of aluminum content are investigated. Aerogels were prepared via sol-gel method using prehydrolysed tetraethoxysilane and aluminium isopropoxide stabilized by acetylacetone. The gelation of the obtained sols took place in the presence of ammonia with the following drying in supercritical isopropanol. It was shown all aluminum reacts with prehydrolyzed tetraethoxysilane forming spherical particles in case the content of Al in the samples is less than 20 mol %. Aluminum drives the increase of interparticle coupling leading to the particle agglomeration, which is associated with the increase of the particle size and decrease of specific surface area and pore volume. For the samples with the aluminum content of >50 mol % the formation of pseudoboehmite plate-like particles is observed. The pseudoboehmite particles prevent the sintering of SiO 2 particles that leads to the increase of the aerogel specific surface area and pore volume. In case the high aluminum content (>80 mol %) the silica particles serve as a connector between boehmite plates. The ratio between Brønsted and Lewis acid sites decreases gradually with the increase of aluminum content of the aluminosilicate aerogels. [ABSTRACT FROM AUTHOR]

Sub- and supercritical alcohols are known as effective hydrogen donors. In this work, transfer hydrogenation (TH) of furfural with C 1 -C 4 alcohols has been studied under sub- and supercritical conditions. In the range of 230–275 °C, the observed activation energy of catalyst-free transformations of furfural into furfuryl alcohol and some minor byproducts has been shown to be 98 ± 8, 64 ± 4 and 79 ± 6 kJ/mol for EtOH, 1-PrOH and 2-PrOH, respectively. The use of a Ni/γ-Al 2 O 3 catalyst results in higher rate constants compared to the catalyst-free TH. Nevertheless, the selectivity to furfuryl alcohol in the presence of the catalyst does not exceed 50% vs 70–80% for the catalyst-free transformations. Thus, this study shows the high donor potential of alcohols in TH under both catalytic and catalyst-free conditions. A special attention is paid to primary alcohols, because they are highly demanded as H-donors due to economic and environmental reasons. [Display omitted] • Primary C 1 -C 4 alcohols demonstrate high donor activity in furfural TH. • Catalyst-free TH of furfural and 1-PrOH has lower activation energy than 2-PrOH. • Selectivity to furfuryl alcohol of catalyst-free furfural TH reaches 70–80%. • Use of Ni/γ-Al 2 O 3 results in higher rate constants but the lower selectivity. [ABSTRACT FROM AUTHOR]

Transfer hydrogenation of anisole in 2-PrOH has been studied as a model reaction for lignocellulose processing. The reaction was studied over high-loaded Ni-based catalysts synthesized via supercritical antisolvent precipitation of a Ni precursor and sols of four oxides: Al 2 O 3 , SiO 2 , TiO 2 , and ZrO 2. It was demonstrated that the oxide support significantly affects the structure of the catalysts, their activity, and selectivity. The best performance in the transfer hydrodeoxygenation of anisole was shown by Ni supported on alumina at 250 °C, which was explained by the highest dispersion of Ni0 particles in this catalyst and by the highest concentration of acid centers. [Display omitted] • Well-dispersed high-loaded Ni catalysts were synthesized by SAS method. • Obtained catalysts show excellent activity in transfer hydrogenation of anisole. • Acid sites and the smaller Ni particles facilitate hydrodeoxygenation of anisole. [ABSTRACT FROM AUTHOR]

[Display omitted] • Poisoning titration is precise approach to quantify Raney® Ni active centers. • Effect of 15 poisons (thiols, amines, acids) on catalyst activity measured. • TOF of Raney® Ni probed by thiophenol titration was 2.4 h–1 at 82 °C. • C–S bond cleavage of thiophenol did not occur during poisoning of Raney® Ni. For the first time, the poisoning effect of 15 different chemical compounds on Raney® nickel catalyst has been comparatively studied in the transfer hydrogenation of camphor using 2-PrOH as a solvent and a hydrogen donor. It has been shown that thiophenol, HCl and H 3 PO 4 demonstrate the strongest poisoning action under the reaction conditions: no camphor conversion was observed at 5 mol.% of poison-to-nickel ratio. A strong chemical binding of thiophenol molecules to the catalyst surface without C S bond cleavage was proved by XRF, TPD methods, CHNS analysis, and FTIR spectroscopy. It was shown that the poisoning titration with thiophenol is an effective and convenient tool to calculate the number of active sites for Ni based catalysts directly, measuring catalytic activity in target chemical reaction, which was defined correspondently as 2.4 h−1 and 9.6 × 10–5 mole for Raney® nickel catalyst in the transfer hydrogenation. [ABSTRACT FROM AUTHOR]

We demonstrate, for the first time, the application of FTIR spectroscopic imaging approach in situ to monitor the precipitation process of oil asphaltenes, induced by n-heptane under flow using microfluidic devices. The aggregation of asphaltenes induced by n-heptane flow with subsequent precipitation and formation of the deposits was studied for solution containing 5 wt % of asphaltenes in benzene. The FTIR spectroscopic approach with an array detector allowed us to assess the spatial distribution of the chemical components and their amounts in the system and display the process of aggregates formation with a spatial resolution of few micrometres. This chemical imaging technique shows that the flow of heptane results in non-equilibrium condition when the local content of the flocculants reaches the threshold amount needed for the asphaltenes aggregation. The relatively slow process of heptane diffusion into the benzene induces the asphaltenes aggregation followed by their precipitation and compaction. Fast asphaltene aggregation process under heptane flow leads to the formation of the deposit firmly fixed to the surface, while the precipitates formed during the diffusion process of heptane into the benzene can be easily taken from the channel. The FTIR spectroscopic imaging of the deposits formed revealed the spatial inhomogeneity of the precipitated asphaltenes in the direction of the heptane flow in microfluidic channel which is reflected in their different chemical composition and the presence of different functional groups (CH 2 –CH 3 , C O, S O). In particular, it was found that asphaltenes of different types and different CH 2 /CH 3 ratios gradually start to precipitate in the direction of n-heptane flow. The data obtained demonstrate the importance of local concentration of flocculants as well as local characteristics of the system for asphaltenes aggregation, and overall precipitation process in flow regime. Image 1 • Asphaltene deposition process was studied with FTIR spectroscopic imaging under flow in situ. • FTIR imaging monitor the changes of the amount and spatial distribution of solvent, asphaltenes and flocculent simultaneously. • The content and average length of alkyl groups increases in the asphaltene deposit in the direction of the heptane flow. • The deposit in different functional groups (CH2–CH3, C=O, S=O) is heterogeneous in the direction of the heptane flow. [ABSTRACT FROM AUTHOR]