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Highly dispersed Ni‐TiO2 catalyst has been studied in the process of preparation and under catalytic transfer hydrogenation reaction conditions in supercritical 2‐propanol (250°C, 70 bar) using electron spin resonance in situ. Electron spin resonance in situ has been used to study the process of the catalyst passivation and subsequent reduction of the oxide layer in the gas flow. Reduction of the NiO layer on the surface of passivated Ni nanoparticles has been detected in supercritical 2‐propanol, which is in agreement with kinetic modeling data. It has been found that the reduction of the nickel oxide layer in supercritical 2‐propanol occurs at a lower temperature compared with the reduction in hydrogen flow, according to in situ electron spin resonance study. [ABSTRACT FROM AUTHOR]

The influence of the reaction medium on the surface structure and properties of a Ni-based catalyst used for the reductive transformations of O-, N-, and S-containing aromatic substrates under hydrogen transfer conditions has been studied. The catalysts were characterized by XRD, XPS, and IR spectroscopy and TEM methods before and after the reductive reaction. It has been shown that the conversion of 1-benzothiophene causes irreversible poisoning of the catalyst surface with the formation of the Ni2S3 phase, whereas the conversion of naphthalene, 1-benzofuran, and indole does not cause any phase change of the catalyst at 250 °C. However, after the indole conversion, the catalyst surface remains enriched with N-containing compounds, which are evenly distributed over the surface. [ABSTRACT FROM AUTHOR]

Transfer hydrogenation (TH) is considered as one of the most promising ways to convert biomass into valuable products. This study aims to demonstrate the performance of high-loaded Ni-based catalysts in the TH of phenolic compounds such as guaiacol and dimethoxybenzenes. The experiments were carried out under supercritical conditions at 250 °C using 2-PrOH as the only hydrogen donor. Ni-SiO2 and NiCu-SiO2 were synthesized using the eco-friendly original method based on supercritical antisolvent coprecipitation. It has been found that guaiacol is rapidly converted into 2-methoxycyclohexanol and cyclohexanol, while the presence of Cu impedes the formation of the latter product. Transformations of dimethoxybenzene position isomers are slower and result in different products. Thus, 1,3-dimethoxybenzene loses oxygen atoms transform into methoxycyclohexane and cyclohexanol, whereas the saturation of the aromatic ring is more typical for other isomers. The Cu addition increases specific catalytic activity in the TH of 1,2-and 1,3-dimethoxybenzene compared to the Cu-free catalyst. [ABSTRACT FROM AUTHOR]

Binary Ni–Cu heterogeneous catalysts are known to demonstrate excellent activity in conventional hydrogenation of phenolic compounds, and Cu addition facilitates hydrodeoxygenation (HDO). In this study, we aimed to show the effect of Cu on the specific catalytic activity and selectivity of Ni–Cu catalysts in transfer hydrogenation, in which 2-PrOH was used as a solvent and an H donor. Catalytic transformations of anisole were studied in sub- and supercritical alcohol at 150 and 250 °C. The catalysts were prepared using an environmentally friendly supercritical antisolvent coprecipitation method, which makes it possible to obtain well-dispersed particles (less than 7 nm) at high metal loading (up to 50 wt.%). When copper is added, deactivation of the catalyst in transformations of anisole, including HDO, is observed. The experimental data and the appropriate kinetic analysis demonstrate that there is a decrease in the rate of anisole conversion accompanied by an increase in the concentration of acetone formed during the dehydrogenation of 2-PrOH. [ABSTRACT FROM AUTHOR]

The effect of amines, imines and heterocycle compounds on conversion has been studied in transfer hydrogenation of camphor and 2-PrOH catalyzed by Raney® nickel. Small amount (5 mol% to nickel) of N-containing compound significantly decreases catalyst activity. It has been shown that the poisoning effect mostly depends on molecular size of amines and heterocyclic compounds. For aniline and cyclohexylamine the dependence of camphor conversion on poison/nickel ratio was obtained. Additionally, benzaldehyde, cinnamaldehyde demonstrated higher reactivity compared corresponding imines under transfer hydrogenation conditions. Obtained data explain low activity of nickel-based catalysts when N-containing compounds are presented in reaction mixture. [Display omitted] • Poisoning effect of N-containing compounds on Raney® Ni activity in TH was shown. • For amines and heterocycles poisoning effect correlates with molecular size. • Using cyclohexylamine as titrant TOF of Raney® Ni in TH was calculated as 1.0 h−1. • Low reactivity of imines compared to carbonyl compounds in TH was demonstrated. [ABSTRACT FROM AUTHOR]

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]

• Ni/Al 2 O 3 and Ni-Co/Al 2 O 3 showed high activity in transfer hydrogenation of phenolics. • Ni/Al 2 O 3 primarily promotes hydrodearomatization of phenolic compounds. • The addition of Co to Ni facilitates hydrodeoxygenation of anisole and guaicol. The study investigated the transfer hydrogenation of guaiacol, anisole, phenol, and positional isomers of dimethoxybenezene using 2-PrOH as the H-donor over Ni, Co, and Ni-Co catalysts. The catalysts, which contained 5 wt% metal, were prepared by the deposition-precipitation method. The results showed that the catalysts had developed a pore structure and fine metal particles. The Ni and Ni-Co catalysts demonstrated exceptional activity in the transfer hydrogenation of phenolic compounds with a substrate to metal molar ratio of 100 to 1. Furthermore, the addition of Co to Ni significantly impacted the selectivity of transfer hydrogenation promoting hydrodeoxygenation of anisole and guaiacol. [Display omitted] [ABSTRACT FROM AUTHOR]

A series of monoterpenoids (citral, carvone, menthone, camphor) as well as cyclohexanone and hex-5-en-2-one were subjected to transfer hydrogenation with PriOH/Raney nickel system at 82 or 150 °C. Among monoterpenoids, citral and carvone underwent full conversion at 82 °C within 5 h. [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]