Marina V. Bukhtiyarova

Alkyl furfuryl ethers are promising additives to motor fuels, which can be produced by reductive etherification of furfural with alkyl alcohol. The Cu/Al₂O₃ catalyst was prepared using a copper ammonia complex as the precursor of active component. The catalytic behavior of the physical mixture of the Cu/Al₂O₃ catalyst and ZSM-5-Al₂O₃ composite was studied in the reductive etherification of furfural in a flow reactor using H₂ as a reducing agent. This process involves the sequential hydrogenation of furfural on the Cu⁰ sites of the Cu/Al₂O₃ catalyst, followed by the etherification of the resulting furfuryl alcohol on the acid sites of zeolite. The highest yield of 2‑(isopropoxymethyl)furan (IMF) of 85% was achieved over the catalytic system (0.25–0.5 mm) including HZSM-5(Si/Al = 40)-Al₂O₃ due to the optimal concentration of strong Brønsted acid sites in the composite. A physical mixture of the Cu/Al₂O₃ catalyst and the 30% ZSM-5(40)-Al₂O₃ composite, in the form of granules (trilobe extrudates of 2–5 × 1.25 mm), showed an IMF yield of 72.5%.

The most common method for the synthesis of copper‐containing supported catalysts is impregnation of the support with a copper salt solution. However, calcination and reduction of the resulting materials can lead to agglomeration of copper species and a decrease in catalytic activity. The synthesis of highly dispersed copper particles on the support surface can be performed using ammonia evaporation method with a copper ammine complex as a precursor. This review considers the effect of copper loading and the support nature on the structure of the obtained catalysts with a focus on the benefits of the ammonia evaporation method for preparation of the Cu/SiO ₂ catalysts compared to other methods. This review summarizes the results concerning influence of the synthesis conditions of the ammonia evaporation method on the morphology and structure of Cu‐based catalysts. The effect of ammonia evaporation temperature and solution pH on copper dispersion, copper particle size, and reducibility of the Cu‐based catalysts is also included. The morphology of the silica support and the particle size of the silica sol have impact on the formation of copper phyllosilicate in the Cu/SiO ₂ catalysts.

This review discusses the use of supported and bulk non-noble metal catalysts for the liquid-phase selective hydrogenation of bi- and polyfunctional organic compounds in flow mode.

Copper nanoparticles supported on alumina have been synthesized from CuAl-layered double hydroxide and have been studied in methanol oxidation at different molar ratios of the components of the reaction feed by in situ XPS and mass-spectrometry.

Recently, bio-jet fuels have attracted significant attention as a prospective additive to conventional aviation fuels since this is the most promising strategy to reduce CO₂ emissions in the aviation sector in the future.

Many research papers describe selective hydrogenation of functional groups, such as nitro groups, carbonyl groups, or unsaturated carbon bonds to obtain fine chemicals or precursors of pharmaceuticals. Quite often, the catalyst performance is investigated in batch or continuous flow reactors without finding advantages and disadvantages of this or that regime. At the same time, the transition from batch processes to continuous flow occurs on the industrial scale. However, the batch process can be preferable for some reactions, in spite of its drawbacks. This review article aims to identify all publications that consider selective hydrogenation of functional groups in organic compounds, both in batch and continuous flow reactors, at the same reaction conditions that allow making conclusions about the benefits of one of the regimes in a particular case.

Cu-containing layered double hydroxides (LDHs) were synthesized by a co-precipitation method at different reaction conditions, such as aging time, pH, precipitation rate and synthesis temperature. The effect of these parameters on the structure and chemical composition of the catalysts were investigated using a set of physical methods, including thermogravimetric analysis (TGA), X-ray diffraction (XRD), H₂-TPR and in situ X-ray photoelectron spectroscopy (XPS). It allowed for checking of the reducibility of the samples. 5-Acetoxymethylfurfural was catalytically hydrogenated to 5-(acetoxymethyl)-2-furanmethanol (AMFM) over Cu-containing catalysts synthesized from layered double hydroxides so as to investigate its catalytic properties in flow reaction. It was shown that synthesis pH decreasing from 10 to 8 resulted in rise of AMF conversion that coincided with the higher surface Cu/Al ratio obtained by XPS. Preferable aging time of LDH materials for obtaining the most active catalyst was 2 h, an amount of time that favored the production of the catalyst with high surface Cu/Al ratio up to 0.38. Under optimized reaction conditions, the AMFM yield was 98%. Finally, a synthesis strategy for the preparation of highly efficient Cu-based hydrogenation catalyst with optimized characteristics is suggested.

Article published online: 01 August 2022 Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Levulinic acid and its esters (e.g., ethyl levulinate, EL) are platform chemicals derived from biomass feedstocks that can be converted to a variety of valuable compounds. Reductive amination of levulinates with primary amines and H₂ over heterogeneous catalysts is an attractive method for the synthesis of N-alkyl-5-methyl-2-pyrrolidones, which are an environmentally friendly alternative to the common solvent N-methyl-2-pyrrolidone (NMP). In the present work, the catalytic properties of the different nickel phosphide catalysts supported on SiO₂ and Al₂O₃ were studied in a reductive amination of EL with n-hexylamine to N-hexyl-5-methyl-2-pyrrolidone (HMP) in a flow reactor. The influence of the phosphorus precursor, reduction temperature, reactant ratio, and addition of acidic diluters on the catalyst performance was investigated. The Ni₂P/SiO₂ catalyst prepared using (NH₄)₂HPO₄ and reduced at 600 °C provides the highest HMP yield, which reaches 98%. Although the presence of acid sites and a sufficient hydrogenating ability are important factors determining the pyrrolidone yield, the selectivity also depends on the specific features of EL adsorption on active catalytic sites.

Aminomethylhydroxymethylfuran derivatives are well known compounds which are used in the pharmaceutical industry. Reductive amination of 5-hydroxymethylfurfural (HMF) derived from available non-edible lignocellulosic biomass is an attractive method for the synthesis of this class of compounds. In the present study, the synthesis of N-substituted 5-(hydroxymethyl)-2-furfuryl amines and 5-(acetoxymethyl)-2-furfuryl amines was performed by two-step process, which includes the condensation of furanic aldehydes (HMF and 5-acetoxymethylfurfural) with primary amines in methanol on the first step and the reduction of obtained imines with hydrogen in a flow reactor over CuAlO_x catalyst derived from layered double hydroxide on the second step. This process does not require isolation and purification of intermediate imines and can be used to synthesize a number of aminomethylhydroxymethylfurans in good to excellent yield.