Alkali and Alkaline Earth Metals (K, Ca, Sr) Promoted Cu/SiO2 Catalyst for Hydrogenation of Methyl Acetate to Ethanol

The advancing effects of various alkali and alkaline earth metals (inclusive of K, Ca, and Sr) modified Cu/SiO2 catalysts, prepared with a modified precipitation-gel method, were investigated for the production of ethanol via hydrogenation of methyl acetate. Our results showed that Sr-doped catalysts exhibited the best and most consistent results during catalytic tests. A series of techniques, including X-ray diffraction technique, Raman spectroscopy, N2 adsorption/desorption, N2O titration method, FTIR spectroscopy, and H2 temperature, programmed desorption and reduction (TPD and TPR), and X-ray Photoelectron Spectroscopy, which was used to check the detailed characterization of Sr modification in the catalyst and its structural impacts on the properties of the catalyst. These results demonstrated that the addition of 5%Sr could strengthen the intrinsic stability of the catalyst by formulating the appropriate ratio of Cu+/(Cu0 + Cu+) to facilitate catalytic outcome improvement. The addition of 5%Sr-30%Cu/SiO2 under the most favorable conditions, resulting in the peak conversion of MA (95%) and ethanol selectivity (96%), indicates its magnificent catalytic stabilizing effects. Furthermore, the best performing catalyst was compared and tested under various conditions (LHSV and temperatures) and a 300 h long life run.

Hydrogenation of Carboxylic Acids, Esters, and Related Compounds over Heterogeneous Catalysts: A Step toward Sustainable and Carbon-Neutral Processes

The catalytic hydrogenation of esters and carboxylic acids represents a fundamental and important class of organic transformations, which is widely applied in energy, environmental, agricultural, and pharmaceutical industries. Due to the low reactivity of the carbonyl group in carboxylic acids and esters, this type of reaction is, however, rather challenging. Hence, specifically active catalysts are required to achieve a satisfactory yield. Nevertheless, in recent years, remarkable progress has been made on the development of catalysts for this type of reaction, especially heterogeneous catalysts, which are generally dominating in industry. Here in this review, we discuss the recent breakthroughs as well as milestone achievements for the hydrogenation of industrially important carboxylic acids and esters utilizing heterogeneous catalysts. In addition, related catalytic hydrogenations that are considered of importance for the development of cleaner energy technologies and a circular chemical industry will be discussed in detail. Special attention is paid to the insights into the structure-activity relationship, which will help the readers to develop rational design strategies for the synthesis of more efficient heterogeneous catalysts.

Recent advances in the routes and catalysts for ethanol synthesis from syngas

Ethanol, as one of the important bulk chemicals, is widely used in modern society. It can be produced by fermentation of sugar, petroleum refining, or conversion of syngas (CO/H₂). Among these approaches, conversion of syngas to ethanol (STE) is the most environmentally friendly and economical process. Although considerable progress has been made in STE conversion, control of CO activation and C-C growth remains a great challenge. This review highlights recent advances in the routes and catalysts employed in STE technology. The catalyst designs and pathway designs are summarized and analysed for the direct and indirect STE routes, respectively. In the direct STE routes (i.e., one-step synthesis of ethanol from syngas), modified catalysts of methanol synthesis, modified catalysts of Fischer-Tropsch synthesis, Mo-based catalysts, noble metal catalysts and multifunctional catalysts are systematically reviewed based on their catalyst designs. Further, in the indirect STE routes (i.e., multi-step processes for ethanol synthesis from syngas via methanol/dimethyl ether as intermediates), carbonylation of methanol/dimethyl ether followed by hydrogenation, and coupling of methanol with CO to form dimethyl oxalate followed by hydrogenation, are outlined according to their pathway designs. The goal of this review is to provide a comprehensive perspective on STE technology and inspire the invention of new catalysts and pathway designs in the near future.

Engineering of Yolk/Core-Shell Structured Nanoreactors for Thermal Hydrogenations

Heterogeneous hydrogenation reactions are of great importance for chemical upgrading and synthesis, but still face the challenges of controlling selectivity and long-term stability. To improve the catalytic performance, many hydrogenation reactions utilize special yolk/core-shell nanoreactors (YCSNs) with unique architectures and advantageous properties. This work presents the developmental and technological challenges in the preparation of YCSNs that are potentially useful for hydrogenation reactions, and provides a summary of the properties of these materials. The work also addresses the scientific challenges in applications of these YCSNs in various gas and liquid-phase hydrogenation reactions. The catalyst structures, catalytic performance, structure-performance relationships, reaction mechanisms, and unsolved problems are discussed too. Also, a brief outlook and opportunities for future research in this field are presented. This work on the advancements in YCSNs might inspire the creation of new materials with desired structures for achieving maximal hydrogenation performances.

Synthesis of cyclohexanol and ethanol via the hydrogenation of cyclohexyl acetate with Cu2Znx/Al2O3 catalysts

The Cu2Zn1.25/Al2O3 catalyst exhibited 93.9% conversion and 97.2% selectivity to ethanol with 97.1% selectivity to cyclohexanol for the hydrogenation of cyclohexyl acetate due to the abundant weak acid sites and the highest ratio of Cu+/(Cu0 + Cu+).

A Ni-foam-structured MoNi4-MoOx nanocomposite catalyst for hydrogenation of dimethyl oxalate to ethanol

We report a Ni-foam-structured MoNi4-MoOx nanocomposite catalyst derived from NiMoO4 spinel in situ grown on Ni-foam, which is highly active, selective (>93%) and stable for the gas-phase hydrogenation of dimethyl oxalate to ethanol. Such a reaction proceeds mainly through ethylene glycol formation, whereas a pathway through methyl acetate (MA) formation also occurs. Catalyst activity and selectivity are primarily governed by the MoNi4 nanoalloy but can be further improved by an MoOx modifier, due to the synergistic MoNi4-MoOx interaction that markedly promotes the MA hydrogenation to EtOH.

Effect of Cu loading on the structural evolution and catalytic activity of Cu–Mg/ZnO catalysts for dimethyl oxalate hydrogenation

Proper Cu loading introduced into the Cu–Mg/ZnO system facilitates strengthening of the Cu–Zn synergistic effect and optical surface chemical properties.

Efficient synthesis of methanol and ethylene glycol via the hydrogenation of CO2-derived ethylene carbonate on Cu/SiO2 catalysts with balanced Cu+–Cu0 sites

The preparation method for Cu/SiO₂ catalysts had a great impact on the Cu⁺/Cu⁰ ratio and catalytic performance.

Effect of Aging Methods on CuZnAl Catalysts for Methyl Acetate Hydrogenation

A series of CuZnAl catalysts derived from layered double hydroxide precursors with different Cu/Zn molar ratios were synthesised by a co-precipitation method for methyl acetate hydrogenation. The best catalytic performance was obtained when the Cu/Zn molar ratio reached 0.25:1. After fixing the Cu/Zn molar ratio at 0.25:1, the effect of aging methods, including ultrasound, high shear mixer stirring, and magnetic stirring, were investigated, which showed that 0.25CuZnAl-u and 0.25CuZnAl-h exhibited a higher conversion and selectivity than that of 0.25CuZnAl-m, especially under low reaction temperatures. The physicochemical properties of the CuZnAl catalysts were characterised by X-ray diffraction, inductively coupled plasma–atomic emission spectroscopy, N2 physisorption, N2O chemisorption, transmission electron microscopy, H2-temperature-programmed reduction, X-ray photoelectron spectroscopy, and H2-temperature-programmed desorption. It was found that compared with 0.25CuZnAl-m, 0.25CuZnAl-u and 0.25CuZnAl-h possessed a stronger interaction between Cu and the support, smaller copper particle size, and higher copper dispersion, which improved the catalytic performance.

Intermediate product regulation over tandem catalysts for one-pass conversion of syngas to ethanol

Selective conversion of syngas (CO/H₂) to ethanol is an attractive but challenging target.

Recent progress in improving the stability of copper-based catalysts for hydrogenation of carbon–oxygen bonds

Five different strategies to enhance the stability of Cu-based catalysts for hydrogenation of C–O bonds are summarized in this review.