Facile Fabrication of Ultrasmall Copper Species Confined in Mesoporous Silica for Chemo-Selective and Stable Hydrogenation Ethylene Carbonate Derived from CO2

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.

Copper phyllosilicate-derived ultrafine copper nanoparticles with plenty of Cu0and Cu+ for the enhanced catalytic performance of ethylene carbonate hydrogenation to methanol

The hydrogenation of CO₂-derived carbonates to methanol is an alternative route for the indirect utilization of abundant C1 sources. Various Cu/SiO₂catalysts with different copper loading content prepared by using an ammonia evaporation hydrothermal method are implemented to evaluate the catalytic performance of ethylene carbonate (EC) hydrogenation to methanol and ethylene glycol (EG). The Cu loading content was identified to significantly affect the Cu nanoparticles (NPs) size and metal-support interaction. Highly dispersed Cu NPs restricted and embedded in copper phyllosilicate presented a smaller average particle size than the impregnated Cu/SiO₂-IM catalyst. ThexCu/SiO₂catalyst with ultrafine Cu NPs showed abundant Cu-O-Si interfaces, acidic sites, and coherent Cu⁰and Cu⁺species. The 5Cu/SiO₂catalyst achieved methanol yield of 76% and EG yield of 98% at EC conversion of 99%, and no obvious deactivation was observed after long-term operation. The superior catalytic performance of the 5Cu/SiO₂catalyst is attributed to the synergetic effect between the appropriate Cu⁰surface area which provides sufficient active hydrogen, and the atomic ratio of Cu⁺for the polarization and activation of carbon-oxygen bonds.

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+).

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.