Mannitol as a novel dopant for Cu/SiO2: A low-cost, environmental and highly stable catalyst for dimethyl oxalate hydrogenation without hydrogen prereduction

Effect of Calcination Atmosphere on the Performance of Cu/Al2O3 Catalyst for the Selective Hydrogenation of Furfural to Furfuryl Alcohol

The selective hydrogenation of the biomass platform molecule furfural (FAL) to produce furfuryl alcohol (FA) is of great significance to alleviate the energy crisis. Cu-based catalysts are the most commonly used catalysts, and their catalytic performance can be optimized by changing the preparation method. This paper emphasized the effect of calcination atmosphere on the performance of a Cu/Al2O3 catalyst for the selective hydrogenation of FAL. The precursor of the Cu/Al2O3 catalyst prepared by the ammonia evaporation method was treated with different calcination atmospheres (N2 and air). On the basis of the combined results from the characterizations using in situ XRD, TEM, N2O titration, H2-TPR and XPS, the Cu/Al2O3 catalyst calcined in the N2 atmosphere was more favorable for the dispersion and reduction of Cu species and the reduction process could produce more Cu+ and Cu0 species, which facilitated the selective hydrogenation of FAL to FA. The experimental results showed that the N2 calcination atmosphere improved the FAL conversion and FA selectivity, and the FAL conversion was further increased after reduction. Cu/Al2O3-N2-R exhibited the outstanding performance, with a high yield of 99.9% of FA after 2 h at 120 °C and an H2 pressure of 1 MPa. This work provides a simple, efficient and economic method to improve the C=O hydrogenation performance of Cu-based catalysts.

Emerging catalysts for the ambient synthesis of ethylene glycol from CO2 and its derivatives

Ethylene glycol (EG), a useful chemical raw material, has been widely applied in many aspects of modern society. The conventional preparation of ethylene glycol mainly uses the petroleum route at high temperatures and pressure. More and more approaches have been developed to synthesize EG from CO₂ and its derivatives under mild conditions. In this review, the ambient synthesis of EG from thermocatalysis, photocatalysis, and electrocatalysis is highlighted. The coal-to-ethylene glycol technology, one of the typical thermal catalysis routes for EG preparation, is relatively mature. However, it still faces some problems to be solved in industrialization. The recent progress in the development of coal-to-ethylene glycol technology is introduced. The main focus is on how to realize the preparation of EG under mild conditions. The strategies include doping promoters, modification of supports, design of catalysts with special structures, etc. Furthermore, the emerging technological progress of photocatalytic and electrocatalytic ethylene glycol synthesis under ambient conditions is introduced. Compared with the thermal catalytic reaction, the reaction conditions are milder. However, there are still many problems in large-scale production. Finally, we propose future development issues and related prospects for the ambient synthesis of EG using different catalytic routes.

Silica-Supported Copper (II) Oxide Cluster via Ball Milling Method for Catalytic Combustion of Ethyl Acetate

Highly dispersed CuO/SiO2 catalysts were successfully synthesized by a green process of ball milling (BM) under solvent-free and room temperature conditions. The structural evolution of CuO/SiO2 catalysts prepared by BM was elucidated by TG-DSC, XRD, FT-IR, and XPS characterizations. We found that the copper acetate precursor was dispersed over the layer of copper phyllosilicate which was formed by reacting between the copper acetate precursor and the silica support during the BM process. The copper phyllosilicate layer over the support might play an important role in the stabilization of the CuO cluster (<2 nm) during thermal pretreatment. The 15% CuO/SiO2 catalyst exhibited the best catalytic activity for the catalytic combustion of ethyl acetate as it owned a highest active surface area of CuO among the CuO/SiO2 catalysts with different copper loadings.

Insights into a New Formation Mechanism of Robust Cu/SiO2 Catalysts for Low-Temperature Dimethyl Oxalate Hydrogenation Induced by a Chelating Ligand of EDTA

The Cu/SiO2 catalyst has been widely used in dimethyl oxalate (DMO) hydrogenation due to its low cost and high efficiency. However, the reaction temperature of DMO hydrogenation is higher than the Hüttig temperature of Cu, and the smaller Cu particles are easier to agglomerate. Therefore, there is much interest in constructing a catalyst with a small particle size and strong stability. In the present work, the effect of introducing EDTA on Cu/SiO2 catalysts is systematically investigated. It not only was beneficial to form smaller copper nanoparticles (CuNPs) but also to enhance the stability of Cu species by introducing a suitable amount of EDTA. Furthermore, the surface Cu species were more evenly dispersed, and the number of active sites was increased with the introduction of EDTA; subsequently, the synergistic effect between Cu+ and Cu0 was enhanced. The best performance of 0.08E-Cu/SiO2 had been achieved in the DMO hydrogenation to ethylene glycol (EG), and the DMO conversion and EG selectivity reached 99.9% and 97.7%, respectively. Above all, the 0.08E-Cu/SiO2 catalyst exhibited a high level of stability during the 1200 h life test at 180 °C.

Boron Modified Bifunctional Cu/SiO2 Catalysts with Enhanced Metal Dispersion and Surface Acid Sites for Selective Hydrogenation of Dimethyl Oxalate to Ethylene Glycol and Ethanol

Boron (B) promoter modified Cu/SiO2 bifunctional catalysts were synthesized by sol-gel method and used to produce ethylene glycol (EG) and ethanol (EtOH) through efficient hydrogenation of dimethyl oxalate (DMO). Experimental results showed that boron promoter could significantly improve the catalytic performance by improving the structural characteristics of the Cu/SiO2 catalysts. The optimized 2B-Cu/SiO2 catalyst exhibited excellent low temperature catalytic activity and long-term stability, maintaining the average EG selectivity (Sel.EG) of 95% at 190 °C, and maintaining the average EtOH selectivity (Sel.EtOH) of 88% at 260 °C, with no decrease even after reaction of 150 h, respectively. Characterization results revealed that doping with boron promoter could significantly increase the copper dispersion, enhance the metal-support interaction, maintain suitable Cu+/(Cu+ + Cu0) ratio, and diminish metallic copper particles during the hydrogenation of DMO. Thus, this work introduced a bifunctional boron promoter, which could not only improve the copper dispersion, reduce the formation of bulk copper oxide, but also properly enhance the acidity of the sample surface, so that the Cu/SiO2 sample could exhibit superior EG selectivity at low temperature, as well as improving the EtOH selectivity at high temperature.

Highly Active CuOx/SiO2 Dot Core/Rod Shell Catalysts with Enhanced Stability for the Reverse Water Gas Shift Reaction

Cu-based catalysts are highly active and selective for several CO₂ conversion reactions; however, traditional monometallic Cu-based catalysts suffer poor thermal stability due to the aggregation of copper particles at high temperatures. In this work, we demonstrate a crystal engineering strategy to controllably prepare copper/silica (CuO_x/SiO₂) catalysts for the reverse water gas shift reaction (RWGS) at high temperatures. We show that CuO_x/SiO₂ catalysts derived from the in situ reduction of pure copper silicate nanotubes in a CO₂ and H₂ atmosphere exhibit superior catalytic activity with enhanced stability compared to traditional monometallic Cu-based catalysts for the RWGS at high temperatures. Detailed structural characterization reveals that there is a strong interaction between Cu and SiO₂ in CuO_x/SiO₂ catalysts, which produces more Cu⁺ sites and smaller CuO_x nanoparticles. Moreover, CuO_x/SiO₂ catalysts possess a unique dot core/rod shell structure, which could prevent the aggregation of Cu particles. This structural confinement effect, enhanced CO₂ adsorption by Cu⁺, and small CuO_x nanoparticles presumably caused the catalyst's extraordinary activity with enhanced stability at high temperatures.

Promotional effect of indium on Cu/SiO2 catalysts for the hydrogenation of dimethyl oxalate to ethylene glycol

CuIn/SiO2 with 1.0 wt% indium shows the best catalytic performance for DMO hydrogenation to EG. The synergistic effect of Cu0–Cu+–CuIn alloy in activating H2 molecules and carbonyl bonds is elucidated.

Recent progress in hydrogenation of esters on heterogeneous bimetallic catalysts

The development and research of highly effective heterogeneous catalysts for the hydrogenation of esters, providing high activity and selectivity of the formation of the corresponding alcohols, is an urgent task of modern heterogeneous catalysis.