Cu-based Catalysts Research Articles

Exploring mesoscopic mass transport effects on electrocatalytic selectivity

Electrocatalytic selectivity is often discussed at the atomic level on the basis of the active site, while ignoring more subtle effects of mesoscopic mass transport. Here we show how transport controls selectivity through the exchange of surface-bound reaction intermediates between the electrode and bulk electrolyte. We argue that the arising kinetic competition changes with the catalyst’s surface area and can become relevant for technologically important reactions including, for example, different products during the electrochemical CO2 reduction on Cu-based catalysts. Combining microkinetic and transport modelling in a multi-scale approach, we specifically explore and quantify this effect for various showcase examples in the experimental literature. Despite its simplicity, our model correctly reproduces selectivity trends with respect to catalyst roughness on all meso-, micro- and atomic scales. The resulting insight provides an alternative or, at least, complementary explanation to changes in electrocatalytic selectivity that have otherwise been attributed to nano-structuring of active sites or electronic effects due to doping or alloying.

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.

Electrocatalytic reduction of CO2 to C2H4 by monometallic Cu4 cluster supported on CeO2(110) surface

Cu-based catalysts have attracted much attention in the field of electrocatalytic CO2 reduction reactions (CRR). In our current work, the electrocatalytic reduction of CO2 by Cu cluster supported on CeO2 is calculated according to the density functional theory (DFT), and some interesting results are obtained. Monometallic copper cluster electrocatalysis of CO2 produce C2 products at lower potentials. The overpotential for the generation of ethylene is much lower than those of other products. The modulation of the substrate CeO2 changed the electronic structure of the Cu clusters and constructed Cu0 and Cu+1 active sites on the catalyst surface, and the coordinated action of Cu0 and Cu+1 made the C–C coupling more likely to take place and facilitated the generation of C2 products. The results of this study help to further understand the role of Cu-based catalysts in the electrocatalytic reduction of CO2 from theoretical point of view and provide guidance for future electrocatalytic experiments based on CRR.

Efficient synthesis of 1,6-Hexanediol via the hydrogenation of dimethyl adipate on CuZn nanoparticles with balanced Cu+-Cu0 sites

In this paper, Cu-based catalyst was prepared by co-precipitation method with DMA hydrogenation as a probe reaction. Compared to the binary Cu-ZnO catalyst, the Cu-ZnO-MxOy (M=Ce, Ti, Zr and Al) catalyst modified with the addition of a third component showed a significant increase in 1,6-Hexanediol (HDO) selectivity. Especially, the dimethyl adipate (DMA) conversion, HDO selectivity and yield of the CZZ catalyst were up to 75.7 %, 53.6 % and 40.6 %, respectively, higher than others. Combining the results of XPS and N2O titration, HDO selectivity was adjusted by varying the Cu+/(Cu0+Cu+) ratio via the third component. The addition of ZrO2 prevented further reduction of Cu+ due to the formation of Cu/ZrO2 or Cu/ZnO species, thus maintaining a constant Cu+/(Cu0+Cu+) ratio and realizing the efficient selectivity of HDO. Furthermore, higher alkaline site density on the CZZ catalyst facilitated CO bond activation further favored the formation of 1,6-hexanediol. In addition, CZZ catalyst had better hydrogen dissociation capacity and smaller catalyst particle size, which will further promote the hydrogen dissociation and thus the hydrogenation process of DMA.

Promotion of Mg(OH)2 in Cu-Based Catalysts for Selective Hydrogenation of Acetylene

Promotion of Mg(OH)2 in Cu-Based Catalysts for Selective Hydrogenation of Acetylene

Toward Developing Superior Cu-Based Metal-Organic Framework-Derived Materials for Electrocatalytic Oxidation of Ethanol.

This project addresses the urgent need for efficient and cost-effective development of electrocatalysts for the ethanol oxidation reaction (EOR). This reaction offers promising renewable energy solutions but faces challenges due to the slow EOR kinetics, typically requiring costly noble metal catalysts. To overcome these limitations, this study focuses on developing CuZn-based EOR catalysts derived from metal-organic frameworks (MOFs), focusing on understanding the structure-performance relationship between pristine MOF-based electrocatalysts and their pyrolyzed counterparts. Herein, bimetallic MOF materials with varying Cu/Zn ratios were synthesized, followed by pyrolysis to produce carbonized counterparts while preserving the fundamental structure but with altered physicochemical properties. Comparative EOR studies revealed the superior performance of pyrolyzed MOFs, demonstrating that optimized Zn-loading is crucial over Cu-based framework for catalyst performance and durability. Overall, this work highlights the potential of MOF-derived Cu-based catalysts for renewable energy applications and provides insights into optimizing their performance through controlled synthesis and post-treatment strategies.

Structure-activity relationships of zirconium-modified copper-based catalysts during methanol steam reforming

Acknowledged as an ideal method for in situ hydrogen generation, methanol steam reforming (MSR) requires high-performance catalysts to enhance production efficiency. Herein, we prepared a series of Zr-modified Cu-based catalysts by a coprecipitation method and conducted a systematic analysis of the impacts of structural variations on MSR performance. Extensive characterization reveals a strong dependence of the catalyst’s surface structure on Zr content. Introducing a moderate amount of Zr to the Cu/ZnO catalysts forms ZnZrOx solid solution and increases Cu dispersion, forming more Cu-ZnZrOx and Cu-ZnO interfacial sites with higher H2 production rate. Further increases in Zr content enlarge Cu nanoparticles and multiply Cu-ZrO2 interfacial sites. The optimal catalyst with a Zn/Zr molar ratio of 5, with the richest Cu-ZnO/Cu-ZnZrOx interfacial sites, achieves the highest H2 production rate of 117.4 mmolH2gcat-1h-1 at 200 °C, which is 1.3 times and 6.8 times higher than those of Cu/ZnO and Cu/ZrO2, respectively.

Insight into the correlation between Cu species and methanol selectivity from CO2 hydrogenation over Cu-based catalyst

The pre-activation of Cu-based catalysts is an important step to fully develop their catalytic potential. The production of active species (Cu+ and Cu0) which play the active site role generally occurs in the activation stage by reducing from Cu2+. Herein, the Cu+/Cu0 ratio of CuZnOAl2O3 (CZA) catalysts was adjusted using different activation atmospheres and the relationship between Cu+/Cu0 ratio of the catalyst and methanol selectivity from CO2 hydrogenation was investigated in detail. Combined with X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), in situ diffuse reflectance infrared Fourier transformation spectroscopy (DRIFTS) characterization, etc. and experimental results, it was observed that the selectivity of methanol was obviously relied on the Cu+/Cu0 ratio of CZA catalyst. This work provides theoretical guidance and feasible scheme to rationally design and optimize the required catalysts.

Steering the Reaction Pathway of CO2 Electroreduction by Tuning the Coordination Number of Copper Catalysts.

Cu-based catalysts are optimal for the electroreduction of CO2 to generate hydrocarbon products. However, controlling product distribution remains a challenging topic. The theoretical investigations have revealed that the coordination number (CN) of Cu considerably influences the adsorption energy of *CO intermediates, thereby affecting the reaction pathway. Cu catalysts with different CNs were fabricated by reducing CuO precursors via cyclic voltammetry (Cyc-Cu), potentiostatic electrolysis (Pot-Cu), and pulsed electrolysis (Pul-Cu), respectively. High-CN Cu catalysts predominantly generate C2+ products, while low-CN Cu favors CH4 production. For instance, over the high-CN Pot-Cu, C2+ is the main product, with the Faradaic efficiency (FE) reaching 82.5% and a partial current density (j) of 514.3 mA cm-2. Conversely, the low-CN Pul(3)-Cu favors the production of CH4, achieving the highest FECH4 value of 56.7% with a jCH4 value of 234.4 mA cm-2. In situ X-ray absorption spectroscopy and Raman spectroscopy studies further confirm the different *CO adsorptions over Cu catalysts with different CN, thereby directing the reaction pathway of the CO2RR.

Hydrophobic SiO2 Armor: Stabilizing Cuδ+ to Enhance CO2 Electroreduction toward C2+ Products in Strong Acidic Environments.

Electroreduction of CO2 in highly acidic environments holds promise for enhancing CO2 utilization efficiency. Due to the HER interference and structural instability, however, challenges in improving the selectivity and stability toward multicarbon (C2+) products remain. In this study, we proposed an "armor protection" strategy involving the deposition of ultrathin, hydrophobic SiO2 onto the Cu surface (Cu/SiO2) through a simple one-step hydrolysis. Our results confirmed the effective inhibition of HER by a hydrophobic SiO2 layer, leading to a high Faradaic efficiency (FE) of up to 76.9% for C2+ products at a current density of 900 mA cm-2 under a strongly acidic condition with a pH of 1. The observed high performance surpassed the reported performance for most previously studied Cu-based catalysts in acidic CO2RR systems. Furthermore, the ultrathin hydrophobic SiO2 shell was demonstrated to effectively prevent the structural reconstruction of Cu and preserve the oxidation state of Cuδ+ active sites during CO2RR. Additionally, it hindered the accumulation of K+ ions on the catalyst surface and diffusion of in situ generated OH- ions away from the electrode, thereby favoring C2+ product generation. In situ Raman analyses coupled with DFT simulations further elucidated that the SiO2 shell proficiently modulated *CO adsorption behavior on the Cu/SiO2 catalyst by reducing *CO adsorption energy, facilitating the C-C coupling. This work offers a compelling strategy for rationally designing and exploiting highly stable and active Cu-based catalysts for CO2RR in highly acidic environments.

Recent progress in understanding the nature of active sites for methanol synthesis over Cu/ZnO catalysts

Copper-zinc-alumina (Cu/ZnO/Al2O3) has been utilized as the leading catalyst for industrial methanol synthesis via hydrogenation of CO and CO2 for more than 50 years. Understanding the nature of active Zn sites at the atomic level is vital for gaining insight into the reaction mechanism and rational design of more efficient Cu/ZnO catalysts for methanol synthesis but remains greatly challenging and has been intensively debated for decades. In this mini-review, we first describe the fundamental insights obtained from well-defined model catalysts and then summarize the recent experimental evidence with respect to dynamic structural and electronic changes in the active Zn phase under realistic working conditions by in situ/operando microscopy/spectroscopy and surface site titration using probing molecules. In the following, we discuss the catalytic mechanism of diverse active structures by theoretical calculations and simulations. Therefore, the critical role of interfacial sites between metallic Cu and ZnO, especially those with oxygen defects, in methanol synthesis via CO2 hydrogenation is emphasized. Finally, we discuss the technical challenges and perspectives in understanding the origins of this Cu-ZnO synergy and rational design of next-generation Cu-based methanol synthesis catalysts.

Building of rich (111) grain boundary in copper for syngas in electrochemical CO2 reduction

Building of grain boundary (GB) in Cu-based catalysts has been demonstrated to be an efficient strategy to control the product selectivity of electrochemical CO2 reduction reaction (eCO2RR). However, the fabrication and modulation of GBs in Cu are still challenging. In this study, a series of bare Cu catalysts with controllable density of Cu(111) GBs were investigated systematically for eCO2RR. These catalysts exhibit superior eCO2RR performance for syngas production with a high FE of ∼80 % and tunable H2/CO ratio of 0.46–2.78. Three-dimensional wormlike Cu with abundant (111) GBs displays a stable H2/CO ratio of ∼0.5 over a wide potential range from −0.9 to −1.2 V (vs. RHE). In situ Raman and ATR-SEIRAS spectroscopy combined with DFT calculations reveal that Cu(111) GBs enhance the adsorption of CO2, lower the energy barriers of CO2 to *COOH and *CO, further highlighting the potential to control syngas production with desirable proportion over Cu-based catalysts.

Theoretical study on CO production mechanism from CO2 reduction on Cu–catalyst surface with different oxidation states

The rational design of copper (Cu)-based catalysts with different oxidation states is essential to achieve highly selective and efficient CO2 electroreduction. However, the effect of different oxide states of Cu-based catalysts has rarely been studied. Herein, the reaction mechanism of CO2 hydrogenation into CO on Cu-based catalysts with different oxidation states, such as Cu(111), Cu2O(111) and CuO(111), was studied using the density functional theory. The most favored pathway for CO production and the rate-controlling step on the three catalyst models were determined. The results show that, Cu2O (111) shows the best catalytic activity among the three catalysts due to the lowest activation barrier. The electronic structure analysis shows that Cu2O has the proper electronic structure to activate CO2 which is further reduced to CO. This work provides an important insight on the effect of oxidation state of Cu-based catalysts on the reduction of CO2 to CO.

Cobalt(II) tetraphenylporphyrin trapped in the pores of Cu2O to enhance the C2+ selectivity towards acidic CO2 electroreduction

Achieving the high selectivity of multicarbon (C2+) products during the acidic CO2 electroreduction remains a formidable challenge due to the serious hydrogen evolution reaction. Herein we report a Cu-based tandem catalyst by implanting molecular cobalt(II) tetraphenylporphyrin (CoTPP) into a porous Cu2O (Cu2O-CoTPP) for improving the C2+ selectivity in acidic media. Specially, CoTPP, as a CO-selective catalyst, is predominantly trapped in the nanopores of Cu2O with the assistance of negative-pressure ultrasonic. The CO2-CO and CO-C2+ tandem catalysis on Cu2O-CoTPP, cooperating with the pore confinement effect of porous Cu2O, boosts the local CO concentration and *CO coverage on Cu sites, evidenced by in-situ Raman spectra and finite element simulations. As a result, Cu2O-CoTPP attains a C2+ Faradaic efficiency of 91.2 % at an industrial-level current density of 800 mA/cm2 in an acidic environment (pH = 1.9), higher than the one (70.6 %) on pristine Cu2O. Meanwhile, such a tandem catalyst obtains a high single-pass carbon efficiency of 52.6 % and the good catalytic stability of at least 20 h. This study offers a spatially-confined Cu-based tandem catalyst for selective C2+ production, presenting the promising application in acidic environments.

Enhanced stability of Cu/AC catalyst with modified hydrophobic layer for methanol oxidative carbonylation to dimethyl carbonate

The by-product water generated in the oxidative carbonylation of methanol to dimethyl carbonate (DMC) causes severe oxidation and deactivation of Cu catalysts, so how to minimize the effect of water on Cu catalysts is a great challenge. Here, we report a strategy to stabilize the Cu+ species in Cu/AC catalyst by hydrophobic modification with methyltriethoxysilane. Compared to Cu/AC catalyst, the modified Cu/ACCH3 catalyst shows that the crystalline structure and the average Cu particle size were not changed, the BET surface area was slightly decreased while the amount of adsorbed methanol was obviously increased. The catalytic stability of Cu/ACCH3 was significantly improved with a deactivation rate of only 11.9 % compared to Cu/AC catalyst (29.2 %). The spent Cu/ACCH3 shows that the water contact angle remained at 119° and Cu+ species were still present as the main component, which was attributed to the confinement effect of the hydrophobic layer that inhibited the aggregation of Cu particles and prevented the Cu+ species from oxidizing water, thus improving the catalyst stability even in the presence of water. This work provides a practical strategy for improving the stability of Cu-based catalysts in the reaction, which produces water as a by-product.

Boosting electrochemical conversion of CO2 to ethanol through the confinement of pyridinic N-B layer on copper nanoparticles

Developing efficient electrocatalysts for CO2 reduction has gained significant attention in the field of sustainable energy, especially the Cu-based catalysts for CO2 conversion to valuable alcohols. In this study, we developed Cu nanoparticles supported on pyridinic N-B doped graphene nanoribbons/amorphous carbon (Cu/BNC-1) as an electrocatalyst for CO2 reduction, exhibiting substantially improved ethanol (EtOH) conversion rate in terms of activity, selectivity, and stability. The Cu/BNC-1 achieved a remarkable 58.64 % Faradaic efficiency (FE) for producing EtOH at −1.0 V vs. RHE with a current density of 20.4 mA cm−2 in 0.5 M KHCO3 electrolyte. In-situ Raman, FT-IR, and density functional theory (DFT) calculations demonstrated that the high C2+ product selectivity of Cu/BNC-1 attributed to the pyridinic N-B modulation, lowering the CO dimerization barrier. Moreover, the synergistic confinement effect of Cu and BNC can stabilize the C-O bond of the *HOCCH intermediate, thereby increasing the yield of EtOH.

Sorption-enhanced intensified CO2 hydrogenation via reverse water–gas shift reaction: Kinetics and modelling

Intensification of CO2 hydrogenation via the reverse water–gas shift (RWGS) reaction for CO production can be achieved through in situ removal of water when hydrophilic adsorbents are incorporated alongside the catalyst in the reaction bed. In this work, seeking to move a step closer to the industrial implementation of this innovative CO2 valorization process, a comprehensive reactor model, validated by experimental data obtained in a fixed-bed reactor, was developed to simulate the behavior of this sorption-enhanced (SE) RWGS process. Simulation and experimental data matched with good accuracy, demonstrating the striking benefits brought by the adsorbent addition, such as an almost doubling of the CO production rate at 300 °C. The kinetics of RWGS reaction over a Cu-based catalyst and H2O adsorption on a 13X zeolite adsorbent were studied both experimentally and theoretically and the kinetic models were integrated into the reactor model to assess the performance of SE-RWGS process. Fitting of the RWGS reaction rates by a Langmuir-Hinschelwood-Hougen-Watson-type heterogeneous kinetic model suggested that the rate-determining step of the reaction is the surface interaction between an adsorbed CO2 molecule and a H* species on catalytic sites of different nature. Meanwhile, the dynamic behavior of water adsorption was effectively simulated by a semi-empirical double-stretched exponential model combined with the Sips isotherm model. The results of this work could be applied to the design and scale-up of the SE-RWGS process, which offers considerable improvements over the thermodynamically constrained conventional process. The intensified approach represents a promising avenue for the effective conversion of carbon dioxide into CO, as well as into other value-added chemicals as part of a multi-stage CO2 reduction process.

Regulating Cu Oxidation State for Electrocatalytic CO2 Conversion into CO with Near-Unity Selectivity via Oxygen Spillover.

Cu-based catalysts are the most intensively studied in the field of electrocatalytic CO2 reduction reaction (CO2RR), demonstrating the capacity to yield diverse C1 and C2+ products albeit with unsatisfactory selectivity. Manipulation of the oxidation state of Cu sites during CO2RR process proves advantageous in modulating the selectivity of productions, but poses a formidable challenge. Here, an oxygen spillover strategy is proposed to enhance the oxidation state of Cu during CO2RR by incorporating the oxygen donor Sb2O4. The Cu-Sb bimetallic oxide catalyst attains a remarkable CO2-to-CO selectivity approaching unity, in stark contrast to the diverse product distribution observed with bare CuO. The exceptional Faradaic efficiency of CO can be maintained across a wide range of potential windows of ≈700mV in 1m KOH, and remains independent of the Cu/Sb ratio (ranging from 0.1:1 to 10:1). Correlative calculations and experimental results reveal that oxygen spillover from Sb2O4 to Cu sites maintains the relatively high valence state of Cu during CO2RR, which diminishes the binding strength of *CO, thereby achieving heightened selectivity in CO production. These findings propose the role of oxygen spillover in CO2RR over Cu-based catalysts, and shed light on the rational design of highly selective CO2 reduction catalysts.

Efficient Descriptor for Designing High-Performance Cu-Based Catalysts for the Hydrogenation of Dimethyl Oxalate to Methyl Glycolate

Efficient Descriptor for Designing High-Performance Cu-Based Catalysts for the Hydrogenation of Dimethyl Oxalate to Methyl Glycolate

Selective hydrogenation of furfural to furfuryl alcohol over copper-cobalt bimetallic catalyst

Cu-based catalysts have been widely studied as selectively hydrogenated furfural. However, due to the weak hydrogenation activity of the mono-metal copper-based catalyst, the interaction with furfural is usually weak, and the accessibility of the active site is severely limited. A micro-doping strategy was proposed in this study to solve these problems. Trace amounts of cobalt metal are doped into copper using equal volume impregnation. Compared with the Cu/MgO catalyst, the bimetallic CuCo/MgO-0.04 catalyst changes metal particles' size and valence and regulates the catalyst surface's electronic environment. Electron transfer occurs between Co and Cu, and many active sites are generated for adsorption and activation of CO double bonds, and hydrogenation reactions occur with adjacent H protons to improve the selectivity of furfuryl alcohol. CuCo/MgO-0.04 catalyst has excellent catalytic performance of 100 % furfural conversion and 99.4 % furfural alcohol selectivity. Combined with experimental data, kinetic studies, and theoretical calculations, it was confirmed that the d-band center shifted up in the catalyst doped with trace metal cobalt, which optimized the adsorption energy and configuration of furfural and reduced the reaction barrier more effectively. This study provides a strategy to support the partial doping of highly dispersed Cu nanoparticles with a small amount of Co metal. It achieves excellent catalytic properties and chemical selectivity in selective hydrogenation reactions.