Catalytic Performance Of Cu Research Articles

The influence of La incorporation on the performance of the CuxCeyLa1-(x+y)O2-δ catalysts for CO2 hydrogenation to methanol

The effect of La incorporation on the catalytic performance of Cu–CeO2 for CO2 hydrogenation to methanol was investigated. The increase of the CeO2 lattice constant and shift in the F2g band from Raman spectroscopy confirmed La incorporation into the CeO2 lattice. The La atomic percent of ≤ 19 % was the upper limit for the amount of La incorporated fully into the CeO2 lattice without any phase segregation. XPS results of Cu0.25Ce0.56La0.19O2-δ assumed to have full La incorporation, showed a maximum concentration of oxygen vacancies that facilitated CO2 adsorption and conversion to methanol.The lattice fringes from HRTEM and lattice expansion confirmed that Cu was located on the catalyst surface for the synthesized catalysts. Cu0.25Ce0.56La0.19O2-δ showed an improvement in the methanol space-time yield when the temperature was increased from 260 °C to 280 °C, in contrast to the catalysts with excess La on the surface. The descriptors for the methanol production were the availability of oxygen vacancies and the metal-metal oxide interaction (Cu–CexLa1−xO2-δ and Cu–La2O2CO3). The smaller metallic Cu crystallite size for Cu0.25Ce0.19La0.56O2-δ suggested increased interactions between Cu0 and the CexLa1−xO2-δ support, which was conducive for methanol formation. The highest performance of Cu0.25Ce0.56La0.19O2-δ at a higher temperature of 280 °C and pressure of 50 bar with a methanol space-time yield of 55.2 gCH3OH.kgcatal.h−1 was attributed to the excellent thermal stability of the formed CexLa1−xO2-δ solid solution support interacting with Cu which prevented sintering.

Toward Durable CO2 Electroreduction with Cu-Based Catalysts via Understanding Their Deactivation Modes.

The technology of CO2 electrochemical reduction (CO2ER) provides a means to convert CO2, a waste greenhouse gas, into value-added chemicals. Copper is the most studied element that is capable of catalyzing CO2ER to obtain multicarbon products, such as ethylene, ethanol, acetate, etc., at an appreciable rate. Under the operating condition of CO2ER, the catalytic performance of Cu decays because of several factors that alters the surface properties of Cu. In this review, these factors that cause the degradation of Cu-based CO2ER catalysts are categorized into generalized deactivation modes, that are applicable to all electrocatalytic systems. The fundamental principles of each deactivation mode and the associated effects of each on Cu-based catalysts are discussed in detail. Structure- and composition-activity relationship developed from recent in situ/operando characterization studies are presented as evidence of related deactivation modes in operation. With the aim to address these deactivation modes, catalyst design and reaction environment engineering rationales are suggested. Finally, perspectives and remarks built upon the recent advances in CO2ER are provided in attempts to improve the durability of CO2ER catalysts.

Ultrahigh peroxidase-like catalytic performance of Cu–N4 and Cu–N4S active sites-containing reduced graphene oxide for sensitive electrochemical biosensing

Carbon-based nanozymes possessing peroxidase-like activity have attracted significant interest because of their potential to replace native peroxidases in biotechnology. Although various carbon-based nanozymes have been developed, their relatively low catalytic efficiency needs to be overcome to realize their practical utilization. Here, inspired by the elemental uniqueness of Cu and the doped elements N and S, as well as the active site structure of Cu-centered oxidoreductases, we developed a new carbon-based peroxidase-mimicking nanozyme, single-atom Cu-centered N- and S-codoped reduced graphene oxide (Cu-NS-rGO), which preserved many Cu–N4 and Cu–N4S active sites and showed dramatically high peroxidase-like activity without any oxidase-like activity, yielding up to 2500-fold higher catalytic efficiency (kcat/Km) than that of pristine rGO. The high catalytic activity of Cu-NS-rGO might be attributed to the acceleration of electron transfer from Cu single atom as well as synergistic effects from both Cu–N4 and Cu–N4S active sites, which was theoretically confirmed by Gibbs free energy calculations using density functional theory. The prepared Cu-NS-rGO was then used to construct an electrochemical bioassay system for detecting choline and acetylcholine by coupling with the corresponding oxidases. Using this system, both target molecules were selectively determined with high sensitivity that was sufficient to clinically determine their levels in physiological fluids. Overall, this study will facilitate the development of nanocarbon-based nanozymes and their electrochemical biosensing applications, which can be extended to the development of miniaturized devices in point-of-care testing environments.

Hydrolysis Precipitation Method for the Preparation of Cu‐ZnO@Al2O3 Catalyst in Methanol Steam Reforming

AbstractA hydrolysis precipitation method was developed to prepare Cu based catalyst for methanol steam reforming. A comparison of the hydrolysis precipitation and the conventional coprecipitation method was conducted. The test results present that Cu‐ZnO@Al2O3 prepared by hydrolysis precipitation exhibits better catalytic activity and stability in MSR reaction. XRD, XRF, EDS, SEM, TPR, XPS and N2 adsorption/desorption reveal that the high catalytic performance of Cu based catalyst from hydrolysis precipitation could be attributed to developed pore organization, surface enrichment of active components and higher reducibility.

Cu modified VOx/Silicalite-1 catalysts for propane dehydrogenation in CO2 atmosphere

Propane dehydrogenation in CO2 atmosphere (PDH-CO2) is of interest with a potential to raise propane conversion. Here the catalytic performance of Cu modified 10VOx/Silicalite-1(S-1) for PDH-CO2 is presented for the first time. The initial propane conversion of 68.8% on 0.5Cu-10VOx/S-1 was reached from 59.3% on 10VOx/S-1, along with the CO2 conversion of 44.5% from 32.4%. The role of S-1 support and Cu modification were elucidated by means of X-ray diffraction (XRD), ultraviolet–visible diffuse reflection (UV–Vis), NH3/CO2 temperature-programmed desorption (NH3/CO2-TPD), H2 temperature-programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) characterization. While dispersing VOx, non-acidic S-1 minimized the side reactions usually occurring on the strong acidic sites. Cu modification promoted the dispersion of VOx and enabled 10VOx/S-1 exposing more weak acidic sites and basic sites, boosting respectively the adsorption of propane and CO2, for concurrently accelerating the reverse water gas shift (RWGS). Moreover, the highly dispersed V5+ was formed on the surface whereas the percentage of inactive V3+ decreased.

Origin of copper as a unique catalyst for C-C coupling in electrocatalytic CO2 reduction.

High yields of C2 products through electrocatalytic CO2 reduction (eCO2R) can only be obtained using Cu-based catalysts. Here, we adopt the generalized frontier molecular orbital (MO) theory based on first-principles calculations to identify the origin of this unique property of Cu. We use the grand canonical ensemble (or fixed potential) approach to ensure that the calculated Fermi level, which serves as the frontier orbital of the metal catalyst, accurately represents the applied electrode potentials. We determine that the key intermediate OCCO assumes a U-shape configuration with the two C atoms bonded to the Cu substrate. We identify the frontier MOs that are involved in the C-C coupling. The good alignment of the Fermi level of Cu with these frontier MOs is perceived to account for the excellent catalytic performance of Cu for C-C coupling. It is expected that these new insights could provide useful guidance in tuning Cu-based catalysts as well as designing non-Cu catalysts toward high-efficiency eCO2R.

Enhancing Fenton-like Degradation of Organic Pollutants at Neutral pH by Multivalent Cu NCs/HAp Nanocatalysts.

Heterogeneous Fenton-like catalysis is a widely used method for the degradation of organic pollutants. However, it still has some limitations such as low activity in the neutral condition, low conversion rates of metals with different valence states, and potential secondary metal pollution. In this study, a Fenton-like nanocatalyst was first created by generating ultrasmall copper nanoclusters (Cu NCs) on the surface of hydroxyapatite (HAp) through a process of doping followed by modification. This resulted in the formation of a composite nanocatalyst known as Cu NCs/HAp. With the help of hydrogen peroxide (H2O2), Cu NCs/HAp exhibits an outstanding Fenton-like catalytic performance by efficiently degrading organic dyes such as methylene blue under mild neutral conditions. The removal rate can reach over 83% within just 30 min, demonstrating ideal catalytic universality and stability. The improved Fenton-like catalytic performance of Cu NCs/HAp can be ascribed to the synergistic effect of the multivalent Cu species through two simultaneous reaction pathways. During route I, the embedded Cu NCs with a core-shell Cu0/Cu+ structure can undergo sequential oxidation to form Cu2+, which continuously activates H2O2 to generate hydroxyl radicals (•OH) and singlet oxygen (1O2). In route II, Cu2+ produced from route I and initially adsorbed on the surface of HAp can be reduced by H2O2, thus regenerating Cu+ species for route I and achieving a closed-loop reaction. This work has confirmed that Cu NCs loaded on HAp may be an alternative Fenton-like catalyst for degradation of organic pollutants and environmental remediation, opening up new avenues for potential applications of other Cu NCs in future water pollution control.

Copper nanoparticles embedded into nitrogen-doped carbon fiber felt as recyclable catalyst for benzene oxidation under mild conditions

Herein, an active and stable nanocatalyst based on copper nanoparticles embedded into nitrogen-doped carbon fiber felts (NCFFs) was fabricated through a co-assembly protocol. The catalytic performance of Cu (20 wt.%)/NCFF was contributed to its structural and morphological features, which were studied by various characterization techniques. The data illustrated that the catalyst showed reasonable activity and excellent selectivity in oxidation of benzene-to-phenol (25.2 and 100% for yield and selectivity respectively) in the presence of an environmentally-friendly oxidant. Furthermore, the microscopic catalyst kept its long-term performance until nine successive runs, which turns it into a bulk alternative in large-scale schemes.

Stepwise conversion of methane to methanol on Cu and Fe/zeolites prepared in solid state: the effect of zeolite type and activation temperature

AbstractBACKGROUNDGrand efforts have been recently devoted to the development of catalysts based on the excellent performance of Cu‐ and Fe‐dependent enzymes in methanotrophic bacteria for the partial oxidation of methane to methanol under ambient conditions. As a continuation of the study on the stepwise manner for this conversion over zeolite‐based catalysts, in this work, the effects of zeolite topology and activation temperature on the catalytic performance of Cu‐ and Fe‐containing zeolites were investigated.RESULTSCu species exchanged in the medium‐pore zeolites (mordenite, ZSM‐5, and ferrierite) afforded better methanol production, while large‐pore zeolites (zeolite β and zeolite γ) were inappropriate to accommodate active Cu sites. Notably, Cu/silicalite‐1 containing CuO species was also reactive to methane after the activation in O2, yielding a minor methanol amount. Furthermore, the activity of Fe/mordenite towards the methanol in the O2‐assisted procedure was reported for the first time but with a much lower yield as compared to that of Cu/mordenite. The methanol yield over Cu/mordenite increased with the activation temperature because increasing the activation temperature favored the Cu‐exchange degree with a higher priority at the side pockets as compared to the main channels of mordenite, as evidenced from infrared analysis.CONCLUSIONThe selective oxidation of methane to methanol by O2 via a stepwise manner can be obtained over both ion‐exchanged Cu species and well‐dispersed CuO nanoparticles with better activity being recorded for the former. The activity of Cu‐exchanged zeolites was considerably dependent on the zeolite topology and the charge‐balancing position of the Cu2+ cations. © 2023 Society of Chemical Industry (SCI).

Rational construction of noble metal-free Cu(I) anchored Zr-MOF for efficient fixation of CO2 from dilute gas at ambient conditions

The utilization of carbon dioxide (CO2) from dilute gas as C1 feedstock for synthesis of high-value chemicals such as α-alkylidene cyclic carbonates is one of the promising approaches towards mitigating the increasing atmospheric CO2 concentration. Consequently, herein, we demonstrate the application of UiO-MOF functionalized with bipyridine sites for facile anchoring of catalytically active noble metal-free copper (I) sites by post-synthetic treatment. The Cu(I) anchored UiO-MOF exhibits an excellent catalytic activity for coupling CO2 with propargylic alcohols affording α-alkylidene cyclic carbonates, valuable commodity chemicals at mild conditions of 1 atm of CO2 (balloon). Furthermore, the MOF catalyst showed good activity for fixation carbon dioxide from dilute gas (CO2:N2 = 13:87%) condition. The superior catalytic performance of Cu(I)@UiO-MOF over the homogeneous counterpart has been attributed to a synergistic effect of high CO2-philicity of MOF and catalytic activity of copper (I) sites exposed in the 1D channels of the MOF. The catalyst can be recycled up to five cycles with retention of catalytic efficiency and its heterogeneity enjoyed over the reaction period. This work demonstrates the rational integration of non-noble metal catalytic sites in functionalized frameworks for the efficient fixation of CO2 from dilute gas into fine chemicals.

Insight into copper-cerium catalysts with different Cu valence states for CO-SCR and in-situ DRIFTS study on reaction mechanism

Copper-cerium catalysts have received extensive attention for their excellent catalytic performance in the field of NO reduction with CO. In this work, Cu+-Ce and Cu2+-Ce systems were designed to examine the catalytic potential of Cu+ and Cu2+. A series of catalysts were characterized by XRD, BET, HRTEM, EDS, H2-TPR, Raman, XPS and in-situ DRIFTS in different NO + CO atmospheres. Cu+-Ce catalyst possesses a large amount of Cu+ that can promote the synergy between Cu+ and Ce4+ and adsorb CO to form Cu+-CO species consuming more active oxygen, thus generating more oxygen vacancies than Cu2+-Ce, which improve the catalytic performance of Cu+-Ce catalyst at low temperatures. In different NO + CO atmospheres, Cu+-Ce catalyst always maintains better catalytic performance to make an excellent universal applicability. In-situ DRIFTS in different NO + CO atmospheres provided evidence to confirm that oxygen vacancy is indeed active site for decomposing NO. And it also demonstrated that the CuCe/CuCe-S (Cu2+-Ce system) and CuCe/Ce-S (Cu+-Ce system) catalysts are dominated by L-H mechanism with different CO adsorption behavior at low temperatures.

Electrochemical Synthesis of Shape‐controlled Cu−Ni Nanocomposite and its Application for Nonenzymatic Glucose Sensing at Nanomolar Level

AbstractThe electrodeposition method was firstly applied to obtain uniform cube‐shaped copper nanoparticles on conductive glass (ITO), and then a layer of tiny nickel nanoparticles. A bimetallic composite electrode (Cu−Ni/ITO), characterized by TEM, XPS and XRD, was prepared to construct the non‐enzyme electrochemical glucose sensor with high catalytic activity. The catalytic performance of Cu−Ni/ITO had been greatly improved, probably due to the synergistic bimetallic catalysis effect. The electrode had a satisfactory linear response in the range of 2.5×10−7 M to 2.6×10−3 M, with detection limit as low as 67 nM. Besides, Cu−Ni/ITO had good anti‐interference ability and reproducibility, indicating the promising application for glucose detection in practical samples.

Spotlight on Cu/SAPO-34 with high hydrothermal stability induced by a small amount of SSZ-39

The stable structure is key to improving the performance of the selective catalytic reduction of nitrogen oxide (NOx) with ammonia (NH3-SCR) on Cu/zeolite catalysts after the high-temperature hydrothermal aging. In this work, the SSZ-39 seed with a stable texture property was introduced into the precursor of SAPO-34 to fabricate the zeolite with a hybrid microstructure of SAPO-34 + SSZ-39 (simplified as SA + SZ). The Si distributions of the original Al-rich SAPO-34 zeolite (simplified as SA) were optimized by the hybrid microstructure of SA + SZ. The results of solid nuclear magnetic resonance (NMR) and ammonia (NH3) adsorption indicate more Si(1OAl) structures with strong acidity on Cu/(SA + SZ) catalyst rather than on Cu/SA. The NH3-SCR performance within the reaction region of 150–550 °C is enhanced on the former. In addition, the Si(nOAl) (n = 2–4) structures of the original SAPO-34 zeolite are retained on Cu/(SA + SZ), which optimizes the low-temperature catalytic performance of Cu/SSZ-39. Furthermore, the SSZ-39 seed induces Cu/(SA + SZ) to form higher content of stable Si(0OAl) structures than Cu/SA. After hydrothermal aging, more isolated copper species can be formed on SA + SZ hybrid zeolite with advanced structural stability compared with Cu/SA, which better activates NOx on the former. And the loss of acid sites is also weakened on Cu/(SA + SZ) than on Cu/SA. These improvements on Cu/(SA + SZ) compensates for its hydrothermal deactivation to some degree. Hence, SA + SZ hybrid zeolite can be the new-generation candidate for NH3-SCR catalyst by introducing the second zeolite SSZ-39 in the synthesis process of SAPO-34. And the catalytic performance of Cu/(SA + SZ) is superior to Cu/SA.

Low-Temperature Selective NO Reduction by CO over Copper-Manganese Oxide Spinels

Selective catalytic reduction of NO with CO (CO-SCR) has been suggested as an attractive and promising technology for removing NO and CO simultaneously from flue gas. Manganese-copper spinels are a promising CO−SCR material because of the high stability and redox properties of the spinel structure. Here, we synthesized CuxMn3−xO4 spinel by a citrate-based modified pechini method combining CuO and MnOx, controlling the molar Cu/Mn concentrations. All the samples were characterized by SEM, EDX, XRD, TEM, H2−TPR, XPS and nitrogen adsorption measurements. The Cu1.5Mn1.5O4 catalyst exhibits 100% NO conversion and 53.3% CO conversion at 200 °C. The CuxMn3−xO4 catalyst with Cu-O-Mn structure has a high content of high valence Mn, and the high mass transfer characteristics of the foam-like structure together promoted the reaction performance. The CO-SCR catalytic performance of Cu was related to the spinel structure with the high ratio of Mn4+/Mn, the synergistic effect between the two kinds of metal oxides and the multistage porous structure.

Excellent catalytic performance of Cu+ modified HZSM-5 to produce para-xylene via the toluene methylation reaction: High catalytic active site combining with channel shape selectivity

The toluene methylation reaction via methanol is an important process to produce high-value para-xylene (PX), it has always been our goal to explore a catalyst with high activity and selectivity for PX. Cu+ is used to modify HZSM-5 (BAS/Cu+-HZSM-5) zeolite, and the microscopic reasons for the excellent catalytic performance to produce PX on BAS/Cu+-HZSM-5 are investigated according to the intrinsic reaction and molecular diffusion. The intrinsic activation energies of methanol dissociation and xylene formation on BAS/Cu+-HZSM-5 are obtained by the density functional theory (DFT). Calculations indicate that the energy required for methanol dissociation is 109.7 kJ mol−1, which is lower than that on pure HZSM-5. In addition, PX, meta-xylene (MX) and ortho-xylene (OX) formed with little activation energies of 12.7, 11.8 and 14.2 kJ mol−1, respectively. Therefore, the formation of these xylenes on BAS/Cu+-HZSM-5 has high activity and strong competition. On the other hand, the self-diffusion coefficients of three xylenes on BAS/Cu+-HZSM-5 are analyzed by molecular dynamics (MD) simulation. And the self-diffusion coefficient of PX is found to be much larger than that of MX and OX in all cases, which indicates that the channel characteristics of BAS/Cu+-HZSM-5 are beneficial to the diffusion and separation of PX. Therefore, it can be concluded that BAS/Cu+-HZSM-5 has better catalytic performance and high PX selectivity for the toluene methylation reaction via methanol.

In-situ construction of Cu–Co4N@CC hierarchical binder-free cathode for advanced and flexible Li–CO2 batteries: Electron structure and mass transfer modulation

Li–CO2 batteries with high energy density presents great promising to meet carbon neutrality. Herein, a binder-free cathode is obtained by in-situ growth of ZIF-67-derived Co4N with Cu integration on carbon cloth (CC), which is developed as the advanced catalytic cathode for Li–CO2 batteries. After optimizing the components, the derived Li–CO2 batteries can present a discharge capacity beyond 31 000 mA h g−1 at a current density of 100 mA g−1 as well as an excellent long-term stable cycle life up to 131 cycles at 200 mA g−1. Benefitting from the reorganization of the electronic structure on the Co4N active surface by the introduction of Cu, the reduction of CO2 and the decomposition of discharge products tend to be smoothly, and the assembled batteries exhibit a low overpotential of 1.32 V (Li/Li+) at 100 mA g−1. The superior catalytic performances of Cu–Co4N@CC cathode are well-demonstrated by the combination of experiments and theoretical calculations. Moreover, this binder-free cathode with flexible feature has been proven to be suitable for the development of wearable electronic devices by the assembled flexible Li–CO2 batteries. These findings shed a new light on the expansion of excellent cathode based on non-noble bimetal for advanced and wearable Li–CO2 batteries.

The Comparative Study of Reaction Mechanisms and Catalytic Performances of Cu–SSZ-13 and Fe–SSZ-13 for the NH3-SCR Reaction

The Comparative Study of Reaction Mechanisms and Catalytic Performances of Cu–SSZ-13 and Fe–SSZ-13 for the NH3-SCR Reaction

Enhancement of Cu+ stability under a reducing atmosphere by the long-range electromagnetic effect of Au.

In conventional thermocatalytic reactions under a reducing atmosphere, stabilization of the active Cu+ component and inhibition of over-reduction into metallic Cu0 are extremely challenging. In this study, Au@Cu2O core-shell nano-catalysts with different Cu2O shell thicknesses were synthesized, and the effect of the Au nano-core on Cu+ stability under a reducing atmosphere and the catalytic performance of Cu+ in the ethynylation of formaldehyde were investigated. The Au nano-core facilitates Cu2O dispersion and leads to an increase of 0.2-0.5 eV in electron binding energies of Cu2O and Cu2C2 in the range of 27-55 nm, attributed to the long-range electromagnetic effect of Au NPs. Specifically, active Cu+ centers exhibit high stability under a reducing atmosphere due to the long-range electromagnetic effect of the Au nano-core. In the ethynylation of formaldehyde as a probe reaction, Cu+/(Cu0 + Cu+) on Au@Cu2O catalysts remained at 88-91%. The catalytic performance in the ethynylation of formaldehyde revealed that the introduction of an Au nano-core into Cu-based catalysts increased the TOF from 0.37 to 0.7 h-1, and decreased the activation energy from 42.6 to 38.1 kJ mol-1. Additionally, the Cu+/(Cu0 + Cu+) ratios and the catalytic performance in the ethynylation of formaldehyde (BD yield = 65%, BD selectivity = 95%) on Au@Cu2O catalysts remained constant after nine cycles, while pure Cu2O readily deactivated due to the dramatically reduced Cu+/(Cu0 + Cu+) ratios and carbyne deposition. In summary, Cu+ in Cu-based catalysts showed high catalytic activity and stability during the ethynylation of formaldehyde due to the long-range electromagnetic effect of the Au nano-core.

Investigation into the Catalytic Performance of Cu(II) Supported Graphene Quantum Dots Modified NiFe2O4 as a Proficient Nano-Catalyst in the Synthesis of Propargylasmines

NiFe2O4 nanoparticles are modified by graphene quantum dots (GQDs) and utilized to stabilize the Cu(II) nanoparticles as a novel magnetically retrievable catalytic system (Cu(II)/GQDs/NiFe2O4) for green formation of propargylamines under solvent-free conditions. The various aldehydes/ketones, amines, and phenylacetylene were reacted at 100 °C in the presence of the catalyst to synthesize propargylamines. The prepared catalyst can be isolated assisted by an outer magnet and recovered for five courses without significant reduction in its efficiency. The as-prepared magnetic heterogeneous nanocomposite was characterized by UV–Vis, FT-IR, XRD, EDS, VSM, TEM, TGA and ICP. Performing the reactions in environmentally friendly and affordable conditions, the low catalyst percentage, high yield of products, short reaction times and easy workup are the merits of this protocol.

Catalytic performance of Cu(II)-supported graphene quantum dots modified NiFe2O4 as a proficient nano-catalyst in the synthesis of 1,2,3-triazoles

NiFe2O4 nanoparticles are modified by graphene quantum dots (GQDs) and utilized to stabilize the Cu(II) nanoparticles as a novel magnetically retrievable catalytic system (Cu(II)/GQDs/NiFe2O4) for green formation of 1,4-disubstituted 1,2,3-triazoles by means of alkyne–aryl azide cycloaddition. The prepared catalyst can be isolated assisted by an outer magnet and recovered for five courses without significant reduction in its efficiency. The as-prepared magnetic heterogeneous nanocomposite was characterized by UV–Vis, FT-IR, XRD, EDS, VSM, TEM, and ICP. Performing the reactions in environmentally friendly and affordable conditions (water), the low catalyst percentage, high yield of products, short reaction times, and easy workup are the merits of this protocol.