Activity Of Cu Catalysts Research Articles

NIR-II light-activated and Cu nanocatalyst-enabled bioorthogonal reaction in living systems for efficient tumor therapy

Bioorthogonal reaction refers to chemical reactions that occur within a biological system without interfering the normal biochemical process, offering the unprecedented versatility in engineering chemical reactions within cells. However, the precise regulation of bioorthogonal reaction in living systems is mired by the complexity of the physiological environment and the toxicity of catalysts. Herein, considering the deeper tissue penetration and reduced phototoxicity compared to visible light and ultraviolet, a second near infrared (NIR-II) light-activated Cu-based bioorthogonal reaction is developed to achieve precise spatiotemporal control and effective switching for Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) mediated chemical transformations in tumor, reducing the off-target effects. The catalytic activity of Cu catalyst through valence state interconversion between Cu(II) and Cu(I) can be precisely regulated in a reversible manner under NIR-II light irradiation-induced photoelectron transfer, which controls the extent of desired drug synthesis in bioorthogonal reaction. Meanwhile, the adverse effects of Cu(I) can be substantially mitigated within normal tissues due to their oxygen-rich condition. By utilizing NIR-II light and oxygen level, the Cu bioorthogonal catalyst achieves a balance between catalytic activity and biocompatibility. The ability to achieve precise spatiotemporal control and reversible catalysis makes this NIR-II light-mediated CuAAC platform an efficient and adaptable tool for bioorthogonal chemistry in living systems.

Effects of Pd doped Cu surface on CO2 and H2O formation in methane total oxidation

To achieve the goal of green and low-carbon sustainable development, the catalytic combustion of methane is particularly important. Based on the density functional theory, CO2 and H2O formation in the process of CH4 oxidation has been calculated on Cu25, Pd2Cu23 and Pd6Cu19. The results show that the addition of Pd changes the adsorption site of some reactive species and increased the adsorption strength. For Cu25, the optimal reaction path is CH*+O* → C*+OH*(+O*) → CO*+O* → CO2*. For Pd2Cu23 and Pd6Cu19, the optimal reaction path is CH*+O* → CHO* → CO*+H*(+O*) → CO2*. Adding Pd significantly reduces the energy barrier when water is generated, and the optimal reaction paths are OH*+OH*→H2O*+O*. Studying on noble metal doping on the activity of Cu catalyst at atomic level is able to provide guidance for the development of catalyst for methane efficient conversion.

Ethanol dehydrogenation to acetaldehyde over a Cuδ+-based Cu-MFI catalyst

Copper catalysts have been extensively investigated for the dehydrogenation of ethanol to acetaldehyde. However, identifying the essential active sites for this reaction is difficult because of the complex coordination structure and variable valences of the Cu species during the reaction. The stability of the Cu catalysts in the reaction also needs to be substantially improved. In this study, Cu-MFI, a well-defined Cu-based Lewis acid catalyst, was prepared using a post-acid treatment method for ethanol dehydrogenation. Different from the widely reported Cu+ and Cu0 species accounting for the activity of Cu catalysts, conditional experiments and in situ characterizations revealed that the highly dispersed Cuδ+ (1 <δ < 2) species on the MFI support are the essential active sites for ethanol dehydrogenation. Due to the strong interaction between Cu and silica via the Cu–O–Si linkage, the Cuδ+ species were very stable in the reaction and played the role of a Lewis acid catalyst in promoting ethanol activation and dehydrogenation. Over the optimal catalyst 5%Cu-MFI-deCu, 95% selectivity of acetaldehyde and approximately 87% ethanol conversion were obtained at 250 °C and a weight hourly space velocity of 0.64 h−1 in 120 h time on stream.

Benzylic C-H Esterification with Limiting C-H Substrate Enabled by Photochemical Redox Buffering of the Cu Catalyst.

Copper-catalyzed radical-relay reactions provide a versatile strategy for selective C-H functionalization; however, reactions with peroxide-based oxidants often require excess C-H substrate. Here, we report a photochemical strategy to overcome this limitation by using a Cu/2,2'-biquinoline catalyst that supports benzylic C-H esterification with limiting C-H substrate. Mechanistic studies indicate that blue-light irradiation promotes carboxylate-to-copper charge transfer, reducing resting-state CuII to CuI, which activates the peroxide to generate an alkoxyl radical hydrogen-atom-transfer species. This "photochemical redox buffering" introduces a unique strategy to sustain the activity of Cu catalysts in radical-relay reactions.

A green solvent diverts the hydrogenation of γ–valerolactone to 1,4 - pentandiol over Cu/SiO2

A new process for the selective hydrogenation of γ-valerolactone (GVL) to 1,4-pentanediol (1,4-PDO), interesting biobased monomer, has been set up. It relies on the use of a non-noble, nontoxic metal such as Cu on a very simple oxide support, namely silica in a green solvent such as Cyclopentyl Methyl Ether (CPME). The role of the solvent was not only to ensure more sustainable experimental conditions but also to influence the activity and selectivity of the catalyst by tuning the surface acidity. Thus, the activity of Cu catalysts supported on different types of silica was found to depend on some parameters, such as: the support wettability, determined through contact angle and TGA measurements, Cu-dispersion, determined by X-ray photoelectron spectroscopy (XPS) and, in particular, on the nature and effective number of the acid sites on the surface. The last ones were measured through volumetric liquid-solid acid-base titrations with 2-phenylethylamine probe carried out in different reaction solvents and pyridine titrations by Fourier-transform infrared spectroscopy (FT-IR), respectively. Once the best silica support in terms of wettability, in turn affecting Cu dispersion, was identified, CPME was found to be able to boost the catalyst activity and selectivity by modifying the number and strenght of surface acidic sites. The use of this solvent and the fine tuning of the hydrophilic/hydrophobic properties of the silica allowed to reach 78% yield in 1,4-PDO at 160 °C and P(H2) of 50 bar.

Spatial Ensembles of Copper-Silica with Carbon Nanotubes as Ultrastable Nanostructured Catalysts for Selective Hydrogenation.

Catalyst deactivation is one of the most important issues in heterogeneous catalysis. Constructing a stable nanoscale structure that maintains efficient activity and prolonged stability under redox conditions for catalysis, particularly hydrogenation reactions, remains attractive albeit the flourishing nanoscience. This work presents a facile route to synthesize a semi-encapsulated transition metal by assembling three-dimensional transition metal silicate nanotubes onto carbon nanotubes (CNTs) as precursors. The obtained materials expose an active surface of the transition metal for efficient catalysis and form a specific structure to inhibit the migration of metal nanoparticles (NPs) by establishing strong metal-support interactions. Cu@SiO2 prepared by common precipitation shows an inferior activity, and its performance is easily attenuated because of the aggregation of Cu NPs. The addition of CNTs as a carrier doubles the intrinsic activity of Cu catalysts. This hybrid catalyst, which consists of Cu species, SiO2, and CNTs, is among the best catalysts for dimethyl oxalate hydrogenation with boosting activity of 25 h-1 and enhanced stability of more than 200 h.

Enhancement of the dispersion and catalytic performances of copper in the hydrogenation of cinnamaldehyde by incorporation of aluminium into mesoporous SBA-15 silica

Copper is active in hydrogenation reactions, but it is a base metal difficult to disperse inside mesostructured supports, with adverse consequences on the catalytic properties. Incorporating aluminium into mesoporous SBA-15 silicas allows solving both problems of Cu dispersion and activity. The incorporation of 20 wt.% Al2O3 in the SBA-15 host structure leads to an increase of the copper metallic surface area by a factor 6 compared to the pure siliceous SBA-15-supported catalyst. The support also proves to be stable upon exposure to the impregnation aqueous solution used for copper introduction. The incorporation of Al provides Lewis acidic sites that favour the transformation of cinnamaldehyde into cinnamyl alcohol, a feature usually assigned to larger metal particles. As a consequence, the catalytic activity of Cu catalysts is enhanced compared to silica-supported Cu catalysts, while the chemoselectivity towards the unsaturated alcohol appears to be similar to that of a mesoporous alumina-supported system.

Effect of Ionic Liquid Additives on the Product Selectivity and Activity in CO2 Electroreduction over Cu Catalysts

Electrochemical reduction of CO2 has been proposed as a promising way to attenuate the CO2 level in the atmosphere and consequently, mitigate the global warming. Furthermore, several valuable chemicals and fuels can be produced by CO2 electroreduction. Although copper catalysts are of interest due to their ability to produce hydrocarbons and alcohols, they produce a wide verity of products and need high overpotentialsin traditional aqueous electrolytes1. One of the methods to address these obstacles is to use ionic liquids (ILs) in the electrolyte. ILs are cation-anion couples which have unique properties such as high CO2 solubility. In CO2 electroreduction, ILs can play different roles such as co-catalyst, electrolyte, or CO2 absorbent. It has been reported that product selectivity and the reaction rate in CO2 electrocution is significantly impacted when using ionic liquids2, 3. Here, the effect of using ionic liquids in CO2 electroreduction on product selectivity and activity of Cu catalysts has been studied. For this purpose, Cu foils were first electropolished in 1M phosphoric acid for 300 sec. CO2 electroreduction was then performed on Cu catalysts for 30 mins at different potentials. According to the results, ionic liquids affected the product selectivity even in a diluted IL/water mixture. The results showed that adding 10 mM 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][NTF2]) to the 0.1 M KHCO3 electrolyte leads to a 63% increase in the total current density at -1.1 V (vs RHE). A 50% increase in formate faradaic efficiency at -0.91 V was also detected when adding the IL to the electrolyte. Moreover, the faradaic efficiency of methane increased by 80% at -1.1 V (vs RHE) in the ionic liquid/water mixture. The results demonstrate how ILs influence the CO2 reduction on Cu catalysts. Hori, Y., Electrochemical CO2 reduction on metal electrodes. In Modern Aspects of Electrochemistry, Vayenas, C. G.; White, R. E.; Gamboa-Aldeco, M. E., Eds. Springer: New York, 2008; Vol. 42, pp 89-189.Mu, T.; Chen, Y., Conversion of CO2 to value-added products mediated by ionic liquids. Green Chemistry 2019.Zhou, F.; Liu, S.; Yang, B.; Wang, P.; Alshammari, A. S.; Deng, Y., Highly selective and stable electro-catalytic system with ionic liquids for the reduction of carbon dioxide to carbon monoxide. Electrochemistry Communications 2015, 55(0), 43-46.

Insight into the Effects of Cu Component and the Promoter on the Selectivity and Activity for Efficient Removal of Acetylene from Ethylene on Cu-Based Catalyst

The selective hydrogenation of C2H2 on five types of Cu(0)/Cu(I), Cu(0), Cu(I), PdCu(0), and PdCu(I) catalysts are investigated to illuminate the effects of Cu component and the promoter on the selectivity and activity toward C2H4 formation. The selectivity and activity toward C2H4 formation on five types of catalysts are examined using density functional theory calculations. The results indicate that Cu(0)/Cu(I) bicomponent catalyst presents higher selectivity but significantly lower activity toward C2H4 formation compared to the individual Cu(0) or Cu(I) catalysts, suggesting that Cu(0)/Cu(I) bicomponent catalyst cannot be selected as an ideal catalyst applied to the selective hydrogenation of C2H2, namely, the catalytic activity of Cu catalyst toward C2H4 formation dominates on the single-component rather than the multicomponent. On the other hand, for the promoter Pd-modified Cu(0) or Cu(I) bimetallic catalysts, PdCu(I) catalyst presents poor selectivity toward C2H4 formation compared to the individua...

Nanoporous Cu Thin Films for Electrochemical CO2 Reduction

Copper catalysts have been extensively researched as catalysts for electrochemical reduction of CO2 (CO2RR) due to their capability to catalyze production of hydrocarbons. The selectivity and activity of Cu catalysts for CO2RR are greatly dependent on the surface structure of the catalysts, and due to this dependence, many forms of Cu (ranging from high quality single crystals to densely populated arrays of supported nanostructures) have been investigated as CO2RR catalysts. Nanoporous (np) metals, which are produced through selective dissolution of an element from a parent alloy or compound, have inherent properties not typically present in other nanostructured materials that can strongly affect their catalytic properties, including concave surfaces with unique surface structures and open porosity that can cause mass transport effects during catalysis. Nanoporous Au and Ag, have been demonstrated as efficient and selective catalysts for oxidation of CO and reduction of CO2 to CO relative to their bulk metals. However, np-Cu has yet to be comprehensively studied as a CO2RR catalyst. To date, np-Cu has been primarily produced from homogeneous bulk materials which are not well suited for practical use as a potential CO2RR catalyst due to long dealloying treatments required to produce np-Cu that remains stable, without continued dealloying of the non-noble metal, at low CO2RR overpotentials. In this work, we demonstrate new electrochemical methods for producing fully dealloyed thin films of high-quality, crack-free np-Cu on inert substrates in significantly shorter processing times compared to bulk samples. We examine the activity and selectivity of np-Cu film catalysts produced by several dealloying methods for CO2RR. These results are presented in relation to other Cu catalysts with focus on the catalytic effects of the unique structural properties of np-Cu and the effects of post dealloying treatments to tune pore and ligament sizes of the np-Cu films. In addition to np-Cu films, we discuss how the presented techniques offer a path for production of stable thin films of other nanoporous metals on complex geometries. This work is supported by the Department of Energy award number DE-SC0008686.

Water gas shift reaction over monometallic and bimetallic catalysts supported by mixed oxide materials

In the present work, the water gas shift activities of Cu on ceria and Gd doped ceria were studied for a further enhancement of hydrogen purity after a steam reforming process. The catalytic properties of commercial catalysts were also studied to compare with our as-prepared catalysts. It was found that copper-containing cerium oxide is suitable for the high temperature reaction. Copper-ceria is a stable high-temperature shift catalyst, unlike iron-chrome catalysts which are deactivated severely in CO2-rich gases. 5%Cu/10%GDC (D) was found to have much higher activity than other copper ceria based catalysts. Finely dispersed CuO species is more favorable due to a higher activity, which explains the activity enhancement of this catalyst. The kinetics of the WGS reaction over Cu catalysts supported by mixed oxide materials were measured in the temperature range 200–400°C. An independence of the CO conversion rate on CO2 and H2 was observed. To improve the catalytic performance of copper catalysts, the behavior of the bimetallic catalysts was compared with that of the monometallic catalysts. It was found that an addition of Re to Cu/GDC significantly improved the activity of copper catalysts. The effect of Re on enhancing the WGS activity of Cu catalysts was due to Re increases the reducibility of the surface ceria, In addition, Re contributes to reduction of Ce4+ to Ce3+. The presence of Ce2O3 at the ceria surface gives rise to oxygen vacancies which facilitate the electron movement at the surface leading to ease of surface reduction.

CO2 Electroreduction to Hydrocarbon Fuels on Carbon-Supported Copper Nanoparticles: Particle Size Effect

Activity of Cu catalysts towards CO2 electroreduction is found to be strongly dependent on the Cu surface structure [1-3]. Hori [1] demonstrated that Cu(100) facets favored C2H4 production, while Cu(111) favored CH4 production during CO2 electrolysis in electrochemical cells. High-index crystal facets such as Cu(311), Cu(511) and Cu(711) were found to be more active towards generation of C2 and C3 compounds. Previously, we reported that product distribution can be inverted by switching from smooth Cu films to carbon-supported Cu nanoparticles. The product distribution was dominated by CH4 over C2H4 for smooth Cu films, while the reverse order was observed for carbon-supported Cu nanoparticles. A similar trend was reported by Norskov’s group [3] for unsupported 50-100 nm Cu nanoparticles. The higher activity of nanoparticles towards C2H4 generation was attributed to a larger amount of under-coordinated sites, such as corners, edges and defects on the surface of nanoparticles compared to a smooth Pt surface. Here we report particle size effect for CO2 electroreduction to hydrocarbon fuels on Vulcan Carbon (VC)-supported Cu nanoparticles. Cu nanoparticles of 5, 12 and 27 nm diameter on carbon supports were synthesized by the reduction of Cu(acac)2 in a mixture of oleylamine and hexane by LiBEt3H . X-Ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) were used for nanoparticles ex-situ analysis. Pb underpotential deposition was used for in-situ evaluation of the electrochemical surface area (ECSA) of Cu nanoparticles [4].The activity of the Cu nanoparticles towards CO2 electroreduction to hydrocarbon fuels was evaluated using a sealed RDE setup connected to a GC. Thin films of three Cu/VC catalysts were deposited on the surface of custom-made 7 mm glassy carbon disks (Pine Instruments, Inc), following a well-established in the PEMFC community protocol [5]. GC sampling from the electrochemical cell was performed at 5, 25, 45 and 65 min from the beginning of each experiment, while holding the electrode potential at -1.2, -1.4, -1.6, -1.8, -2 and -2.2 V vs. Ag/AgCl reference electrode. Our preliminary results show that the ratio of C2H4 to CH4 increases with a decrease in the Cu particle size. This presentation will discuss different aspects of CO2 electroreduction reaction on Cu nanoparticles. Acknowledgements OAB is grateful to the Office of Naval Research for financial support of this project.

Redox properties and VOC oxidation activity of Cu catalysts supported on Ce1−xSmxOδ mixed oxides

A series of Cu catalysts supported on Ce1−xSmxOδ mixed oxides with different molar contents (x=0, 0.25, 0.5, 0.75 and 1), was prepared by wet impregnation and evaluated for volatile organic compounds (VOC) abatement, employing ethyl acetate as model molecule. An extensive characterization study was undertaken in order to correlate the morphological, structural and surface properties of catalysts with their oxidation activity. The optimum performance was obtained with Cu/CeO2 catalyst, which offers complete conversion of ethyl acetate into CO2 at temperatures as low as 260°C. The catalytic performance of Cu/Ce1−xSmxOδ was interpreted on the basis of characterization studies, showing that incorporation of samarium in ceria has a detrimental effect on the textural characteristics and reducibility of catalysts. Moreover, high Sm/Ce atomic ratios (from 1 to 3) resulted in a more reduced copper species, compared to CeO2-rich supports, suggesting the inability of these species to take part in the redox mechanism of VOC abatement. Sm/Ce surface atomic ratios are always much higher than the nominal ratios indicating an impoverishment of catalyst surface in cerium oxide, which is detrimental for VOC activity.

Kinetics of ethynylation of formaldehyde to butynediol

Activity of Cu catalysts and kinetics of ethynylation of formaldehyde using Cu2C2 catalyst has been studied. The reaction was found to be 0.41 and 0.58 order with respect to acetylene and formaldehyde concentrations, respectively. The activation energy of the reaction was found to be 15.13 kcal/mol.