CuO Species Research Articles

In-Depth Investigation of Copper Surface Chemistry Modification by Ultrashort Pulsed Direct Laser Interference Patterning.

Surface patterning in the micro- and nanometer-range by means of pulsed laser interference has repeatedly proven to be a versatile tool for surface functionalization. With these techniques, however, the surface is often changed not only in terms of morphology but also in terms of surface chemistry. In this study, we present an in-depth investigation of the chemical surface modification occurring during surface patterning of copper by ultrashort pulsed direct laser interference patterning (USP-DLIP). A multimethod approach of parallel analysis using visualizing, topography-sensitive, and spectroscopic techniques allowed a detailed quantification of surface morphology as well as composition and distribution of surface chemistry related to both processing and atmospheric aging. The investigations revealed a heterogeneous surface composition separated in peak and valley regions predominantly consisting of Cu2O, as well as superficial agglomerations of CuO and carbon species. The evaluation was supported by a modeling approach for the quantification of XPS results in relation to heterogeneous surface composition, which was observed by means of a combination of different spectroscopic techniques. The overall results provide a detailed understanding of the chemical and topographical surface modification during USP-DLIP, which allows a more targeted use of this technology for surface functionalization.

Grain size effect on the high-temperature hydrothermal stability of Cu/SAPO-34 catalysts for NH3-SCR

The high-temperature hydrothermal (HTH) stability is always a key factor that affects the NH3-SCR performance and limits the industrial applications of Cu/SAPO-34. Herein, two Cu/SAPO-34 catalysts with different grain sizes are HTH aged to investigate the role of the grain size of Cu/SAPO-34 in holding the structure stability of catalysts and the relationships between the grain size and deNOx performance over Cu/SAPO-34 during the HTH treatment. Characterization results illustrates that the relationship between the grain size and the stability of SAPO framework and the content of isolated Cu2+ ions. During the HTH treatment, CuO species more easily transfer to isolated Cu2+ species via migrating into the framework from the external surface of SAPO-34 for the larger-sized catalyst rather than the smaller-sized one. The re-distribution of Cu2+ in the larger-sized catalyst prevents Si-O(H)-Al from H2O attacking during HTH treatment. Therefore, the larger-sized Cu/SAPO-34 maintains stronger structural stability and higher deNOx activity than smaller-sized one after HTH treatment. This work provides a new strategy for design of high-temperature hydrothermal stabilized Cu/SAPO-34 for eliminating NOx emitted from diesel engines.

α-Fe2O3/Cu2O heterostructure: Brief characterization and kinetic aspect of degradation of methylene blue

The α-Fe2O3/Cu2O heterostructure (HS) was prepared via the hydrothermal precipitation method and used in the kinetic study of the methylene blue (MB) photodegradation. The samples were subjected to the photoluminescence spectroscopy (PL) to evaluate the e/h recombination rate and the results showed a significant decrease in PL intensity of the heterostructure with respect to the individual semiconductors. The band gap energy of 2.28 eV for the single Fe2O3 semiconductor was red-shifted to 1.95 eV by introducing Cu2O species. EDX analysis of the heterostructure showed 74.36% (65.66% atomic%) Cu and 22.21% (22.32 atomic%) Fe in weight%. The heterostructure showed an increased photocatalytic activity towards MB molecules with respect to the individual systems. The degradation process obeyed the first order Hinshelwood kinetic model and an apparent first-order rate constant of 0.025 min−1 with a t1/2 value of 27 min was obtained. The degradation extent of MB was confirmed by the chemical oxygen demand (COD) method that of results confirmed about 90% of MB molecules can be removed during the photodegradation process in the applied conditions.

The Study on Higher Alcohols Synthesis from Syngas over CuZnAl Catalysts Derived from Hydrotalcite‐Like Precursors

AbstractA series of CuZnAl catalysts with different Al contents were derived from hydrotalcite‐like precursors prepared by the coprecipitation method. Activity evaluation of the catalyst for higher alcohols synthesis from syngas was investigated, and the catalysts were characterized by XRD, BET, H2‐TPR, CO2‐TPD‐MS and CO‐TPD‐MS. The results revealed that different Al content showed an influence on the dispersion of the reducible Cu species, the specific surface area, the surface alkali strength and the adsorption capacity of CO, which affecting the CO conversion and the selectivity of higher alcohols. Catalysts with strong interaction between CuO and Al species, more medium and strong basic sites, and adequate CO dissociation adsorption benefited production of higher alcohols.

Highly dispersed boron-nitride/CuOx-supported Au nanoparticles for catalytic CO oxidation at low temperatures

Supported-Au catalysts show excellent activity in CO oxidation, where the nature of the support has a significant impact on catalytic activity. In this work, a hexagonal boron nitride (BN) support with a high surface area and adequately exposed edges was obtained by the ball-milling technique. Thereafter, impregnation of the BN support with Cu(NO3)2 followed by calcination under air at 400 °C yielded a CuO-modified support. After Au loading, the obtained Au-CuOx/BN catalyst exhibited high CO oxidation activity at low temperatures with a 50% CO conversion temperature (T50%) of 25 °C and a complete CO conversion temperature (T100%) of 80 °C, well within the operational temperature range of proton exchange membrane fuel cells. However, the CO oxidation activity of Au/BN, prepared without CuOx for comparison, was found to be relatively low. Our study reveals that BN alone disperses both Cu and Au nanoparticles well. However, Au nanoparticles on the surface of BN in the absence of CuO species tend to aggregate upon CO oxidation reactions. Conversely, Au nanoparticles supported on the surface of CuO-modified BN remain small with an average size of ∼2.0 nm before and after CO oxidation. Moreover, electron transfer between Au and Cu species possibly favors the stabilization of highly dispersed Au nanoparticles on the BN surface and also enhances CO adsorption. Thus, our results demonstrate that thermally stable and conductive CuO-modified BN is an excellent support for the preparation of highly dispersed and stable Au catalysts.

Small-sized cuprous oxide species on silica boost acrolein formation via selective oxidation of propylene

Oxide-supported copper-containing materials have attracted considerable research attention as promising candidates for acrolein formation. Nevertheless, the elucidation of the structure-performance relationships for these systems remains a scientific challenge. In this work, copper oxide clusters deposited on a high-surface-area silica support were synthesized via a deposition-precipitation approach and exhibited remarkable catalytic reactivity (up to 25.5% conversion and 66.8% selectivity) in the propylene-selective oxidation of acrolein at 300 °C. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy combined with X-ray absorption fine structure measurements of the catalyst before and after the reaction confirmed the transformation of the small-sized copper oxide (CuO) clusters into cuprous oxide (Cu2O) clusters. With the aid of in situ X-ray diffraction and in situ dual beam Fourier transform infrared spectroscopy (DB-FTIR), the allyl intermediate (CH2=CHCH2*) was clearly observed, along with the as-formed Cu2O species. The intermediate can react with oxygen atoms from neighboring Cu2O species to form acrolein during the catalytic process, and the small-sized Cu2O clusters play a crucial role in the generation of acrolein via the selective oxidation of propylene.

In situ grown Cu-Based metal-organic framework on copper foam as high-performance electrocatalysts for oxygen evolution reaction

It is of great significance to develop highly efficient and robust oxygen evolution reaction (OER) electrocatalysts derived from earth-abundant and inexpensive elements for future hydrogen economy via electrochemical water splitting. Herein, Cu-based metal-organic framework (MOF) is directly supported on conductive Cu foam (CF) by a simply chemical oxidation of Cu substrate to grow Cu(OH)2 nanowire arrays, followed by solvothermal treatment to obtain in situ grown Cu-based MOF electrode (MOF [Cu(OH)2]/CF). The as-prepared 3D electrode shows superior OER activity with a low potential of 330 mV to deliver a current density of 10 mA cm−2, a Tafel slope of 108 mV dec−1, and excellent durability in alkaline media (1.0 M KOH). After electrolysis, XRD confirms that the initial MOFs have been transformed into CuO species, which are essentially active components for OER performance. This demonstrates that the MOFs can serve as efficient precursors for formation of highly active Cu oxide catalysts towards OER. This work provides a new strategy to develop MOFs-derived electrocatalysts for future clean energy conversion and storage systems.

Titania Morphology‐Dependent Catalysis of CuOx/TiO2 Catalysts in CO Oxidation and Water Gas Shift Reactions

AbstractCuOx/TiO2 nanocatalysts (x=0 or 1) with ∼11 % wt. Cu loading employing TiO2 nanocrystals with various morphologies predominantly exposing {001}, {100}, and {101} facets as supports have been synthesized as catalysts for CO oxidation with excess of O2 (oxidative atmosphere) and water gas shift (WGS) reaction (reductive atmosphere). Strong TiO2 morphology effects were observed. The strongest Cu2O−TiO2 interaction was observed in CuO−TiO2{001} nanocatalyst, while the strongest Cu‐TiO2 interaction occurred in Cu‐TiO2{100} nanocatalyst. Catalytic activities of various CuO/TiO2 nanocatalysts in CO oxidation and of various Cu/TiO2 nanocatalysts in WGS reaction follow the same order of CuOx/TiO2{100}>CuOx/TiO2{101}>CuOx/TiO2{001}, and all CuO/TiO2 nanocatalysts are stable in CO oxidation but all Cu/TiO2 nanocatalysts suffer from serious deactivation in WGS reaction. The active structure of CuO/TiO2 nanocatalysts in CO oxidation was found to be the CuO species, while the active structure of Cu/TiO2 nanocatalysts in WGS reaction to be the Cu‐TiO2 interface which is relevant to the Cu‐TiO2 interaction. The supported Cu nanoparticles in Cu/TiO2 nanocatalysts tend to agglomerate at high temperatures in 5 %CO/Ar atmosphere, responsible for the deactivation in WGS reaction. These results not only demonstrate the morphology‐dependent CuOx‐TiO2 interaction in CuOx/TiO2 nanocatalysts, but also reveal reaction‐dependent active structures of CuOx/TiO2 nanocatalysts.

Enhanced Electrochemical CO2 Reduction of Cu@CuxO Nanoparticles Decorated on 3D Vertical Graphene with Intrinsic sp3‐type Defect

AbstractDefective 3D vertical graphene (VG) with a relatively large surface area, high defect density, and increased surface electrons is synthesized via a scalable plasma enhanced chemical vapor deposition method, together with a postsynthesis Ar‐plasma treatment (VG‐Ar). Subsequently, Cu@CuxO nanoparticles are deposited onto VG‐Ar (Cu/VG‐Ar) through a galvanostatic pulsed electrodeposition method. These Cu@CuxO nanocatalyst systems exhibit a superior electrochemical CO2 reduction performance when compared to Cu‐based catalysts supported on commercial graphene paper or pristine VG without postsynthesis Ar‐plasma treatment. The Cu/VG‐Ar achieves the highest CO2 reduction Faradaic efficiency of 60.6% (83.5% of which are attributed to liquid products, i.e., formate, ethanol, and n‐propanol) with a 5.6 mA cm−2 partial current density at −1.2 V versus reversible hydrogen electrode (RHE). The improved CO2 reduction performance of Cu/VG‐Ar originates from the well‐dispersed Cu@CuxO nanoparticles deposited on the defective VG‐Ar. The intrinsic carbon defects on VG‐Ar can suppress the hydrogen evolution reaction as well as tune the interaction between VG and Cu@CuxO, thus impeding the excessive oxidation of Cu2O species deposited on VG‐Ar. The defective VG‐Ar and stabilized Cu@CuxO enhances CO2 adsorption and promotes electron transfer to the adsorbed CO2 and intermediates on the catalyst surface, thus improving the overall CO2 reduction performance.

Hydrodeoxygenation of Benzofuran over Bimetallic Ni-Cu/γ-Al2O3 Catalysts

Bimetallic NixCu(10−x)/γ-Al2O3 catalysts (where x is the mass fraction of Ni) with different Ni/Cu mass ratios were prepared. The catalysts were characterized by X-ray diffractometry, N2 adsorption–desorption, inductively coupled plasma mass spectrometry, X-ray photoelectron spectroscopy, H2-temperature programmed reduction, and transmission electron microscopy. The effect of Ni/Cu mass ratio on benzofuran hydrodeoxygenation was investigated in a fixed-flow reactor. Cu addition improved the NiO reducibility. The strong interaction of Ni and Cu led to the formation of smaller and highly dispersed CuO and NiO species over γ-Al2O3, which favors an improvement in catalytic activity. Among the as-prepared catalysts, the Ni5Cu5/γ-Al2O3 showed the highest deoxygenated product yield (79.9%) with an acceptable benzofuran conversion of 95.2%, which increased by 18.3% and 16.9% compared with that of the monometallic Ni/γ-Al2O3 catalyst. A possible reaction network was proposed, which would provide insight into benzofuran hydrodeoxygenation over the Ni5Cu5/γ-Al2O3 catalyst.

Novel Bimetallic Cu–Pd Nanoparticles as Highly Active Low-Temperature WGS Catalysts

Water gas shift (WGS) reaction is a key industrial process to produce hydrogen from CO and H2O. However, conventional Cu-based WGS catalysts are easily deactivated by sulfur compounds, which are ubiquitous in syngas. Cu–Pd nanoparticles of size 8–10 nm were synthesized as a function of the Cu/Pd ratios and investigated as promising sulfur-tolerant WGS catalysts. Significant improvement in the WGS activity was observed in the Cu–Pd catalysts after calcination at 800 °C in air. Pd addition enhanced the reducibility of CuO and Cu0 dispersion and limited the formation of CuAl2O4 spinel during calcination at 800 °C. The additional reducible and catalytically active CuO species was generated by the Cu migration from the CuO shell covering the Cu–Pd nanoparticles onto the γ-Al2O3 support during the 800 °C calcination. The optimal Cu–Pd catalyst characterized by the CuO/CuAl2O4 ratio of 2.37 showed the highest WGS activity, thermal stability, and sulfur tolerance among all Cu-based catalysts reported in this study.

Probing into the multifunctional role of copper species and reaction pathway on copper-cerium-zirconium catalysts for CO2 hydrogenation to methanol using high pressure in situ DRIFTS

A series of ternary copper-cerium-zirconium catalysts containing two kinds of copper species, surface CuO and Cu-Ce-Zr solid solution, are prepared and studied for catalytic properties of CO2 hydrogenation to methanol. The copper-cerium- zirconiumcatalyst calcined at 450 °C (CCZ-450) is much more favorable for improving the nature of surface CuO species and forming Cu-Ce-Zr solid solution than others. The best catalytic behavior in terms of methanol selectivity (T = 280 °C, SCH3OH = 71.8%), turnover frequency (TOFCO2 = 13.4 × 10−2 s−1) and activation energy (Ea = 28.5 kJ/mol) are achieved using CCZ-450. The excellent catalytic performance of CCZ-450 is attributed to the stronger H2 adsorption ability arising from highly dispersed surface CuO specie with higher copper surface area and higher concentration of active bi/m-HCOO* intermediate caused by the formation of Cu-Ce-Zr solid solution. Both the dispersion and surface area of active sites and the activation abilities of CO2 are critical for catalyst activity and product selectivity. In situ diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) experiments at 3 MPa confirm that both bi-HCOO* and m-HCOO* are the active intermediates for CO2 hydrogenation to methanol. The accumulation of m-HCOO* on the catalyst surface is the crucial step of CO2 hydrogenation to methanol.

Hybridization of CuO with Bi2MoO6 Nanosheets as a Surface Multifunctional Photocatalyst for Toluene Oxidation under Solar Irradiation.

Herein, CuO/Bi2MoO6 hybrid nanosheets were prepared as a surface multifunctional photocatalyst for gas-phase toluene oxidation with high conversion (>99%). Aberration-corrected scanning transmission electron microscopy suggested that CuO species were highly dispersed on the nanosheets. X-ray absorption fine structure spectra indicated that the distorted and stretched Cu-O coordination structures in CuO/Bi2MoO6 nanosheets would provide open active sites. In situ Fourier transform infrared and density functional theory results showed that toluene molecules could be chemisorbed and activated on the active sites of CuO/Bi2MoO6 nanosheets by the C-H group forming CuO/Bi2MoO6···Ph-CH3 surface complex compounds. These would induce electron-hole transfer and initiate photocatalytic reactions under visible light irradiation. The corresponding intermediates of benzaldehyde and benzoic acid would be detected by in situ diffuse reflectance infrared Fourier transform spectroscopy. Furthermore, the synergistic effect of CuO and Bi2MoO6 nanosheets could monitor charge dynamics to facilitate their respective transmission from photoexcitation sites to active centers. This work provides new insights into the essence of visible-light-driven surface photocatalysis and is expected to promote the design of novel and more effective photocatalysts at the molecular level.

The influence of the Cu2O deposition method on the structure, morphology and photoresponse of the ordered TiO2NTs/Cu2O heterojunction

The increased interest in highly ordered titania structures exhibiting tubular shape that could be directly formed onto the stable substrate is related with the intensive research on their modification enabling absorption of light within the wide solar spectrum and its further conversion into electric or chemical energy. Among others, formation of uniform 3D heterojunctions based on the TiO2 nanotubes attracts attention since porous structure provides highly developed surface area whereas tubular shape ensures facilitated charge transport. Following that, we focus on the comparison of different electrochemical routes leading to the formation of Cu2O onto the titania nanotubes platform to improve energy harvesting. Proposed approach includes optimized potentiostatic and pulsed polarization of titania immersed in the basic electrolyte composed of Cu2+ ions stabilized by lactic acid. In this work, we demonstrate that at strictly selected deposition parameters, namely time, pulse width and cycle number, one can obtain titania nanotubes overgrown by Cu2O species uniformly distributed across the whole TiO2 layer as proved by secondary ion mass-spectrometry. X-ray photoelectron spectroscopy studies indicated purely Cu(I) oxide formation for pulsed deposition route. The photoactivity of obtained materials was verified both under vis and UV–vis irradiation. Depending on the incident light spectrum, variation in photoactivity was observed that is directly related with the charges generation and their transport within the junction. The transient photocurrent measurements show strong photocurrent enhancement for Cu2O modified titania comparing to pristine support and satisfactory photostability under visible light without any protective coating.

An investigation of Zr/Ce ratio influencing the catalytic performance of CuO/Ce1-Zr O2 catalyst for CO2 hydrogenation to CH3OH

Abstract A series of CuO/Ce1-xZrxO2 catalysts (x = 0.2, 0.4, 0.6 and 0.8) are applied to elaborate the effect of the Zr/Ce ratio on the catalytic performance of CO2 hydrogenation to CH3OH. The best catalytic performance is achieved with CuO/Ce0.4Zr0.6O2, exhibiting XCO2 = 13.2% and YCH3OH = 9.47% (T = 280 °C, P = 3 MPa). The formation of dispersed surface CuO species and larger number of oxygen vacancies are detected over CuO/Ce0.4Zr0.6O2 due to stronger interaction between CuO and Ce0.4Zr0.6O2, resulting in the superior activation ability for H2 and CO2 respectively. Additionally, the evidence is provided by in situ DRIFTS under the activity test pressure (3 MPa) that bi/m-HCOO* species are preferable for accumulating over ceria-rich (CuO/Ce0.6Zr0.4O2 and CuO/Ce0.8Zr0.2O2) catalysts while zirconia-rich (CuO/Ce0.4Zr0.6O2 and CuO/Ce0.2Zr0.8O2) catalysts are benefit to encourage the transformation of bi/m-HCOO* species to CH3OH. The abundant population and high activity of intermediate species over CuO/Ce0.4Zr0.6O2 give a strong positive effect on the catalytic performance.

Construction of mesoporous Cu/ZrO2-Al2O3 as a ternary catalyst for efficient synthesis of γ-valerolactone from levulinic acid at low temperature

A ternary base metal catalyst, which contained metallic Cu, oxygen deficiencies derived from ZrO2, and acidic Al2O3, was constructed for the efficient synthesis of γ-valerolactone by levulinic acid hydrogenation under mild conditions. Excellent catalytic performance was obtained by fine tuning the proportion of these three active components. The optimized Cu/Zr-Al-3 catalyst achieved superior catalytic activity with a high mass activity of 220.5 mmol GVL·h−1·g−1 surf. Cu at 130 °C, which was nearly eight times higher than Cu/Al and nine times higher than Cu/Zr. More importantly, Cu/Zr-Al-3 also possessed excellent recycling stability, making it as a potential catalyst for industrial applications. The presence of ZrO2 in the ternary catalysts weakened the Cu–Al2O3 interaction and formed Zr–O–Al interaction in the form of Al2O3–ZrO2 solid solution, which facilitated the reduction of CuO species and in turn enhanced the formation of more Cu0 active sites on the catalyst surface. The existence of a large number of oxygen vacancies and acid sites on the optimized ternary catalysts was also demonstrated by XPS and NH3 temperature-programmed desorption results. Levulinic acid can be adsorbed strongly on oxygen vacancies by its carboxylic or carbonyl groups and then readily attached by active H atoms dissociated on Cu0 sites to form active intermediates, while the acid sites presented on the ternary catalyst surface promote subsequent dehydration and intramolecular esterification of adsorbed active intermediates and consequently facilitate the formation of γ-valerolactone. The adsorption of levulinic acid onto oxygen vacancies also avoided the leaching of active Cu metal via the formation of soluble Cu metal carboxylate complexes, resulting in outstanding recycling stability for the optimized ternary catalysts. The intimate synergies of these ternary active sites mainly accounted for the superior catalytic activity and excellent recycling stability of the Cu/Zr-Al-3 catalyst.

Silicon nitride as a new support for copper catalyst to produce acrolein via selective oxidation of propene with very low CO2 release

To obtain thermally stable copper-based catalysts with excellent catalytic performance in the selective propene (C3H6) oxidation reaction, amorphous silicon nitride (Si3N4) was selected to anchor active copper species using a deposition–precipitation approach followed by air calcination at different temperatures. We found that the thermal treatment temperature remarkably modified the reactivity of the copper catalyst, and the 800 °C-calcined 10 wt% Cu/Si3N4 showed superior catalytic activity with 24.0% propene conversion and 86.2% acrolein selectivity at 325 °C, featuring a turnover frequency as high as 80.6 h−1. With the help of transmission electron microscopy, X-ray absorption fine structure, and in situ X-ray diffraction, we have identified that the larger Cu2O species account for the highly efficient formation of acrolein at 325 °C. From the CO temperature-programmed reduction results, we have confirmed that the presence of surface copper hydroxyls (Cu–OH) was closely related to the acrolein selectivity, since they favored CO2 generation at the beginning of the reaction. Furthermore, surface copper hydroxyls can be effectively tuned by optimizing the air calcination temperature and thus improve the catalytic activity.

Single and Dual Metal Oxides as Promising Supports for Carbon Monoxide Removal from an Actual Syngas: The Crucial Role of Support on the Selectivity of the Au–Cu System

A catalytic screening was performed to determine the effect of the support on the performance of an Au–Cu based system for the removal of CO from an actual syngas. First, a syngas was obtained from reforming of ethanol. Then, the reformer outlet was connected to a second reactor, where Au–Cu catalysts supported on several single and dual metal oxides (i.e., CeO2, SiO2, ZrO2, Al2O3, La2O3, Fe2O3, CeO2-SiO2, CeO2-ZrO2, and CeO2-Al2O3) were evaluated. AuCu/CeO2 was the most active catalyst due to an elevated oxygen mobility over the surface, promoting CO2 formation from adsorption of C–O* and OH− intermediates on Au0 and CuO species. However, its lower capacity to release the surface oxygen contributes to the generation of stable carbon deposits, which lead to its rapid deactivation. On the other hand, AuCu/CeO2-SiO2 was more stable due to its high surface area and lower formation of formate and carbonate intermediates, mitigating carbon deposits. Therefore, use of dual supports could be a promising strategy to overcome the low stability of AuCu/CeO2. The results of this research are a contribution to integrated production and purification of H2 in a compact system.

Green Synthesis of a Cu/SiO2 Catalyst for Efficient H2-SCR of NO

In this work, the synthesis of Cu/SiO2 catalysts starting from pre-formed copper nanoparticle (CuNP) colloidal suspensions was carried out. Two different protocols for the CuNP synthesis were tested: (i) a green approach using water as solvent and ascorbic acid as reducer and stabilizing agent, and (ii) a second solvothermal method involving the use of diethylene glycol as solvent, sodium hypophosphite (NaH2PO2) as reducer, and polyvinylpyrrolidone (PVP) and cetyltrimethylammonium bromide (CTAB) as stabilizing agents. In addition, and for the sake of comparison, a third catalyst was prepared by solid state conventional grinding of CuO with SiO2. The catalysts were tested in the environmentally relevant catalytic reduction of NOX with H2, in a temperature range from 300 to 500 °C. The catalysts were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR) cycles, Raman spectroscopy, and N2 adsorption for specific surface BET measurements. From these techniques CuO and Cu(0) species were detected depending on the synthesis protocol. CuNP size and size distribution in the colloid suspensions were determined by transmission electronic microscopy (TEM). The catalyst prepared from the aqueous suspension (CuAsc/SiO2) exhibited higher NO conversion (100%) and selectivity (85%) toward N2 at the lower reaction evaluated temperature (300 °C). The CuCTAB/SiO2 catalyst obtained by the solvothermal approach showed activity at high reaction temperature (400 °C) preferentially. The metal–support mechanical mixture exhibited a negligible response at low temperature and low conversion (68%) and selectivity (88%) at 500 °C. Nanoparticle size and distribution on the support, together with the metal–support interaction, were postulated as the most plausible parameters governing the catalytic performance of the different Cu/SiO2 materials.

Facile assembly of Cu-Cu2O/N-reduced graphene oxide nanocomposites for efficient synthesis of 2-methylfuran

The hydrodeoxygenation of furfural to 2-methylfuran is of great significance for biomass valorization. However, the design of efficient catalysts based on non-noble metals is still a huge challenge for this transformation. In this work, a uniformly dispersed Cu-Cu2O/N-RGO nanocomposite was assembled via microwave assisted reduction and ammonia evaporation synthetic strategy. Under the optimum conditions, the yield of 2-methylfuran reached 95.5%, and there was no catalyst deactivation was observed within 5 cycles. The characterization results confirmed that the activity of the catalyst was mainly attributed to the synergistic effects of surface Cu0 and Cu+ species in catalyst, which were originated from partial reduction of CuO species due to the strong interaction between Cu precursors and support. Furthermore, this strong interaction also promised stability of the catalyst which could immobilize copper particles to resist leaching.