Ni-Cu Bimetallic Catalysts Research Articles

CH4 Cracking over the Cu–Ni/Al-MCM-41 Catalyst for the Simultaneous Production of H2 and Highly Ordered Graphitic Carbon Nanofibers

The Cu-Ni bimetallic catalysts dispersed on various silica supports were examined for catalytic cracking of CH4 to produce pure H2 with near zero COx emissions and fine quality carbon nano fibers. The 27Al MAS NMR spectra of Al containing MCM-41 samples revealed the existence of framework and extra framework decorated Al species. Insertion of Al species into the framework of MCM-41, significantly improved the accessible active surface Ni sites, which was confirmed from the simultaneous H2 and N2O pulse titration techniques. NH3 TPD measurements demonstrated a high ratio of moderate and strong acid sites upon Al- insertion into the silica matrix. The framework tetrahedral -Al in MCM-41 stabilized the surface Cu-Ni alloy sites and protected from the sintering and fragmentation of Ni consequently enhanced the H2 yields of 270 Nm3/(molNi)-1 were obtained with Si/Al ratio = 150 with catalyst. The better performance of the Cu-Ni/Al-MCM-41 (Si/Al = 150) was rationalized using the physicochemical characteristics ...

Theoretical Study of the Mechanism of Furfural Conversion on the NiCuCu(111) Surface.

The full potential energy surface for the hydrodeoxygenation of furfural to furan and other ring-opening products has been systematically investigated using periodic density functional theory including dispersion corrections (PBE-D3) on the bimetallic NiCuCu(111) surface. For furan formation, the most favorable first step is the dehydrogenation of furfural into furoyl (F-CHO + H = F-CO + 2H), the successive step is decarbonylation of furoyl into furanyl (F-CO + H = F + CO + 2H), and the third step of furan formation from the hydrogenation of furanyl (F + CO + 2H = FA + CO + H) is the rate-determining step. In addition, on the basis of the most stably adsorbed furan and H, the ring opening of furan was found to be more favorable for producing many chemicals such as propane, butanal, butanol, and butene. In summary, furan is the main product of furfural conversion on the NiCuCu(111) surface. Since results have been obtained only for the NiCuCu(111) surface constructed by replacing the topmost Cu atoms by Ni atoms, the entire experimentally observed reactivity and selectivity of bimetallic CuNi catalysts for different construction methods cannot be fully rationalized. Nevertheless, the results provide the basis for investigating the intrinsic activity of CuNi catalysts in the hydrodeoxygenation of oxygenates involved in the refining of biomass-derived oils.

Development of Simultaneous Measurement System for X-ray Absorption Spectra at Two Absorption Edges.

Dispersive X-ray absorption fine structure (DXAFS) spectroscopy is a versatile measurement technique for analyzing chemical reactions in real time. We have developed a novel time-resolved DXAFS instrument based on two polychromators and a wide-range position-sensitive detector that permits direct observation of the synergistic effects of two elements. This system enables simultaneous acquisition of the X-ray absorption spectra for two different elements without any mechanical movement of the X-ray optics. The developed system was successfully applied to monitor both the synthesis of a Ni-Cu bimetallic catalyst, which revealed that the reduction of Ni occurred at a higher temperature than that of Cu, and the charge-discharge processes of a LixNi0.5Mn1.5O4-based lithium-ion battery, which demonstrated that the redox reactions of Ni and Mn occurred sequentially at specific electrode potentials.

Identification of an Active NiCu Catalyst for Nitrile Synthesis from Alcohol

Development of heterogeneous catalysts for alcohol transformation into nitriles under oxidant-free conditions is a challenge. Considering the C–H activation on α-carbon of primary alcohols is the rate-determining step, decreasing the activation energy of C–H activation is critical in order to enhance the catalytic activity. Several NiM/Al2O3 bimetallic catalysts were synthesized and scrutinized in catalytic transformation of 1-butanol to butyronitrile. Ni–Cu was identified as a suitable combination with the optimized Ni0.5Cu0.5/Al2O3 catalyst exhibiting 10 times higher turnover frequency than Ni/Al2O3 catalyst. X-ray absorption spectroscopy (XAS) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) revealed that the NiCu particles in the catalyst exist in the form of homogeneous alloys with an average size of 8.3 nm, providing an experimental foundation to build up a catalyst model for further density functional theory (DFT) calculations. Calculations were done over a series of NiM catalysts, and the experimentally observed activity trend could be rationalized by the Brønsted–Evans–Polanyi (BEP) principle, i.e., catalysts that afford reduced reaction energy also feature lower activation barriers. The calculated activation energy (Ea) for C–H activation with coadsorbed NH3 dropped from 63.4 kJ/mol on pure Ni catalyst to 49.9 kJ/mol on the most active NiCu-2 site in NiCu bimetallic catalyst, in good agreement with the experimentally measured activation energy values. The Ni0.5Cu0.5/Al2O3 catalyst was further employed to convert 11 primary alcohols into nitriles with high to near-quantitative yields, at a Ni loading 10 times less than that of the conventional Ni/Al2O3 catalyst.

Hierarchical Flower-like Bimetallic NiCu catalysts for Catalytic Transfer Hydrogenation of Ethyl Levulinate into γ-Valerolactone

Due to fast exploitation and consumption of fossil resources, efficient transformation of renewable biomass would be of vital significance for the production of biofuels and value-added chemicals. ...

Ceria Promoted Cu-Ni/SiO2 Catalyst for Selective Hydrodeoxygenation of Vanillin.

A ceria (CeO2) promoted Cu-Ni bimetallic catalyst supported on SiO2 (Cu-Ni/CeO2-SiO2) was prepared and evaluated for catalytic hydrodeoxygenation (HDO) of vanillin. Silica supported monometallic Cu and Ni catalysts and bimetallic Cu-Ni catalyst (Cu/SiO2, Ni/SiO2, and Cu-Ni/SiO2), without a ceria promoter, were also synthesized and tested for the same application. The highest conversion of vanillin was achieved with the Cu-Ni/CeO2-SiO2 catalyst. Vanillyl alcohol was the sole product in the initial 2 h, followed by the formation of 2-methoxy-4-methylphenol, which was observed. Characterization of the synthesized catalysts revealed the presence of overlapping crystalline phases of CuO, NiO, and CeO2 on the Cu-Ni/CeO2-SiO2 surface. We extended our study to find out the results of using CeO2 as the support of the Cu-Ni bimetallic catalyst (Cu-Ni/CeO2). Partial incorporation of Cu and Ni cations into the ceria lattice took place, leading to the decrease of specific surface area and a concomitant compromise in the conversion. In the case of the Cu-Ni/CeO2-SiO2 catalyst, the higher conversion was accredited to the facile formation of Cu+ active centers by the synergistic interaction between Ce+4/Ce+3 and Cu+2/Cu+ redox couples and the incorporation of oxygen vacancies on the catalyst surface.

Operando monitoring of metal sites and coke evolution during non-oxidative and oxidative ethanol steam reforming over Ni and NiCu ex-hydrotalcite catalysts

Ni and NiCu bimetallic catalysts derived from hydrotalcite-like compounds have been studied by operando time-resolved X-ray Absorption Spectroscopy/Raman Spectroscopy/Mass Spectrometry during ethanol steam reforming (ESR) reaction followed by oxidative regeneration and also during oxidative ethanol steam reforming (OSR) reaction. The presence of copper in the NiCu bimetallic catalyst enhanced nickel reducibility, promoted higher H2 production and mitigated the deposition of graphitic carbon. Carbon deposition evidenced by Raman was the main cause of the catalyst deactivation. Exposure to O2/He atmosphere allowed the regeneration of spent catalysts by burning coke deposits, and also, contributed to improve the nickel redispersion on alumina. Differently to the conventional reactivation, which requires further reductive treatment for recovering active metallic species, H2 produced after regeneration under ESR conditions promoted the self-reactivation of the catalyst and restored the activity at 98% of ethanol conversion. The addition of O2 to the ethanol/water feed in the OSR decreased the amount of deposited filamentous-like coke but also the selectivity to H2.

Catalytic hydrotreatment of pyrolysis-oil with bimetallic Ni-Cu catalysts supported by several mono-oxide and mixed-oxide materials

Catalytic hydrotreatment of pyrolysis-oil from biomass is an important process to improve oil characteristics for use as liquid fuel. Bimetallic NiCu catalysts are currently attractive for use in hydrotreatment process due to its highly active for hydrogenation, hydrodeoxygenation and hydrocracking reactions. In this study, NiCu catalyst supported by several mono-oxide (i.e. γ-Al2O3, ZrO2, SBA-15 and MCM-41) and mixed-oxide (ZrO2-SBA-15 and ZrO2-MCM-41) materials was tested for hydrotreatment of guaiacol (as pyrolysis-oil model compound) and pyrolysis-oil from eucalyptus under several reaction temperatures (200–350 °C) and times (1–6 h). Among all catalysts, NiCu/ZrO2-SBA-15 showed the highest activity toward the hydrotreatment of guaiacol, from which hydrodeoxygenation yield of 87.3% with relatively low carbon deposition (3.4 wt%) was achieved from the reaction at 325 °C for 2 h. For the hydrotreatment of pyrolysis-oil in the presence of NiCu/ZrO2-SBA-15, ungraded oil with favorable qualities (i.e. high H/C ratio and low thermogravimetric residue) was obtained from the reaction at 350 °C for 3 h. After reaction test, catalyst regeneration and reusability were also studied. The regeneration of spent NiCu/ZrO2-SBA-15 by oxidation with O2 at 600 °C for 3 h can remove most of carbon species from catalyst surface with insignificant change in catalyst surface properties. In addition, the regenerated catalyst can be reused for at least 5 reaction cycles without significant deactivation observed.

Highly active and stable Ni-Cu supported catalysts prepared by combustion synthesis for hydrogen production from ethanol

We report on the high activity and stability towards deactivation during ethanol decomposition of mono (Ni, Cu) and bimetallic Ni-Cu catalysts supported on ceria and silica that were prepared by impregnated support solution combustion synthesis (ISCS). Ni supported on ceria, behaves much like bulk Ni, as it deactivates within a few hours of time on stream (TOS). Addition of Cu improves the stability of ceria supported Ni-Cu bimetallic catalysts but it still deactivates during 10 h of TOS. Ni prepared by dry impregnation on silica deactivates completely during a few h of TOS. Ni supported on silica prepared by ISCS, show a remarkable high stability for over 30 h TOS and Ni-Cu is stable over 100 h of TOS operating at 100% conversion.XRD, XPS, HRTEM, in-situ XAS and textural characterization of these catalysts show that the surface Ni concentration is small on silica-supported catalysts due to partial encapsulation of Ni by the silica support, which protects the metal particles from carbon formation, thus hindering deactivation. Addition of Cu to silica increases the number of active sites, but also decreases CO chemisorption on Ni indicating the formation of a Cu-Ni alloy, which had been reported to inhibit carbon formation on Ni. The combined effect of encapsulation and formation of Ni-Cu surface alloys result in the remarkable stability of the Cu-Ni silica supported catalyst.

A Direct Ammonia Microfluidic Fuel Cell using NiCu Nanoparticles Supported on Carbon Nanotubes as an Electrocatalyst.

This work demonstrates the use of a NiCu electrocatalyst prepared by hydrothermal method with different Ni/Cu mass ratios (70:30, 50:50 and 30:70) supported on carbon nanotubes (CNTs), which was studied with regards to its electrochemical behavior in the ammonia oxidation reaction and direct ammonia microfluidic fuel cell (DAMFC) performance. XRD and SEM-EDX showed the formation of NiCu alloy while TEM showed the particles size to be 15-20 nm. Cyclic voltammetry and chronoamperometry showed that NiCu had higher catalytic activity than pure Ni and pure Cu, and that the active species was a NiCu oxyhydroxide. In DAMFC tests, 50 wt % Ni50 Cu50 /CNTs was found to be the most suitable one since it showed a 43 % higher peak power density and 65 % higher maximum current density than Ni electrode. The improved performance was attributed to the NiCu oxyhydroxides formation, which improved the anodic catalytic activity by increasing amounts of active sites and the combined electronic effect of the Ni-Cu bimetallic catalysts.

Catalytic conversion of furfural-acetone condensation products into bio-derived C8 linear alcohols over Ni[sbnd]Cu/Al-SBA-15

The production of C8 linear diols from a furfural-acetone condensation product has been achieved for the first time using a non-noble metal based catalyst. In particular, SBA-15 supported NiCu bimetallic catalyst showed the best hydrogenating activity reaching an outstanding yield (ca. 63%) of the fully saturated product. The incorporation of acidity by the preparation of NiCu/Al-SBA-15 resulted in the promotion of ring-opening steps, which led to a remarkable yield of C8 linear diols (28%). These results establish a competitive catalytic route for the production of bio-based diols over cost-efficient 3d transition metal-based catalysts.

Efficient and stable Cu-Ni/ZrO2 catalysts for in situ hydrogenation and deoxygenation of oleic acid into heptadecane using methanol as a hydrogen donor

In this work, a series of ZrO2-supported Cu, Ni and bimetallic Cu-Ni catalysts were synthesized and evaluated for their activity and stability in the in situ hydrogenation and decarboxylation of oleic acid using methanol as a hydrogen donor. High-angle annular dark-field scanning transmission electron microscopy (HADDF-STEM), energy dispersive X-ray spectroscopy (EDS-mapping), X-ray diffraction (XRD) and temperature programmed reduction (TPR) characterizations revealed that the as-synthesized Cu-Ni/ZrO2 was a Cu-Ni alloy that was highly dispersed on mixed m-ZrO2 and t-ZrO2. The bimetallic Cu-Ni/ZrO2 nanostructures not only exhibited better catalytic activity for the conversion of oleic acid compared to monometallic Cu/ZrO2 and Ni/ZrO2 catalysts but also demonstrated good reuse performance. The formation of the Cu-Ni alloy facilitated the decarboxylation reaction and inhibited the cracking reaction, leading to enhanced catalytic performance. The good stability of Cu-Ni/ZrO2 was primarily due to the good hydrothermal stability of the ZrO2 support.

Screening of Ni-Cu bimetallic catalysts for hydrogen and carbon nanofilaments production via catalytic decomposition of methane

The catalytic decomposition of methane (CDM) is a H2 production process in which the CO2 emission of conventional processes is avoided and from which carbon nanofilaments can be obtained as a high added value by-product. In this work, we present a thermogravimetry-based screening of catalysts according to their carbon production in the CDM reaction. Catalysts studied were based on Ni as active phase, using two textural promoters (Al2O3 or MgO) and Cu as dopant element in different proportions: 2.5, 5.0, 7.5 and 10 mol %. Cu doping resulted in an increase in both the maximum temperature of activity (>100 °C) and the carbon formation rate, which were maximum for a Cu content of 7.5 mol %, regardless of the textural promoter used. The formation of a solid solution of Ni(x)Cu(1-x), with lattice constants and particle size distribution highly dependent on the Cu content, led to the formation of fishbone carbon nanofibers with different morphological features, such as the α angle between the graphene stacks and the growth axis of the nanofilament, the diameter, the length and the formation or not of an inner hollow.

Phase-Contact Engineering in Mono- and Bimetallic Cu-Ni Co-catalysts for Hydrogen Photocatalytic Materials.

Understanding how a photocatalyst modulates its oxidation state, size, and structure during a photocatalytic reaction under operando conditions is strongly limited by the mismatch between (catalyst) volume sampled by light and, to date, the physicochemical techniques and probes employed to study them. A synchrotron micro-beam X-ray absorption spectroscopy study together with the computational simulation and analysis (at the X-ray cell) of the light-matter interaction occurring in powdered TiO2 -based monometallic Cu, Ni and bimetallic CuNi catalysts for hydrogen production from renewables was carried out. The combined information unveils an unexpected key catalytic role involving the phase contact between the reduced and oxidized non-noble metal phases in all catalysts and, additionally, reveals the source of the synergistic Cu-Ni interaction in the bimetallic material. The experimental method is applicable to operando studies of a wide variety of photocatalytic materials.

Phase‐Contact Engineering in Mono‐ and Bimetallic Cu‐Ni Co‐catalysts for Hydrogen Photocatalytic Materials

AbstractUnderstanding how a photocatalyst modulates its oxidation state, size, and structure during a photocatalytic reaction under operando conditions is strongly limited by the mismatch between (catalyst) volume sampled by light and, to date, the physicochemical techniques and probes employed to study them. A synchrotron micro‐beam X‐ray absorption spectroscopy study together with the computational simulation and analysis (at the X‐ray cell) of the light‐matter interaction occurring in powdered TiO2‐based monometallic Cu, Ni and bimetallic CuNi catalysts for hydrogen production from renewables was carried out. The combined information unveils an unexpected key catalytic role involving the phase contact between the reduced and oxidized non‐noble metal phases in all catalysts and, additionally, reveals the source of the synergistic Cu‐Ni interaction in the bimetallic material. The experimental method is applicable to operando studies of a wide variety of photocatalytic materials.

Diseño experimental para determinar el efecto del tamaño del pellet de catalizadores bimetálicos Cu-Ni en la reacción de desplazamiento de agua

Se sintetizaron catalizadores bimetálicos de Cu-Ni en relación molar 2-1 en pellets cilíndricos de carbón activado de diferentes diámetros (0,2 cm; 0,3 cm y 0,4 cm) y longitud (0,4 cm y 0,6 cm); se evaluaron en la reacción de desplazamiento de agua a 330 °C y presión atmosférica. Se realizó un diseño experimental para evaluar el efecto de las variables, diámetro y longitud, sobre la conversión del monóxido de carbono. La importancia de los principales factores y sus interacciones se examinaron por medio del análisis de varianza (ANOVA). Los resultados mostraron que tanto el diámetro como la longitud afectan significativamente la conversión del monóxido de carbono. Los resultados de la actividad catalítica, bajo las mejores condiciones de diámetro (0,4 cm) y longitud (0,6 cm) de los pellets, mostraron una conversión del monóxido de carbono del 96%.

Steam reforming of phenol-ethanol to produce hydrogen over bimetallic Ni[sbnd]Cu catalysts supported on sepiolite

A series of NiCu bimetallic catalysts supported on sepiolite (NixCuy/SEP) were prepared by co-precipitation method. The all as-prepared catalysts were characterized by using XRD, FT-IR, H2-TPR, and TEM. The results shown the NiCu alloys were successfully synthesized in bimetallic catalysts, and the addition of Cu promoter decreased the particles size, improved the redox ability and metal dispersion of bimetallic catalysts. Specially, the Ni1Cu0.25/SEP catalyst exhibited the smallest particles (10.2 nm) and highest metal dispersion (8.2%). In addition, the catalytic performance of prepared catalysts was evaluated during the mixture of phenol and ethanol steam reforming (PESR) reaction under the following conditions: steam to carbon ratio (S/C) = 1, WHSV = 3.2 h−1 and different temperatures (550 °C and 650 °C). The experimental results shown the high temperature was positive for increasing carbon conversion and H2 yield. Moreover, the Ni1Cu0.25/SEP catalyst exhibited the highest carbon conversion (83.5%) and H2 yield (67.5%) with relating to the lowest CH4 selectivity (8.8%), which was attributed to the formation of NiCu alloy and the smallest particle size in Ni1Cu0.25/SEP catalyst, leading to inhibit methanation reaction and enhance the steam reforming (SR) of methane. Additionally, the effect of steam S/C ratios (1, 5, 8) on the carbon conversion and H2 yield over Ni1Cu0.25/SEP was also tested at 650 °C, it shown that the carbon conversion was increased with the increase of S/C. Meanwhile, the test of stability was carried out over different catalysts at 650 °C. It found that the Ni1Cu0.25/SEP catalyst exhibited the outstanding stability during 24 h on steam, while the Ni1Cu0/SEP and Ni0Cu1/SEP shown rapidly deactivation after 10 h on steam. In order to illuminate the deactivation mechanism, the spent catalysts after 24 h of reaction were also characterized by XRD, TEM and TGA. The results shown Ni1Cu0.25/SEP catalyst exhibited smaller amount of carbon deposition in comparison with Ni1Cu0/SEP and Ni0Cu1/SEP catalysts, suggesting that the formation of NiCu alloy plays an important role in resisting to coke formation.

Water as a cosolvent – Effective tool to avoid phase separation in bimetallic Ni-Cu catalysts obtained via supercritical antisolvent approach

A series of Ni-Cu metal catalysts were synthesized using supercritical antisolvent (SAS) approach under conditions of controlled water content in the initial solution of precursors. It is shown that low content of water in methanol (up to 9 vol.%) helps to adjust the structure, texture and morphology of the obtained materials. The water additives promote the formation of carbonate phase that during further decomposition and reduction steps allows obtaining the solid Ni1‐xCux solution without phase separation. In particular the addition of 7 and more vol.% of water leads to the complete introduction of Cu into the Ni crystal lattice without formation of separate enriched phases of Ni or Cu.

Vapor-phase hydrogenation of levulinic acid to γ-valerolactone over Cu-Ni bimetallic catalysts

Vapor-phase hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) was performed over SiO2-supported Cu-Ni bimetallic catalysts with different Cu/Ni weight ratios under ambient H2 pressure. Characterization of the catalysts was carried out using powder X-ray diffraction, temperature-programmed reduction and thermogravimetric analysis. In contrast to the monometallic catalysts i.e. Ni/SiO2 and Cu/SiO2, the Cu-Ni/SiO2 bimetallic catalyst with a Cu/Ni weight ratio of 6/14 exhibits an excellent catalytic activity, and gave a GVL yield higher than 99% with a productivity of 1.64kgGVLkgcat.−1h−1 at 250°C and at a high WHSV of 1.65h−1 for 50h.

Bimetallic Cu-Ni catalysts supported on MCM-41 and Ti-MCM-41 porous materials for hydrodeoxygenation of lignin model compound into transportation fuels

The design of novel, efficient supported bimetallic catalysts for the transformation of renewable lignin model compounds into valuable products is currently an emerging research topic. This study investigates the synthesis, characterization and the catalytic application of bimetallic Cu-Ni catalysts supported on pure MCM-41 and Ti incorporated MCM-41 porous materials for the valorization of a lignin model compound (i.e. guaiacol) into the transportation fuels via hydrodeoxygenation route (HDO). The investigated characterization results revealed that the Ti species are well-dispersed within the MCM-41 framework by a tetrahedral coordination. NH3-TPD studies show that the incorporation of Ti into the MCM-41 framework generates large amounts of acidic sites. It was also found that, the coordinated Ti species enhance the dispersion of CuO and NiO species on the surface of Ti-MCM-41 support. The CuNi/Ti-MCM-41 catalyst shows excellent reducible properties due to the co-operative effects of CuO and NiO with the Ti-MCM-41 support. The catalytic experiments revealed that the CuNi/Ti-MCM-41 catalyst exhibits a higher guaiacol conversion (~90.49%) and superior selectivity to cyclohexane (~50.09%) than the CuNi/MCM-41 catalyst which exhibits only ~10.57% cyclohexane selectivity with a guaiacol conversion of ~37.03%. The guaiacol conversion and cyclohexane selectivity were found to increase with the increase of reaction pressure from 40 to 100bar for CuNi/Ti-MCM-41 catalyst. It has been demonstrated that the HDO of guaiacol proceeds via demethoxylation (CAR-OCH3 cleavage) over the CuNi/Ti-MCM-41 catalyst and both demethylation (CARO-CH3 cleavage) and demethoxylation (CAR-OCH3 cleavage) pathways are possible over the CuNi/MCM-41 catalyst in HDO of guaiacol.