Ni Nanoparticle Catalysts Research Articles

Catalytic propane dehydrogenation by anatase supported Ni single-atom catalysts

With the increasing production of propane from shale gas and the growing demand for propylene, propane dehydrogenation (PDH) has gained significant attention as a promising route for the on-purpose production of propylene. As a cheap yet efficient catalyst, Ni-based catalysts have attracted interest because of its ability to activate alkane. Single-atom catalysts (SACs) can maximize the metal atom utilization. Here, we demonstrate that anatase TiO2 supported Ni SAC (Ni1/A-TiO2) exhibits not only superior intrinsic activity and propylene selectivity but also much better stability than the corresponding Ni nanoparticle (NP) catalyst (NiNP/A-TiO2) in PDH reaction at 580 °C. The rate of propylene production on Ni1/A-TiO2 is about 1.96 molC3H6 gNi−1 h−1, about 65 times higher than that of NiNP/A-TiO2 sample (0.03 molC3H6 gNi−1 h−1). In combination of high-angle annular dark-field scanning transmission electron microscopy, in-situ diffuse reflectance infrared Fourier transform spectra, in-situ X-ray photoelectron spectroscopy and X-ray absorption spectroscopy characterizations, we confirm that the Ni SAC mainly contains individual Ni atom singly dispersed on the support in positive Ni (II) valence state. In addition, as a result of strong metal-support interaction (SMSI) between Ni NP and TiO2 carrier under reduced conditions, the Ni NPs sites are encapsulated by TiOx overlayer (~2 nm thick) thus display poor reaction performance.

Nanocatalysts Based on Ni Nanoparticles in Functionalized Ionic Liquids for Chemoselective Hydrogenation and Transfer Hydrogenation of α,β‐unsaturated Carbonyl Compounds

AbstractFor the development of catalytically active and selective Ni nanoparticle (NP) catalysts both the choice of the synthesis method and the selection of stabilizer are key parameters. A series of Ni NPs were synthesized in various ionic liquids (Ni/ILs) and applied as catalysts for the chemoselective reduction of 2‐cyclohexen‐1‐one (1), as a representative of the group of α,β‐unsaturated carbonyl compounds with industrial relevance. The Ni/ILs systems were found to be efficient catalysts for the selective hydrogenation of 1 to cyclohexanone (2) under quite mild reaction conditions (130‐170 °C, 10 bar H2, 1/Ni molar ratio of 100/1), achieving high conversions in a short reaction time (1 h). The oxidized counterparts (Ni‐NiO/ILs) showed to be active for the selective catalytic transfer hydrogenation (CTH) of 1 to 2‐cyclohexen‐1‐ol (3) with 2‐propanol, also under mild reaction conditions (150 °C, 48 h, 1/Ni ratio of 50/1).

Nitric Acid-Pretreated Natural Halloysite Nanotubes as Ni Nanoparticle Catalyst Supports for CO2 Methanation

Nitric Acid-Pretreated Natural Halloysite Nanotubes as Ni Nanoparticle Catalyst Supports for CO₂ Methanation

Heterogeneously catalyzed decarbonylation of thioesters by supported Ni, Pd, or Rh nanoparticle catalysts.

Decarbonylation of thioesters has been actively studied using homogeneous metal catalysts as an attractive approach for synthesizing thioethers, which are widely utilized in various fields, because decarbonylation ideally requires no additives and produces CO as the sole theoretical byproduct. However, heterogeneously catalyzed decarbonylation of thioesters has not been reported to date, despite its importance for the construction of environmentally-friendly and practical catalytic systems. This study demonstrated a heterogeneously catalyzed system for the decarbonylation of various aryl thioesters to produce thioethers and CO by utilizing CeO2- or hydroxyapatite-supported Ni, Pd, or Rh nanoparticle catalysts. The Ni catalysts showed high catalytic activity, while the Pd catalysts possessed excellent functional group tolerance. The Rh catalysts were suitable for the selective decarbonylation of unsymmetrically substituted thioesters.

Structure Sensitivity of CO2 Hydrogenation on Ni Revisited.

Despite the large number of studies on the catalytic hydrogenation of CO2 to CO and hydrocarbons by metal nanoparticles, the nature of the active sites and the reaction mechanism have remained unresolved. This hampers the development of effective catalysts relevant to energy storage. By investigating the structure sensitivity of CO2 hydrogenation on a set of silica-supported Ni nanoparticle catalysts (2-12 nm), we found that the active sites responsible for the conversion of CO2 to CO are different from those for the subsequent hydrogenation of CO to CH4. While the former reaction step is weakly dependent on the nanoparticle size, the latter is strongly structure sensitive with particles below 5 nm losing their methanation activity. Operando X-ray diffraction and X-ray absorption spectroscopy results showed that significant oxidation or restructuring, which could be responsible for the observed differences in CO2 hydrogenation rates, was absent. Instead, the decreased methanation activity and the related higher CO selectivity on small nanoparticles was linked to a lower availability of step edges that are active for CO dissociation. Operando infrared spectroscopy coupled with (isotopic) transient experiments revealed the dynamics of surface species on the Ni surface during CO2 hydrogenation and demonstrated that direct dissociation of CO2 to CO is followed by the conversion of strongly bonded carbonyls to CH4. These findings provide essential insights into the much debated structure sensitivity of CO2 hydrogenation reactions and are key for the knowledge-driven design of highly active and selective catalysts.

Size sensitivity of supported Ni nanoparticles on carbon for the synthesis of secondary amines from acceptorless dehydrogenation-hydrogenation of primary amines

Earth-abundant metal catalysts, especially Ni, are highly favourable in heterogeneous reactions compared with noble metal ones. Herein, Ni nanoparticle catalysts supported on Vulcan carbon (VCX) support were prepared through a simple impregnation-reduction method and utilized for the acceptorless dehydrogenation of primary amines to secondary amines. The best performance was achieved with Ni(A)/VXC with Ni particle size of 11.9 nm at 150 °C. Smaller or larger particle sizes resulted in a lower TOF, indicating a structure-sensitive activity. This work may serve as inspiration for further investigation into acceptorless dehydrogenation using non-noble metal catalysts.

Mesoscale study of crystal-plane effects of Ni catalysts on CO2 hydrogenation.

Crystal-plane effects have pivotal roles in the design of catalysts. In this study, a branched Ni (Ni-BN) catalyst was mainly exposed at the Ni(322) surface and was synthesized in the presence of H2. A Ni nanoparticle (Ni-NP) catalyst was mainly exposed at Ni(111) and Ni(100) surfaces and was synthesized without H2. The Ni-BN catalyst showed higher CO2 conversion and methane selectivity than the Ni-NP catalyst. DRIFTS revealed that, unlike the formate route for methanation over the Ni-BN catalyst, the main methanation pathway over the Ni-NP catalyst was the CO2 direct dissociation route, which revealed that the diversity of reaction mechanisms of CO2 methanation on different crystal planes led to the disparity in catalyst activity. DFT calculation of the CO2 hydrogenation reaction over various surfaces showed that the energy barriers on Ni(110) and Ni(322) surfaces were lower than those of Ni(111) and Ni(100) surfaces, which was also related to different pathways of the reaction mechanism. Microkinetic analysis showed the reaction rates on Ni(110) and Ni(322) surfaces were higher than those of other surfaces, and CH4 was the main product on all calculated surfaces, whereas the yields of CO on Ni(111) and Ni(100) surfaces were higher. Kinetic Monte Carlo simulations revealed that the Ni(322) surface with stepped sites was responsible for CH4 generation, and that simulated methane selectivity was consistent with experimental results. The crystal-plane effects of the two morphologies of Ni nanocrystals explained why the reaction activity of the Ni-BN catalyst was greater than that of the Ni-NP catalyst.

Selective mono-N-methylation of amines using methanol as a methylating reagent over heterogeneous Ni catalysts

Mixed oxide (ZnAlOx) supported heterogeneous Ni nanoparticle catalysts (Ni/ZnAlOx-600) for the direct synthesis of mono-N-methylamines from amines and methanol.

Bimetallic CoNi single atoms supported on three-dimensionally ordered mesoporous chromia: highly active catalysts for n-hexane combustion

Developing the alternative supported noble metal catalysts with low cost, high catalytic efficiency, and good resistance toward carbon dioxide and water vapor is critically demanded for the oxidative removal of volatile organic compounds (VOCs). In this work, we prepared the mesoporous chromia-supported bimetallic Co and Ni single-atom (Co1Ni1/meso-Cr2O3) and bimetallic Co and Ni nanoparticle (CoNPNiNP/meso-Cr2O3) catalysts adopting the one-pot polyvinyl pyrrolidone (PVP)- and polyvinyl alcohol (PVA)-protecting approaches, respectively. The results indicate that the Co1Ni1/meso-Cr2O3 catalyst exhibited the best catalytic activity for n-hexane (C6H14) combustion (T50% and T90% were 239 and 263 °C at a space velocity of 40,000 mL g−1 h−1; apparent activation energy and specific reaction rate at 260 °C were 54.7 kJ mol−1 and 4.3 × 10−7 mol gcat−1 s−1, respectively), which was associated with its higher (Cr5+ + Cr6+) amount, large n-hexane adsorption capacity, and good lattice oxygen mobility that could enhance the deep oxidation of n-hexane, in which Ni1 was beneficial for the enhancements in surface lattice oxygen mobility and low-temperature reducibility, while Co1 preferred to generate higher contents of the high-valence states of chromium and surface oxygen species as well as adsorption and activation of n-hexane. n-Hexane combustion takes place via the Mars−van Krevelen (MvK) mechanism, and its reaction pathways are as follows: n-hexane → olefins or 3-hexyl hydroperoxide → 3-hexanone, 2-hexanone or 2,5-dimethyltetrahydrofuran → 2-methyloxirane or 2-ethyl-oxetane → acrylic acid → COx → CO2 and H2O.

Effect of Impregnation with Ammonia vs Silica Support Textural Properties on Ni Nanoparticle Catalysts for Dry Reforming of Methane

In this work, Ni(0) nanoparticles (3.5 and 5 wt %) highly dispersed on silica were obtained by reducing the calcined solid resulting from the impregnation of a nonporous siliceous support (here Aerosil-380) by aqueous nickel(II) nitrate in the presence of aqueous ammonia. The great effect of that base could be emphasized by the comparison with the solid prepared in the absence of ammonia. It was also clearly shown to be superior to the physical barrier effect induced by SBA-15, a mesostructured silica support, impregnated, using a “two-solvents” method, with a similar amount of aqueous precursor (5 wt % of Ni) in the absence of ammonia. In the protocol involving NH3, nickel phases could be hardly detected by X-ray diffraction (XRD) before and after reduction. However, the presence of Ni could be confirmed by X-ray photoelectron spectroscopy (XPS) and H2-TPR. After reduction, transmission electron microscopy (TEM) observations as well as H2 chemisorption highlighted the important dispersion of Ni(0) nanoparticles (up to 42% for 3.5 wt % of Ni). Aerosil-380-based catalysts prepared in the presence of NH3 revealed great performances in the dry reforming of methane at 650 °C for 12 h using a gas hourly space velocity of 960 L g–1 h–1 and an equimolar ratio of CH4 and CO2 reactants. Moreover, they showed a great resistance toward sintering and coke deposition. The formation of Ni phyllosilicate intermediate phases, which are at the origin of this excellent stability, could be evidenced by Fourier transform infrared (FTIR) and 29Si solid-state nuclear magnetic resonance (NMR).

Growth of Carbon Nanotubes on Diamond with a Robust Structural Connection via Microwave Plasma Chemical Vapor Deposition

In this paper, we present a novel method for growing carbon nanotubes (CNTs) via microwave plasma chemical vapor deposition (MPCVD) on diamond and silicon substrates. Scanning electron microscopy (SEM) and Raman spectroscopy analyses revealed dense, multi-walled carbon nanotubes growing on the diamond substrate. Optical Emission Spectroscopy (OES) showed that in the process of growing carbon nanotubes with the MPCVD method, the CH4 introduced into the system is excited by microwaves and dissociated to form active radicals such as C2 and CH, which are considered the C source of the synthesized carbon nanotube. Observation with high-resolution transmission electron microscopy (HRTEM) showed that most Ni catalyst nanoparticles that catalyze the growth of carbon nanotubes are located close to the diamond surface. In contrast, on the Si substrate, Ni catalyst nanoparticles were randomly distributed. A unique transition layer was observed between the diamond and carbon nanotubes, with the Ni particles being immersed into this transition layer and acting as anchors to fix the carbon nanotubes, resulting in a robust connection between the diamond and the CNT coating.

Influence of the roughness of the barrier layer on the formation of nanoparticles of the catalyst for the growth of carbon nanotubes

Usually, the synthesis of carbon nanotubes arrays for use in nanoelectronics is carried out on a two-layer catalyst. The lower layer is a barrier for the interaction of the upper catalyst layer with the substrate. When heated to the synthesis temperature, the upper layer 2–4 nm thick melts and catalyst nanoparticles are formed on the surface of the barrier layer. The novelty of the presented research is the search for a technology that provides a smaller spread in the size of catalyst nanoparticles and, accordingly, a higher quality vertical array of carbon nanotubes during subsequent synthesis. To this end, the paper compares two methods of forming a TiN barrier layer, electron beam evaporation (EBE) and atomic layer deposition (ALD), to obtain Ni catalyst nanoparticles with the smallest average diameter and narrow distribution dispersion. The layers obtained by EBE have a roughness 1.5 times higher than the layers deposited by ALD (Ra = 1 nm and Ra = 0.6 nm respectively). The roughness of the barrier layer affects the dispersion of the size distribution of nanoparticles. Thus, the average size of nanoparticles on the EBE layer is about 30 nm, and the distribution dispersion is 1.3 times larger compared to the ALD layer. Wetting of the surface of the TiN barrier layer for EBE samples is better than for ALD samples. The contact angle for the catalyst nanoparticle on the surface of the TiN layer is about 30° for EBE samples and approaches 80° for ALD samples. In this case, the surface relief is filled with metal, which corresponds to the Wenzel model. It is assumed that the higher surface roughness of the EBE samples is associated with a higher temperature of titanium nitride film formation compared to ALD. ALD deposition of TiN barrier layers is preferable for the formation of catalytic nanoparticles on their surface for the growth of carbon nanotubes.

Electrodeposition of a Li-Al Layered Double Hydroxide (LDH) on a Ball-like Aluminum Lathe Waste Strips in Structured Catalytic Applications: Preparation and Characterization of Ni-Based LDH Catalysts for Hydrogen Evolution

A functionally structured catalyst was explored for ethanol steam reforming (ESR) to generate H2. Aluminum lathe waste strips were employed as the structured catalytic framework. The mixed metal oxide (Li-Al-O) was formed on the surface of Al lathe waste strips through calcination of the Li-Al-CO3 layered double hydroxide (LDH), working as the support for the formation of Ni catalyst nanoparticles. NaOH and NaHCO3 titration solutions were, respectively, used for adjusting the pH of the NiCl2 aqueous solutions at 50 °C when developing the precursors of the Ni-based catalysts forming in-situ on the Li-Al-O oxide support. The Ni precursor on the Al structured framework was reduced in a H2 atmosphere at 500 °C for 3 h, changing the hydroxide precursor into Ni nanoparticles. The titration agent (NaOH or NaHCO3) effectively affected the physical and chemical characterizations of the catalyst obtained by the different titrations. The ESR reaction catalyzed by the structured catalysts at a relatively low temperature of 500 °C was studied. The catalyst using NaHCO3 titration presented good stability for generating H2 during ESR, achieving a high rate of H2 volume of about 122.9 L/(gcat·h). It also had a relatively low acidity on the surface of the Li-Al-O oxide support, leading to low activity for the dehydration of ethanol and high activity to H2 yield. The interactions of catalysts between the Ni precursors and the Li-Al-O oxide supports were discussed in the processes of the H2 reduction and the ESR reaction. Mechanisms of carbon formation during the ESR were proposed by the catalysts using NaOH and NaHCO3 titration agents.

One-Step Solvothermal Synthesis of Ni Nanoparticle Catalysts Embedded in ZrO2 Porous Spheres to Suppress Carbon Deposition in Low-Temperature Dry Reforming of Methane

Ni nanoparticle catalysts embedded in ZrO2 porous spheres and ZrO2 porous composite spheres, SiO2-ZrO2, MgO-ZrO2, and Y2O3-ZrO2, with 83−115 nm diameter and 167–269 m2/g specific surface area were prepared by a one-pot and one-step solvothermal reaction from precursor solutions consisting of Ni(NO3)2‧6H2O, Zr(OnBu)4, and acetylacetone in moist ethanol combined with either Si(OEt)4, magnesium acetylacetate, or Y(OiPr)3. The obtained Ni catalysts have high specific surface areas of 130–196 m2/g, even after high-temperature reduction by H2 at 450 °C for 2 h. They were utilized as catalysts for low-temperature dry reforming of methane (DRM) at 550 °C to suppress carbon deposition on Ni nanoparticles. The Ni catalysts embedded in SiO2-ZrO2 and Y2O3-ZrO2 demonstrated high catalytic activity and long stability in the reaction. Moreover, carbon deposition on Ni nanoparticles in the DRM reaction was effectively suppressed in when using the SiO2-ZrO2 and Y2O3-ZrO2 composites.Graphical abstract

Direct synthesis of imines from nitro compounds and biomass-derived carbonyl compounds over nitrogen-doped carbon material supported Ni nanoparticles

A kind of nitrogen-doped carbon material and MgO co-supported Ni nanoparticle catalyst has been developed and demonstrates high activity, selectivity and stability.

Catalytic Steam Reforming of Bio-Oil-Derived Acetic Acid over CeO2-ZnO Supported Ni Nanoparticle Catalysts.

The steam reforming of bio-oil-derived acetic acid over the developed Ni/CeO2-ZnO nanoparticle catalysts for hydrogen production was studied. The correlations of CeO2 to ZnO mass ratio (CZMR) and nickel loading with the properties and performances of Ni/CeO2-ZnO catalysts were explored. The H2, CO, and potential H2 yields followed a Gaussian normal distribution with increasing the CZMR. An exponential function equation was established to correlate the H2, CO, and potential H2 yields with Ni loading. As the CZMR increased from 0 to 1/3, the H2 yield increased from 57.8 to 69.4%, with a growth rate of 20.1%. Further, on increasing the CZMR from 1/3 to 3, the H2 yield decreased by 37.6%. The CO yield showed a similar trend for the H2 yield on increasing the CZMR, which first increased to a peak value, then started to decrease rapidly and finally stabilized. The yield of H2 increased significantly from 20.6 to 73.5%, with the increase of nickel loading from 0 to 15%. Further, on increasing the nickel loading from 15 to 25%, the H2 yield increased by only 5.8%. With the CZMR of 1/3 and the nickel loading of 15%, the selectivities of H2 and CO were as high as 91.6 and 42.3%, respectively.

Highly Active and Carbon-Resistant Nickel Single-Atom Catalysts for Methane Dry Reforming

The conversion of CH4 and CO2 to syngas using low-cost nickel catalysts has attracted considerable interest in the clean energy and environment field. Nickel nanoparticles catalysts suffer from serious deactivation due mainly to carbon deposition. Here, we report a facile synthesis of Ni single-atom and nanoparticle catalysts dispersed on hydroxyapatite (HAP) support using the strong electrostatic adsorption (SEA) method. Ni single-atom catalysts exhibit excellent resistance to carbon deposition and high atom efficiency with the highest reaction rate of 1186.2 and 816.5 mol.gNi−1.h−1 for CO2 and CH4, respectively. Although Ni single-atom catalysts aggregate quickly to large particles, the polyvinylpyrrolidone (PVP)-assisted synthesis exhibited a significant improvement of Ni single-atom stability. Characterizations of spent catalysts revealed that carbon deposition is more favorable over nickel nanoparticles. Interestingly, it was found that, separately, CH4 decomposition on nickel nanoparticle catalysts and subsequent gasification of deposit carbon with CO2 resulted in CO generation, which indicates that carbon is reacting as an intermediate species during reaction. Accordingly, the approach used in this work for the design and control of Ni single-atom and nanoparticles-based catalysts, for dry reforming of methane (DRM), paves the way towards the development of stable noble metals-free catalysts.

High performance Ni catalysts prepared by freeze drying for efficient dry reforming of methane

For supported metal catalysts, the architectures of the supports are as important as the chemical compositions of the catalysts and the morphologies of the supported metal particles. In this work, we report a simple and versatile method for preparing Ni nanoparticle catalysts supported on Mg-Al mixed oxides for the dry reforming of methane. The catalysts were prepared by freeze drying of Ni-Mg-Al layered double hydroxide precursors, followed by calcination and H2 reduction. Compared to Ni/Mg-Al-O catalysts prepared by oven drying, the freeze-dried catalysts retain a unique, loosely packed platelet structure with high macroporosity, which gives rise to high dispersion, high DRM activity and high resistance against deactivation. At 800 °C, the catalyst consistently achieves equilibrium CH4 conversion of 95% over 100 h time on stream with a of 40 L-CH4 h−1 g-cat−1. The DRM activity seen in the present study supersedes other Ni-based catalysts reported in the literature.

Steam Reforming of Tetrahydrodicyclopentadiene over Socketed Nickel Perovskite Catalysts with an Applied Electric Field

The steam reforming of a complex hydrocarbon, tetrahydrodicyclopentadiene (JP‐10), is investigated in strong electric fields using a modified coaxial capacitor reactor without bulk plasma generation over socketed Ni nanoparticle catalysts. Bulk plasma is suppressed in the reactor system by applying the fields as short‐duration, high‐frequency pulses (200 ns pulses of 3.0 kV at 50 kHz). Field strengths generated in this system are estimated using a reactive formic acid probe measurement and found to be on the order of 0.16 V nm−1 at the active site. Analysis of the JP‐10 reaction behavior by mass spectrometry shows that the applied high electric field decreases its reaction temperature, increases its hydrogen production rate, and enhances its catalyst lifetime. Although a complete model of this complex system is still lacking, a coarse thermodynamic analysis is provided which shows a strong linear dependence of the key reforming performances (e.g., JP‐10 conversion, water conversion, hydrogen yield, and hydrogen production rate) on field strength and direction.

Rechargeable-battery chemistry based on lithium oxide growth through nitrate anion redox.

Next-generation lithium-battery cathodes often involve the growth of lithium-rich phases, which enable specific capacities that are 2-3 times higher than insertion cathode materials, such as lithium cobalt oxide. Here, we investigated battery chemistry previously deemed irreversible in which lithium oxide, a lithium-rich phase, grows through the reduction of the nitrate anion in a lithium nitrate-based molten salt at 150 °C. Using a suite of independent characterization techniques, we demonstrated that a Ni nanoparticle catalyst enables the reversible growth and dissolution of micrometre-sized lithium oxide crystals through the effective catalysis of nitrate reduction and nitrite oxidation, which results in high cathode areal capacities (~12 mAh cm-2). These results enable a rechargeable battery system that has a full-cell theoretical specific energy of 1,579 Wh kg-1, in which a molten nitrate salt serves as both an active material and the electrolyte.