Structural transformations of highly porous nickel catalysts during ethanol conversion towards hydrogen

Manukyan, Khachatur V.; Yeghishyan, Armenuhi V.; Danghyan, V.; Rouvimov, Sergei; Mukasyan, Alexander S.; Wolf, E. L.

doi:10.1016/j.ijhydene.2018.04.242

Cited by 12 publications

(7 citation statements)

References 34 publications

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“…A modified method of nickel nitrate hexahydrate (Ni(NO 3 ) 2 ·6H 2 O) reduction with sodium borohydride (NaBH 4 ) was used to prepare amorphous Ni nanoparticles. − Briefly, 2.5 g of Ni(NO 3 ) 2 ·6H 2 O (Alfa Aesar) was dissolved in absolute ethyl alcohol (Koptec) under a continuous flow (100 cm 3 /min) of argon (Airgas, 99.9998%), followed by the addition of 2.5 g of NaBH 4 (MP Biomedicals, 99%) to the solution, with vigorous stirring. The reaction was allowed to proceed for 30 min.…”

Section: Experimental and Theoretical Methodsmentioning

confidence: 99%

Spontaneous Crystallization for Tailoring Polymorphic Nanoscale Nickel with Superior Hardness

et al. 2022

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Hexagonal close-packed (hcp) Ni exists only on a nanometric scale and readily converts into the stable face-centered cubic (fcc) polymorph. This work reports a spontaneous crystallization (SC) process in amorphous nanoparticles to tailor polymorphism in nanoscale Ni. The heat generated during the amorphous−crystalline transition enables SC to self-sustain. The combination of thermal analysis methods, X-ray photoelectron spectroscopy, electron microscopy, and diffraction methods with molecular dynamics (MD) simulations allows us to reveal the mechanism of the SC. This process consists of multiple exothermic steps: nuclei formation and growth of hcp/fcc-Ni grains within the amorphous nanoparticles, neck formation between particles, and defect-stimulated recrystallization (grain growth). The use of SC in conjunction with a rapid (minutes) and low-temperature (780 K) processing method allows for obtaining compact (94 ± 2% relative density) hcp/fcc-Ni nanomaterials. Rapid cooling during this process prevents the hcp → fcc phase transition, making it possible to preserve the metastable hcp-Ni phase. hcp/fcc-Ni materials possess a unique nanostructure and superior hardness to single-phase fcc-Ni. Detailed high-resolution imaging results show that hcp-Ni can be found in round-shape (less than 10 nm) or ultrathin (0.5−5 nm) laminated grains. Ultrasmall features reduce the dislocation motion at grain boundaries and significantly enhance the hardness of these materials.

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Section: Experimental and Theoretical Methodsmentioning

confidence: 99%

Spontaneous Crystallization for Tailoring Polymorphic Nanoscale Nickel with Superior Hardness

et al. 2022

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“…Nickel oxide reduction by hydrogen or methane ,,,− is of immense importance in catalysis and metallurgy. Reduction of NiO-based materials plays a significant role in many catalytic processes − such as reforming reactions for hydrocarbons and alcohols as well as biomass conversion. The use of methane instead of carbon as a reducer in extractive metallurgy decreases the operating temperature and reduces the emission of pollutants such as heavy metals and sulfur dioxide. − In chemical looping combustion, cyclic oxidation and reduction of Ni-based oxygen carriers are essential for clean power generation with simultaneous separation of CO 2 . − …”

Section: Introductionmentioning

confidence: 99%

Kinetics and Mechanism of Nickel Oxide Reduction by Methane

2019

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Nickel oxide reduction by methane is of particular importance in catalysis, extractive metallurgy, and clean power generation technologies. Despite extensive investigations of the NiO + CH 4 reaction, many questions remain about its kinetics and molecular and structural transformation mechanisms. This work reports the reduction kinetics of bulk polycrystalline NiO by CH 4 using a new calorimetric method. The method permits rapid, controllable heating of the NiO/Ni wires and continuous data (electrical power, the electrical resistivity of the wire, and temperature) acquisition with a frequency of 10 kHz. The method also allows arresting and preservation of the structure of the sample by programmed termination of electric power in thin specimens. This approach, coupled with ex situ electron microscopy, allows determination of the reaction rate and tracking of the ongoing structural transformations. The mechanism of NiO reduction by methane is suggested based on direct correlations between reaction kinetics and the observed microstructure transformations. The kinetic data treatment revealed that the nucleation−growth model describes the reaction kinetics. Ex situ microscopy observations of reacted specimens showed that the first nuclei rapidly accelerate the process. Pore formation occurs at the nucleation sites, and the porous structure then quickly grows into the bulk NiO. The second type of reduced Ni microstructure, compact layer, can be observed only on the outer surface of the wire. Based on kinetic data and microstructural observations, a mechanism of reduction was suggested according to which porous microstructure forms predominantly by NiO reduction with carbon. The compact layer observed on the outer surface of the wire forms through the diffusion-controlled hydrogen reduction.

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“…It is established in the literature that the carbon deposited on the catalyst surface dissolves into the nickel lattice and transforms into nickel carbide (Ni 3 C), further promoting filamentous carbon growth and nucleation. [65,66] Notably, in mitigating the bulk metallic phase, the whiskers' filamentous carbon does not really cause the direct deactivation of the catalyst but instead blocks the catalytic bed or fractures the pellet when continuously accumulated. [63] Meanwhile, metallic (Ni) crystallite size is significant; likewise, the smaller the size, the smaller the carbon clusters formed on the step edges, which are not large enough to exceed the critical cluster size to form stable C nuclei.…”

Section: Active Metalsmentioning

confidence: 99%

Recent advances in hydrogen production through catalytic steam reforming of ethanol: Advances in catalytic design

2023

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Catalytic reforming is a promising technology for producing renewable fuels; however, developing highly stable, efficient, green, and economical metallic catalysts that reduce metal sintering and carbon formation while improving catalyst activity, selectivity, and stability remains a major issue. In this regard, numerous studies have been documented in the past couple of decades evaluating the effects of various supports and promoters using ethanol as a co‐reactant in the catalytic steam reforming to produce energy‐efficient gaseous fuel, that is, hydrogen. This review article compiles research work focused on the catalytic reforming of ethanol reported in the last decade. Also, the outcomes of experimental studies have been presented and discussed for parametric analysis as case studies. The review shows that ethanol conversion, hydrogen selectivity, and catalyst stability are strongly influenced by the physicochemical properties of the catalyst, synthesis method, support choice, promoters, temperature, pressure, steam‐to‐ethanol ratio, and hourly space velocity. Noble metals (e.g., Pt, Rh, Ru, Pd, and Au), transition metals (e.g., Ni, Co, and Cu), and bimetallic composites were the most used catalysts in ethanol‐steam reforming reactions. Also, proper selection of support and promoter plays a significant role in modifying catalyst morphology, surface area, and particle size, enhancing selectivity, and reducing catalyst carbon deposition.

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Structural transformations of highly porous nickel catalysts during ethanol conversion towards hydrogen

Cited by 12 publications

References 34 publications

Spontaneous Crystallization for Tailoring Polymorphic Nanoscale Nickel with Superior Hardness

Spontaneous Crystallization for Tailoring Polymorphic Nanoscale Nickel with Superior Hardness

Kinetics and Mechanism of Nickel Oxide Reduction by Methane

Recent advances in hydrogen production through catalytic steam reforming of ethanol: Advances in catalytic design

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