Analysis of the Morphology and Structure of Carbon Deposit Formed on the Surface of Ni3Al Foils as a Result of Thermocatalytic Decomposition of Ethanol

This article presents the results of investigations of the morphology and structure of carbon deposit formed as a result of ethanol decomposition at 500 °C, 600 °C, and 700 °C without water vapour and with water vapour (0.35 and 1.1% by volume). scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) observations as well as energy dispersive X-ray spectrometry (EDS), X-ray diffraction (XRD), and Raman spectroscopic analyses allowed for a comprehensive characterization of the morphology and structure of cylindrical carbon nanostructures present on the surface of the Ni3Al catalyst. Depending on the reaction mixture composition (i.e., water vapour content) and decomposition temperature, various carbon nanotubes/carbon nanofibres (CNTs/CNFs) were observed: multiwalled carbon nanotubes, herringbone-type multiwall carbon nanotubes, cylindrical carbon nanofibers, platelet carbon nanofibers, and helical carbon nanotubes/nanofibres. The discussed carbon nanostructures exhibited nickel nanoparticles at the ends and in the middle part of the carbon nanostructures as catalytically active centres for efficient ethanol decomposition.

Aqueous-phase effects on ethanol decomposition over Ru-based catalysts

The effects of an aqueous phase on the ethanol decomposition for hydrogen production over a Ru(0001) catalyst surface model have been investigated from first principles. Solvent effects on the reaction...

Design of a Small-Scale Supercritical Water Oxidation Reactor. Part II: Numerical Modeling and Validation

<p>The experimental data from the laboratory-scale supercritical water oxidation reactor was leveraged to validate the CFD approach allowing for efficient and accurate modeling of the process. The reactor operating on ethanol as a pilot fuel was modeled using CFD with global oxidation mechanism. Fluid properties were determined using polynomial fit approximations, which yielded excellent agreement with NIST data over a range of temperatures at an isobaric pressure of 25 MPa. The model predicts the fluid temperature within 30°C of measured values for different inlet fuel concentrations. The ethanol decomposition of ~99% occurs within 20% of the reactor length at T~600 °C. The analysis of Damkohler (<i>Da</i>) and Reynolds (<i>Re</i>) numbers shows that the reactor operates in a distributed reaction region, owing to the excellent combustion stability of the inverted gravity reactor configuration. The modeling approach can aid the design of future more complex SCWO reactors and process optimization. </p>

Design of a Small-Scale Supercritical Water Oxidation Reactor. Part II: Numerical Modeling and Validation

<p>The experimental data from the laboratory-scale supercritical water oxidation reactor was leveraged to validate the CFD approach allowing for efficient and accurate modeling of the process. The reactor operating on ethanol as a pilot fuel was modeled using CFD with global oxidation mechanism. Fluid properties were determined using polynomial fit approximations, which yielded excellent agreement with NIST data over a range of temperatures at an isobaric pressure of 25 MPa. The model predicts the fluid temperature within 30°C of measured values for different inlet fuel concentrations. The ethanol decomposition of ~99% occurs within 20% of the reactor length at T~600 °C. The analysis of Damkohler (<i>Da</i>) and Reynolds (<i>Re</i>) numbers shows that the reactor operates in a distributed reaction region, owing to the excellent combustion stability of the inverted gravity reactor configuration. The modeling approach can aid the design of future more complex SCWO reactors and process optimization. </p>

Catalytic Decomposition of Ethanol over Bimetallic Nico Catalysts for Carbon Nanotube Synthesis

In this work we investigate the use of NiCo bimetal/oxide as catalyst for hydrogen production from ethanol, with a focus on the deactivation pattern and the nature of the observed carbon deposition. It is well known that sintering and coke deposition during decomposition reaction significantly reduces the activity of the catalysts at higher temperature, by blocking the active sites of the catalysts. During ethanol decomposition reaction, the cleavage of C-C bond produces adsorbed *CH4 and *CO species that further decompose to form carbonaceous compounds. FTIR in-situ analysis was conducted between 50 to 400°C for all the catalysts to understand the reaction mechanism and product selectivity. Cobalt was found to be selective for aldehyde and acetate, whereas bimetallic Ni-Co was selective for the formation of CO at 400°C along with aldehyde. Complete conversion of ethanol was observed at 350°C and 420°C for NiCo and Cobalt respectively indicating an improvement in the rate of conversion when Ni was added to cobalt. The crystallinity, morphology and particle analysis of the used catalyst after reaction were studied using XRD, SEM and TEM respectively. The XRD shows the complete phase change of porous NiCoO2 to NiCo alloy and SEM indicates the presence of fibrous structure on the surface with 91.7 % of carbon while keeping 1:1 ratio of Ni and Co after the reaction. The detailed analysis of carbon structure using HRTEM-STEM shows the simultaneous growth of carbon nano fibers (CNFs) and multiwalled carbon nanotubes (MWCNTs) that were favored on larger and smaller crystallites respectively. Analysis of carbon formation on individual Co catalyst and bimetallic NiCo catalyst shows a clear difference in the initiation pattern of carbon deposition. Metallic Co nanoparticles were found to be more mobile where Co disperses along the catalysts surface, whereas NiCo nanoparticles were relatively less mobile, and maintained their structure.

Ethanol decomposition in supercritical water: An operating parametric experimental and kinetic study

Ethanol is an intermediate of the supercritical water decomposition of lignocellulosic biomass or biomass-derived compounds. In this study, experiments on ethanol decomposition in supercritical water were performed at different reaction temperatures (500 °C to 600 °C), residence times (6 s to 12 s), and initial ethanol concentrations (0.05 mol·L-1 to 0.20 mol·L-1). Temperature had larger impacts on the ethanol conversion than the other factors. Higher temperatures and feedstock concentrations facilitated gas production. In addition, the higher temperature promoted the scissions of C-C and C-O bonds of ethanol. However, longer residence times did not improve the yields of H2, CO, and C2. Because the H2-to-CO2 ratio was much greater than 1, the water-gas shift reaction was not the dominant route during the ethanol conversion process. Further, the mechanism and kinetic model of ethanol supercritical water decomposition were proposed. The kinetics revealed that ethanol gasification in supercritical water was mainly dominated by ethanol dehydrogenation, the hydrogenation of intermediates, and the coke formations of CO and CH4. In addition, H2 was mainly formed via ethanol dehydrogenation and consumed via the hydrogenation of intermediates. The rate of coke formation was relatively low during ethanol decomposition.