Synthesis and Characterization of NiMo Catalysts Supported on Fine Carbon Particles for Hydrotreating: Effects of Metal Loadings in Catalyst Formulation

The by-products collected during the synthesis of carbon nanohorns via the arc discharge synthesis method is comprised of other carbon particles (OCP). At a hydrotreating operating temperature of 370°C, preliminary investigations using a bimetallic catalyst with support originating from the fine fractions of other carbon particles (OCPf) and containing 13 wt% Mo and 2.5 wt% Ni resulted in an HDS and HDN conversion of 78 and 25%, respectively. Variation of metal compositions in catalyst formulation and its impact on hydrotreating activity was therefore considered in this study to enhance the hydrotreating activity of OCPf–supported catalyst, and to determine if the best NiMo/OCPf catalyst achieved from this study could be a viable catalyst for hydrotreating applications. The co-incipient wetness impregnation was used in preparing series of hydrotreating catalysts with Ni and Mo loadings within the range of (2.5–5.0 wt%) and (13–26 wt%) respectively. Overall, the catalyst samples with maximum Ni loading of 5.0 wt% and Mo loadings of either 13 or 19 wt% showed higher dispersion and the ability to form a Type II Ni-Mo-S phase with enhanced activity. The effects of metal compositions on both HDS and HDN activities were correlated with their physicochemical properties.

In-line measurement of absorbed solar irradiance using nanofluids

In this paper a novel technique for the in-line evaluation of the absorption rate of solar radiation by nanofluids in a volumetric solar receiver is presented. This method allows to experimentally investigate the optical behaviour of a nanofluid when circulating in a volumetric solar receiver under non-concentrated solar irradiance and it is based on the combined use of pyranometers. This technique is used in the present work to study the absorption capability of a Single-Wall-Carbon-NanoHorns (SWCNHs) based nanofluid. From the experiments, it can be seen that after some hours of circulation, the absorption rate of the nanofluid decreases, due to a loss of nanoparticles in the suspension.

Thermal behavior of a flat-plate direct absorption with water-nanohorn mixture

A numerical analysis on a two-dimensional steady state forced convection inside a solar collector with direct absorption due to a nanofluid composed of water and nanoparticles of carbon nanohorns is carried out. The analysis allows to provide the main fluid flow and thermal characteristics of a simple flat solar collector with a distance between the glass and the collecting plate of 1.2 mm and a length of 1.0 m. The solar collector presents heat losses from the upper wall towards the ambient by an external surface heat transfer coefficient. The governing flow equations for the nanofluid are written assuming the single-phase flow and the heat transfer due to the radiation, for the local absorption of nanoparticles, is evaluated by the non-grey discrete ordinates method. The carbon nanohorns optical and thermal properties are estimated by the data available in literature. The finite volume method is used to solve the problem and the results are carried out employing the ANSYS-FLUENT code. The results are given in terms of temperature and velocity fields and transversal profiles inside the channel for different values of mass flow rates, solar irradiance, volumetric nanoparticle concentrations and assigned values of external surface heat transfer coefficient and temperature.

Quaternary Holey Carbon Nanohorns/SnO2/ZnO/PVP Nano-Hybrid as Sensing Element for Resistive-Type Humidity Sensor

In this study, a resistive humidity sensor for moisture detection at room temperature is presented. The thin film proposed as a critical sensing element is based on a quaternary hybrid nanocomposite CNHox//SnO2/ZnO/PVP (oxidated carbon nanohorns–tin oxide–zinc oxide–polyvinylpyrrolidone) at the w/w/w/w ratios of 1.5/1/1/1 and 3/1/1/1. The sensing structure consists of a Si/SiO2 dielectric substrate and interdigitated transducers (IDT) electrodes, while the sensing film layer is deposited through the drop-casting method. Morphology and composition of the sensing layers were investigated through scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction, and Raman spectroscopy. Each quaternary hybrid nanocomposite-based thin film’s relative humidity (RH) sensing capability was analyzed by applying a direct current with known intensity between two electrodes and measuring the voltage difference when varying the RH from 0% to 100% in a humid nitrogen atmosphere. While the sensor with CNHox/SnO2/ZnO/PVP at 1.5/1/1/1 as the sensing layer has the better performance in terms of sensitivity, the structure employing CNHox//SnO2/ ZnO/PVP at 3/1/1/1 (mass ratio) as the sensing layer has a better performance in terms of linearity. The contribution of each component of the quaternary hybrid nanocomposites to the sensing performance is discussed in relation to their physical and chemical properties. Several alternative sensing mechanisms were taken into consideration and discussed. Based on the measured sensing results, we presume that the impact of the p-type semiconductor behavior of CNHox, in conjunction with the swelling of the hydrophilic polymer, is dominant and leads to the overall increasing resistance of the sensing film.