Studies on influence of hydrogen and carbon monoxide concentration on reduction progression behavior of molybdenum oxide catalyst

Temperature programmed reduction (TPR) analysis was applied to investigate the chemical reduction progression behavior of molybdenum oxide (MoO₃) catalyst. The composition and morphology of the reduced phases were characterized by X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FE-SEM). The reduction progression of MoO₃ catalyst was attained with different reductant types and concentration (10% H₂/N₂, 10% and 20% CO/N₂ (%, v/v)). Two different modes of reduction process were applied. The first approach of reduction involved non-isothermal mode reduction up to 700 °C, while the second approach of reduction involved the isothermal mode reduction for 60 min at 700 °C. Hydrogen temperature programmed reduction (H₂-TPR) results showed the reduction progression of three-stage reduction of MoO₃ (Mo⁶⁺ → Mo⁵⁺ → Mo⁴⁺ → Mo⁰) with Mo⁵⁺ and Mo⁴⁺. XRD analysis confirmed the formation of Mo₄O₁₁ phase as an intermediate phase followed by MoO₂ phase. After 60 min of isothermal reduction, peaks of metallic molybdenum (Mo) appeared. Whereas, FESEM analysis showed porous crater-like structure on the surface cracks of MoO₂ layer which led to the growth of Mo phase. Meanwhile, the reduction of MoO₃ catalyst in 10% carbon monoxide (CO) showed the formation of unstable intermediate phase of Mo₉O₂₆ at the early stage of reduction. Furthermore, by increasing 20% CO led to the carburization of MoO₂ phase, resulted in the formation of Mo₂C rather than the formation of metallic Mo, as confirmed by XPS analysis. Therefore, the presented study shows that hydrogen gave better reducibility due to smaller molecular size, which contributed to high diffusion rate and achieved deeper penetration into the MoO₃ catalyst compared to carbon monoxide reductant. Hence, the reduction of MoO₃ in carbon monoxide atmosphere promoted the formation of Mo₂C which was in agreement with the thermodynamic assessment.     

Fabrication and characterization of highly efficient three component CuBTC/graphene oxide/PSF membrane for gas separation application

Metal organic frameworks (MOFs) with marvelous properties have aroused enormous attention for different application especially gas adsorption and separation. In this regard, fabrication of MOF hybrids with carbon based materials is new strategy to upgrade MOF performance. In this study CuBTC (Copper benzene-1,3,5-tricarboxylic acid)/graphene oxide (GO) composite was synthesized and characterized by BET, SEM, TGA, XRD and FT-IR techniques. Then CuBTC and CuBTC/GO composite were incorporated into polysulfone (PSF) polymer to construct mixed matrix membranes (MMMs). The obtained membranes were characterized by SEM, TGA, XRD and tensile tests and their gas permeability was measured. The results were compared to those of CuBTC/PSF MMMs. It was revealed that CuBTC/GO composite as filler showed superior performance relative to CuBTC. For instance, 15 wt% loading of CuBTC/GO in PSF represented outstanding gas separation behavior while the same loading of CuBTC in PSF deteriorated performance of MMM. Well particle dispersion and favorable polymer-filler interaction were responsible for such observed difference. A high H₂/CH₄ and H₂/N₂ selectivity of 80.03 and 70.46 were recorded for CuBTC/GO in PSF (15 wt%) compared to 44.56 and 40.92 for CuBTC in PSF (15 wt%).     

Boosted hydrogen evolution activity from Sr doped ZnO/CNTs nanocomposite as visible light driven photocatalyst

CNTs were decorated onto Sr doped ZnO nanoparticles to construct an efficient photocatalyst via a facile sol-gel method. The as-fabricated Sr doped ZnO/CNTs with recyclability exhibits Sr and CNTs content dependent hydrogen evolution activit under visible light illumination. The Sr doped ZnO/CNTs photocatalyst shows the highest hydrogen evolution rate of 2732.2 μmolh^?1g^?1, which is 33.7 and 2.83 times higher than pure ZnO and Sr doped ZnO photocatalysts, respectively. The improved hydrogen evolution activity of Sr doped ZnO/CNTs is primarily assigned to high surface area, Sr doping and construction of heterojunction, which can extend the light absorption, decrease the optical band gap and improve the charge separation. Moreover, the underlying photocatalytic mechanism is proposed on the basis of Mott-Schottky study and explains the interfacial charge transfer process from ZnO to CNTs and Sr. This work open new strategies to synthesize CNTs based nanocomposite for hydrogen evolution.     

Novel composite membrane based on zirconium phosphate-ionic liquids for high temperature PEM fuel cells

Composite membranes composed of zirconium phosphate (ZrP) and imidazolium-based ionic liquids (IL), supported on polytetrafluoroethylene (PTFE) were prepared and evaluated for their application in proton exchange membrane fuel cells (PEM) operating at 200 °C. The experimental results reported here demonstrate that the synthesized membrane has a high proton conductivity of 0.07 S cm^?1, i.e, 70% of that reported for Nafion. Furthermore, the composite membranes possess a very high proton conductivity of 0.06 S cm^?1 when processed at 200 °C under completely anhydrous conditions. Scanning electron microscopy (SEM) images indicate the formation of very small particles, with diameters in the range of 100–300 nm, within the confined pores of PTFE. Thermogravimetric analysis (TGA) reveals a maximum of 20% weight loss up to 500 °C for the synthesized membrane. The increase in proton conductivity is attributed to the creation of multiple proton conducting paths within the membrane matrix. The IL component is acting as a proton bridge. Therefore, these membranes have potential for use in PEM fuel cells operating at temperatures around 200 °C.     

Interactions between hybrid nanosized particles and convection melting inside an enclosure with partially active walls: 2D lattice Boltzmann-based numerical investigation

The ice melting is investigated inside a square cavity with two isothermally partially active walls. The concept of dispersing hybrid alumina–Cu nanoparticles and hybrid silica–multiwalled carbon nanotubes (MWCNTs) nanoparticles is recommended for thermal performance enhancement in this thermal energy storage (TES) system. The two-dimensional explicit lattice Boltzmann convection melting scheme in the single-phase model is applied to account for the natural convection flow induced in the melt region and evolution of the solid–liquid interface. The complete melting time for the pure phase change material (PCM) using case (II) is 33.3% lower compared with other cases. If the price of hybrid Al₂O₃–Cu nanoparticles and heat storage capacity is important, the full melt time diminishes by 16.6% with a volume fraction of 0.01 in case (II). Once hybrid silica–MWCNT nanoparticles with a volume fraction of 0.01 are utilized inside case (II), the lowest charging time is achieved. The complete melting time abates by 23.66% in contrast to the pure PCM melting. The use of single/hybrid nanoparticles to enhance the PCM melting is not necessarily economical as efficient positions of active parts could further lessen the charging time. The efficiency of hybrid nanoparticles is linked to the type and weight proportions of nanoparticles, and positions of thermally active parts.     

Thermal performance and energy saving investigation in a modified baseboard radiator and compare it with conventional heating systems—Experimental and CFD approach

In the present work, thermal performance of a new modified baseboard radiator is investigated experimentally based on the European Standard EN-442. Temperature distribution and thermal comfort conditions of the floor heating system and panel radiator is compared with the present system numerically. To validation of the simulation results, a comparison has been made between the simulation and the experimental obtained results. Comparison shows that there is a good agreement between them. The heat output rate of the new system increased about 46.06% compared with conventional baseboard radiant model and also the baseboard heating system is capable of providing better thermal comfort conditions than two other systems. Energy consumption in three systems is investigated experimentally by smart temperature control mechanism. Results show that energy consumption in the baseboard radiant is 83.03% and 55.96% lower than floor heating system and panel radiator, respectively.     

Enhanced electrocatalytic activity and stability of platinum,gold, and nickel oxide nanoparticles-based ternary catalyst for formic acid electro-oxidation

The global interest to realize and commercialize the direct formic acid fuel cells has motivated the development of efficient and stable anodes for the formic acid (FA) electro-oxidation (FAO). In this investigation, a ternary catalyst composed of Pt nanoparticles (PtNPs), Au nanoparticles (AuNPs) and nickel oxide nanoparticles (nano-NiO_x), all were sequentially electrodeposited onto the surface of a glassy carbon (GC) electrode, was recommended for this reaction. The surface morphology investigation revealed the deposition of grain-shaped PtNPs (25 nm average particle size), and flower-shaped nanospheres (less than 60 nm average particle size) of AuNPs and nano-NiO_x. Interestingly, the ternary modified NiO_x-Au-Pt/GC electrode has shown an outstanding electrocatalytic activity towards the direct FAO, concurrently with a complete suppression for the indirect route. It further exhibited excellent stability that extended for 7 h of continuous electrolysis. While PtNPs furnished a suitable base for FA adsorption, AuNPs played a significant role to interrupt the contiguity of the Pt surface sites, which is necessary for CO poisoning. On the other hand, nano-NiO_x acted as a catalytic mediator facilitating the charge transfer of FAO and the oxidative removal of CO at a lower potential.     

Estimation of the effect of biomass moisture content on the direct combustion of sugarcane bagasse in boilers

Many of the large-scale biomass combustion systems for producing heat, hot water, or steam accept biomass fuels containing relatively large amounts of moisture. Dry biomass burns at higher temperatures and thermal efficiencies than wet biomass. Flame temperature is directly related to the amount of heat necessary to evaporate the moisture contained in the biomass, the lower the moisture content, the lower the amount of energy needed to remove the water and the higher the boiler efficiency. In this article, a simple predictive tool is developed to estimate boiler efficiency as a function of stack gas temperature and sugarcane bagasse moisture content. The method quantitatively illustrates the effect of moisture content on the performance of a thermochemical process, for the direct combustion of sugarcane bagasse in a conventional boiler. The results are found to be in excellent agreement with reported data in the literature with average absolute deviation being around 1%. The tool developed in this study can be of immense practical value for engineers to have a quick check on biomass moisture content on the boiler performance at various conditions without opting for any experimental trials. In particular, engineers would find the approach to be user-friendly with transparent calculations involving no complex expressions.     

3D numerical investigation of ZnO/Zn hydrolysis for hydrogen production

The current research is focused on the hydrogen production through a two‐step ZnO/Zn thermochemical water splitting cycle. In the present paper, numerical modeling of the second step is conducted using Computational Fluid Dynamics (CFD)2, where steam reacts with zinc to produce hydrogen. The parametric study shows that the hydrogen yield is relatively insensitive to the steam/zinc molar ratio and inversely proportional to the argon/steam molar ratio. For large argon to steam molar ratios, hydrogen yield is relatively insensitive to the inlet temperature of zinc and steam, and increases marginally with an increase in the argon inlet temperature. Five different reactor configurations were evaluated comprehensively. Among all configurations, a cylindrical reactor with a tangential inlet for argon and zinc, and a radial inlet for steam (both in the bottom plane of the reactor) and a tangential outlet in the top plane of the reactor produced the highest hydrogen yield of 88%. Copyright © 2013 John Wiley & Sons, Ltd.     

Numerical investigation of thermal disassociation of ZnO for hydrogen production: Parametric study and reactor configuration

The present research is focused on the two‐step ZnO/Zn thermochemical water splitting cycle for hydrogen production. In the present paper, the numerical modeling of the first step, which involves endothermic reduction of zinc oxide (ZnO), is carried out in a cylindrical reactor using Computational Fluid Dynamics (CFD). The parametric study shows that the fractional conversion of ZnO increases with an increase in the flow rate of ZnO, while it decreases with an increase in the ZnO particle diameter and carrier gas mass flow rate. Six different reactor configurations are also assessed comprehensively. It is observed that a cylindrical reactor with a tangential inlet at the top plane and a tangential outlet at the bottom plane has higher robustness to the variation of various operating parameters with consistently high ZnO fractional conversion. Copyright © 2013 John Wiley & Sons, Ltd.