Promotional roles of second metals in catalyzing methane decomposition over the Ni-based catalysts for hydrogen production: A critical review

The thermocatalytic decomposition (TCD) of methane is considered as a milestone towards the production of valuable CO_x-free hydrogen and carbon nanomaterials without the use of steam or O₂. Previous reviews have been aimed at methane decomposition over the different catalysts, such as nickel-based catalysts, non-nickel-based catalysts, metal oxide-supported catalysts, and carbon-supported catalysts. The Ni-based catalysts are suitably applied for methane TCD process due to their high activity and low cost. However, the loss of activity and/or stability with reaction time is one of the most notable challenges in the use of Ni-based catalysts, and a number of studies on the roles of various factors in overcoming such a problem can be found in the literature. Recently, the use of the second metal as a promoter to control catalyst deactivation has attracted much attention. The present review focuses on classification of the different promoters based on the periodic table of elements, such as alkali metals, alkaline earth, transition metals, noble metals, and rare earth metals, and makes a detailed discussion on promotional roles in influencing their physicochemical properties and catalytic performance of the Ni-based catalysts. The generalized structure-performance relationship of the metals-doped catalysts may give an appreciated reference to the design of catalysts with highly pure hydrogen production and carbon nanomaterials. In addition, this review also covers the works on effects of the promoters on nature and morphology of the formed carbon nanomaterials. The use of transition metals (Fe, Co or Cu), noble metal (Pd or Pt), and rare earth metal (La) with a suitable loading as a promoter influenced performance and lifespan of the catalyst and the interaction of Ni particles with the support. Among these promoters, Cu, Pd, La, and Cu–Pd as a dopant have demonstrated superior performance, which was attributed to the capability of these elements in prohibiting carbon accumulation on the active Ni components.     

Thermocatalytic decomposition of methane over mesoporous Ni/xMgO·Al2O3 nanocatalysts

This paper describes a facile method to produce mesoporous nanostructure Ni/Al₂O₃, Ni/MgO, and Ni/xMgO.Al₂O₃ (x: MgO/Al₂O₃ molar ratio) catalysts prepared by “one-pot” evaporation-induced self-assembly (EISA) method with some modifications for investigating in the thermocatalytic decomposition of methane. Detailed characterizations of the material were performed with X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and N₂ adsorption/desorption, hydrogen temperature-programmed reduction (H₂-TPR), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and temperature-programmed oxidation (TPO). The characterizations demonstrated that the synthesized catalysts with various MgO/Al₂O₃ molar ratios possessed mesoporous structure with the high BET area in the range of 216.79 to 31.74 m² g^?1. The effect of different surfactants and calcination temperatures on the characterizations and catalytic activity of the catalysts were also examined in details. The experimental results showed that the catalysts exhibited high catalytic potential in this process and the 55 wt.% Ni/2 MgO·Al₂O₃ catalyst calcined at 600^οC possessed an acceptable methane conversion (～60%) under the harsh reaction conditions (GHSV = 48000 (mL h^?1 g_cat^?1)).     

A highly active and stable chromium free iron based catalyst for H2 purification in high temperature water gas shift reaction

In this work mesoporous nanocrystalline chromium free Fe–Al–Ni catalysts with various Fe/Al and Fe/Ni ratios were prepared by coprecipitation method for high temperature water gas shift reaction. The prepared catalysts were characterized using X-ray diffraction (XRD), N₂ adsorption (BET), temperature-programmed reduction (TPR) and transmission electron microscopy (TEM) techniques. The catalytic results revealed that the catalyst with Fe/Al = 10 and Fe/Ni = 5 weight ratios exhibited the highest catalytic activity among the prepared catalysts and the commercial chromium containing one. This catalyst possessed a high surface area of 177.4 m² g⁻¹ with an average pore size of 4.3 nm with a high stability during 20 h time on stream. Furthermore, the effect of calcination temperature, GHSV and steam/gas ratio on the structural properties and catalytic performance of the catalyst with the highest activity was investigated.     

Preparation and evaluation of Ni/γ-Al2O3 catalysts promoted by alkaline earth metals in glycerol reforming with carbon dioxide

Glycerol is the main by-product in the biodiesel process and can be considered as a promising and renewable source for hydrogen generation through the reforming process. In this work, catalysts with 15 wt% Ni supported on 3 wt% M ? Al₂O₃ (M = MgO, CaO, SrO, and BaO) were prepared and employed in the glycerol dry reforming (GDR) reaction to produce hydrogen and carbon monoxide. The textural characteristics of the fresh and spent catalysts were determined using the ICP, BET, TPR, TPO, and SEM analyses. Based on the obtained results, the catalyst promoted by SrO had the highest catalytic activity. The results indicated that adding various alkaline-earth oxides into the catalyst support decreased the Ni crystalline size from 17.2 nm to 7.4–10.9 nm. Moreover, all promoted catalysts showed better catalytic performance and the promoted sample with 3 wt% SrO possessed higher stability than unpromoted catalyst during 20 h on stream.     

Statistical factor-screening and optimization in slurry phase bioremediation of 2,4,6-trinitrotoluene contaminated soil

Since slurry phase bioremediation is a promising treatment for recalcitrant compounds such as 2,4,6-trinitrotoluene (TNT), a statistical study was conducted for the first time to optimize TNT removal (TR) in slurry phase. Fractional factorial design method, 2(IV)(7-3), was firstly adopted and four out of the seven examined factors were screened as effective. Subsequently, central composite design and response surface methodology were employed to model and optimize TR within 15 days. A quadratic model (R(2) = 0.9415) was obtained, by which the optimal values of 6.25 g/L glucose, 4.92 g/L Tween 80, 20.23% (w/v) slurry concentration and 5.75% (v/v) inoculum size were estimated. Validation experiments at optimal factor levels resulted in 95.2% TR, showing a good agreement with model prediction of 96.1%. Additionally, the effect of aeration rate (0-4 vvm) on TR was investigated in a 1-liter bioreactor. Maximum TR of 95% was achieved at 3 vvm within 9 days, while reaching the same removal level in flasks needed 15 days. This reveals that improved oxygen supply in bioreactor significantly reduces bioremediation time in comparison with shake flasks.     

The effect of 3-(triethoxy silyl) propyl amine concentration on surface modification of multiwall carbon nanotubes

Abstract

The influence of 3-(triethoxy silyl) propyl amine (TESPA) concentration on Multi Wall Carbon Nanotubes (MWCNTs) modification, is experimentally investigated. The MWCNTs modification were performed by 150, 75 and 25 weight percent (wt.%) of TESPA with respect to MWCNTs weight and the properties of the prepared samples were compared with each other and pristine MWCNTs. The MWCNTs silylation has been confirmed by Fourier Transformation Infrared Spectroscopy due to O-H stretching absorption peak disappearing. The 75?wt.% silyl grafted MWCNTs with increasing at about 26.7% in mean value diameters size owns more uniform morphology among the samples based on Scanning Electron Microscopy images. Also, Thermo Gravimetric Analysis shows that this sample has higher thermal stability because of lower weight loss (9.97%) in coupling agent decomposition temperature range at about 119.5–480?°C. Furthermore, X-Ray Diffraction indicates that the mentioned sample has higher level of amorphous structure with 39% reduction in crystallite size in comparison with the pristine MWCNTs. So, the 75?wt.% of TESPA introduced as the optimal concentration for this type of MWCNTs modification.

• Highlights

• Introduction of silyl compounds as a proper coupling agent to modify the carbon nanotube surfaces

• Determination of optimal silyl compounds concentration to modify the carbon nanotube surface

• Cristallinity in XRD pattern can determine the success of CNTs grafted with silyl compounds

     

One-step synthesis of tenorite (CuO) nano-particles from Cu4 (SO4) (OH) 6 by direct thermal-decomposition method

In this research work, CuO nano-particles were synthesized at 750 °C (for 2 h) by the direct thermal-decomposition method using the brochantite as precursor. The nano-particles were characterized using X-ray diffraction (XRD), energy dispersive spectra (EDS), infrared spectrum (IR), and scanning electron microscope (SEM). SEM image showed that the CuO nano-particles were of rod shape with diameter and length of 235 ± 5 nm and 856 ± 5 nm, respectively. As a result, this method could be used at an industrial scale as a cheap and convenient way in production of pure tenorite nano-particles.     

The frequency and predictors of helmet use among Iranian motorcyclists: A quantitative and qualitative study

Objective

This study examines the rate of helmet use and identifies barriers and facilitators of wearing helmets among Iranian motorcyclists. A mixed-method approach was used, including a structured seasonal survey with specific observations of a random sample of 6010 riders and qualitative methods that included 29 in-depth interviews and seven focus groups (n = 31).

Results

Only 10% of motorcyclists wear a standard helmet while riding. However, another 23% of motorcyclists used non-standard or partial helmets that covered only part of the head and do not prevent head trauma injuries effectively. We observed only 2 of 264 child passengers and 22 of 1951 adult passengers wearing helmets. Almost no one used protective pants or clothing made to be more visible in traffic. Themes emerged from qualitative interviews and were grouped into three main categories: (1) helmet characteristics; (2) social and cultural factors; and (3) personal and psychological factors.

Conclusion

Overall, the motorcyclists in our study believed that wearing a safety helmet protects them against serious injuries or death during a crash; however, only a small percentage of the motorcyclists used safety helmets. National intervention programs addressing motorcycle safety should aim to overcome barriers to and promote facilitators of helmet use, including providing inexpensive standard helmets, banning manufacturing/using unsafe partial or dummy helmets, as well as enforcing helmet use on a consistent basis.