Catalytic hydrotreating of pyro-oil derived from green microalgae spirulina the (Arthrospira) plantensis over NiMo catalysts impregnated over a novel hybrid support

Upgrading of pyrolysis bio-oil by a novel catalytic hydrotreating process, including hydrodeoxygenation (HDO) and hydrodenitrogenation (HDN) was found as an effective technical method for the improvement of biofuel characteristics. In this study, for the first time, the performance of a novel meso-microporous composite material, HMS-ZSM-5, as a support on the catalytic activity of NiMo-based catalysts in the bio-oil hydrotreating was evaluated. The experiments were carried out in a flow fixed-bed reactor at the temperature range of 300–360 °C, 30 bar pressure, and LHSV = 4 h-1. Also, the results were and compared with those of HMS, ZSM-5, and γ-Al2O3 supports. For all catalysts, the increase in temperature resulted in the enhancement of HDO and HDN reactions efficiency. NiMo/HMS-ZSM-5 possessed a high acid property which contributed to the removal of oxygen and nitrogen from bio-oil, with the conversion of 84.10% and 69.60%, respectively. Therefore, the novel catalyst of this study represented much superior upgrading performances compared with those of stand-alone NiMo/HMS and NiMo/ZSM-5 catalysts and also the conventional catalyst of NiMo/γ-Al2O3.     

Pyrolysis of Alternanthera philoxeroides (alligator weed): Effect of pyrolysis parameter on product yield and characterization of liquid product and bio char

In the present work, fast pyrolysis of Alternanthera philoxeroides was evaluated with a focus to study the chemical and physical characteristics of bio-oil produced and to determine its practicability as a transportation fuel. Pyrolysis of A.philoxeroides was conducted inside a semi batch quartz glass reactor to determine the effect of different operating conditions on the pyrolysis product yield. The thermal pyrolysis of A. philoxeroides were performed at a temperature range from 350 to 550 °C at a constant heating rate of 25 °C/min & under nitrogen atmosphere at a flow rate of 0.1 L/min, which yielded a total 40.10 wt.% of bio-oil at 450 °C. Later, some more sets of experiments were also performed to see the effect on pyrolysis product yield with change in operating conditions like varying heating rates (50 °C/min, 75 °C/min & 100 °C/min) and different flow rates of nitrogen (0.2, 0.3, 0.4 & 0.5 L/min). The yield of bio-oil during different heating rate (25, 50, 75 and 100 °C/min) was found to be more (43.15 wt.%) at a constant heating rate of 50 °C/min with 0.2 L/min N₂ gas flow rate and at a fixed pyrolysis temperature of 450 °C. The High Heating Value (HHV) value of bio-oil (8.88 MJ/kg) was very less due to presence of oxygen in the biomass. However, the high heating value of bio-char (20.41 MJ/kg) was more, and has the potential to be used as a solid fuel. The thermal degradation of A. philoxeroides was studied in TGA under inert atmosphere. The characterization of bio-oil was done by elemental analyser (CHNS/O analyser), FT-IR, & GC/MS. The char was characterized by elemental analyser (CHNS/O analysis), SEM, BET and FT-IR techniques. The chemical characterization showed that the bio-oil could be used as a transportation fuel if upgraded or blended with other fuels. The bio-oil can also be used as feedstock for different chemicals. The bio-char obtained from A. philoxeroides can be used for adsorption purposes because of its high surface area.     

1-hexene isomerization over bimetallic M-Mo-ZSM-5 (M: Fe,Co, Ni) zeolite catalysts: Effects of transition metals addition on the catalytic performance

The aim of this study is to investigate the promotional effect of Fe–Mo, Co–Mo, and Ni–Mo bimetallic additives on the activity and stability of H-ZSM-5 zeolite for isomerization of 1-hexene. The catalysts were synthesized by wet-impregnation method and characterized by XRD, FTIR, BET, ICP-AES, HRSEM-EDS, HRTEM, H₂-TPR, NH₃-TPD, and pyridine-DRIFT analysis. The isomerization of 1-hexene was carried out in a micro-scale system under the conditions: T = 250 °C, P = 4.0 MPa, FR = 0.1 ml/min, WHSV = 1 h⁻¹. The conversion of 1-hexene over the 4 g bed of catalyst was in the range of 95–97% after 74 h time-on-stream with cis-3-hexene and cis-2-hexene as the principal products. It was shown that the appearance of the new strong Lewis acid sites, decreases the ratio of Brönsted/Lewis acid sites. Increase of the weak Lewis acid sites in the 2.5 wt%Ni2.5 wt%Mo-ZSM-5 catalyst facilitated the isomerization of 1-hexene and showed higher C6 olefin selectivity (48.4 mol%), research octane number (99.7), and bromine number (148.3) than other studied catalysts.     

A comparative study of the catalytic performance of nickel supported on a hibonite-type La-hexaaluminate synthesized from aluminum saline slags in the dry reforming of methane

In this work, a hibonite-type Ni/La-hexaaluminate (Ni/LHA) synthesized from an industrial waste is used and compared as catalyst in the dry reforming of methane (DRM) at 973 K. The structure, catalytic behavior, and stability during a run time of at least 50 h of three Ni-catalysts obtained from two commercial supports and two preparation methods were used for comparison. An aluminum solution (9.40 g/L) obtained from an aluminum saline slag waste by acid extraction was used to synthesize the hexaaluminate by mixing with a stoichiometric amount of lanthanum nitrate and methanol/Peg400/PegMn400 under hydrothermal conditions at 493 K for 16 h. The Ni/LHA catalyst (10 wt% NiO) was obtained by impregnation of the synthesized support, calcined previously at 1473 K for 2 h. The resulting solids were characterized by several techniques as: X-ray diffraction (XRD), N₂ adsorption at 77 K, temperature-programmed reduction (TPR), scanning electron microscopy (SEM) and transmission electron microscopy (HR-TEM). In order to compare the catalytic behavior and properties of the Ni/LHA catalyst, three Ni catalysts obtained from two commercial supports (γ-Al₂O₃ and SiO₂) and two preparation methods (wet impregnation (I) and precipitation-deposition (PD)) were synthesized. Analysis of the TPR patterns for the catalysts allowed the type of metal support interaction and NiO species to be determined, with a weak interaction with the support being observed in Ni/LHA and Ni–I/SiO₂. The NiO species observed, with crystallite sizes between 9.7 and 40.4 nm, confirm the X-ray structural analyses. The Ni/LHA catalyst was found to be active and very stable in the DRM reaction after 50 h. The catalytic behavior was evaluated from the CO₂ and CH₄ conversions, as well as the H₂/CO selectivity, with values of 99% over almost all the time range evaluated. The behavior of this catalyst is comparable to that of Ni–I/Al₂O₃ and Ni-PD/SiO₂. The results found indicating that the strong interaction of nickel with the support favors the stability of the catalysts in the DRM reaction.     

A comparative study on the catalytic activities and stabilities of atomic-layered platinum on dispersed Ti0.9Cu0.1N nanoparticles supported by N-doped carbon nanotubes (N-CNTs) and reduced graphene oxide (N-rGO)

In our previous research, titanium-based nitride with high conductivity and superior corrosion resistance were developed as an ideal core material for replacing noble metal to form Pt-based core-shell catalysts by pulse electrodeposition. Meanwhile, the smaller sizes of nitride cores would also be available for pulse electrodeposition by dispersing them on carbon nanotubes (CNT). To achieve a better practice on the preparation of the Pt-based core-shell catalysts, in this work, both nitrogen-doped carbon nanotubes (N-CNT) and reduced graphene oxide (N-rGO) were used to support the copper-doped titanium nitride (Ti_0.9Cu_0.1N) cores. In the course of pulse electrodeposition, their influences as supports on the electronic states of electrodeposited Pt as well as their catalytic activities were compared. The results showed that the Pt preferred to electrodeposit on Ti_0.9Cu_0.1N cores supported by N-CNT and formed a core-shell structure. While with the same electrodeposition process, the Pt was found to be electrodeposited not only on the Ti_0.9Cu_0.1N cores supported by N-rGO with heavy aggregations but also on the N-rGO support. Raman spectroscopy analysis indicated that the higher degree of structural defects on N-rGO, as support, might have contributed to such divergence observation.     

A comparative study on the electrocatalytic and photocatalytic activity of reduced graphene oxide (rGO) and doped rGO based Cu5FeS4 composite

Chemical doping of reduced graphene oxide (rGO) oxide has been a major trend as photocatalyst and electrocatalyst owing to large number of active sites they bring in. In the present work ternary copper iron sulphide (Cu₅FeS₄) has been successfully synthesized using hydrothermal method and incorporated with rGO, N/rGO and B/rGO. The structural, morphological and compositional changes were analyzed using XRD, XPS, SEM, TEM and EDAX results respectively. The bandgap of the materials was confirmed using UV-DRS results. The photoluminescence (PL) spectra of the samples revealed the reduction of recombination with the presence of rGO and doped rGO. The photocatalytic studies of the composites were carried out using methylene blue(MB) as a model pollutant where CFS-N/rGO shows the highest degradation rate of 70%.The electrocatalytic tests were conducted in order to study the performance of the composites as catalyst for HER where CFS-N/rGO showed an enhanced activity with higher current density and lower Tafel slope.The higher C_dl value of CFS-N/rGO indicates the increased number of exposed active sites when doped with N/rGO. The results indicate a considerable amount of change in the photocatalytic and electrocatalytic properties of CFS when doped with rGO, B/rGO and N/rGO.     

Fast and catalytic pyrolysis of xylan: Effects of temperature and M/HZSM-5 (M= Fe,Zn) catalysts on pyrolytic products

Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was employed to achieve fast pyrolysis of xylan and on-line analysis of pyrolysis vapors. Tests were conducted to investigate the effects of temperature on pyrolytic products, and to reveal the effect of HZSM-5 and M/HZSM-5 (M= Fe, Zn) zeolites on pyrolysis vapors. The results showed that the total yield of pyrolytic products first increased and then decreased with the increase of temperature from 350°C to 900°C. The pyrolytic products were complex, and the most abundant products included hydroxyacetaldehyde, acetic acid, 1-hydroxy-2-propanone, 1-hydroxy-2-butanone and furfural. Catalytic cracking of pyrolysis vapors with HZSM-5 and M/HZSM-5 (M= Fe, Zn) catalysts significantly altered the product distribution. Oxygen-containing compounds were reduced considerably, and meanwhile, a lot of hydrocarbons, mainly toluene and xylenes, were formed. M/HZSM-5 catalysts were more effective than HZSM-5 in reducing the oxygen-containing compounds, and therefore, they helped to produce higher contents of hydrocarbons than HZSM-5.     

A comparative study of dry reforming of methane over nickel catalysts supported on perovskite-type LaAlO3 and commercial α-Al2O3

A systematic and comparative study was made to determine the influence of perovskite-type LaAlO₃ and commercial α-Al₂O₃ on the performance of nickel-based catalysts in dry reforming of methane (DRM). The perovskite-type LaAlO₃ was selected due to its characteristics of solid state semiconductor with oxygen vacancies and high structural stability. The catalysts were characterized by X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), N₂ adsorption-desorption, temperature programmed reduction (TPR-H₂), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The catalyst performance was evaluated based on activity tests (600–800 °C) and short- and long-term stability (10 and 20 h) at 700 °C at a GHSV (Gas Hourly Space Velocity) of 18 and 72 L g^?1 h^?1. The TPR-H₂ profiles indicate that the oxygen vacancies on the perovskite surface exerted a strong effect on the reduction temperature and reducibility of the NiO nanoparticles, resulting in weak Ni⁰/support interaction. The results of the tests after 10 h under GHSV of 18 L g^?1 h^?1 indicate that the Ni/LaAlO₃ catalyst is 7.8 and 11.5% more stable than Ni/α-Al₂O₃ in the conversions of CH₄ and CO₂, respectively. The higher stability and activity of Ni/LaAlO₃ is directly ascribed to the presence of NiO (3.38 wt%) after activation, which promoted the formation of carbon nanotubes (CNT) and increased the dispersion of the metallic phase. Even under severe conditions of activation and reaction (high GHSV), as in the long-term test, the Ni/LaAlO₃ catalyst showed a 37.2% higher H₂ yield than the Ni/α-Al₂O₃. Analyses by TEM indicate that the Ni/α-Al₂O₃ catalyst exhibited deactivation problems associated with sintering effects. Thus, the presence of structural defects and surfaces rich in oxygen vacancies makes LaAlO₃ perovskite a potential support for application in methane catalytic reforming processes.     

Optimization of renewable hydrogen-rich syngas production from catalytic reforming of greenhouse gases (CH4 and CO2) over calcium iron oxide supported nickel catalyst

Multi-response optimization of hydrogen-rich syngas from catalytic reforming of greenhouses (methane and carbon dioxide over Calcium iron oxide supported Nickel (15 wt%Ni/CaFe₂O₄) catalyst was performed by varying reaction temperature (700–800 °C), feed ratio (0.4–1.0) and gas hourly space velocity (10,000–60,000 h^?1)) using response surface methodology. Four response surface methodology (RSM) models were obtained for the prediction of reactant conversion and the product yield. The analysis of variance (ANOVA) conducted on the model showed that the parameters have significant effect on the responses. Optimum conditions for the methane dry reforming over the 15 wt%Ni/CaFe₂O₄ catalyst were obtained at reaction temperature, feed ratio and gas hourly space velocity (GHSV) of 832.45 °C, 0.96 and 35,000 mL g^?1 h^?1 respectively with overall desirability value of 0.999 resulting in the highest methane (CH₄) and carbon dioxide (CO₂) conversions of 85.00%, 88.00% and hydrogen (H₂) and carbon monoxide (CO) yields of 77.82% and 75.76%, respectively.     

A study on the effects of Fex/Niy/MgO(1−x−y) catalysts on the volumetric and electrochemical hydrogen storage of multi-walled carbon nanotubes

The effects of various ratios of Fe/Ni/MgO and growth temperatures on yield, diameter and quality of multi-walled carbon nanotubes (MWCNTs) were studied. Thermal gravimetric analysis (TGA) confirmed that the MWCNT yield depends on Fe/Ni ratio with the following order; Fe_0.5 Ni_0.5 > Fe > Fe_0.75 Ni_0.25 > Fe_0.25 Ni_0.75 > Ni. The results indicated that there is an optimum temperature (940 °C) for the MWCNT growth both from quality and quantity (yield) aspects as compared to other temperatures. Moreover, the changes on Fe/Ni to MgO ratio for the MWCNT growth revealed that Fe/Ni/MgO with the ratio of 17.5/17.5/65 had the highest quality and surface area as compared to the other ratios. The hydrogen storage capacities of MWCNTs grown on Fe/Ni/MgO with various ratios obtained by using volumetric technique were in ascending order as 17.5/17.5/65, 15/15/70, 12.5/12.5/75, 10/10/80, 20/20/60, 22.5/22.5/55 and 25/25/50. In addition, the defective sites and mean diameter of the MWCNTs influenced the desorption temperature of stored hydrogen. Hydrogen storage by using electrochemical technique showed that Fe/Ni/MgO with the ratio of 17.5/17.5/65 had the highest hydrogen storage capacity compared with the other ratios. Based on electrochemical analysis, there are two regimes for hydrogen adsorption on the MWCNTs, one at about 0.8 V and the other at 0.15 V. The study on two kinds of adsorption region showed that the ratio of hydrogen storage capacity at 0.8 V to hydrogen storage capacity at 0.15 V increased with the increasing of the mean diameter of MWCNTs. The ratio reached to maximum value for the MWCNTs grown on Fe/Ni/MgO with the ratio of 20/20/60 as compared to the other ratios.