ZnO was doped into coprecipitated Ni-Al2O3 catalyst to promote the activity and the stability in methane decomposition to hydrogen and carbon nanofibers. The promoting effects were examined with XRD, ...TPR, XPS and TEM, using an in situ thermal balance reactor and a tubular fixed-bed reactor. The results showed that there was a strong interaction between Ni-Al2O3 and the doped ZnO, which may result in the formation of ZnAl2O4 spinel-like structure. The doping of ZnO could improve both the activity and the stability of nickel particles in methane decomposition. Such promotion effects became more pronounced with the increase of ZnO content. The evolution of the morphologies of the carbon produced and of the catalyst particles with the reaction temperature suggested that the doping of ZnO may delay the appearance of the quasi-liquid state of the catalyst particles to the range of higher temperatures and may weaken the interfacial wetting effect between catalyst particles and the growing carbon layers to delay the encapsulation process of the catalyst particles.
•A sulfonated hydrothermal carbon (SHTC) catalyst is prepared.•Ethanolysis of microcrystalline cellulose is examined.•Complete conversion of cellulose is achieved in supercritical ethanol.•Ethyl ...glucoside and ethyl levulinate are produced with high yields.•The reaction conditions have strong effects on the catalytic performance.
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The catalytic ethanolysis of microcrystalline cellulose in supercritical ethanol is examined over a sulfonated hydrothermal carbon catalyst (SHTC). SHTC is amorphous carbon containing −OH, −COOH and −SO3H groups with total acidity of 7.15 mmol/g and −SO3H acidity of 1.72 mmol/g. SHTC shows high catalytic activity towards the ethanolysis of cellulose in supercritical ethanol. Complete conversion of microcrystalline cellulose with high yields of ethyl levulinate and ethyl glucoside is obtained. The reaction temperature, time and catalyst amount have significant effects on the catalytic performances of SHTC. Appropriate reaction time and less catalyst amount are favorable for the production of ethyl glucoside, while prolonged reaction time and appropriate catalyst amount favor the production of ethyl levulinate. The highest yield of ethyl glucoside as 420.9 mg/g cellulose is obtained over 0.1 g SHTC at 245 ºC for 1 h. The highest yield of ethyl levulinate as 817.6 mg/g cellulose is achieved over 0.3 g SHTC at 245 ºC for 1 h. SHTC shows good stability in the recycle experiments with slight loss of catalytic activity.
Vertically aligned multi-walled carbon nanotube (CNT) membranes are grown on the porous α-alumina support by a multi-step method consisting of growth of vertical CNTs by chemical vapor deposition, ...filling of inter-CNT gaps with polystyrene and removal of the polystyrene over-layer and CNT tips by polishing and acid treatment. The membranes are defect free and exhibit gas permeance independent of mean transmembrane pressure. CNT membranes grown on the porous alumina support have lower areal tube density of 1.87
×
10
9
CNT/cm
2, lower than the CNT membranes on dense silicon and quartz support reported in the literature. The CNT layer consists of fairly straight carbon nanotubes of 6.3
nm in pore diameter running parallel to each other with a tortuosity factor of about 1.3. Gas permeance through the porous alumina-supported CNT membranes is inversely proportional to the squared root of the gas molecules suggesting a Knudsen diffusion mechanism. However, the diffusivity values measured are about four times larger than the values predicted from the pore size, molecular weight and temperature using the Knudsen diffusion model.
The direct current four-probe method has been employed to investigate the conduction of oxide ion and proton in a doped ceria–carbonate composite electrolyte for fuel cells. The measurements are ...conducted in oxygen and in hydrogen atmospheres in the temperature range of 425–650°C. The conductivities of both of O2− and H+ increase with the increase of carbonate content above the melting point of the carbonate. The ionic conductivities of the composite electrolytes have also been simulated using the effective medium percolation theory. The deviations between experimental results and simulated values of O2− conductivity are caused by the associating effect of ceramic and carbonate phases, which leads to a higher O2− migration energy through the phase interface. According to the comparison of experimental data and simulated values, the conduction mechanisms of O2− and H+ have been proposed.
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► The conductivities of H+ and O2− are measured by the four-probe method. ► The effective medium percolation theory is used to simulate the ionic conductivity. ► The effects of sample composition and temperature on its conductivity are reported. ► The O2− conduction through the phase interface needs a higher activation energy. ► The conduction mechanisms of H+ and O2− are investigated.
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•Re2O7 catalyzes the demethoxylation of guaiacol in ethanol without H2 input.•Guaiacol is mainly converted to phenol and alkylphenols via demethxoylation and alkylation.•The ...saturation of benzene ring occurs but is negligible.
Re2O7 is used to convert guaiacol in alcohols at 280–320 °C. In ethanol, guaiacol is deoxygenated and alkylated, and the major products are phenol and alkylphenols (including ethylphenol, diethylphenol, diisopropylphenol, di-tert-butylphenol and 2,6-di-tert-butyl-4-ethylphenol), accounting for 97 mol% of all products after 6 hour reaction at 320 °C. Both catechol and phenol are the intermediates of guaiacol demethoxylation. Among the substituents, ethyl is directly provided by ethanol while isopropyl and tert-butyl are formed by the addition of methyl to ethyl step by step. In addition, Re2O7 has negligible activity for the saturation of benzene ring so it does not cause considerable over-consumption of reductant. The actual catalyst for guaiacol demethoxylation is likely a ReIV−VI species.
In this study, exhausted olive pomace (EOP) biochar prepared by carbonization at 400 °C is investigated as a fuel in a direct carbon fuel cell (DCFC) with an electrolyte-supported configuration. The ...feasibility of using the EOP biochar in the DCFC is confirmed, showing a maximum power density of 10 mW·cm−2 at 700 °C. This limited DCFC performance is compared with other biochars prepared under similar conditions and interrelated with various biochar physico-chemical characteristics, as well as their impact on the DCFC’s chemical and electrochemical reaction mechanisms. A high ash content (21.55%) and a low volatile matter (40.62%) content of the EOP biochar are among the main causes of the DCFC’s limited output. Silica is the major impurity in the EOP biochar ash, which explains the limited cell performance as it causes low reactivity and limited electrical conductivity because of its non-crystal structure. The relatively poor DCFC performance when fueled by the EOP biochar can be overcome by further pre- and post-treatment of this renewable fuel.
Mesoporous molecular sieves SBA-15 and MCM-41 supported Ni catalysts were prepared via a post-synthesis grafting method. The catalytic properties of these catalysts were investigated in CO
2 ...reforming of CH
4 under atmospheric pressure and compared with the impregnated catalysts. Characterization using powder X-ray diffraction, N
2 physisorption, H
2 temperature-programmed reduction, TG/DTA, Raman spectra and transmission electron microscopy techniques revealed that both catalyst preparation method and the nature of support play important roles in controlling the catalytic performance. The highest catalytic activity and long-term stability were obtained over a 5
wt.% Ni-grafted SBA-15 catalyst. This superior catalytic behavior was closely related with the strong resistance toward carbon formation and active metal sintering. Furthermore, the improved properties of the catalyst was caused by the formation of highly dispersed small Ni particles anchored by silica matrix, rather ordered pore structure, and structural stability of SBA-15 material under reaction conditions.
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► High yield of catechol from guaiacol is obtained. ► Hydrogen chloride is the best catalyst. ► pH decides the kinetics and the reaction mechanism. ► High hydrogen partial pressure ...enhances the reaction.
The conversion of guaiacol to catechol in high temperature water by catalysis of mineral hydrochloric acid is examined. The effects of pH and H2 pressure are measured in the conversion of guaiacol. Hydrogen enhances the reaction dramatically. Moreover, low pH and high hydrogen pressure favor the reaction. The highest conversion of guaiacol and best yield of catechol of 99% and 89%, respectively, are achieved with 1MPa hydrogen at pH=1.8 for 3h at 280°C. Based on the experimental results and kinetics, possible reaction mechanisms are proposed. Besides ionic mechanism and water catalysis, hydrogen polarization also occurred without metal catalyst.
This work examines the doping effects of Al and Mg individually and of Ni–Al and Mg–Al simultaneously on the properties of a Hopcalite catalyst. The reaction and the deactivation mechanisms of ...ethylene combustion in a carbon dioxide stream are discussed.
Complete combustion of trace amounts of ethylene in food grade CO
2 over a Cu–Mn Hopcalite catalyst has been investigated. A mesoporous structure is identified in the catalyst. Low temperature calcined samples are found to be more active than the high temperature calcined ones. The presence of Cu
2+ and Mn
3+ is essential for the high activity of the catalyst. The Cu–Mn catalyst without a third component deactivates quickly in the reaction stream. However, doping with Al or Mg individually and with Ni–Al or Mg–Al simultaneously increases the lifetime.
In situ DRIFTS measurements provide evidence that hydroxyl groups form and adsorb on Mn species. With the doping of Al, Mg and Ni ions, the amount of hydroxyl groups adsorbed reduces and the stability improves. Doping with Al and Mg simultaneously gives the best stability. A synergetic effect between CuO and amorphous Cu–Mn oxide phases is also confirmed.
The structural “memory effect” of a hydrotalcite (HT)-derived mixed oxide is utilized to prepare a shell–core Ni/Mg–Al catalyst for ethanol steam reforming (ESR). The reconstruction proceeds rapidly ...in a Ni2+ nitrate solution on the outer layer of the Mg–Al mixed oxide particle, being accompanied with the growth of large flake-like sheets. A part of Ni2+ ions can incorporate into the reconstructed HT-like structure, leading to the formation of the shell-type Ni loading catalyst after calcination. At 700 °C, the shell–core catalysts with much lower Ni contents perform better activities than that of the bulk Ni/Mg–Al catalyst prepared directly via the calcination of the HT-like precursor. Further investigations reveal that temperature and space-time significantly affect the contribution of WGS, CH4 reforming reactions to the product distribution in the ESR reaction. Most interestingly, C2H4 is observed in the reactions carried out at 700 °C and very low space-time.
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•A shell–core catalyst is formed employing structural memory effect of a mixed oxide.•The shell–core Ni/Mg–Al catalyst shows perfect activity in ethanol steam reforming.•The shell–core catalyst performs much better than the bulk one.•The reaction temperature and space-time affect the product distribution.•C2H4 is observed at very low space-time.
