•We report a new low temperature solvothermal method to synthesize MoS2 nanomaterials.•The morphology of MoS2 solids depends on the electrolyte concentration (ionic strength).•Formation of MoS2 ...nanospheres occurs at low electrolyte concentration.•At higher electrolyte amounts, MoS2 nanotubes are preferentially formed.
Different MoS2 nanostructures have been obtained following an innovative one-step solvothermal method by changing the concentration and type of the electrolyte while avoiding the use of surfactant. It was found that the chemical nature of the studied electrolyte ((NH4)2CO3 or KCl) do not significantly affect the morphology and structure of the obtained MoS2 nanomaterials. Nevertheless, increasing the electrolyte concentration yields to a remarkable modification of the morphology of the resulting MoS2 from nanospheres to worm-shaped then finally to nanotubes. All the obtained nanomaterials were characterized by X-ray diffraction, (XRD), transmission electron microscopy (TEM, HRTEM), Fourier transformation infra-red spectroscopy (FTIR), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS).
In this study, performance and feasibility of a hollow fibre membrane reactor (HFMR), consisting of a packed catalyst bed around a Pd coated Al2O3 hollow fibre membrane, has been studied and compared ...with both conventional Pd based tubular membrane reactor (TMR) fabricated from a stainless steel substrate and traditional fixed-bed reactor (FBR). The ceramic based HFMR presents several advantages over MRs such as the deposition of ultra thin Pd membranes and the possibility to scale up the whole multifunctional process by module configuration. The results obtained at 450°C during the methane dry reforming (MDR) reaction showed that, although CH4 conversion using the HFMR was almost the same as that of a catalytic TMR, the amount of Pd employed for the Pd layer deposition in the HFMR was fifteen times less than that in TMR. Moreover, the CH4 conversion using the HFMR was 72% higher than that in a traditional FBR and 34% higher than thermodynamic equilibrium. Also, a high purity COX-free H2 production (10.5ml/mgh) was achieved at 525°C using a sweep gas of 100ml/min in the lumen side of the HFMR.
► A new hollow fibre membrane reactor (HFMR) has been developed. ► The HFMR combines the processes of generating and separating H2 in a single step. ► Its performance was compared with that in a tubular membrane and fixed-bed reactors. ► The low-cost HFMR allows a possible large-scale COX free H2 production.
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► Rh supported on TiO2 catalysts are active for methane partial oxidation. ► Anatase-rich support gives better performances than rutile-rich support. ► In anatase-rich support, Rh is ...highly dispersed and it is highly reduced. ► In rutile-rich support, Rh is poorly dispersed and it is oxidized.
The effect of TiO2 phase composition on the catalytic and physico-chemical properties of supported Rh catalysts in the partial oxidation of methane were studied. Two types of TiO2 with different rutile/anatase crystalline phase compositions were used as support. The performance of supported Rh catalysts depends on the nature of the TiO2 support. CH4 conversion and selectivity towards H2 and CO are improved when using an anatase-rich TiO2 support, probably because it improves dispersion and reducibility of rhodium particles compared with the rutile-rich carrier. Both Rh/TiO2 catalysts produced more CO than H2, which suggests the involvement of other reactions such as dry reforming, steam reforming and water gas shift reactions. The anatase-rich catalyst is remarkably stable but its rutile-rich counterpart becomes deactivated after a few hours. This loss of activity is attributed to the oxidation of rhodium. With anatase-rich TiO2 catalyst the dispersion of rhodium is stabilized and its oxidation is avoided.
Three Ru catalysts supported on SiO
2, ZrO
2–SiO
2 and ZrO
2–La
2O
3 have been prepared, characterized and tested in the methane steam reforming (SR) reaction, and for comparative purposes a Ni/SiO
2 ...catalyst has also been studied. Conditions of catalytic studies have been selected for the subsequent application in a hydrogen extraction Pd membrane reactor. That is, reaction temperatures in the range of 400–550
°C and with different amounts of catalyst in order to work under and/or close to the equilibrium conversion conditions. All the supported Ru samples exhibit high catalytic activity and similar CO and H
2 yields. Finally these catalysts are fully stable under reaction conditions at 550
°C for 15
h, while the Ni/SiO
2 sample suffers a significant deactivation. The main deactivation process affecting this latter catalyst is the carbon deposition of partially dehydrogenated intermediates as detected by Raman spectroscopy. Hence, these Ru catalysts appear to be suitable for application combined with metallic (Pd) membrane.
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► Small amounts of N2O are added in the feed during partial oxidation of methane. ► Yield and selectivity towards H2 and CO increase after co-feeding N2O. ► N2O inhibits adsorption ...of O2 in sites where it forms electrophilic oxygen species. ► In the presence of N2O, Rh works in a reduced state. ► Reduced Rh modifies the kinetic of reactions, promoting synthesis gas.
New results studying the effects brought about by the introduction of small amounts of N2O in the gas feed (promoter) during the partial oxidation of methane (POM) over Rh/γ-Al2O3 and Rh/MgO catalysts are presented. Standard tests were performed with 5vol.% CH4, 2.5vol.% O2, and balanced with N2. When small amounts of N2O (300ppm, 1000ppm) were added to the feed, yield and selectivity to H2 and CO increased. Under these conditions rhodium works in a reduced state, resulting in the enhancement of syngas selectivity and the inhibition of the total oxidation of methane. This effect tends to disappear after a certain period of time when N2O supply is cut. The effect is reversible. It is suggested that N2O is adsorbed on the vacancies where O2 does, inhibiting the formation of oxidant (electrophilic) oxygen species produced by dissociation of O2 on the same vacancies. In the presence of N2O, rhodium remains in a reduced oxidation state. Reduced rhodium modifies the kinetics of all reactions involved under POM reaction conditions and promotes synthesis gas.
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▶ Co-feeding of H
2, CO or CO
2 (reaction products) affects catalytic performances. ▶ The observed results are not explained by thermodynamics but by kinetic changes. ▶ The ...modifications on catalytic performances induced by gas co-feeds are reversible. ▶ An optimal oxidation state of Rh could explain the high selectivity of syngas. ▶ H
2/CO ratio can be modulated by adding proper amounts of co-feeds during POM.
The influence of the addition of 1, 2 or 5
vol.% of CO, H
2 or CO
2 to the feed during the partial oxidation of methane (POM) was studied over Rh/Ti-modified support catalysts (Rh/Ti–SiO
2, Rh/Ti–Al
2O
3 and Rh/Ti–MgO). The changes observed in the conversion and syngas selectivity in the presence of gaseous co-feeds are due to changes in the kinetics of POM and may be mainly explained by modifications in the oxidation state of rhodium during the reaction. A higher reduction of Rh is observed when 5% of H
2 or CO is co-fed while Rh is maintained in a higher oxidation state in the presence of CO
2 co-feed. Reversibility tests show that the modifications induced by the gaseous promoters in the catalytic performances are reversible. Such changes can alter not only the kinetics of POM but also the kinetics of the other reactions involved (dry reforming and the reverse water-gas shift) during POM reaction. Results have implications in the expression of the reaction kinetics to be used in the modelling of POM reaction mechanism.
The partial oxidation of methane over the supported Rh (0.8
wt.%) catalysts was investigated. Two kinds of supports were used, MgO and Ti-modified MgO (prepared by grafting technique). Among the ...Ti-modified MgO supports, two different compounds were used as source of Ti: inorganic (chloride) and organic (alkoxide). The catalytic performance of Rh-supported catalysts depends on the support and varies in the sequence: Ti-MgO/I
>
Ti-MgO/O
>
MgO. Ti-containing catalysts exhibited higher activity and selectivity compared to MgO, which is especially noticeable at low temperature. Possible explanations for the phenomena observed were proposed on the basis of characterization results.
