Journal of Natural Gas Chemistry最新文献

Cobalt supported on carbon nanotubes (CNTs)-covered alumina has been recently developed and successfully utilized as a catalyst in Fischer-Tropsch synthesis (FTS). Problems associated with shaping of Co/CNTs into extrudates or pellets as well as catalyst attrition rendered these materials unfavorable for industrial applications. In this investigation regular γ- and nano-structured (N-S) alumina as well as CNTs-covered regular γ- and N-S-alumina supports were impregnated by cobalt nitrate solution to make new cobalt-based catalysts which were also promoted by Ru. The catalysts were characterized and tested in a micro reactor to evaluate their applicability in FTS. γ-Al₂O₃ was prepared by calcination of bohemite and N-S-Al₂O₃ was prepared by sol-gel method using aluminum chloride as starting material. Catalyst evaluations indicated that N-S-Al₂O₃ was superior to regular γ-Al₂O₃ and that CNTs-covered alumina supports were favored over non-covered ones in terms of activity and heavy hydrocarbon selectivity. These were justified by porosimetric characteristics of the catalysts and existence of CNTs points of view. CNTs-covered catalysts also showed higher wax selectivity and better resistance to deactivation. Furthermore, TPR analysis indicated that the cobalt aluminate phase, which is responsible for the permanent deactivation of alumina supported Co-based catalysts, did not form on alumina supported Co-based catalysts covered with CNTs due to weaker interactions between cobalt and alumina.

The formation and dissociation of methane gas hydrate at an interface between synthetic seawater (SSW) and methane gas have been experimentally investigated in the present work. The amount of gas consumed during hydrate formation has been calculated using the real gas equation. Induction time for the formation of hydrate is found to depend on the degree of subcooling. All the experiments were conducted in quiescent system with initial cell pressure of 11.14 MPa. Salinity effects on the onset pressure and temperature of hydrate formation are also observed. The dissociation enthalpies of methane hydrate in synthetic seawater were determined by Clausius-Clapeyron equation based on the measured phase equilibrium data. The dissociation data have been analyzed by existing models and compared with the reported data.

Direct synthesis of liquefied petroleum gas (LPG) from syngas was carried out over hybrid catalyst consisting of methanol synthesis catalyst and Y zeolite modified with Pd and Ca by different methods. The decrease of CO conversion was mostly attributable to the sintering of Cu in methanol synthesis catalyst. On the other hand, coke deposition on the Y zeolite was the main reason for the decrease of LPG selectivity. The introduction of Ca decreased the strong acid sites of Y zeolite, suppressed coke formation, and thus improved the stability of hybrid catalyst.

In this investigation, a novel thermally coupled reactor (TCR) containing methyl formate (MF) production in the endothermic side and methanol synthesis in the exothermic side has been investigated. The interesting feature of this TCR is that productive methanol in the exothermic side could be recycled and used as feed of endothermic side for MF synthesis. Other important advantages of the proposed system are high production rates of hydrogen and MF. The configuration consists of two thermally coupled concentric tubular reactors. In these coupled reactors, autothermal system is obtained within the reactor. A steady-state heterogeneous model is used for simulation of the coupled reactor. The proposed model has been utilized to compare the performance of TCR with the conventional methanol reactor (CMR). Noticeable enhancement can be obtained in the performance of the reactors. The influence of operational parameters is studied on reactor performance. The results show that coupling of these reactions could be feasible and beneficial. Experimental proof-of-concept is required to validate the operation of the novel reactor.

Three industry-supplied, well-shaped Mo/HZSM-5 catalysts, two binder-added and one binder-free, were tested for the first time in methane dehydroaromatization to benzene at 1073 K and 10000 mL/(gh) in periodic CH₄-H₂ switch operation mode, and their catalytic performances were compared with those of three self-prepared, binder-free powder Mo/HZSM-5 catalysts. XRD, ²⁷Al NMR, SEM, BET and NH₃-TPD characterizations of all the catalysts show that the zeolites in the two binder-added catalysts are comparable to those in the three binder-free powder catalysts in crystallinity, crystal size, micropore volume and Brønsted acidity. The test results, on the other hand, show that the catalytic performances of the two binder-added catalysts are worse than those of the four binder-free catalysts on both catalyst mass and zeolite mass bases. Then, TPO and BET measurements of all spent samples were conducted to get a deep insight into the negative effects of binder addition, and the results suggest that the binder additives functioned mainly to enhance the polyaromatization of formed aromatics to coke on their external surfaces and consequently lower the benzene formation activity and selectivity of the catalyst.

The present work aims at utilizing compressed natural gas (CNG) as carbon source for the synthesis of carbon nanotubes (CNTs) over CoO-MoO/Al₂O₃ catalyst via catalytic chemical vapor deposition (CCVD) method. The as-produced carbonaceous product was characterized by thermal gravimetric analyzer (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The experimental finding shows that CNTs were successfully produced from CNG while carbon nanofibers (CNFs) were formed as the side products. In addition, the catalytic activity and lifetime were found sustained and prolonged, as compared with using high purity methane as carbon source. The present study suggests an alternative route which can effectively produce CNTs and CNFs using low cost CNG.

Anodic aluminium oxide (AAOM) membranes were used for template growth of carbon nanotubes (CNT) inside their pores by chemical vapour deposition (CVD) of different hydrocarbons, in the absence of transition metal catalyst. A composite material, containing one nanotube for each channel, having the same length as the membrane thickness and the external diameter close to the diameter of the membrane holes, was obtained. Yield, selectivity, and quality of CNTs in terms of diameter (up to very thin CNT), carbon order, length, arrangement (i.e. number of tubes for each channel), purity, that are critical requisites for several applications were optimized by investigating the effect of changing the hydrocarbon feedstock gas, also in the presence of hydrogen. The samples produced using methane as a feedstock have a well ordered structure. The role of the alumina channels surface during the CNT growth has been investigated and its catalytic activity has been proved for the first time.

The mechanism of dimethyl oxalate hydrogenation to ethylene glycol over Cu/SiO₂ catalyst was investigated by in situ Fourier transform infrared (FTIR) spectroscopy. It was found that dimethyl oxalate and methyl glycolate proceeded via dissociative adsorption on Cu/SiO₂ catalyst, and four main intermediates, CH₃OC(O)(O)C-M (1655 cm⁻¹), M-C(O)(O)C-M (1618 cm⁻¹), HOCH₂(O)C-M (1682 cm⁻¹) and CH₃O-M (2924-2926 cm⁻¹), were identified during the reaction. It was concluded that dimethyl oxalate hydrogenation to ethylene glycol mainly proceeded along the route: dimethyl oxalate → CH₃OC(O)(O)C-M → methyl glycolate → HOCH₂(O)C-M → ethylene glycol. Finally a schematic reaction network was proposed.

LaFeO₃ perovskite supported Ni and Ni-Fe catalysts were prepared and applied to methanation reaction of syngas. Two preparation methods were employed. One was one-step citrate complexing method, and the other was a two step method using citrate complexing method to produce LaFeO₃ and followed by loading nickel oxide on it with impregnation. The structure evolution of the sample as prepared was investigated by XRD, TPR and TEM techniques. For the former, the chemical composites of the calcined sample are NiO-Fe₂O₃/LaFe_1–xNi_xO₃. After reduction and reaction of CO methanation, its composites convert to Fe-Ni@Ni/LaFeO₃-La₂O₂CO₃, in which Fe-Ni@Ni is metal particles in nano-size composed of nickel core and Fe-Ni alloy shell. For the latter, the chemical composites of the calcined sample are NiO/LaFeO₃; and after reduction and reaction of CO methanation, its chemical composites change to Ni/LaFeO₃. Ni/LaFeO₃ catalyst is a little more active, while Fe-Ni@Ni/LaFeO₃-La₂O₂CO₃ is much more stable and shows very good resistance to carbon deposition. In this work it is aimed to show that the structure and composites of the catalysts can be tailored using perovskite-type oxide as precursor prepared with different methods and conditions. Therefore, it is a promising route to prepare supported bi-metal catalysts in nano-size for a lot of metals with desired catalytic performances.