Methane activation without using oxidants over Mo/HZSM-5 zeolite catalysts

The effect of Mo loading, calcination temperature, reaction temperature and space velocity on the catalytic performance of methane dehydrogenation and aromatization without using oxidants over Mo/HZSM-5 has been studied. The XRD and BET measurements show that Mo species are highly dispersed in the channels of the HZSM-5 zeolite, resulting from the interaction between the Mo species and the zeolite, which also leads to a decrease in its crystallinity. The Brønsted acidity, the channel structure and the state and location of Mo species in the zeolite seem to be crucial factors for its catalytic performance. It was found that 2% Mo/HZSM-5 calcined at 773 K showed the best aromatization activity among the tested catalysts, the methane conversion being 9% at 1013 K with the selectivity to aromatics higher than 90%. The experimental results obtained from the variation of space velocity gave evidence that ethylene is an initial product. On the basis of these results a possible mechanism for methane dehydrogenation and aromatization has been proposed in which both the heterolytic splitting of methane in a solid acid environment and a molybdenum carbene-like complex as an intermediate are of significance.     

Effective Coke Removal in Methane to Benzene (MTB) Reaction on Mo/HZSM-5 Catalyst by H2 and H2O Co-addition to Methane

The catalytic dehydro-aromatization reaction over Mo/HZSM-5 catalyst was drastically stabilized by the co-addition of 5.4% H₂ and 1.8% H₂O to methane feed at 750 °C, 0.3 MPa and methane space velocity of 3000 mL g⁻¹ h⁻¹, suppressing the coke formation effectively, compared with single hydrogen or steam addition.     

Pulse study of methane partial oxidation to syngas over SiO2-supported nickel catalysts

Methane was pulsed over pure CuO and NiO as well as Cu/La₂O₃ and Ni/La₂O₃ catalysts at 600° C. Results indicate that the mechanisms for methane activation over copper and nickel are quite different. Over CuO, methane is converted to CO₂ and H₂O, most likely via the combustion mechanism; whereas metallic copper does not activate methane. Over NiO in the presence of metallic nickel sites, methane activation follows the pyrolysis mechanism to give CO, CO₂, H₂ and H₂O. Similar results were obtained over the Cu/La₂O₃ and Ni/La₂O₃ catalysts. XRD investigations indicate that copper and nickel existed as CuLa₂O₄ and LaNiO₃ respectively in the La₂O₃-supported catalysts. The effect of La₂O₃ on the activation of methane is discussed.     

Combined Single-Pass Conversion of Methane Via Oxidative Coupling and Dehydroaromatization

A new reaction mode, i.e., the combined single-pass conversion of methane via oxidative coupling (OCM) over mixed metal oxide (SLC) catalysts and dehydroaromatization (MDA) over Mo/HZSM-5 catalysts, is reported. With the assistance of an OCM reaction over SLC catalysts in the top layer of the reactor, the deactivation resistance of Mo/HZSM-5 catalysts is remarkably enhanced. Under the selected reaction conditions, the CH₄ conversion decreased from 18 to 1% and the aromatics yield decreased from 12.8 to 0.1%, respectively, after running the reaction for 960min on both 6Mo/HZSM-5 and SLC-6Mo/HZSM-5 catalyst system without O₂ in the feed. On the other hand, for the SLC-6Mo/HZSM-5 catalyst system with O₂ in the feed, the deactivation was improved greatly, and after 960min onstream the CH₄ conversion and aromatics yield were still as high as 12.0 and 8.0%, respectively. The promotion effect mainly appears to be associated with in situ formation of CO₂ in the OCM layer, which reacts with coke via the reverse Boudouard reaction.     

Decomposition of nitric oxide over perovskite oxide catalysts: effect of CO2, H2O and CH4

Direct nitric oxide decomposition over perovskites is fairly slow and complex, its mechanism changing dramatically with temperature. Previous kinetic study for three representative compositions (La_0.87Sr_0.13Mn_0.2Ni_0.8O_3−δ, La_0.66Sr_0.34Ni_0.3Co_0.7O_3−δ and La_0.8Sr_0.2Cu_0.15Fe_0.85O_3−δ) has shown that depending on the temperature range, the inhibition effect of oxygen either increases or decreases with temperature. This paper deals with the effect of CO₂, H₂O and CH₄ on the nitric oxide decomposition over the same perovskites studied at a steady-state in a plug-flow reactor with 1 g catalyst and total flowrates of 50 or 100 ml/min of 2 or 5% NO. The effect of carbon dioxide (0.5–10%) was evaluated between 873 and 923 K, whereas that of H₂O vapor (1.6 or 2.5%) from 723 to 923 K. Both CO₂ and H₂O inhibit the NO decomposition, but inhibition by CO₂ is considerably stronger. For all three catalysts, these effects increase with temperature. Kinetic parameters for the inhibiting effects of CO₂ and H₂O over the three perovskites were determined. Addition of methane to the feed (NO/CH₄=4) increases conversion of NO to N₂ about two to four times, depending on the initial NO concentration and on temperature. This, however, is still much too low for practical applications. Furthermore, the rates of methane oxidation by nitric oxide over perovskites are substantially slower than those of methane oxidation by oxygen. Thus, perovskites do not seem to be suitable for catalytic selective NO reduction with methane.     

In situ ellipsometric study of a palladium catalyst during the oxidation of methane

Ellipsometry is used to follow the growth of a PdO layer on the surface of a thick Pd-film catalyst during methane oxidation at 500°C. The oxide layer that develops under rich conditions (excess CH₄) is quite porous and roughens with time. Little CO is formed during this period, but the CO₂ formation rate increases until spontaneous oscillations develop, which correlate with changes in the ellipsometric data. These changes indicate that the porous oxide rapidly converts to a metal-rich state, which has decreased catalytic activity, and then slowly reoxidizes.     

二氧化碳催化加氢研究进展

介绍了近年来由 CO2 催化加氢制取甲醇、烃类、醛类、甲酸和二甲醚等反应的研究进展     

DCS在酸相法氯化聚乙烯生产中的应用

把DCS应用于酸法生产CPE中，描述了DCS的硬件配制，生产中的控制要点及自控方案，在工业化生产中取得了良好效果。     

Synthesis, structure and catalytic properties of Fe-substituted barium hexaaluminates

A sol–gel method using Ba and Al isopropylates and iron nitrate has been used to synthesise barium hexaaluminate partially substituted with iron. After calcination under oxygen at 1200°C the -alumina structure was obtained. Formation of the mixed BaFe_xAl_12-xO₁₉ phase occurred for x=1–4. XRD measurements showed a good crystallinity of the structure and expansion of unit cell parameters due to the presence of larger Fe³⁺ ions substituting Al³⁺ ones in octahedral sites only. Mössbauer spectroscopy revealed that Fe³⁺ ions are present in four different octahedral sites slightly distorted. Catalytic activity in methane combustion showed that an optimum was obtained for solid containing 2 Fe ions per unit cell: the increase of the amount of introduced iron was counterbalanced by the decrease of specific surface area. Intrinsic activities have been calculated for the four solids in both the fresh and aged states. It is observed that increasing iron content increases relative activities in the same ratio as the populations of iron located in two sites as deduced from Mössbauer spectroscopy. It is then tentatively assumed that activity is attributed to octahedrally coordinated Fe³⁺ ions in some specific sites.     

Preparation of microporous chlorinated poly(vinyl chloride) membrane in fabric and the characterization of their pore sizes and pore‐size distributions

Chlorinated poly(vinyl chloride) (CPVC)/poly(vinyl pyrrolidone) (PVP) membranes were prepared by using the solvent system tetrahydrofuran (THF)/n‐butyl alcohol (n‐BA) to investigate the possibility of pore size and pore‐size distribution control. The coagulation of CPVC/PVP solution was induced by the exposure to water vapor at 25 (±0.5)°C. The average pore diameter, d_p, and the size distribution of pores on the surface of the membrane were quantified through the image analyzer from the images visualized by field emission scanning electron microscope (FE‐SEM). Surface pore size and distribution of the prepared CPVC/PVP membrane were strongly affected by the relative humidity (RH) in the environment and the content of PVP used as an additive. Particularly, in the case of CPVC membrane without PVP, the mean pore size was 0.15–0.2 μm, depending on the RH. The pore distribution became broad with the increase of the RH. The membranes had open pores as confirmed by the hydraulic permeation experiment. In addition, the water flux and membrane resistance (R_m) were greatly affected by the composition of polymer solution and the RH. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1195–1202, 2002