Low temperature oxidative coupling of methane over a La(2)O(3)catalyst

The oxidative coupling of Methane could take place at 723 K over the La2O3 catalyst prepared by the precipitation method, which was about 100 K lower than the startup temperature over the commercial La2O3 catalyst. Under the conditions of 723 K, CH4/O-2 molar ratio of 3, and GHSV = 7 500 ml/(g . h), the conversion of methane and selectivity for C-2 hydrocarbons reached 26.6% and 40.8%, respectively. The characterization results showed that there was only hexagonal La2O3 over the two catalyst samples, but the catalyst prepared by precipitation had a larger specific surface area and a distinct desorption peak of adsorbed O-2 at 598 K

In situ infrared Spectroscopy of active oxygen species for oxidative coupling of methane over BaF2/La2O3 catalyst

In situ IR spectroscopy was used to study the superoxide species (O-2(-)) for oxidative coupling of methane (OCM) over the BaF2,/La2O3 catalyst. After the pretreatment of the catalyst with O-2, the IR peak at 1108-1118 cm(-1) appeared, which was assigned to O-O bond stretching vibration in O-2(-) species. After the introduction Of 1802 isotope, the IR peak at 1.108-1118 cm-1 was weakened, and the absorption peaks appeared at 1086 and 1051 cm(-1), which was consistent with the assignment of the O-18O bond and O-18 O-18 bond stretching vibrations in the superoxide species, respectively. At 700 degrees C, the superoxide species could react with CH4, accompanied by the formation of gas phase C2H4. A good correlation between the rate of O-2 consumption and the rate of C2H4 formation was observed, so the superoxide species was believed to be responsible for the OCM reaction over the BaF2/La2O3 catalyst

Reconstruction of surface structure of MoBiTeO/SiO2 catalyst during propane selective oxidation

The catalytic performance of MoBiTeO/SiO2 for selective oxidation of propane to acrolein was investigated, and the catalyst was characterized by means of X-ray powder diffraction, in-situ laser Raman spectroscopy, in-situ laser Raman spectroscopy, and X-ray photoelectron spectroscopy. The results showed that Te-polymolybdate species were the main active phase on the fresh catalyst. Under the conditions of 570 degrees C and C3H8/O-2/N-2 = 1.2/1/4, some Te species in the catalyst were reduced to metal Te which was volatilized during the reaction, and therefore the active surface phase of the catalyst was reconstructed, leading to the formation of MoO3 species. Along with the active surface reconstruction, both the conversion of propane and the selectivity for acrolein were increased, which was attributed to the synergistic effect between Te-polymolybdate and MoO3

Nano-lanthanum Oxyhalide Prepared by Nonaqueous Sol-Gel for Oxidative Coupling of Methane

LaOX (X = Cl, Br) nanoparticles with tetragonal crystal structure were successfully prepared via sol-gel approach with non-aqueous solvents. Characterizations by X-ray powder diffraction and scanning electronic microscopy show that the LaOX nanoparticles are regularly in shape and highly uniform in size with an average diameter of about 47 nm. For oxidative coupling of methane (OCM), the nanosize LaOX catalysts have higher methane conversion and C(2) selectivity than the LaOX catalysts with conventional size and show good stability in activity and selectivity during the catalyst life test at 650 degrees C. At conventional size, the methane conversion and C(2) selectivity for OCM over the LaOBr catalyst are higher than that over the LaOCl catalyst, and at nanosize, there is not so much difference in methane conversion between LaOBr and LaOCl. However, the C(2) selectivity for OCM reaction over LaoBr is significantly higher than that over LaOCl, especially at low temperature.National Basic Research Program of China (973 Program)[2010CB732303]; National Natural Science Foundation of China[21033006, 20923004, 20373054

Enhanced photodegradation activity of methyl orange over Z-scheme type MoO3-g-C3N4 composite under visible light irradiation

National Natural Science Foundation of China [21003109, 51108424]; Opening-foundation of State Key Laboratory Physical Chemistry and Solid Surfaces, Xiamen University, China [201311]; School of Energy Resources at University of WyomingNovel Z-scheme type MoO3-g-C3N4 composites photocatalysts were prepared with a simple mixing-calcination method, and evaluated for their photodegradation activities of methyl orange (MO). The optimized MoO3-g-C3N4 photocatalyst shows a good activity with a kinetic constant of 0.0177 min(-1), 10.4 times higher than that of g-C3N4. Controlling various factors (MoO3-g-C3N4 amount, initial MO concentration, and pH value of MO solution) can lead to the enhancement of the photocatalytic activity of the composite. Only MoO3 and g-C3N4 are detected with X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) spectra. N-2 adsorption and UV-vis diffuse reflectance spectroscopy (DRS) results suggest that the addition of MoO3 slightly affects the specific surface area and the photoabsorption performance. The transmission electron microscopy (TEM) image of MoO3-g-C3N4 indicates a close contact between MoO3 and g-C3N4, which is beneficial to interparticle electron transfer. The high photocatalytic activity of MoO3-g-C3N4 is mainly attributed to the synergetic effect of MoO3 and g-C3N4 in electron-hole pair separation via the charge migration between the two semiconductors. The charge transfer follows direct Z-scheme mechanism, which is proven by the reactive species trapping experiment and the (OH)-O-center dot-trapping photoluminescence spectra

Oxidative dehydrogenation of ethane to ethylene over LiCl/SO42--ZrO2 catalyst

Sulfated zirconia (SO42--ZrO2) samples were prepared by a modified two-step method (refluxing ZrO(OH)(2) precursor in basic solution followed by drying and (NH4)(2)SO4 impregnation) and then impregnated with a LiCl solution to give the SO42--ZrO2-supported LICI catalysts with Li mass content of 0.5% similar to 15%. The catalysts were characterized by X-ray diffraction, scanning electron microscopy, N-2 adsorption, temperature-programmed desorption-mass spectrometry, and X-ray photoelectron spectroscopy. The results show that with increasing LiCl loading, the specific surface area and acidity of the catalysts as well as the volume fraction of tetragonal zirconia in the catalysts decrease, while the catalytic performance of the catalysts for oxidative dehydrogenation of ethane (ODHE) to ethylene increases. Over the LiCl/SO42--ZrO2 catalyst with a Li content of 15% ethylene yield of 77.8% with an ethane conversion of 90.6% is achieved at 650 degrees C, and the yield higher than 71% is maintained over a period of 24 h. The textural structure of ZrO? has little effect on the catalytic behavior of the LiCl/SO42--ZrO2 catalysts. The specific surface area of SO42--ZrO2 samples prepared by the fled two-step method is much bigger than that of the SO42--ZrO2 samples made by the method reported in literature, and therefore more LiCl call be loaded on unit mass of support. This is favorable to improve the catalyst stability and slow down catalyst deactivation during the ODHE reaction due to the loss of LiCl

Catalytic performance of MoVBiTeO/SiO2 for selective oxidation of propane to acrolein

A series of MoVBITeO/SiO2 catalyst samples with different Mo/V ratios were prepared by the impregnation method. The catalyst structure, reducibility, and acidity were characterized by XRD, Raman, XPS, TPR, and FT-IR techniques, and the catalytic performance of the catalyst for selective oxidation of propane to acrolein was evaluated. The results indicated that the interaction between Mo and V components modified the catalyst structure, and the redox cycle of V5+ + Mo5+ V4+ + Mo6+ was formed. The improvement in the reducibility of the catalyst might be responsible for the increase in propane conversion. The V and Mo components were responsible for B acid and L acid, respectively. When the Mo/V ratio increased, the amount of B acid decreased, and the catalyst selectivity for acrolein increased. Among the investigated catalyst samples, the sample with a Mo/V molar ratio of 6 exhibited the best catalytic performance

Photodegradation of RhB over YVO4/g-C3N4 composites under visible light irradiation

National Natural Science Foundation of China [21003109, 51108424]; Opening-foundation of State Key Laboratory Physical Chemistry and Solid Surfaces, Xiamen University, China [201311]; Science Foundation of Zhejiang Normal University [KJ20120028]A series of novel YVO4/g-C3N4 photocatalysts were prepared by a facile mixing and calcination method. The obtained composites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, ultraviolet visible diffuse reflection spectroscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, and a photocurrent-time experiment. The rhodamine B dye was selected as a model pollutant to evaluate the photocatalytic activity of the as-prepared YVO4/g-C3N4 composite. It shows that the photocatalytic activity of g-C3N4 can be largely improved by the doping of YVO4. The optimal YVO4 content is determined to be 25.8 wt%; and the corresponding degradation rate is 2.34 h(-1), about 2.75 folds that of pure g-C3N4. A possible mechanism of YVO4 on the enhancement of visible light performance is proposed. It suggests that YVO4 plays a key role, which may lead to efficiently suppressing the recombination of photogenerated charge carriers, consequently, improving the visible light photoactivity

Reaction mechanism of selective oxidation of propane to acrolein over MoPO/SiO2 catalyst

To elucidate possible reaction pathways for propane selective oxidation to acrolein over the MoPO/SiO2 catalyst, oxidative conversions of propane and possible intermediates or their probe molecules as well as the reaction products of the selective oxidation of propane to acrolein on the catalyst were studied. The results suggested that isopropoxy species is one of the intermediates for the selective oxidation of propane to acrolein over the MoPO/SiO2 catalyst. The isopropoxy species can be converted either to acetone by dehydrogenation or to propene by beta-hydrogen elimination, and the latter can be further converted to acrolein through an allylic process