Selective oxidation of ethane and propane over sulfated zirconia‐supported nickel oxide catalysts

The oxidative dehydrogenations of ethane and propane were investigated over a series of zirconia and nickel‐oxide supported on zirconia catalysts. It was found that zirconia, sulfated zirconia as well as NiO‐based zirconia catalysts showed high catalytic activities for oxidative dehydrogenation of ethane and propane. However, conversion and selectivity differed depending on the nature of the catalysts. Zirconia, sulfated zirconia (SZ) and their supported NiO catalysts showed high ethane conversions but lesser selectivities to olefins while NiO/Li₂ZrO₃ exhibited high selectivities to ethylene and propylene. Addition of an LiCl promoter in the NiO/SZ catalyst increased the catalytic activity and olefin selectivity, thus resulting in a higher olefin yield. In the oxidative dehydrogenations of ethane and propane NiO–LiCl/SZ exhibited 79% ethylene selectivity at 93% ethane conversion at 650 °C and 52% selectivity to propylene at 20% propane conversion at 600 °C, respectively. Characterization showed that the physico‐chemical properties of the catalysts determine the catalytic activity and selectivity. © 2001 Society of Chemical Industry     

Oxidative dehydrogenation of propane to propene in the presence of H2S at short contact times

The oxidative dehydrogenation of propane to propene at short contact times over V₂O₅/A1₂O₃ was remarkably enhanced by the introduction of H₂S in the feed mixture. Overall conversion of propane over this catalyst at 700 °C and 5 ms contact time was 53.7% with selectivity to propene of 56.5%, providing a net propene yield of 30.4%.     

Vanadium Oxide Based Nanostructured Materials: Novel Oxidative Dehydrogenation Catalysts

Novel vanadium oxide based catalyst derived from the open-framework solid, [Co₃V₁₈O₄₂(H₂O)₁₂(XO₄)]·24 H₂O (X = V, S) (1) catalyses oxidative dehydrogenation of propane to propylene. Catalyst activity was evaluated in the temperature range 250–400 °C with varying gas hourly space velocity (GHSV). At 350 °C and GHSV of 9786 h^?1 and at 1.3% propane conversion the selectivity to propylene was 36.8%. The major products obtained were propylene and CO _x (CO₂ and CO). The ratio of the propylene to CO _x depended directly on the catalytic sites present. Thus, as the amount of the catalyst was decreased, the conversion decreased with an increase in the propylene selectivity and a decrease in the selectivity to carbon oxides—CO _x . The catalyst has been characterized by temperature programmed reduction and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS).     

Correlation Between the Characteristics and Catalytic Performance of Ni–V–O Catalysts in Oxidative Dehydrogenation of Propane

Ni–V–O series catalysts for the oxidative dehydrogenation (ODH) of propane were prepared and characterized by BET, XRD, H₂-TPR, O₂-TPD-MS and electrical conductivity. At 425°C a C₃H₆ selectivity of 49.9% was observed on Ni_0.9V_0.1O _Y at a C₃H₈ conversion of 19.4%, and the obtained selectivity is almost two times higher than that over NiO at the roughly same conversion of C₃H₈. The mobile oxygen species created by the interaction of NiO and V₂O₅ has been found in the composite catalysts by O₂-TPD-MS and electrical conductivity studies, which seems to be responsible for the enhanced selectivity of the propane oxidative dehydrogenation.     

CeO2‐CrOy/γ‐Al2O3 redox catalyst for the oxidative dehydrogenation of propane to propylene

CeO₂‐CrO_y loaded on γ‐Al₂O₃ was investigated in this work for the oxidative dehydrogenation (ODH) of propane under oxygen‐free conditions. The ODH experiments of propane were conducted in a fluidized bed at 500°C‐600°C under 0.1 Mpa. The prepared catalyst was characterized by N₂ adsorption‐desorption measurements, H₂‐temperature‐programmed reduction, O₂‐temperature‐programmed desorption, NH₃‐temperature‐programmed desorption, x‐ray photoelectron spectroscopy, and x‐ray diffraction. The change in the selectivity of propylene resulted from the thermal cracking of the propane and the competition for lattice oxygen in the catalyst between propylene formation and propane and propylene combustion. Therefore, to achieve higher propylene yield in the industry, the reaction temperature should be 550°C‐575°C for the 17.5Cr‐2Ce/Al catalyst. The results of H₂‐TPR (from 0.2218 mmol/g‐0.3208 mmol/g) revealed that the addition of CeO₂ can enhance the oxygen capacity of CrO_y. Compared with that for 17.5Cr/Al, the conversion can be enhanced from 22.4% to 28.5% and the selectivity of propylene can be improved from 72.2% to 75.9% for the 17.5Cr‐2Ce/Al catalyst. In addition, CeO₂ can inhibit the evolution of lattice oxygen (O^2?) to electrophilic oxygen species (O₂^?), causing the average CO_x (CO and CO₂) selectivity to decrease from 9.64% to 6.31%.     

Synthesis and thermal property of boron–silicon– acetylene hybrid polymer

Inorganic–organic boron–silicon–acetylene hybrid polymer (PABS) was prepared by the polycondensation reaction between phenylboric acid and diphenyldichlorosilane and then terminated by phenylacetylene. The structure was characterized by using FTIR, ¹³C‐NMR, ¹H‐NMR, and GPC. PABS was a kind of resin exhibited high viscous at room temperature and good solubility in common organic solvents. The thermal and oxidative properties were evaluated by DSC and TGA. Exothermal peak at 370°C observed by DSC was attributed to reaction of the acetylene units. PABS showed excellent thermal and oxidative stability, and TGA exhibited the temperature of 5% weight loss (Td₅) was 625°C and char yield at 900°C was 90.0% in nitrogen. Surprisingly, both Td₅ and char yield at 900°C showed slightly increase in air, which was 638°C and 90.9%, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Research of the Activity of Catalysts on the Base of H3PW12O40 in Partial Oxidative Conversion of C3–C4 alkanes

Catalysts from heteropoly acid H₃PW₁₂O₄₀ and its Cs, Na, Ba, Pb, Ca, Cd, Cr, Mn, V, La salts supported on clinoptilolite, alumosilicate are highly active in oxidative conversion of propane–butane (OCPB) mixture and formation of C₂–C₄ olefins, oxygen-containing compounds at temperatures T = 100–800 °C. Optimum yields of ethylene and propylene are achieved on heteropoly acid its Cs and Cr salts. The processes of oxidative dehydrogenation (ODPB) and cracking are concurrent in formation of olefins. High activity is caused by dispersity of supported catalysts (XRD, IRS) both formation of crystal hydrates and an amorphous phase of heteropoly acid in a condition of interaction with the carrier.     

Bismuth‐Doped Ceria,Ce0.90Bi0.10O2: A Selective and Stable Catalyst for Clean Hydrogen Combustion

Bismuth‐doped cerias are successfully applied as solid “oxygen reservoirs” in the oxidative dehydrogenation of propane. The lattice oxygen of the ceria is used to selectively combust hydrogen from the dehydrogenation mixture at 550 °C. This process has three key advantages: it shifts the dehydrogenation equilibrium to the desired products side, generates heat, aiding the endothermic dehydrogenation, and simplifies product separation (water vs. hydrogen). Furthermore, the process is safer, since it uses the catalyst’s lattice oxygen instead of gaseous oxygen. We show here that bismuth‐doped cerias are highly active and stable towards hydrogen combustion, and explore four different approaches for optimising their application in the oxidative dehydrogenation of propane: first, the addition of extra hydrogen which lowers hydrocarbon conversion by suppressing both combustion and coking; second, the addition of tin which completely inhibits coking; third, the addition of platinum which increases selectivity, but at the expense of lower activity. The best results are obtained through tuning the reaction temperature. At 400 °C, high activity and selectivity were obtained for the bismuth‐doped ceria Ce_0.90Bi_0.10O₂. Here, 90% of the hydrogen feed is converted at 98% selectivity. This optimal reaction temperature can be rationalised from the hydrogen and propene temperature‐programmed reduction (TPR) profiles: 400 °C lies above the reduction maximum of hydrogen, yet below that of propene. That is, this temperature is sufficiently high to facilitate rapid hydrogen combustion, but low enough to prevent hydrocarbon conversion.     

Novel phenyl acetylene terminated poly(carborane‐silane): Synthesis,characterization, and thermal property

Phenyl acetylene terminated poly(carborane‐silanec) (PACS) was synthesized by the couple reaction of methyldichlorosilane with 1,7‐dilithio‐m‐carborane and lithium phenylacetylide. The structure was characterized using FTIR, ¹H‐NMR, ¹³C‐NMR, ²⁹Si‐NMR, and gel permeation chromatography. PACS exhibits solubility in common organic solvents. Thermal and oxidative properties were evaluated by thermogravimetric analysis (TGA). Thermoset exhibits extremely thermal and oxidative property and TGA curves show that the temperature of 5% weight loss (Td₅) is 762°C and char yield at 800°C is 94.2% in nitrogen. In air, surprisingly, both Td₅ and char yield at 800°C show slight increase, which is greater than 800°C and 95.6%, respectively. After pyrolysis, the char has no additional weight loss up to 800°C in air. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2498–2503, 2007     

Highly Selective Ce–Ni–O Catalysts for Efficient Low Temperature Oxidative Dehydrogenation of Propane

Doughnut-like structured CeNiO, prepared by a novel oxalate gel co-precipitation method, exhibited significantly higher activity in oxidative dehydrogenation of propane at a temperature as low as 275 °C than conventional catalysts such as VMgO. It is suggested that oxygen vacancy formed in CeO₂ lattice due to the incorporating of Ni atoms adsorbs and activates the molecular oxygen to form active oxygen species. The superior performance for propane oxidative dehydrogenation over CeNiO catalyst can be attributed not only to the properties of the CeNiO catalyst but also to its unique doughnut-like structure.     

Influence of Catalyst Pretreatments on Propane Oxidation Over Ru/γ-Al2O3

The influence of different treatments (in H₂ or in O₂ at 250 or 600 °C) of alumina supported Ru catalysts on the total oxidation of propane was investigated. Ruthenium catalysts were prepared using RuCl₃ as metal precursor and characterized by H₂ chemisorption, O₂ uptake, BET, XRD and TEM. The presence of chloride on the catalyst surface was found to exert an inhibiting effect on the activity of Ru. The reduced Ru/γ-Al₂O₃ catalysts after partial removing chlorine ions were more active than the same samples oxidized at 250 °C. The higher activity of the reduced Ru/γ-Al₂O₃ catalysts was attributed to the presence of a large amount of active sites on small Ru _x O _y clusters without well defined stoichiometry or on a poorly ordered layer of a ruthenium oxide on the larger Ru particles. The formation of highly dispersed, but in some extent crystallized RuO₂ phase in catalysts oxidized at 250 °C, leads to slightly lower activity of the Ru phase. Strong decline of the activity was found for catalysts oxidized at 600 °C. At this temperature, the Ru particles were completely oxidized to well-crystallized RuO₂ oxide, and the mean crystallite size of the Ru oxide phase was much higher (9–25 nm) than that of after oxidation at 250 °C (~4 nm). The effect of the regeneration treatment in H₂ on the activity of the Ru/γ-Al₂O₃ catalysts was also studied. The active ruthenium species for propane oxidation were discussed based on the catalytic and characterization data both before and after activity tests.     

Propane conversion over a Ru/CGO catalyst and its application in intermediate temperature solid oxide fuel cells

A Ru/CGO catalyst was investigated in combination with a Cu current collector for the direct electro-oxidation and internal reforming of propane in a solid oxide fuel cell. The electrochemical power densities for the direct oxidation were larger than in the internal reforming process at 750 °C. The electrochemical performance in the presence of propane was significantly affected by the polarization resistance which was about three times larger than that obtained for the SOFC fed with hydrogen at 750 °C. However, out-of-cell steam reforming tests showed a C₃H₈ conversion to syngas approaching 90% at 800 °C. Thus, significant enhancements may be achieved by properly optimizing the anode structure. No formation of carbon deposits was observed both upon operation of the anode in the direct oxidation and internal reforming processes at 750 °C.     

Novel heat resistant methyl‐tri(phenylethynyl)silane resin: Synthesis,characterization and thermal properties

Methyl‐tri(phenylethynyl)silane (MTPES) was successfully synthesized by the reaction of lithium phenylacetylide with methyltrichlorosilane. The structure was characterized by HRMS, FTIR, ¹H‐NMR, ¹³C‐NMR, ²⁹Si‐NMR, and elementary analysis. Thermal cure process was monitored by DSC, DMA, and FTIR. MTPES was heated to free flowing liquid around 130°C and thermally polymerized at 327–377°C to form thermoset. Thermal and oxidative properties were evaluated by TGA analysis. Thermoset exhibits extremely high heat‐resistance and TGA curve in nitrogen shows the temperature of 5% weight loss (Td₅) of 695°C and total weight loss at 800°C of 7.1%. TGA shows a high Td₅ of 565°C even in air, although the total weight loss at 800°C was 56.1% of the initial weight, much higher than that in nitrogen. The high heat resistance of MTPES was ascribed to crosslinking reaction concerning ethynyl groups. Aging studies performed at elevated temperatures in air on a thermoset showed that MTPES is oxidatively stable to 300°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2488–2492, 2006     

Preparation and characterization of poly(silyl ester)s containing 2,2‐bis(p‐dimethylsiloxy‐phenyl)propane units in the polymer backbones

The two poly(silyl ester)s containing 2,2‐bis(p‐dimethylsiloxy‐phenyl)propane units in the polymer backbones have been prepared via polycondensation reaction of di‐tert‐butyl adipate and di‐tert‐butyl fumarate with 2,2‐bis(p‐chloro dimethylsiloxy‐phenyl)propane to give tert‐butyl chloride as the condensate. The polymerizations were performed under nitrogen at 110°C for 24 h without addition of solvents and catalysts to obtain the poly(silyl ester)s with weight average molecular weights typically ranging from 5000 to 10,000 g/mol. Characterization of the poly(silyl ester)s included ¹H NMR and ¹³C NMR spectroscopies, infrared spectroscopy, ultraviolet spectroscopy, differential scanning calorimetry, thermogravimetric analysis (TGA), gel permeation chromatography, and Ubbelohde viscometer. The glass transition temperatures (T_g) of the obtained polymers were above zero because of the introducing 2,2‐bis(p‐dimethylsiloxy‐phenyl)propane units in the polymer backbones. The TGA/DTG results showed that the obtained poly(silyl ester)s were stable up to 180°C and the residual weight percent at 800°C were 18 and 9%, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1937–1942, 2006     

Catalytic dehydrogenation of propane on chromia,palladium and platinum supported catalysts

The dehydrogenation of propane to propylene over Cr₂O₃/Al₂O₃, Pd/Al₂O₃ and Pt/SiO₂ has been investigated in the temperature range 580–618°C. Runs were performed on propane, alone or in the presence of nitrogen (as a diluent), with complete analysis of the reaction products. The reaction was carried out in a fixed bed reactor at space velocities from 450–800 h^?1 which are close to industrial values and at pressures from 0.3 to 1 atm. A set of runs was made over a commercial chromia-alumina catalyst (10% Cr₂O₃) and over a promoted catalyst prepared in the laboratory by impregnation (16.8% Cr₂O₃ + 2% K₂O). The latter catalyst showed high selectivity and stability even when subjected to continuous cycles of dehydrogenation, regeneration and purging. Of the two noble metal supported catalysts used, reduced Pd/Al₂O₃ showed higher activity than Pt/SiO₂ at 618°C. The former catalyst gave a propylene yield of around 98% at 20% conversion level.     

Conductivity studies of sol-gel prepared BaCe0.85−xZrxY0.15O3−δ solid electrolytes using impedance spectroscopy

A systematic investigation on doped barium cerate perovskites on conductivity was performed by means of ac electrochemical impedance spectroscopy technique. BaCe_0.85?xZr_xY_0.15O_3?δ powders (x = 0, 0.1, 0.2, 0.3, 0.4) were prepared by a modified sol-gel Pechini method and sintered at 1,250 °C–1,450 °C, depending on Zr content, to obtain good densities (93–97% of the theoretical ones). The measured total conductivities for these solid solutions in three different atmospheres were reported: in dry oxygen, in dry nitrogen and wet (0.5 bar H₂O) hydrogen (5%H₂/Ar) atmospheres. Arrhenius plots recorded in dry oxygen as well as in dry nitrogen showed some residual hydration which remained in the specimens upon initial heating. The compositions with x = 0.3 and 0.4 gave conductivities close to 10^?2 S/cm in 5%H₂/Ar/H₂O atmosphere at 600 °C. The isothermal conductivities values showed a little variation for x from 0.2 to 0.4 between 500 and 800 °C.     

Synthesis,curing behavior and thermal properties of silicon‐containing hybrid polymers with Si−C≡C units

Three novel kinds of linear silicon‐containing hybrid polymers with Si?C≡C units were synthesized by polycondensation reactions using the Grignard reagent method. All the polymers were thermosetting, highly heat‐resistant, moldable and easily soluble in common organic solvents. The structure, curing behavior, thermal and oxidative properties were characterized using Fourier transform infrared spectroscopy, ¹H NMR, ¹³C NMR, gel permeation chromatography, differential scanning calorimetry and thermogravimetric analysis. The results obtained can provide theoretical guidance for determining the curing of the resin system. In addition, the cured polymers exhibit excellent thermal and oxidative stabilities with temperatures of 5% weight loss (T_d5) above 480 °C and 450 °C in nitrogen and air respectively; the residues at 1000 °C were above 70.0% and 45.0% respectively. The thermal and oxidative stabilities of the polymers are attributed to a crosslinking reaction between the Si?H and C≡C bonds or C≡C bonds. These polymers have the potential for use as high‐temperature‐resistant resins and ceramic precursors. © 2013 Society of Chemical Industry     

Effect of the post-heating temperatures on the microstructure,mechanical and electrical properties of silicon nitride thin films

Silicon nitride (SiN_x) thin film is a potential candidate for the fabrication of the insulating layer of thin-film thermocouples, which can be utilised to measure cutting temperatures, owing to its excellent insulation properties and hardness and a thermal expansion coefficient similar to that of carbide tool. Thus, it is necessary to investigate the stability of the SiN_x microstructure and its mechanical and electrical properties at high temperatures. In this study, SiN_x thin films were deposited using reactive magnetron sputtering, followed by post-heating in an air atmosphere at 200–600 °C. The microstructure, adhesion, and sheet resistance were investigated using atomic force microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, scratch tests, and four-probe resistance tests. The results showed that the SiN_x film had a typical amorphous structure. During the heating process, the grain size increased, as did the content of columnar structures. When the temperature was increased from room temperature to 200 °C, the SiN_x film was oxidised to SiN_xO_y. The oxidative product (SiO₂) and escaping nitrogen gas were not observed until the film was heated above 400 °C, revealing the different oxidation reactions and products induced by the elevated temperature. The adhesive strength of the SiN_x film increased monotonically with increasing temperature but was severely weakened when the film was heated to temperatures above 400 °C. Oxygen could not completely invade the deeper layers of the film until the temperature reached 600 °C. The sheet resistance of the SiN_x film improved at 200 °C, but reduced severely when the temperature exceeded 400 °C.     

Synthesis of Ti(C,N) ultrafine powders by carbothermal reduction of TiO2 derived from sol–gel process

Experimental results demonstrate that TiC_1−XN_X ultrafine powders can be synthesized by the sol–gel process. The factors influencing the powder synthesizing process, such as temperature, C/Ti ratio in raw materials, holding time and flow rate of nitrogen gas, are discussed. TiC_0.5N_0.5 powders with particle sizes less than 100 nm were produced at 1550°C. The microhardness of hot-pressed TiC_0.5N_0.5 samples at 1750°C was 19.6 GPa and the relative density was 98.9%.     

Synthesis,characterization, and properties of silylene–acetylene preceramic polymers

A series of silylene–acetylene preceramic polymers 3a–e were synthesized by polycondensation reaction of dilithioacetylene with dichlorosilane (H₂SiCl₂) or/and methyldichlorosilane (MeSiHCl₂). Their structures were confirmed by infrared spectra (IR), and ¹H and ²⁹Si NMR spectroscopies. Differential scanning calorimetry (DSC) diagrams show exotherms centered at 200 to 233°C temperature range, attributed to crosslinking reaction of the acetylene and Si? H groups. After thermal treatment, the obtained thermosets 4a–e possess excellent thermal stability. Thermogravimetric analysis (TGA) under nitrogen show the T_d5s (temperature of 5% weight loss) for all the thermosets are above 600°C, and the overall char yields are between 95.62% and 89.67% at 900°C. After pyrolysis at 1200°C, the obtained ceramic residues 5a–e exhibit good thermo‐oxidative stability with final weight retention between 98.76% and 91.66% at 900°C under air. In particular, perhydroploy(silylene)ethynylene 3a , which has the highest Si/C ratio in silylene–acetylene polymers, has the highest char yield, and the derived ceramic material 5a displays the best thermo‐oxidative stability. Based on Scanning electron microscopy and its associated energy‐dispersive X‐ray microanalysis (SEM EDX) and ¹³C magic angle spinning nuclear magnetic resonance (MAS NMR) analysis, ceramic 5a contains the highest SiC content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008