Oxidative Dehydrogenative Coupling Research Articles

Selective PP and POP Bond Formations through Copper‐Catalyzed Aerobic Oxidative Dehydrogenative Couplings of H‐Phosphonates

Unterschiedliche Kupferkomplexe katalysieren selektiv die aerobe oxidative Kupplung von H-Phosphonaten zur Bildung der Hypophosphate oder Pyrophosphate in hohen Ausbeuten und mit hoher Selektivität (siehe Schema; tmeda=N,N,N′,N′-Tetramethylethylendiamin).

Selective PP and POP Bond Formations through Copper‐Catalyzed Aerobic Oxidative Dehydrogenative Couplings of H‐Phosphonates

Selective PP and POP Bond Formations through Copper‐Catalyzed Aerobic Oxidative Dehydrogenative Couplings of H‐Phosphonates

Controlling Homogeneous Chemistry in Homogeneous−Heterogeneous Reactors: Application to Propane Combustion

Operation strategies for controlling the extent of homogeneous chemistry in homogeneous−heterogeneous (HH) reactors were developed for a catalytic plate microreactor using a two-dimensional computational fluid dynamics model for propane combustion on Pt as our prototype system. The effect of the reactor gap size (distance between plates) was analyzed. We found that homogeneous chemistry is sustained for gaps well below the quenching diameter as a result of enhanced catalyst-induced heating. This finding has important ramifications for catalyst lifetime and safety and could be used to produce chemicals, for example, in oxidative dehydrogenation and oxidative coupling reactions. The homogeneous chemistry contribution decreases with decreasing gap size. Catalytic chemistry alone can occur under suitable flow rates, compositions, and heat loss/heat exchange rates. The synergism or competition between homogeneous and catalytic chemistries is delineated.

Simultaneous oxidative coupling of methane and oxidative dehydrogenation of ethane on the Na +/CaO catalyst

The co-feeding of ethane during oxidative methane coupling (OCM) decreases methane conversion, the more so, the higher the concentration of added ethane. At about 20% ethane content, methane reaction almost ceases. The amount of ethane remaining in post-reaction gases begins to be smaller than that supplied to the reaction only at its concentrations in the methane+ethane+oxygen mixture exceeding 2 mol%. At higher concentrations of ethane fed into the reaction, the magnitude of its conversion becomes stabilized at a constant level of 20–60%, depending on the conditions of the reaction. Along with the rising concentration of added ethane, the carbon contained in methane and ethane undergoing reaction towards the formation of ethylene and hydrocarbons C 3+ rises, mainly in consequence of the transformations of more highly reactive ethane. Although the presence of ethane among reagents increases ethylene content in post-reaction gases, still the ethylene/ethane ratio in these gases rises only slightly, regardless of the amount of ethane in the initial mixture of methane+ethane+oxygen. A significant finding is the lack of dependence of the value of the conversion of carbon introduced into the reaction in the form of methane and ethane to carbon dioxide on the amount of added ethane, so that the overall selectivity of hydrocarbons C 2+ formation does not deteriorate, either.

Catalytic performance, structure, surface properties and active oxygen species of the fluoride-containing rare earth (alkaline earth)-based catalysts for the oxidative coupling of methane and oxidative dehydrogenation of light alkanes

The fluoride-containing catalysts, mostly of the rare earth (alkaline earth)-based system, demonstrate good catalytic performances for the oxidative coupling of methane and oxidative dehydrogenation of ethane, propane as well as iso-butane. The results of structural analysis of the catalysts for oxidative coupling of methane show that the promoting effects of the fluoride in the catalysts may be principally related to the phase–phase interaction between fluoride and oxide. Compared to the corresponding alkaline earth oxide promoted rare earth oxide catalyst system, an alkaline earth fluoride-promoted rare earth oxide catalyst system is less basic and will therefore be favorable to reduce CO 2 inhibition in the reaction of methane oxidative coupling. However, there is no simple correlation between the acidity/basicity of a methane oxidative coupling catalyst and its catalytic performance. In the experiments of in situ spectroscopic characterizations carried out at the temperature from 650°C to 800°C, O − 2 species was detected over five fluoride-containing rare earth (alkaline earth)-based catalysts for methane oxidative coupling reaction, and the reactions between O − 2 species and CH 4 to form C 2H 4 and the corresponding side-products were observed using in situ IR over four catalysts, which suggest that O − 2 is probably the active oxygen species for the methane oxidative coupling reaction over the corresponding catalysts.

Oxidative coupling of methane and oxidative dehydrogenation of ethane over strontium-promoted rare earth oxide catalysts

Sr-promoted rare earth (viz. La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er and Yb) oxide catalysts (Sr/rare earth ratio = 0.1) are compared for their performance in the oxidative coupling of methane (OCM) to C 2 hydrocarbons and oxidative dehydrogenation of ethane (ODE) to ethylene at different temperatures (700 and 800°C) and CH 4 (or C 2 H 6 )/O 2 ratios (4-8), at low contact time (space velocity = 102000 cm 3 g -1 h -1 ). For the OCM process, the Sr-La 2 O 3 catalyst shows the best performance. The Sr-promoted Nd 2 O 3 , Sm 2 O 3 , Eu 2 O 3 and Er 2 O 3 catalysts also show good methane conversion and selectivity for C 2 hydrocarbons but the Sr-CeO 2 and Sr-Dy 2 O 3 catalysts show very poor performance. However, for the ODE process, the best performance is shown by the Sr-Nd 2 O 3 catalyst. The other catalysts also show good ethane conversion and selectivity for ethylene; their performance is comparable at higher temperatures (≥800°C), but at lower temperature (700°C) the Sr-CeO 2 and Sr-Pr 6 O 11 catalysts show poor selectivity.

Constituent selection and performance characterization of catalysts for oxidative coupling of methane and oxidative dehydrogenation of ethane

The catalytic property of BaF 2-doped tetragonal LaOF catalysts for oxidative coupling of methane and oxidative dehydrogenation of ethane was evaluated in detail by independently varying the concentration of BaF 2 in the catalysts. The results indicate that addition of BaF 2 into the tetragonal LaOF significantly improves the catalytic performance of LaOF for both reactions, and the best results are observed over the BaF 2/LaOF catalysts with BaF 2 content of ca. 10 mol%. The XRD analysis of the fresh catalysts suggests that, for the catalysts with BaF 2 content less than 15 mol%, most of the Ba 2+ ions together with the accompanying F − and O 2− may be dispersed in the LaOF, forming a Ba 2+-doped LaOF phase in which some of the La 3+ lattice points might be replaced by the less positively charged Ba 2+, leading to the formation of an F-center, anion vacancies or O − species in the LaOF lattice which will be favorable to the adsorption and activation of O 2. The results of in situ Raman characterization of the surface dioxygen species over the LaOF and 10% BaF 2/LaOF catalysts suggest that the improvement of alkane conversions on a BaF 2-doped LaOF may be explained by the relative abundance of the dioxygen adspecies over the catalyst. While one of the possible reasons for the significant improvement of the selectivities may have resulted from the favorable effect of F − ions for the isolation of the surface oxygen adspecies.

Coupling of Oxidative Dehydrogenation and Aromatization Reactions of Butane

Coupling of oxidative dehydrogenation and aromatization of butane by using a dual function catalyst has led to a significant enhancement of the yields (from 25 to 40%) and selectivities to aromatics (from 39 to 64%). Butane is converted to aromatics by using either zinc-promoted [Ga]-ZSM-5 or zinc and gallium copromoted [Fe]-ZSM-5 zeolite as a catalyst. However, the formation of aromatics is severely limited by hydrocracking of butane to methane, ethane, and propane due to the hydrogen formed during aromatization reactions. On the other hand, the oxidative dehydrogenation of butane to butene over molybdate catalysts is found to be accompanied by a concurrent undesirable reaction, i.e., total oxidation. When two of these reactions (oxidative dehydrogenation and aromatization of butane) are coupled by using a dual function catalyst they have shown to complement each other. It is believed that the rate-limiting step for aromatization (butane to butene) is increased by adding an oxidative dehydrogenation catalyst (Ga-Zn-Mg-Mo-O). The formation of methane, ethane, and propane was suppressed due to the removal of hydrogen initially formed as water. Studies of ammonia TPD show that the acidities of [Fe]-ZSM-5 are greatly affected by the existence of metal oxides such as Ga 2O 3, MgO, ZnO, and MoO 3.

Catalytic properties of bismuth vanadates based catalysts in oxidative coupling of methane and oxidative dehydrogenation of propane

The oxidative coupling of methane (OCM) and the oxidative dehydrogenation of propane (ODHP) have been performed on new mixed Bi-V oxides having a -γ-Bi2MoO6-like structure. The results yield a correlation between the methane conversion and the oxygen diffusivity. The introduction of metals (Fe, Cu, Sr with 10 mol%) improves the C2 selectivity. The use of an oxide with a scheelite structure (BiVO4) shows that, under catalytic conditions, this oxide has the same behaviour as the above solids.