Selective oxidation of propylene to acrolein by silica-supported bismuth molybdate catalysts

Silica-supported bismuth molybdate catalysts have been prepared by impregnation, structurally characterized and examined as improved catalysts for the selective oxidation of propylene to acrolein. Catalysts with a wide range of loadings (from 10 to 90 wt%) of beta bismuth molybdate (??-Bi₂Mo₂O₉) were studied to provide a better understanding about the distribution of active sites, and to elucidate the role of lattice oxygen in the reaction. The catalyst containing 50 wt% of beta bismuth molybdate on SiO₂ was found to possess good distribution of active sites and sufficiently high lattice oxygen, which resulted in an extraordinary increase of the catalytic activity.     

Effect of bismuth species on propylene aromatization over BiHZSM-5 catalysts

The catalytic behavior of Bi-impregnated HZSM-5 zeolites in propylene aroma-tization and the surface properties of the zeoh'tes were determined by microreactor, XRD, XPS, NH3-TPD and IR-TPD. The mechanism of the reaction and the effect of surface properties of the zeolites on the reaction were also investigated. Experimental data showed that Bi-impregnation made the strength of B-acid sites decrease, the strength of L-acid sites and the concentration of both strong B-acid sites and strong L-acid sites increase. Bi-impregnation also induced sub-strong acid sites. These were the factors that made the aromatic products of the reaction increase. The strong interaction between the impregnant and zeolite surface reached maximum at Bi2O3 = 3.5 wt%. Above this value, covering effect of impregnant caused a decrease of aromatic products.     

铋、铈钼酸盐催化剂的丙烯选择氧化动力学研究

本文目的在于研究稀土对钼酸铋的丙烯选择氧化影响,不同比例的催化剂呈现了比较复杂的动力学行为,随着催化剂组成变化,氧反应级数可由零级经过0.5级直至无一定反应级数,对丙烯的反应级数也随组成改变有很大变化,为解释这一现象,本文提出了统一反应机理,即随着催化剂组成变化,催化剂表面活性中心由晶格氧经历吸附原子态氧至吸附分子态氧变化,通过X光、红外及其它实验结果表明,预期这样的活性中心变化是由于铈的存在形成了钼酸铈晶相,破坏了钼酸铋晶体形成而促使钼酸铋更加分散缘故。     

Selectivities of bismuth vanadate catalysts for toluene oxidation

Oxidation of toluene vapors over fused bismuth vanadate catalysts of various compositions in fixed bed has been studied. The optimum conversion of toluene to benzaldehyde is related to the Bi₂O₃ content of the catalyst. The composition Bi₂O₃–V₂O₅(2575) and Bi₂O₃–V₂O₅ (4060) are highly active and selective for the oxidation of toluene to benzaldehyde.

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. Bi₂O₃ . Bi₂O₃V₂O₅, 2575 4060, .

     

Nonsteady-state oxidation of propylene on supported silver catalysts

Nonsteady-state epoxidation of propylene on silver has been studied to establish the reason for the low catalyst activity and selectivity that appear to be due to side reactions of the formation of hydrogen-deficient deposits.

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Methanol oxidation to formaldehyde on bismuth phosphate-based catalysts

A bismuth (III) phosphate catalyst has been prepared by precipitation and characterized by X-ray diffraction, thermogravimetric analysis, and X-ray photoelectron and infrared spectroscopy. Its activity and selectivity toward selective methanol oxidation to formaldehyde has been studied by a flow method. A high selectivity has been found, similar to that reported for typical catalysts used for this reaction. The possible importance of the strength and covalency of the P–O bonds is discussed.     

Active state of molybdenum in molybdenum-alumina catalysts for propylene oxidation

Catalytic properties of molybdenum-alumina catalysts for propylene oxidation are shown to be determined by water-soluble molybdenum compounds, being apparently aluminomolybdenum heteropoly acids bonded to the catalyst surface.

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Catalytic properties of silica-molybdenum catalysts in propylene oxidation

The activity of silica-molybdenum catalyts in propylene oxidation is shown to be determined by the partially dehydrated silica-molybdenum heteropolyacid stabilized by the SiO₂ surface.

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Dependence of oxidation activity on the structure of bismuth tungstate catalysts

The structures of bismuth tungstate catalysts with Bi/W ratios of 2/3, 1/1, 2/1 and 6/1 have been studied by X-ray diffraction. The presence of corner sharing W–O octahedra in the bulk of Bi/W=2/1 and 1/1 compositions has been established. The Bi/W=2/3 catalyst appears to contain edge-shared W–O octahedra whereas W in the Bi/W=6/1 sample form WO₄ tetrahedra. An apparent correlation has been obtained between the structures of the catalysts and their activities in the oxidation and ammoxidation of propylene and 1-butene.

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Bi/W, 23, 11, 21 61, . , W–O Bi/W=21 11. Bi/W=23 W–O , Bi/W=61 . 1-.

     

On the nature of active centers in catalysts for propylene oxidation to acetone

Acid-base properties of binary tin-oxide catalysts for the oxidation of propylene to acetone have been studied. It has been revealed that active catalysts should have both Brönsted acid- and base centers.

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On the mechanism of propylene oxidation over gallium-molybdenum oxide catalysts

The products of selective oxidation are shown to be formed via a stepwise mechanism with participation of surface allylic complexes. A successive transformation of -allyl to -allyl and further to acrolein is possible. The products of complete oxidation may be formed through surface carbonate-carboxylate complexes via either a stepwise mechanism involving the catalyst's oxygen, or a concerted mechanism with the participation of molecular oxygen.

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Influence of ammonia on propylene oxidation on tin-antimony and bismuth-antimony catalysts

The influence of ammonia on the direction of the oxidative transformations of propylene has been studied. Ammonia has been shown to block the surface oxygen of antimony catalysts. As a result, an increase in the selectivity with respect to the products of partial oxidation is observed.

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钼催化剂结构对其催化气相丙烯环氧化反应选择性的影响

考察了Mo基催化剂上空气气相氧化丙烯反应。从无机的和有机金属Mo前驱体出发,采用浸渍法和物理气相沉积法(PVD)制备了不同类型的SiO2负载氧化钼和Mo-Bi复合氧化物催化剂。透射电镜结果证实,所制催化剂上环氧化反应活性与其纳米结构直接有关。催化剂中出现部分或完全结晶的氧化钼相,它们与载体SiO2的相互作用较弱,使得反应生成环氧丙烷的选择性低于10%,而锚合在SiO2上的非结晶的八配位Mo物种上的环氧丙烷选择性达55%以上,此时丙烯转化率约为11%。不同形貌氧化钼的电化学表征结果证实了结构缺陷的重要性。另外,还讨论了Bi对氧化钼催化环氧化活性的直接促进效应。     

Bi-Mo-Nb复合氧化物的结构与对丙烯氧化的催化活性

本文用XRD, IR, Raman, SEM和ESR等方法研究了系列氧化物Bi~2Mo~3-3XNb~2xO~12-4X(X=0.00, 0.02, 0.05, 0.10, 0.15, 0.20, 0.25) 的结构和对丙烯氧化的催化活性。结果表明, 在X<0.25范围内, 催化剂基本保持典型的α-Bi~2Mo~3O~12结构, 少量Nb^5+的掺杂, 可取代晶格中的Mo^6+, 产生氧空位,无序分布的氧空位的浓度先随X值的增加而增加, 当X=0.15时达到最大值, 催化剂对丙烯氧化的催化活性与这种氧空位的浓度成正比, 反应遵循Redox机理。     

Catalytic properties of Ti?Mo oxide catalysts in propylene oxidation

Catalytic properties of Ti–Mo oxide catalysts are shown to be determined to a great extent by the Ti–Mo heteropoly acid anchored to the TiO₂ surface which is formed during the catalyst preparation.

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Prediction of the catalytic action of oxide catalysts in allyl oxidation of propylene

Concepts are described according to which an efficient catalyst of propylene oxidation to acrolein should contain oxygen of two types — nucleophilic and electrophilic. This can be ensured by a combination of an amphoteric oxide and an oxide of a high-valent element. The distribution of the products of allyl oxidation also depends on the collective properties of a catalyst.

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Bond energy of surface oxygen in multicomponent oxide catalysts for propylene oxidation to acrolein

Bond energy of surface oxygen for the multicomponent oxide catalyst Mo₁₂Bi₁Ni_2.5Fe₃Co_4.5K_0.07P₁/SiO₂ has been measured in conditions of propylene oxidation and found to be 272 kJ/mol.

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Mo₁₂Bi₁Ni_2,5Fe₃Co_4,5K_0.07P₁/SiO₂, , 272 /.

     

Effect of alumina in multicomponent bismuth phosphate catalyst supported on silica-alumina for propylene ammoxidation reaction

The effect of compositions of silica-alumina support on multicomponent bismuth phosphate catalyst (MBP) was investigated for the propylene ammoxidation. It is appears that small amounts of Al₂O₃ cause retardation of the ammoxidation reaction, which would be due to activation of the selective oxidation pathway. It is understood from such results that the catalytic action of the MBP is essentially different with that of the multicomponent bismuth molybdate catalyst (MBM), which is generally used as propylene ammoxidation catalyst. This revised version was published online in June 2006 with corrections to the Cover Date.