Hydrodeoxygenation of Furfural over Unsupported,SiO2-supported or Metal-promoted Mo Carbides: Tunning the Selectivity between 2-Methylfuran and C10 Furoins Diesel Precursors

The hydrodeoxygenation of furfural (FF) over Mo carbides in liquid phase at 200 °C, 30 bar of H₂ for 4 h in 2-butanol was investigated. Unsupported and SiO₂-supported Mo carbide with different crystallographic phases (β-Mo₂C/SiO₂ and α-MoC/SiO₂), and in the presence of Cu and Ni as promoters were studied. The reactivation treatment under H₂ atmosphere of the passivated Mo carbides was investigated by XAS. The results show that Mo is present in different states of oxidation in the passivated catalysts, with more severe oxidation in the bimetallic systems, in which the original carbides are not restored after reactivation. Finally, the product distribution in the HDO of furfural is modified as a function of catalyst oxidation degree. Using the less oxidized Mo carbide (β-Mo₂C), a higher yield to 2-methylfuran is obtained, while C₁₀ condensation products are formed for the more oxidized catalysts.     

丙烷氧化反应中多组分氧化物Bi－V－Mo－O催化作用的红外光谱研究

迄今对于含有铝、秘复合氧化物催化剂的活性中心和作用机理存在不同看法,本文采用红外光谱法,探讨了复合氧化物钥钒酸秘在丙烷选择氧化反应中的催化作用机理.     

The selective catalytic oxidation of toluene

It was found for the first time that the selectivity of toluene transformations into benzaldehyde and benzoic acid decreased and into maleic anhydride and deep oxidation products increased as the ability of vanadium-containing catalysts of toluene oxidation to generate the singlet form of molecular oxygen grew. A scheme of the formation of the products of toluene oxidation with oxygen was suggested. Quinones were shown to be final rather than intermediate oxidation products. The selectivity of the reaction with respect to mild oxidation products in the presence of V₂O₅, MoO₃, and V₂O₅ · MoO₃ could be increased by changing the temperature of catalyst preparation from 400 to 500°C.     

钼钒酸铋体系催化剂上丙烷的选择氧化反应

钼钒酸铋体系催化剂上丙烷的选择氧化反应李静，宋伟，窦伯生（中国科学院长春应用化学研究所长春１３００２２）关键词丙烷，选择氧化，钼钒酸铋，助剂，丙烯醛合理利用天然气及石油裂解气为人们所关注。由于烷烃较相应烯烃反应活性低，使其在工业上的应用远不及烯烃，相...     

Horseradish Peroxidase-Catalyzed Generation of Acetophenone and Benzophenone in the Triplet State*

Horseradish peroxidase catalyzes the aerobic oxidation of 2-phenylpropanal and diphenylacetaldehyde at physiological pH to yield acetophenone and benzophenone partly in the triplet state, respectively. These excited products plus formic acid are expected from the thermolysis of dioxetane intermediates. The presence of acetophenone was demonstrated spectrophotometr-ically and the chemiluminescence spectrum (δ_max - 430 nm) was consistent with its triplet state. Energy transfer to 9,10-dibromoanthracene-2-sulfonate ion, a triplet carbonyl counter, but not to anthracene-2-sulfonate ion, a singlet carbonyl acceptor, occurred, confirming the triplet nature of the main emitter. In the case of the diphenylacetaldehydelperoxidase system, benzophenone could also be detected spectrophotometrically but the corresponding chemiluminescence spectrum showed only red emission (δ_max - 630 nm), which was tentatively attributed to singlet oxygen formed by triplet-triplet energy transfer to ground state oxygen. Horseradish peroxidase can be replaced by other he-meproteins such as myoglobin, hemoglobin and micro-peroxidase as catalyst of the chemiluminescent reaction. The distinct emission spectra achieved with different hemeproteins suggest a role of the microenvi-ronment in totally or partly protecting the excited species from oxygen collisions, resulting in emission maxima around 430 nm, 630 nm or both.     

Selective Oxidation of Glucose to Gluconic Acid over Bimetallic Pd–Me Catalysts (Me = Bi,Tl, Sn,Co)

Catalytic properties of bimetallic Pd–Bi, Pd–Tl, Pd–Sn, and Pd–Co catalysts supported on C (from plum stones) and SiO₂ were studied in the reaction of glucose oxidation to gluconic acid. Catalysts modified with Bi show the best selectivity and activity. The results obtained from research on 5% Pd–5% Bi/C and 5% Pd–5% Bi/SiO₂ catalytic systems were compared with the results for a commercial catalyst containing 1% Pt–4% Pd–5% Bi supported on active carbon (Degussa). For both Pd–Bi/support catalysts and 1% Pt–4% Pd–5% Bi/C, similar selectivity in the reaction of glucose oxidation was observed. XRD studies proved the presence of intermetallic compounds BiPd and Bi₂Pd, which probably increase the selectivity of PdBi/SiO₂ catalysts.     

Catalytic behavior of a silica-supported polystannazane-copper complex for the oxidation of methanol to formaldehyde at mild reaction conditions

A very cheap catalyst, a silica-supported polystannazane-copper complex (abbreviated as SiO₂ Sn N Cu) was prepared by the reaction of the silica-supported polystannazane ligand with CuCl₂ in ethanol. The results showed that SiO₂ Sn N Cu can catalyze the oxidation of methanol to formaldehyde in high yield at mild conditions, i.e. at 40°C and 1 atm of oxygen. The catalyst could be recovered and could catalyze the reaction repeatedly.     

M-Na-P-Mo-V/SiO2系列催化剂对异丁烯氧化反应的催化性能

 以浸渍法制备了M－Na－P－Mo－V／SiO2系列催化剂,并用FT－IR和TPR对催化剂进行了表征,考察了催化剂上的异丁烯化反应．结果表明,在空速900h－1和345℃的反应条件下,过渡金属的引入可提高甲基丙烯醛的选择性．其中Cu对催化性能的改善最佳,甲基丙烯醛选择性可达65．7％;而在Na－P－Mo－V／SiO2催化剂上,乙酸选择性可达50％,但甲基丙烯醛选性仅为4．1％．在催化剂中引入过渡金属时,Cu在提高甲基丙烯醛选择性的同时,也抑制了完全氧化产物COx的生成;Fe提高双键断裂产物和完全氧化产物选择性的同时,使甲基丙烯醛选择性下降;Zn对反应的影响不很大．TPR结果表明,在入Cu的催化剂中,Cu与杂多酸阴离子之间可能存在“溢流”作用．     

Reaction mechanism-based design of efficient VPO catalysts for <Emphasis Type="Italic">n</Emphasis>-C<Subscript>5</Subscript>H<Subscript>12</Subscript> oxidation into phthalic,maleic, and citraconic anhydrides

Hypotheses as to possible ways of enhancing the selectivity of partial n-pentane oxidation with respect to phthalic, maleic, and citraconic anhydrides are suggested based on the mechanistic concepts of the formation of these products. The hypotheses are checked by studying the properties of vanadium-phosphorus oxide (VPO) catalysts upon the introduction of different concentrations of La, Bi, Fe, W, Te, Ti, Zr, or Mo. It is shown by various physicochemical methods (x-ray diffraction, IR spectroscopy, X-ray photoelectron spectroscopy, and pyridine and 2,6-dimethylpyridine adsorption) that the phase composition of the VPO catalyst and the oxidation states of its elements on the surface are not changed in most cases upon the introduction of these additives. The additives mainly affect the number of Lewis acid sites, whereas the Brønsted acidity changes only slightly. The existence of a correlation between the citraconic anhydride selectivity and the total acidity of the modified catalyst surface is confirmed. In agreement with the assumptions as to the process selectivity, it was discovered that the phthalic anhydride selectivity increases with an increase in the number of Lewis acid sites. The observed regularities open up the way to the purposeful synthesis of catalysts with enhanced selectivity with respect to these products.     

Spin-Enhanced O−H Cleavage in Electrochemical Water Oxidation

Herein we report the vital role of spin polarization in proton-transfer-mediated water oxidation over a magnetized catalyst. During the electrochemical oxygen evolution reaction (OER) over ferrimagnetic Fe₃O₄, the external magnetic field induced a remarkable increase in the OER current, however, this increment achieved in weakly alkaline pH (pH 9) was almost 20 times that under strongly alkaline conditions (pH 14). The results of the surface modification experiment and H/D kinetic isotope effect investigation confirm that, at weakly alkaline pH, during the nucleophilic attack of Fe^IV=O by molecular water, the magnetized Fe₃O₄ catalyst polarizes the spin states of the nucleophilic attacking intermediates. The spin-enhanced singlet O−H cleavage and triplet O−O bonding occur synergistically, which promotes the O₂ generation more significantly than the strongly alkaline case involving only spin-enhanced O−O bonding.     

Phosphorus modified MoO<Subscript>3</Subscript>–Bi<Subscript>2</Subscript>SiO<Subscript>5</Subscript>/SiO<Subscript>2</Subscript> catalyst for gas-phase epoxidation of propylene by molecular oxygen

The phosphorus (P) modified MoO₃–Bi₂SiO₅/SiO₂ catalyst was prepared by a simple co-impregnation method and investigated in the epoxidation of propylene by molecular oxygen. The catalyst was characterized by X-ray diffraction (XRD), N₂ adsorption–desorption analysis, NH₃-temperature-programmed desorption (NH₃-TPD), transmission electron microscopy, and Raman spectroscopy. It was found that the P-modified MoO₃–Bi₂SiO₅/SiO₂ catalyst with a P/Mo molar ratio of 0.5 exhibits the best catalytic performance for epoxidation of propylene by O₂, the TOFs for propylene oxide (PO) formation was four times higher than that of the unmodified one at 633 K. The modification by P could promote the dispersion of MoO₃ nanoparticles and increase the number of weak and moderate acid sites with respect to the phosphorus-free MoO₃–Bi₂SiO₅/SiO₂ catalyst, which were beneficial to the formation of PO. Moreover, the introduction of P also could protect the mesoporous structure by inhibiting the formation of Bi₂Mo₃O₁₂, which was beneficial to the dispersion of active species. We suppose that the phosphorus, bismuth and molybdenum species of P-modified MoO₃–Bi₂SiO₅/SiO₂ catalyst play important roles for propylene epoxidation by molecular oxygen.     

Enhancement of singlet oxygen generation based on incorporation of oxoporphyrinogen (OxP) into microporous solids

Singlet oxygen, ¹O₂, generating compounds are highly useful for photodynamic therapy or organic oxidative transformations. In this work, the synthesis and photochemical performances for singlet oxygen generation of a range of oxoporphyrinogen-containing porous coordination polymers (OxP-PCPs) are reported. Oxoporphyrinogens, a previously unreported class of singlet oxygen generators derived from the oxidation of the antioxidant-substituted porphyrin tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)porphyrin, were converted to molecular tectons by the introduction of oligophenylene-carboxylate linkers and incorporated into porous coordination polymers using well-known oxo-Zr(IV)₆ cluster chemistry. Their structures and textural properties were analyzed revealing substantial surface areas up to 650 m² g^?1 for the optimum linker length (biphenylyl). The oxoporphyrinogen precursors exhibit good quantum yields of singlet oxygen generation (up to Φ = 0.37), and a high level of activity is maintained in the resulting coordination polymers, which appear to be superior for singlet oxygen generation to the precursors and to a reported reference material. These OxP-PCP materials were applied for the selective oxidation of sulfides to sulfoxides. This work demonstrates that the excellent singlet oxygen generator oxoporphyrinogens can be successfully incorporated as porous solids and conveniently applied in heterogeneous oxidative transformations.     

Bismuth as an additive modifying the selectivity of palladium catalysts

The influence of bismuth addition on the activity and selectivity of palladium catalysts supported on SiO₂ in the reaction of glucose oxidation to gluconic acid was studied. The catalysts modified with Bi show much better selectivity and activity than palladium catalysts. The XRD studies proved the presence of intermetallic compounds BiPd and Bi₂Pd, which probably increase activity and selectivity of PdBi/SiO₂ catalysts in the oxidation of glucose. The TPO studies of catalysts containing 5 wt.% Pd/SiO₂, 3 wt.% Bi/SiO₂ and 5 wt.% Pd–5 wt.% Bi/SiO₂ show that palladium oxidation occurs at much higher temperatures than in the case of bismuth. The maximum rate of Pd oxidation occurs at around 580 K while the maximum rate of Bi oxidation takes place at around 430 K. Considering the above facts, a reaction involving bimetallic catalysts in oxidizing atmosphere at 333 K should not lead to surface oxidation of palladium and thus their deactivation.     

Selective oxidation of anthracene to 9,10-anthraquinone over silica supported vanadium catalyst

The inner-ring oxidation of anthracene over V₂O₅/SiO₂ catalyst was investigated at various oxygen concentrations, contact times of the reactants and reaction temperatures. Up to 90 % yield to 9,10-anthraquinone is obtained at 218-220^oC.     

Study of the mobility of lattice oxygen in complex oxide catalysts for partial oxidation of propylene to acrolein

The amount of oxygen in the lattice of solids that participates in the elementary stages of partial propylene oxidation is determined for two types of Co-Mo-Bi-Fe-Sb-K-O catalysts (I, II) differing in the method of introduction of antimony and potassium. Two independent methods are used: (1) on the basis of the yield of the oxygen-containing products of propylene oxidation by oxygen of the catalyst in a pulse regime and (2) with the use of Möessbauer spectroscopy. Coincidence of the results obtained by both methods indicates that the active oxygen of the catalyst lattice is formed during redox transformations of iron(III) molybdate entering the composition of the catalysts. Data on the reduction of the catalysts in a pulse regime at various temperatures, which were processed in the framework of the diffusion model, allowed the estimation of the rate constants for diffusion of the lattice oxygen. An increase in the mobility of the lattice oxygen in catalyst I, which is modified with a small amount of antimony as compared to catalyst II, results in an increase in the overall productivity of the sample and in a decrease in the selectivity of propylene oxidation to acrolein. This correlates with the increase in the total amount of the lattice oxygen participating in the process.     

铋钼复合氧化物表面上激光促进异丁烷选择氧化制甲基丙烯酸

 用共沉淀法制备了Bi和Mo的复合氧化物固体材料．运用XRD,IR,TPD和激光促进表面反应（LSSR）技术研究了其晶体结构、表面构造、化学吸附特性和激光促进异丁烷选择氧化反应性能．结果表明：Bi－Mo－O复合氧化物含有α－Bi2Mo3O12和少量γ－Bi2MoO6晶相;其表面上存在着Lewis碱位（MoO和Mo—O—Bi键中的O）及Lewis酸位（Bi3＋）;异丁烷的两个甲基H分别吸附在两个相邻的Lewis碱位MoO上,形成双位分子吸附态;在常压和200℃条件下,用一定频率的激光激发MoO键1000次,异丁烷的转化率可达11．2％,其反应产物是异丁烯、甲基丙烯醛和甲基丙烯酸,其中甲基丙烯酸的选择性为90％．根据实验结果,探讨了激光促进异丁烷选择氧化为甲基丙烯酸的表面反应机理．     

Ethylene production by the oxidative condensation of methane in the presence of MnMW/SiO<Subscript>2</Subscript> catalysts (M = Na,K, and Rb)

The samples of MnMW/SiO₂ (M = Na, K, and Rb) were synthesized using various synthesis methods under varied heat treatment conditions and their physicochemical properties and activity in the reaction of the oxidative condensation of methane (OCM) were studied for the development of an effective catalyst for the resource-saving process of natural gas conversion into ethylene. It was found that the preparation method exerts an effect on the textural characteristics of the samples and the reducing properties of the cations of manganese and tungsten. It was determined that the composition of a W-containing phase depends on the alkali metal, and a ratio between the polymorphous modifications of SiO₂ is controlled by the method of synthesis and the conditions of catalyst heat treatment. It was established that the yield of C₂ hydrocarbons in the OCM reaction increased with the use of incipient wetness impregnation instead of the method of mixing with a suspension for catalyst preparation and with an increase in the catalyst heat treatment temperature from 700 to 1000°C. The optimum composition of the catalyst and the condition of its synthesis were found: 2Mn_0.8Na₃W/SiO₂ obtained by the impregnation method and calcined at 1000°C ensured the yield of target products of ~20% with a CH₄ conversion of ~35% at a reaction temperature of 850°C.     

BiMo基复合氧化物催化剂晶格氧性质与丙烷选择氧化性能

研究了不同组成、结构的BiMo基复合氧化物催化剂的丙烷选择氧化至丙烯醛的性能.X射线衍射(XRD)、X光电子能谱(XPS)、原位傅里叶变换激光拉曼光谱(FT-LRS)、电子顺磁共振(ESR)等多种表征结果表明,BiMo基复合氧化物催化剂上丙烷经由中间物丙烯选择氧化至丙烯醛,催化剂的晶格氧为选择性活性氧物种.丙烷直接氧化下丙烷至丙烯醛的选择性和收率与催化剂的Mo=O物种的氧化-还原性质密切关联,而Mo=O物种的性质又取决于Mo离子的配位环境,Mo=O物种的选择性转化丙烷经由丙烯至丙烯醛活性随畸变MoO6八面体、共顶点八面体、共边八面体、MoO4四面体配位环境递增.组成、结构优化调变的催化剂上丙烷选择氧化至丙烯醛选择性和收率可达45%和13.5%,催化剂中具有选择氧化活性的晶格氧物种数可达258 μmol/g.     

Aza‐BODIPY Derivatives: Enhanced Quantum Yields of Triplet Excited States and the Generation of Singlet Oxygen and their Role as Facile Sustainable Photooxygenation Catalysts

A new series of aza‐BODIPY derivatives ( 4 a – 4 c , 5 a , c , and 6 b , c ) were synthesized and their excited‐state properties, such as their triplet excited state and the yield of singlet‐oxygen generation, were tuned by substituting with heavy atoms, such as bromine and iodine. The effect of substitution has been studied in detail by varying the position of halogenation. The core‐substituted dyes showed high yields of the triplet excited state and high efficiencies of singlet‐oxygen generation when compared to the peripheral‐substituted systems. The dye 6 c , which was substituted with six iodine atoms on the core and peripheral phenyl ring, showed the highest quantum yields of the triplet excited state (Φ_T=0.86) and of the efficiency of singlet‐oxygen generation (Φ_Δ=0.80). Interestingly, these dyes were highly efficient as photooxygenation catalysts under artificial light, as well as under normal sunlight conditions. The uniqueness of these aza‐BODIPY systems is that they are stable under irradiation conditions, possess strong red‐light absorption (620–680 nm), exhibit high yields of singlet‐oxygen generation, and act as efficient and sustainable catalysts for photooxygenation reactions.     

The role of the geometric factor in the selective oxidation of lower paraffins at VPO catalysts

For the most widely published oxidation of n-butane at vanadium-phosphorus catalysts it was shown that the geometric factor plays a deciding role in the formation of the selective oxidation products. The mechanism proposed for the transformation of the paraffin at the [100] plane of the vanadyl pyrophosphate, which takes account of the geometry of the molecule being oxidized, explains the observed experimental facts, i.e., the increase in the oxidation rate with increase in the effective negative charge at the oxygen atoms of the catalyst, the positive effect of the hyperstoichiometric phosphorus on the selectivity of oxidation, the increased selectivity of oxidation with the introduction of additives that form phosphates, and the difference in the characteristics and mechanism of the oxidation of a paraffin and C₄ olefins. On the basis of the proposed mechanism suggestions are made about possible paths for the transofrmation of C₂−C₆ paraffins at VPO catalysts and the factors that could affect the selectivity of these processes. A number of the suggestions were confirmed by the author's own investigations and by published investigations. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 5, pp. 265–276, September–October, 1999.