NaOH 改性WO_3/SiO_2 催化剂催化2-丁烯和乙烯复分解制丙烯(英文)

A WO3 /SiO2 catalyst is used in industry to produce propylene from 2-butene and ethylene metathe-sis. Catalysts with various WO3 loading(4% to 10%) were prepared by impregnation and tested for the metathesis of ethene and trans-2-butene. Ion exchange of NaOH onto the WO3/SiO2 catalyst was used to mitigate the acidity of the catalysts in a controlled way. At low WO3 loading, the treatment with large amounts of NaOH resulted in a significant decrease in metathesis activity concomitant with significant W leaching and marked structural changes(XRD, Raman). At higher WO3 loading (6% to 10%), the treatment with NaOH mainly resulted in a decrease in acidity. FT-IR experiments after adsorption of pyridine showed that the Lewis acidic sites were poisoned by sodium. Never-theless, the metathesis activity remained constant after the NaOH treatment. This suggested that the remaining acidity on the catalyst was enough to ensure the efficient formation of the carbene active sites. Interestingly, Na poisoning resulted in some modification of the selectivity. The mitigation of acidity was shown to favor propene selectivity over the formation of isomerization products (cis-2-butene, 1-butene, etc.). Moreover, treatment with NaOH led to a shorter induction period and reduced coke formation on the WO3 /SiO2 catalyst.     

Poisoning Deactivation of Mesoporous Titanosilicate-Supported WO<Subscript>3</Subscript> During Metathesis of Butene to Propene

Deactivation by poisoning is studied in the metathesis of 2-butene to propene on mesoporous titanosilicate-supported WO₃ (WO₃/MTS–9), for which we focus on the effect of polar organic oxygenates on the activity of the catalyst. It is found that deactivation is strongly influenced by these oxygenates in feedstock, and the rate of deactivation increases with the increase of the polarity of the organic oxygenates. The deactivation by poisoning is reversible. The deactivation catalyst can be recovered by treatment in a nitrogen atmosphere at a high temperature.     

NaOH改性WO3/SiO2催化剂催化2-丁烯和乙烯复分解制丙烯SurasaMaksasithorn,DamienP.Debecker,PiyasanPraserthdam,JoongjaiPanpranot,KongkiatSuriye,SirachayaKunjaraNaAyudhya简

A WO₃/SiO₂ catalyst is used in industry to produce propylene from 2-butene and ethylene metathesis. Catalysts with various WO₃ loading (4% to 10%) were prepared by impregnation and tested for the metathesis of ethene and trans-2-butene. Ion exchange of NaOH onto the WO₃/SiO₂ catalyst was used to mitigate the acidity of the catalysts in a controlled way. At low WO₃ loading, the treatment with large amounts of NaOH resulted in a significant decrease in metathesis activity concomitant with significant W leaching and marked structural changes (XRD, Raman). At higher WO₃ loading (6% to 10%), the treatment with NaOH mainly resulted in a decrease in acidity. FT-IR experiments after adsorption of pyridine showed that the Lewis acidic sites were poisoned by sodium. Nevertheless, the metathesis activity remained constant after the NaOH treatment. This suggested that the remaining acidity on the catalyst was enough to ensure the efficient formation of the carbene active sites. Interestingly, Na poisoning resulted in some modification of the selectivity. The mitigation of acidity was shown to favor propene selectivity over the formation of isomerization products (cis-2-butene, 1-butene, etc.). Moreover, treatment with NaOH led to a shorter induction period and reduced coke formation on the WO₃/SiO₂ catalyst.     

d0 Re-based olefin metathesis catalysts, Re([triple bond]CR)(=CHR)(X)(Y): the key role of X and Y ligands for efficient active sites

DFT(B3PW91) calculations show that the reaction pathways for ethylene metathesis with Re([triple bond]CMe)(=CHMe)(X)(Y) (X/Y = CH2CH3/CH2CH3; CH2CH3/OSiH3; OSiH3/CH2CH3; OCH3/OCH3, CH2CH3/OCH3, and OCF3/OCF3) occur in two steps: first, the pseudo-tetrahedral d0 Re complexes distort to a trigonal pyramid to open a coordination site for ethylene, which remains far from Re (early transition state for C-C bond formation). The energy barrier, determined by the energy required to distort the catalyst, is the lowest for unsymmetrical ligands (X not equal Y) when the apical site of the TBP is occupied by a good sigma-donor ligand (X) and the basal site by a poor sigma-donor (Y). Second, the formation of metallacyclobutanes (late transition state for C-C bond formation) has a low energy barrier for any type of ligands, decreasing for poor sigma-donor X and Y ligands, because they polarize the Re-C alkylidene bond as Re(+delta)=C(-delta), which favors the reaction with ethylene, itself polarized by the metal center in the reverse way. The metallacyclobutane is also a TBP, with apical alkylidyne and Y ligands, and it is stabilized by poor sigma-donor X and Y. The best catalyst will have the more shallow potential energy surface, and will thus be obtained for the unsymmetrical set of ligands with X = a good sigma-donor (alkyl) and Y = a poor sigma-donor (O-based ligand). This rationalizes the high efficiency of well-defined Re alkylidene supported on silica, compared to its homogeneous equivalent, Re([triple bond]CMe)(=CHMe)(OR)2.     

Stability of the first-generation Grubbs metathesis catalyst in a continuous flow reactor

Ethylene pretreatment of the (PCy₃)₂Cl₂RuCHPh catalyst (1) prior to cross-metathesis of ethylene and cis-2-butene to form propylene in the continuous flow reactor produced a direct effect on catalyst deactivation. Similar cis-2-butene pretreatment of the same catalyst exhibited far less change in the catalyst activity. These results support the assumption that the ruthenium methylidene intermediate generated from ethylene and 1 is unstable and promotes catalyst loss while ruthenium alkylidenes, e.g. derived from 2-butene, exhibit significantly enhanced stability and sustained catalyst integrity. Continuous removal of products in the continuous flow reactor was important for separating the catalyst decay and the catalyst deactivation caused by a terminal olefin, in this case propylene.The amount of produced propylene during the 1 lifespan was determined in a series of tests using identical catalyst concentrations ([Ru] = 60 ppm) in pentadecane while varying the olefin pretreatment times from 0 to 420 min. The catalyst turnover numbers in the cross-metathesis experiments proved inversely proportional to the duration of ethylene treatment prior to the reaction. The activity of 1 pre-exposed to ethylene closely matched with the activity of the catalyst that decayed in the reaction mixture containing ethylene and cis-2-butene for the same period of time. A significant contribution of the Ru-methylidene decay to the activity losses in metathesis reactions was demonstrated directly in the cross-metathesis reaction environment. The catalyst proved to be less sensitive to cis-2-butene pretreatment and showed turnover numbers for subsequent cross-metathesis essentially similar to the reference cross-metathesis test.     

Production of propylene from an unconventional metathesis of ethylene and 2-pentene over Re2O7/SiO2-Al2O3 catalysts

An unconventional metathesis of ethylene and 2-pentene over Re2O7/SiO2-Al2O3 catalysts has been studied as an alternative route for the production of propylene. Complete conversion of 2-pentene and propylene yield as high as 88 wt% were obtained under mild reaction conditions at 35°C and atmospheric pressure. Unlike the conventional metathesis of ethylene and 2-butenes in which isomerization is a competing side reaction, the isomerization of 1-butene product from the unconventional metathesis of ethylene and 2-pentene to 2-butenes can further react with excess ethylene in the feed, resulting in additional increase in propylene yield. The secondary metathesis reaction was found to be favored under ethylene/2-pentene (E/2P) molar ratio 3 and gas hourly space velocity (GHSV) 1000 h-1 at the reaction temperature of 35°C. No catalyst deactivation was observed during the 455 min time-on-stream under the selected reaction conditions.     

Preparation of mesoporous alumina with large pore size and their supported rhenium oxide catalysts in metathesis of 1-butene and 2-butene to propene

Mesoporous γ-aluminas with large pore size(up to 19 nm,denoted as MA19) are prepared from dispersed pseudo-boehmite using pluronic P123 as template.It is found that these mesoporous alumina supported rhenium oxide catalysts were more active and have far longer working life-span in gas-phase metathesis of 1-butene and 2-butene to propene than rhenium oxide on conventional alumina with small pore size(5 nm).At 60°C and atmospheric pressure with WHSV = 1 h-1,the similar stable conversions of butene(ca.55%) for all the 13 wt% Re 2 O 7 /alumina catalysts were obtained near the chemical equilibrium,and the stable working life-spans of Re 2 O 7 /MA19 were far longer than that of Re 2 O 7 /Al 2 O 3,being about 70 h and 20 h,respectively.     

Gas-phase kinetics of hydroxyl radical reactions with C3H6 and C4H8: product branching ratios and OH addition site-specificity

Products of the reaction of OH radicals with propene, trans-2-butene, and 1-butene have been investigated in a fast flow reactor, coupled with time-of-flight mass spectrometry, at pressures between 0.8 and 3.0 Torr. The product determination includes H atom abstraction channels as well as site-specific OH addition. The OH radicals are produced by the H + NO(2) → OH + NO reaction or by the F + H(2)O → OH + HF reaction, the H or F atoms being produced in a microwave discharge. The gas mixture is ionized using single photon ionization (SPI at 10.54 eV), and products are detected using time-of-flight mass spectrometry (TOF-MS). The H atom abstraction channels are measured to be <2% for OH + propene, 8 ± 3% for OH + 1-butene, and 3 ± 1% for OH + trans-2-butene. Analysis of ion fragmentation patterns leads to 72 ± 16% OH addition to the propene terminal C atom and 71 ± 16% OH addition to the 1-butene terminal C atom. The errors bars represent 95% confidence intervals and include estimated uncertainties in photoionization cross sections.     

Dramatic enhancement of the alkene metathesis activity of Mo imido alkylidene complexes upon replacement of one tBuO by a surface siloxy ligand

[(triple bond SiO)Mo(triple bond NAr)(=CHCMe2R)(OtBu)], a well-defined silica supported alkene metathesis catalyst precursor, shows a dramatic enhancement of activity and selectivity compared to [Mo(triple bond NAr)(=CHCMe2R)(OtBu)2] and [(triple bond SiO)Mo(triple bond NAr)(=CHCMe2R)(CH2tBu)], respectively.     

钨含量对W/SiO2/Al2O3催化剂上1-丁烯自歧化反应的影响

采用浸渍法制备了一系列钨负载量不同的W/SiO₂/Al₂O₃ 催化剂. 采用X 射线衍射(XRD)、激光拉曼(Raman)光谱、紫外-可见(UV-Vis)光谱、氢气程序升温还原(H₂-TPR)和氨程序升温脱附(NH₃-TPD)等技术对催化剂进行了表征. 实验结果表明: 钨的负载量对催化剂上氧化钨物种的分散程度、还原性以及催化剂的酸性有非常重要的影响. 对该类催化剂上1-丁烯自歧化反应进行了详细考察, 结果表明: 当钨的质量分数为6.0%时,W/SiO₂/Al₂O₃催化剂表现出最佳的歧化活性和稳定性. 原因在于6.0%的钨负载量可以使催化剂上氧化钨物种具有中等程度的分散性、合适的还原性, 并且使催化剂具有一定程度的酸性, 这些因素有利于在催化剂上形成烯烃歧化活性位.     

Detailed structural investigation of the grafting of [Ta(=CHtBu)(CH2tBu)3] and [Cp*TaMe4] on silica partially dehydroxylated at 700 degrees C and the activity of the grafted complexes toward alkane metathesis

The reaction of [Ta(=CHtBu)(CH2tBu)3] or [Cp*Ta(CH3)4] with a silica partially dehydroxylated at 700 degrees C gives the corresponding monosiloxy surface complexes [([triple bond]SiO)Ta(=CHtBu)(CH2tBu)2] and [([triple bond]SiO)Ta(CH3)3Cp*] by eliminating a sigma-bonded ligand as the corresponding alkane (H-CH2tBu or H-CH3). EXAFS data show that an adjacent siloxane bridge of the surface plays the role of an extra surface ligand, which most likely stabilizes these complexes as in [([triple bond]SiO)Ta(=CHtBu)(CH2tBu)2([triple bond]SiOSi[triple bond])] (1a') and [([triple bond]SiO)Ta(CH3)3Cp*([triple bond]SiOSi[triple bond])] (2a'). In the case of [(SiO)Ta(=CHtBu)(CH2tBu)2([triple bond]SiOSi[triple bond])], the structure is further stabilized by an additional interaction: a C-H agostic bond as evidenced by the small J coupling constant for the carbenic C-H (JC-H = 80 Hz), which was measured by J-resolved 2D solid-state NMR spectroscopy. The product selectivity in propane metathesis in the presence of [([triple bond]SiO)Ta(=CHtBu)(CH2tBu)2([triple bond]SiOSi[triple bond])] (1a') as a catalyst precursor and the inactivity of the surface complex [([triple bond]SiO)Ta(CH3)3Cp*([triple bond]SiOSi[triple bond])] (2a') show that the active site is required to be highly electrophilic and probably involves a metallacyclobutane intermediate.     

One step formation of propene from ethene or ethanol through metathesis on nickel ion-loaded silica

Increased propene production is presently one of the most significant objectives in petroleum chemistry. Especially the one-step conversion of ethene to propene (ETP reaction, 3C?H? →2C?H?) is the most desired process. In our efforts, nickel ion-loaded mesoporous silica could turn a new type of ETP reaction into reality. The one-step conversion of ethene was 68% and the propene selectivity was 48% in a continuous gas-flow system at 673 K and atmospheric pressure. The reactivity of lower olefins and the dependences of the ETP reaction on the contact time and the partial pressure of ethene were consistent with a reaction mechanism involving dimerization of ethene to 1-butene, isomerization of 1-butene to 2-butene, and metathesis of 2-butene and ethene to yield propene. The reaction was then expanded to an ethanol-to-propene reaction on the same catalyst, in which two possible reaction routes are suggested to form ethene from ethanol. The catalysts were characterized mainly by EXAFS and TPR techniques. The local structures of the nickel species active for the ETP reaction were very similar to that of layered nickel silicate, while those on the inert catalysts were the same as that of NiO particles.     

Role of support nature （γ-Al2O3 and SiO2-Al2O3） on the performances of rhenium oxide catalysts in the metathesis of ethylene and 2-pentene

The metathesis of ethylene and 2-pentene was studied as an alternative route for propylene production over Re2O7/γ-Al2O3 and Re2O7/SiO2-Al2O3 catalysts. Both NH3 temperature-programmed desorption (NH3-TPD) and H2 temperature-programmed reduction (H2-TPR) results showed that Re2O7/SiO2-Al2O3 exhibited stronger acidity and weaker metal-support interaction than Re2O7/γ-Al2O3. At 35 60℃, isomerization free metathesis was observed only over Re2O7/γ-Al2O3, suggesting that the formation of metal-carbene metathesis active sites required only weak acidity. Our results suggest that on the Re2O7/SiO2-Al2O3, hydrido-rhenium species ([Re]-H) were formed in addition to the metathesis active sites, resulting in the isomerization of the initial 1-butene product into 2-butenes. A subsequent secondary metathesis reaction between these 2-butenes and the excess ethylene could explain the enhanced yields of propylene observed. The results demonstrate the potential for high yield of propylene from alternative feedstocks.     

Selective ruthenium-catalyzed transformations of enynes with diazoalkanes into alkenylbicyclo[3.1.0]hexanes

Reaction of a variety of CCH bond-containing 1,6-enynes with N2CHSiMe3 in the presence of RuCl(COD)Cp* as catalyst precursor leads, at room temperature, to the general formation of alkenylbicyclo[3.1.0]hexanes with high Z-stereoselectivity of the alkenyl group and cis arrangement of the alkenyl group and an initial double-bond substituent, for an E-configuration of this double bond. The stereochemistry is established by determining the X-ray structures of three bicyclic products. The same reaction with 1,6-enynes bearing an R substituent on the C1 carbon of the triple bond results in either cyclopropanation of the double bond with bulky R groups (SiMe3, Ph) or formation of alkylidene-alkenyl five-membered heterocycles, resulting from a beta elimination process, with less bulky R groups (R = Me, CH2CH=CH2). The reaction can be applied to in situ desilylation in methanol and direct formation of vinylbicyclo[3.1.0]hexanes and to the formation of some alkenylbicyclo[4.1.0]heptanes from 1,7-enynes. The catalytic formation of alkenylbicyclo[3.1.0]hexanes also takes place with enynes and N2CHCO2Et or N2CHPh. The reaction can be understood to proceed by an initial [2+2] addition of the Ru=CHSiMe3 bond with the enyne CCH bond, successively leading to an alkenylruthenium-carbene and a key alkenyl bicyclic ruthenacyclobutane, which promotes the cyclopropanation, rather than metathesis, into bicyclo[3.1.0]hexanes. Density functional theory calculations performed starting from the model system Ru(HCCH)(CH2=CH2)Cl(C5H5) show that the transformation into a ruthenacyclobutane intermediate occurs with a temporary eta3-coordination of the cyclopentadienyl ligand. This step is followed by coordination of the alkenyl group, which leads to a mixed alkyl-allyl ligand. Because of the non-equivalence of the terminal allylic carbon atoms, their coupling favors cyclopropanation rather than the expected metathesis process. A direct comparison of the energy profiles with respect to those involving the Grubbs catalyst is presented, showing that cyclopropanation is favored with respect to enyne metathesis.     

DFT prediction and experimental observation of substrate-induced catalyst decomposition in ruthenium-catalyzed olefin metathesis

Ruthenacyclobutane decomposition, involving competitive beta-hydride transfer to Ru and reductive olefin elimination during ruthenium-catalyzed olefin metathesis, is predicted by density functional theory calculations and experimentally confirmed by propene and butene formation during degenerate Ru-methylidene-catalyzed metathesis of ethylene. The results provide new focus on the nature of ruthenium metathesis catalyst decomposition under catalytic conditions.     

Optimizing packing heterogeneity for sorption enhanced metathesis reaction

An equilibrium-limited heterogeneous catalytic reaction, propene metathesis is suitable for process intensification via sorption enhanced reaction. In this work, we investigate the effect of catalyst/adsorbent configuration for propene metathesis in conjunction with pressure swing reaction. The catalyst and adsorbent configuration variations were defined in terms of packing heterogeneity index (PHI) and their effects were investigated experimentally and theoretically. Model predictions were tested against experimental data with variable PHI and adsorption/reaction conditions, including the absence of heterogeneity and of separation process. The product 2-butene was strongly adsorbed and retained by the intermediate adsorbent layers, thereby increasing reactant concentration in the reaction zone and enhancing conversion and rate of reaction in the subsequent layer. Model predictions were found to agree reasonably with experimental data and were used to elucidate the mechanism and optimizing principle for such reactors.     

Structure-reactivity relationship in alkane metathesis using well-defined silica-supported alkene metathesis catalyst precursors

Alkane metathesis can be performed by using well-defined silica-supported alkene metathesis catalyst precursors as long as the coordination sphere of the metal centre contains both alkyl and alkylidene groups, such as in [([triple chemical bond]SiO)Mo([triple chemical bond]NAr)(=CHtBu)(CH2tBu)]. This system transforms mainly linear alkanes, from propane to hexane, into their lower and higher homologues. Mechanistic studies clearly show that alkene metathesis is a key step of this reaction and also suggest that this system is a single-site single-component system, namely, alkenes are formed and transformed on one site, which is in contrast to that observed with a mixture of catalysts.     

Electroswitchable photoluminescence activity: synthesis, spectroscopy, electrochemistry, photophysics, and X-ray crystal and electronic structures of [Re(bpy)(CO)3(C[triple bond]C[bond]C6H4[bond]C[triple bond]C)Fe(C5Me5)(dppe)][PF6](n) (n = 0, 1)

A novel heterobimetallic alkynyl-bridged complex, [Re(bpy)(CO)(3)(C[triple bond]C[bond]C(6)H(4)[bond]C[triple bond]C)Fe(C(5)Me(5))(dppe)], 1, and its oxidized species, [Re(bpy)(CO)(3)(C[triple bond]C[bond]C(6)H(4)[bond]C[triple bond]C)Fe(C(5)Me(5))(dppe)][PF(6)], 2, have been synthesized and their X-ray crystal structures determined. A related vinylidene complex, [Re(bpy)(CO)(3)(C[triple bond]C[bond]C(6)H(4)[bond](H)C[double bond]C)Fe(C(5)Me(5))(dppe)][PF(6)], 3, has also been synthesized and characterized. The cyclic voltammogram of 1 shows a quasireversible reduction couple at -1.49 V (vs SCE), a fully reversible oxidation at -0.19 V, and a quasireversible oxidation at +0.88 V. In accord with the electrochemical results, density-functional theory calculations on the hydrogen-substituted model complex Re(bpy)(CO)(3)(C[triple bond]C[bond]C(6)H(4)[bond]C[triple bond]C)Fe(C(5)H(5))(dHpe) (Cp = C(5)H(5), dHpe = H(2)P[bond](CH(2))(2)[bond]PH(2)) (1-H) show that the LUMO is mainly bipyridine ligand pi* in character while the HOMO is largely iron(II) d orbital in character. The electronic absorption spectrum of 1 shows low-energy absorption at 390 nm with a 420 nm shoulder in CH(2)Cl(2), while that of 2 exhibits less intense low-energy bands at 432 and 474 nm and additional low-energy bands in the NIR at ca. 830, 1389, and 1773 nm. Unlike the related luminescent rhenium(I)-alkynyl complex [Re(bpy)(CO)(3)(C[triple bond]C[bond]C(6)H(4)[bond]C[triple bond]C[bond]H)], 4, complex 1 is found to be nonemissive, and such a phenomenon is attributed to an intramolecular quenching of the emissive d pi(Re) --> pi*(bpy) (3)MLCT state by the low-lying MLCT and LF excited states of the iron moiety. Interestingly, switching on of the luminescence property derived from the d pi(Re) --> pi*(bpy) (3)MLCT state can be demonstrated in the oxidized species 2 and the related vinylidene analogue 3 due to the absence of the quenching pathway.     

Kinetics of oxidation of lower olefins with Fe(III) aqua ions in the presence of the Pd/ZrO2/SO4 precatalyst in a chloride-free system

The kinetics of oxidation of ethene, propene, and 1-butene with Fe(III) aqua ions to the corresponding carbonyl compounds in the presence of the 1% Pd/ZrO₂/SO₄ precatalyst in aqueous perchloric acid at 40–80°C was studied. The oxidation rate increases in the order C₂H₄ < C₄H₈ < C₃H₆ and with increasing catalyst weight and in the acid and Fe(III) concentrations; it is independent of the olefin pressure. The ethene oxidation rate is described by the Michaelis-Menten equation. In the case of 1-butene, the reaction is accompanied by migration of the double bond with the formation of 2-butene.     

1-Butene isomerization and metathesis over Mo/mordenite-alumina: Factors influencing product distribution and induction period

Effects of space velocity, reaction temperature and support acidity on product distribution and induction period in 1-butene isomerization and metathesis over Mo/mordenite-alumina were investigated. As revealed by the catalytic performance results, induction period and objective product were closely related to the reaction conditions. Lower space velocity led to longer induction period and higher propene yield. The optimal reaction temperature for propene production is around 150 °C and it shifted to 100 °C for ethene production. 1-Butene auto-metathesis predominated in the reaction network if the support with lower degree of sodium exchanged. And propene gradually became the dominant product upon increasing the support sodium exchange degree. 6Mo/H₁₀₀Na₀M-30Al catalyst with a support of full sodium exchange degree exhibited the highest propene yield.