碳纳米管负载铑催化剂上丙烯氢甲酰化

Effect of carbon nanotubes, as a novel support material, on the performance of Rh-catalyst supported by them was studied. Catalysts based on carbon nanotubes, SiO2, carbon molecular sieves, active carbon, and GDX-l02(a copolymer of styrene with divinylbenzene),were prepared, and their catalytic behaviors for propene hydroformylation were investigated and compared. The results showed that, over the carbon nanotubes-supported Rh-catalyst, C3H6 conversion and regioselectivity of butyric aldehyde (represented by n/i, a ratio of n-butyric aldehyde to its isomer, i-butyric aldehyde, in the products) were pronouncedly improved: the average turnover frequency(TOF) for the catalytic hydroformylation of propene was 0.079 s-1 at 393K, which was 2.1 times faster than that over the Rh catalyst based on SiO2, and the n/i ratio of the aldehyde products reached to 11.6, which was 1.9 times higher than that over the catalyst based on SiO2. The roles of six-membered C-ring at the surface of the carbon-nanotubes on the stability of the catalytically active Rh-complexes and of the tubular nano-channel on the spatiospecific seletivity of reaction intermediate state and butyric aldehyde produced were discussed.     

Conversion of Ethene to Propene on Nickel Ion-loaded Mesoporous Silica Prepared by the Template Ion Exchange Method

Although surface of amorphous silica is widely accepted to be neutral or slightly acidic, siliceous mesoporous materials have been found to act as excellent acid catalysts by us and other groups. On the other hand the increment in propene production is one of the significant objectives to be achieved in the present petroleum chemistry. Especially the one-path conversion of ethene to propene (ETP reaction, 3C₂H₄ → 2C₃H₆) is the most desired process. In our efforts, the specific acid catalysis of mesoporous silica was combined with the catalysis of nickel ion, which could turn the new type of ETP reaction into reality. The one-path conversion of ethene was 68% and the propene selectivity was 48% with 43% of butenes in a continuous gas-flow system at 673 K and an atmospheric pressure. The reactivity of lower olefins and the dependences of the ETP reaction on the contact time and the partial pressure of ethene followed the reaction mechanism consisting of dimerization of ethene to 1-butene, isomerization of 1-butene to 2-, and metathesis of 2-butene and ETP. The Ni-loaded mesoporous silica 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.

Two New On-Purpose Processes Enhancing Propene Production: Catalytic Cracking of C4 Alkenes to Propene and Metathesis of Ethene and 2-Butene to Propene

A brief review of the work carried out at Dalian Institute of Chemical Physics, Chinese Academy of Sciences for development of two new on-purpose processes enhancing propene production is presented. This includes the processes of catalytic cracking of C₄ alkenes to propene and metathesis of ethene and 2-butene to propene, by which the large amounts of the C₄ recourses from the petrochemical can be upgraded and the severity of demand for propene can be lessened.     

Promoting effect of Mg in supported Mo/HBeta–Al2O3 catalyst for cross-metathesis of ethene and butene-2 to propene

Promoting effects of Mg in heterogeneous Mo/HBeta–Al₂O₃ catalyst have been carefully studied for cross-metathesis of ethene and butene-2 to propene. The catalyst shows good stability with Mg content in the range of 1–2 wt%. Such effect may be attributed to the elimination of weak acid sites through introduction of Mg which suppresses the side olefin oligomerization reaction, as evidenced from NH₃-TPD and ¹H MAS NMR results. Addition of more Mg content to 3 wt% may change the state and reducibility of Mo species, as indicated from the UV–vis, UV-Raman and H₂-TPR measurements. The increasing difficulty for the reduction of Mo(VI) species is closely related with the poor performance of 3 wt% Mg–4Mo/HBeta–30% Al₂O₃ catalyst in the metathesis reaction.     

Olefin insertion in Pd-acyl complexes modified with 1,4-Cs-symmetrical diphosphine ligands

The insertion of ethene and propene was investigated in palladium(II) acyl complexes of the type [PdC(O)CH₃(P^∧P′)(CH₃CN)](OTf) modified with the C_s-symmetric diphosphines 2-4 and the parent ligand 1, described by C_2v-symmetry and taken as a reference.Ethene insertion was investigated for acyl complexes containing the ligands 2 and 3. Two insertion products formed in a ratio of approximately 1:1 for both systems, irrespective of the electronic properties of the ligands.Propene as an α-olefin can insert according to a 1,2- or 2,1-insertion mode into a palladium acyl bond, arising regioselectivity issues. Moreover, due to the C_s-symmetry of the ligands, two stereoisomers can result upon insertion, as the alkyl group of the formed five-membered metallacycle can be cis or trans to each non-equivalent moiety. Propene insertion was indeed neither stereo- nor regioselective in the cases of 3 and 4, in which the products arising from both 1,2- and 2,1-insertion were observed. 2 displayed total control of stereo- and regioselectivity, with the formation of one primary insertion product. Similar regioselectivity was observed for the reference ligand 1. The regioisomeric distribution was different from equimolar for propene insertion, where the ratio of the products might be controlled by a combination of steric and electronic factors.     

Pressure and temperature dependence of the reaction of vinyl radical with alkenes II: Measured rates and predicted product distributions for vinyl + propene

This work reports measurements of the absolute rate coefficients and Rice-Ramsperger-Kassel-Markus (RRKM) master equation (ME) simulations of the C₂H₃ + C₃H₆ reaction. Direct kinetic studies were performed over a temperature range of 300-700 K and pressures of 15, 25, and 100 Torr. Vinyl radicals were generated by laser photolysis of vinyl iodide at 266 nm, and time-resolved absorption spectroscopy was used to probe vinyl radicals through absorption at 423.2 nm. A weighted modified Arrhenius fit to the experimental rate constant is k₁ = (1.3 ± 0.2) × 10⁻¹² cm³ molecule⁻¹ s⁻¹(T/1000)^1.6 exp[−(1510 ± 80/T)]. Fifteen stationary points and 48 transition states on the C₅H₉ potential energy surface (PES) were calculated using the G3 method in Gaussian 03. RRKM/ME simulations were performed using VariFlex on a simplified PES to predict pressure dependent rate coefficients and branching fractions for the major channels. For temperatures between 350 and 700 K, the calculated rate coefficient agrees with the experimental rate coefficient within 20%. At low temperatures, the primary products are the initial adducts 4-penten-2-yl and 2-methyl-3-buten-1-yl. At higher temperatures, the dominant products are 1,3-butadiene + methyl, allyl + ethene, and 1,3-pentadiene + H. Although C₂H₃ + C₃H₆ → allyl + ethene is thermodynamically favored, the simulations predict that it does not become the dominant product until 1700 K.     

水热处理对纳米HZSM-5分子筛酸性及催化甲醇制丙烯反应性能的影响

对纳米HZSM-5分子筛进行水热处理,利用N2吸附-脱附、X射线衍射(XRD)、铝固体核磁共振(27AlMASNMR)、氨-程序升温脱附(NH3-TPD)和吡啶吸附傅立叶变换红外(FT-IR)光谱等技术对改性前后样品的结构和酸性进行了详细表征,并在常压、500℃和甲醇质量空速(WHSV)为1.0h-1的反应条件下,在连续流动微型固定床反应器上考察了其催化甲醇转化制丙烯反应的性能.结果表明,适度的水热处理使纳米HZSM-5分子筛骨架脱铝并经柠檬酸洗涤而除去,酸量减少,酸强度降低,孔容和孔径增大,从而使丙烯的选择性和维持甲醇完全转化的反应时间(即催化剂寿命)分别由改性前的30.1%和75h显著提高至38.9%和160h.但过高温度的水热处理使纳米HZSM-5分子筛的酸性明显减弱,强酸中心几乎完全消失,故使丙烯的选择性和催化剂的稳定性反而大大降低.     

Hexafluoropropene Oxide — A Key Compound in Organofluorine Chemistry

Of the important C₃-compounds in organofluorine chemistry, namely hexafluoropropene, hexafluoroacetone and hexafluoropropene oxide, the latter is chemically the most versatile compound. Hexafluoropropene oxide provides another example of the frequently observed change in reactivity when hydrocarbon compounds are converted into their perfluorinated derivatives. The overwhelming majority of the known reactions of hexafluoropropene oxide are initiated through attack by a nucleophile. The conversion of hexafluoropropene oxide into hexafluoroacetone in the presence of Lewis acids is the basis of further development of the chemistry of this synthetic chemical. Hexafluoropropene oxide is also regarded as a convenient source of difluorocarbene. In industrial chemistry it now plays a significant part in the manufacture of high-grade organofluorine products.     

Acrylonitrile from Propylene,Ammonia, and Atmospheric Oxygen

Acrylonitrile was produced in pilot plant from propylene, ammonia, and atmospheric oxygen in a fixed-bed reactor in the presence of Bi/Mo/Si oxide shell catalyst. The propylene conversion, which can amount to about 70% under optimal conditions, was studied as a function of structural properties and the chemical composition of the catalyst, and of the composition of the starting mixture. Acrylonitrile of adequate purity for use in polymerizations could be obtained by multi-stage processing of the crude product.     

EFFECTS OF EXTERNAL DONOR ON ACTIVE CENTER DISTRIBUTION OF SUPPORTED ZIEGLER-NATTA CATALYST

The composition distribution (CD) and microisotacticity distribution (ID) of propene/1-hexene copolymer synthesized by MgCl_2/DIBP/TiCl_4 (DIBP: diisobutyl phthalate) weredetermined by fractionating the copolymers according to crystallinity and characterizingthe fractions by ~(13)CNMR. The effects of two alkoxysilane donors, triethoxyphenylsilane(PTES) and dimethoxydi-tert-butylsilane (TBMS), on CD and ID of the copolymrs werecompared. Three main parts in the CD diagram of each copolymer were distinguished,which were correlated to active center distribution (ACD) based on three groupe of dif-ferent active centers. By studying the changes in 1-hexene content, microisotacticity andreactivity ratio product of three typical fractions, the effects of external donor on ACDwere better elucidated. It was found that TBMS shows much stronger effects on ACD thanPTES. In the former system, most fractions were produced on active centers with relativelylower r_1r_2, higher reactivity to 1-hexene, and higher stereospecificity as compared to thesystem without external donor. It is concluded that the observed very extensive changesin ACD are mainly resulted by the formation of new types of active centers, possibly bycoordination of external donor to certain positions on the catalyst.