Ni晶粒粒径对Ni/SiO_2催化月桂酸甲酯脱氧制烃性能的影响

采用等体积浸渍-干燥-还原法及等体积浸渍-干燥-焙烧-还原法制备了3种具有不同Ni晶粒粒径的Ni/SiO2催化剂,利用H2-TPR、XRD、TEM、H2-TPR、NH3-TPD及TGA技术对其及前驱体进行了表征,并在固定床反应器上评价了其催化月桂酸甲酯脱氧制十一烷(C11)和十二烷(C12)的性能,分析了Ni晶粒粒径对其脱氧性能的影响。结果表明,采用等体积浸渍-干燥-还原法制备的催化剂中Ni晶粒粒径较小,提高还原温度可以促进Ni晶粒长大。随Ni晶粒粒径增大,月桂酸甲酯的转换频率提高,而C11和C12总选择性、C11/C12物质的量比及裂解产物选择性降低,Ni/SiO2催化剂上月桂酸甲酯脱氧为结构敏感反应。此外,还考察了重时空速对Ni/SiO2催化剂脱氧性能的影响,随重时空速提高,月桂酸甲酯转化率、C11和C12总选择性、C11/C12物质的量比及裂化产物选择性降低。月桂酸甲酯通过脱羰/脱羧反应路径生成的CO/CO2几乎全部加氢转化为CH4,表明Ni/SiO2催化剂具有很高的甲烷化活性。研究还发现,较小Ni晶粒烧结、有机物种吸附及积炭会导致催化剂失活。     

不同温度焙烧的Au-Pd/SiO2催化剂上甲醇选择性氧化制备甲酸甲酯

以溶胶固定法制备了Au-Pd/SiO₂催化剂,考察了催化剂焙烧温度对甲醇选择氧化制甲酸甲酯反应性能的影响。在200~500℃,400℃焙烧的Au-Pd/SiO₂具有最好的低温催化性能,在室温下就有活性,反应温度为100℃时甲醇转化率为25.3%,甲酸甲酯的选择性为100%。采用BET、XRD、UV-vis DRS、XPS、TEM和DRIFTS技术对催化剂进行表征,结果表明,催化剂中活性组分Au和Pd的高分散性,合适的Au和Pd粒径,Au-Pd合金的形成以及Au和Pd之间的强相互作用力,有利于甲醇氧化为甲酸甲酯反应的进行。初步推测出了甲醇在Au-Pd/SiO₂上氧化为甲酸甲酯的反应机理,甲醇在Au-Pd/SiO₂催化剂上是通过甲氧基中间体得到甲酸甲酯的。     

Role of metal Cu species on methyl laurate catalytic hydrogenation to oxygen-containing compounds

The Cu/γ-Al₂O₃ catalysts with different Cu loadings were prepared by impregnation method. The physicochemical properties of these Cu/γ-Al₂O₃ catalysts were characterized by H₂-TPR, XRD, and in-situ XPS. The catalytic hydrogenation performances of methyl laurate over Cu/γ-Al₂O₃ catalysts were studied. The results show that the hydrogenation performances of methyl laurate on Cu/γ-Al₂O₃ catalyst are related to the dispersion, crystallite size, and content of the active component Cu⁰. The 10CA catalyst has the best hydrogenation performances for methyl laurate to produce C₁₂ alcohol. At 300 °C, the conversion of methyl laurate and the selectivity of C₁₂ alcohol are 55.6% and 30.4%, respectively.     

Transformation of methyl laurate to tricosanone-12 over Sn-Ce-Rh-O catalyst

The catalytic conversion of methyl laurate to tricosanone-12 in the gas phase over Sn-Ce-Rh-O catalyst has been studied. The yield of ketone in excess of 62% shows that the new catalyst can be applied to the ketonization of esters. Also long-chain esters can be used as substrates.     

焙烧温度对氧化锌纳米棒光催化生产H2O2活性的影响

过氧化氢作为一种对环境友好的、重要的化学原料,被广泛用于化学工业、漂白剂和废水处理等领域.近几十年来,过氧化氢主要通过蒽醌工艺生产.然而,该方法需要多步蒽醌加氢和氧化反应,导致较高的生产成本和能量消耗,同时伴随着大量的二氧化碳排放.另一种替代策略是在贵金属催化剂的辅助下,由氢气和氧气的混合气体在高温下直接合成.但是,氢气和氧气的混合气体在高温下存在爆炸的危险,从而限制了其大规模应用.因此,探索一种低能耗、温和条件下生产过氧化氢具有重要的意义.太阳能驱动光催化生产过氧化氢是解决上述问题的理想途径.通常认为,过氧化氢是由直接双电子还原(E(O2/H2O2)=0.68 V vs.NHE)或间接单电子O2还原(E(O2/?O2?)=-0.33 V vs.NHE)产生的.氧化锌半导体具有很的稳定性好、环保和成本低等优点,因此经常被用于二氧化碳的光催化还原、污水处理和气体传感器等领域.氧化锌的导带电势(ECB=-0.5 V vs.NHE)比氧还原电势更负,意味着它在热力学上满足光催化过氧化氢生产的要求.然而,目前关于氧化锌的光催化生产过氧化氢的研究尚未受到较多的关注.本文采用简单的水热法制备了一维氧化锌纳米棒,在不同温度下热处理后,对其形貌和结构、光学性质和电化学性质进行了表征.同时,系统地研究了以乙醇为牺牲剂光催化生产过氧化氢的性能.结果表明,随着焙烧温度的升高,氧化锌纳米棒内部的氧空位被空气中的氧气重新填充,其催化生成过氧化氢的活性先升高后降低.经300oC焙烧的氧化锌光催化产过氧化氢的活性最好,为285μmol L-1 h-1.同时,对过氧化氢的生成机理研究结果表明,该过程中为间接单电子O2还原过程.氧气先与一个电子反应生成超氧自由基,再与两个质子和一个电子反应生成过氧化氢分子.综上,本文为氧化锌纳米棒光催化产过氧化氢的机理研究提供了新认识,并提出了一种有前途的过氧化氢生产策略.     

Nonoxidative conversion of methane into aromatic hydrocarbons on Ni-Mo/ZSM-5 catalysts

The nonoxidative conversion of methane into aromatic hydrocarbons on high-silica zeolites ZSM-5 containing nanosized powders of molybdenum (4.0 wt %) and nickel (0.1–2.0 wt %) was studied. Data on the acid characteristics of the catalysts and the nature and amount of coke deposits formed on the surface of the catalysts were obtained using the thermal desorption of ammonia and thermal analysis. The microstructure and composition of Ni-Mo/ZSM-5 catalysts were studied by high-resolution transmission electron microscopy and energy-dispersive X-ray analysis. The formation of various chemical species in the samples was detected: oxide-like clusters of Mo within zeolite channels (∼1 nm), molybdenum carbide particles (5–30 nm) on the outer surface of the zeolite, and Ni-Mo alloy particles with different compositions (under reaction conditions, carbon filaments grew on these particles). It was found that, as the Ni content was increased from 0.1 to 2.0 wt %, the rate of deactivation of the catalytic system increased because of blocking pores in the zeolite structure by filamentous carbon up to the formation of condensed coke deposits.     

Vibrational relaxation in methyl hydrocarbons at high temperatures: propane, isobutene, isobutane, neopentane, and toluene

Vibrational relaxation has been seen in shock waves in propane, isobutene, isobutane, neopentane, and toluene dilute in krypton with the laser-schlieren technique. These experiments cover about 600-2200 K and post-shock pressures from 5 to 29 Torr. The process cannot be resolved in any for T<600 K, or in any for large molecule fraction. All the ultrasonic measurements of relaxation in these at room temperature show characteristic times in the 1-5 ns atm range, corresponding to fewer than five collisions, whereas the relaxation times in the shock waves range from 20 to 200 ns atm, with a clearly defined negative or "inverted" temperature dependence. It would seem the observed slowdown of relaxation with increasing T is simply a consequence of the much increased energy transfer required at high temperature in such large polyatomics when this is combined with a collision efficiency, here interpreted as down, already so large it cannot much increase. The simple method for the extraction of a down from relaxation data offered here by consideration of the energy relaxation equation for Evib=0 appears to be original and should prove quite useful in connecting thermal relaxation data to values obtained from spectroscopy and master-equation analyses. Here it is found that the derived down extrapolate well to room temperature ultrasonic measurements, showing a slight increase with temperature.     

Effect of precursor calcination temperature on the microstructure and thermoelectric properties of Ca3Co4O9 ceramics

Ca₃Co₄O₉ (CCO) powder precursors were prepared by the chemical sol–gel route and calcined at various temperatures between 923?K (CCO-923?K) and 1,073?K (CCO-1,073?K). The calcination temperature was found to be a critical factor affecting the microstructure and thermoelectric properties of CCO ceramic bulk samples. The grain size increases with calcination temperature. The nano-crystals with size about 100?nm in the powders calcined at 923?K promote large crystal growth and texture development during sintering. Bulk pellets made from CCO-923?K powder have large crystal grains, uniform grain size distribution, and a high degree of crystal alignment. By contrast, pellets made from CCO powders at higher calcination temperatures have a bimodal distribution of large and small grains and a large amount of randomly oriented grains. Transmission electron microscopy analysis shows that each crystal grain (identified in SEM images) consists of bundles of CCO nano-lamellas. The nano-lamellas within one bundle share the same c-axis orientation and have fiber texture. The electrical resistivity of CCO-923?K is weakly dependent on operating temperature. Compared to the CCO-1,073?K sample, the CCO-923?K sample has the highest power factor, a lower thermal conductivity, and higher electrical conductivity.     

Non-oxidative dehydro-oligomerization of methane to higher molecular weight hydrocarbons at low temperatures

The non-oxidative dehydro-oligomerization of methane to higher molecular weight hydrocarbons such as aroma tics and C2 hydrocarbons in a low temperature range of 773-973 K with Mo/HZSM-5,Mo-Zr/HZSM-5 and Mo-W/HZSM-5 catalysts is studied.The means for enhancing the activity and stability of the Mo-containing catalysts under the reaction conditions is reported.Quite a stable methane conversion rate of over 10% with a high selectivity to the higher hydrocarbons has been obtained at a temperature of 973 K.Pure methane conversions of about 5.2% and 2.0% have been obtained at 923 and 873 K,respectively.In addition,accompanied by the C2-C3 mixture,tht- methane reaction can be initiated even at a lower temperature and the conversion rate of methane is enhanced by the presence of tne initiator of C2-C3 hydrocarbons.Compared with methane oxidative coupling to ethylene,the novel way for methane transformation is significant and reasonable for its lower reaction temperatures and high selectivity to the desired prod     

Density functional study of methyl chemisorption on polycyclic aromatic hydrocarbons.

The reactions of methyl radicals with large (up to C(96)H(24)) polycyclic aromatic hydrocarbons (PAHs) are studied by density functional calculations to shed light on the experimentally observed deposition of carbon on highly oriented pyrolytic graphite (HOPG), which occurs when hot HOPG (decorated by nanometre-sized defects) is exposed to methyl radicals. The equilibrium structures of the reaction products, together with transition structures for PAHs up to the size of phenanthroperylene, are determined using the density functionals B3LYP, TPSSh, BP86 and TPSS. The structures are analysed by computing the pi orbital axis vector (POAV) and the altitude of the reactive carbon above the molecular plane of the PAH. The strongest C-CH(3) bonds are found at the edges of the PAHs, where the s character of the C orbital involved in the bond is roughly 25 % (sp(3) hybrid orbital). Carbon atoms inside the PAH form bonds with the methyl radical through atomic orbitals with about 16 % s character in the POAV analysis. These bonds are much weaker than those at the edges of the PAH, while the reactive carbon has moved about 40 pm above the molecular plane. At the edges, the PAH carbon atoms do not leave the molecular plane to this extent. The computed barrier heights and geometrical parameters of the transition structures are in agreement with Hammond's postulate, and the relative energies of all of the equilibrium structures can be rationalized by Hückel molecular orbital (HMO) theory.     

Conformational effect of silica-supported poly(octadecyl acrylate) on molecular-shape selectivity of polycyclic aromatic hydrocarbons in RP-HPLC.

Poly(octadecyl acrylate) with a terminal reactive group was synthesized by radical telomerization in various solvents. The polymers were grafted onto porous silica for use in RP-HPLC, and the molecular recognition ability was investigated along with the selectivity for the structural isomers of polycyclic aromatic hydrocarbons. The mechanism of selectivity was also investigated with differential scanning calorimetry and NMR spectroscopic observations.     

Catalytic Deoxygenation of Xylitol to Renewable Chemicals: Advances on Catalyst Design and Mechanistic Studies

Xylitol is commonly known as one of the top platform intermediates for biomass conversion. Catalytic deoxygenation of xylitol provides an atomic and energetic efficient way to produce a variety of renewable chemicals including ethylene glycol, 1,2‐propanediol, lactic acid and 1,4‐anhydroxylitol. Despite a few initial attempts in converting xylitol into those products, improving catalyst selectivity towards C?O and C?C cleavage reactions remains a grand challenge in this area. To our best knowledge, there is lack of comprehensive review to summarize the most recent advances on catalyst design and mechanisms in deoxygenation of xylitol, offering important perspective into future development of xylitol transformation technologies. Therefore, in this mini‐review, we have critically discussed the conversion routes involved in xylitol deoxygenation over solid catalyst materials, the nanostructures of supported metal catalysts for C?H, C?C and C?O bond cleavage reactions, and mechanistic investigation for xylitol conversion. The outcome of this work provides new insights into rational design of effective deoxygenation catalyst materials for upgrading of xylitol and future process development in converting hemicellulosic biomass.     

Effect of BaO on the calcination and hydration characteristic of CA

Phosphoaluminate cement (PAC) clinker had good mechanical properties at early and long-term period. In comparison, the compressive strength of PAC clinker modified by BaO was more prominent. As primary mineral phase for PAC clinker, CA’s mineralogical structure and hydration characteristics were intimately related to the compressive strength of hardened cement paste. In this study, the effects of BaO content on the calcination, mineralogical structure and hydration characteristics of CA were investigated. Experimental results showed that the appropriate calcination temperature of CA was 1400 °C. No more than 11% (the substitution ratio of BaO for CaO) addition of BaO can promote the conversion of C₁₂A₇ to CA and increase the formation ratio of CA. Appropriate content of 7 mol% BaO could endow the hardened paste with excellent compressive strength. In CA mineral phase the high limit addition of BaO was 15 mol%. The addition of BaO decreased and even restrained the formation of C₂AH₈ and C₃AH₆ of CA hydration products and also improved the content of CAH₁₀. The addition of BaO dramatically decreased the hydration velocity and cumulative heat of CA mineral.

     

Effect of a second metal(Co,Fe, Mo and W) on performance of Ni_2P/SiO_2 for hydrodeoxygenation of methyl laurate

Ni_2P/SiO_2 and bimetallic Ni MP/Si O2(M = Co, Fe, Mo, W; Ni/M atomic ratio=5) catalysts were prepared by the temperature-programmed reduction method. The catalysts and their precursors were characterized by means of UV–Vis DRS, H_2-TPR, XRD, TEM, CO chemisorption and NH_3-TPD. Their performance for the deoxygenation of methyl laurate was tested on a fixed-bed reactor. The results show that the main phase was Ni_2 P in all catalysts, and M(M = Co, Fe, Mo, W) entered the lattice of Ni_2 P forming solid solution. Different from Fe and Co, the introduction of Mo and W into Ni_2P/SiO_2 reduced the phosphide particle size and increased the acid amount. In the deoxygenation reaction, the turnover frequency of methyl laurate increased on the catalysts in the order of NiMoP/SiO_2, Ni_2P/SiO_2, Ni WP/Si O2, NiFeP/SiO_2 and NiCoP/SiO_2, which is influenced by the size of phosphide particles and the interaction between Ni and M(M = Fe, Co, Mo or W). The introduction of the second metal(especially Mo and W) into Ni_2P/SiO_2 promoted the hydrodeoxygenation pathway. This is mainly attributed to the interaction between Ni and the second metal. Finally, the Ni MoP/SiO_2 catalyst was tested at 340 oC, 3 MPa, methyl laurate WHSV of 14 h-1and H_2/methyl laurate molar ratio of 25 for 132 h, and its deactivation took place. We found that the catalyst deactivation mainly resulted from carbonaceous deposit rather than the sintering of metal phosphide crystallites.     

Manipulating Catalytic Pathways: Deoxygenation of Palmitic Acid on Multifunctional Catalysts

The mechanism of the catalytic reduction of palmitic acid to n‐pentadecane at 260 °C in the presence of hydrogen over catalysts combining multiple functions has been explored. The reaction involves rate‐determining reduction of the carboxylic group of palmitic acid to give hexadecanal, which is catalyzed either solely by Ni or synergistically by Ni and the ZrO₂ support. The latter route involves adsorption of the carboxylic acid group at an oxygen vacancy of ZrO₂ and abstraction of the α‐H with elimination of O to produce the ketene, which is in turn hydrogenated to the aldehyde over Ni sites. The aldehyde is subsequently decarbonylated to n‐pentadecane on Ni. The rate of deoxygenation of palmitic acid is higher on Ni/ZrO₂ than that on Ni/SiO₂ or Ni/Al₂O₃, but is slower than that on H‐zeolite‐supported Ni. As the partial pressure of H₂ is decreased, the overall deoxygenation rate decreases. In the absence of H₂, ketonization catalyzed by ZrO₂ is the dominant reaction. Pd/C favors direct decarboxylation (?CO₂), while Pt/C and Raney Ni catalyze the direct decarbonylation pathway (?CO). The rate of deoxygenation of palmitic acid (in units of mmol mol_{total metal}^?1 h^?1) decreases in the sequence r_{(Pt black)}≈r_{(Pd black)}>r_{(Raney Ni)} in the absence of H₂. In situ IR spectroscopy unequivocally shows the presence of adsorbed ketene (C?C?O) on the surface of ZrO₂ during the reaction with palmitic acid at 260 °C in the presence or absence of H₂.     

Synthesis of cyclic dimeric methyl morpholinoside—a common synthetic precursor to cyclic dinucleotide analogs

An eight-step synthesis of cyclic dimeric methyl morpholinoside (c-di-MM), a common synthetic precursor to a number of cyclic dinucleotide analogs is reported. The synthesis of c-di-MM proceeds through a morpholine monomer prepared from readily available inexpensive starting materials and culminates with a key macrolactamization reaction to provide the macrocycle in 15% overall yield.     

焙烧温度对含Mg助剂的铁基催化剂F-T合成反应性能的影响

采用连续共沉淀和喷雾干燥技术相结合的方法制备了Mg助剂的Fe/Cu/K/SiO2催化剂,采用N2物理吸附、XRD、MES 和H2-TPR等表征手段,考察了焙烧温度对催化剂比表面积、体相结构和还原性能的影响。结果表明,随着焙烧温度的升高,催化剂的比表面积降低,平均孔径增大,体相中α-Fe2O3晶粒逐渐增大,催化剂变的越来越难还原,其结构更加稳定。在H2/CO （摩尔比）= 2.2、250 ℃、2.0 MPa和2 000 h－1于固定床反应器考察了焙烧温度对该催化剂F-T合成反应性能的影响,结果表明,随着焙烧温度的升高,催化剂的F-T合成反应活性降低,在运行过程中反应活性逐渐增加直至达到平稳,但达到平稳所需的诱导期越来越长;提高焙烧温度使烃产物分布向重质烃方向转移,有利于降低CH4的选择性,促进重质烃的生成。     

焙烧温度对MgAlOx复合氧化物催化甲醛和乙醛合成正丙醛反应性能的影响

采用共沉淀法制备了镁铝水滑石前驱体,通过在不同温度下焙烧得到系列MgAlO_x复合氧化物催化剂,采用XRD、TG、N₂吸附-脱附、NH₃-TPD和CO₂-TPD等技术对催化剂的物理和化学性质进行了表征,采用甲醛和乙醛缩合反应对催化剂反应性能进行了评价。结果表明,随着焙烧温度的提高,乙醛转化率以及正丙醛时空收率先增加后减少,C-550催化剂最大,分别达到39.22%和103.86 g/（kg·h）,这与催化剂中强碱和强碱数目变化趋势一致。此外,提高催化剂中强碱和强碱数目还会促进副产物甲醇和CO₂的生成。     

Synthetic studies on the dienophile unit of methyl isosartortuoate. Part 1: Assembly of the acyclic precursor

A strategically functionalized compound, as the acyclic precursor of the dienophile unit of methyl isosartortuoate has been synthesized, and its stereochemistry was also assigned.     

Reaction of palladium bisacetylacetonate with elemental phosphorus. Effect of water on the composition of palladium phosphides

Reaction of palladium bisacetylacetonate with elemental phosphorus in an inert atmosphere is shown to proceed as a redox process forming palladium phosphides of different compositions: PdP₂, Pd₅P₂, Pd_4,8P, and Pd₁₂P_3,2. The conversion of Pd(acac)₂ and the composition of palladium phosphides formed in benzene is established to be affected by water. A tentative scheme of the formation of palladium phosphides is suggested.