Cu-Cr-Ca-Ba催化剂上糠醛加氢制备2-甲基呋喃

采用固定床反应器,研究了Cu Cr Ca Ba催化剂上糠醛常压选择加氢制2 甲基呋喃的反应.详细考察了反应条件对催化性能的影响.结果表明,添加Ca Ba助剂显著提高了催化剂对目的产物的选择性,Cu Cr Ca Ba催化剂在200～220℃,液时空速0.2～0.6h-1,氢醛摩尔比6～16的条件下,具有良好的活性和选择性,糠醛转化率 99.8%,2 甲基呋喃选择性 90.3%.     

镍基催化剂：制备及水相催化糠醛加氢脱氧反应性能

以SiO₂-Al₂O₃、γ-Al₂O₃为载体采用浸渍法制备了不同负载量的镍基催化剂,以XRD、H₂-TPR、NH₃-TPD与低温N₂吸附等技术对催化剂特性进行了表征,并进行了水相催化糠醛加氢脱氧实验研究以制备以C₅为主要成分的生物汽油。重点考察了催化剂的镍负载量、载体种类及反应温度对糠醛转化率、目标产物C₅选择性的影响,并对催化剂的重复利用性能和糠醛水相加氢脱氧反应机理进行了探讨。结果表明,Ni/SiO₂-Al₂O₃催化性能明显优于Ni/γ-Al₂O₃。在140 ℃、氢冷压3.0 MPa的优化反应条件下,14wt% Ni/SiO₂-Al₂O₃催化糠醛反应的转化率为63%,C₅选择性高达93%。升高反应温度可以提高糠醛的转化率,但反应产物的选择性降低。催化剂在第3次重复使用时糠醛的转化率明显降低,催化剂表面有明显的残留有机聚合物和积碳,达到25wt%左右。     

不同方法制备的Cu-Cr/γ-Al2O3的结构及其对糠醛加氢制2-甲基呋喃反应的催化性能

 利用普通浸渍法、共沉淀法和溶剂化金属原子浸渍法制备了一系列Cu－Cr／γ－Al2O3催化剂，并用X射线衍射、扫描电镜、透射电镜和X射线光电子能谱等技术对这些催化剂进行了表征．结果表明，不同方法制备的催化剂的金属粒度的顺序为溶剂化金属原子浸渍法＜共沉淀法＜普通浸渍法；金属还原程度的顺序为溶剂化金属原子浸渍法＞普通浸渍法≈共沉淀法．糠醛加氢反应实验结果表明，催化活性顺序为溶剂化金属原子浸渍法＞普通浸渍法＞共沉淀法；生成2－甲基呋喃选择性顺序为共沉淀法＞普通浸渍法＞溶剂化金属原子浸渍法．     

Synthesis of g-butyrolactone and 2-methylfuran through the coupling of dehydrogenation and hydrogenation over copper-chromite catalyst

The new coupling process of the dehydrogenation of 1,4-butanediol (BDO) and the hydrogenation of furfural (FFA) over a copper-chromite catalyst was carried out in a continuous fixed-bed reactor. The effects of the reaction conditions on the coupling process were investigated in detail. The results show that the coupling process has some advantages over the individual dehydrogenation and hydrogenation ones, such as optimal hydrogen utilization, good energy efficiency, improved yield and mild reaction condition. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of Mo2C loading and H2S concentration on Mo2C/Al2O3 catalyst applied in sulfur‐resistant methanation

Mo₂C/Al₂O₃ catalyst was prepared by the impregnation method with urotropine and ammonium paramolybdate. The catalytic effect of Mo₂C as a typical transition‐metal carbide in sulfur‐resistant methanation was studied. The catalysts prepared were characterized by N₂ adsorption–desorption, X‐ray diffraction, transmission electron microscopy, H₂‐temperature‐programmed reduction, and Raman spectra, with the results confirming the formation of β‐molybdenum carbide on the surface of the catalysts. Studies on catalysts with different loading doses indicate that the optimal loading of Mo₂C/Al₂O₃ is about 15 wt.%, which enables CO conversion rate of up to 47%, with methane selectivity of up to 53%. This work further explored the effect of different concentrations of H₂S in the raw gas on the performance of the catalyst, with the results showing that high concentration of H₂S (>1500 ppm) can lead to sulfuration of active species on the catalyst, while resulting in a decrease in the catalytic activity.     

On the interaction of Mo and Mo2 with NH3, C2H4, and C3H6

The reactivity of Mo and Mo₂ with ammonia, ethene, and propene molecules has been investigated by using Density Functional Theory. Different gradient‐corrected and hybrid exchange‐correlation functionals have been employed. Coordination modes, binding energies, geometrical structures, vibrational frequencies have been computed and compared with the available experimental counterparts. The results obtained show that the molybdenum atom is able to react with C₂H₄ and C₃H₆, and binds weakly with NH₃. The dimer Mo₂ gives a stable complexes with ammonia, ethene, and propene. For the Mo₂NH₃ complex, all the employed levels of theory give binding energies in good agreement with the experimental value, while in the case of the MoC₂H₄ system, the use of model core potentials coupled with gradient‐corrected exchange‐correlation functionals overestimates the binding energies. For MoC₃H₆, Mo₂C₂H₄, and Mo₂C₃H₆ we predict a binding energy of 14–15, 20–24, and 18–20 kcal/mol, respectively. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1557–1564, 2001     

Energetic and topological analysis of the reaction of Mo and Mo2 with NH3, C2H2, and C2H4 molecules

The Density functional theory has been applied to characterize the structural features of Mo(1,2)-NH(3),-C(2)H(4), and -C(2)H(2) compounds. Coordination modes, geometrical structures, and binding energies have been calculated for several spin multiplets. It has been shown that in contrast to the conserved spin cases (Mo(1,2)-NH(3)), the interaction between Mo (or Mo(2)) and C(2)H(4) (or C(2)H(2)) are the low-spin (Mo-C(2)H(4) and -C(2)H(2)) and high-spin (Mo(2)-C(2)H(4) and -C(2)H(2)) complexes. In the ground state of Mo(1,2)-C(2)H(4) and -C(2)H(2), the metal-center always reacts with the C-C center. The spontaneous formation of the global minima is found to be possible due to the crossing between the potential energy surfaces (ground and excited states with respect to the metallic center). The bonding characterization has been performed using the topological analysis of the Electron Localization Function. It has been shown that the most stable electronic structure for a pi-acceptor ligand correlates with a maximum charge transfer from the metal center to the C-C bond of the unsaturated hydrocarbons, resulting in the formation of two new basins located on the carbon atoms (away from hydrogen atoms) and the reduction of the number of attractors of the C-C basin. The interaction between Mo(1,2) and C(2)H(4) (or C(2)H(2)) should be considered as a chemical reaction, which causes the multiplicity change. Contrarily, there is no charge transfer between Mo(1,2) and NH(3), and the partners are bound by an electrostatic interaction.     

Hydrodeoxygenation of benzofuran over sulfided and reduced Ni–Mo/γ-Al2O3 catalysts: Effect of H2S

Effect of H₂S on the catalytic performance of the reduced and sulfided Ni–Mo/Al₂O₃ catalysts in hydrodeoxygenation of benzofuran is studied. The steady-state reaction experiments showed a decrease in activity for both reduced and sulfided catalysts when H₂S was introduced into the feed. The reaction conversion of benzofuran over the reduced catalyst still remained superior to that of the sulfided catalyst in the presence of H₂S, however, at high reaction temperatures, the product distribution over the pre-reduced catalyst is similar to the sulfided catalyst. The studies with temperature-programmed desorption (TPD), temperature-programmed reaction (TPRxn) and X-ray photoelectron spectroscopy (XPS) techniques showed a partial sulfidation of the reduced catalysts when exposed to H₂S under reaction conditions, however, the catalyst does not go through a complete conversion to a molybdenum sulfide phase. Instead oxygen–sulfur exchange on the surface leaves behind oxisulfide species, with catalytic activity closely resembling that of the reduced catalysts. The effect of H₂S on the reaction performance is mainly coming from the competitive adsorption between H₂S and benzofuran and the formation of SH groups with decomposition of H₂S at high temperatures.     

掺Cu对MoO3-TiO2/SiO2上光促甲烷和水表面反应的影响

 在固定床环隙反应器中,借助紫外光的激发,气相甲烷和水在MoO3-TiO2/SiO2催化剂表面生成了甲醇和氢气,当在催化剂中掺杂Cu2+后,光催化剂的活性明显提高. XRD,IR,UVDRS和TPD的研究结果表明,在催化剂表面形成了具有Mo-O-Ti和Mo-O-Cu基元的高度分散物种,不但使得吸光带边明显蓝移,而且扩展了催化剂的光响应范围. 所形成的复合结构还可以优化单组分的吸光性能并促进对反应物分子的吸附活化,同时可以有效地转移光生电子和空穴. 掺杂Cu2+能够进一步延长光生电子-空穴对的寿命,进而提高反应的量子产率.     

Synthesis,Crystal Structure,and Bonding of (PCl4)2[Mo2Cl10], the First Compound in Mo–P–Cl System

An ampule reaction between Mo and PCl₅ at 200 °C yielded (PCl₄)₂[Mo₂Cl₁₀], the first ternary compound in Mo–P–Cl system. Single crystal X-ray diffraction gave a triclinic unit cell: a = 6.870(1), b = 8.892(2), c = 9.423(2) Å, α = 100.24(2), β = 95.55(2), γ = 96.12(2)° (V = 559.3(2) ų, Z = 1, sp. gr. P1, wR₂ = 0.0575 and R₁ = 0.0279. The ionic compound is built from edge sharing bioctahedra [Mo₂Cl₁₀]^2– and two tetrahedra PCl₄⁺. The averaged Mo–Cl_b distance, 2.503(1) Å, is longer than the Mo–Cl_t distance, 2.33(2) Å. The Mo … Mo distance, 3.77 Å, indicates the absence of a direct Mo–Mo interaction. Semiempirical and ab initio calculations showed the possibility for [Mo₂Cl₁₀]^2– to exist with long and short Mo to Mo distances, the letter corresponding to the Mo–Mo bond.     

反应条件对Mo2C/Al2O3催化的POM制合成气的影响

考察了反应温度、气体空速和进料中CH4：O2比值对Mo2C／Al2O3催化的POM反应制合成气的影响．结果发现较高的温度具有较高的甲烷转化率、CO和H2的选择性；而在较低的温度下，对CO的选择性比对H2的影响更大．反应气体的空速较小时对于甲烷的转化率、CO和H2的选择性是有利的；而在较高的气体空速下，氢气的选择性则更低．进料中CH4：O2比值稍高于2：1时有利于获得高的甲烷转化率、CO和H2的选择性．并且还可以增加催化剂的稳定性．当CH4：O2比值低于2：1时．甲烷转化率、CO和H2选择性随反应的进行急剧下降．而当此比值调整到高于2：1时．转化率和选择件都可以得到恢复。     

Relationship between the molybdenum phases and the conversion of n-butane over Mo/HZSM-5

The conversion of n-C₄H₁₀ was undertaken on MoO₃/HZSM-5 catalyst at 773–973 K and the phases of molybdenum species were detected by XRD. The XRD results show that bulk MoO₃ on HZSM-5 can be readily reduced by n-C₄H₁₀ to MoO₂ at 773 K and MoO₂ can be gradually carburized to molybdenum carbide above 813 K. The molybdenum carbide formed from the carburization of MoO₂ with n-C₄H₁₀ below 893 K is -MoC_1−x with fcc-structure, while hcp-molybdenum carbide formed above 933 K. During the evolution of MoO₃ to MoO₂ (>773 K) or the carburization of MoO₂ to molybdenum carbide (>813 K), deep oxidation, cracking and coke deposition are serious, in particular at higher reaction temperatures, these lead to the poor selectivity to aromatics. Aromatization of n-C₄H₁₀ can proceed catalytically on both Mo₂C/HZSM-5 and MoO₂/HZSM-5, the distribution of the products for the two catalysts is similar below 813 K, but the activity for Mo₂C/HZSM-5 is much higher than that for MoO₂/HZSM-5.     

Zn/SiO_2气相催化裂解1,1,2-三氯乙烷脱HCl:酸性与失活

用浸渍法制备了一系列SiO_2负载的过渡金属催化剂M/SiO_2(M为第Ⅳ周期过渡金属),用于气相催化裂解1,1,2-三氯乙烷(TCE)脱HCl的反应。研究发现,在M/SiO_2催化剂中,Zn/SiO_2催化性能最好,TCE转化率能达到98%,顺-1,2-二氯乙烯(cis-DCE)的选择性为82%。随着Zn负载量的增加,Zn/SiO_2催化剂上TCE转化率逐渐增加,与催化剂上总酸量变化一致。将总酸量以Zn负载量归一化得到比酸量,则比酸量越大,Zn/SiO_2催化剂比活性越高,表明Zn/SiO_2催化剂表面酸性中心是TCE脱氯反应的活性中心。Zn/SiO_2催化剂在TCE脱HCl反应中存在一定的失活现象,归因于反应过程中催化剂表面积炭。低Zn负载量催化剂上会产生较多积炭,归因于其具有较多强酸性中心,表明催化剂表面强酸中心是导致催化剂积炭和失活的主要原因。     

Synthesis,Structure, Bonding,and Reactivity of Metal Complexes Comprising Diborane(4) and Diborene(2): [{Cp*Mo(CO)2}2{μ‐η2:η2‐B2H4}] and [{Cp*M(CO)2}2B2H2M(CO)4], M=Mo,W

The reaction of [(Cp*Mo)₂(μ‐Cl)₂B₂H₆] ( 1 ) with CO at room temperature led to the formation of the highly fluxional species [{Cp*Mo(CO)₂}₂{μ‐η²:η²‐B₂H₄}] ( 2 ). Compound 2, to the best of our knowledge, is the first example of a bimetallic diborane(4) conforming to a singly bridged C_s structure. Theoretical studies show that 2 mimics the Cotton dimolybdenum–alkyne complex [{CpMo(CO)₂}₂C₂H₂]. In an attempt to replace two hydrogen atoms of diborane(4) in 2 with a 2e [W(CO)₄] fragment, [{Cp*Mo(CO)₂}₂ B₂H₂W(CO)₄] ( 3 ) was isolated upon treatment with [W(CO)₅?thf]. Compound 3 shows the intriguing presence of [B₂H₂] with a short B?B length of 1.624(4) Å. We isolated the tungsten analogues of 3 , [{Cp*W(CO)₂}₂B₂H₂W(CO)₄] ( 4 ) and [{Cp*W(CO)₂}₂B₂H₂Mo(CO)₄] ( 5 ), which provided direct proof of the existence of the tungsten analogue of 2 .     

基于一氧化碳、二氧化碳和氧气分子吸附为探针的碳化钼、碳化钨、氮化钼和氮化钨的表面化学性质：密度泛函理论分析

作为具有吸引力的电极材料,过渡金属碳化物与氮化物被应用在许多电化学储能及能量转换领域. 本工作中,通过密度泛函理论计算,以及一氧化碳 （CO）, 二氧化碳（CO₂）和 氧气（O₂）分子的吸附来表征钼和钨的碳化物及氮化物,如碳化钼（Mo₂C）、碳化钨（W₂C）、氮化钼（Mo₂N）和氮化钨（Mo₂C）的表面化学性质. 这些探针分子可为研究钼和钨的碳化物及氮化物表面在酸性/碱性的氧化还原性质提供衡量方法. 计算结果表明,CO₂分子的吸附发生在路易斯碱位,其碱性降低顺序为α-W₂C(001) > α-W₂N(001) > β-Mo₂C(001) > γ-Mo₂N(100). 此外,CO和O₂分子吸附可用于评估上述碳化物及氮化物的还原能力,其还原性减小顺序为β-W₂C(100) > α-Mo₂C(100) > α-W₂N(001) > α-W₂C(001) > β-Mo₂C(001) > γ-Mo₂N(100). 由于还原本性,使得上述这些碳化物和氮化物成为在各种催化反应中有可能取代贵金属的良好候选材料.     

Energetic and topological analyses of the oxidation reaction between Mo(n) (n = 1, 2) and N2O

The interaction between molybdenum, atom, and dimer, with nitrous oxide has been investigated using density functional theory. The analysis of the potential energy surfaces for both reactions has revealed that a single molybdenum atom can activate the N--O bond of N2O requiring a small activation energy. However, the presence of several intersystem crossings between three different spin states, namely, septet, quintet and triplet states, seems to be the major constraint to the Mo + N2O reaction. Contrarily, the low-lying excited states (triplet and quintet) do not participate in the reaction between the molybdenum dimer and N2O. The latter reaction fully evolves on the singlet spin surface. Three different regions have been distinguished along the pathway: formation of an adduct complex, formation of an inserted compound, and the N2 detachment. The connection between the two first regions has been characterized by the formation of a special complex in which the N--O bond is so weakened that it could be considered as a first step in the insertion process. It has been shown that the topological changes along the pathways provide a clear explanation for the geometrical changes that occur along the reaction pathway. In summary, the detachment of the N2 molecule is found to be kinetically an effective process for both reactions, owing to the high exothermicity and consequently to the high internal energy of the insertion intermediates. However, in the case of Mo atom, the reaction should be a slow process due to the presence of spin-forbidden transitions. These results fully agree with previous experimental works.     

Preparation and crystal structure of the Isotypic Carbides Ln4Ni2C5 (Ln = Er,Tm, Yb and Lu)

The title compounds were prepared from the elemental components in a lithium flux. Their crystal structure was determined for the ytterbium compound from single-crystal X-ray data. It is orthorhombic, Pmm2, a = 352.88(6) pm, b = 1 143.0(3) pm, c = 366.16(6) pm, Z = 1, R = 0.020 for 1 261 structure factors and 29 variable parameters. The structure may be viewed as an intergrowth of slabs consisting of the CeNiC₂ and the ScC (NaCl type) structures. It thus contains C₂ pairs with a C? C distance of 138(1) pm and isolated carbon atoms. Together with the nickel atoms the C₂ pairs form one-dimensionally infinite building elements [Ni₂C₄]_n. The fifth carbon atom is octahedrally coordinated by ytterbium atoms. Accordingly the compound may be rationalized to a first approximation with the formula (Yb³⁺)₄[Ni₂C₄^8?]C^4?. Yb₄Ni₂C₅ shows Curie-Weiss behaviour with a magnetic moment of μ_exp = 4.44 μ_B per ytterbium atom in good agreement with the theoretical moment of μ_eff = 4.53 μ_B for Yb³⁺.     

Hydrogen‐Permeable Tubular Membrane Reactor: Promoting Conversion and Product Selectivity for Non‐Oxidative Activation of Methane over an Fe©SiO2 Catalyst

Non‐oxidative methane conversion over Fe©SiO₂ catalyst was studied for the first time in a hydrogen (H₂) permeable tubular membrane reactor. The membrane reactor is composed of a mixed ionic–electronic SrCe_0.7Zr_0.2Eu_0.1O_3?δ thin film (≈20 μm) supported on the outer surface of a one‐end capped porous SrCe_0.8Zr_0.2O_3?δ tube. Significant improvement in CH₄ conversion was achieved upon H₂ removal from the membrane reactor compared to that in a fixed‐bed reactor. The Fe©SiO₂ catalyst in the H₂ permeable membrane reactor demonstrated a stable ≈30 % C₂₊ single‐pass yield, with up to 30 % CH₄ conversion and 99 % selectivity to C₂ (ethylene and acetylene) and aromatic (benzene and naphthalene) products, at the tested conditions. The selectivity towards C₂ or aromatics was manipulated purposely by adding H₂ into or removing H₂ from the membrane reactor feed and permeate gas streams.