Ethanol conversion to aromatic hydrocarbons over several zeolite catalysts

Summary H-ZSM-5 (Si/Al₂ = 29) zeolite showed especially high activity in the conversion of ethanol to BTX (benzene, toluene, xylenes), while other zeolites exclusively formed ethylene. Noble metal catalysts supported on H-ZSM-5 (29) zeolite have high activity for the formation of BTX. Of these, Au/H-ZSM-5 catalyst can partially inhibit carbon deposition during the reaction, thus maintaining constant catalytic activity for BTX formation.     

竹浆纤维素转化制低碳多元醇反应中有机氮对金属催化剂稳定性影响的研究

采用等体积浸渍法制备了一系列多孔竹炭负载的有机氮掺杂的镍钨催化剂,并将其应用于催化竹浆纤维氢解制C_2,3多元醇反应。有机氮源与催化剂前驱体中Ni²⁺络合,高温煅烧时载体表面碳、氮和金属离子相互作用后生成一定量的C₃N₄、氮化物和合金物相。通过XRD、XPS和TEM等表征手段分析了催化剂Ni-W/MBC表面物理化学性质与催化活性间的关系。结果表明,除了金属镍、氧化钨物相外,表面还含有Ni-W合金（NiWO₄为主）;金属粒子表面包围了一层石墨化C₃N₄物相。XPS分析表明,有机氮源高温分解反应后形成了C₃N₄物相。在反应条件下,15% Ni-20% W/MBC@M-0.25催化剂得到乙二醇收率为55.8%,而未添加有机氮源的催化剂15% Ni-20% W/MBC获得的乙二醇收率仅为36.9%。催化剂稳定性实验结果表明,Ni-W合金和C₃N₄物相的形成显著增强了Ni-W/MB催化剂的稳定性,延长了催化剂寿命。     

不同钨基催化剂上葡萄糖和纤维二糖催化转化制备乙二醇

以葡萄糖和纤维二糖为模型化合物研究了逆羟醛缩合速率与加氢速率之间的匹配对纤维素转化产物分布的影响。葡萄糖和纤维二糖在共浸渍的Ni-WO₃/SBA-15催化剂和物理混合的Ni/SBA-15、WO₃/SBA-15催化剂上具有不同的产物分布。葡萄糖和纤维二糖在不同钨基催化剂上具有不同的乙二醇收率,其顺序为WO₃ < WO₃/SBA-15 < (NH₄)₆W₇O₂₄·6H₂O (偏钨酸铵),这与它们的颗粒粒径成反比。在相同钨基催化剂用量条件下,葡萄糖转化中乙二醇收率小于纤维二糖。     

A Useful,Reliable and Safer Protocol for Hydrogenation and the Hydrogenolysis of O‐Benzyl Groups: The In Situ Preparation of an Active Pd0/C Catalyst with Well‐Defined Properties

A simple, highly reproducible protocol for the hydrogenation of alkenes and alkynes and for the hydrogenolysis of O‐benzyl ethers has been developed. The method features the in situ preparation of an active Pd⁰/C catalyst from Pd(OAc)₂ and charcoal, in methanol. The mild reaction conditions (25 °C) and low catalyst loading required (0.025 mol %), as well as the absence of contamination of the product by palladium residues (<4 ppb), make this a sustainable, useful process for organic chemists. Alternatively, the protocol can be carried out under microwave activation, to shorten the reaction times, with cyclohexene as the hydrogen source.     

Nanoparticle‐Supported and Magnetically Recoverable Ruthenium Hydroxide Catalyst: Efficient Hydration of Nitriles to Amides in Aqueous Medium

Magnetic attraction not filtration : A magnetic nanoparticle‐supported ruthenium hydroxide catalyst (see figure) was readily prepared from inexpensive starting materials and shown to catalyze the hydration of nitriles with excellent yield in a benign aqueous medium. Catalyst recovery using an external magnetic field, superior activity, and the inherent stability of the catalyst system are additional sustainable attributes of this protocol.

     

自还原双功能催化剂催化木质纤维素生物质氢解制低碳多元醇的研究

利用生物碳源在煅烧过程中产生的还原性气体还原金属氧化物来制备自还原型双功能催化剂Ni-W/SBA-15,将其直接应用于催化木质纤维素生物质氢解制备低碳多元醇,省去了催化剂还原步骤。TG和XRD结果表明,制备过程中引入的蔗糖含量为3.0 g时,催化剂中被还原的活性金属含量最高;随着Ni含量的增加,镍粒子逐渐增大;W物种为非晶态。SEM和TEM分析表明,SBA-15均匀地负载Ni、W粒子,且粒径小、分散性好。在自还原型催化剂10%Ni-15%W/SBA-15催化作用下,在反应温度为240℃、氢压为5.0 MPa和反应时间为6 h的条件下,微晶纤维素完全转化,低碳多元醇的收率达68.14%;当以小麦秸秆粉作为反应物时,转化率为85.32%,低碳多元醇总收率为44.71%。     

Using Soluble Polymers to Enforce Catalyst‐Phase‐Selective Solubility and as Antileaching Agents to Facilitate Homogeneous Catalysis

The enforced phase‐selective solubility of polyisobutylene (PIB)‐bound Rh^II catalysts in biphasic heptane/acetonitrile mixtures can be used not only to recycle these catalysts but also to minimize bimolecular reactions with ethyl diazoacetate. When cyclopropanation and O? H insertion reactions are carried out with PIB‐bound Rh^II catalysts either with or without addition of an unfunctionalized hydrocarbon polymer cosolvent, dimer by‐product formation is suppressed even without slow syringe pump addition of the ethyl diazoacetate. This suppression of by‐product formation is shown to be due to increased phase segregation of the soluble polymer‐bound catalyst and the ethyl diazoacetate reactant. These studies also reveal that added hydrocarbon polymer cosolvents can function as antileaching agents, decreasing the already small amount of a soluble polymer‐bound species that leaches into a polar phase in a biphasic mixture during a liquid/liquid separation step.     

Direct and Oriented Conversion of CO2 into Value-Added Aromatics

The oriented conversion of CO₂ into target high-value chemicals is an effective way to reduce carbon emissions, but still presents a challenge. In this communication, we report the oriented conversion of CO₂ into value-added aromatics, especially para-xylene, in a single pass by combining core–shell structured Zn-doped H-ZSM-5 (Zn-ZSM-5@SiO₂) and a Cr₂O₃ component. Through precise regulation of the acidity of Zn-ZSM-5@SiO₂, high para-xylene selectivity (38.7 % in the total products) at a CO₂ conversion of 22.1 % was achieved. Furthermore, a CO₂-assisted effect in the synthesis of aromatics during the tandem process has been clarified through a control experiment. The CO₂ reactant can act as a hydrogen acceptor to accelerate the dehydrogenation of alkenes, intermediates in the synthesis of aromatics, thereby increasing the driving force towards aromatics in the tandem reaction process.     

Interfacial impregnation chemistry in the synthesis of nickel catalysts supported on titania

The interfacial chemistry of the impregnation step involved in the preparation of nickel catalysts supported on titania is presented. Several methodologies based on deposition data, pH measurements, potentiometric mass titrations, and microelectrophoresis have been used in conjunction with diffuse reflectance UV/Vis/NIR spectroscopy, simulations, and semiempirical quantum chemical calculations. Three mononuclear inner-sphere complexes were formed at the compact layer of the "titania/electrolyte solution" interface: A monosubstituted, dihydrolyzed complex above a terminal oxo group, a disubstituted, dihydrolyzed complex above two terminal adjacent oxo groups, and a disubstituted, nonhydrolyzed complex above one terminal and one bridging adjacent oxo groups. The monosubstituted, dihydrolyzed complex predominates. The contribution of the disubstituted configurations is also important at very low Ni(II) surface concentration, but it decreases as the Ni(II) surface concentration increases. In addition, bi- and trinuclear inner-sphere complexes were formed. The receptor site involves one bridging and two terminal oxo groups in the first case and two bridging and three terminal oxo groups in the second case. The relative surface concentrations of these configurations increase initially with Ni(II) surface concentration and then remain practically constant. The understanding of these interfacial processes at a molecular level is very important to shift the catalytic synthesis from an art to a science as well as to obtain strict control of the impregnation step and, to some extent, of the whole preparative sequence. This study is very relevant to the synthesis of submonolayer/monolayer nickel catalysts supported on TiO(2) following equilibrium deposition filtration (otherwise called equilibrium adsorption).     

Role of Re Species and Acid Cocatalyst on Ir‐ReOx/SiO2 in the C–O Hydrogenolysis of Biomass‐Derived Substrates

The catalytic performance of ReO_x‐modified Ir metal catalyst in the hydrogenolysis of C–O bonds is strongly dependent on the choice of solvent. The acidic property of the Re species becomes obvious in the alkane solvent, and the hydrogenolysis reaction proceeds mainly by acid‐catalyzed dehydration and the subsequent metal‐catalyzed hydrogenation. The acidic property of the Re species is weakened in water; however, the hydrogenolysis reaction proceeds in water via a direct mechanism involving S_N2‐like attack of a hydride species at the interface between Ir and ReO_x on the adsorbed Re alkoxide species. This mechanism enabled the selective dissociation of the C–O bond neighboring the CH₂OH group.     

Hydrogenolysis of Furfuryl Alcohol to 1,2-Pentanediol Over Supported Ruthenium Catalysts

Hydrogenolysis of the furan rings of furfural and furfuryl alcohol, which can be obtained from biomass, has attracted attention as a method for obtaining valuable chemicals such as 1,2-pentanediol. In this study, we examined the hydrogenolysis of furfuryl alcohol to 1,2-pentanediol over Pd/C, Pt/C, Rh/C, and various supported Ru catalysts in several solvents. In particular, we investigated the effects of combinations of solvents and supports on the reaction outcome. Of all the tested combinations, Ru/MgO in water gave the best selectivity for 1,2-pentanediol: with this catalyst, 42 % selectivity for 1,2-pentanediol was achieved upon hydrogenolysis of furfuryl alcohol for 1 h at 463 K. In contrast, reaction in water in the presence of Ru/Al₂O₃ afforded cyclopentanone and cyclopentanol by means of hydrogenation and rearrangement reactions.     

Pickering Interfacial Catalysis for Biphasic Systems: From Emulsion Design to Green Reactions

Pickering emulsions are surfactant‐free dispersions of two immiscible fluids that are kinetically stabilized by colloidal particles. For ecological reasons, these systems have undergone a resurgence of interest to mitigate the use of synthetic surfactants and solvents. Moreover, the use of colloidal particles as stabilizers provides emulsions with original properties compared to surfactant‐stabilized emulsions, microemulsions, and micellar systems. Despite these specific advantages, the application of Pickering emulsions to catalysis has been rarely explored. This Minireview describes very recent examples of hybrid and composite amphiphilic materials for the design of interfacial catalysts in Pickering emulsions with special emphasis on their assets and challenges for industrially relevant biphasic reactions in fine chemistry, biofuel upgrading, and depollution.     

Stabilizing catalytic pathways via redundancy: selective reduction of microalgae oil to alkanes

A new route to convert crude microalgae oils using ZrO(2)-promoted Ni catalysts into diesel-range alkanes in a cascade reaction is presented. Ni nanoparticles catalyze the selective cleavage of the C-O of fatty acid esters, leading to the hydrogenolysis of triglycerides. Hydrogenation of the resulting fatty acids to aldehydes (rate-determining step) is uniquely catalyzed via two parallel pathways, one via aldehyde formation on metallic Ni and the second via a synergistic action by Ni and ZrO(2) through adsorbing the carboxylic groups at the oxygen vacancies of ZrO(2) to form carboxylates and subsequently abstracting the α-hydrogen atom to produce ketene, which is in turn hydrogenated to aldehydes and decarbonylated on Ni nanoparticles.