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. 相似文献
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. 相似文献
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.
The enforced phase‐selective solubility of polyisobutylene (PIB)‐bound RhII 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 RhII 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. 相似文献
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. 相似文献
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). 相似文献
The catalytic performance of ReOx‐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 SN2‐like attack of a hydride species at the interface between Ir and ReOx on the adsorbed Re alkoxide species. This mechanism enabled the selective dissociation of the C–O bond neighboring the CH2OH group. 相似文献
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. 相似文献
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. 相似文献
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. 相似文献