RESUMEN
Chemoselective hydrogenation of 3-nitrostyrene to 3-vinylaniline is quite challenging because of competitive activation of the vinyl group and the nitro group over most supported precious-metal catalysts. A precatalyst comprised of thiolated Au25 nanoclusters supported on ZnAl-hydrotalcite yielded gold catalysts of a well-controlled size (ca. 2.0â nm)-even after calcination at 500 °C. The catalyst showed excellent selectivity (>98 %) with respect to 3-vinylaniline, and complete conversion of 3-nitrostyrene over broad reaction duration and temperature windows. This result is unprecedented for gold catalysts. In contrast to traditional catalysts, the gold catalyst is inert with respect to the vinyl group and is only active with regard to the nitro group, as demonstrated by the results of the control experiments and attenuated total reflection infrared spectra. The findings may extend to design of gold catalysts with excellent chemoselectivity for use in the synthesis of fine chemicals.
RESUMEN
Ultrathin iridium nanowires have been synthesized using a convenient method mediated by microemulsion via oriented attachment growth for the first time. The interconnected polycrystalline Ir nanowires possess high aspect ratio, small average diameter of 2 nm, and length up to several hundred nanometers. The 1D growth of surfactant-encapsulated primary nanoparticles, which is determined by the inherent crystal growth habit and the specific interactions of nanocrystals with surfactant molecules, accounts for the formation of Ir nanowires. The as-prepared Ir nanowires show high activity and selectivity toward the hydrogenation production of industrially valuable chloroaniline from o-chloronitrobenzene. Theoretical evidence based on DFT calculation indicates that H2 could be dissociated more easily and quickly on Ir(100) surface than on Ir(111), accounting for the higher hydrogenation rate over Ir nanowires exposing both (200) and (111) crystal facets rather than only (111) facet for Ir nanoparticles.
RESUMEN
The stability of Rh-based heterogeneous catalysts is a key issue in the hydroformylation of olefins. Confinement of active Rh species has been considered an effective strategy to achieve stable catalysts. In this work, a phosphine ligand was successfully confined in ZIF-8 material and coordinated with Rh metal by a reduction procedure to develop an efficient and stable Rh-based catalyst for hydroformylation of 1-octene. The results indicate that the catalyst reduced at 300 °C under H2 atmosphere exhibits better stability than that with NaBH4 as reductant and undoped P catalyst. Various characterization studies demonstrate that the superior performance is due to the strong interaction between Rh metal and P, which inhibits the leaching of active Rh species. This work reveals an effective strategy for the synthesis of highly stable catalysts for use in the hydroformylation reaction.
RESUMEN
1-Butene, as one of the widely used chemical raw materials, can be produced by the double bond isomerization of 2-butene. However, the current yield of the isomerization reaction is only up to 20% or so. It is therefore an urgent issue to develop novel catalysts with higher performances. In this work, a high-activity ZrO2@C catalyst that is derived from UiO-66(Zr) is fabricated. The catalyst is prepared by calcining the precursor UiO-66(Zr) at high temperature in nitrogen, and characterized by XRD, TG, BET, SEM/TEM, XPS and NH3-TPD. The results demonstrate that the calcination temperature has significant influences on the catalyst structure and performance. Regarding the catalyst ZrO2@C-500, the selectivity and yield of 1-butene are 94.0% and 35.1%, respectively. The high performance is due to multiple aspects, including the inherited octahedral morphology from parent UiO-66(Zr), suitable medium-strong acidic active sites and high surface area. The present work will lead to a better understanding of the ZrO2@C catalyst and guide the rational design of high-activity catalysts for the double bond isomerization of 2-butene to 1-butene.
RESUMEN
Chemoselective hydrogenation of quinoline and its derivatives under mild reaction conditions still remains a challenging topic, which requires a suitable interaction between reactants and a catalyst to achieve high performance and stability. Herein, FePO4-supported Rh single atoms, subnano clusters and nanoparticle catalysts were synthesized and evaluated in the chemoselective hydrogenation of quinoline. The results show that the Rh subnano cluster catalyst with a size of â¼1 nm gives a specific reaction rate of 353 molquinoline molRh-1 h-1 and a selectivity of >99% for 1,2,3,4-tetrahydroquinoline under mild conditions of 50 °C and 5 bar H2, presenting better performance compared with the Rh single atoms and nanoparticle counterparts. Moreover, the Rh subnano cluster catalyst exhibits good stability and substrate universality for the hydrogenation of various functionalized quinolines. A series of characterization studies demonstrate that the acidic properties of the FePO4 support favors the adsorption of quinoline while the Rh subnano clusters promote the dissociation of H2 molecules, and then contribute to the enhanced hydrogenation performance. This work provides an important implication to design efficient Rh-based catalysts for chemoselective hydrogenation under mild conditions.
RESUMEN
Supported metal catalysts play a significant role in heterogeneous catalysis in liquid phase reaction systems, but they usually suffer from a stability problem. Encapsulation of active metal species without the compromise of catalytic performance has been considered as an effective strategy. Here, we report an ultrastable Ru-based catalyst with particle size of around 1.1 nm for selective hydrogenation reaction. The highly dispersed Ru species are covered by the in situ formed porous N-C-ZnO overlayer, which is induced through the transforming of ZIF-8 shell that derives from a ZnO substrate. The resulting Ru/ZnO@N-C-ZnO catalyst can exhibit good stability in the hydrogenation of p-chloronitrobenzene after 20 cyclic runs with 100% selectivity toward p-chloroaniline. Comparatively, the naked Ru/ZnO catalyst with larger Ru particles shows serious metal leaching issue with inferior stability and poor selectivity. It is revealed that the excellent performance of Ru/ZnO@N-C-ZnO is attributed to the porous overlayer, which strengthens the bonding of Ru nanoparticles on ZnO.
RESUMEN
Hydroformylation of olefins is one of the most important industrial processes for aldehyde production. Therein, the leaching of active metals for heterogeneous catalysts is an important issue in the hydroformylation reaction, particularly for higher olefins to produce higher alcohols. Here, different Rh/ZnO catalysts with diverse ZnO as a support were investigated and a home-made ZnO50 support was selected to prepare the Rh/ZnO50@ZIF-8 core-shell structure catalyst, which was synthesized by the growth of ZIF-8 with ZnO50 as the sacrificed template to afford Zn source. Compared with the Rh/ZnO50 catalyst, the Rh/ZnO50@ZIF-8 catalyst demonstrated a better cyclic stability in the hydroformylation of 1-dodecene. Combining the experiment and characterization results, it was concluded that the ZIF-8 shell on the Rh/ZnO50 catalyst effectively prevented the leaching of metal Rh into the reaction solution. Moreover, the Rh/ZnO50@ZIF-8 catalyst exhibited good universality for other higher olefins. This work provides a useful guideline for immobilizing the active species in heterogeneous catalysts for the hydroformylation reaction.
RESUMEN
Gold nanoparticles have a high activity for CO oxidation, making them suitable to be used in a CO2 laser which maintains its efficiency and stability via the recombination of CO and O2 produced by the CO2 decomposition. However, the high concentration of CO2 in the working environment greatly reduces the activity of the catalyst and makes the already unstable gold nanoparticles even more so. A novel Au/Ce-Co-O x /Al2O3 gold catalyst, prepared by a deposition precipitation method in this study, displays high activity and good stability for CO oxidation in a simulated atmosphere of a CO2 laser with the feed gases containing a high concentration of CO2 up to 60 vol% but a low concentration of O2 for the stoichiometric reaction with CO. An excellent performance for CO oxidation under CO2-rich conditions could be achieved by decorating the surface of the Al2O3 support with Ce-Co composite oxides. The strong interaction between gold and the composite support, accompanied by the increase of labile lattice oxygen species and the decrease of surface basicity, led to a high CO oxidation rate and resistance towards CO2 poisoning.
RESUMEN
Oxygen surface groups of activated carbon, produced by nitric acid treatment, are not only able to prevent Ni particles from sintering but are also able to preferentially interact with the nitro group of substituted nitroarenes. The resulting Ni/ACOX catalyst is highly active and chemoselective for hydrogenation of nitroarenes to produce functionalized anilines and oximes.
RESUMEN
The chemoselective hydrogenation of substituted nitroarenes to form the corresponding functionalized anilines is an important type of reaction in fine chemistry, and the chemoselectivity is critically dependent on the rational design of the catalysts. This reaction has rarely been accomplished over high-loading Pt catalysts due to the formation of Pt crystals. Here, for the first time, we report that alkali metals (Li+, Na+, K+, etc.) can transform the non-selective high loading Pt/FeO x catalyst to a highly chemoselective one. The best result was obtained over a 5% Na-2.16% Pt/FeO x catalyst, which enhanced the chemoselectivity from 66.4% to 97.4% while the activity remained almost unchanged for the probe reaction of 3-nitrostyrene hydrogenation to 3-aminostyrene. Using aberration-corrected HAADF-STEM, in situ XAS, 57 and Fe Mössbauer and DRIFT spectroscopy, the active site of a Pt-O-Na-O-Fe-like species was proposed, which ensures that the Pt centers are isolated and positively charged for the preferential adsorption of the -NO2 group.
RESUMEN
FeOx -supported single Pt atoms are used for the first time as counter electrodes (CEs) in dye-sensitized solar cells (DSCs), which are mesoporous photovoltaic devices. This system enables the investigation of the electrocatalytic behavior of a single-atom catalyst (SAC). Compared with conventional Pt CEs, the SAC-based CEs exhibit better reversibility as indicated by the peak-to-peak separation (Epp ). A high degree of atom utilization is demonstrated.
RESUMEN
The catalytic hydrogenation of nitroarenes is an environmentally benign technology for the production of anilines, which are key intermediates for manufacturing agrochemicals, pharmaceuticals and dyes. Most of the precious metal catalysts, however, suffer from low chemoselectivity when one or more reducible groups are present in a nitroarene molecule. Herein we report FeOx-supported platinum single-atom and pseudo-single-atom structures as highly active, chemoselective and reusable catalysts for hydrogenation of a variety of substituted nitroarenes. For hydrogenation of 3-nitrostyrene, the catalyst yields a TOF of ~1,500 h(-1), 20-fold higher than the best result reported in literature, and a selectivity to 3-aminostyrene close to 99%, the best ever achieved over platinum group metals. The superior performance can be attributed to the presence of positively charged platinum centres and the absence of Pt-Pt metallic bonding, both of which favour the preferential adsorption of nitro groups.
RESUMEN
OBJECTIVE: To study the burning characteristics of moxa stick. METHODS: A self-designed moxa stick burning temperature measuring device, which was assembled with ALTEC intelligence digital setter and SJ-600 thermocouple, was used to conduct next four experiences: 1) embedding a thermocouple inside a moxa stick to measure peak burning temperature; 2) pulling a thermocouple embedded in the moxa stick at the proper rate to detect combustion stability; 3) elucidating temperature distribution of transverse section by measuring the temperature in the center, radius midpoint and lateral; 4) drawing temperature-time-space curves by pulling the thermocouples in the former three observation points. RESULTS: The experiment indicated that the burning temperature peak of three-year moxa stick (Hubei Herbal Medicine St. Qichun Technology Co., Ltd.) was 848 degrees C which had good combustion stability. Furthermore, the temperature in the center, radius midpoint and lateral of transverse section were 843 degrees C, 731 degrees C and 410 degrees C, respectively, and its burning temperature-time-space curves was drawn, which showed the real-time burning temperature and the peak burning temperature and were regarded as ultimate indice to integrate the formers. CONCLUSION: The measuring system elaborately reflecting the burning features of moxa stick may provide reference for manufacture industry of moxa stick quality criteria for its convenience and accuracy.