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Long-Term Stability against H2S Poisoning on Pd Composite Membranes by Thin Zeolite Coatings
No full textParts per million levels of H2S can lead to fast deactivation of Pd-based membranes due to preferential adsorption on the membrane surface or the formation of metal sulfides. This study provides an effective approach to protect Pd-based membranes against sulfur poisoning by a thin zeolite layer of ca. 2 mu m thickness coating on the Pd surface. Both NaA and KA zeolite layers act as barriers at 673-773 K under 5-15 ppm of H2S atmosphere, for the H2S cannot reach the Pd surface due to dissociation within the supercages and molecular sieving mechanism. The long-term stability in 10 ppm of H2S at 673 K demonstrates the capability of the zeolite layer to improve H2S resistance of Pd membranes and simultaneously maintain a relatively high H-2 permeance (4.6 X 10(-7) mol m(-2) s(-1) Pa-1 in this study) under practical operation conditions
Synthesis of micro-mesoporous molecular sieve ZSM-5/SBA-15: tuning aluminium content for tert-butylation of phenol
No full textMicro-mesoporous ZSM-5/SBA-15 molecular sieve was derived from mesoporous molecular sieves SBA-15 by hydrothermal crystallization approach. The silica-alumina ratio significantly affects the structure and catalytic performance of ZSM-5/SBA-15. When the nSi/nAl is less than 25, the two-dimensional hexagonal pore structure of SBA-15 keeps intact with relatively low crystallinity of the pore wall. However, when the nSi/nAl is larger than 50, the SBA-15 pores are severely damaged. When nSi/nAl is 25, the catalyst ZSM-5/SBA-15 retains relatively good pore structure and shows excellent catalytic performance with 96.2% phenol conversion and 53.5% selectivity to 2,4-ditert-butyl phenol in the tert-butylation of phenol.Graphical Abstract SYNOPSIS Micro-mesoporous ZSM-5/SBA-15 molecular sieve was derived from mesoporous molecular sieve SBA-15 by hydrothermal crystallization approach. ZSM-5/SBA-15 (nSi/nAl=25) retains relatively good pore structure and shows excellent catalytic performance with 96.2% phenol conversion and 53.5% selectivity to 2,4-ditert-butyl phenol in the tert-butylation of phenol
Oxygen vacancy mediated La1-xCexFeO3-delta perovskite oxides as efficient catalysts for CWAO of acrylic acid by A-site Ce doping
No full textThe influence of Ce amount on catalytic behaviour of perovskite catalysts La1-xCexFeO3-delta, prepared by coprecipitation was examined in catalytic wet air oxidation (CWAO) of high concentrated acrylic acid pollutant. The catalysts with the molar ratio of Ce/(La + Ce) upper than 0.4 exhibit high catalytic activity, and outstanding stability. Because Ce doping into the skeleton of LaFeO3 could cause the change of iron valence state as well as the change of the reactive oxygen species and oxygen vacancies of the catalyst. Three ways of O-2 involved in this reaction were considered, a synergistic mechanism of oxygen vacancies, the reversible electronic transition Fe3+ Fe2+, and direct oxidization of acrylic acid. First-principles calculations revealed that the oxygen vacancy is more easily to form in the case of Ce content increasing in La1-xCexFeO3-delta, and oxygen would adsorb on oxygen vacancy to form reactive oxygen species. Consequently, the reactive oxygen species (O*) could oxidize acrylic acid. In this process, Fe ions of higher valence sate which would attack organic compounds and itself was reduced to Fe2+ to achieve catalytic cycles. Finally, the reaction was verified as first order, which was well explained by a proposed generalized kinetic model, in good accordance with our experimental data
Rhodium(iii)-catalyzed diverse [4+1] annulation of arenes with 1,3-enynes via sp(3)/sp(2) C-H activation and 1,4-rhodium migration
No full textNitrogen-rich heterocyclic compounds have a profound impact on human health. Despite the numerous synthetic methods, diversified, step-economic, and general synthesis of heterocycles remains limited. C-H bond functionalization catalyzed by rhodium(iii) cyclopentadienyls has proven to be a powerful strategy in the synthesis of diversified heterocycles. Herein we describe rhodium(iii)-catalyzed sp(2) and sp(3) C-H activation-oxidative annulations between aromatic substrates and 1,3-enynes, where alkenyl-to-allyl 1,4-rhodium(iii) migration enabled the generation of electrophilic rhodium(iii) -allyls via remote C-H functionalization. Subsequent nucleophilic trapping of these species by various sp(2)-hybridized N-nucleophiles delivered three classes (external salts, inner salts, and neutral azacycles) of five-membered azacycles bearing a tetrasubstituted saturated carbon center, as a result of [4 + 1] annulation with the alkyne being a one-carbon synthon. All the reactions proceeded under relatively mild conditions with broad substrate scope, high efficiency, and excellent regioselectivity. The synthetic applications of this protocol have also been demonstrated, and experimental studies have been performed to support the proposed mechanism
Synergy of Single-Atom Ni-1 and Ru-1 Sites on CeO2 for Dry Reforming of CH4
No full textHeterogeneous catalysis performs on specific sites of a catalyst surface even if specific sites of many catalysts during catalysis could not be identified readily. Design of a catalyst by managing catalytic sites on an atomic scale is significant for tuning catalytic performance and offering high activity and selectivity at a relatively low temperature. Here, we report a synergy effect of two sets of single-atom sites (Ni-1 and Ru-1) anchored on the surface of a CeO2 nanorod, Ce0.95Ni0.025Ru0.025O2. The surface of this catalyst, Ce0.95Ni0.025Ru0.025O2, consists of two sets of single-atom sites which are highly active for reforming CH4 using CO2 with a turnover rate of producing 73.6 H-2 molecules on each site per second at 560 degrees C. Selectivity for producing H-2 at this temperature is 98.5%. The single-atom sites Ni-1 and Ru-1 anchored on the CeO2 surface of Ce0.95Ni0.025Ru0.025O2 remain singly dispersed and in a cationic state during catalysis up to 600 degrees C. The two sets of single-atom sites play a synergistic role, evidenced by lower apparent activation barrier and higher turnover rate for production of H-2 and CO on Ce0.95Ni0.025Ru0.025O2 in contrast to Ce0.95Ni0.05O2 with only Ni-1 single-atom sites and Ce0.95Ru0.05O2 with only Ru-1 single-atom sites. Computational studies suggest a molecular mechanism for the observed synergy effects, which originate at (1) the different roles of Ni-1 and Ru-1 sites in terms of activations of CH4 to form CO on a Ni-1 site and dissociation of CO2 to CO on a Ru-1 site, respectively and (2) the sequential role in terms of first forming H atoms through activation of CH4 on a Ni-1 site and then coupling of H atoms to form H-2 on a Ru-1 site. These synergistic effects of the two sets of single-atom sites on the same surface demonstrated a new method for designing a catalyst with high activity and selectivity at a relatively low temperature
Widespread distribution of PET and PC microplastics in dust in urban China and their estimated human exposure
No full textDust is a fate of many contaminants and may be an important medium for the human exposure to these contaminants. Microplastics (MPs) have been observed in dust in previous studies. However, the mass concentrations of dominant MPs in dust and the exposure risk to human remain unclear. In this study, indoor and outdoor dust samples were collected from 39 major cities of China. The mass concentrations of polyethylene terephthalate (PET) and polycarbonate (PC) MPs were determined through alkali-assisted thermal depolymerization-liquid chromatography-tandem mass spectrometry, and the shape and component distribution of MPs were analyzed by optical microscopy and micro-Fourier transform infrared spectroscopy. PET MPs were detected in all the samples at high concentrations of 1550-120,000 mg/kg (indoor) and 212-9020 mg/kg (outdoor) and PC MPs were detected in approximately 70% of the samples, with median concentrations of 4.6 mg/kg (indoor) and 2.0 mg/kg (outdoor). Fiber was the main shape of suspected MPs, and polyester (including PET) was identified as an important component in MPs from dust. Indoor dust is a non-negligible source of human exposure to MPs, accounting for a geomean daily intake of 17,300 ng/kg-bw of PET MPs in children
A lotus leaf based random laser
No full textRandom lasing in a lotus leaf, with a wide tunable spectrum from planar liquid waveguide gain channels is described. The lotus leaf shows multiple scattering from the micro-papilla and nanoscale coralloid tomentum on its surface. The Fraunhofer diffraction pattern demonstrates excellent coherence and directionality for our random laser. The emission spectrum wavelength can be tuned by changing the pump position due to the random distribution of the micro/nano-scale features on the lotus leaf. Potential applications of the random laser include probing micro/nano-scale structural alterations, optical biosensors on chips, and developing a multi-color random laser
Selective reduction of CO2 to CO under visible light by controlling coordination structures of CeOx-S/ZnIn2S4 hybrid catalysts
No full textEngineering the electronic properties of heterogeneous catalysts is an important strategy to enhance their activity towards CO2 reduction. Herein, we prepared partially sulfurized cerium oxide (CeOx-S) nanoclusters with the size less than 2 nm on the surface of ZnIn2S4 layers. Surface electronic properties of Ce0,,-S nanoclusters are facilely modulated by cerium coordination to sulfur, inducing the emergence of abundant Ce3+ and oxygen vacancies. For the photoreduction of CO2, CeOx-S/ZnIn2S4 hybrid catalysts exhibited a CO productivity of 1.8 mmol g-1 with a rate of 0.18 mmol g(-1)h(-1), which was twice as higher as that of ZnIn2S4 catalyst using triethylamine as a sacrificial electron donor. Further mechanistic studies reveal that the photogenerated electrons are trapped by oxygen vacancies on CeOx-S/ZnIn2S4 catalysts and subsequently transfer to CO2, benefiting the activation of CO2. Moreover, the extremely high selectivity of CO is derived from the weak adsorption of CO on the surface of CeOx-S/ZnIn2S4 catalysts