Visualizing the importance of oxide-metal phase transitions in the production of synthesis gas over Ni catalysts

Synthesis gas, composed of H2 and CO, is an important fuel which serves as feedstock for industrially relevant processes, such as methanol or ammonia synthesis. The efficiency of these reactions depends on the H2: CO ratio, which can be controlled by a careful choice of reactants and catalyst surface chemistry.Here, using a combination of environmental scanning electron microscopy(ESEM) and online mass spectrometry, direct visualization of the surface chemistry of a Ni catalyst during the production of synthesis gas was achieved for the first time. The insertion of a homebuilt quartz tube reactor in the modified ESEM chamber was key to success of the setup. The nature of chemical dynamics was revealed in the form of reversible oxide-metal phase transitions and surface transformations which occurred on the performing catalyst. The oxide-metal phase transitions were found to control the production of synthesis gas in the temperature regime between 700 and 900 ℃ in an atmosphere relevant for dry reforming of methane(DRM, CO2: CH4=0.75). This was confirmed using high resolution transmission electron microscopy imaging, electron energy loss spectroscopy, thermal analysis, and C18O2 labelled experiments.Our dedicated operando approach of simultaneously studying the surface processes of a catalyst and its activity allowed to uncover how phase transitions can steer catalytic reactions.

Increased chemical reactivity of single-walled carbon nanotubes on oxide substrates： In situ imaging and effect of electron and laser irradiations

We studied the oxygen etching of individual single-walled carbon nanotubes on silicon oxide substrates using atomic force microscopy and high-temperature environmental scanning electron microscopy. Our in situ observations show that carbon nanotubes are not progressively etched from their ends, as frequently assumed, but disappear segment by segment. Atomic force microscopy, before and after oxidation, reveals that the oxidation of carbon nanotubes on substrates proceeds through a local cutting that is followed by a rapid etching of the disconnected nanotube segment. Unexpectedly, semiconducting nanotubes appear more reactive under these conditions than metallic ones. We also show that exposure to electron and laser beams locally increases the chemical reactivity of carbon nanotubes on such substrates. These results are rationalized by considering the effect of substrate-trapped charges on the nanotube density of states close to the Fermi level, which is impacted by the substrate type and the exposure to electron and laser beams.

Microscopic Observations of the Lotus Leaf for Explaining the Outstanding Mechanical Properties

The leaf of lotus （Nelumbo nucifera） exhibits exceptional ability to maintain the opening status even under adverse weather conditions, but the mechanism behind this phenomenon is less investigated. In this paper, lotus leaves were investigated using environmental scanning electron microscopy in order to illustrate this mechanism. The macro-observations show that the primary veins are oriented symmetrically from leaf center and then develop into fractal distribution, with net-shaped arrangement of the side veins. Further micro-observations show that all the veins are composed of honeycomb micro-tubes viewed from cross section, the inner of micro-tubes are patterned with extended closed-hexagons from vertical section. Different positions of leaf possess diverse mechanical properties by size variation of diameter and inner hexagons of veins, which is theoretically analyzed by building a regular honeycomb model. Specifically, the central area of lotus tends to be stiffer while its margin be softer. These special distribution and composition of the veins mainly account for the distinct behavior of lotus.

Triptolide-loaded microemulsion-based hydrogels: physical properties and percutaneous permeability

Triptolide is a diterpenoid compound that inhibits the inflammation of rheumatoid arthritis(RA).However,the use of triptolide is limited due to its strong gastrointestinal toxicity.The purpose of this work was to develop a transdermal delivery system for triptolide to reduce this toxicity.A microemulsion-based hydrogel(MBH)was prepared from the combination of Gemseal 40-oleic acid as oil phase,Tween 80-labrasol as surfactant,anhydrous ethanol as co-surfactant,water as aqueous phase and Poloxamer 407 as hydrogel matrix.Rheological measurements,environmental scanning electron microscopy(ESEM)and transdermal experiments in vitro were used to characterize triptolide-loaded and blank MBH preparations.The effects of Poloxamer 407 and triptolide on the rheological properties and microstructures of the MBH were determined.Transparent and homogeneous MBH could only be formed when the concentration of Poloxamer 407 in the selected O/W microemulsion was in the range of 14.0–16.0%(w/w).When the concentration of Poloxamer 407 increased,the rheological properties such as the yield stresses(sy),storage and loss moduli(G′,G″)of the formulations increased,and the network structures became more compact.The addition of triptolide did not change the interconnected network structures of the MBH preparations.MBH preparations afford a better sustained release profile when compared to microemulsions,a finding confirmed by an in vitro permeation test in mice.MBH appears to be a promising vehicle for transdermal delivery of triptolide.