Isosynthesis via CO hydrogenation over SO4–ZrO2 catalysts

Catalytic performances of sulfated zirconia catalysts with various contents of sulfur (from 0.1 to 0.75%) on isosynthesis were studied. It was firstly found that undoped-zirconia synthesized from zirconyl nitrate provided higher activity towards isosynthesis reaction (106 μmol kg-cat^?1 s^?1) compared to that synthesized from zirconyl chloride (84.9 μmol kg-cat^?1 s^?1). Nevertheless, the selectivity of isobutene in hydrocarbons was relatively lower. It was then observed that the catalytic reactivity and selectivity significantly improved by sulfur loading. The most suitable sulfur loading content seems to be at 0.1%, which gave the highest reaction rate and selectivity of isobutene. By applying several characterization techniques, i.e. BET, XRD, NH₃- and CO₂-TPD and SEM, it was revealed that the high reaction rate and selectivity towards isosynthesis reaction of sulfated zirconia catalysts are related to the acid–base properties, Zr³⁺ quantity and phase composition.     

Direct observation of a noncatalytic growth regime for GaAs nanowires

We identify a new noncatalytic growth regime for molecular beam epitaxially grown GaAs nanowires (NWs) that may provide a route toward axial heterostructures with discrete material boundaries and atomically sharp doping profiles. Upon increase of the As/Ga flux ratio, the growth mode of self-induced GaAs NWs on SiO(2)-masked Si(111) is found to exhibit a surprising discontinuous transition in morphology and aspect ratio. For effective As/Ga ratios <1, in situ reflection high-energy electron diffraction measurements reveal clear NW growth delay due to formation of liquid Ga droplets since the growth proceeds via the vapor-liquid-solid mechanism. In contrast, for effective As/Ga ratios >1 an immediate onset of NW growth is observed indicating a transition to droplet-free, facet-driven selective area growth with low vertical growth rates. Distinctly different microstructures, facet formation and either the presence or absence of Ga droplets at the apex of NWs, are further elucidated by transmission electron microscopy. The results show that the growth mode transition is caused by an abrupt change from As- to Ga-limited conditions at the (111)-oriented NW growth front, allowing precise tuning of the dominant growth mode.     

Improvement of thermal performance of mortars by using heat storage aggregate made with industrial by-product to reduce cooling load

The usage of waste materials as building materials can be an important method to reduce energy consumption and decrease natural resource usage in the construction industry. In this work, phase change materials (PCMs) were incorporated with industrial by-product materials as an aggregate to produce mortars, which can improve the energy efficiency and improve the environment of buildings. Bottom ash (BA), a by-product from coal-fired power plants, was directly impregnated into paraffin, a PCM, to produce a heat storage aggregate (HSA). The raw materials of the HSA production were characterized by X-ray diffraction, scanning electron microscope, and differential scanning calorimeter. The mortar mixes had a water to cement ratio of 1:2 and a sand to cement ratio of 2.5:1. Six mixtures were prepared with different HSA amounts of 0%, 10%, 20%, 30%, 40%, and 50% by volume. The compressive strength, density, and thermal properties of the mortars were investigated. The results and analyses showed that the compressive strength and density of the mortars decreased with increasing HSA amounts. The thermal conductivity of HSA mortars slightly decreased for increasing levels of HSA. In addition, HSA mortars showed a significant increase in time lags when the HSA content increased, up to approximately 165% to 197% higher than that of the control mortars. HSA levels in mortars can play an important role in improving the heat conductance into buildings.