We present the use of a coiled-flow inverter (CFI) for continuous-flow photochemistry at competitive photon efficiencies. The static mixer is placed inside a reaction chamber, whereas a dark adjacent chamber allows for orthogonal online reaction monitoring via fluorescence spectroscopy. The study of the aqueous visible-light induced degradation of fluorescein with ZnO-APTMS-Au photocatalyst showcases the challenge of uniformly irradiating photoreactors with nonplanar surfaces. Fluorescence imaging is introduced as a simple method to visualize spatial gradients in the irradiance at the outer surface of such complex photoreactor geometries, allowing the analysis of photoreactor efficiency as a function of lighting configuration. We compared uniaxial and multiaxial lighting configurations and discuss the challenges associated with attaining uniform irradiance distribution of incident light on coiled-flow inverters, where chaotic advection combats light attenuation. A first calculation of the photochemical space-time yield (PSTY) for a "photo-CFI" indicates that a competitive photon efficiency can be reached as compared to other photoreactor designs.
Al2O3-TiO2 (AT) mixed oxide with atomic ratio Al/Ti = 25 and Al2O3 (A) supports were prepared by the sol-gel method and impregnated to obtain monometallic Pd and Pt (1 wt % of metal), and bimetallic PdPt (Pd/Pt = 4) catalysts. These catalysts were tested in the gas-phase hydrodechlorination of 1,2 dichloroethane. The materials were characterized by nitrogen physisorption, X-ray diffraction analysis (XRD), temperature-programmed reduction (TPR) and high-resolution transmission microscopy (HRTEM). AT support showed a BET area (422 m2/g), slightly higher than A(374 m2/g). The specific activity for the AT supported catalysts was higher than that for the A supported catalysts. The order of activity for the AT supported catalysts was as follows: Pd> PdPt> Pt and in terms of selectivity towards non-chlorinated compounds the order was PdPt> Pd> Pt. The differences in the activities and the selectivities can be explained by the presence of different species of Pd in the supported catalysts.
A systematic study over different treatment conditions, including hydrothermal and acid-thermal, was successfully carried out to determine the most suitable conditions to enhance the textural properties and surface chemical composition of natural dolomite. The reconstruction of dolomite after various treatments enhanced the surface area by 4–5 times and diminished the pore diameter between 70% and 81% compared to the untreated parent dolomite. The Rietveld analysis of the X-ray diffraction (XRD) patterns revealed changes in the crystalline compositions after each treatment. When the treated dolomite was used as a catalyst to produce glycerol carbonate via a transesterification reaction of glycerol and dimethyl carbonate, the crystalline Ca(OH)2 concentration of the modified dolomite and the apparent glycerol carbonate formation rate (rgc) are well-correlated. The results suggest that an increase of the crystalline Ca(OH)2 concentration could be related with surface basicity at the weak and moderate strength sites that may lead to an increase in catalytic activity. The hydrothermal treated dolomite showed a selectivity of glycerol carbonate greater than 99% and rgc value 3.42 mmol/min·gcat, which was higher than that achieved on other samples. This study could aid to the proper selection of dolomite treatment for the desired crystalline composition, depending on the applications of this highly available mineral.
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