Ultrasmall
Au, Pd, and AuPd nanoparticles (NPs) stabilized by PVP
were prepared in a microfluidic reactor with cyclone micromixers for
rapid mixing of reactants. In this system, pulsation-free flow of
reactants was achieved at a total flow rate of 2.6 L h–1. A rapid homogeneous mixing within 2 ms was obtained with three
cyclone micromixers. Controlled NP nucleation and growth occur in
a following meandering microchannel. The resulting colloidal NPs were
characterized thoroughly by various complementary techniques, e.g.,
high-resolution transmission electron microscopy (HRTEM), energy-dispersive
X-ray spectroscopy (EDX), and ultraviolet–visible spectroscopy.
The average NP diameter was about 1 nm with a narrow size distribution,
and electron microscopy showed homogeneously alloyed NPs. Moreover,
the particles were supported on TiO2 for catalytic tests
and further structural characterization. Electron microscopy showed
a uniform distribution of NPs on the support with some aggregation.
X-ray absorption spectroscopy (XAS) confirmed the formation of well-mixed
AuPd alloys in NP cores with Pd-rich surfaces. Finally, 1 wt % metal-loaded
supports showed catalytic activities in CO oxidation in the following
order: Au/TiO2 ≥ Au
x
Pd
y
/TiO2 ≥ Pd/TiO2. Hence, the physical and chemical properties of these catalysts
can be fine-tuned.
In order to obtain a better understanding of the physical and chemical processes within micromixers or microreactors and to optimize these devices it is necessary to monitor the concentrations within the microchannels. To get chemical information, laser Raman spectroscopy can be used. This method is very selective for individual chemical compounds, allows a spatial resolution of 10 lm within fluids and a quantitative analysis. We examined the hydrolysis of the acetal 2,2-dimethoxypropane to acetone and methanol in the presence of hydrogen ions as catalyst. This reaction can be used to characterize micromixers. The aim of this work is the in situ monitoring of concentrations of acetal and its products, acetone and methanol, during the hydrolysis of acetal within a T-shaped micromixer with a channel width of 0.4 mm and a channel depth of 0.2 mm. In these experiments a continuous-wave argon ion laser was used as an excitation source. The laser radiation was coupled into a microscope and into the micromixer covered with a quartz plate. A special microscope objective was used. It allows the correction of optical aberrations resulting from quartz plates up to a thickness of 2 mm. Concentration profiles of acetal, methanol, and acetone were measured across the width of the microchannel.
EXTENDED ABSTRACTMicro heat exchangers, micro mixers and micro reactors have gained importance in chemical, pharmaceutical and life sciences applications. Due to the large surface to volume ratio these devices provide efficient mass and heat transfer. This results in greater selectivity and higher yield for chemical reactions. The Institute for Micro Process Engineering is working on the development, manufacturing, and testing of micro channel devices mainly manufactured of stainless steel, where channel widths and depths lie in the range of 0.2 mm.In order to obtain a better understanding of the physical and chemical processes within such components and to optimize these devices it is necessary to get a look into these micro channels during a mixing process or a chemical reaction. For this purpose laser Raman spectroscopy can be applied. This method is very selective for individual chemical compounds and allows a spatial resolution better than 0.01 mm. Figure 1 shows the experimental setup. The light of an air cooled cw argon ion laser is focused by a microscope objective into a micro channel, measuring the Raman bands over its cross section at several distances from the mixing point. A spectrograph with a CCD-array detects the Raman light, which consists of lines that are characteristic for the chemical compounds flowing through the micro channels and can therefore be used to calculate their concentrations. Figure 1 -Experimental setup for Raman spectroscopy.
Raman-SpectrumLaser Micro-Mixer Downloaded From: http://proceedings.asmedigitalcollection.asme.org/ on 03/28/2015 Terms of Use: http://asme.org/terms
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