Abstract
The use of metal-assisted HF chemical etching as a convenient technique to produce a few microns thick porous layer in silicon microchannels was demonstrated. Gas phase selective oxidation of rosalva to its aldehyde (costenal) was performed in glass/silicon microstructured reactors at temperatures of 375–475 °C on silver catalyst which was deposited on both porous and flat silicon surface by sputter-coating. The effects of temperature (375–475 °C), rosalva concentration (1.17%–3.43%), O2 to rosalva ratio (0.5–20) and residence time on the reaction were investigated. The reactivity of rosalva on the porous silicon supported silver was 5.7–6.4 times higher than on the thin film silver catalyst at 450 °C. Furthermore, activation energy for the porous silicon supported silver was lower. Isothermal conditions in the microreactors allowed high conversion and selectivity to be achieved in a wide range of temperature and oxygen concentration. At typical reaction conditions (1.75% rosalva, O2/rosalva = 3, residence time 18 ms and 450 °C), conversion of 97% and selectivity of 95% to costenal was achieved, corresponding to a turnover frequency of 268 h−1.
Highlights
Catalytic selective oxidation of alcohols is a fundamental process in synthetic chemistry as carbonyl compounds have widespread applications in the flavor, pharmaceutical, agrochemical, and fragrance industries [1,2]
We report the investigation of the gas phase rosalva oxidation on silver catalyst in microstructured reactors
The BET surface area measured in this work is comparable to those reported by Tiggelaar et al [31] for porous silicon obtained by anodic oxidation, showing that the thicker the porous layer the larger the surface area
Summary
Catalytic selective oxidation of alcohols is a fundamental process in synthetic chemistry as carbonyl compounds have widespread applications in the flavor, pharmaceutical, agrochemical, and fragrance industries [1,2]. Gas phase oxidation of alcohols with air or oxygen represents an attractive route for the industrial production of carbonyl compounds, but successful industrial application rely on the catalyst to provide high reactivity and selectivity and the reactor design to prevent the degradation of reactants and products at high reaction temperature. Costenal (9-decenal) has an extremely powerful aldehydic olfactive note and is used in flavors and fine fragrances It can be prepared from rosalva (9-decen-1-ol) via a Swern oxidation [25] or other liquid phase oxidation methods which involve many reaction steps and product purification processes [26,27,28]. Enhanced performance of the reaction on the porous silicon supported silver catalyst was demonstrated
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