Continuous synthesis of Cu/ZnO/Al2O3 nanoparticles in a co-precipitation reaction using a silicon based microfluidic reactor

CuO/ZnO/Al2O3 catalysts were continuously synthesized in a microfluidic reactor, analyzed by X-ray diffraction (XRD), physisorption (BET), chemisorption, electron microscopy and X-ray absorption spectroscopy (XAS), and tested for methanol synthesis from CO-rich synthesis gas. The results were compared to those obtained from CuO/ZnO and CuO/ZnO/Al2O3 produced by conventional co-precipitation in a batch reactor. The predominant phase of the aged precursor from microfluidic co-precipitation was identified as zincian malachite. After calcination the microfluidically synthesized catalyst exhibited smaller CuO crystallites, a larger BET surface area, a rather uniform morphology and a homogeneous distribution of Cu and Zn compared to catalysts prepared by batch co-precipitation. H-2-Temperature programmed reduction (TPR) showed that Cu species in CuO/ZnO/Al2O3 from microfluidic co-precipitation were more easily reducible. In situ Cu and Zn K-edge XAS during the TPR indicated reduction of Cu2+ to Cu-0 between 150 degrees C and 240 degrees C, without detectable reduction of Zn. N2O pulse chemisorption evidenced an enlarged Cu surface area of the nanoparticles from the microfluidic synthesis. Based on activity tests in methanol synthesis, at 250 degrees C the microfluidically synthesized Cu/ZnO/Al2O3 catalysts showed better performance than the catalyst from batch preparation when 1 mol% CO2 was present in the synthesis gas. Dimethyl ether formed as a side product. As the microreactor is specially designed for high X-ray transmission with a thin Si/glass observation window, this study opens interesting perspectives for investigating the formation of catalyst precursors at the early stage of precipitation in future.