Abstract
Bifunctional Al2O3/Cu/ZnO catalysts with Al composition of between 30 mol% and 80 mol% were prepared by sequential precipitation (SP) for the conversion of CO2 into dimethyl ether (DME). In the SP synthesis, the concentration of a precipitation agent managed to be high enough to induce the complete precipitation of Al3+. The prepared precipitates were composed of zincian malachite and amorphous AlO(OH). Furthermore, the calcined mixed metal oxide materials of 60% and 80% Al exhibited a higher acidity than commercial Al2O3 and the H2-reduced catalysts showed the similar Cu dispersion of 6%–7% at all Cu loadings. In the activity test at 573 K and 50 bar, the SP-derived catalyst of 80% Al (SP-80) displayed the best performance corresponding to CO2 conversion of 25% and DME selectivity of 75% that are close to equilibrium values. In order to overcome the thermodynamic limitation, a dual-bed catalyst system was made up of SP-80 in the first layer and zeolite ferrierite in the next. This approach enabled DME selectivity to be enhanced to 90% while CO2 conversion increased a little. Consequently, the studied catalyst system based on the SP-derived catalysts can contribute greatly to selective DME production from CO2.
Highlights
To limit the detrimental impacts of climate change caused by the rise in global CO2 concentration, a variety of methods and technologies have been explored worldwide to remove CO2 from the atmosphere and from the flue gas, followed by recycling the CO2 for utilization and securing safe and sustainable storage options, which is the general concept of carbon capture, utilization, and storage (CCUS)
For Al2 O3 /Cu/ZnO catalysts used in this work, a series of Cu,Zn,Al precursors were prepared in such a manner that Al3+ was precipitated onto the aged Cu,Zn precipitate, where the nominal Al composition (= [Al]/{[Cu] + [Zn] + [Al]} × 100%) varied from 30% to 80%
We have developed Al2 O3 /Cu/ZnO catalysts of 60%–80% Al compositions for CO2 hydrogenation to dimethyl ether
Summary
To limit the detrimental impacts of climate change caused by the rise in global CO2 concentration, a variety of methods and technologies have been explored worldwide to remove CO2 from the atmosphere and from the flue gas, followed by recycling the CO2 for utilization and securing safe and sustainable storage options, which is the general concept of carbon capture, utilization, and storage (CCUS). Among them, converting CO2 into useful chemicals has been attracting much attention in recent years even if economic issue is still under debate. A well-known chemical is methanol produced by CO2 hydrogenation, which was first commercialized in Iceland [1]. The thermodynamic equilibrium limits the methanol synthesis process to a low conversion, recycling the outlet stream in order to approach a desired conversion value. Another option to circumvent this limitation is coupling methanol synthesis with methanol-consumed reactions in series. Among a Catalysts 2019, 9, 524; doi:10.3390/catal9060524 www.mdpi.com/journal/catalysts
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