Synthesis and activities of copper-based catalysts for CO2 conversion and biomass hydrogenation

Abstract

therefore, ZrO2 particles tended to exist in a separated form from Cu/ZnO particles. When the quaternary Cu,Zn,Al,Zr precursors were prepared by co-precipitation, the relative population of zM and HT phases was controlled by tuning the Al/Zr ratio in the synthesis. The prepared ternary and quaternary catalysts were tested in CO2 hydrogenation to methanol. In the above study, Cu,Zn,Al precursors were comprised of the HT phase but not a mixed phase of zM and Al, thus not showing the intrinsic properties of Al2O3. Due to this limitation, sequential precipitation (SP) method was employed such that Al is precipitated onto the pre-formed Cu,Zn precursors. This method made it possible to control the catalytic effects of zM and HT phases on the methanol production rate. Therefore, the differences in catalyst characteristics and activity were investigated by changing the characteristics of Cu,Zn precursors as a response to the time of Al injection. Furthermore, calcination and reduction yielded Al2O3/Cu/ZnO catalyst. When the content of Al ranged from 60% to 80%, this catalyst showed acidity enough to initiate the dehydration of methanol to DME. Therefore, formation of DME at high selectivity was possible from CO2. Furthermore, the conversion of DME to MA was confirmed through the dual-bed system packed with a zeolite layer packed after Al2O3/Cu/ZnO layer. The afore-mentioned Cu catalysts proved to be active in gas-phase reactions but did not show stable and high activity in liquid-phase reactions because of intimate contact with liquid substrates. An example in this thesis is selective hydrogenation of HMF derived from biomass. Hence, Cu–Al2O3 catalysts were prepared by the SDP method, showing mesoporosity and a high specific surface area. Moreover, they exhibited high activity and stability compared to the reference catalysts prepared by co-precipitation and impregnation. The effects of impurities in HMF feed and various operating parameters were also investigated. Thus, a continuous HMF hydrogenation process scheme was proposed and large-scale catalyst synthesis was accessed for commercial process. Herein, Cu-based catalysts were used for CO2 conversion (target products: methanol, DME, and MA) and HMF hydrogenation. The presented activity results depend on the employed catalyst synthesis method such as co-precipitation, sequential precipitation, solvent deficient precipitation. Although several fundamental issues still remain unclear in catalyst synthesis, it is considered that the findings reported here can contribute to finding and designing new Cu catalysts in many environmentally friendly applications.; Today’s industrial development has been causing emission of greenhouse gases, mainly CO2, thereby resulting in various environmental issues. To mitigate such negative effects, a number of approaches are being introduced and investigated nowadays. Among them, much attention has been paid to catalytic conversion of carbon dioxide and transformation of biomass-derived molecules to produce valuable fuels and chemicals that can replace petroleum-based ones. Thus, three catalytic reactions were studied in this thesis, where the catalysts used for each reaction consisted of metallic copper (Cu) and support materials. The first effort was made on CO2 hydrogenation of methanol over co-precipitated Cu/ZnO-based catalysts. The next was to convert CO2 to dimethyl ether (DME) and methyl acetate (MA) with sequentially precipitated Al2O3/Cu/ZnO catalysts. The last work was related with biomass conversion, that is, selective hydrogenation of 5-(hydroxymethyl)furfural (HMF) into furan diol over mesoporous Cu–Al2O3 catalysts prepared by solvent deficient precipitation (SDP). In producing methanol by CO2 hydrogenation, Cu/ZnO-based catalysts have been widely used along with addition of several promoters such as Al2O3 and ZrO2 to enhance the hydrogenation activity of active Cu metal. As a result of characterizing Cu,Zn precursors (obtained before calcination), a zincian malachite (zM) phase was observed at the Cu:Zn atomic ratio of 7/3. When Al component was added, the properties of zM was changed by formation of hydrotalcite (HT) phase. In contrast, the zM phase was maintained in case of Zr addition