論文の公開元へStudies on the Conversion of Syngas to Low-Carbon Energy Products
概要
As concerns about oil depletion grow and environmental friendliness increases, chemical synthesis on non-oil routes is seen as the way forward. Choosing the rational reaction transformation route and using the suitable catalyst, syngas can convert to various hydrocarbons or oxygenates and form an abundant product system. The key technology is the structure regulation of the catalyst. The catalytic activity, the selectivity of the target product and the catalytic life of the catalyst play a decisive role in the reaction process. Therefore, the development and improvement of high efficiency catalysts has always been a research hotspot in the field of syngas catalysis. Based on this goal, here the doctoral thesis is composed of four sections.
In chapter 1, two kinds of different structure catalysts were designed and studied focus on the dimethyl ether carbonylation to methyl acetate then hydrogenation to ethanol reaction. In the process, catalyst deactivation due to coking, chemical or mechanical failures, coupled with higher resultant selectivity for by-product (methanol), are still a serious cause of concern due to inevitable yield losses. In this work, we synthesised highly ordered Cu-MOR@SiO2 core shell microcapsules, employing a facile scalable surfactant-directed sol-gel technique. Comparably, the microcapsules displayed higher activity during DME carbonylation (83.8%) coupled with a remarkable product yield (48.7% ethanol). Furthermore, confinement of Cu-MOR particles in SiO2 crystals, cushions Cu clusters from inevitable sintering during exposure to higher temperatures, paving way for an effective regeneration process. However, this catalyst will function in tandem with the already commercialised Cu/ZnO/Al2O3 (CZA) catalyst in a dual catalyst bed setup. The novel Cu-MOR@SiO2 encapsulated catalyst besides being regenerable and stable, displayed a long service life and high product yield, providing the dual bed ethanol synthesis pathway from co-feeding dimethyl ether and syngas, an opportunity towards commercial production.
In chapter 2, in order to further study the influence of catalyst structure on the catalytic reaction of ethanol synthesis from DME and syngas, a tailor-made microcapsule catalyst was presented that integrates a metal oxide (Cu/ZnO) catalyst as core and modified zeolite (Cu-MOR) as shell, into one multifunctional composite catalyst (CZ@Cu-MOR) for one-step ethanol synthesis strategy. The proposed synthesis mechanism of the microcapsule catalyst hugely creates surface area owing to catalyst size, and a uniquely compact interface between the two active centers where they work synergistically to accelerate parallel reactions involving MA formation and its subsequent conversion to EtOH. The addition of a porogen, such as CTAB, to the as-synthesized microcapsule catalyst, enhanced zeolite shell porosity without leaching metal active components, and stepped up access of reactants to catalytic sites, reaching a remarkable 26.4% conversion of DME and 45.8% selectivity of EtOH. The higher metal (promoter) dispersion provided by the zeolite shells, suppressed coking and enhanced stability, with unchanging activity for 50 h time on stream. Furthermore, the CZ@Cu-MOR microcapsule catalyst could be easily regenerated. Therefore, micro-encapsulation using the linker-seeds-shell approach demonstrates a promising research strategy in developing alternative energy sources from heterogeneous catalytic processes.
In chapter 3, an advanced core-shell hybrid catalyst was presented for syngas convert to liquid petroleum gas, which was facilely prepared by the physical coating method, promoting not only high product yield, but also effectively eliminating design limitations accrued on employing the hydrothermal synthesis technique. The designed capsule catalyst, named CZZA@H-β-P-3, has Cu/ZnO/ZrO2/Al2O3 (CZZA) catalyst as core and H-β zeolite as shell. CZZA@H-β-P-3 capsule catalyst was then used for direct synthesis of liquefied petroleum gas from syngas. CZZA@H-β-P-3 exhibited excellent activity, in comparison. At optimal conditions, CZZA@H-β-P-3 increased CO conversion from 40.94% to 54.8%, and LPG selectivity from 17.01% to 26.04%. DME selectivity decreased to zero. The excellent catalytic activity displayed on CZZA@H-β-P-3 capsule catalyst was credited to the special core-shell structure constructed from highly synergetic materials with a confined reaction affection, which uniquely accelerated syngas conversion to LPG.
In chapter 4, we realized a composite catalyst, comprising MnxZry oxides and SAPO-34 zeolite, which can convert syngas (CO+H2) into light olefins. MnxZry oxide catalysts with different Mn/Zr molar ratios were facilely prepared using the coprecipitation method prior to physical mixing with SAPO-34 zeolite. The redox properties, surface morphology, electronic state, crystal structure, and chemical elemental composition of the catalysts were examined using H2-TPR, SEM, XPS, XRD, and EDS techniques, respectively. Tandem reactions involved activation of CO and subsequent hydrogenation over the metal oxide catalyst, producing methanol and dimethyl ether as the main reaction intermediates, which then migrated onto SAPO-34 zeolite for light olefins synthesis. Effects of temperature, pressure and reactant gas flow rate on CO conversion and light olefins selectivity were investigated in detail. The Mn1Zr2/SAPO-34 catalyst (Mn/Zr ratio of 1:2) attained a CO conversion of 10.8% and light olefins selectivity of 60.7%, at an optimized temperature, pressure and GHSV of 380 oC, 3 MPa and 3000 h-1 respectively. These findings open avenues to exploit other metal oxides with CO activation capabilities for a more efficient syngas conversion and product selectivity.
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