論文の公開元へNew reaction and new device in C1 catalysis chemistry
概要
C1 catalysis refers to the conversion of one-carbon compounds, such as carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), and methanol (CH3OH) into petrochemical intermediates, clean fuels, and high-value-added chemicals. The resources of those sample carbon molecules mainly come from e coal, natural gas, organic waste, and biomass. With the strongly fluctuating prices and decreasing reserves of petroleum and the increasingly serious problems of environmental pollution, C1 catalysis chemistry has been attracting widespread academic and industrial interest and became one of the most attractive research fields in heterogeneous catalysis Especially in recent years, thanks to the development of advanced technology, precise and controllable material synthesis methods and powerful computational simulation capabilities, C1 catalysis have been achieved in many aspects, including the understanding of the reaction mechanism, the identification of the active site structure, the in-depth reaction mechanism, the new catalysis processes and new reactor designs.
The most important and fundamental part of C1 catalysis chemistry is the conversion of syngas (the mixture of CO and H2). Best known are the Fischer−Tropsch synthesis and methanol synthesis, both of which are extensively applied industrially. The Fischer−Tropsch synthesis are mainly produce hydrocarbons and oxygenated products. However, the products controlling is still a great challenge in Fischer−Tropsch synthesis. As the most important greenhouse gas, CO2, the strategies and technologies to effectively reduce CO2 emissions have attracted widespread attention. CO2 hydrogenation into high-value chemicals and fuels seems to be an efficient and replaceable solution suffice fulfilling the requirements of sustainable processes and renewable carbon sources. The direct synthesis of methanol from methane has been studied for a few decades as a holy grail reaction in C1 catalysis chemistry, it remains one of the considerable challenges in the sector of methane utilization. Because methane molecule with strong C-H bond energy has extremely chemical inertness, and overoxidation of methanol to formic acid or carbon dioxide are difficult to be controlled.
Thus, in the thesis, our work is focusing on new catalysts exploits, new catalytic reaction process develops, and new reactor designs in C1 catalysis chemistry.
In chapter 1, we report an integrated catalytic process for the direct conversion of syngas (CO/H2) into different types of liquid fuels without subsequent hydrorefining post-treatments of Fischer–Tropsch waxes. As we all know, to tune the product selectivity by controlling the complicated reaction path is a big challenge in Fischer– Tropsch synthesis. Here, outstanding selectivities for gasoline (C5-11), jet fuel (C8-16) and diesel fuel (C10-20) as high as 74, 72 and 58% are achieved, respectively, by only using mesoporous Y-type zeolites in combination with cobalt nanoparticles. The types of liquid fuels can be readily tuned by controlling the porosity and acid properties of the zeolites. We further build a new product-distribution model for the bifunctional catalysts, which do not obey the traditional Anderson–Schulz–Flory (ASF) distribution. The present work offers a simple and effective method for the direct synthesis of different types of liquid fuels.
In chapter 2, we show that metal 3D printing products themselves can simultaneously serve as chemical reactors and catalysts (denoted as self-catalytic reactor or SCR) for direct conversion of C1 molecules (including CO, CO2 and CH4) into high value-added chemicals. Mechanical properties and geometries of printed products have been extensively studied in metal 3D printing. However, chemical properties and catalytic functions, introduced by metal 3D printing itself, are rarely mentioned. The Fe-SCR and Co-SCR successfully catalyze synthesis of liquid fuel from Fischer-Tropsch synthesis and CO2 hydrogenation; the Ni-SCR efficiently produces syngas (CO/H2) by CO2 reforming of CH4. Further, the Co-SCR geometrical studies indicate that metal 3D printing itself can establish multiple control functions to tune the catalytic product distribution. The present work provides a simple and low-cost manufacturing method to realize functional integration of catalyst and reactor, and will facilitate the developments of chemical synthesis and 3D printing technology.
In chapter 3, we report a class of carbon material catalysts for this direct synthesis. The carbon materials such as carbon nanotubes (CNTs), activated carbon (AC), and reduced graphene oxide (rGO) are employed as catalyst support, and the palladium- gold (Pd-Au) nanoparticles are used as active center. Direct conversion of methane to methanol under mild conditions remains a great challenge in decades. Here, by using oxygen/hydrogen as oxidant in the direct synthesis, the catalyst of Pd-Au/CNTs shows outstanding methanol productivity and selectivity. Compared with the Pd-Au/CNTs, the Pd-Au/CNTs-n with a treatment of nitric acid for the support enhances the methanol selectivity, but decreases the methanol productivity. In addition, our characterization results reveal that a weak interaction between Pd-Au nanoparticles and CNTs support is in favor of methanol productivity and selectivity. In contrast, a strong interaction between Pd-Au and AC or rGO catalysts inhibits the reaction activity. This work offers a simple and effective strategy to directly synthesize methanol from methane under the mild conditions.
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