이산화탄소 수소화 반응을 위한 철 기반 전구체 촉매 개발

Abstract

The global warming caused by greenhouse gas is critically expected to develop the new path to mitigate and alleviate CO2 into value-added products, which are chemical (methanol, formic acid, olefin) and fuel (gasoline, diesel, jet fuel). Furthermore, increasing price and limited resource from fossil fuel tend to concentrate utilization of C1 chemistry and renewable energy supplies, eco-friendly. Among many option to use CO2 with hydrogen as chemical reactant, CO2 hydrogenation that converting CO2 to liquid products is an advisable way to overcome environmental and energy problems when it is considered as economical and practical views. Compared to chemical products including methanol, formic acid and olefin, liquid fuels such as gasoline, diesel and jet fuel are integrated with social demand and supply, directly. Especially, the problems from transportation and storage are easily solved without additional charge. Iron-based catalyst in contrast with cobalt, nickel and noble metal of ruthenium has a benefit to convert CO2 and H2 with chain of hydrocarbon on the active site including RWGS (Reverse Water Gas Shift) and FT (Fischer Tropsch) synthesis. Different with other active metal, it is composed of weak CO2 adsorption and suppression of H2, relatively. In this work, delafossite-CuFeO2 derived from Cu and Fe and spinel structure of ZnFe2O4 are investigated for production of liquid fuels and increase CO2 conversion in CO2 hydrogenation. In addition, a diverse study for liquid products is applied to CO2 hydrogenation due to complex hydrocarbon distribution. In chapter 3, delafossite-CuFeO2 synthesized by hydrothermal is considered as a new catalyst that produces liquid hydrocarbons and olefins from CO2 hydrogenation in the same manner as from traditional CO-based FT synthesis. The catalyst is treated by pure-hydrogen as reduction of delafossite-CuFeO2 and carburized by in-situ formation of Hägg carbide (χ-Fe5C2). The catalyst derived from CuFeO2 has better active and productive toward heavier hydrocarbon than reference catalyst: bare Fe2O3, CuO-Fe2O3 mixture, and spinel CuFe2O4. The unique role of delafossite-CuFeO2 as a Cu-Fe catalyst precursor with impurity of tiny amounts of Na is its swift reduction to metals during the pre-reduction step followed by effective in-situ carburization to χ-Fe5C2, the active phase of heavy hydrocarbon formation. Relatively, the delafossite-derived catalyst presents improved higher hydrocarbon from 2 % to 65 %, and olefin to paraffin ratio by 150 times, whereas methane selectivity is greatly suppressed to 2 -3 %. All samples are investigated by XRD, XPS, TEM, SEM, BET, H2-TPR, in-situ reaction and XAFS studies. In chapter 4, the ZnFe2O4 with impurity of residue sodium as a precursor catalyst, synthesized by a microwave-assisted hydrothermal method shows improved CO2 conversion and heavier hydrocarbon containing gasoline and diesel ranges with high olefin to paraffin ratios (~ 11). With comparison to reference catalysts including Fe2O3 and physically mixed ZnO-Fe2O3, spinel structure ZnFe2O4 catalyst takes advantage of structural and electronic promoter effect: dispersion of iron particles and improved selectivity toward liquid hydrocarbons. The ZnFe2O4 catalyst derived from Zn and Na promoter exhibits great performance of CO2 hydrogenation in line with FT synthesis by in-situ forming Hägg carbide (χ-Fe5C2) as the active site for liquid fuels during reaction.