(603d) Higher Alcohols Synthesis From Syngas Over Three-Dimentionally Ordered Macroporous Cu-Fe Catalysts: The Active Site

Higher alcohols (C₂+OH) synthesis is the challenging area in the field of C1 chemistry. Higher alcohols have higher water tolerance, reduced fuel volatility, lower vapor lock tendency and higher volumetric heating values. Higher alcohols synthesis from syngas or syngas derived from biomass, coal, or natural gas reforming is an important process for the production of oxygenates fuels, fuels additives and other intermediates for value-added chemical feedstock such as medicine, cosmetic, lubricants, detergents, and polyester. Cu-based catalysts containing metal active toward Fischer–Tropsch synthesis such as Cu-Fe based catalyst, is considered as the most promising catalysts for higher alcohols synthesis. Recently, three-dimensionally ordered macroporous (3DOM) materials with pores sized in the submicrometer had got much attention. Connected macropores with high porosity in 3DOM catalysts can permit facile transport of guest molecules, and increase the catalytic activity in potential catalysis.

In the paper, 3DOM Cu-Fe catalyst was synthesized by using poly (methyl methacrylate) (PMMA) colloidal crystal template (CCT) method. 3DOM Cu-Fe catalyst was characterized by SEM, HRTEM, XRD, XPS, Mössbauer spectroscopy. The catalytic performance of 3DOM Cu-Fe based catalyst was evaluated under model syngas in a half-inch fixed-bed reactor system. The results showed that 3DOM Cu-Fe catalysts have high selectivity of C₂⁺OH. Cu⁰ species is the active site for alcohols synthesis. χ-Fe₅C₂ is the active site for olefin and paraffin synthesis and it also plays a very important role for chain growth. There is a synergetic effect between Cu⁰ and χ-Fe₅C₂ for higher alcohols synthesis. High activity and selectivity was generated by two factors. First, the presence of steps at the Cu surface is required, which can be stabilized by bulk defects like stacking faults or twin boundaries terminating at the surface. The second requirement is the presence of χ-Fe₅C₂ around the defective (stepped) Cu surface, which in the high-performance catalyst is a result of a synergetic effect leading to partial coverage of the Cu particles with χ-Fe₅C₂.