(15d) In Situ Surface Chemistries and Catalytic Performances of Three-Dimensionally Ordered Macroporous Cu-Fe Catalysts for Higher Alcohols Synthesis from Syngas

Higher alcohols synthesis (HAS) from carbon monoxide hydrogenation has drawn much attention due to its potential application as a promising route for the production of clean fuels, fuel additives, and petrochemical feedstocks from coal, natural, shale gas and biomass etc. Generally, there are four catalytic systems for HAS, including Rh-based catalysts, modified methanol synthesis catalysts, Mo-based catalysts, and Modified Fischer–Tropsch catalysts. Among them, modified Fischer–Tropsch Cu-Fe based catalyst is considered as one of the most promising candidates for higher alcohols synthesis from synthesis gas (syngas). A fundamental understanding of HAS from syngas on this type of catalyst is important for the development of catalysts with high activity and selectivity for this process.

Three-dimensionally ordered macroporous (3DOM) Cu-Fe catalysts were synthesized by using a facile glyoxylate route poly(methyl methacrylate) (PMMA) colloidal crystal template method. The catalytic activity and selectivity in the synthesis of higher alcohols on these 3DOM Cu-Fe catalysts as well as their surface chemistries during catalysis were investigated. In situ studies of their surface chemistries during catalysis, using ambient-pressure X-ray photoelectron spectroscopy (AP–XPS), revealed the active sites of the 3DOM Cu-Fe catalysts for HAS. In combination with the techniques of ex situ XRD, HRTEM, Mössbauer spectroscopy, we concluded that the high intrinsic activity of the 3DOM Cu-Fe catalysts was ascribed to three factors. First, the unique ordered structure has a large pore size and interconnected macroporous tunnels of the catalyst with a large accessible surface area improves the catalytic activity. Second, a high density of uniformly distributed defective Cu⁰ and Hägg carbide χ-Fe₅C₂ nanoparticles derived from the glyoxylate route helps to provide abundant, active, stable dual sites. Third, atomic steps on the Cu surface, induced by planar defects and lattice strain, serve as high-activity oxygenation sites; and active χ-Fe₅C₂ chain-growth sites surrounds the defective and strained form of Cu surface intimately, which results in a synergetic effect between the active and stable Cu–Fe_xC_y dual sites for higher alcohols synthesis.