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• Carbon nanotubes constrain growth of LDO nanoparticles. • Carbon nanotubes promote dissociation of CO molecules. • Carbon nanotubes lead to distortion of unit structure of LDHs. • Carbon nanotubes enhance hydrogenation of carbon species. In this work, CuZnAl layered double oxides (LDOs) were encapsulated in carbon nanotubes (CNTs) with different diameters by an ultrasonic-assisted sol-gel method. The CuZnAl LDOs filled in CNTs showed higher catalytic activity and good selectivity for higher alcohols. The catalysts were investigated by varied characterization technologies in order to explore confinement effect of CNTs. It is found that distortion of octahedral unit structure in LDH precursor is enhanced by confinement effect of CNTs. The electron-deficient inner surfaces of CNTs are responsible for the efficient dissociation of CO adsorbed inside CNTs. In addition, hydrogenation ability of the LDOs filled in CNTs is improved due to an obvious decrease in reduction temperature and auto-reduction effect of CNTs, and the restriction effect of CNTs on growth of LDO nanoparticles lead to a rise in their specific surface area. As mentioned above, the changes in structure and properties of LDOs loaded inside CNTs facilitate conversion of syngas into higher alcohols. Moreover, CNTs with small inner size show stronger confinement effect. [Display omitted] [ABSTRACT FROM AUTHOR]

The Cu/ZnO/Al 2 O 3 catalysts (CuZnAl) can be utilized to directly synthesize isobutanol from syngas at low temperatures, and complexants are new and efficient modifiers for the catalysts used to synthesize higher alcohols. However, little is known about effects of the complexants such as ethylene diamine tetra-acetic acid (EDTA) and triethanolamine (TEA) on structure and catalytic activity of CuZnAl. In this work, the precursors of CuZnAl, hydrotalcite-like compounds (HTLCs), were treated with EDTA and TEA to obtain the CuZnAl modified by EDTA (CuZnAl-EDTA) and TEA (CuZnAl-TEA). The catalytic performances of CuZnAl, CuZnAl-EDTA and CuZnAl-TEA were evaluated. Addition of EDTA or TEA increased CO conversion and selectivity for isobutanol and ethanol compared with pure CuZnAl. All the samples were characterized by BET, XRD, SEM, CO–TPD, CO 2 –TPD, H 2 –TPR and FTIR spectroscopy to further disclose the reason for better catalytic performance of CuZnAl-EDTA and CuZnAl-TEA. We found that the EDTA and TEA promote reduction of CuO, increase in concentration of basic sites and formation of floccule-like structure, which efficiently improves catalytic activity of CuZnAl-EDTA and CuZnAl-TEA for synthesis of isobutanol and ethanol. However, EDTA restrains CO desorption from the surface of the catalysts, and thus the strongly adsorbed CO molecules may lead to lower catalytic activity of CuZnAl-EDTA compared with CuZnAl-TEA. [ABSTRACT FROM AUTHOR]

• ATMP promotes synthesis of iso -butanol and ethanol from syngas. • ATMP leads to lattice strain and defects. • ATMP changes layered structure of HTDO. Ethanol and iso -butanol have received considerable interest to be used in automobiles as additives or as potential substitutes for gasoline. The Cu–Zn–Al hydrotalcite-derived oxides (CuZnAl-HTDO) can be used to catalyze synthesis of higher alcohols from syngas, and the complexing agents such as amino trimethylene phosphonic acid (ATMP) were used as novel modifiers to improve the catalytic activities of CuZnAl-HTDO. However, there is some lack of knowledge about the intrinsic relation between structure of the ATMP-modified CuZnAl-HTDO and its catalytic activities. Therefore, characterization techniques including FT–IR, XRD, N 2 adsorption–desorption, H 2 –TPR, CO–TPD, CO 2 –TPD and SEM were carried out to investigate the composition, crystal structure, textural properties, reducibility, alkalinity, CO adsorption behavior and morphology of the ATMP-modified CuZnAl-HTDO and its precursors. The complexation reaction between Cu2+ ions and ATMP leads to expansion of crystal structure for the precursors (Cu–Zn–Al hydrotalcite-like compounds), and thus the amount of strained and defective lattices in CuZnAl-HTDO increases after calcination of the precursors. The lattice strain and defects improve hydrogen reduction of CuO in CuZnAl-HTDO and enhance CO adsorption and dissociation on Cu active sites. In addition, a network structure formed by Cu(II)-ATMP chelate delays desorption of alcohols from Cu active sites and thus promotes CO insertion reaction. These structural changes caused by ATMP promote catalytic synthesis of iso -butanol and ethanol from syngas. [ABSTRACT FROM AUTHOR]