Effects of amino trimethylene phosphonic acid on structure and properties of Cu–Zn–Al hydrotalcite-derived oxides for catalytic synthesis of iso-butanol and ethanol from synthesis gas

Abstract

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, N2 adsorption–desorption, H2–TPR, CO–TPD, CO2–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.