Preparation of complexant-modified Cu/ZnO/Al2O3 catalysts via hydrotalcite-like precursors and its highly efficient application in direct synthesis of isobutanol and ethanol from syngas

Abstract

The Cu/ZnO/Al2O3 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, CO2–TPD, H2–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.