The real active sites over Zn–Cr catalysts for direct synthesis of isobutanol from syngas: structure-activity relationship

Abstract

A series of Zn–Cr oxides nanoparticles were prepared by a coprecipitation procedure. The structure of different catalysts was investigated by X-ray Absorption Fine Structure (XAFS), X-ray photoelectron spectroscopy (XPS), temperature programed reduction of hydrogen (H₂-TPR) and in situ infrared spectrum (in situ IR). Both EXAFS and XANES demonstrated the cation disorder distribution became more serious with decreasing annealing temperature and increasing Zn/Cr molar ratios. The cation distribution also affected the oxygen state on the surface over Zn–Cr spinel. The population of surface hydroxyl species increased with more serious cation disorder distribution and they facilitated the formate formation which was a significant intermediate C1 species for alcohol synthesis. This study was the first time to investigate the situation of cation distribution in Zn–Cr spinel by XAFS and related it to catalyst performance. The results revealed that the isobutanol productivity presented a linear relationship to the level of cation disorder distribution in Zn–Cr spinel, unambiguously revealing the real active sites and structure-activity relationship.