Cu-Zn-Cr2O3 catalysts for dimethyl ether synthesis: Structure and activity relationship

The CuO dispersed on ZnCr2O4 catalysts derived from Cu-Zn-Cr hydrotalcite like layered double hydroxide precursors with varying Zn/Cr ratios have been synthesized, characterized by BET-Surface area, X-ray diffraction (XRD), temperature programmed reduction (TPR), electron spin resonance (ESR), N2O titrations and the activities were evaluated for single step dimethyl ether (STD) synthesis from syngas. It is observed that the copper species were in highly dispersed state over Cu-ZnO-Cr2O3 at high Zn/Cr ratios while the copper cluster were present at low Zn/Cr ratios. The ESR analysis revealed signals due to isolated Cu2+ at high Zn/Cr ratios and clustered Cu2+ at low Zn/Cr ratio in fresh catalysts and only Cr3+ species in used catalysts. The TPR results indicated that the reduction peak shifted to high temperatures with an increase in chromium content due to large copper crystallites, which was supported by XRD analysis. The conversion of syngas to DME was well correlated with the copper metal surface areas, indicating that STD synthesis can be controlled by methanol synthesis rate.