Higher alcohol synthesis reaction study using K- promoted ZnO catalysts. III

Abstract

Recent results indicate that modified high- temperature, high- pressure, Zn/Cr spinel methanol synthesis catalysts consist primarily of ZnO at the catalyst surfaces. Nonpromoted and K- promoted ZnO powders, therefore, were tested for methanol and isobutanol production using a 1:1 H₂ and CO syngas feedstream at two operating pressures (6.9 and 10.3 MPa) and two reactor bed temperatures (400 and 440°C). No isobutanol formation occurs over the nonpromoted ZnO. The highest isobutanol production is obtained using a 1 wt% K-containing ZnO catalyst while operating the reactor at 440°C and 10.3 MPa, but the greatest hydrocarbon byproduct rate also is obtained under these conditions. Although the isobutanol product rates are lower than the best values presented in the literature, the product rate of isobutanol formation is limited by a lower surface area of the promoted ZnO catalysts in comparison to the Zn/Cr spinel catalysts. The ratio of the BET surface areas of the K/ZnO catalysts to the surface area of an alkali-modified, commercial Zn/Cr spinel catalyst is approximately 0.23. Comparison of the catalysts on a surface area basis could result in the promoted ZnO samples performing better than the alkali- promoted Zn/Cr spinel catalysts. Most importantly, this study demonstrates that the promoted ZnO is the active catalyst phase for this reaction and that the spinel structure is not required for high activity.