1434
Energy & Fuels 2001, 15, 1434-1440
Selective Formation of Isobutene from CO Hydrogenation over Zirconium Dioxide Based Catalysts Yingwei Li, Dehua He,* Yubin Yuan, Zhenxing Cheng, and Qiming Zhu State Key Laboratory of C1 Chemistry and Technology, Department of Chemistry, Tsinghua University, Beijing 100084, China Received March 19, 2001. Revised Manuscript Received July 20, 2001
Zirconium dioxide based catalysts were prepared by mechanical mixing method and evaluated in the direct synthesis of isobutene and isobutane (i-C4) from CO hydrogenation. The acid and base properties of the catalysts were altered by varying the content of additives (Al2O3, KOH) on ZrO2. Al2O3-KOH showed to be effective promoters that could remarkably enhance the i-C4 selectivity in total hydrocarbons while maintaining high activity. A CO conversion of 30% was achieved at 698 K, 5.0 MPa, 1/1 CO/H2 ratio, and 650 h-1 space time over 23.7%Al2O3-0.5%KOHZrO2. Meanwhile, the i-C4 selectivity in total hydrocarbons was about 62%. The performance of the catalysts depended on the acid-base properties of the catalysts, and the appropriate amount of acid and base and the ratio of the base to acid sites are significant for an isosynthesis catalyst to selectively produce isobutene and isobutane from CO hydrogenation.
1. Introduction Isosynthesis is the process to directly synthesize isobutene and isobutane (i-C4) from coal derived synthesis gas (CO + H2). Pichler and Ziesecke1-4 performed much of the pioneering work on isosynthesis using ThO2-based catalysts under very severe reaction conditions (150-1000 atm). Although high CO conversions were obtained, in most cases, the isobutene selectivity in total hydrocarbons was very low. Maruya5,6 studied the performance of some oxide catalysts in the isosynthesis at very moderate reaction conditions (0.68 atm, 673 K) and found that ZrO2 was an active catalyst for this reaction. Though extensive studies7-13 on ZrO2 have been made in the isosynthesis, most of the studies were performed at low i-C4 selectivity in total hydrocarbons (
