Effects of redox properties and acid-base properties on isosynthesis over ZrO2-based catalysts

ZrO2-based catalysts doped with CeO2 or Y2O3 were prepared by coprecipitation and the catalytic performance of each was evaluated in the selective synthesis of isobutene and isobutane (i-C-4) from CO hydrogenation at 673 K, 5.0 MPa, and 650 h(-1). The physical properties and chemical properties (acid-base and redox) of the catalysts were systematically characterized and related to the catalytic performance. The catalytic activities and selectivities of the ZrO2-based catalysts varied with the quantity of CeO2 and Y2O3 doped. The physical properties, such as surface areas, cumulative pore volumes, average pore diameters, crystal phases, and crystal sizes had no appreciable effects on the catalytic performance of the catalysts. Temperature-programmed reduction (TPR) of H-2 measurements showed that the addition of CeO2 or Y2O3 into ZrO2 enhanced the reduction properties of the catalysts. The highest activities and C-4 selectivities in total hydrocarbons were obtained over the catalysts which have a maximum amount of H-2 consumption measured by TPR technology for both CeO2- and Y2O3-doped ZrO2-based catalysts. The selectivity to i-C-4 in total hydrocarbons also achieved a maximum over the catalyst (50% CeO2-doped ZrO2) which has a maximum amount of H-2 consumption in the TPR for the CeO2-ZrO2 mixed oxide catalysts. For the Y2O3-ZrO2 mixed oxide catalysts, high selectivities to i-C-4 in total hydrocarbons were obtained over the catalysts with the contents of doped Y2O3 ranging from 4.5 to 8.6%; whereas the maximum H-2 consumption was attained at 8.6% Y2O3 doped. The acid-base properties also played a significant role in determining the activity and selectivity of the ZrO2-based catalysts in the CO hydrogenation. A coordination of redox and acid-base properties accounts for the remarkable improvement of reaction activities and selectivities over the CeO2- or Y2O3-doped ZrO2-based catalysts in this investigation. (C) 2003 Elsevier Inc. All rights reserved.