Noncatalytic and catalytic conversion of ethane over V-Mg oxide catalysts prepared via solid reaction or mesoporous precursors

This paper deals with both noncatalytic and catalytic conversions of ethane. The effects of reactor configuration (empty tube, tube containing inert material or containing catalyst, and inert material), reaction temperature, reactant composition, and flow rate, as well as catalyst composition and structure, were systematically investigated. Two groups of V-Mg oxides, namely Meso-VMg (originated from mesostructured V-Mg oxide) and Mix-VMg (prepared via a solid reaction between vanadia and magnesia), were employed as catalysts. High conversions and selectivities were obtained at high temperatures during the ethane thermolysis to ethene, accompanied, however, by high carbon depositions, especially in the presence of a catalyst. The contribution of homogeneous reactions to the ODH of ethane was important at high, but less important at low temperatures particularly when the fraction of reactor occupied by inert silica granules was large. For the Mix-VMg catalysts, the ethane conversion and the ethene yield increased but the selectivity to ethene decreased with decreasing V/Mg atomic ratio. The Meso-VMg catalysts exhibited in most cases higher yields and selectivities to ethene than the Mix-VMg ones. In addition, a higher fraction of ethane converted to oxygenates (mainly formaldehyde) as liquid products was obtained over the Meso-VMg catalysts. Magnesium vanadates were identified in the Mix-VMg catalysts; they may represent the active phase for this series of catalysts. A V2O3 phase, which may contain highly dispersed magnesia, was identified and suggested to be responsible together with the large surface area for the high performance of the Meso-VMg catalysts. (C) 2003 Elsevier Inc. All rights reserved.