CATALYTIC SELECTIVE OXIDATION OF PROPANE

Results on the oxidative conversion of propane on three types of catal ysts on which different mechanisms of propane activation prevail are d iscussed, whereby the reaction conditions and final product distributi on are affected. In the case of the redox-mechanism on V2O5-based cata lysts the degree of catalyst reduction which is affected by the propan e-to-oxygen ratio determines the catalyst activity and selectivity. On rare-earth oxide-based catalysts, activation of propane by adsorbed o xygen takes place. As derived from transient experiments under vacuum conditions, adsorbed oxygen species convert propane into C3H6, C2H4, C H4, and COx. Continuous flow experiments on Na-P/Sm2O3 (Na:P:Sm=2:1:70 0) and Ln(2)O(3)/SrO (Ln=Sm, La, Nd; Ln:Sr=5:l) catalysts at I bar sho wed that due to high catalyst activity the ignition of the reaction mi xture takes place at 420-450 degrees C. The heat produced by the oxida tive conversion of propane was sufficient to sustain the reactions aft er ignition with the preheat of the feed gas under conditions chosen. Higher selectivity to C2H4 (ca. 30%) compared to C3H6 (ca. 20%) was ob served in the whole range of the reaction conditions indicating that C -C splitting prevails when adsorbed oxygen participates in the reactio n. Finally, propane activation via redox-mechanism and adsorbed oxygen is ruled out for B2O3/Al2O3 catalysts. The involvement of Lewis acid sites in the generation of propyl radicals is assumed; olefins and C-1 -C-3 oxygenates are formed with high selectivities even in excess of o xygen most probably via secondary reactions of propyl radicals and oxy gen in the gas phase. (C) 1998 Elsevier Science B.V. All rights reserv ed.