THE EFFECT OF HYDROGEN ON THE CARBONACEOUS LAYER FORMED ON MOLYBDENUMMODEL CATALYSTS DURING HIGH-TEMPERATURE PROPYLENE METATHESIS

The formation and hydrogen removal of the thick carbonaceous layer acc umulated during metathesis of propylene at 880 R on molybdenum and mol ybdenum oxide model catalysts is examined, It is determined that a hyd rocarbon layer several monolayers thick forms rapidly during reaction, and that a portion of tills layer may be easily removed by healing th e used catalyst in hydrogen. An activation energy of 6.4 +/- 0.4 kcal/ mol is observed fur this process. A graphitic layer also forms slowly on the catalyst surface during reaction, and tills layer is difficult to remove by reaction with hydrogen. It is demonstrated that addition of hydrogen to the metathesis reaction mixture reduces the thickness a f the carbonaceous layer on the catalyst surface during reaction, ther eby enhancing the observed metathesis rate. (C) 1998 Academic Press.