Surface acidity of vanadyl pyrophosphate, active phase in n-butane selective oxidation

The surface acidity of two (VO)2P2O7 catalysts with similar specific activities per square meter of surface area in 1-butene selective oxidn., but different specific activities in n-butane selective oxidn., was studied by ammonia, pyridine, acetonitrile, CO, and CO2 adsorption, by ammonia temp.-programmed desorption, and by 2-propanol oxidn. The results for both catalysts indicate the presence of strong Broensted sites attributed to surface P-OH groups and of medium strong Lewis sites attributed to V(IV) coordinatively unsatd. ions exposed on the surface. The presence of these centers was related to the (VO)2P2O7 structure itself and is fairly independent of the (VO)2P2O7 prepn. method. However, in the (VO)2P2O7 prepd. in an org. medium and to a lesser extent in the (VO)2P2O7 prepd. in an aq. medium, the presence of very strong Lewis sites also was obsd. The enhancement of the rate of n-butane activation in the (VO)2P2O7 prepd. in an org. medium was attributed to the presence of these sites. The role of the prepn. method in the formation of such very strong Lewis sites also is discussed. [on SciFinder(R)]