Oxydehydrogenation of ethylbenzene to styrene over metal pyrophosphates: 1. Catalyst composition and reaction variables

Abstract

A wide variety of metal pyrophosphate catalysts shows high selectivity for oxydehydrogenation of ethylbenzene to styrene which is superior to that of the orthophosphates or oxides. Whether the metal cation has only one valence state such as calcium or lanthanum or several states such as nickel or cerium has no effect on the activity. Surface treatment of common supports like alumina or silica with ammonium phosphates improves the selectivity and activity appreciably. The selectivity is sensitive primarily to the oxygen/ethylbenzene ratio and steam as a diluent permanently damages the catalyst. A variety of other alkyl aromatics can be oxydehydrogenated over these catalysts with good selectivity unless the product contains allylic or benzylic hydrogens or heteroatoms. A catalyst model is proposed in which a carbonaceous overlayer common to the various pyrophosphate substrates is the actual catalytic surface.