Abstract: Chemically and thermally stable monolithic catalysts are disclosed having platinum or alkali metal-vanadium active phases for use in the conversion of sulfur dioxide to sulfur trioxide. The platinum catalyst comprises a foraminous ceramic support which has at its wall surfaces a high surface area substrate for an active catalyst phase, and a combination of a platinum active phase and a promoter on the substrate. The substrate preferably comprises silica, provided, for example, by application of a silica washcoat. The promoter is selected from among compounds of zirconium, hafnium and titanium.The alkali-vanadium catalyst comprises a foraminous ceramic support having a porous silica substrate for the active phase at its foraminal wall surfaces. An alkali metal-vanadium active catalyst is in the pores of the porous silica.

Abstract: An improved process for the preparation of conjugated dienes, particularly isoprene, from the corresponding aliphatic aldehyde using an acidic dehydration catalyst is disclosed. The present invention embraces the surprising discovery that catalyst activity and selectivity, particularly for boron phosphate catalyst, can be substantially prolonged by reducing the aldehyde liquid hourly space velocity to less than about 3.0 hr.sup.-1 and preferably to less than about 1.0 hr.sup.-1.