Catalyst and dehydrogenation process

#Unsaturated lower aliphatic acids and esters, and particularly methacrylic acid and its esters, are used in the preparation of polymers which find wide commercial applicability.

#The preparation of such unsaturated lower aliphatic acids and esters is typically carried out by the catalytic oxidative dehydrogenation of the corresponding saturated acids and esters. A wide variety of catalysts has been proposed for such reactions. However, the catalysts previously proposed share one or more deficiencies. Earlier catalysts, for example, frequently result in an undesirably low conversion in the catalytic process or low selectivity for the desired unsaturated acid product. Others exhibit short catalytic life or higher cost than would be commercially acceptable. Accordingly, continued effort has been directed toward the development of better catalysts for this oxidative dehydrogenation reaction.

#The present invention provides an improved catalyst that results in high selectivity and yield in the oxidative dehydrogenation of saturated lower aliphatic acids and esters to the corresponding unsaturated acids and esters.

#The instant invention is further illustrated by the following specific examples, in which parts and percentages are by weight unless otherwise indicated.

#In Examples 1-14 and Comparative Examples A-H, the catalytic compositions were prepared by first forming a solution of ferric nitrate enneahydrate, chromium nitrate enneahydrate, alkali metal nitrate and lead nitrate in distilled water at 50.degree. C., each of the nitrates being present in quantities that will result in the desired atomic ratio of the metal in the final product. To this solution was added 85% phosphoric acid, also in quantities sufficient to provide the required amount of phosphorus in the final product. This solution was stirred for ten minutes, and had a highly acidic character, exhibiting a pH of less than 1.0.

#In those examples using colloidal silica as a catalyst support, the silica was added to the solution with additional stirring for ten minutes.