Production of methacrylonitrile

A process for preparing methacrylonitrile by reacting isobutylene or tertiary butanol with ammonia and oxygen in a gaseous phase, comprising:

• (A) carrying out the reaction
• (i) on a catalyst system consisting essentially of (1) 30-70% by weight of a silica catalyst carrier and (2) a catalyst having a composition represented by the following general formula:
• A.sub.a Mo.sub.12 Bi.sub.b Fe.sub.c Na.sub.d P.sub.e O.sub.x
• wherein
• A is at least one element selected from the group consisting of potassium, rubidium and cesium, and a, b, c, d, e and x are the atomic ratios of A, bismuth, iron, sodium, phosphorus and oxygen, respectively, relative to twelve atoms of molybdenum, wherein:
• a is between 0.05 and 1.0
• b is between 1 and 18,
• c is between 2 and 10,
• d is between 0 and 3.6,
• e is between 0 and 3, and
• x is the number of oxygen atoms required to satisfy the valence requirements of the other elements present, said catalyst having a surface area of 2.5-6.2 m.sup.2 /g, and a feedstock conversion rate with no substantial decrease in conversion percentage points from the initial value while producing carbon deposition of less than 0.05 g carbon/100 g catalyst, after 1000 hours of continuous use;
• (ii) at a reaction temperature of 380.degree. C. to 480.degree. C.;
• and
• (iii) at a contact time of 1 to 10 seconds;
• and
• (B) maintaining the oxygen volume concentration in the gaseous reaction mixture at the outlet of the catalyst bed below about one percent.