Gas phase oxidation of benzene to phenol using Pd–Cu composite catalysts. Part 2. Performance of CuSO4-based catalysts

Abstract

Gas phase oxidation of benzene to phenol has been studied using Pd–Cu composite catalysts which were prepared mainly by impregnating the respective metal salts on silica gel. If one of the two metal species is absent from the catalyst, no catalytic activity is observed. Good performance is obtained with catalysts having 5–10 × 10^–6 mol Pd and 5–10 × 10^–3 mol CuSO₄ per gram silica over the temperature range 140–250°C. When Pd is loaded by means of ion exchange instead of impregnation, the performance is nearly doubled. The reaction rate is rather high and the use of a higher gas flow rate is also advantageous. The water content of the catalyst affects the performance appreciably, and an external supply of steam improves the performance by a factor of almost two. A rate of phenol production of 0.7 × 10^–4 mol (h g-cat)^–1 with more than 90% selectivity is readily achieved. How to suppress the predominant formation of water is the remaining task to be studied.