Masahiro Nitta

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

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.

Performance of Pd catalysts for aromatic oxidation in acetic acid

Abstract The performance of silica-supported Pd catalysts for the hydroxylation of naphthalene and benzoic acid has been studied in moist acetic acid. The reaction was carried out by feeding hydrogen and oxygen simultaneously to produce hydrogen peroxide in situ. Particular attention was focused on the effect of Cl− ion in the solution. When there is no Cl−, the yield of products is very low; the yield increases drastically upon addition of Cl−. On the other hand, when Cu(II) salt is added to the solution containing no Cl−, the product yield becomes much higher. The behavior of the system in the absence of Cu species closely resembles the formation reaction of hydrogen peroxide, indicating that hydrogen peroxide is the key intermediate. When Cl− is added to a Cu-containing system, the formation of Cu(I)Cl− complex(es), which reduce the reactivity, is indicated. The possibility of a Wacker-type reaction mechanism is excluded in all of our reaction systems.

Gas Phase Oxidation of Benzene to Phenol using Pd/Cu Salt Catalysts: Effect of Counter Anion in Copper Salts

The catalyst, Pd, Cu 3 (PO 4 )/SiO 2 , impregnated by H 3 PO 4 exhibits a powerful activity for the title reaction. The rate of phenol production obtained is 0.5mmol(h g-cat) −1 that is about ten times higher than that obtained with the Pd, CuSO 4 /SiO 2 catalyst studied previously. The improvement of the catalyst activity may be ascribed to the presence of a liquid film of phosphoric acid over the silica surface.