Oxidation of propene in the absence of gaseous oxygen: II. Bismuth molybdates and iron antimonates

Abstract

Propene oxidation in the absence of gaseous oxygen has been studied on unsupported bismuth molybdate with atomic ratio Mo Bi = 2.66 , and on unsupported iron antimonates prepared according to various procedures. The study was carried out in a flow reactor: the distribution of the products and the oxygen consumption were followed. The experimental conditions were: temperature, 450–550 °C; C 3H 6 WHSV, 0.1–0.2 hr −1; and C 3H 6 partial pressure, 108 mbar. On bismuth molybdate and iron antimonate with ratio Sb Fe = 2 the main oxidation product was acrolein, whereas for Sb Fe = 1 deep oxidation products were obtained. The structural modifications occurring during the reduction of bismuth molybdate are pointed out and the structure of the intermediate phase was elucidated. The chemical composition of this intermediate is close to 2Bi 2O 3 · MoO 3 and the structure is monoclinic pseudo-tetragonal ( a = b = 5.58 A ̊ ; c = 11.62 A ̊ ; γ = 89.00 ° ). The different behavior of iron-antimony catalysts obtained varying the chemical composition and the thermal treatment of the samples supports the hypothesis that the two phases of the catalyst, FeSbO 4 and Sb 2O 4, cooperate in producing acrolein with a higher selectivity than on each phase alone. A mechanism has been proposed to explain the phenomenon.