The background and main points of recent works on vapor phase oxidation of C
3, C
4 olefins and ethylbenzene with multi-component oxide catalysts are described.
Fe-As and Mo-Ce (or Al, Ba, Sr) -As oxides were found to have high catalytic activity for producing acrolein by vapor phase oxidation of propylene with air. The activity of Fe-As oxide decreased with reaction time because of the escape of As component, especially in the reaction at high temperature, such as oxidation of i-butylene to methacrolein.
This defect was eliminated and initial activity was kept by adding Li component to Fe-As system. With Fe-Li-As oxide of atomic ratio= 1 : 2 : 2.5 1 : 3 : 3, high yield of methacrolein was obtained from
i-butylene at the temperature of 470°C.
By means of searching direct oxidation of the olefins with Fe-As
5+ oxide systems and formation of As
5+ in As
3+ oxide systems and studying the structure of catalyst, following conclusions were obtained.
The catalytic oxidation of α-CH bond to aldehyde is carried out by a cycle consisting of two reactions :
2 As
5+ oxide + CH
2 = CR-CH
3 → 2 As
3+oxide CH
2= CR-CHO and
2 As
3+oxide + O
2 → 2 As
5+oxide (R : H or -CH
3).
The former reaction, remarkably promoted by the Fe component in the catalyst, is always accompanied with formation of CO
2, but proceeds more dominantly when As
5+ concentration is high. Two structures of -Fe-O-As- and -Li -O-As- were observed in Fe-Li-As oxide catalyst; the former is more easily reduced with olefin than the latter.
-Fe-O-As- structure has at least two kinds of active site. Unsaturated aldehyde forms on one site and CO
2 on another site. Li-O-As structure is stable and instrumental in preventing the escape of As component into vapor phase.
The activity of Mo-X-As (X : alkaline earth metal) oxide catalyst for oxidative dehydrogenation of 1-butene was studied in connection of its preparation and physical property.
A Si-Ce-Sb oxide catalyst of new type showed relatively high activity for styrene formation by oxidative dehydrogenation of ethylbenzene.
抄録全体を表示