The catalytic oxidation of cyclopentadiene (CPD) has been studied using $V_2O_5$-Ag (V:Ag = 1:0.003) as the active component of the catalyst system.
The reaction of CPD oxidation is complex giving many kinds of reaction products. Maleic anhydride (MA) was a major oxidation- product and phthalic anhydride (PA) was a important byproduct. It seemed that MA was formed through direct as well as indirect routes proceeding via intermediates such as cyclopentenone and cyclopentenedione. The direct route gave higher selectivity.
Mars and van Krevelen kinetic model was applied and it appeared the reoxidation of catalyst was the rate determining step.
The high selectivity of silver-added vanadia may be attributed to the formation of $AgV_6O_{15}$ phase in $V_2O_5$. The addition of silver lowers the activation energy in CPD oxidation.
Effects of the supports, α-alumina and titania (anatase), were also investigated. Catalysts supported on α-alumina showed very poor dispersion of vanadia. The size of vanadia crystallites on α-alumina increased with the amount of loading. The small vanadia crystallites exsisting at low loading showed higher PA selectivity compared with the bulk vanadia.
Catalysts supported on titania (anatase), however, showed high dispersion of vanadia, existing as monolayer and scattered small crystallites. The crystallites size was almost constant independently of loading. PA selectivity was high on titania support. The favoring of PA production seemed to be intrinsic property of small sized vanadia.
