Hydroxyapatite supported molybdenum oxide catalyst for selective dehydrogenation of cyclohexane to cyclohexene: studies of dispersibility and chemical environment

The selective oxidative dehydrogenation of cyclohexane to cyclohexene was conducted using molybdenum oxide (MoO_x) as a catalyst and hydroxyapatite (HAP) and Ca₅(OH)(PO₄)₃ as carriers. Two series of MO_x/HAP catalysts with varying MoO_x loading capacity and calcination temperature were prepared via the co-impregnation method. The impact of dispersibility and chemical environment on the catalytic performance of MoO_x was investigated. The catalysts were characterized using XRD, XPS, H₂-TPR, and UV-Vis spectra. These MoO_x/HAP catalysts were employed for the oxidative dehydrogenation (ODH) of cyclohexane to cyclohexene. MoO_x/HAP catalysts with lower loading capacity exhibited higher dispersion of MoO_x and selectivity towards cyclohexane. The calcination temperature directly influenced the chemical environment of MoO_x, thereby affecting its catalytic performance. Samples calcinated at lower temperatures (500 °C and 600 °C) demonstrated higher conversion rates for cyclohexane, while samples calcinated at higher temperatures (above 700 °C) displayed greater selectivity towards cyclohexane. At 430 °C, when the conversion rate of cyclohexane reached 13.1%, the selectivity of cyclohexene over MHAP-0.05-800 catalyst reached 58.2%.