Promoted VOC oxidation over homogeneous porous CoxNiAlO composite oxides derived from hydrotalcites: effect of preparation method and doping

Abstract

Homogeneous porous and curve plated Co_xNiAlO composite metal oxide catalysts are obtained from the thermal decomposition of Co_xNiAl-layered double hydroxide (LDH) precursors, which are prepared by urea co-precipitation with surfactant, followed by a hydrothermal treatment. The as-prepared samples were characterized by XRD, BET, SEM, TEM, H₂-TPR and XPS. The Co₃AlO sample shows 90% benzene conversion (T₉₀) at 236 °C at a high space velocity (SV = 60 000 mL g⁻¹ h⁻¹), and possesses much higher activity than Co₃AlO prepared with NaOH co-precipitation without surfactant, with T₉₀ = 288 °C. This is mainly correlated with the narrower pore size (2.9 vs. 17.2 nm) and lower temperature reducibility (319 vs. 360 °C). The Co₂NiAlO sample exhibits enhanced activity at T₉₀ = 227 °C with the low activation energy of 39.0 kJ mol⁻¹, and its lower temperature reducibility is ascribed to the larger amount of surface accessible Co³⁺. The Co₂NiAlO sample owns good reproducibility and superior reversibility and long stability with prolonged time on benzene stream in the presence of 3.5% water vapor. Moreover, a monolithic Co₂NiAlO film catalyst is fabricated by the thermal decomposition of an LDH film precursor through an in situ growth methodology, with a high reaction rate of 1.21 mmol g⁻¹ h⁻¹ under T₉₀ = 275 °C.