Enhancing the Catalytic Oxidation of Carbon Monoxide Using K-OMS-2 by Surface Modification with Binary Oxides of Copper and Other Metals

With the goal of finding low-cost materials that can completely substitute the precious- and noble-containing catalysts and be active toward the oxidation of CO at low temperatures (around 100 °C), transition metal oxide-doped cryptomelane (e.g., K-OMS-2, MeO_x/K-OMS-2, and CuO_x-MeO_x/K-OMS-2; Me = Ni, Fe, Cd, Sn, Mn, Cr, Co, Zn, and Al) were obtained by the impregnation method with different synthesis conditions. The synthesized samples were then tested for CO conversion and characterized by means of powder X-ray diffraction, elemental mapping and composition, as well as scanning electron microscopy. It was demonstrated that the K-OMS-2 support doped by a composite of CuO_x-NiO_x (promoter) and calcined at 400 °C gave higher catalytic activity than the other samples, with a 90% CO conversion at around 120 °C. Other factors that could be controlled for increasing CuO_x-NiO_x/K-OMS-2_400 activity were to set the mass percentage of dopants and the atomic ratio of Cu:Ni to about 15 mass% and 1:1, respectively. Under different catalytic reaction conditions such as various inlet CO concentrations (C_CO, 750–4000 ppm), amounts of catalyst (m_cat, 0.25–1.25 g), and gas-air flow rates (F_gas, 0.5–1.25 L/min), the catalyst activity was found to be enhanced when the C_CO and F_gas were reduced and the m_cat raised. Moreover, the CuO_x-NiO_x/K-OMS-2_400 catalyst exhibited high stability and durability. The calculated average size of K-OMS-2 crystallites was approximately 12 nm, while the composite phase was in its amorphous state. This sample showed a morphology of nanofiber-like shapes with different lengths.