Preparation-Properties Relation of Mn-Cu Hopcalite Catalyst

Abstract

Problem statement: The Mn-Cu hopcalite catalyst was used for the conversion of CO to CO₂ at low temperatures. It was the catalyst of choice in the gas masks for respiratory protection in mines, aircrafts, military, spatial laboratories. Approach: The efficiency of hopcalite catalyst depends on its surface parameters. Its surface characteristics can be influenced from the chosen way of the MnO₂ and CuO precipitation and from the pressure of pelletizing. Results: The hopcalite samples has been prepared by precipitation of MnO₂ and by adding CuSO₄ further in the solution the adsorption of Cu²⁺ ions on MnO₂ particles surface is achieved. After acidification of the solution up to pH = 3 the copper is precipitated in form of Cu (OH)₂CuCO₃ by adding NaHCO₃. Precipitate was washed, dried, pressed, crushed, sieved (1-2 mm) and calcined at 180°C for 3 h. MnO₂ and hopcalite samples were characterized by XRD. The activity was evaluated by determination of its protection time and it was 610 min, better than activity of a commercial catalyst. Specific surface area, pore volume and density were measured by nitrogen adsorption and mercury intrusion porosimetry. The X-Ray diffractograms shows that the only crystallinity of hopcalite comes from MnO₂, which is present mainly in amorphous form. By increasing the pressure in the pelletizing step, a significant decrease in the specific surface area (247.64-147.77 m² g^-1) and in the total pore volume (446-278 mm³ g^-1) is observed in the hopcalite samples. Conclusion: The obtained hopcalite catalyst by the two step precipitation method shows high catalytic activity. The increasing pressure increases the strength and reduces the specific surface area and pore volume. A pressure of 500 kg cm^-2 is recommended for the hopcalite production procedure.