Preparation And Characterization Of Metallic Monolithic Catalyst For Catalytic Combustion

Catalytic combustion of natural gas is one of the most promising processes to produce environmentally clean energy. Metallic monolithic catalyst possesses several advantages over the other possibilities. However, the development of metallic monolithic catalyst is prevented by a low activity and a poor adhesion of the active component with the support. In this work, metallic monolithic catalysts were prepared by various catalytic coatings, hexaaluminate, perovskite and composite oxides on a FeCrAlloy support. The effects of pre-treatment condition of support, the preparation method of the catalyst precursor and the preparation condition of the coating slurry on the activity and adhesion strength of the final catalyst were investigated. The influence of mirror plane cations on the structure, thermal stability and catalytic activity of hexaaluminate phase was examined. It shows that La³⁺ is superior to Ba²⁺ offering a better catalytic activity, and a better thermal and structural stability. Ce was doped during the preparation of hexaaluminate, however, it does not substitute into the mirror plane but stay as CeO₂. It was found also that Ce⁴⁺ ion does not cause any effect on catalytic activity if calicned at 1000 ℃, but it decreases the catalytic activity if calcined at 1200 ℃. Mn-Substitution of aluminum ion promotes the formation of hexaaluminate under lower temperature and enhances the catalytic activity. The pretreatment of the metal support, the preparation conditions of catalyst precursor and coating slurry all have strong influence on the activity and stability of the final catalyst. For the metal supported hexaaluminate composite catalyst. It shows that the final loading is obviously higher for the coating slurry containing Al₂O₃ sol, and is similar for the catalyst precursors calcined at different temperatures. For specific coating slurry, the support oxidized at 900℃ gives the best activity among the three pre-treatment conditions. The acid eroded surface produces the best stability. The result of activity measurement indicates also that coating with well-crystallized hexaaluminate precursor is far more active than those made from the mixed oxides or non-well crystallized hexaaluminate coating slurries. For the metal supported perovskite composite catalysts, the catalyst prepared by spray-pyrolsis of sol possesses the best adhesion strength, the catalyst prepared by dip-coating of sol has better adhesion whereas the sample prepared by dip-coating of slurry is inferior to the above two samples. The sequence of catalytic activity is as follows: spray-pyrolysis>dip-coating of slurry > dip-coating of sol. For metal supported composite oxide catalysts, the sequence of the adhesion stability is Co>Mn>Cu, if FC was used as precursor and calcined at the same temperature. The temperature of methane total conversion is 730oC for the Co catalyst calcined at 800oC. The monolithic catalyst has higher activity and stable adhesion if prepared using LaMn2Al10O19 or La-Al2O3 as a first coating layer and using impregnated Co, Mn and Ce as the active component. The activity and adhesion strength were obviously affected by nature and loading amount of the first coating layer. The active component has a strong effect on catalytic activity. At the same condition of coating, the sequence of activity is as Co> Mn >Ce. High calcination temperature improves adhesion strength of catalytic material on support and decreases the activity of the final catalyst. The stability of adhesion can be modified with maintaining a high catalytic activity by adopting a method of many cycles of small amount coating.