Cation exchanged and impregnated Ti-pillared clays for selective catalytic reduction of NOx by propylene

Ti-pillared interlayer clay (PILC)-based catalysts ion exchanged with Cu, Ni and Fe were prepared and used for the selective catalytic reduction of NOx using propylene as the reducing agent. The influence of the metal loading in the SCR activity was studied. Likewise, catalytic activity of Cu-ion exchanged samples was compared to that of Cu-ones. In both cases, the catalytic activity increased with increasing metal loading, reaching a maximum of NOx conversion, and then decreased at higher loading. The maximum of NOx conversion was achieved in each set of catalysts for the samples NiTi-3.4, FeTi-8.0 and CuTi-7.4. Ti-PILCs-ion exchanged with Cu was the most active catalyst for the SCR of NOx by propylene. H2-TPR results showed that Ni2+ in Ti-PILC-based catalysts was harder to reduce than Cu2+ in the same material. It was observed that, as the Cu content is increased, CuO and isolated Cu2+ species became easier to reduce in ion exchanged samples. Likewise, it was also noted that the relative H2 consumption decreased with the Cu content, due to a lower accessibility of H2 to the metal. It can be verified a correlation between NOx conversion and the H2 consumption for the Cu2+→Cu+ reduction process, reaching the maximum for the sample CuTi-7.4. Finally, it was observed that the presence of 10% water in the feed inhibited the SCR of NO activity of this catalyst. However, this effect was completely reversible following the removal of water from the gas stream.