Abstract
Effects of the incorporation of Cr, Ni, Co, Ag, Al, Ni and Pt cations in titanate nanotubes (NTs) were examined on the NOx conversion. The structural and morphological characterizations evidenced that the ion-exchange reaction of Cr, Co, Ni and Al ions with the NTs produced catalysts with metals included in the interlayer regions of the trititanate NTs whereas an assembly of Ag and Pt nanoparticles were either on the nanotubes surface or inner diameters through an impregnation process. Understanding the role of the different metal cations intercalated or supported on the nanotubes, the optimal selective catalytic reduction of NOx by CO reaction (SCR) conditions was investigated by carrying out variations in the reaction temperature, SO2 and H2O poisoning and long-term stability runs. Pt nanoparticles on the NTs exhibited superior activity compared to the Cr, Co and Al intercalated in the nanotubes and even to the Ag and Ni counterparts. Resistance against SO2 poisoning was low on NiNT due to the trititanate phase transformation into TiO2 and also to sulfur deposits on Ni sites. However, the interaction between Pt2+ from PtOx and Ti4+ in the NTs favored the adsorption of both NOx and CO enhancing the catalytic performance.
Highlights
Titanate nanotubes are fascinating solids that have spurred significant interest as catalysts for several reactions [1,2]
The Na2Ti3O7 structure has an edgeshared TiO6 octahedron in a zigzag-like patterned arrangement, where the Na+ ions reside between these layers and occupy two different crystallographic sites bound to the oxygen anions [26,27]
As NOx can be physically adsorbed on the surface of the solids at low temperatures [6,48], the subsequent increase of the activity is observed at higher temperatures
Summary
Titanate nanotubes are fascinating solids that have spurred significant interest as catalysts for several reactions [1,2]. With the use of metal center intercalated into the titanate nanotubes structure, the NH3-SCR reaction proceeds in the presence of a bifunctional catalyst through the formation of intermediate species such as hydrogen cyanide (HCN), isocyanate (–NCO), nitromethane (CH3NO2) and oxygenated hydrocarbons (CxHyOz) [5,8,18], which are accompanied by nitrogen and carbon dioxide. These solids have gathered much information, they did not show details about the catalyst’s active site features, neither it was proposed proper reaction conditions to apply the solids.
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