Carbon nanotube-supported metal catalysts for NOxreduction using hydrocarbon reductants. Part 1: Catalyst preparation, characterization and NOxreduction characteristics

A dual catalyst system for the Selective Catalytic Reduction of NO x with hydrocarbons (HC-SCR), including distinct low and high temperature formulations, is proposed as a means to abate NO x emissions from diesel engines. Given that satisfactory high temperature HC-SCR catalysts are already available, this work focuses on the development of an improved low temperature formulation. Pt supported on multiwalled carbon nantubes (MWCNTs) was found to exhibit superior NO x reduction activity in comparison with Pt/Al 2 O 3 , while the MWCNT support displayed a higher resistance to oxidation than activated carbon. Refluxing the MWCNT support in a 1:1 mixture of H 2 SO 4 and HNO 3 prior to the metal deposition step proved to be beneficial for the metal dispersion and the NO x reduction performance of the resulting catalysts. This support effect is ascribed to the increased Brønsted acidity of the acid-treated MWCNTs, which in turn enhances the partial oxidation of the hydrocarbon reductant. Further improvements in the HC-SCR performance of MWCNT-based formulations were achieved using a 3:1 Pt-Rh alloy as the supported phase.