NO reduction by CH4 over well-structured Pt nanocrystals supported on γ-Al2O3

Platinum nanocrystals, with an average diameter of 12 nm, were prepared by reduction of K2PtCl4 with H2 in the presence of a structure-directing agent (polymer of N-isopropylacrylamide). The Pt nanocrystals, having mainly (1 0 0) structure (≈64%), were supported on γ-Al2O3 and then tested for the reduction of NO (1%) with CH4 (0.6%) in the temperature range 300–500 °C. The NO was completely converted to N2 and N2O starting from 400 °C. The formation of NH3 as side product could not be evidenced below 600 °C. In the temperature range investigated, the only product of methane oxidation was CO2. The highest selectivity to N2 (≈73%) was observed at 500 °C. In contrast to Pt(1 0 0)/Al2O3 catalyst, substantial amounts of CO and NH3 are formed over the conventionally prepared Pt/γ-Al2O3 catalyst (NH3 starts to be formed at temperatures as low as 400 °C). The remarkable differences observed between Pt(1 0 0)/Al2O3 and Pt/Al2O3 (conventional) catalysts reveal the importance of the morphology of the supported Pt particles for NO/CH4 reaction. Both, the size and dominant crystallographic orientation of the supported Pt particles have been found to be determining factors for the catalyst activity and selectivity. The formation of NH3 and CO can be suppressed by using as catalyst the large, well-defined Pt nanocrystals supported on alumina.