No abstract

Nowadays, the most attractive technology for the elimination of nitric oxides from the exhaust gas of diesel vehicles is the selective catalytic reduction with ammonia (NH3-SCR-NOx) using Cu zeolite with the chabazite structure as the catalyst. Isolated copper species are the active sites, but the reaction intermediates and the overall reaction mechanism are still under debate. Here, we study the interaction of ammonia with zeolite Cu-SSZ-13 (CHA topology) with a uniform distribution of Cu(2+) sites prepared in one pot and a conventional Cu-ZSM-5 (MFI topology) for comparison. In situ EPR and solid-state NMR spectroscopies combined with DFT calculations have allowed the identification of NH4(+), [Cu(NH3)5](2+), [Cu(Of)2(NH3)2](2+), [Cu(Of)3NH3](2+), [Cu(NH3)2](+), and [CuOf(NH3)](+) (Of being framework oxygen) under different conditions. The results demonstrate that ammonia is able to reduce Cu(2+) to Cu(+) and provide new information on the species formed in Cu-SSZ-13, which have important implications for the elucidation of the SCR reaction mechanism.

We report here an electrochemical method for precise and accurate quantification of hydrogen absorption in palladium materials. We demonstrate that conventional chronocoulometry over-reports adsorbed hydrogen due to charge from the accompanying hydrogen oxidation reaction (HOR). We designed and built a bespoke electrochemical flow cell that mitigates the concurrent HOR reaction and consequently provides improved accuracy and reproducibility relative to other existing electrochemical techniques. The efficacy of this technique is demonstrated experimentally for a series of palladium sample types: a 100 nm electron-beam deposited thin film, a 20 μm electrodeposited palladium film, a casting of 21 nm edge-length cubic nanoparticles, and a casting of 27 nm edge-length octahedral nanoparticles. We contend that this method is the most effective for measuring hydrogen uptake in different palladium samples.