Ammonia SCR is an important technique for removing NOx from diesel vehicles, where Cu/SSZ-13 is a commonly used catalyst. However, the catalysts are exposed to different chemical poisons, for example sulfur and phosphorous are present in the lubricant oil. Moreover, sulfur is also present in the fuel and since biomass contain phosphor lipids there can be phosphorous present in alternative fuels. The objective of this work is therefore to study the deactivation mechanisms for sulfur and phosphorous poisoning of Cu/SSZ-13. We use flow reactors to measure the activity and selectivity of fresh and poisoned monolith samples and we use a broad range of experimental techniques for characterization, such as BET, hydrogen TPR, XPS, UV-vis, ICP-SFMS and NMR. SO2 TPD experiments, with various gases during storage of sulfur, was used to examine the effect of gas composition on the poisoning. This in combination with XPS, UV-vis and ICP-SFMS data resulted in the finding that water significantly enhances the sulfur poisoning, especially increasing the copper sulfate species formation which decompose at high temperature. In addition, catalysts poisoned in the presence of ammonia resulted in large formation of loosely bound sulfates, likely ammonium sulfates and indeed the XPS showed a clear shift to lower binding energies indicating that different sulfate species was formed. Another interesting aspect is that when the catalyst is hydrothermally aged prior to the sulfur poisoning it results in more stable copper sulfates. We have studied the phosphporous poisoning using both incipient wetness impregnation with (NH4)2HPO4 and with gas phase evaporation of phosphoric acid and clear poisoning effect is observed for both cases for ammonia SCR and oxidation experiments. The results of XPS and NMR demonstrate the formation of copper phosphates in the P-impregnated Cu-SSZ-13. These results are consistent with the H2 TPR data, where the poisoned sample had the reduction peaks at almost 200°C higher temperature, showing that the copper species are blocked. The reduction at this high temperature is likely associated with the removal of the phosphates.

Chemical poisoning of Cu/SSZ-13 used for ammonia selective catalytic reduction

254th National Meeting (2017)

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