The influence of Fe speciation on the decomposition rates of N2O over Fe-ZSM-5 catalysts prepared by Chemical Vapour Impregnation were investigated. Various weight loadings of Fe-ZSM-5 catalysts were prepared from the parent zeolite H-ZSM-5 with a Si:Al ratio of 23 or 30. The effect of Si:Al ratio and Fe weight loading was initially investigated before focussing on a single weight loading and the effects of acid washing on catalyst activity and iron speciation. UV/Vis spectroscopy, surface area analysis, XPS and ICP-OES of the acid washed catalysts indicated a reduction of ca. 60% of Fe loading when compared to the parent catalyst with a 0.4 wt% Fe loading. The TOF of N2O decomposition at 600 °C improved to 3.99 × 103 s-1 over the acid washed catalyst which had a weight loading of 0.16%, in contrast, the parent catalyst had a TOF of 1.60 × 103 s-1. Propane was added to the gas stream to act as a reductant and remove any inhibiting oxygen species that remain on the surface of the catalyst. Comparison of catalysts with relatively high and low Fe loadings achieved comparable levels of N2O decomposition when propane is present. When only N2O is present, low metal loading Fe-ZSM-5 catalysts are not capable of achieving high conversions due to the low proximity of active framework Fe3+ ions and extra-framework ɑ-Fe species, which limits oxygen desorption. Acid washing extracts Fe from these active sites and deposits it on the surface of the catalyst as FexOy, leading to a drop in activity. The Fe species present in the catalyst were identified using UV/Vis spectroscopy and speculate on the active species. We consider high loadings of Fe do not lead to an active catalyst when propane is present due to the formation of FexOy nanoparticles and clusters during catalyst preparation. These are inactive species which lead to a decrease in overall efficiency of the Fe ions and consequentially a lower TOF.

中文翻译：

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研究铁形态对Fe-ZSM-5催化剂上N2O分解的影响。

研究了化学气相浸渍法制备的Fe-ZSM-5催化剂上，铁的形态对N2O分解速率的影响。由母体沸石H-ZSM-5以23:30的Si：Al比制备了各种重量负载的Fe-ZSM-5催化剂。单重负载和酸洗对催化剂活性和铁形态的影响。酸洗催化剂的UV / Vis光谱，表面积分析，XPS和ICP-OES表明ca的减少。与具有0.4 wt％Fe含量的母体催化剂相比，Fe含量为60％。与重量为0.16％的酸洗催化剂相比，在600°C下N2O分解的TOF改善为3.99×103 s-1，相比之下，母体催化剂的TOF为1.60×103 s-1。将丙烷添加到气流中以充当还原剂并去除残留在催化剂表面上的任何抑制性氧。当存在丙烷时，比较具有较高和较低铁负载量的催化剂可达到相当水平的N2O分解。当仅存在N2O时，低金属负载的Fe-ZSM-5催化剂由于活性骨架​​Fe3 +离子和骨架外的α-Fe物种的接近度低而无法实现高转化率，这限制了氧气的解吸。酸洗从这些活性位点提取铁，并将其作为FexOy沉积在催化剂表面，导致活性下降。使用UV / Vis光谱法鉴定催化剂中存在的Fe物种，并推测活性物种。我们认为当丙烷存在时，由于在催化剂制备过程中会形成FexOy纳米颗粒和团簇，因此高含量的Fe不会导致活性催化剂。这些是非活性物质，导致Fe离子的整体效率降低，因此TOF降低。