2 research outputs found

    Nanosize Effect of Al<sub>2</sub>O<sub>3</sub> in Ag/Al<sub>2</sub>O<sub>3</sub> Catalyst for the Selective Catalytic Oxidation of Ammonia

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    Ammonia (NH<sub>3</sub>) has potentially harmful effects on human health and has recently been found to be an important factor in the formation of haze; thus, its emission control is urgent, especially during haze pollution periods. In this work, two kinds of Ag/Al<sub>2</sub>O<sub>3</sub> catalysts with different Al<sub>2</sub>O<sub>3</sub> particle sizes (micro-Al<sub>2</sub>O<sub>3</sub> and nano-Al<sub>2</sub>O<sub>3</sub>) were prepared and tested for the selective catalytic oxidation of ammonia (NH<sub>3</sub>-SCO). It was shown that Ag/nano-Al<sub>2</sub>O<sub>3</sub> was much more active than Ag/micro-Al<sub>2</sub>O<sub>3</sub> for NH<sub>3</sub>-SCO in the low-temperature range. The results of characterization by BET, TEM, NH<sub>3</sub>-TPD, XRD, H<sub>2</sub>-TPR, UV–vis, and XAFS revealed that Ag/nano-Al<sub>2</sub>O<sub>3</sub> possesses much smaller Ag particles and more metallic Ag species (Ag<sub>NPs</sub>) and also contains abundant acid sites, which facilitate the adsorption and dissociation of NH<sub>3</sub>, therefore resulting in much higher NH<sub>3</sub>-SCO activity. In addition, on the basis of in situ DRIFTS, kinetic measurements, and DFT calculation results, we discovered that the NH<sub>3</sub>-SCO reaction over Ag/nano-Al<sub>2</sub>O<sub>3</sub> follows a reaction pathway we call the N<sub>2</sub><sup>–</sup> mechanism

    Effects of the Metal–Support Interaction in Ru/CeO<sub>2</sub> Nanostructures on Active Oxygen Species for HCHO/CO Oxidation

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    Catalysts comprising Ru supported on CeO2 with different morphologies have been widely investigated in various reactions, and the Ru/CeO2-nanorod catalysts have generally demonstrated higher performance. The strong interaction between Ru and CeO2 nanorods, which is beneficial to oxygen activation, is usually considered to be responsible for the higher oxidation activity of the Ru/CeO2 nanostructures. However, how the metal–support interaction of Ru/CeO2 affects the activation of oxygen species still remains elusive. In this work, we prepared two nanostructures consisting of Ru supported on CeO2 nanorod (NR) and nanocube (NC), and the Ru/CeO2-NR catalyst exhibited higher catalytic activity than Ru/CeO2-NC in the oxidation of formaldehyde (HCHO) and carbon monoxide (CO) at low temperatures. The results of complementary characterization techniques revealed that the interaction between Ru and CeO2-NC is actually stronger than that of Ru/CeO2-NR, and more interestingly, we observed that the different Ru–CeO2 interactions induce distinct active oxygen species responsible for the oxidation reactions over Ru/CeO2-NR and Ru/CeO2-NC. The stronger interaction between Ru and CeO2-NC leads to the activation of lattice oxygen on CeO2-NC and a weakened redox capacity of RuOx species. In contrast, the moderate interaction between Ru and CeO2-NR induces a higher redox capacity of RuOx species but weak activation of lattice oxygen on CeO2-NR. The active RuOx on Ru/CeO2-NR is identified as being responsible for the high activity for HCHO/CO oxidation, while the activated lattice O of CeO2-NC in the Ru–CeO2 interfacial domain is the active species on Ru/CeO2-NC, rather than RuOx, resulting in low activity. These findings on Ru/CeO2 nanostructures provide insight into understanding the metal–support interaction over Ru/CeO2 catalysts
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