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
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
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