Regeneration of atomic Ag sites over commercial γ-aluminas by oxidative dispersion of Ag metal particles
Regeneration of atomic Ag sites over commercial γ-aluminas by oxidative dispersion of Ag metal particles
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通过银金属颗粒的氧化分散来再生商用 γ-氧化铝上的原子银位点
DOI：
10.1039/d2cy01950g
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发表时间：
2023
期刊：
影响因子：
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通讯作者：
Shimizu Ken-ichi
中科院分区：
文献类型：
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作者：
Kubota Hiroe;Mine Shinya;Toyao Takashi;Shimizu Ken-ichi
采用四种市售氧化铝粉末（CTB、PUR、VGL和CFF）制备了Ag（3wt%）负载的γ-Al 2 O3（Ag/Al 2 O3）催化剂。基于载体的不同，这些催化剂对H2辅助NH3或C3 H6选择性催化还原（SCR）NO的活性依次为CTB > PUR > VGL > CFF。在烧结处理（在800 °C下的H2还原）之后，Ag金属纳米颗粒（NP）的粒度改变，并且发现其与催化活性相关（CTB < PUR < VGL < CFF）。H2还原的Ag/Al 2 O3在500 °C下再氧化后，原位红外（IR）光谱在3762 cm−1处显示出由于HO-μ1-AlVI位点而产生的负谱带，其中谱带强度以CTB > PUR > VGL > CFF的顺序增加。对吡啶在无银γ-Al 2 O3上吸附的红外光谱研究表明，负载Ag后，强刘易斯酸中心（不饱和AlIV 3+）的数量按CTB > PUR > VGL > CFF的顺序增加，而强刘易斯酸中心的数量减少。在400 °C下在NO + O2下烧结的Ag/Al 2 O3的原位X射线吸收近边结构（XANES）和UV-vis研究显示Ag金属NP的氧化再分散以再生原子Ag（I）位点。由原位紫外-可见光谱结果估计的再分散Ag金属的量和再分散的初始速率按以下顺序变化：CTB > PUR > VGL > CFF。这些结果表明，与不饱和AlIV 3+位相邻的HO-μ1-AlVI位是Ag原子物种的锚定位，随着HO-μ1-AlVI位数量的增加，Ag/Al 2 O3的烧结阻力增加。在H2辅助SCR过程中，H2和NO + O2同时进入催化剂，随着HO-μ1-AlVI位数的增加，催化剂上高分散的Ag物种（活性位）数量增加，因此NO转化率随着载体上HO-μ1-AlVI位数的增加而增加。目前的研究结果提供了分子水平的见解，设计的抗烧结Ag/Al 2 O3催化剂的SCR。
Ag(3 wt%)-loaded γ-Al2O3 (Ag/Al2O3) catalysts were prepared using four types of commercially available alumina powders (CTB, PUR, VGL, and CFF). Based on the support, the activity of these catalysts for the H2-assisted selective catalytic reduction (SCR) of NO by NH3 or C3H6 decreased in the order CTB > PUR > VGL > CFF. After sintering treatment (H2 reduction at 800 °C), the particle size of the Ag metal nanoparticles (NPs) changed and was found to be correlated with the catalytic activity (CTB < PUR < VGL < CFF). After re-oxidation of H2-reduced Ag/Al2O3 at 500 °C, the in situ infrared (IR) spectra showed negative bands at 3762 cm−1 due to the HO-μ1-AlVI site, where the band intensity increased in the order CTB > PUR > VGL > CFF. IR study of pyridine adsorbed on Ag-free γ-Al2O3 showed that the number of strong Lewis acid sites (unsaturated AlIV3+) increased in the same order, CTB > PUR > VGL > CFF, and the number of strong Lewis acid sites decreased when Ag was loaded on the supports. In situ X-ray absorption near-edge structure (XANES) and UV-vis studies of Ag/Al2O3 sintered under NO + O2 at 400 °C showed oxidative redispersion of the Ag metal NPs to regenerate atomic Ag(I) sites. The amount of redispersed Ag metal and the initial rates of redispersion estimated from the in situ UV-vis results changed in the following order: CTB > PUR > VGL > CFF. These results suggest that the HO-μ1-AlVI site adjacent to the unsaturated AlIV3+ site on γ-Al2O3 is the anchoring site of the atomic Ag species, and the sintering resistance of Ag/Al2O3 increases with the number of HO-μ1-AlVI sites. During H2-assisted SCR, where both H2 and NO + O2 were co-fed to the catalysts, the number of highly dispersed Ag species (active sites) increased with the number of HO-μ1-AlVI sites; hence, NO conversion increased with the number of HO-μ1-AlVI sites on the support. The present results provide molecular-level insights into the design of sintering-resistant Ag/Al2O3 catalysts for SCR.