During steam reforming, the performance of a catalyst and amount/property of coke are closely related to reaction intermediates reaching surface of a catalyst. Herein, modification of reaction intermediates by placing Mg-Al-hydrotalcite above Ni/KIT-6 catalyst in steam reforming of glycerol was conducted at 300 to 600 °C. The results revealed that the catalytic activity of Ni/KIT-6 in the lower bed was enhanced with either Mg₁-Al₅-hydrotalcite (containing more acidic sites) or Mg₅-Al₁-hydrotalcite (containing more alkaline sites) as upper-layer catalyst. The in situ infrared characterization of steam reforming demonstrated that Mg-Al-hydrotalcite catalyzed the deoxygenation of glycerol, facilitating the reforming of the partially deoxygenated intermediates over Ni/KIT-6. Mg-Al-hydrotalcite as protective catalyst, however, did not protect the Ni/KIT-6 from formation of more coke. Nonetheless, this did not lead to further deactivation of Ni/KIT-6 while Mg₅-Al₁-hydrotalcite even substantially enhanced the catalytic stability, even though the coke was much more significant than that in the use of single Ni/KIT-6 (52.7% vs. 28.6%). The reason beneath this was change of the property of coke from more aliphatic to more aromatic. Mg₅-Al₁-hydrotalcite catalyzed dehydration of glycerol, producing dominantly reaction intermediates bearing C=C, which formed the catalytic coke of with carbon nanotube as the main form with smooth outer walls as well as higher aromaticity, C/H ratio, crystallinity, crystal carbon size, thermal stability, and resistivity toward oxidation on Ni/KIT-6 in the lower bed. In comparison, the abundance of acidic sites on Mg₁-Al₅-hydrotalcite catalyzed the formation of more oxygen-containing species, leading to the formation of carbon nanotubes of rough surface on Ni/KIT-6.

摘要

在蒸汽重整过程中，催化剂的性能和焦炭的量/性质与到达催化剂表面的反应中间体密切相关。在此，在甘油的蒸汽重整中，通过将Mg-Al-水滑石置于Ni/KIT-6催化剂上方来对反应中间体进行改性，反应温度为300至600℃。结果表明，下层床中Ni/KIT-6的催化活性随着Mg ₁ -Al ₅ -水滑石（含有更多的酸性位点）或Mg ₅ -Al _{1 -}水滑石（含有更多的碱性位点）作为上床层的催化活性而增强。层催化剂。蒸汽重整的原位红外表征表明，Mg-Al-水滑石催化甘油脱氧，促进部分脱氧中间体在 Ni/KIT-6 上的重整。然而，Mg-Al-水滑石作为保护性催化剂并不能保护Ni/KIT-6免于形成更多的焦炭。尽管如此，这并没有导致Ni/KIT-6的进一步失活，而Mg ₅ -Al ₁ -水滑石甚至大大增强了催化稳定性，尽管焦炭比使用单一Ni/KIT-6要显着得多。 （52.7%对比28.6%）。其背后的原因是焦炭的性质从更脂肪族变为更芳香族。Mg ₅ -Al ₁ -水滑石催化甘油脱水，主要生成C=C的反应中间体，形成以碳纳米管为主要形态的催化焦，其外壁光滑，具有较高的芳香度、C/H比、结晶度、晶体碳尺寸、热稳定性和下层 Ni/KIT-6 的抗氧化性。相比之下，Mg ₁ -Al ₅ -水滑石上丰富的酸性位点催化了更多含氧物质的形成，导致Ni/KIT-6上形成了粗糙表面的碳纳米管。