首页> 外文期刊>Applied Catalysis, A. General: An International Journal Devoted to Catalytic Science and Its Applications >Influence of the compensating anions of Ni/Al and Ni/Mg/Al layered doubled hydroxides on their activation under oxidising and reducing atmospheres
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Influence of the compensating anions of Ni/Al and Ni/Mg/Al layered doubled hydroxides on their activation under oxidising and reducing atmospheres

机译:Ni / Al和Ni / Mg / Al层状双金属氢氧化物的补偿阴离子对其在氧化和还原气氛下的活化的影响

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The activities and selectivities in the hydrogenation of acetonitrile on catalysts obtained from Ni/Al and Ni/Mg/Al layered double hydroxides (LDHs) precursors depend on the nature of their compensating anions: CO~(2-)_3, NO~-_3or Cl~-. The latter gives rise to sample with low activity and the less selective to primary amine. Studies by XRD, TG-DSC, mass spectrometry and TRP experiments show that the anion influences the thermal stability and the reducibility of the Ni-containing LDHs. The thermal decomposition of LDH into the mixed oxide form involves the dehydration, then the dehydroxylation of the layers with the concurrent decomposition of CO~(2-)_3 and NO~-_3 which occurs at similar temperature in air or H_2 atmosphere. In TPR experiments the reduction of Ni~(2+) to Ni~0 takes place at above 800 K. A specific behaviour is observed when Cl~- is the compensating anion, with a better reducibility of Ni~(2+) and the existence of Ni species reduced at low temperatures, not observed with CO~(2-)_3 and NO~-_3 as anions. In addition, all the mixed oxides are poorly reconstructed in water, and a clear segregation of bayerite occurs on the chloride samples. This last phenomenon is enhanced in the Mg-containing compound. It is proposed that the presence of both Cl and Mg favours the extraction of aluminium and makes the accessibility to a significant amount of Ni~(2+) cations easier, thus increasing their reducibility. In this case, Ni~0 particles with an average size around 65 nm are detected after reduction at 723 K, while the other samples, Poorly reduced, still contain the mixed oxide structure.
机译:从Ni / Al和Ni / Mg / Al层状双氢氧化物(LDHs)前驱体获得的催化剂上乙腈加氢的活性和选择性取决于其补偿阴离子的性质:CO〜(2-)_ 3,NO〜-_3或Cl〜-。后者导致样品的活性低,对伯胺的选择性较低。通过XRD,TG-DSC,质谱和TRP实验研究表明,阴离子会影响含Ni的LDH的热稳定性和还原性。 LDH热分解为混合氧化物形式涉及脱水,然后层脱羟基,同时发生CO〜(2-)_ 3和NO〜-_3分解,这在相似的温度下在空气或H_2气氛中发生。在TPR实验中,Ni〜(2+)还原为Ni〜0发生在800 K以上。当Cl〜-为补偿性阴离子时,观察到特定行为,Ni〜(2+)和Ni〜(2+)的还原性更好。低温下Ni的存在减少,而CO〜(2-)_ 3和NO〜-_3为阴离子则没有观察到。此外,所有混合氧化物在水中的重建效果均较差,氯化物样品上发生了透明的偏黄石偏析。最后一种现象在含镁化合物中得到增强。有人提出,Cl和Mg的存在有利于铝的提取,并使大量Ni〜(2+)阳离子的可及性变得更容易,从而提高了它们的还原性。在这种情况下,在723 K下还原后,会检测到平均粒径约为65 nm的Ni〜0粒子,而其他还原性差的样品仍包含混合氧化物结构。

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