Ternary and quaternary Cr or Ga-containing ex-LDH catalysts-Influence of the additional oxides onto the microstructure and activity of Cu/ZnAl2O4 catalysts
Ternary and quaternary Cr or Ga-containing ex-LDH catalysts-Influence of the additional oxides onto the microstructure and activity of Cu/ZnAl2O4 catalysts
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DOI：
10.1016/j.cattod.2014.08.029
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发表时间：
2015-05-15
期刊：
影响因子：
5.3
通讯作者：
Behrens, Malte
中科院分区：
文献类型：
--
作者：
Kuehl, Stefanie;Schumann, Julia;Behrens, Malte
Al被Cr和Ga逐步取代，形成了四元LDH前驱体Cu/ZnM_2O_4(M=Al，Ga，Cr)催化剂。在催化剂制备过程中，由于氧化铬相参与了氧化还原过程，随着铬的取代，铜相与氧化物基质的相互作用逐渐减弱。这种活性氧化铬基质在稳定铜/锌催化剂特殊微观结构方面不如惰性氧化铝基质有效。这些减弱的相互作用导致了铜颗粒嵌入的降低，与还原过程中明显的铜微晶生长相一致。这两种效应部分地相互补偿，在铜表面观察到中间铬含量的最大值。在Ga替代催化剂中，发现了两种不同的铜物种以获得较高的Ga含量。这归因于部分晶态尖晶石的存在以及CuO相与晶态氧化物和非晶态氧化物界面作用强度的不同。还原后的催化剂具有相近的平均铜颗粒尺寸和铜比表面积。在这两个样品系列中，催化合成甲醇的活性并不随铜比表面积的变化而变化，实验表明，要获得铜相的稳定性和活性，必须与氧化物发生较强的相互作用。因此，Al取代证实了铜和氧化物之间的界面相互作用似乎有利于影响铜颗粒的活性，而最佳催化剂需要暴露表面和界面之间的折衷。(C)2014爱思唯尔B.V.保留所有权利。
The stepwise substitution of Al by Cr and Ga leads to quaternary LDH precursors for Cu/ZnM2O4 (M = Al, Ga, Cr) catalysts. With the substitution of Al by Cr the interaction of the Cu phase with the oxide matrix is gradually weakened, which is caused by the participation of the chromium oxide phase in the redox processes during catalyst preparation. Such reactive Cr oxide matrix is less efficient than the inert Al oxide matrix in stabilizing the special microstructure of Cu/ZnM2O4 catalysts. These weakened interactions led to a lowering of the Cu particle embedment, coinciding with a pronounced Cu crystallite growth during reduction. Both effects partially compensate each other and a maximum in Cu surface area is observed for intermediate Cr contents. In the Ga-substituted catalysts, two distinct Cu species were found for high Ga contents. This is attributed to the presence of partially crystalline spinel and the resulting different strength of interface interaction of the CuO phase with the crystalline and the amorphous oxide. After reduction Cu catalysts with similar average Cu particle sizes as well as Cu surface areas were obtained. In both sample series, the catalytic activity in methanol synthesis does not scale with the Cu surface area and the experiments show that a strong interaction to the oxide is necessary to gain stability and activity of the Cu phase. Al substitution thus confirms that interface interactions between Cu and the oxide seem to beneficially affect the activity of the Cu particles and the optimal catalyst requires a compromise of exposed surface and interface. (C) 2014 Elsevier B.V. All rights reserved.