Institute of Inorganic Chemistry, University of Duisburg-Essen, Universitätsstr. 7, 45141 Essen, Germany.
Institute of Inorganic Chemistry, Kiel University, Max-Eyth-Str. 2, 24118 Kiel, Germany.
Dalton Trans. 2023 Apr 25;52(16):5321-5335. doi: 10.1039/d3dt00253e.
The preparation of Al-doped ZnO thermal decomposition of crystalline precursors, with a particular emphasis on kinetic effects on the solubility limits, was studied. The promoting effect of Al on the catalyst system is discussed for methanol synthesis where ZnO:Al is employed as a support material for copper nanoparticles. The synthesis of the Al-doped zinc oxides in this study was inspired by the industrial synthesis of the methanol synthesis catalyst a co-precipitated crystalline precursor, here: hydrozincite Zn(OH)(CO). To determine the aluminium speciation and the solubility limit of the aluminium cation on zinc positions, a series of zinc oxides with varying aluminium contents was synthesized by calcination of the precursors. Short precipitate ageing time, low ageing temperature and aluminium contents below 3 mol% metal were advantageous to suppress crystalline side-phases in the precursor, which caused an aluminium segregation and non-uniform aluminium distribution in the solid. Even if zinc oxide was the only crystalline phase, TEM revealed such segregation in samples calcined at 320 °C. Only at very low aluminium contents, the dopant was found preferably on the zinc sites of the zinc oxide structure based on the signal dominating the Al NMR spectra. The solubility limit regarding this species was determined to be approximately = 0.013 or 1.3% of all metal cations. Annealing experiments showed that aluminium was kinetically trapped on the site and segregated into ZnAlO upon further heating. This shows that lower calcination temperatures such as applied in catalyst synthesis conserve a higher aluminium doping concentration on that specific site than is expected thermodynamically.
研究了 Al 掺杂 ZnO 的热分解结晶前体，特别强调了动力学效应对溶解度极限的影响。讨论了 Al 对甲醇合成中催化剂体系的促进作用，其中 ZnO:Al 被用作铜纳米颗粒的支撑材料。本研究中 Al 掺杂氧化锌的合成受到甲醇合成催化剂工业合成的启发——共沉淀结晶前体，即氢氧锌矿 Zn(OH)(CO)。为了确定铝的形态和铝阳离子在锌位上的溶解度极限，通过前驱体的煅烧合成了一系列具有不同铝含量的氧化锌。较短的沉淀陈化时间、较低的陈化温度和低于 3 mol%金属的铝含量有利于抑制前驱体中的晶相侧相，这会导致铝偏析和固体中铝分布不均匀。即使氧化锌是唯一的晶相，TEM 也揭示了在 320°C 煅烧的样品中存在这种偏析。仅在非常低的铝含量下，基于主导 Al NMR 光谱的信号，才发现掺杂剂优先存在于氧化锌结构的锌位上。该物种的溶解度极限约为所有金属阳离子的 = 0.013 或 1.3%。退火实验表明，铝在动力学上被捕获在该位置上，并在进一步加热时 segregation 成 ZnAlO。这表明，与催化剂合成中应用的较低煅烧温度相比，在该特定位置上保留了更高的铝掺杂浓度，这超出了热力学预期。
