Atomic Layer Deposition (ALD) as a Way to Prepare New Mixed-Oxide Catalyst Supports: The Case of Alumina Addition to Silica-Supported Platinum for the Selective Hydrogenation of Cinnamaldehyde
Atomic Layer Deposition (ALD) as a Way to Prepare New Mixed-Oxide Catalyst Supports: The Case of Alumina Addition to Silica-Supported Platinum for the Selective Hydrogenation of Cinnamaldehyde
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DOI：
10.1007/s11244-019-01163-4
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发表时间：
2019-09
影响因子：
3.6
通讯作者：
Zhihuan Weng;F. Zaera
中科院分区：
文献类型：
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作者：
Zhihuan Weng;F. Zaera
这里的案例是为了证明使用原子层沉积（ALD）作为一种方法来诱导在许多催化过程中用作载体的氧化物的性质发生变化。 ALD 提供了一种以保形方式生长薄膜并具有亚单层厚度控制的途径，从而可以创建具有新反应位点的独特混合氧化物结构。这里以使用铂基催化剂氢化不饱和醛的情况为例说明了这种方法。二氧化硅负载的催化剂采用氧化铝薄膜进行改性，使用三甲基铝 (III) (TMA) 和水通过 ALD 生长，其性能与纯 Pt/SiO2 和 Pt/Al2O3 样品以及我们之前报道的在 Pt/Al2O3 上通过二氧化硅 ALD 制备的催化剂进行了对比。首先通过使用 N2 吸附-解吸等温线并结合 SBA-15（一种具有明确的一维圆柱形孔的介孔材料）来评估在 Pt/SiO2 上生长的氧化铝薄膜的质量。根据这些测量结果，每个 ALD 循环的初始沉积量约为 1.5 Å 的氧化铝薄膜，同时保留了孔径的狭窄分布，表明整个孔隙长度的均匀覆盖。与氧化铝相比，二氧化硅载体的肉桂醛催化氢化速度较慢，但选择性更高。在 Pt/SiO2 中添加半个单层氧化铝会降低总活性，但影响很小。作为交换，新型混合氧化物催化剂对以高转化率生产所需的不饱和醇表现出更高的选择性，并且其随后加氢为饱和醇的活性较低。这些趋势与新的布朗斯台德和路易斯酸性位点的形成有关，可能基于混合的 Si-O-Al 表面结构。
The case is made here for the power of using atomic layer deposition (ALD) as a way to induce changes in the nature of the oxides used as supports in many catalytic processes. ALD provides a route to grow thin films in a conformal way and with submonolayer thickness control, affording the creation of unique mixed-oxide structures with new reaction sites. This approach is exemplified here for the case of the hydrogenation of unsaturated aldehydes with platinum-based catalysts. Silica-supported catalysts were modified with thin alumina films, grown by ALD using trimethylaluminum(III) (TMA) and water, and their performance contrasted with pure Pt/SiO2and Pt/Al2O3samples as well as with catalysts previously reported by us made by silica ALD on Pt/Al2O3. The quality of the alumina films grown on Pt/SiO2was first evaluated by using N2adsorption–desorption isotherms in conjunction with SBA-15 as the support, a mesoporous material with well-defined 1D cylindrical pores. An initial deposition of approximately 1.5 Å of the alumina film per ALD cycle was estimated from those measurements, with retention of the narrow distribution of pore diameters indicative of homogeneous coverage throughout the length of the pores. The catalytic hydrogenation of cinnamaldehyde was then determined to be slower but more selective with silica supports compared to alumina. Addition of a half of a monolayer of alumina to Pt/SiO2reduces the total activity, but only marginally. In exchange, the new mixed-oxide catalysts exhibit a higher selectivity toward the production of the desirable unsaturated alcohol at high conversions, and a lower activity for its subsequent hydrogenation to the saturated alcohol. These trends were associated with the formation of new Brønsted and Lewis acidic sites, possibly based on mixed Si–O–Al surface structures.