在Al 2 O 3上沉积SiO 2：制备可调谐布朗斯台德酸催化剂的途径,ACS Catalysis

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在Al ₂ O ₃上沉积SiO ₂：制备可调谐布朗斯台德酸催化剂的途径
ACS Catalysis ( IF 11.3 ) Pub Date : 2016-08-16 00:00:00 , DOI: 10.1021/acscatal.6b01077
M. Alexander Ardagh ₁ , Zhenyu Bo ₂ , Scott L. Nauert ₁ , Justin M. Notestein ₁

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强烈的布朗斯台德酸性二氧化硅-氧化铝材料是石油工艺（包括裂化，异构化和烃合成）中的主力催化剂。在此，通过在碱性条件下逐步添加原硅酸四乙酯，在预先存在的Al ₂ O ₃载体上合成了TEM薄的SiO ₂厚度为2–5 nm的保形外涂层，并通过N ₂物理吸附和NH ₃询问了表面和吡啶的化学吸附。厚度大于5 nm的SiO ₂层在很大程度上形成惰性表面，但仅添加2 nm的SiO ₂结果显示，该反应可淬灭潜在的Lewis酸度，并意外地形成足够强的质子化气相吡啶的布朗斯台德酸位。或者，使用在SiO ₂沉积之前接枝到氧化铝表面的分子模板选择性地保留了最具反应性的AlOH。在1，3，5-三异丙基苯在450℃下的催化裂化中，被2nm SiO ₂包覆的Al ₂ O ₃被证明是高活性催化剂，其转化率是Al ₂ O _3的10倍。最后，故意将二氧化硅覆盖层开裂以暴露出很强的界面部位，可能在四面体Al和SiO _2之间。与具有完整覆盖层的材料相比，该催化剂对包括枯烯和苯在内的深度脱烷基化产物的转化率高1.5倍，选择性高3倍。这种核壳型SiO ₂ @Al ₂ O ₃催化剂的单位表面积总脱烷基率与传统制备的SiO ₂ -Al ₂ O ₃或沸石Y催化剂相似，同时为催化剂优化提供了新的合成方法。

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Depositing SiO2 on Al2O3: a Route to Tunable Brønsted Acid Catalysts

Strongly Brønsted acidic silica–alumina materials are workhorse catalysts in petroleum processes, including cracking, isomerization, and hydrocarbon synthesis. Here thin, conformal overcoats of SiO₂, 2–5 nm by TEM, were synthesized on pre-existing Al₂O₃ supports by stepwise addition of tetraethyl orthosilicate under basic conditions, and the surfaces were interrogated by N₂ physisorption along with NH₃ and pyridine chemisorption. SiO₂ layers thicker than 5 nm give largely inert surfaces, but adding only 2 nm of SiO₂ is shown to quench the underlying Lewis acidity and unexpectedly form Brønsted acid sites strong enough to protonate gas-phase pyridine. Alternately, the use of a molecular template grafted to the alumina surface before SiO₂ deposition selectively preserves the most reactive AlOH. In the catalytic cracking of 1,3,5-triisopropylbenzene at 450 °C, Al₂O₃ overcoated by 2 nm of SiO₂ proved to be a highly active catalyst with 10 times higher conversion in comparison to that of Al₂O₃. Finally, the silica overlayer was deliberately cracked to expose strong interfacial sites, likely between tetrahedral Al and SiO₂. In comparison to a material with an intact overlayer, this catalyst had 1.5 times higher conversion and 3 times higher selectivity to deep dealkylation products, including cumene and benzene. This core–shell SiO₂@Al₂O₃ catalyst gives total dealkylation yields, per surface area, similar to those of conventionally prepared SiO₂–Al₂O₃ or zeolite Y catalysts while providing for new synthetic handles for catalyst optimization.

更新日期：2016-08-16

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