Gao Jiaxin, Perras Frédéric A, Conley Matthew P
Department of Chemistry, University of California, Riverside, California 92507, United States.
Chemical and Biological Sciences Division, Ames National Laboratory, Ames, Iowa 50011, United States.
J Am Chem Soc. 2025 May 28;147(21):18145-18154. doi: 10.1021/jacs.5c04524. Epub 2025 May 13.
Thermolysis of the well-defined aluminum fluoroalkoxide supported on silica (≡SiOAl(OC(CF))(O(Si≡)), , 0.20 mmol g) at 200 °C forms a fluorinated amorphous silica-alumina (F-ASA) containing a distribution of Al(IV), Al(V), and Al(VI) sites that maintain relatively strong Lewis acidity. Small amounts of Brønsted sites are also present in F-ASA. Solid-state NMR studies show that a majority of the aluminum centers in F-ASA are not close to the Si-F groups that form during thermolysis. F-ASA is exceptionally reactive in cracking (or pyrolysis) reactions of neat polymer melts. Catalyst loadings as low as 2 wt % (0.017 mol % aluminum) efficiently break down isotactic polypropylene, high-density polyethylene, ethylene/1-octene copolymer, and postconsumer wastes. The major products of this reaction are hyperbranched liquid paraffins containing internal olefins and very small amounts of aromatics. Under continuous distillation of oils from the reaction mixtures, pyrolysis on 50 g reaction scales is feasible. F-ASA cokes and deactivates during this reaction but can be reactivated by calcination in air. These properties are complementary to other state-of-the-art catalysts for polymer breakdown, but unlike those catalysts F-ASA does not require an additional cofed reactant (e.g., H, olefin, etc.) to drive the reaction.
负载在二氧化硅上的结构明确的氟代烷氧基铝（≡SiOAl(OC(CF))(O(Si≡))，0.20 mmol g）在200 °C下进行热解，形成一种含氟的无定形硅铝酸盐（F-ASA），其中含有分布的Al(IV)、Al(V)和Al(VI)位点，这些位点保持相对较强的路易斯酸度。F-ASA中也存在少量的布朗斯台德位点。固态核磁共振研究表明，F-ASA中的大多数铝中心并不靠近热解过程中形成的Si-F基团。F-ASA在纯聚合物熔体的裂解（或热解）反应中具有极高的反应活性。低至2 wt%（0.017 mol%铝）的催化剂负载量就能有效地分解等规聚丙烯、高密度聚乙烯、乙烯/1-辛烯共聚物和消费后废料。该反应的主要产物是含有内烯烃和极少量芳烃的超支化液态石蜡。在从反应混合物中连续蒸馏出油的情况下，50 g反应规模的热解是可行的。F-ASA在该反应过程中会结焦并失活，但可通过在空气中煅烧进行再活化。这些性质与其他用于聚合物分解的先进催化剂互补，但与那些催化剂不同的是，F-ASA不需要额外的共进料反应物（如H、烯烃等）来驱动反应。
