Development of Highly Active Catalysts for Chemical Recycling of Waste Plastics

研究了h -硼硅酸盐、介孔二氧化硅MCM-41及其混合物对聚烯烃降解的催化活性，以期开发废塑料化学回收技术。以MFI微孔结构和低酸性为特征的硼硅酸盐对聚丙烯转化为碳数为2-5的低烯烃具有良好的催化作用，而平均孔径为3.8 nm、酸性极低的有序介孔MCM-41对该反应的催化作用较差。然而，当硼硅酸盐与MCM-41物理混合时，可以制备出高效的催化剂。复合催化剂对低烯烃的选择性高于纯催化剂。在1:1的混合条件下，选择性最高。用NH_3-TPD测定酸度显示复合材料上没有形成新的酸性位点。因此，复合催化剂的优异性能归因于MCM-41的介孔适合将大分解碎片转化为小分子。

The catalytic activities of H-borosilicate, mesoporous silica MCM-41, and their mixtures for the degradation of polyolefins have been investigated in order to develop a technology for chemical recycling of waste plastics. The borosilicate characterized by an MFI microporous structure and a low acidity was effective as a catalyst for the conversion of polypropylene to lower olefins with carbon numbers of 2-5, while ordered mesoporous MCM-41 with an average pore diameter of 3.8 nm and a very low acidity was less effective for the reaction. However, highly efficient catalysts were prepared when the borosilicate and MCM-41 were physically mixed. The composite catalysts showed higher selectivities to the lower olefins than those of the pure catalysts. The highest selectivity was observed at 1:1 mixture. Acidity measurements using NH_3-TPD revealed no formation of newly acidic sites on the composite. It is therefore suggested the excellent performance of the composite catalyst is attributed to the mesopores of MCM-41 that are appropriate to convert large decomposed fragments to small molecules.