The removal of volatile organic compounds is an important aspect of sustainability and environmental protection. Catalytic oxidation is one of the most efficient routes to achieve this. The K+ form of an aluminium-rich Beta zeolite-supported Pt nanoparticle (2.2 nm) [Pt/KBeta-seed-directed synthesis (SDS)] catalyst is very active for the low-temperature catalytic removal of toluene and results in full conversion at a much lower temperature than a conventional KBeta-supported Pt nanoparticle (Pt/KBeta-TEA) catalyst. The higher activity of the Pt/KBeta-SDS catalyst compared with the Pt/KBeta-TEA catalyst is related to the advantages of the higher K+ content and fewer terminal silanol defects in the KBeta-SDS catalyst than in the KBeta-TEA catalyst. The higher K+ content is helpful for the formation of more Pt0 species, and both the higher K+ content and the lower number of terminal silanol defects are favourable for the adsorption of toluene, as evidenced by XPS and the toluene-TPD profiles. More importantly, the Pt/KBeta-SDS catalyst shows very stable activities in the presence of H2O and CO2 in the feed gases. The combination of this extraordinary activity and excellent stability in the catalytic removal of toluene over the Pt/KBeta-SDS catalyst are important for future environment protection.
Xingyang Li,Dandan Zhang,Quanwei Zheng,Jiakui Chang,Xuan Liu,Renchun Yang,Meng Pan
In industry, it is highly desired to prepare Al-rich hierarchical zeolites by conventional alkali treatment without the use of costly chemical and special process. Here we provide an alternative strategy in which crystal defects are employed as mesopore directing agents. The effective elimination of the intracrystalline defects induces the generation of mesoporous structure in the alkali treatment process. Thus, the limitation originating from the framework Si/Al ratio of parent zeolite is circumvented. This strategy holds all merits of the conventional alkali treatment approach, which is industrially unfavorable. As an example, the Al-rich hierarchical ZSM-5 zeolites with very low Si/Al ratios were successfully prepared. The obtained Al-rich hierarchical zeolites were characterized by XRD, XRF, SEM, TEM, N 2 adsorption-desorption, in-situ IR, MAS NMR and NH 3 -TPD. The results showed that Si/Al ratios of the prepared hierarchical ZSM-5 zeolites were around 10 and the increases of external surface area and mesoporous volume were up to 2.6 and 3.7 times respectively in comparison with parent zeolite. Moreover, the constructed mesopores were interconnected open channels. In the catalytic cracking of 1,3,5-triisopropylbenzene, the Al-rich hierarchical ZSM-5 zeolites exhibited an excellent performance because of the improved diffusion of reactant and product.
Aluminum-rich hierarchical MFI-type zeolites with high acidic-site density exhibit excellent activity and selectivity in bulky molecule-involved reactions. However, it is challenging to develop a facile and environmentally benign method for fabricating them. Herein, we employ a polymer that does not contain nitrogen and halogen elements to successfully synthesize aluminum-rich hierarchical ZSM-5 zeolite with a Si/Al ratio of 8 and a significant number of mesopores comprised of oriented-assembled nanocrystals. It is demonstrated that the nitrogen- and halogen-free polymer is instrumental in the formation of the ZSM-5 zeolite by serving as a template for constructing the hierarchical micro/mesoporous structure. Moreover, this polymer also acts as a crystal growth modifier to form a single-crystalline zeolite. Notably, the resultant zeolite shows a better catalytic performance in converting waste plastic into hydrocarbons than a commercial one. Our work enables the synthesis of high-quality hierarchical zeolites without requiring quaternary ammonium templates.Keywords:hierarchical ZSM-5 zeolites;aluminum-rich;nitrogen- and halogen-free polymer;waste plastics cracking
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