No abstract

Propane dehydrogenation (PDH) is the extensive pathway to produce propylene, which is as a very important chemical building block for the chemical industry. Various catalysts have been developed to increase the propylene yield over recent decades; however, an active site of monometallic Pt nanoparticles prevents them from achieving this, due to the interferences of side-reactions. In this context, we describe the use of promoter-free hierarchical Pt/silicalite-1 nanosheets in the PDH application. The Pt dispersion on weakly acidic supports can be improved due to an increase in the metal-support interaction of ultra-small metal nanoparticles and silanol defect sites of hierarchical structures. This behavior leads to highly selective propylene production, with more than 95% of propylene selectivity, due to the complete suppression of the side catalytic cracking. Moreover, the oligomerization as a side reaction is prevented in the presence of hierarchical structures due to the shortening of the diffusion path length.

As the catalytic performances typically depend on various factors, especially the distribution of Al species in the zeolite framework, in this contribution, hierarchical nanospherical ZSM-5 zeolites have been successfully synthesized using uniform aluminosilicate (AS) nanobeads containing silica and alumina species as a starting material to improve the Al dispersion in the framework. The synthesized zeolites were characterized by means of XRD, TEM, SEM, EDS, N 2 physisorption, 27 Al MAS NMR, and NH 3 -TPD. This example demonstrates that the use of AS nanobeads can effectively control the uniform Al distribution. Subsequently, the synthesized materials were tested for their catalytic activity in the alkylation of benzene with ethanol to ethylbenzene. Interestingly, the designed ZSM-5 nanospheres prepared by using AS nanobeads clearly exhibit an improvement of the catalytic performance in terms of benzene conversion and ethylbenzene selectivity compared with the conventional ZSM-5 and the ZSM-5 nanospheres prepared by using a typical synthesis method. The reason for the improved benzene conversion (60%) and ethylbenzene selectivity (62%) on Hie-SZSM-5-AS relates to the generated mesoporous structure as well as a homogeneous distribution of Al frameworks directed by AS nanobeads. The synthesis approach reported herein illustrates an efficient way to control Al species as well as Al distribution in the zeolite framework, eventually enhancing the catalytic performance in acid catalyzed reaction, such as in the case of benzene alkylation with ethanol.