Acidity And Improving Catalytic Properties In Benzene Alkylation Over Preformed Aluminosilicate Precursors

The alkylation of benzene with propylene or isopropanol produces cumenc, which is an important intermediate mainly used for the production of phenol and acetone. In the petrochemical industry, two of the processes in industry for benzene alkylation are catalyzed by AlCl3-HCl, H2SO4, HF and "phosphoric acid supported on silica". However, the use of both catalysts gives rise to many problems concerning handing, safety, corrosion, and waste disposal. Therefore, much effort has been put into developing alternative catalysts systems. Zeolite catalysts have been extensively studied and several zeolites including Y, Beta, ZSM-5, MCM-22 and modenite, are reported to be good catalysts in this reaction. These zeolites exhibit high activity and selectivity, which can be attributed to the presence of micropores with well-defined structures that are responsible for the shape-selectivity. However, in many cases, the relatively small micropores in zeolites can also limit the mass transportation including reactants and products during the reactions, resulting in coke formation and deactivation of catalysts. The introduction of mesopores into zeolite crystals leads to a significant increase of catalytic activity and anti-deactivation ability in benzene alkylation reaction.The discovery of ordered mesoporous materials such as MCM-41 and SBA-15 offers an opportunity for silicate and aluminosilicate as versatile catalysts and catalyst supports for catalytic conversion of large molecules, but the relatively low acidity of these mesoporous materials, as compared with that of microporous crystals, greatly limits their catalytic applications in industry. The weaker hydrothermal stability and catalytic activity of mesoporous materials is attributed to the amorphous nature of their pore wall.A small amount of zeolite "precursors" can effectively induce the nucleation and the crystallization of zeolite in a template free system. It has been proved that there are zeolite primary structure units in the zeolite "precursors solution". The NH3-TPD results show that the zeolites exhibit distinguishable. For example, the order of acidic strength is as follows: ZSM-5 > Beta > Y > L. Acidic strength of various mesoporous aluminosilicates assembled from various zeolite precursors is also distinguishable. The order of acidic strength is as follows: MAS-9 > MAS-7 > MAS-2 > MAS-3, which is the same as acidic strength of microporous crystals. These results suggest that acidic strength of these mesoporous aluminosilicates is related to the use of preformed zeolite precursors. Therefore, the acidic strength of ordered mesoporousaluminosilicates could be tailored and controlled.On the other hand, it is well known that oxide-supported catalysts are very usefulin catalytic reactions, and their preparation is generally from impregnation of catalytically active sites with oxide supports. Herein, we describe a new approach for the synthesis of supported performed aluminosilicate precursors from simple impregnation of preformed aluminosilicate precursors with an ordered mesoporous silica (SBA-15), and the samples (PASP/SBA-15) obtained exhibit goodhydrothermal stability and strong acidity. These samples combine the advantages of both mesoporous materials (high surface area and large pore) and zeolites (strong acidity). More importantly, these samples exhibit much higher activity and selectivity in benzene alkylation than those of both zeolites and conventional mesoporous aluminosilicates as well as ordered mesoporous aluminosilicates assembled from preformed zeolite nanoclustcrs.Here we supported the preformed aluminosilicatc precursors of ZSM-5and Beta onto SBA-15, and the samples were named as PASP/sm-5/SBA-15 and PASPbcu/SBA-15. The NH3-TPD studies show the PASPzsm-s/SBA-15 has the similar acidity strength with zeolite ZSM-5 and the PASPzsmo/SBA-15 has the similar acidity strength with zeolite Beta. The nitrogen isotherms of two samples exhibit the typical behavior of a mesostructurc. Interestingly, after the supporting of preformed aluminosilicatc precursors...