Alkylation of Biphenyl over Zeolites: Shape-Selective Catalysis in Zeolite Channels

Abstract

Steric interaction of reactants, products, and transition state intermediates with zeolites with 12-and 14-membered ring pore entrances is discussed in the alkylation of biphenyl (BP) by propene, 1-butene, and 2-methylpropene as alkylating agents. The selectivities for the least bulky 4,4 0 -dialkylbiphenyl (4,4 0 -DAB) depended on the types of zeolite and alkylating agent. The zeolites are classified as two types: Category I: mordenite (MOR), SSZ-24 (AFI), SSZ-31 (STO), CIT-5 (CFI), MCM-68 (MSE), and ZSM-12 (MTW) with straight (or slightly corrugated) channels with 12-MR or 14-MR pore entrances. Category II: SSZ-42 (IFR), SSZ-55 (ATS), SSZ-60 (SSY), Y (FAU), b (BEA), CIT-1 (CON), UTD-1 (DON), and SSZ-53 (SFH) with large channels. Category I zeolites have shape-selective natures in their channels in the isopropylation. Among them, MOR supported the highest selectivities around 85 % for 4,4 0 -diisopropylbipneyl (4,4 0 -DIPB) at moderate temperatures as 250 o C. The selectivities of 4,4 0 -DIPB are: MOR [ AFI, MSE [ MTW, CFI, STO: the differences are due to the recognition of 4,4 0 -and 3,4 0 -DIPB by the channels. Category II zeolites allow the accommodation and the formation of bulky DIPB isomers in their channels, resulting in non-shape selective catalysis under kinetic and/or thermodynamic controls. Bulky alkylating agents, 1-butene and 2-methylpropene, enhance selective formation of the least bulky 4,4 0 -DAB: 4,4 0 -di-sec-butylbiphenyl (4,4 0 -DSSB) and 4,4 0 -di-tert-butylbiphenyl (4,4 0 -DTBB), respectively, even over Category II zeolites. The bulky moieties enhance the exclusion of bulky isomers by their interaction with zeolite channels. The selectivities for 4,4 0 -DSSB were increased remarkably to higher than 80 % for Category I zeolites and to 70 % for ATS in Category II zeolites in the sec-butylation. However, kinetic and thermodynamic controls still worked with the formation of bulky isomers over Category II zeolites: IFR, FAU, BEA, CON, DON, and SFH in the secbutylation. The high selectivities for 4,4 0 -DTTB higher than 80 % were observed for the zeolites, except FAU in the tertbutylation. These results indicate that the selectivities for 4,4 0 -DAB are controlled primarily by space and shape of zeolite channels for active sites, and not always by the size of pore entrances.

H-Mordenite as a Molecular Reactor for the Isopropylation of Biphenyl

“…These mechanisms are keys to achieve the highly shape-selective catalysis in the alkylation of BP [4,[5][6][7][8][9][10]. In particular, it is important that the sizes of pores and channels of the zeolite precisely fit the molecular dimensions of the reactants and products.…”

“…The thermodynamic properties of the isomers lead to the more stable isomers [1]. Inorganic solid acids, such as zeolites and amorphous silica-alumina, also serve as the active catalysts for the alkylation [2]- [6]. Particularly, the catalysis of the zeolites is due to their confined microporous environments, and can lead to the third reaction control by the steric restriction by their pores and channels.…”

“…Particularly, the catalysis of the zeolites is due to their confined microporous environments, and can lead to the third reaction control by the steric restriction by their pores and channels. The steric restriction by the channels of some zeolites invokes the selective formation of the least bulky isomers by shape-selective catalysis [3]- [6]. Thus, zeolites can work as intelligent materials for a molecular reactor if the steric restriction of the channels works effectively by their characteristic steric structures.…”

“…The isopropylation of biphenyl (BP) has been investigated by many researchers over various zeolites. Different isomers can be obtained by varying the types of zeolite [5][6][7][8][9][10][11][12][13]. We have observed the selective formation of 4,4'-DIPB, the least bulky isomers, over H-mordenite (MOR).…”

“…[5]- [11]. We have proposed that the difference is due to the microporous nature of these zeolites, and that only MOR can afford the reaction sites for selective formation of the least bulky 4,4'-DIPB in the channels [6]- [10]. On the other hand, the other zeolites can accommodate the bulky isomers in their pores and channels, resulting in the formation of the bulkier products with 2-and/or 3-isopropyl moieties [11].…”