Shogo Tawada

Shape-selective isopropylation of biphenyl over H-mordenites: Relationships of bulk products and encapsulated products in the pores

Abstract Shape-selective formation of 4,4′-diisopropylbiphenyl (4,4′-DIPB) was observed in the isopropylation of biphenyl (BP) over H-mordenite (HM). Shape-selectivity was governed by spatial restriction in transition states in the microporous environment of HM. The selectivity for 4,4′-DIPB was influenced by many factors such as the SiO2/Al2O3 ratio, reaction temperature, and propylene pressure. On the other hand, high selectivities for 4,4′-DIPB were observed in encapsulated products under all of our conditions because of shape-selective catalysis in the HM pores. However, the decrease in the selectivity for 4,4′-DIPB occurred with the decrease in the SiO2/Al2O3 ratio and with change in the reaction conditions, such as increase in temperature and decrease in propylene pressure. The discrepancies in bulk products and in encapsulated products in the HM pores are discussed to understand where and why shape-selective catalysis occurs. The decrease in the selectivity for 4,4′-DIPB over HM with a low SiO2/Al2O3 ratio is due to non-regioselective reactions because of choking of the pore entrance by coke-deposition. The decrease in the selectivity for 4,4′-DIPB under high reaction temperatures, or under low propylene pressures was ascribed to the isomerization of 4,4′-DIPB at external acid sites. These conclusions are also supported by discrepancies of bulk and encapsulated products in the isomerization of 4,4′-DIPB under high the corresponding conditions. No significant isopropylation of 4,4′-DIPB to triisopropylbiphenyls (TrIPB) was observed even under high propylene pressure or at high reaction temperatures. This is presumably due to there not being enough space in the pores for the transition state of further isopropylation of 4,4′-DIPB, and it is one of the reasons for the shape-selective formation of 4,4′-DIPB.

Ceria-modification of H-mordenites. The deactivation of external acid sites in the isopropylation of biphenyl and the isomerization of 4,4'-diisopropylbiphenyl

Ceria-modification is an effective method for the deactivation of external acid sites of H-mordenite (HM). The selectivity for 4,4′-diisopropylbiphenyl (4,4′-DIPB) in the isopropylation of BP over dealuminated HM such as HM(128) decreased with raising reaction temperatures or with decreasing propylene pressures. The decrease of the selectivity during the isopropylation is due to the isomerization of 4,4′-DIPB. Ceria-modification of HM(128) was highly effective for the prevention of the isomerization. The selectivity for 4,4′-DIPB was also improved in the case of HM with low SiO2/Al2O3 ratio such as HM(10). The enhancement of the selectivities of 4,4′-DIPB by ceria-modification is ascribed to the decrease of external acid sites which are active in non-regioselective alkylation and isomerization of products.

Synthetic investigation of CIT-5 catalyst

Abstract Syntheses of the all-silica and the aluminosilicate versions of CIT-5 (International Zeolite Association Code: CFI) were studied. As structure-directing agent (SDA), N(16)-methylsparteinium (MeSPA+) cation was used. Under static conditions, combination of this SDA and lithium cations was considered to be a key factor for efficient synthesis of the zeolite. The synthesis vessel has been observed to play a significant role during the synthesis. Synthesis in a sealed quartz tube succeeded whereas that in a Teflon-lined stainless steel autoclave failed. CIT-5 with high purity was obtained inside the autoclave in the presence of hollow quartz tubes. When rotating the Teflon-lined autoclave, CIT-5 was obtained in the absence of the quartz tubes. With or without rotation, very high silica [Al]-CIT-5 was synthesized using fumed silica (Cab-O-Sil) and aluminum nitrate as silica source and aluminum source, respectively. With rotation, [Al]-CIT-5 with relatively lower Si/Al ratio was obtained by using highly dealuminated Y zeolite (HDY) as silica source and aluminum nitrate as aluminum source. In each aluminosilicate sample, only tetrahedral aluminum was observed. The particle size of the product was highly dependent on the synthesis method.

Effects of SiO2/Al2O3 ratio of H-mordenite on encapsulated products inside the pores in shape-selective isopropylation of biphenyl

The effects of SiO2/Al2O3 ratio of H-mordenite on the selectivity of encapsulated products in the pores and of bulk products were investigated in the isopropylation of biphenyl. The selectivity of 4,40 -diisopropylbiphenyl (4,40 -DIPB) of bulk products was varied with SiO2/Al2O3 ratio. Highly dealuminated H-mordenite gave a selectivity higher than 80%, whereas the selectivity was low for H-mordenite with SiO2/Al2O3 ratio of 10-20. On the other hand, the selectivity of 4,40 -DIPB in encapsulated DIPB isomers was higher than 85% for all H-mordenites regardless of SiO2/Al2O3 ratio. These results show that all H-mordenites catalyze the isopropylation of biphenyl with high shape-selectivity inside the pore. The low selectivity of 4,40 -DIPB in bulk products for H-mordenites with low SiO2/Al2O3 ratio was not due to a lack of shape-selectivity of the H-mordenites, but to non-regioselective isopropylation at the external acid sites. Non-regioselective catalysis over H-mordenite with low SiO2/Al2O3 ratio could be induced by choking pores by coke deposition.

Effects of ceria-modification of H-mordenite on the isopropylation of naphthalene and biphenyl

Abstract Ceria-modification is an effective method for the deactivation of external acid sites of Hmordenite (HM). The selectivity of 2,6-diisopropynaphthalene (2,6-DIPN) in the isopropylation of naphthalene (NP) was enhanced by the modification with 10–50 wt-% of cerium without significant decrease of catalytic activity: the highest selectivity for 2,6-DIPN was up to 70% over HM (SiO 2 /Al 2 O 3 = 128) with 30 wt-% of cerium. The selectivity for 4,4′- diisopropylbiphenyl (4,4′-DIPB) in the isopropylation of biphenyl (BP) over HM decreased with reaction temperature because of the isomerization of 4,4′-DIPB. However, ceria-modification of HM was highly effective for the prevention of the isomerization. The enhancement of the selectivities of 2,6-DIPN and 4,4′-DIPB by ceria-modification is ascribed to the decrease of external acid sites which are active in non-regioselective alkylation and isomerization of products.

Direct hydrothermal synthesis of B-SSZ-31 from silica and sodium borate using 1,3,3,6,6-pentamethyl-6-azoniabicyclo[3.2.1]octane hydroxide as structure-directing agent

The direct synthesis of a borosilicate version of SSZ-31 was investigated starting from fumed silica and sodium borate as the silicon and boron source, respectively. As-synthesized boron Beta as a seed material was required for synthesizing fully crystalline material. The synthesis vessel has been observed to play a major role during the synthesis. Synthesis inside quartz tubes succeeded whereas that inside a teflon-lined stainless steel autoclave failed. Crystalline material was obtained inside the autoclave in presence of hollow quartz tubes. Part of the tetrahedral boron could be substituted by aluminum refluxing the as-calcined sample with aluminum nitrate solution.

The roles of 3- and 4-isopropylbiphenyls in the isopropylation of biphenyl over a H-mordenite

The isopropylation of mixtures of 3- and 4-isopropylbiphenyls (3- and 4-IPBPs) was examined over a dealuminated H-mordenite (HM) to elucidate the role of 3- and 4-IPBPs in the isopropylation of biphenyl (BP). 4-IPBP was consumed much faster than 3-IPBP in all cases. 4-IPBP was an exclusive precursor to diisopropylbiphenyls (DIPBs), particularly 4,4′-DIPB, and 4,4′-DIPB was found in encapsulated products during the reaction. These results show that 4-IPBP can allow establishment of an active complex with propylene and acid site in HM pores, whereas 3-IPBP cannot. It is concluded that the isopropylation of BP over HM occurs through a reactant selectivity mechanism, and through a restricted transition state mechanism, but not through a product selectivity mechanism.

Shape-Selective Alkylation of Biphenyl over H-[Al]-SSZ-31 with Propylene

Isopropylation of biphenyl (BP) over [Al]-SSZ-31, a large-pore, one-dimensional zeolite has been studied. Effects of temperature, pressure and SiO2/Al2O3 ratio were examined. SSZ-31 was found to be an active catalyst in the isopropylation of biphenyl with propylene. The selectivity for 4-isopropylbiphenyl (4-IPBP) and 4,4′-diisopropylbiphenyl (4,4′-DIPB) was high among isopropylbiphenyl (IPBP) and diisopropylbiphenyl (DIPB) isomers, respectively, indicating SSZ-31 shows shape-selective catalysis. The selectivity for 4,4′-DIPB decreased with temperature increase; correspondingly the selectivity for thermodynamically more stable isomers (3,3′- and 3,4′ DIPB) increased with temperature. The yield of IPBP isomers decreased while that of DIPB isomers increased with temperature increase. Pressure showed less effect on conversion; however, increase in pressure suppresses the isomerization of 4,4′-DIPB to 3,3′- and 3,4′-DIPB. Conversion decreased with increase in SiO2/Al2O3 ratio. At low SiO2/Al2O3 ratio of 136, relatively high triisopropylbiphenyl (TriIPB) isomers were formed in bulk products and their amount decreased with increase in SiO2/Al2O3 ratio.

25-P-06-Isopropylation of naphthalene over large pore zeolites

Publisher Summary This chapter discusses the isopropylation of naphthalene over large pore zeolites. [Al]-SSZ-31 is active in isopropylation of naphthalene; however, the selectivity is lower as compared to mordenite. Large pore zeolites, such as ZSM-12, CIT-5, SSZ-31, CIT-5, and HY are compared. CIT-5 and HY are very active, however, less selective. ZSM-12 and SSZ-31 shows better selectivity for 2,6-diisopropylnaphthalene (DIPN) than CIT-5 and HY. Mordenite is the best catalyst.