M. Matsumoto

Cerium impregnated H-mordenite as a catalyst for shape-selective isopropylation of naphthalene. Selective deactivation of acid sites on the external surface

Abstract The impregnation of cerium is the effective method for the deactivation of external acid sites of H-mordenite. The selectivity of 2,6-DIPN in the isopropylation of naphthalene was enhanced by the impregnation with such a large amount as 30–50 wt.-% of cerium without significant decrease of catalytic activity. The highest selectivity of 2,6-DIPN was achieved up to 70% over a highly dealuminated H-mordenite, (HM(128); SiO 2 /Al 2 O 3 = 128, with 30 wt.-% of cerium. The enhancement of the selectivity is ascribed to the deactivation of external acid sites judging from the activity of the cracking reaction of 1,3,5-triisopropylbenzene. The effective pore radius was not reduced by the modification. The ceria is highly dispersed only on the external surface of H-mordenite without any formation of new kinds of acid sites. The 129 Xe NMR observation suggfests that cerium is not in the pores, but on the external surfaces. The deactivation of the external acid sites is a characteristic property for cerium. Lanthanum and neodymium inhibited catalytic activity of the isopropylation because the pores were narrowed by their impregnation. A possible reason of the deactivation is ascribed to the amphoteric property of ceria.

Effect of SiO2Al2O3 ratio of H-mordenite on the propylation of naphthalene with propylene

Abstract The effect of the SiO 2 Al 2 O 3 ratio of H-mordenite on shape-selective catalysis was studied in the isopropylation of naphthalene with propylene. Aluminum concentrations at intracrystalline and external surfaces of H-mordenite are not directly related to catalyst performances. Dealuminated H-mordenite with a SiO 2 Al 2 O 3 ratio higher than 30 exhibited high catalytic activity and high selectivity for 2,6-diisopropylnaphthalene (2,6-DIPN). The enhancement of catalyst performances with the increase of SiO 2 Al 2 O 3 ratio is due to the suppression of coke deposition and the increase of shape-selective catalysis in the pores because the dealumination caused the decrease of acid density and strength. Coke deposition at the initial stage of the alkylation over H-mordenite with a low SiO 2 Al 2 O 3 ratio occurs at the pore entrances to inhibit the reaction in the pores. Low selectivity for 2,6-DIPN is due to non-selective catalysis at external acid sites which are active in spite of severe coke deposition. Naphthalene derivatives encapsulated in the pores showed that 2,6-DIPN was formed shape-selectively in the pores over all H-mordenites because of the minimum steric requirement at the transition state composed of substrates and acid sites, and that polyisopropylnaphthalenes in the pores were precursors of deposited coke.

Shape-selective alkylation of biphenyl over mordenite: cerium exchanged sodium mordenite and unmodified H-mordenite with low SiO2/Al2O3 ratio

Liquid phase isopropylation of biphenyl with propylene was studied over a cerium exchanged sodium mordenite (Ce/NaM25) and a H-mordenite (HM25) with the same SiO2/Al2O3 ratio of 25. Shape-selective catalysis occurred to give 4,4′-diisopropylbiphenyl (4,4′-DIPS) in high selectivity over Ce/NaM25 under any propylene pressures. HM25 gave 4,4′-DIPS shape-selectively under high propylene pressures. However, the reaction was severely deactivated at a conversion of ca. 60% under such a low pressure as 0.8 kg/cm2 because of coke formation in the pore. The yields of 4-isopropylbiphenyl (4-IPBP) and 4,4′-DIPB decreased with the increase of those of 3-IPBP and 3,4′-DIPB because of non-selective alkylation and isomerization at external acid sites that are alive in spite of severe deactivation. No significant isomerization of 4,4′-DIPB over Ce/NaM25 was observed even at low propylene pressure. In the case of HM25, the isomerization of 4,4′-DIPB to 3,4′-DIPB occurred significantly under low propylene pressures, while it decreased under high pressure. These differences are ascribed to the differences of nature of acid sites between Ce/NaM25 and HM25 zeolites.

Shape-selective isopropylation of biphenyl over a highly dealuminated mordenite: effect of propylene pressure

A highly dealuminated H-mordenite (H-M) catalyzed the selective isopropylation of biphenyl to 4,4′-diisopropylbiphenyl (4,4′-DIPB). The high selectivity is ascribed to the shape-selective catalysis in mordenite pores. The selectivity of 4,4′-DIPB decreased during the isopropylation of biphenyl due to isomerization of 4,4′-DIPB under low propylene pressure. The increase of propylene pressure suppressed the isomerization in the isopropylation. 4,4′-DIPB itself was isomerized over highly dealuminated H-M under low propylene pressure.

The isopropylation of naphthalene over cerium-modified H-mordenite

H-Mordenite (HM) catalysts impregnated with cerium exhibited high activity and selectivity of 2,6-diisopropylnaphthalene (2,6-DIPN) for the isopropylation of naphthalene with propylene. Cerium modification with such a large amount as 30-50 wt% improved the catalyst performance for every HM catalyst with SiO 2 /Al 2 O 3 ratio between 10 and 220. The highest selectivity of 2,6-DIPN was achieved up to 70% over a highly dealuminated HM catalyst with 30 wt% of cerium. The effective pore dimension of HM catalyst is not reduced by the modification. The improvement of the catalyst performance is ascribed to the selective deactivation of acid sites on the external surface by cerium impregnation.

Shape-selective alkylation of biphenyl over mordenites : effects of dealumination on shape-selectivity and coke deposition

To understand the relationships between shape-selectivity and coke deposition in the alkylation of biphenyl over H-mordenite (HM), thermogravimetric analyses were examined for the catalyst after the reaction. The coke deposition during the catalysis was very severe over HM with low SiO/Al2O3 ratio, however, dealumination enhanced the decrease of coke deposition. Over highly dealuminated HM, volatile organic compounds, mainly biphenyl derivatives, were observed in addition to carbonaceous deposits. The deposits are produced from biphenyl derivatives on acid sites in the HM pore, and the ease of their formation is governed by acid site density and acid strength. The decrease of carbonaceous deposits and the increase of encapsulated biphenyl derivatives are related with the increase of both selectivity and yield of 4,4′-diisopropylbiphenyl (4,4′-DIPB). The increase of reaction temperature up to 250°C enhanced the catalysis over highly dealuminated HM, however, further increase of the temperature resulted in extensive decrease of the selectivity of 4,4′-DIPB. Coke deposition also increased with the temperature although its level was low. The composition of 4,4′-DIPB in encapsulated DIPB isomers remained as high as 80% in spite of a change of the distribution of bulk products.

The effect of propylene pressure on shape-selective isopropylation of biphenyl over H-mordenite

Abstract The effect of propylene pressure on the isopropylation of biphenyl was investigated over highly dealuminated H-mordenite. The selectivity of 4,4′-diisopropylbiphenyl (4,4′-DIPB) in liquid phase products was achieved up to 90% under a high propylene pressure of 0.8 MPa, whereas the decrease of the selectivity of 4,4′-DIPB by the isomerization to 3,4′-DIPB was observed under low pressure of 0.1 MPa. However, the formation of IPBP isomers was not influenced by the pressure. The yield of 4-isopropylbiphenyl (4-IPBP) reached a maximum at 50–60% conversion of biphenyl, whereas that of 3-IPBP increased monotonously. The isomerization of 4,4′-DIPB occurred extensively under low propylene pressure, but decreased with the increase of the pressure. No significant isopropylation of 4,4′-DIPB was observed even under high pressure. The selectivities of 4,4′-DIPB encapsulated in the catalysts were more than 90% in both cases for the isopropylation of biphenyl and for the isomerization of 4,4′-DIPB under every pressure. These results of the isopropylation and the isomerization suggest that selective formation of 4,4′-DIPB occurred in the pores, and that high selectivity under high pressures is due to the prevention of the adsorption of 4,4′-DIPB at external acid sites because of preferential adsorption of propylene. The isomerization of 4,4′-DIPB under low pressures occurred on external acid sites where no propylene was adsorbed.

4.5 Shape-selective Isopropylation of Naphthalene and Biphenyl over Dealuminated H-Mordenites

Abstract Dealumination of H-mordenite enhanced catalyst performance in the isopropylation of naphthalene and biphenyl. The activity for naphthalene and biphenyl to diisopropylnaphthalene (DIPN) and diisopropylbiphenyl (DIPB) isomers was increased by the dealumination, but further alkylation to polyisopropylated compounds was inhibited. The selectivity of 2,6-DIPN and 4,4′-DIPB increased with the increase of SiO 2 /Al 2 O 3 (Si/Al 2 ) ratio. The enhancement of catalytic activity by the dealumination is ascribed to the decrease of coke deposition because of the decrease of acid sites and strength. The increase of the selectivities of 2,6-DIPN and 4,4′-DIPB is due to the decrease of acid sites at the external surface. The selectivity of 4,4′-DIPB was varied with the change of propylene pressure in the isopropylation of biphenyl over a highly dealuminated mordenite HM220. The selectivity of 4,4′-DIPB was achieved up to 90 % under high propylene pressures such as 10 kg/cm 2 , whereas the decrease of the selectivity of 4,4′-DIPB due to the isomerization to 3,4′-DIPB was observed during the reaction under low propylene pressure such as 0.8 kg/cm 2 . Propylene prevents the isomerization because of its preferential adsorption on acid sites. The yield of 4-IPBP reached maximum at 50-60 % conversion, whereas the yield of 3-IPBP increased monotonously. These results are explained by two-stage alkylation mechanism: in the first stage, biphenyl is alkylaied to IPBP isomers, in which 4-IPBP is predominant. 4-IPBP only participates in the second stage alkylation, to yield 4,4′-DIPB shape-selectively. Coke deposition occurred rapidly at the early stages in the isopropylation of biphenyl over HM220. However, the oligomerization of propylene began after the yield of DIPB isomers reached 20 %. Propylene adsorbed on acid sites is preferentially consumed by the isopropylation, especially at the early stages. Principal biphenyl derivatives encapsulated in HM pore were identified as 4-IPBP and 4,4′-DIPB.

Shape-selective ethylation of biphenyl over a highly dealuminated H-mordenite

Abstract The shape-selective ethylation of biphenyl over a highly dealuminated mordenite was examined. The ethylation, occurring stepwise, resulted in the formation of ethylbiphenyls (EBP), diethylbiphenyls (DEBP) and tri- and tetraethylbiphenyls (polyethylbiphenyls, PEBP). In the first step, the ethylation was non-shape-selective and gave 17% 4-EBP, with large amounts of the bulkier 2-EBP and 3-EBP isomers. In the second step, the pores of H-mordenite differentiated the diffusion of the EBP isomers, leading to a preferential ethylation of 4-EBP; 4-EBP was consumed rapidly. 3-EBP gradually and 2-EBP did not participate in the further ethylation. Moreover, the transition state of the ethylation of 4-EBP underwent steric restriction by H-mordenite pores, leading to an increase of the selectivity of 4,4′-DEBP up to 30%. The lack of shape selectivity in the first step and the low selectivity for 4,4′-DEBP over HM220 indicate that the space of a H-mordenite pore is too large for highly shape-selective ethylation.

The influence of reagents on shape-selective alkylation of biphenyls over H-mordenite

The alkylations of biphenyl (BP), 4-alkylbiphenyl (4-ABP), and p -terphenyl (TP) with ethene, propene, and 1-butene were examined to understand the influence of reagents over H-mordenite (HM). The selectivity was highly dependent on the alkenes. The ethylation of BP to ethylbiphenyls (EBP) and diethylbiphenyls (DEBP) was non-shape-selective, although the formation of EBP and DEBP isomers with 2-ethyl groups in encapsulated products were lower than that in liquid phase products. The isopropylation and the sec -butylation of BP and the isopropylation of TP occurred shape-selectively to yeild the slimmest isomers. These results show that the isopropylation and the sec -butylation occur in pores, and that catalytic active acid sites in the ethylation of BP are both in pores and on external surface.