Toshiaki Hanaoka

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 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.

Hydrogenation of carbon monoxide over highly dispersed cobalt catalysts derived from cobalt(II) acetate

Abstract Highly dispersed cobalt metal catalysts supported on SiO2 were prepared by using cobalt(II) acetate as a precursor promoted with noble metals such as Ir, Ru, Rh, Re, Pt or Os. The catalysts were active for the formation of oxygenates by CO hydrogenation and the vapor phase hydroformylation of ethene. The selectivity of oxygenates, especially C2-oxygenates, was strongly enhanced by a further modification with basic additives such as alkali and alkaline earth cations. By the characterization of the catalysts using XPS, EXAFS, XRD, FT-IR, etc., it is revealed that highly dispersed Co2+ particles are formed on SiO2 by the decomposition of Co(II) acetate at an elevated temperature in flowing H2. The noble metals promote the reduction of the Co2+ particles to cobalt metals by spilt-over hydrogen activated on the noble metal sites. The effects of the basic additives were discussed.

Microalgal cultivation in a solution recovered from the low-temperature catalytic gasification of the microalga

Microalgal cultivation in a solution recovered from the low-temperature catalytic gasification of the microalga itself was studied. The growth of Chlorella vulgaris in 75-300-fold diluted recovered solution containing phosphate, magnesium ions and micro-elements was comparable to that in the standard culture medium. It was suggested that C. vulgaris could use ammonium in the recovered solution as its nitrogen source and at the same time could provide a source of biomass which was recycled via gasification.

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.

Heterogeneous palladium catalysts for the Heck reaction

Abstract The vinylation of iodobenzene with methyl acrylate was studied using palladium-based heterogeneous catalysts. Methyl cinnamate was formed as vinylation product and benzene as side product. All catalysts were of the type SiO2X-(NH)2-Pd-L2, where L = P(C6H5)3 or C6H5CN and X = Sn, Al or Ti. The catalysts were stable and could be reused several times in normal atmosphere without suffering appreciable loss in catalytic activity. The activity of the catalysts was good even at low temperature, and selectivities were very high. Strong interaction indicating the existence of chemical bonding was found between the modified silica support and palladium complex. A model of the active surface compound is proposed and confirmed.

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.

Alkylation of Biphenyl Catalyzed by Zeolites

Catalysis of 12-membered zeolites, H-mordenite (HM), HY, and HL was studied in the alkylation of biphenyl. The para-selectivities were up to 70% for isopropylbiphenyl (IPBP), and 80% for diisopropylbiphenyl (DIBP) in HM catalyzed isopropylation. Catalysis of HY and HL zeolites was nonselective. These differences depend on differences in pore structure of zeolites. Catalysis of HM to give the least bulky isomer is controlled shape-selectively by steric restriction of the transition state and by the entrance of IPBP isomers. Alkylation with HY and HL is controlled by the electron density of reactant molecule and by the stability of product molecules because these zeolites have enough space for the transition state to allow all IPBP and DIBP isomers. Dealumination of HM decreased coke deposition to enhance shape selective alkylation of biphenyl.