Yoshihiro Sugi

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.

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.

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.

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.

The vinylation of bromobiphenyls using homogeneous nickel catalysts

The vinylation of 4-bromo-4′-hydroxybiphenyl and ethyl acrylate was studied using the catalyst NiCl2-H2O/PPh3 in the presence of inorganic base. Ethyl 4-(4′-hydroxyphenyl)cinnamate was formed as vinylation product with a selectivity as high as 98%. The effect of solvent, ligand and base for some halides was examined to show the applicability of the catalyst system.