Takehiko Matsuzaki

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.

Effect of transition metals on oxygenates formation from syngas over Co/SiO2

Effects of precursors and modification on Co/SiO2 catalyst for carbon monoxide hydrogenation were studied at elevated pressures. Although Co/SiO2 derived from cobalt (II) acetate (Co(A)/SiO2) was quite inactive, it exhibited dramatically high activity especially for the formation of ethanol by modification with some transition metals such as iridium, ruthenium, rhodium, rhenium, osmium and platinum. At the same time, ethanol productivities of other Co/SiO2 catalysts derived from cobalt(II) nitrate (Co(N)/SiO2) or chloride (Co(Cl)/SiO2) were not so much improved by modification with rhenium as to Co(A)/SiO2. Chloride compounds were especially unfavorable as precursors of the component elements for the formation of oxygenated compounds. The catalytic activities and product distributions of Co(A)-Sr/SiO2 catalysts modified with these noble metals were very similar to each other. An ethanol selectivity of more than 20% was obtained using these catalysts. On the other hand, iridium and ruthenium did not have any important effect as modifiers of Co/SiO2 catalyst derived from Co2(CO)8 (Co(CO)/SiO2) which itself had an activity similar to that of modified Co(A)/SiO2 catalysts. Using X-ray diffraction, X-ray photoelectron spectroscopy and extended X-ray absorption fine structure to characterize the catalyst, it is concluded that highly dispersed cobalt metal is the main active site on the Co(A)/SiO2 catalyst and that transition metals promote the reduction of Co2+ cation to a metallic state by a hydrogen spill-over mechanism.

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.

Alcohol synthesis from syngas over cobalt catalysts prepared from Co2(CO)8

Carbon monoxide hydrogenation catalyzed by silica-supported cobalt catalysts prepared from dicobalt octacarbonyl [Co2(CO)8] yields alcohols with greater than 20% selectivity accompanied by 80% hydrocarbons. Modification by alkaline earth metal oxides enhanced the formation of alcohols in the order: Mg ⪡ Ca < Sr ⩽ Ba. A maximum selectivity as high as 60% for oxygenated compounds was observed at a Ba:Co mole ratio of 1.5 – 2.2. Extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD) studies of these catalysts show that Co2(CO)2 supported on SiO2 changes to Co4(CO)12in vacuo, and then to highly dispersed cobalt metal when heated in a stream of hydrogen at 673 K. High-pressure in situ FT-IR studies show that the formation of alcohols may be related to the presence of bridged-CO species on the surface of the catalysts.

Zeolite Catalyzed Alkylation of Biphenyl. Where Does Shape-Selective Catalysis Occur?

Liquid-phase alkylation of biphenyl (BP) was studied over large-pore zeolites. Selective formation of the least bulky products, 4,4′-diisopropylbiphenyl (4,4′-DIPB) occurred only in the isopropylation of BP over one- or two-dimensional zeolites, H-mordenite (HM), ZSM-12, SSZ-24, SAPO-5, SSZ-31, and CIT-5. These shape-selective catalyses are ascribed to steric restriction of transition state and to easiness of the substrates to enter into the pores. HM gave the highest selectivity among them. The dealumination of HM enhanced catalytic activity and the selectivity for 4,4′-DIPB because of the decrease of coke deposition. Non-regioselective catalysis occurs on external acid sites over HM with the low SiO2/Al2O3 ratio because severe coke deposition deactivates the acid sites inside the pores by blocking pore openings. The selectivity of DIPB isomers was changed with propylene pressure and/or with reaction temperature. Selective formation of 4,4′-DIPB was observed at moderate temperatures such as 250 °C, whereas the decrease of the selectivity of 4,4′-DIPB occurred at higher temperatures as 300 °C. 4,4′-DIPB yielded selectively under high propylene pressure (<0.3 MPa) at 250 °C, while the selectivity of 4,4′-DIPB decreased under low propylene pressure as 0.2 MPa. However, 4,4′-DIPB was almost exclusive isomer in the encapsulated DIPB isomers inside the pores under every temperature and pressure. The decrease of the selectivity of 4,4′-DIPB is due to the isomerization of 4,4′-DIPB on the external acid sites. The deactivation of external acid sites of HM was examined by the modification with cerium and other rare earth metal oxide on HM. Selectivities of 4,4′-DIPB were improved over modified HM even at high temperatures because of the suppression of non-regioselective alkylation and isomerization at the external acid sites. The ethylation of BP to ethylbiphenyls (EBPs) and diethylbiphenyls (DEBPs) was non-regioselective. The ethylation of BP to EBPs was controlled kinetically. However, there was difference in reactivities of EBPs and DEBPs for their further ethylation. 4-EBP was ethylated preferentially among the isomers, although the formation of 4,4′-DEBP was less selective. 4-EBP and 4,4′-DEBP have the highest reactivities among EBPs and DEBPs for the ethylation to polyethylbiphenyls (PEBPs). These results show that the environments of HM pores are too loose for shape-selective formation of the least bulky isomers, 4-EBP and 4,4′-DEBP, in the ethylation of BP, and that HM pores have enough space for the further ethylation of 4,4′-DEBP.

Synthesis of C2-oxygenates from syngas over cobalt catalysts promoted by ruthenium and alkaline earths

Abstract Silica-supported cobalt catalysts doubly modified with ruthenium and alkaline earths were active for the synthesis of C 2 -oxygenates (C 2 O) from syngas. Triruthenium dodecacarbonyl was more effective than ruthenium trichloride as a ruthenium precursor. Ruthenium increased the catalytic activity by promoting the reduction of cobalt. Alkaline earths improved the selectivity of C 2 O by controlling the oxidation states of the cobalt catalysts. The chain-growth probabilities of hydrocarbons, oxygenates and total products in the Schultz-Flory equation on a Co Ru Sr/ SiO 2 catalyst were 0.48–0.49.

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.