Teruyuki Nakato

Water-tolerant solid acid catalysis of Cs2.5H0.5PW12O40 for hydrolysis of esters in the presence of excess water

Abstract Hydrolysis reactions of esters, ethyl acetate, cyclohexyl acetate, 2-methylphenyl acetate, and 2-nitrophenyl acetate in the presence of a large excess of water were investigated by using various solid acids. Inorganic solid acids such as an acidic cesium salt of 12-tungstophosphoric acid Cs 2.5 H 0.5 PW 12 O 40 , H-ZSM-5, SO 4 2− /ZrO 2 , and Nb 2 O 5 , and polymer resins, Amberlyst-15, Amberlite-200C, and Nafion-H catalyzed the reactions, whereas H-Y, H-mordenite, SiO 2 —Al 2 O 3 , and γ-Al 2 O 3 were inactive. Among inorganic solid acids, Cs 2.5 H 0.5 PW 12 O 40 was most active for all reactions in the unit of the activity per catalyst weight. Cs 2.5 H 0.5 PW 12 O 40 was comparable to Nafion-H in the catalytic activity per unit acid amount of catalysts, and much more active than H-ZSM-5, SO 4 2− /ZrO 2 , and Amberlyst-15. The activities of liquid acid catalysts, such as H 2 SO 4 , H 3 PW 12 O 40 , and p-toluenesulfonic acid, per unit acid amount were less than that of Cs 2.5 H 0.5 PW 12 O 40 , although the relative activities per catalyst weight of the liquid acids were higher than that of Cs 2.5 H 0.5 PW 12 O 40 . The activity of Cs 2.5 H 0.5 PW 12 O 40 relative to the other catalysts became higher for hydrolysis of bulky esters like 2-methylphenyl acetate and 2-nitrophenyl acetate for which H-ZSM-5 was inactive, demonstrating that Cs 2.5 H 0.5 PW 12 O 40 is a widely applicable water-tolerant solid acid. When Cs 2.5 H 0.5 PW 12 O 40 was separated from the reactant solution and reused for the hydrolysis of ethyl acetate repeatedly, the reaction rate of the 5th run was more than 90% that of the 1st run, whereas the rate on SO 4 2− /ZrO 2 decreased by repeating once to become less than half that of the 1st run.

Reaction of layered vanadium phosphorus oxides, VOPO4·2H2O and VOHPO4·0.5H2O, with amines and formation of exfoliative intercalation compounds

Reactions of layered vanadium phosphorus oxides, VOPO4·2H2O and VOHPO4·0.5H2O, with aliphatic and aromatic amines were investigated with regard to the formation of intercalation compounds. VOPO4·2H2O was intercalated with 4-butylaniline, and the obtained intercalation compound was exfoliated by stirring in THF. The layered structure of the intercalation compound was reconstructed by removal of the solvent from the suspension of exfoliated solid, while ordering of the restacked layers was sensitive to the experimental conditions. The reactions with 4-butylaniline for prolonged periods caused partial collapse of the layered structure, indicating metastability of the intercalated structure. VOPO4·2H2O formed intercalation compounds with aniline and 4-anilinoaniline as well as 4-butylaniline. On the other hand, reactions with n-alkylamines, which are more basic than aromatic amines, brought about collapse of the layered structure of VOPO4·2H2O. In addition, VOHPO4·0.5H2O did not react with aromatic amines such as aniline and pyridine, while reactions with n-alkylamines did not give intercalation compounds but led to the formation of salts, where the structure of the host lattice was not retained.

Effect of hydrogen sulphate ion on the hydrogen ionization and methanol oxidation reactions on platinum single-crystal electrodes

The effect of hydrogen sulphate ion on the hydrogen and methanol oxidation reactions was examined on Pt(111), PT(100) and Pt(110) electrodes by a voltammetric method. The comparison of the voltammograms obtained with and without the dissolved H2 and CH3OH showed a strong specific adsorption of hydrogen sulphate ion on Pt(111) and then on Pt(100) but no effect on Pt(110) in the time interval of a potential scan of 50 mV s−1. The methanol oxidation reaction proceeded ca. 80 times faster on Pt(110) than on Pt(111) in 0.5 M H2SO4 and suffered self-poisoning most strongly on Pt(110) and least on Pt(111). Common to both the hydrogen ionization and methanol oxidation reactions, a strong retardation appeared in a potential region just before the commencement of the oxygen wave on the respective planes in H2SO4 and HClO4 solutions. A compact reorientation of the water molecule in this potential region is discussed as a candidate for the retardation.

Catalysis by porous heteropoly compounds

This paper attempts to review recent works on catalysis of porous heteropoly compounds. The salts of heteropolyacids having Keggin structure with large cations like Cs+ are porous materials. For Cs hydrogen salts, the pore width can be controlled by the Cs content. Cs2.5H0.5PW12O40 has the largest amount of protons on the surface among the acidic Cs salts and possesses pores with bimodal distribution in the micro and meso region. Efficient performances were demonstrated for acid-catalyzed reactions such as skeletal isomerization of η-butane in solid-gas system, alkylation and acylation in solid-liquid system, and hydrolysis and hydration in solid-water system. A microporous salt, Cs2.2H0.8PW12O40, exhibited reactant shape selectivity towards direct decomposition of esters. Furthermore, an ultramicroporous bifunctional catalyst, Pt–Cs2.1H0.9PW12O40 of which the pore width is around 5 Å, exhibits reactant shape selectivity for hydrogenation of alkenes and oxidation of hydrocarbons, and product shape selectivity for skeletal isomerization of η-butane.

Effects of adsorbed CO on hydrogen ionization and CO oxidation reactions at Pt single-crystal electrodes in acidic solution

CO was adsorbed on the three low index planes of Pt single-crystal electrodes, and the hydrogen ionization and the dissolved CO oxidation reactions on the CO-covered electrodes were investigated in acid solution. The oxidation wave of CO adsorbed at 50 mV vs. a reversible hydrogen electrode had two peaks; a small prepeak at around 0.5 V and a main oxidation peak at around 0.7 V. Fourier transform IR measurement and the number of electrons per site for adsorbed CO indicated that these oxidation peaks could not be assigned individually to the linear and the bridged CO species. These peaks reflect the difference in the kinetic stability among the adsorbed CO. The stripping of the prepeak CO (CO1(a)) initiated both the hydrogen ionization and the dissolved CO oxidation reactions to a value close to the diffusion-limited values. These reactions required only a very small number of free sites which are provided in the present case by the removal of the kinetically unstable CO1(a). CO1(a) was absent in the adsorbed CO at 0.4 V. The voltammograms for the dissolved CO oxidation on the CO-covered electrodes revealed the presence of other two adsorbed states, COII(a) and COIII(a), where COII(a) was most stable and gave the main peak of the oxidation wave of the adsorbed CO. COIII(a) was very sensitive to the experimental conditions and was responsible for the hump that appeared in the dissolved CO oxidation.

Pore structure and shape selective catalysis of bifunctional microporous heteropoly compounds

Abstract The pore structure of Pt-promoted microporous cesium salts of H 3 PW 12 O 40 and their shape selective catalysis were studied. Pt-Cs 2.1 H 0.9 PW 12 O 40 (0.5 wt% Pt) has only ultramicropores of about 5 A in width; Pt-Cs 2.5 H 0.5 PW 12 O 40 (0.5 wt% Pt) possesses mesopores as well as micropores. These were revealed by pore size distributions derived from N 2 adsorption-desorption isotherms and adsorption of a variety of molecules having different sizes. While Pt-Cs 2.5 H 0.5 PW 12 O 40 as well as 0.5 wt% Pt/SiO 2 were active for hydrogenation of ethylene, cyclohexene, or cyclooctene, only ethylene was hydrogenated over Pt-Cs 2.1 H 0.9 PW 12 O 40 , indicating that Pt-Cs 2.1 H 0.9 PW 12 O 40 exhibits reactant shape selectivity by its constrained pores. In skeletal isomerization of n -butane, the selectivity to isobutane was found to depend significantly on the pore width of Pt-promoted heteropoly compounds and Pt-exchanged zeolites; the selectivity decreased as the pore width became smaller, this is probably due to product shape selectivity.

Reduction of NO on Au single-crystal electrodes in alkaline solution

Abstract The electrochemical behavior of nitrogen compounds on Au(111), Au(100) and Au(110) was investigated in alkaline solution. Each crystal plane was identified by Pb underpotential deposition (UPD) waves in perchloric acid solution. The UPD waves were unchanged after oxidation and reduction of a surface monolayer of Au atoms on the respective electrodes. NO underwent a “disproportionation” to NO − 2 and reduced species in the alkaline solution. However, only NO was electrochemically active. Cyclic voltammograms obtained in an alkaline solution containing dissolved NO showed a main reduction peak at ca. 0 V RHE and an oxidation peak at ca. 0.6 V, almost independent of the crystal plane in contrast with the case of Pt electrodes. We concluded from the voltammetric study that the former peak is due to the production of NH 2 OH, and that oxidation of NH 2 OH remaining near the surface gives the latter peak. The products in the two peaks were identified using in-situ “one-point touch” differential electrochemical mass spectroscopy: NH 2 OH was mainly oxidized to NO; N 2 H 4 , which apparently gave the same oxidation peak at ca. 0.6 V, yielded N 2 exclusively.

Selective oxidation of n-butane over novel V-P-O/silica-composites prepared through intercalation and exfoliation of layered precursor

Vanadium-phosphorus oxides-silica composites were prepared through intercalation-exfoliation of layered VOPO 4 2H 2 O. Intercalated compounds of VOPO 4 2H 2 O with 4-butylaniline, acrylamide and 2-octanol were formed retaining its morphology and lattice structure. These compounds were exfoliated in polar solvents into delaminated sheets. The composites of silica were obtained by impregnating silica with the solution containing the delaminated layers. It was found that the SiO 2 -composite obtained by exfoliation and reduction only with 2- octanol was highly selective (54%-selectivity), while the SiO 2 -intercalated materials with the N-containing compounds were less selective.

A water-tolerant solid acid, Cs2.5H0.5PW12O40, for hydrolysis of esters in water

Abstract Hydrolysis of esters in large excess water catalyzed by various solid and liquid acids has been studied. It was found that a solid Cs2.5H0.5PW12O40 was remarkably active for the hydrolysis of 2-methylphenylacetate in excess water, while other inorganic solid acids like H-ZSM-5, Nb2O5, orSO42−/ZrO2, were almost inactive. In addition, only the solution after the removal of the solid did not show any activity, and the activity of Cs2.5H0.5PW12O40 remained almost unchanged after it was treated in water (353 K) for 72 h.

Intercalation of a free-base porphyrin into layered tetratitanic acid

An intercalation compound of layered H2Ti4O9 with 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin (H2tmpyp4+) was synthesised by a guest-exchange method using the NPrH3+–HxTi4O9 intercalation compound as intermediate. The porphyrin is present as the free base without protonation. Its molecules are arranged with their planes inclined to the [Ti4O9]2– layers because of the high charge density of the host layers. Whereas the fluorescence spectrum of the intercalated H2tmpyp4+ indicated that the porphyrin is present as a monomer without stacked aggregation, the fluorescence decayed as rapidly as that of solid powders of H2tmpyp4+ 4I–, suggesting the porphyrin molecules interact with one another in the interlayer space.