Yusuke Yoshinaga

Effect of alkaline metal on microporosity of acidic alkaline salts of 12-tungstophosphoric acid

Abstract A series of M 2.1 H 0.9 PW 12 O 40 (M=Cs, Rb, and K) was synthesized and their pore structure was characterized. The pore-width was evaluated by adsorption of various molecules with different size. The micropore and the mesopore size-distributions were systematically analyzed with Ar and N 2 adsorption–desorption isotherms, respectively. It was found that the pore-width of M 2.1 H 0.9 PW 12 O 40 increased as the cation size of alkali metal decreased. It should be emphasized that Rb 2.1 H 0.9 PW 12 O 40 as well as Cs 2.1 H 0.9 PW 12 O 40 possesses uniform ultramicropores, while the pore-width of K 2.1 H 0.9 PW 12 O 40 distributed widely. It is further worthy to note that the pore-width of Rb 2.1 H 0.9 PW 12 O 40 was estimated to about 0.60 nm and the external surface area was only 3% that of the total surface area. These results demonstrate that Rb 2.1 H 0.9 PW 12 O 40 is a novel ultramicroporous material having the pore-width similar to that of H-ZSM-5.

Selectivity and mechanism for skeletal isomerization of alkanes over typical solid acids and their Pt-promoted catalysts

Abstract Selectivities for skeletal isomerizations of n -butane and n -pentane catalyzed by typical solid acids such as Cs 2.5 H 0.5 PW 12 O 40 (Cs2.5), SO 4 2− /ZrO 2 , WO 3 /ZrO 2 , and H-ZSM-5 and their Pt-promoted catalysts were compared. High selectivities for n -butane and low selectivity for n -pentane were observed over Cs2.5 and SO 4 2− /ZrO 2 , while H-ZSM-5 was much less selective, and WO 3 /ZrO 2 was highly selective for both reactions. The Pt-promoted solid acids were usually selective for these reactions in the presence of H 2 except for Pt-H-ZSM-5 for n -butane isomerization. Both the acid strength and pore structure would be factors influencing the selectivity. Mechanism of skeletal isomerization of n -butane was investigated by using 1,4- 13 C 2 - n -butane over Cs2.5 and Pt–Cs2.5. It was concluded that n -butane isomerization proceeded mainly via monomolecular pathway with intramolecular rearrangement on Pt–Cs2.5, while it occurred through bimolecular pathway with intermolecular rearrangement on Cs2.5. The higher selectivity on Pt–Cs2.5 would be brought about by the monomolecular mechanism. In the skeletal isomerization of cyclohexane, Pt–Cs2.5/SiO 2 was highly active and selective, while Pt–Cs2.5 was less selective. Control in the acid strength of Cs2.5 by the supporting would be responsible for the high selectivity.

Characterization and Optimization of Mixed Thiol-Derivatized β-Cyclodextrin/Pentanethiol Monolayers with High-Density Guest-Accessible Cavities

Mixed per-6-thio-beta-cyclodextrin (CD-SH)/pentanethiol (C(5)SH) monolayers were constructed by the sequential immersion of a Au(111) electrode into solutions of CD-SH, ferrocene, and a mixed solution of ferrocene and C(5)SH. Highly compact CD-SH self-assembled monolayers (SAMs) with the surface CD-SH density of 74.0 +/- 6.3 pmol cm(-2) on a true surface area basis were formed in 1 mM CD-SH with the immersion time of more than 48 h as confirmed by reductive desorption voltammetry. Based on the concentration dependence of the adsorption amount, a Langmuir adsorption coefficient was determined to be 1.9 x 10(7) M(-1). Chronocoulometry in a ferrocene solution at the CD-SH SAM and the mixed CD-SH/C(5)SH monolayers revealed the following inclusion properties. (1) All the CD-SH cavities can be used for the inclusion of a guest compound before and after the adsorption of C(5)SH, as shown by the fact that the maximum inclusion amounts of ferrocene, 68.0 +/- 3.4 and 73.0 +/- 2.0 pmol cm(-2) before and after the adsorption of C(5)SH, respectively, were very close to the surface CD-SH density. (2) The association constant between the surface-confined CD-SH and ferrocene (7.6 x 10(4) M(-1)) is greater than the corresponding association constant in solution. (3) The intermolecular vacancies between the adsorbed CD-SH molecules are completely filled with C(5)SH. This ensures that the CD cavities are the only accessible sites for guest compounds and any other reactants.

Shape-selective oxidation catalysed by a Pt-promoted ultramicroporous heteropoly compound

Pt-promoted porous heteropoly compounds, Pt-CsxH3-xPW12O40, have been synthesized and their micro- and meso-pore size distributions determined by adsorption of variously sized molecules and the Dollimore–Heal N2 isotherm method, respectively. 0.5 wt.% Pt-Cs2.1H0.9PW12O40 showed a Type I N2 adsorption isotherm with a plateau, indicating the presence of nearly uniform micropores; 1.0 wt.% Pt-Cs2.1H0.9PW12O40, 1.5 wt.% Pt-Cs2.1H0.9PW12O40 and 0.5 wt.% Pt-Cs2.5H0.5PW12O40 gave Type IV isotherms, as usually observed for mesoporous materials. Adsorption of molecules such as N2 [molecularsize (MS) = 0.36 nm], n-butane (MS = 0.43 nm), isobutane (MS = 0.50 nm), benzene (MS = 0.59 nm), 2,2-dimethylpro-pane (MS = 0.62 nm), and 1,3,5-trimethylbenzene (MS = 0.75 nm) demonstrated that the pore width of 0.5 wt.%Pt-Cs2.1H0.9PW12O40 was in the range 0.43–0.50 nm and that the external surface area was very small. Owing to the restricted pore size, 0.5 wt.% Pt-Cs2.1H0.9PW12O40 exhibited efficient shape selectivity for catalytic oxidation; smaller molecules such as methane (MS = 0.38 nm) and CO (MS = 0.38 nm) were readily oxidized, whereas benzene (MS = 0.59 nm) was not oxidized. This efficient shape selectivity indicates that Pt is present exclusively in the pores and not on the external surface of 0.5 wt.%Pt-Cs2.1H0.9PW12O40.

Unusual acceleration of acid-catalyzed reactions by water in the presence of Mo/Zr mixed oxides calcined at high temperatures

Various acid-catalyzed reactions, such as hydrolysis of ethyl acetate, esterification of acetic acid with ethanol, dehydration of 2-butanol, isomerization of 1-butene, and skeletal isomerization of n-butane, in the presence of Mo–Zr mixed oxides and other solid acids have been studied. MoO3/ZrO2 exhibited high activities only for the hydrolysis and esterification reactions, in which these high catalytic activities could not be explained by the acidic property of MoO3/ZrO2 alone, as shown by NH3–temperature programmed desorption (TPD) studies. It was found that the addition of water significantly accelerated the esterification and dehydration in the presence of MoO3/ZrO2 (calcined above 973 K), wheras SiO2–Al2O3 was greatly deactivated by water under similar reaction conditions. Furthermore, in the presence of water vapor, the activity of MoO3/ZrO2 for the isomerization of 1-butene did not decline, whereas SiO2–Al2O3 became inactive completely. IR measurements revealed that the water adsorbed on MoO3/ZrO2 (calcined at 1073 K) gave a sharp peak at 1628 cm−1, and that this peak gradually decreased at 423 K, while ZrO2 only or MoO3/ZrO2 (calcined at 673 K) did exhibit well-defined peaks. Since the adsorption-desorption behavior of water was in good agreement to the catalytic activity for dehydration of 2-butanol, the acceleration by water was presumably a result of the generation of acid sites by the dissociation of water molecules that are coordinated on the Mo species of MoO3/ZrO2.

Pore Structure and Shape Selectivity of Platinum-Promoted Cesium Salts of 12-Tungstophosphoric Acid

Pore-widths and pore-size distributions of 0.5 wt% Pt-CsxH3-xPW12O40 have been studied by means of adsorption of various molecules. For the distributions of micropore and mesopore, isotherms of Ar and N2 adsorption were analyzed, respectively. Pt-Cs2.1H0.9PW12O40 possessed only ultramicropores. On the other hand, the pores of Pt-CsxH3-xPW12O40 (x = 2.3, 2.5, 2.8 and 3.0) showed bimodal distributions in the range from micropore to mesopore, and the widths of both pores tended to increase as the Cs content increased. From the amounts and rates of adsorption for n-butane and isobutane, the pore width of Pt-Cs2.1H0.9PW12O40 was determined to be close to the molecular size of n-butane, that is, 0.43 nm. The fraction of external surface area in the total surface area of Pt-Cs2.1H0.9PW12O40 was estimated to be only 0.06 from the adsorption of 1,3,5-trimethylbenzene and t-plot of N2 adsorption. Pt- Cs2.1H0.9PW12O40 exhibited a shape selectivity due to the uniform ultramicropores and small external surface area; it catalyzed the oxidation of n-butane but not that of isobutane. SEM and TEM measurements revealed the primary crystallites and their aggregated states.

Unprecedented acceleration effects of water on acid-catalyzed reactions over molybdena -zirconia catalysts

Effects of water on various acid-catalyzed reactions have been studied mainly using MoO3/ZrO2. While the reaction rate of gas-phase esterification of acetic acid with ethanol and the dehydration of 2-butanol over SiO2-Al2O3 decreased significantly by the addition of water vapor in the feed gas, these reactions over MoO3/ZrO2 were found to be greatly enhanced by the presence of water. The enhancement by water was reversible and was remarkable when MoO3/ZrO2 was calcined at a temperature range of 773-1073 K. IR spectroscopy of H2O adsorbed on MoO3/ZrO2 suggests that the acceleration effect of water would be due to the generation of acidic sites from water coordinated to Mo species on the surface of MoO3/ZrO2.

Active sites of WO3ZrO2 for metathesis and isomerization of 1-butene characterized by ESR

Abstract The surface of WO 3 ZrO 2 prepared by a co-precipitation has been characterized by ESR. Three kinds of O 2 − radicals having different g 1 values (S I : g = 2.028, S II : g = 2.026, and S III : g = 2.015) were formed on the surface of WO 3 ZrO 2 by introduction of O 2 at room temperature. The ESR signals were divided into two groups from the changes of their intensities by the W Zr ratio; S I and the other two (S II and S III ). It was found that the W Zr ratio dependence of catalytic activity for metathesis of 1-butene was very close to those of the intensities of S II and S III . This indicates that the active sites for metathesis concern with those giving S II and S III , where S II and S III are presumed to be W 4+ and W 5+ to form O 2 − W 5+ and O 2 − W 6+ , respectively.

Development of Electronic Lab-book for College Chemistry-Experiment - SN1 a SN2 Reactions -.

We developed a computer graphics (CG) teaching material (TM) for university students, concerning reactions involving drastic changes in the structure of the reactants in the following chlorination, for example SN1: formation of tert-butyl chloride from tert-butanol and SN2: formation of 1-chlorobutane from 1-butanol. The CG-TM could clearly demonstrate the changes in the structures during the reaction by the ball-and-stick model, in addition to the image of the energy change in terms of the reaction profile. An electronic lab-book for chemical experiments in the students’ laboratory at the university was produced, aiming at the integration of observable-level experiments, symbolic chemical equations, and the molecular world. The lab-book displays pictures of apparatus, flow-chart of experimental procedures, and reaction mechanisms with the CG-TM. A preliminary study on the effectiveness of the CG-TM suggested that students were able to obtain images of SN1 and SN2 reactions.

An Approach to Developing Electronic Textbook for Chemical Experiment - Taking Walden’s Inversion as an Example

We are developing electronic textbook for of basic chemistry-experiment for university students in which reaction mechanisms are shown by computer graphics (CG). The CGs of chemical reactions was made based on the empirical molecular orbital calculations. The CGs include following reactions as a model of Walden’s inversion where drastic change in structure takes place, such as, formation of 2-butyl alcohol and 1-butyl bromide. The CGs could simultaneously demonstrates the nature of the reaction such as structural change by the space-filling model and by the ball-and-stick model in addition to providing image of energy change by the reaction profile. The electronic textbook also displays picture of apparatus and flow-chart of small-scale experiment. Result of preliminary study on effectiveness of the CG is included.