Using an IRMS-TPD (temperature programmed desorption) of ammonia, we studied the nature, strength, crystallographic location, and distribution of acid sites of mordenite. In this method, infrared spectroscopy (IR) and mass spectroscopy (MS) work together to follow the thermal behavior of adsorbed and desorbed ammonia, respectively; therefore, adsorbed species were identified, and their thermal behavior was directly connected with the desorption of ammonia during an elevation of temperature. IR-measured TPD of the NH4(+) cation was similar to MS-measured TPD, thus showing the nature of Brønsted acidity. From the behavior of OH bands, it was found that the Brønsted acid sites consisted of two kinds of OH bands at high and low wavenumbers, ascribable to OH bands situated on 12- and 8-member rings (MR) of mordenite structure, respectively. The amount and strength of these Brønsted hydroxyls were measured quantitatively based on a theoretical equation using a curve fitting method. Up to ca. 30% of the exchange degree, NH4(+) was exchanged with Na+ on the 12-MR to arrive at saturation; therefore, in this region, the Brønsted acid site was situated on the large pore of 12-MR. The NH4(+) cation was then exchanged with Na+ on 8-MR, and finally exceeded the amount on 12-MR. In the 99% NH4-mordenite, Brønsted acid sites were located predominantly on the 8-MR more than on the 12-MR. Irrespective of the NH4(+) exchange degree, the strengths deltaH of Brønsted OH were 145 and 153 kJ mol(-1) on the 12- and 8-MR, respectively; that is, the strength of Brønsted acid site on the 8-MR was larger than that on the 12-MR. A density functional theory (DFT) calculation supported the difference in the strengths of the acid sites. Catalytic cracking activity of the Brønsted acid sites on the 8-MR declined rapidly, while that on the 12-MR was remarkably kept. The difference in strength and/or steric capacity may cause such a difference in the life of a catalyst.

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Cobalt(ii)-tetraphenylporphyrin (CoVpp)-fixed glassy carbon (GC) electrodes were prepared using 4-aminopyridine (pyNH2) in the form of Colltpp-pyNH-CO/GC, which were active for electroreduction of C 0 2 to CO at potentials 100 mV more positive than water-soluble Coil porphyrins, and the overall turnover number of Coiltpp for CO production exceeded 105.Metalloporphyrins have been reported to be active as catalysts in the electroreduction of C 0 2 in aqueous' and nonaqueous2 media. In aqueous media, water-soluble CoIItetraphenylporphyrin sulphonate and CoTTrneso-tetracarboxyphenylporphyrin have been reported to be catalytically active for the electroreduction of C 0 2 . Pyridine (py) is reported to coordinate at the axial position of planar CoII(sa1en) (H2salen = bissalicylideneethylenediamine) and stabilizes C 0 2 in the opposite coordination site.3 In the present work, we attempted to obtain a CoIItpp-py (tpp = tetraphenylporphyrin) complex-fixed electrode by applying the water-insoluble CoIItpp on glassy carbon (GC) substrate plates modified initially with 4-aminopyridine (pyNH2). 4-Aminopyridine is expected not only to immobilize CoIItpp on the G C electrode, but also to provide the CoIItpp-fixed GC electrode with new properties.CoIItpp-pyNH-CO/GC (I) was prepared as follows Glassy carbon (GC) plates (Tokai GC-30, 27 mm x 5 mm, 1 mm thick) were subjected to anodic oxidation in 0.5 mol dm-3 H2S04, and refluxed in SOC12 for 24 h, for chlorination as COCl/GC. The electrodes were then immersed in 4-aminopyridine-saturated benzene solution for 24 h at room temperature to produce pyNH-CO/GC (11). Finally, the electrodes were refluxed in a 0.6 mmol dm-3 CoIItpp solution in benzene for 24 h to produce I.The fixation of 4-aminopyridine was confirmed by the diffuse reflectance FT IR spectrum of 11, which showed a peak at 1665 cm-1 due to C=O stretching of the -CO-NH-amide group together with pyridine ring C=C and C=N stretching peaks at 1610 and 1537 cm-1, respectively. These results showed that 4-aminopyridine was fixed in the form of pyNH-CO/GC. Fig. l(a) shows the diffuse reflectance UV-VIS spectrum of I, together with spectra of ( b ) CoIItpp and (c) CoIItpp-py in CH2C12 for comparison. Spectra ( a ) and (c) show the Soret band at 440 nm, whereas that of ( b ) is at 420 nm. These spectra indicated that Co**tpp was fixed as the pyridine complex, CoIItpp-py, and the electron density of the central ColI ions of I was increased by the pyridine 1igand.s Fig. 2 shows cyclic voltammograms (CV) of I in standard phosphate buffer solution at pH 6.86 saturated with He or C02. No CoIItpp/CoItpp redox peak was observed, but this is probably due to the small amount of CoIItpp distributed on the electrode which has a high roughness factor (3 x 103). The surface concentration of CoIItpp of (10-12 mol cm-2; apparent surface area) was evaluated by ESCA. A pronounced increase of the cathodic current was observed at potentials more negative than -0.95 V [vs. saturated calomel electrode (SCE)] in C02-saturated solution, this increase st...

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