Naonobu Katada

Measurements of acidic property of zeolites by temperature programmed desorption of ammonia

The overall view of the TPD of ammonia to measure the acidic property of zeolites is described. The desorption peaks were identified and the significance of readsorption of ammonia was pointed out for the first time. This part of the work was done using reference catalysts of the Catalysis Society of Japan. The theoretical equation for the TPD with free readsorption of ammonia was then derived. Two methods for determining the strength of zeolite acidity based on the derived equation were proposed. A curve fitting method was then proposed to determine the zeolite acidity; based on this method, not only the strength of acidity but also its distribution could be determined. This method was applied to mordenite and ZSM-5 zeolites with different contents of Al and Na cations, and a simple conclusion was reached; namely, the strength of the acidity was not influenced by the number of acid sites but by the structure of the zeolite. Finally, water vapor treatment to rub out the l-peak (lower temperature peak) was briefly mentioned. This method was applied to precisely determine the acidity of Y-zeolite. A case study about the beta zeolite as the catalyst for the amination of phenol was exemplified; the catalytic activity was discussed in terms of the measured acidity.

COMPLETE OXIDATION OF METHANE ON SUPPORTED PALLADIUM CATALYST: SUPPORT EFFECT

Abstract A palladium loaded catalyst was examined in order to reveal the effect of the support on the activity of oxidation of methane. The activity was declined or enhanced with time on stream, and its behavior depended upon the kind of support. The change of activity was accompanied with sintering of palladium metal. The stabilized activity of the palladium was ordered in the sequence; on SiO2 > on Al2O3 > on SiO2-Al2O3. The turn-over frequency of methane oxidation was about 50 times greater than that of platinum supported catalysts, and the activity sequence of support was opposite to that of platinum. The effect of support on the activity of palladium was smaller than on platinum from the viewpoint of activation energy as well as the turn-over frequency. The palladium dispersed on the support was less active, but the large particle which was not interacted strongly with the support was active; the behavior may be related to the small support effect on the palladium activity. Higher activity of the loaded palladium oxide than that of platinum oxide was caused by the higher reducibility of PdO chemical bonds, as confirmed by the temperature-programmed reduction. Silica deposited alumina, prepared by a method of chemical vapor deposition, was designed to create new active sites for the loading of silica-rimmed palladium; the sintering of palladium was suppressed to obtain the durable activity.

New Method for the Temperature‐ Programmed Desorption (TPD) of Ammonia Experiment for Characterization of Zeolite Acidity: A Review

In this review, a method for the temperature-programmed desorption (TPD) of ammonia experiment for the characterization of zeolite acidity and its improvement by simultaneous IR measurement and DFT calculation are described. First, various methods of ammonia TPD are explained, since the measurements have been conducted under the concepts of kinetics, equilibrium, or diffusion control. It is however emphasized that the ubiquitous TPD experiment is governed by the equilibrium between ammonia molecules in the gas phase and on the surface. Therefore, a method to measure quantitatively the strength of the acid site (∆H upon ammonia desorption) under equilibrium-controlled conditions is elucidated. Then, a quantitative relationship between ∆H and H0 function is proposed, based on which the acid strength ∆H can be converted into the H0 function. The identification of the desorption peaks and the quantitative measurement of the number of acid sites are then explained. In order to overcome a serious disadvantage of the method (i.e., no information is provided about the structure of acid sites), the simultaneous measurement of IR spectroscopy with ammonia TPD, named IRMS-TPD (infrared spectroscopy/mass spectrometry-temperature-programmed desorption), is proposed. Based on this improved measurement, Brønsted and Lewis acid sites were differentiated and the distribution of Brønsted OH was revealed. The acidity characterized by IRMS-TPD was further supported by the theoretical DFT calculation. Thus, the advanced study of zeolite acidity at the molecular level was made possible. Advantages and disadvantages of the ammonia TPD experiment are discussed, and understanding of the catalytic cracking activity based on the derived acidic profile is explained.

Analysis of Acidic Properties of Zeolitic and Non-Zeolitic Solid Acid Catalysts Using Temperature-Programmed Desorption of Ammonia

A method of ammonia temperature-programmed desorption (TPD) for analysis of acidic property of a solid was improved by introduction of a water vapor treatment method and development of a theory for calculation of ammonia adsorption heat from the TPD profile. The improved method was applied to various solid acid catalysts to establish relationships between the acidic properties and catalytic performances for various acid-catalyzed reactions. Here, examples of the applications to some important acid catalysts are reviewed. The exact analysis of acidic property of Y zeolite and its change by such modifications as steaming and ethylenediaminetetraacetic acid (EDTA) treatment gave a new interpretation on the generation of alkane (paraffin) cracking activity on an ultra stable Y (USY) zeolite. The surface density and strength of acid sites on WO3/ZrO2 and SO42−/ZrO2 catalysts were determined, and their relations with catalytic activities for Friedel–Crafts type alkylation and skeletal isomerization of alkane were found.

Activity of palladium loaded on zeolites in the combustion of methane

Activity of Pd loaded on zeolite for the methane combustion was examined using various kinds of mordenite and ZSM-5 zeolites with different compositions of aluminum and cation. The activity strongly depended on the composition as well as on the structure of zeolites. Among tested catalysts, the highest and durable activity was found on the catalyst which was prepared from an ion exchange with palladium amine complex on the H-type siliceous mordenite such as Pd/H-mordenite (Si/Al2=145). Reaction orders with respect to the partial pressures of methane and oxygen indicated that the oxidized form of palladium was the active species. Characterization using TEM and XPS showed the high dispersion of palladium in the framework of zeolite. TPR using methane as a reductant showed that the high activity of Pd on the siliceous H-mordenite could be explained qualitatively and quantitatively; i.e., Pd was affected by the qualitative alteration caused by the induced effects by Al and Na cations, whereas the number of active oxygens on Pd was quantitatively enhanced in the zeolite, particularly mordenite. The micropores of zeolite may have a role in preventing the sintering into large particles to stabilize the activity.

Ammonia IRMS-TPD measurements and DFT calculation on acidic hydroxyl groups in CHA-type zeolites

Brønsted acidity of H-chabazite (CHA) zeolites (Si : Al(2) = 4.2) was investigated by means of ammonia infrared-mass spectrometry/temperature-programmed desorption (IRMS-TPD) methods and density functional calculations. Four IR bands were observed at 3644, 3616, 3575 and 3538 cm(-1), and they were ascribable to the acidic OH groups on four nonequivalent oxygen sites in the CHA structure. The absorption band at 3538 cm(-1) was attributed to the O(4)H in the 6-membered ring (MR), and ammonia adsorption energy (DeltaU) of this OH group was the lowest among the 4 kinds of OH groups. The other 3 bands were assigned to the acidic OH groups in 8MR. It was observed that the DeltaU in 8 and 6MR were 131 (+/-3) and 101 kJ mol(-1), respectively. On the other hand, the density functional theory (DFT) calculations within periodic boundary conditions yielded the adsorption energies on these OH groups in 8 and 6MR to be ca. 130 and 110 kJ mol(-1), respectively, in good agreement with the experimentally-observed values.

Novel supporting materials of lipase PS suitable for use in an ionic liquid solvent system

Seven types of immobilized lipase PS were prepared using supporting materials such as metal oxides, ceramics, and mesoporous silica. They were then evaluated for use in an ionic liquid solvent system. The reaction rate was significantly dependent on the combination of the source of the supporting materials and solvent system. Tungsten(VI) oxide coated-metal oxides were thus found as novel supporting materials for lipase PS.

Catalytic Activity of Mesoporous Silica for Synthesis of Methyl N-Phenyl Carbamate from Dimethyl Carbonate and Aniline

Mesoporous silica MCM-41, especially an Al-containing one, showed high catalytic activity for synthesis of methyl N-phenyl carbamate from dimethyl carbonate and aniline at 363-383 K. It was easily separated from the product solution, and the catalyst was able to be used repeatedly.

Synthesis of aniline from phenol and ammonia over zeolite beta

Vapor-phase synthesis of aniline from phenol and ammonia was examined over various zeolites. Zeolite beta showed a high activity. Study of a theoretical interpretation of temperature-programmed desorption (TPD) of ammonia could correlate the catalytic activity with the acidic property. The activity for formation of aniline is almost proportional with the acid amount on each crystal phase of zeolite, and the turnover frequency of acid site seems to be ordered as FAU (faujasite)≈BEA (beta) > MFI (ZSM5) > MOR (mordenite). On the other hand, the acid strength was determined as FAU

Thermally stable environmental catalyst: oxidation of methane over calcined palladium loaded on silica monolayer

Abstract Enhancement of thermal stability of the Pd loaded on alumina for the complete oxidation of hydrocarbons was studied by preparing the surface of a support consisting of a partially covered silica monolayer and remaining alumina by a chemical vapor deposition of silicon alkoxide. The thermal stability of the Pd-loaded silica-deposited alumina was tested after the calcination at 1493 K. The silica monolayer not only maintained the high surface area, but also suppressed the sintering of palladium. After the calcination, the catalytic activity of Pd/10 wt% SiO2/Al2O3 was double that on Pd/Al2O3, although it decreased to 1/10 of the initial activity. The support and loaded palladium were characterized by BET, XRD, TEM and TPR measurements.