One-Step Conversion of Glutamic Acid into 2-Pyrrolidone on a Supported Ru Catalyst in a Hydrogen Atmosphere: Remarkable Effect of CO Activation.

Glutamic acid, an abundant nonessential amino acid, was converted into 2-pyrrolidone in the presence of a supported Ru catalyst under a pressurized hydrogen atmosphere. This reaction pathway proceeded through the dehydration of glutamic acid into pyroglutamic acid, subsequent hydrogenation, and the dehydrogenation-decarbonylation of pyroglutaminol into 2-pyrrolidone. In the conversion of pyroglutaminol, Ru/Al2 O3 exhibited notably higher activity than supported Pt, Pd, and Rh catalysts. IR analysis revealed that Ru can hydrogenate the formed CO through dehydrogenation-decarbonylation of hydroxymethyl groups in pyroglutaminol and can also easily desorb CH4 from the active sites on Ru. Furthermore, Ru/Al2 O3 showed the highest catalytic activity among the tested catalysts in the conversion of pyroglutamic acid. Consequently, the conversion of glutamic acid produced a high yield of 2-pyrrolidone by using the supported Ru catalyst. This is the first report of this one-pot reaction under mild reaction conditions (433 K, 2 MPa H2 )" which avoids the degradation of unstable amino acids above 473 K.

Direct Methylation of Benzene with Methane Catalyzed by Co/MFI Zeolite.

Cobalt-loaded MFI zeolite showed distinct activity for direct methylation of benzene with methane into toluene. High activity was found at around 0.6 of Co/Al molar ratio. Incorporation of carbon from methane into the methyl group of toluene was confirmed with isotope tracer experiments and mass spectroscopy. Ammonia infrared-mass spectroscopy temperature-programmed desorption, transmission electron microscopy, X-ray absorption near edge spectroscopy and extended X-ray absorption fine structure indicated that Lewis acidic divalent (+II of oxidation state) Co species mono-atomically dispersed on the ion exchange site of MFI zeolite was the active species.

Selecting strong Brønsted acid zeolites through screening from a database of hypothetical frameworks.

The database of prospective zeolites () has been screened in search of feasible zeolites with the condition of having at least one strong Brønsted site. Several criteria of zeolite feasibility have been tested using energetic and structural concepts, allowing a fast elimination of unsuitable candidates. Based on improved definitions to count and enumerate rings in zeolites, Brønsted acidity has been assessed in a fast albeit inaccurate way, by calculating a structural descriptor related to ammonia desorption energy. In each zeolite, the value of this descriptor was calculated for all the possible centres where a Brønsted acid site can be located. Ranking each zeolite through the value of the strongest candidate acid site allowed obtaining a selection of potentially strong acid zeolites. With further selection criteria, a final short list of 12 structures was obtained, where accurate calculations using periodic DFT indicate that 6 of them must contain a Brønsted site of very strong acidity.

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.

Ammonia IRMS-TPD measurements on Brønsted acidity of proton-formed SAPO-34.

By utilizing the advantages of a combined method of IRMS-TPD of ammonia and DFT calculations, the solid acidity of HSAPO-34 was studied. The number, strength and structure of the Brønsted OH were measured experimentally. The quantitative measurements and DFT calculations supported the identification of Brønsted OH to account for the generation model of the Brønsted OH primarily located in the edge of the Si domain (island). The acid strength of SAPO-34 was slightly weaker than that of chabazite, a zeolite with the same structure. Thus, some important insights were obtained to understand the acid site generation of SAPO-34.

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.

Identification and measurements of strong Brønsted acid site in ultrastable Y (USY) zeolite.

By using the IRMS-TPD method in which IR (infrared) and MS (mass spectroscopy) worked together, acid sites of USY (ultrastable Y) zeolite were studied. A new band of OH playing a role of Brønsted acid was clearly detected on Na2H2-ethylenediaminetetraacetic acid (EDTA)-treated USY at 3595 cm(-1) during an elevation in temperature after the adsorption of ammonia. MS-measured TPD (temperature-programmed desorption) of NH3 and IR-measured TPD of the NH4+ cation coincided well to show that this zeolite consisted of the Brønsted acid sites. The MS-TPD profile at higher temperatures corresponded to the IR-TPD of the 3595-cm(-1) band, and therefore, this OH was identified as a strong acid site. From comparison between IR-TPD of OH and MS-TPD, numbers of three kinds of Brønsted OH (i.e., those in super and sodalite cages of a Y zeolite structure) and created strong Brønsted acid site were quantified. On the other hand, strength of the Brønsted acid site DeltaH was determined individually by a simulation method, where the corrected IR-TPD of OH was simulated based on the proposed equation. Thus, a new strong Brønsted acid site was identified in the EDTA-treated USY, and the amount and strength was measured quantitatively.

Ammonia IRMS-TPD study on the distribution of acid sites in mordenite.

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.