Synthesis of aniline from phenol and ammonia over zeolite beta

Katada, Naonobu; Iijima, Shinsuke; Igi, Hirofumi; Niwa, Miki

doi:10.1016/s0167-2991(97)80761-6

Cited by 33 publications

(23 citation statements)

References 11 publications

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“…The difference between the H-and HNa-types, namely, the presence of sodium, did not affect the acid strength. In this figure, the acid strength of aluminosilicates determined by our previous study 52,57,58,62,63 is overlapped. On all kinds of zeolites, the acid strength distribution was small (<ca.…”

Section: Identification Of Peaksmentioning

confidence: 85%

Acidic Property of MFI-Type Gallosilicate Determined by Temperature-Programmed Desorption of Ammonia

et al. 1998

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Temperature-programmed desorption of ammonia was applied to gallosilicate with MFI structure using the water vapor treatment method to remove the unnecessary low-temperature peak and the curve-fitting method to calculate the acid strength and its distribution based on the thermodynamics. The determined acid amount approximately agreed with the [Ga]-[Na] content in the low gallium content region, showing the stoichiometric generation of one acid site by the substitution of one gallium atom, and stoichiometric neutralization of one acid site by one sodium atom. The acid strength (adsorption heat of ammonia) due to the framework gallium was ca. 130 kJ mol -1 with the small distribution, close to that on the ZSM-5 type aluminosilicate, and was independent of the composition. This shows that the substitution of Al and Ga into the zeolitic crystal generates the similar acid strength, and the acidic strength is mainly determined by the crystal structure. The extraframework gallium on the ion-exchange site, which was readily formed with the gallium content higher than 0.3-0.4 mol kg -1 , generated the additional type of acid site with the higher adsorption heat of ammonia. IntroductionZeolite, which consists of SiO 2 and Al 2 O 3 , has widely been used as a heterogeneous catalyst. 1-6 In place of the aluminum, various kinds of metals can be incorporated into the framework, and the obtained metallosilicates are being considered as novel functionalized materials. 7 Especially, gallosilicate with MFI structure has a remarkable catalytic activity for the conversion of alkane into aromatics. [8][9][10][11][12][13][14][15][16][17][18] Generation of acidity by isomorphous substitution of silicon by gallium is presumed to be the origin of the catalytic functions. Analysis of the acidic property, namely, the number, strength, and nature (Brønsted or Lewis) of the acid sites, is therefore important to interpret the catalytic functions and, moreover, must be important also from the physicochemical viewpoint.The acidic property of gallosilicate has been investigated by means of the infrared (IR) spectroscopy of surface hydroxide, 19-22 the adsorbed pyridine, 23 carbon monoxide 24,25 and nitrogen, 25 and the nuclear magnetic resonance of proton ( 1 H NMR), 26 supported by quantum chemical calculations. 27-30 These spectroscopic methods mainly deal with the quality of the acid site, but the quantitative measurement is difficult. Traditional indicator 31 and amine titration 32 methods to quantify the acid amount have a disadvantage, because they are confused by the slow diffusion of liquid molecules in the micropore. Test reactions have widely been used, but they cannot be related simply to the acidic property. Measurement of adsorption heat of such a small base as ammonia by calorimetry 33 is one powerful method to evaluate the number and strength of acid sites. By this method, the interaction between the acidic and basic materials is directly evaluated, and this gives an absolute measure of the amount and strength of acid.Temperature...

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Section: Identification Of Peaksmentioning

confidence: 85%

Acidic Property of MFI-Type Gallosilicate Determined by Temperature-Programmed Desorption of Ammonia

et al. 1998

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“…According to the NH 3 -TPD study reported by Katada et al [71][72][73], the heat of adsorption of NH 3 on H-form zeolites is in the order MOR (145 kJ mol )1 ) > MFI (130 kJ mol )1 ) > BEA (120 kJ mol )1 ) > Y (110 kJ mol )1 ). This order agrees well with that of the stability of Ag + ions under C 3 H 8 -SCR conditions.…”

Section: Effect Of Zeolite Supportmentioning

confidence: 98%

Ag Clusters as Active Species for HC-SCR Over Ag-Zeolites

et al. 2005

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The addition of hydrogen in the reaction atmosphere is effective in promoting the activity of Ag/alumina and Ag-zeolites on the selective reduction of NO by hydrocarbons (HC-SCR) at low temperatures. The increment of NO conversion over Ag-MFI corresponds to the periodic addition of hydrogen into C 3 H 8 -SCR conditions. The UV-VIS spectra of Ag-MFI have revealed that the addition of hydrogen results in the formation of Ag n d+ clusters due to partial reduction and agglomeration of Ag species . The coincidence of the formation of the Ag n d+ clusters and the increment of NO conversion suggests that Ag n d+ clusters are the highly active species for HC-SCR. From analysis by H 2 -TPR, UV-VIS, and EXAFS, the structure of Ag n d+ clusters on Ag-MFI is identified as being Ag 4 2+ on average. The formation of Ag clusters was strongly affected by the type of zeolites: The major Ag species are Ag + ions for MOR, Ag n d+ clusters for MFI and BEA, and relatively large metallic Ag m particles for Y. The sequence of Ag agglomeration (MOR < MFI < BEA < Y) is in accordance with the strength of the acid sites of zeolites. It can be expected that the interaction between the positive charge of Ag n d+ clusters and acid sites, i.e., the ion-exchange site of zeolites, stabilizes Ag n d+ clusters. The type of Ag species under HC-SCR conditions depends on the concentration of gas-phase oxidants (NO, O 2 ) and reductants (H 2 , HC), and also on the number and strength of the zeolite acid sites.

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“…After C 3 H 8 -SCR in the presence of 0.5% H 2 , the spectrum of Ag-MOR was hardly changed, while new bands appeared at 260 and 285 nm due to the Ag ). [143][144][145] It can be rationalized that the stronger acid sites, i.e., the ion-exchange sites of zeolite, stabilize the positively charged Ag + ions or Ag n d+ clusters, while weaker acid sites easily release Ag + to form partially reduced Ag species by reduction with H 2 . Comparing Fig.…”

Section: Active Species In Presence Of Hydrogenmentioning

confidence: 99%

Selective catalytic reduction of NO over supported silver catalysts—practical and mechanistic aspects

Shimizu

Satsuma

2006

Phys. Chem. Chem. Phys.

150

134

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Selective catalytic reduction of NO by hydrocarbons (HC-SCR) is one of the promising technologies for removal of NO in exhausts containing excess oxygen, such as diesel and lean burn gasoline engines. Supported Ag catalysts, especially Ag/Al2O3, are thought to be the promising candidates for use in diesel exhausts, as confirmed by several reports on engine bench tests. The HC-SCR performance of supported Ag catalysts is very sensitive to the reaction conditions, especially the type of hydrocarbons and the addition of H2. The control of reaction conditions would be key for practical use. The current research of supported Ag catalysts is reviewed from the viewpoints of practical use and the reaction mechanism, i.e., the reaction scheme, the role of surface adsorbed species, and the structure of active Ag species.

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Synthesis of aniline from phenol and ammonia over zeolite beta

Cited by 33 publications

References 11 publications

Acidic Property of MFI-Type Gallosilicate Determined by Temperature-Programmed Desorption of Ammonia

Acidic Property of MFI-Type Gallosilicate Determined by Temperature-Programmed Desorption of Ammonia

Ag Clusters as Active Species for HC-SCR Over Ag-Zeolites

Selective catalytic reduction of NO over supported silver catalysts—practical and mechanistic aspects

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