Masahiko Sawa

Relationship between acid amount and framework aluminum content in mordenite

Acid amount of mordenites and dealuminated mordenites with framework aluminum contents of 0.28–2.33 mmol g−1 was measured by temperature-programmed desorption of ammonia. Framework Al content was distinguished from nonframework Al based on 27Al MAS n.m.r. measurements. The relationship between the acid amount and the framework Al content represented a volcano relationship with the maximum acid amount at 1.65 mmol g−1 framework Al content. Below 1.65 mmol g−1 framework Al content, the acid amount was approximately proportional to the framework Al content, whereas the amount decreased as the framework Al content increased above 1.65 mmol g−1. The decrease of acid amount of mordenite with the framework Al content above 1.65 mmol g−1 seems to be due to the generation of nonacidic framework Al atoms owing to paired Al atoms in 4-rings.

Derivation of new theoretical equation for temperature-programmed desorption of ammonia with freely occurring readsorption

A new theoretical equation for temperature-programmed desorption of ammonia, in which readsorption of ammonia occurs freely, is derived: In T m − In A 0 W F = Δ H R T m + In β ( 1 − θ m ) 2 ( Δ H − R T m ) P 0 exp ( Δ S / R )

Acid-leached dealuminated mordenite: Effect of acid concentration on catalyst life in methanol conversion

Abstract In order to obtain a long-life zeolite catalyst for conversion of methanol into hydrocarbons, H-mordenite was dealuminated by leaching with hydrochloric acid of different concentrations (1–12 mol dm−3). The catalyst life was prolonged significantly, and the optimum acid concentration was 8 mol dm−3. The improvement in the catalyst life was related to the weakening of acid strength on dealumination; this is discussed in detail.

Mordenite with long life and selectivity for methanol conversion to gasoline : mordenite modified by barium ion exchange, dealumination and chemical vapor deposition of silicon methoxide

Abstract In order to develop a long-life and selective mordenite catalyst for methanol conversion to gasoline, the physico-chemical properties of mordenite were modified by three methods: dealumination, barium ion exchange and chemical vapor deposition (CVD) of silicon methoxide. Catalyst life was improved significantly by controlling acid properties both by dealumination and barium exchange. Barium ion-exchanged dealuminated mordenite with low acid site density and weak acid site strength showed the longest life amongst the catalyst so far studied by the authors. On the other hand, in order to improve the selectivity, by suppression of the formation of heavy aromatics such as pentamethylbenzene, the pore-opening sizes of dealuminated mordenite and barium ion-exchanged dealuminated mordenite were modified by CVD of silicon methoxide. In dealuminated mordenite, activity was decreased rapidly by the CVD method. In the barium ion-exchanged dealuminated mordenite, however, the formation of heavy aromatics with more than 11 carbon atoms was almost inhibited by the CVD method, while the lifetime was unchanged.

Change of pore-opening structure of mordenite upon dealumination by hydrochloric acid

Abstract The structure of dealuminated mordenites prepared at 340–358 K of hydrochloric acid was studied. 27Al MAS n.m.r. and XPS were measured to determine the species and depth profile of alumina, and these were corroborated with adsorption experiments using adsorbates of different sizes. Adsorption capacity of nitrogen was unaltered so that the structure of mordenite was retained, while that of 2,2,4-trimethylpentane with a larger kinetic diameter increased below 358 K of dealumination temperature, but then decreased above that. The H-mordenite (HM, Norton 100-H) contained a large amount of octahedral aluminum species (ca. 28%), and the nonframework aluminum was removed preferentially by the dealumination. Aluminum depth profile showed the homogeneous distribution on the inherent HM, but the enrichment on the samples prepared above 350 K. Based upon these findings, the following conclusions were drawn: (1) On the inherent HM, a small portion of nonframework aluminum near the pore opening disturbs the adsorption of large molecules: (2) The pore-opening size of the sample dealuminated at 358 K was large enough to adsorb 2,2,4-trimethylpentane: (3) However, upon the dealumination above 358 K, the pore opening was partly destroyed or blocked by nonframework alumina again to inhibit the adsorption of large molecules. Most of the aluminum impurity species seemed to be occluded as blocks or clusters in the mordenite. These variations of structure of the pore opening can be well related to those of the catalyst activity.

One-point method for the determination of strength of zeolite acidity by temperature programmed desorption of ammonia based on trouton's rule

Summary We propose a one-point method to measure the strength of zeolie acidity from temperature programmed deorption (TPD) of ammonia. Based on the assumption of constancy of ΔS, one can determine the ΔH from the theoretical equation describing the TPD of ammonia which was derived by the authors. The constancey of ΔS upon desorption of ammonia is in agreement with the Troutons rule about the vaporization of liquids.

Special articles on zeolite chemistry and technology. Development of long-life catalyst for the methanol conversion into hydrocarbons. Influence of barium ion on the ion-exchanged dealuminated mordenite.

ZSM-5以外のゼオライトによる長寿命メタノール転化反応用触媒を開発するために, イオン交換率の異なる4種類のバリウムイオン交換脱アルミモルデナイトを調製し, バリウムイオン交換の寿命に対する影響を調べた。常圧固定床流通反応装置を使用し, 反応温度350℃でメタノール転化反応を行なったところ, 寿命の改良が見られた。とくに, 73%バリウムイオン交換した触媒は高活性で, 反応開始後 6 時間経過しても活性の低下はほとんどみられなかった。NH3のTPDによってこれらの触媒の酸性質を調べたところ, バリウムイオン交換率の増加とともに強い酸点は減少し, 逆に中程度の強度の酸点が発現した。これらのことから, バリウムイオン交換によって脱アルミモルデナイトの酸強度が低下したために, コークの生成が抑倒され, その結果, 寿命が長くなったものと結論した。